AIR

AIR

INTRODUCTION

Air is the invisible gaseous, substance surrounding the earth, a mixture mainly of oxygen and nitrogen. Air is a precious resource that most of us take for granted. Air supplies us with O₂, which is essential for our bodies to live. Without it, we would die within minutes. Pure air is a mixture of several gases that are invisible and odourless. It consists of about 78% nitrogen, 21% oxygen, and less than 1% of argon, carbon dioxide, and other gases — as well as varying amounts of water vapour. Adults breathe in about 10-20 cubic metres of air every day. That’s about 20,000 breaths. Children breathe almost twice that amount because they are smaller, and their respiratory systems are still maturing. 

The environment consists of four segments namely Biosphere, Lithosphere, Hydrosphere and Atmosphere.

Biosphere: The environment which supports life and sustains various human activities is known as biosphere. Word Biosphere is derived from Latin word, BIO, which means Life.

Lithosphere: It is the outer mantle of the solid earth i.e. earth crust consisting of rocks and soil. The soil is the most important part of lithosphere. Word lithosphere is derived from Latin word, LITHO, which means stone.

Hydrosphere: It includes all kinds of water resources, oceans, rivers, lakes, streams, glaciers, polar ice caps and ground water. Word Hydrosphere is derived from Latin word, HYDRO, which means Air.

Atmosphere: It is the protective blanket of gases surrounding the earth. The main components of the atmosphere are nitrogen (78%), oxygen (20.95%) and minor components are argon, hydrogen, ozone and other inert gases like helium and neon. Word Atmosphere is derived from Latin word, ATMO, which means Air.

Composition of Air

Air is invisible, colourless, odourless and tasteless. Air has mass and it exerts pressure. Air is not a single gas. It is a mixture of many gases, water vapour and other particulate matter. The actual composition of air varies from place to place.  Near the earth’s surface, air mainly consists of nitrogen and oxygen, carbon dioxide and water vapour. Of all the components of air, carbon dioxide (CO₂) has the highest solubility in water.

The actual average composition of the air near the earth’s surface (atmosphere) is given below in table: The percentage of almost all the gases except carbon dioxide, remain nearly constant. The proportions of carbon dioxide (CO₂), water vapour (H₂O) and dust/smoke particles in the air keep changing from time to time and place to place. For example, the air around an industrial area contains more carbon dioxide.

IMPORTANCE

Air is used to burn things, for example, a log. The oxygen in the air reacts with the stuff in the log to make a bunch of new stuff. The air we breathe in (this is important - if we don't breath, we die pretty quick) is used to burn the stuff we eat to make energy that we can use to eat more. The oxygen in the air pretty much drives our life. Plants use the carbon dioxide in the air to make sugars which they will later burn for energy. Air also suspends clouds, which are water and turn into rain. This means that water moves around a lot. If water just sat around, a lot of things could only grow in a river. Air also suspends objects. Think of it as swimming in water - just harder, so hard that it takes a bunch of smart people to figure out just how. Planes "float" on air. Air holds heat, too. If there was no air, night would be colder than that stuff the doctor uses to freeze off your warts. All that energy from the sun would just leave instead of being held in by the air. Air can also be a problem, it is hard for things to move around in it and it can push things. When you are walking around your living room this is not noticeable, but when you are driving a car really fast and watching that gas tank empty (or being impaled by flying debris in a hurricane) the "push" of air becomes a lot more noticeable.

·         Air also suspends clouds, which are water and turn into rain.

·         The air we breathe in (this is important - if we don't breath, we die pretty quick) is used to burn the stuff we eat to make energy that we can use to eat more. The oxygen in the air pretty much drives our life.

·         Plants use the carbon dioxide in the air to make sugars which they will later burn for energy.

·         Air also suspends objects.

·         Air holds heat, too.

·         Air maintain temperature

·         Due to the air movement, we can dry things & it can covert to electricity.

·         Air plays major role in chemical process

VENTILATION

Ventilation can be defined as the process of applying fresh air and removing contaminated air by natural or mechanical means to or from an enclosed area or any particular environment to provide excellent condition for working and living. Adequate ventilation is prime requirement but air movement, temperature, humidity conditions and purity of fresh air also equally important.

The rate of air change will depend upon the volume of the room. The changes of the air required as for the activity going on that premises, number of persons using premises etc. It will also depend on high velocity of fresh air quantity of heat, moisture and odour present in the room. The rate of air change should not be too frequent as it will result in discomfort due to high velocity of temperature and humidity.

Air conditioning: It can be defined as the simultaneous control of temperature humidity and air motion.

Industrial ventilation: Ventilation is the mechanical system in a building that brings in "fresh" outdoor air and removes the "contaminated" indoor air. In a workplace, ventilation is used to control exposure to airborne contaminants. It is commonly used to remove contaminants such as fumes, dusts, and vapours, in order to provide a healthy and safe working environment. Ventilation can be accomplished by natural means (e.g., opening a window) or mechanical means (e.g., fans or blowers). Industrial systems are designed to move a specific amount of air at a specific speed (velocity), which results in the removal (or "exhaust") of undesirable contaminants. While all ventilation systems follow the same basic principles, each system is designed specifically to match to the type of work and the rate of contaminant release at that workplace.

There are four purposes of ventilation: 

1.      Provide a continuous supply of fresh outside air.

2.      Maintain temperature and humidity at comfortable levels.

3.      Reduce potential fire or explosion hazards.

4.      Remove or dilute airborne contaminants.

Necessity of ventilation

• To create air movement.
• To prevent an undue accumulation of CO₂ and moisture.
• To prevent depletion of O₂ content in air.
• To prevent flammable concentration of gas vapour and dust.
• To prevent undue concentration of body odours, Fumes, dust and other industrial products.
• To prevent undue concentration of bacteria carrying particles.
• To prevent condensation in the building.
• To remove body heat liberated by other equipment. When heat gain or solar radiation is excessive, then air –conditioning should be considered.
• To prevent suffocating conditions in halls, cinema halls and other such building where mass assembly is of the regular feature.
• To admit fresh air and push out contaminated air.

Factors affecting ventilation

• Rate of fresh air change.
• Control on humidity.
• Quality of air.
• Temperature.
• Use of the building.

Saturated air: When a specific volume of air at a specify temperature holds as much water vapour as it can. It is said to be saturated air at that temperature.

Relative humidity: The relative humidity of the air is the amount of water that is present in the air compared to the greatest amount it would be possible for the air to hold at that temperature: If relative humidity is more or less than the desired value at specific temperature, It causes discomfort to the occupants for eq. at 21°C range of 30° to 70°C relative humidity is considered desirable.

Essentials of a good ventilating system

1)      It should admit required amount of fresh air in the room.

2)      It should effectively extract the contaminated air in the room.

3)      All the corners of the room should get proper ventilation.

4)      The value of the desired relative humidity should be maintained.

5)      Effective temperature should be maintained with regard to human comfort.

6)      It should exercise full control or incoming air and extracted air.

7)      The ventilating air should be free from impurity like dust odour etc.

TYPES OF VENTILATION

 Mechanical or forced ventilation: through an air handling unit or direct injection to a space by a fan. A local exhaust fan can enhance infiltration or natural ventilation, thus increasing the ventilation air flow rate.

Natural ventilation occurs when the air in a space is changed with outdoor air without the use of mechanical systems, such as a fan. Most often natural ventilation is assured through operable windows but it can also be achieved through temperature and pressure differences between spaces. Open windows or vents are not a good choice for ventilating a basement or other below ground structure. Allowing outside air into a cooler below ground space will cause problems with humidity and condensation.

Mixed Mode Ventilation or Hybrid ventilation: utilises both mechanical and natural ventilation processes. The mechanical and natural components may be used in conjunction with each other or separately at different times of day. The natural component, sometimes subject to unpredictable external weather conditions may not always be adequate to ventilate the desired space. The mechanical component is then used to increase the overall ventilation rate so that the desired internal conditions are met. Alternatively the mechanical component may be used as a control measure to regulate the natural ventilation process, for example, to restrict the air change rate during periods of high wind speeds.

Infiltration is separate from ventilation, but is often used to provide ventilation air.

Infiltration is the unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope and through use of doors for passage. Infiltration is sometimes called air leakage. The leakage of room air out of a building, intentionally or not, is called exfiltration. Infiltration is caused by wind, negative pressurization of the building, and by air buoyancy forces known commonly as the stack effect.

SYSTEM OF VENTILATION

There are two systems of ventilation Natural ventilation and Mechanical or artificial ventilation.

1.         Natural ventilation

Natural system of ventilation is considered suitable for small houses and not for big buildings like assembly hall, theatre, Auditorium and large factory, workshops. The systems of ventilation largely depend upon the scientific location of doors, windows, ventilation etc. The wind is supply inside the building, doors, windows and other opening. The wind enters the room and gets heated of and lifted of induce cores of time. Heated air is driven out through ventilation provided near ceiling. An opening area equal to not less than 1/20th of the floor area of the room should be provided for proper ventilation. The top of this opening area should be not more than 45cm bellow the ceiling. The rate of ventilation by natural means depends upon two effects and principals. First principal is depends on wind effect or wind actions upon the

a.       Wind effect or wind action

b.      Stack effect

Wind effect or wind action: Ventilation by wind effect is affected by the direction and velocity of outside wind and sizes and positions of the openings. Wind create pressure difference and when it blows against a building causes a positive pressure on the wind ward side and suction on the lee ward side. This pressure difference causes wind to blow through the building and causes air change if proper opening are provided. This action is known as wind effect or wind action.

Stack effect: Fresh admitted air inside the building is cool and heavy. This become hot after some time and is lifted up. Lifted up air is escaped through ventilators or openings in the roof. Fresh again comes in the building gets lifted up by heating and again escape through opening provided near the ceiling. This effect cause flow is the wind in upward direction and is known as stack effect.

2. Mechanical system of ventilation

The system of ventilation in which some mechanical arrangement are make to provide adequate ventilation in the room is called as mechanical system of ventilation. It is costly method but it result in considerable increase in the efficiency of the person working under such condition. This system is applicable for big offices, bank, theatres, auditoriums and industrial plants. Mechanical ventilation is broadly classified into 4 types.

a.      Extract or exhaust system: In this system, partial vacuum is developed inside the room by extracting contaminated air by fixing fans or blowers at the outlets. The pressure inside being low, the fresh air from outside force in through doors and windows and through available opening. In this system continuous fresh air flow inside the room can be maintained.

b.      Supply or Plenum system: This system is reverse of exhaust system. Fresh air is poured with the help of input fans or blowers into the room and polluted air allowed to leave the room by it-self. In this case pressure inside the room is greater than that of the atmospheric and as such all leakage of air is outwards. Mostly this system is use in Bakery.

c.       Balancing system: This system use it supply fan to supply and to extract air. It enables full control over air movement and conditions to be obtain, and should be used where accurate performance is required. Recirculation of air is possible in this system.

d.      Air Condition: The process of creating, controlling and maintaining indoor atmospheric condition suited to requirement for man or to the needs of thing is called A.C. This process consist of conditioning of air with respect to humidity, temperature, odour, bacteria content, dust content and air movement and so that comfortable condition are maintained inside the room.

Packaged air condition: Window air cooled packaged units are available up to a limited capacity. Floor mounted self-contained packaged units are made to meet the requirements for large capacity. This unit comprises a compressor, condenser, evaporator, fans, filters and controls. It may also include means for heating, humidifying or ventilating air. This units are a designed for application is residences and in the smaller commercial market, shops, restaurants, small office units etc. The package unit can be mounted within air conditions space or remote in a separate enclosure commercial packaged air conditioners are available in sizes of normal cooling capacity 10,000W and above.

Temperature control

*  Temperature range which is liked by majority of people is called comfortable zone.

*  The comfortable zones are different for winter and summer due to the changes in the body temperature.

*  Effective temperature zones for summer and winter range between 20 to 23°C and 18 to 22°C respectably.

*  The temperature of 21°C to 22.5°C is regarded as most likely comfort temperature in a room. Regardless of outside temperature.

AIR POLLUTION

Air pollution is the introduction into the atmosphere of chemicals, particulates, or biological materials that cause discomfort, disease, or death to humans, damage other living organisms such as food crops, or damage the natural environment or built environment. The atmosphere is a complex dynamic natural gaseous system that is essential to support life on planet Earth. Stratospheric ozone depletion due to air pollution has long been recognized as a threat to human health as well as to the Earth's ecosystems. There are two types of pollutants: Primary pollutants are those gases or particles that are pumped into the air to make it unclean. They include carbon monoxide from automobile exhausts and sulphur dioxide from the combustion of coal. Secondary pollutants: When pollutants in the air mix up in a chemical reaction, they form an even more dangerous chemical. Photochemical smog is an example of this, and is a secondary pollutant.

Air pollutants consist of gaseous pollutants, odours, and SPM, (suspended particulate matter) such as dust, fumes, mist, and smoke. The concentration of these in and near the urban areas causes severe pollution to the surroundings. The largest sources of human-created air pollution are energy generation, transportation, and industries that use a great deal of energy sources. Depending on their source and interactions with other components of the air, they can have different chemical compositions and health impacts. Since these pollutants are generally concentrated in and around urban areas, the outdoor urban pollution levels are far higher than in the rural areas.

Fires are another major source of air pollution and can lead to severe problems if the smoke is inhaled for a period of time. These fires can either be forest fires, oil well fires, burning of leaves in the backyard or as in the case of rural areas, large-scale burning of agricultural waste. Other sources include industries and power plants located in these areas. Some of the common pollutants and there effects on health are:

Indoor air pollution

Cooking and heating with solid fuels on open fires or traditional stoves results in high levels of indoor air pollution. Indoor smoke contains a range of health-damaging pollutants, such as small particles and carbon monoxide. Indoor cooking and heating with biomass fuels (agricultural residues, dung, straw, wood) or coal produces high levels of indoor smoke that contains a variety of health-damaging pollutants. There is consistent evidence that exposure to indoor air pollution can lead to acute lower respiratory infections in children under five, and chronic obstructive pulmonary disease and lung cancer (where coal is used) in adults.

PREVENTION OF AIR POLLUTION:

Solution efforts on pollution are always a big problem. This is why prevention interventions are always a better way of controlling air pollution. These prevention methods can either come from government (laws) or by individual actions. In many big cities, monitoring equipment has been installed at many points in the city. Air pollution can be avoided by using simple practices like:

*        Using smokeless sources of energy like smokeless stoves, which use biogas, solar energy, etc.

*        Using devices for filtering smoke in chimneys of factories and powerhouses.

*        Planting more trees.

*        Locating industries away from residential areas.

*        Strictly checking pollution levels in automobiles’ exhaust emission.

*        Bifurcate smoking and non-smoking areas of hotel.

*        Smoking zones should be there in open air and it should be denoted as smoking zone.

*        Encourage the guest to not smoke in non-smoking areas, rooms, public areas etc.

*        The smoking zone should be nearby Bar to assist drunken guest for smoking.

A “green” lodging property is a property that is managed to be environmentally-friendly, by making a conscious effort to reduce pollution. Many people prefer to stay at a hotel that follows “green” principles; this may result in increased income. Being a “green” hotel, which includes improving air quality, tells the world that the environment is important to you. Being a “green” hotel also raises the awareness of both your staff and guests about the need to be as environmentally-friendly as possible. When your guests learn about a hotel’s environmental activities, they provide positive feedback, indicating increased customer satisfaction.

Health effects of CFCs

Chlorofluorocarbons (CFCs) are organic compounds, and contain carbon, fluorine and chlorine atoms. The most notable effect of CFCs on the environment is the depletion of the ozone layer. The ozone layer is essential to most life on Earth, as it shields life forms from a large portion of the UV (ultraviolet) rays from the sun. Depletion of the ozone layer can lead to various problems for humans and other life forms on Earth, which lead to strong regulation, imposed on CFCs. CFCs damage the ozone layer. One example of the consequences of CFCs is the ozone layer hole right above the South Pole. There is evidence to suggest that CFCs, or chlorofluorocarbons, deplete the ozone layer. The problem with this is that with the depletion of the ozone layer comes a loss of protection from harmful UV radiation from the sun. For example, in New Zealand where the air is purest and the ozone layer thinner, rates of skin cancer are among the highest in the world. Since the appearance of an ozone hole over the Antarctic in the early 1980s, Americans have become aware of the health threats posed by ozone depletion, which decreases our atmosphere's natural protection from the sun's harmful ultra-violet (UV) rays. Eye Damage, Immune Suppression Skin Cancer etc. are most common disease due to CFC.

SUMMARY

The only reason Earth can sustain life is because of its atmosphere, which keeps air readily available for chemical reactions. A number of different gases, including oxygen, make up the Earth's atmosphere in a mixture that keeps plants, animals and people alive. In addition to sustaining life, air plays a role in many other important functions that are best performed when air quality is high.

Since the onset of the industrial revolution, there has been a steady change in the composition of the atmosphere mainly due to the combustion of fossil fuels used for the generation of energy and transportation. Hotels can be blamed to produce more pollution as compare to other industry and sector. Lodging properties can produce toxic air pollutants and ozone-depleting substances. Cleaning supplies, synthetic materials, paints, and pesticides can release toxic air pollutants and volatile organic compounds (VOC). Although emitted indoors, these air pollutants will also eventually leak into the outdoor air through doors, ventilation systems, and other

Air pollution is contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere. Household combustion devices, motor vehicles, industrial facilities and forest fires are common sources of air pollution. Pollutants of major public health concern include particulate matter, carbon monoxide, ozone, nitrogen dioxide and sulphur dioxide. Outdoor and indoor air pollution cause respiratory and other diseases, which can be fatal. Air is mainly composed of nitrogen, oxygen, and argon, which together constitute the major gases of the atmosphere. The remaining gases are often referred to as trace gases, among which are the greenhouse gases such as water vapour, carbon dioxide, methane, nitrous oxide, and ozone. Filtered air includes trace amounts of many other chemical compounds. Many natural substances may be present in tiny amounts in an unfiltered air sample, including dust, pollen and spores, sea spray, and volcanic ash. Various industrial pollutants also may be present, such as chlorine (elementary or in compounds), fluorine compounds, elemental mercury, and sulphur compounds such as sulphur dioxide [SO₂]. Dry air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapour, on average around 1%.

Recycle and re-use things. This will minimize the dependence of producing new things. Remember manufacturing industries create a lot of pollution, so if we can re-use things like shopping plastic bags, clothing, paper and bottles, it can help.

FACTS

ü  CNG  (Compressed natural gas)  is a clean fuel

ü  DDT causes excessive growth of algae in water bodies.

ü  Ozone hole is largest over Antarctica.

ü  Carbon monoxide is a pollutant because it Causes burning of eyes

DEFINITIONS FOR TERMS

1.      SPM: suspended particulate matter

2.      Ventilation rate: the amount of outdoor air that is provided into the space, and the quality of the outdoor air.

3.      Acid Rain: Rain that is especially acidic (pH is less than 5.2). Principal components of acid rain typically include nitric and sulphuric acid. These may be formed by the combination of nitrogen and sulphur oxides with water vapour in the atmosphere.

4.      Air Pollution: Degradation of air quality resulting from unwanted chemicals or other materials occurring in the air.

5.      Air Pollutants: Amounts of foreign and/or natural substances occurring in the atmosphere that may result in adverse effects to humans, animals, vegetation and/or materials.

6.      Catalyst: A substance that can increase or decrease the rate of a chemical reaction between the other chemical species without being consumed in the process.

7.      Volatile organic compounds (VOCs) -- Organic chemicals all contain the element carbon (C). Organic chemicals are the basic chemicals found in living things and in products derived from living things, such as coal, petroleum, and refined petroleum products. Many of the organic chemicals we use do not occur in nature, but were synthesized by chemists in laboratories. Volatile chemicals readily produce vapours at room temperature and normal atmospheric pressure. Vapours escape easily from volatile liquid chemicals. Volatile organic chemicals include gasoline, industrial chemicals such as benzene, solvents such as toluene and xylene, and tetrachloroethylene (perchloroethylene, the principal dry cleaning solvent). Many volatile organic chemicals, such as benzene, are also hazardous air pollutants.

8.      Zero Air -- Pure air, used for calibrating air monitoring instruments. The EPA requires zero air to have less than 0.1 ppm of hydrocarbons.

9.      Sulphur dioxide -- A criteria air pollutant. Sulphur dioxide is a gas produced by burning coal, most notably in power plants. Some industrial processes, such as production of paper and smelting of metals, produce sulphur dioxide. Sulphur dioxide is closely related to sulphuric acid, a strong acid. Sulphurs dioxide plays an important role in the production of acid rain.

10.  Ozone depletion -- The reduction in the stratospheric ozone layer. Stratospheric ozone shields the Earth from ultraviolet radiation. The breakdown of certain chlorine and/or bromine-containing compounds that catalytically destroy ozone molecules in the stratosphere can cause a reduction in the ozone layer.

11.  Cyclone: An air pollution control device that removes larger particles -- generally greater than one micron -- from an air stream through centrifugal force.

12.  Combined Heat and Power (CHP): An approach to generating power and thermal energy from a single fuel source. CHP application involves the recovery of otherwise wasted thermal energy to produce additional power or useful thermal energy.

13.  Asthma: a medical condition characterized by abnormal restriction of breathing, especially in response to allergens or air contaminants.

14.  Greenhouse Effect: the warming of the earth's atmosphere caused by a build-up of carbon dioxide and other trace gases. This build-up allows light from the sun's rays to heat the earth but prevents a counterbalancing loss of heat

15.  Global Warming: An increase in the temperature of the Earth's troposphere. Global warming has occurred in the past as a result of natural influences, but the term is most often used to refer to the warming predicted by computer models to occur as a result of increased emissions of greenhouse gases.

16.  Greenhouse Gas: A gas, such as carbon dioxide or methane, which contributes to potential climate change.

17.  Smog is a type of air pollution; the word "smog" was made in the early 20th century as a portmanteau of the words smoke and fog to refer to smoky fog.

References: Principles of Food Sanitation (Fifth Edition) Norman G. Marriottand Robert B. Gravani, food sanitation (Rufus K. Guthrie http://labspace.open.ac.uk/course/view.php?id=6724

                                         

TEST YOURSELF

Fill in the blanks

1.      The environment consists of _________ segments.

2.      Atmosphere consists of about ___________ nitrogen.

3.      Atmosphere consists of about ___________ oxygen.

4.      Stack effect is due to ___________ type of ventilation

5.      Word Atmosphere is derived from _________ word, ATMO, which means Air.

6.      Word Biosphere is derived from _________ word BIO, which means _________.

7.      Word CHP stands for ___________.

8.      The only reason Earth can sustain life is because of its ________________.

9.      Smog is mixture of _________ and _________.

10.  Carbon monoxide is a pollutant because it Causes _____________.

11.  Refrigerators and air conditioners have _________ gas.

12.  Acid rains are due to __________________.

13.  Use of excessive fertilizer in fields leads to the deficiency of _______in the nearby water body.

14.  CNG stands for ______________.

Answer the Questions:

1.      What is air pollution? Describe common pollutant.

2.      Write a brief description of components of air.

3.      Write importance and function of air.

4.      What is ventilation? Describe types of ventilation.

5.      Explain how CFC is harmful for health.

6.      What are the environmental effects of pollutant gases?

7.      What is stack effect?

ANSWER KEYS

Fill in the blanks

1.      4

2.      78%

3.      21%

4.      Mechanical or artificial

5.      Natural

6.      Latin

7.      Latin , Life

8.      Combined Heat and Power

9.      Atmosphere

10.  smoke and fog

11.  Burning of eyes

12.  Chlorofluorocarbons

13.  Oxides of sulphur

14.  Oxygen

15.  Compressed natural gas

SEWAGE DISPOSAL

SEWAGE DISPOSAL

INTRODUCTION

Sewage means while bathing, cleaning utensils, washing clothes, cleansing the house cooking etc. the man uses water and throws away the used water. This is broadly classified as sullage. Human excreta and urine form “sewage” which may also include the animals waste the dung and urine. Liquid wastes which include waste water from sinks and drains from the kitchen, dish washing areas, laundry, bathrooms , toilets, and other drains from the building and yard which is normally carried away by underground sewages. It contains human excreta, chemicals like detergents, pesticides, and oil. It is one of the most dangerous sources of human pathogens and should not come in contact with food, water, utensils, equipment or any other food contact surface. Sewage must be kept separate from other wastes because of the presence of pathogens. Disposal of sewage in a sanitary manner thus forms a pre-requisite for good food sanitation, As far as possible sewage should be disposed of in a public sewage system or in a manner approved by the health authority.

Sewage is the mixture of liquid, faeces, toilet paper and food wastes produced by people. The liquid in sewage includes urine (piss) and wastewater which comes from the toilet, kitchen, bathroom and laundry.

Sewage contains lots of disease-causing germs and parasites. Sewage is treated to get rid of as much of the solid matter as possible. The remaining liquid is called effluent.

Getting rid of sewage and effluent is called sewage disposal. If sewage is not disposed of or contained correctly people may come into contact with it and get very sick. There are different ways to dispose of sewage. Whichever method is used, it is important to make sure that it does not:

·         cause dangerous conditions which allow people to come into contact with disease-causing germs

·         cause pollution of a water supply

·         allow the breeding of insects such as mosquitoes or cockroaches which can carry disease-causing germs inside or on their bodies as a result of eating or walking in sewage

·          produce bad smells

Disease-causing germs can be spread from sewage if it is not disposed of properly or if people do not practise proper toilet hygiene (cleanliness). If a sewage disposal system is not properly maintained it will not be able to get rid of the sewage safely. For a sewage system to be properly maintained, all faulty (blocked, damaged, broken or worn-out) parts must be mended as soon as possible after they stop working correctly.

Diseases caused by germs:

Bacterial: salmonellosis, shigellosis, diarrhoea, trachoma, melioidosis

Viral: gastroenteritis, hepatitis A

Diseases caused by parasites: giardiasis, dwarf tapeworm infection, threadworm infection, hookworm infection, strongyloidasis

These disease-causing germs and parasites can be spread:

·         directly by people coming into contact with sewage or toilet waste (this can happen, for example, when people walk through sewage which has leaked onto the ground from broken sewage pipes)

·          Indirectly by people: coming into contact with animals such as flies and cockroaches which carry the germs and parasites in or on their bodies. Dogs and cats can carry germs and parasites to drinking water which has been contaminated by sewage.

 Sewage or effluent collecting in pools as a result of an overflowing sewage lagoon or broken sewage pipes. This sewage and effluent contains disease-causing germs and parasites and allows mosquitoes to breed, Uncovered or broken septic tanks which allow effluent to escape, meaning that people or pets can directly be exposed, Blocked, overflowing toilets which make it easy for children to come into contact with germs, Leach drains from septic tanks which are too close to drinking water supplies so that effluent soaks through the soil into the water supply

IMPORTANCE

Sewage Disposal, or wastewater disposal various processes involved in the collection, treatment, and sanitary disposal of liquid and water-carried wastes from households and industrial plants. The issue of sewage disposal assumed increasing importance in the early 1970s as a result of the general concern expressed in the United States and worldwide about the wider problem of pollution of the human environment, the contamination of the atmosphere, rivers, lakes, oceans, and groundwater by domestic, municipal, agricultural, and industrial waste.

The sewage treatment process facilitates the achievement of water quality objectives. In addition to nutrient recycling, advanced treatment of wastewater often includes associated unit processes which support the optimization of resource use. Some of these unit processes include the conversion of sludge into various beneficial by-products, and the process of extracting thermal energy from sewage and wastewater. In addition, the sewage collection system can be used as a conduit for optical fibre cables and other communications infrastructure. Sewage facilities must operate under severe conditions created by the constant flow of highly corrosive wastewater and have to continuously pump and treat wastewater on a 24-hour basis. To ensure the provision of safe and reliable services, it is necessary to operate and maintain these facilities in an efficient manner.

COLLECTION OF SEWAGE:

Domestic Wastewater (from homes, offices, hotels, institutions) comprises sewage (human waste) and grey water from bathrooms, kitchens, laundries). Industrial Wastewater is the liquid discharge from manufacturing processes; for example soft drink and beer companies; sugar processing; metal processing; photo finishing.

The collection and removal of refuse is called sewage system. In cities which have comprehensive sewerage system the total wastes- the sullage and sewage- is collected in the system taken to point outside the city, treated and disposed of since sewage contains faecal matter it is more in-sanitary in character than the sullage. Thus, when the two are not taken care of together in regular sewerage system the sewage part has to be dealt with sufficient care. In catering industry we have got two types of collection system of sewage. One is Open type system and second is close type system.

Sewage Collection: There are two types of sewage collection principles - combined and separate. Combined sewers carry away both rainwater and wastewater, while separate sewers take care of wastewater and rainwater in separate pipes. Combined sewage collection systems are often used because the cost of construction is less than that of a separate system. In a combined sewage collection system, the rainwater mixed with wastewater is allowed to flow directly into rivers and adjacent water bodies during wet weather conditions. In a separate sewage collection system, rainwater mixing with wastewater is minimal, but the problem of pollutants on road surfaces being carried into rivers and coastal waters still exists. These garbage are collected from various sources like Service Latrines, Un-serviced latrine, Sewerage system, Pipes, Manholes, Pumping station, Treatment, Disposal etc.

A separate drainage system is one were the foul water and the surface water are always kept separate. When a separate system is used then the sewerage treatment plant will not get overloaded in periods of wet weather.

A separate sewer system consists of two different sewer pipes running one on top of the other, or “piggyback.” In most instances, the sanitary pipe is below the storm pipe. The sanitary sewer pipe transports sanitary sewage collected from the laterals (plumbing connections) of homes, businesses, and industry to treatment plants. The rainstorm water sewer pipe carries water collected from street inlets, building downspouts, and other storm sewer lines to a nearby receiving stream and is discharged through a Rainstorm water Outfall. The construction of a separate sewage collection system is relatively expensive and more complex due to the need to install two sets of pipes.

Pumping Stations:

Wastewater collected by the sewers flows by gravity and is relayed to treatment plants by pumping stations. In flat land, sewers tend to be laid deeper and pumping stations must be used to lift the sewage closer to the surface where it can be treated in a sewage treatment plant. Pumping stations often have both wastewater and rainwater pumping facilities. Where this is the case, the rainwater is usually pumped into subsurface aquifers below sea level or into the sea directly to prevent inundation of rivers and surface waters.

Wastewater Treatment Plants

The principal role of a wastewater treatment plant is to remove pollutants from wastewater and to discharge the treated effluent into an adjacent water body such as a river or the sea. Treatment plants can be divided into discrete unit processes as outlined below.

Grit Chamber - Within a wastewater treatment plant, raw wastewater first enters a grit chamber. As the wastewater flows gently through the chamber, solids (such as sand, grit and gravel) settle to the bottom, and are removed by buckets, while large suspended matter is removed by screens. The wastewater is then pumped into a primary sedimentation tank.

Primary Sedimentation Tank - As the wastewater flows slowly in a primary sedimentation tank for two to three hours, organic solids gradually settle to the bottom. This mass of solids is called raw sludge, and is sent to a sludge treatment facility for further treatment. To make the most of available land, double-decker sedimentation tanks are used at some wastewater treatment plants.

Aeration Tank - The major role of the aeration tank is to remove the soluble organic material that escaped treatment in the primary sedimentation tank and to provide further removal of suspended solids. In order to ensure the sufficient and rapid decomposition of organic material, it is necessary to promote the growth of microorganisms capable of absorbing these soluble organic materials. In the activated sludge process, the aeration tank mixes and agitates wastewater and activated sludge. During the 6 to 8- hour aeration period, the microorganisms absorb the organic matter as nutrients, and they grow as a result. This decomposes the organic matter into inorganic substances such as water and carbonic acid gas. The suspended solids adhere to microorganisms and then form clots that can be easily removed as sediment.

Activated sludge contains a large quantity of microorganisms and is based on the same principle as nature's process of purifying water. The activated sludge process involves putting activated sludge into wastewater and decomposing organic matter into such inorganic substances as water and carbon dioxide through the metabolic activity of the microorganisms.

Secondary Sedimentation Tank - While the mixture from the aeration tank flows slowly in a secondary sedimentation tank, it is separated into solids (activated sludge) and an aqueous portion (or supernatant). Part of the activated sludge is returned to the aeration tank, and the rest is treated in a sludge treatment facility. The secondary effluent is usually discharged into the receiving environment after chlorination. Following advanced treatment, part of the sewage treatment plant effluent is often used for miscellaneous purposes in the plant and as water for toilets in buildings. In addition, it can be used to augment the flow of smaller streams. In some cities such as Tokyo, double-decker secondary sedimentation tanks are used to make more effective use of available land.

Sludge Treatment - The raw sludge from the primary sedimentation tank and the excess sludge are pumped to thickening tanks. In the thickening tank, the volume of the sludge is reduced to about one-quarter of the volume of the raw sludge. The thickened sludge is then mechanically dehydrated. The sludge is sometimes sent to a digestion tank after being thickened. There are different types of sludge drying (or dehydrating) machines, including vacuum, centrifugal, filter press, and belt press. Dehydrated sludge is often burned and becomes ash. The ash generated by incinerating sludge is usually about 1% of the original sludge volume.

A combined sewer is a type of sewer system that collects sanitary sewage and rainstorm water runoff in a single pipe system. Combined sewers can cause serious water pollution problems due to combined sewer overflows, which are caused by large variations in flow between dry and wet weather. This type of sewer design is no longer used in building new communities, but many older cities continue to operate combined sewers. The image of the sewer recurs in European culture as they were often used as hiding places or routes of escape by the scorned or the hunted, including partisans and resistance fighters in World War II. Fighting erupted in the sewers during the Battle of Stalingrad. The only survivors from the Warsaw Uprising and Warsaw Ghetto made their final escape through city sewers. Some have commented that the engravings of imaginary prisons by Piranesi were inspired by the Cloaca Maxima, one of the world's earliest sewers.

A combined system is no longer used and joins some or all of the surface water into the foul water drainage system. This means that both surface water and foul water will discharge into the sewerage treatment plant. To avoid the treatment plant being overloaded, it may be possible to extract some foul water at various points in the drainage network. This can be achieved if the surface water is less dense than the foul water and tends to flow at the top in a drain. A separating device can be used to divert surface water into a storm water channel or drain. It is generally agreed that the installation and running costs of sewerage treatment plant can be minimised if a separate system is adopted. For this reason the separate system is favoured by local authorities. During dry weather, the combined sewer system and wastewater treatment plants have the capacity to transport and treat all the sanitary sewage entering the system. However, when flow in the sewer increases as a result of rainfall or snowmelt, the sewer pipes or treatment plants may reach their capacity.

Methods of sewage treatment

Every community should have a way of disposing of sewage so that people, animals and flies cannot touch it. This is called a sewage system. There are different types of sewage systems which can be described as on-site systems and sewage or effluent systems. An on-site system is one which treats the sewage in a septic tank so that most of the sewage becomes effluent and is disposed of in an area close to the house or buildings. An example of an on-site disposal system consists of a septic tank and leach drains. A sewage or wastewater system disposes of the effluent from a community at a central place usually called a sewage lagoon or effluent pond. The sewage can be treated:

·         in a septic tank at each building

·         just before the lagoon in a large septic tank or macerator system, or

·         in the lagoon itself

On-site disposal systems: All the liquid waste from the toilet, bathroom, laundry and sink goes into pipes which carry it to a septic tank. The effluent from the tank is then disposed of through effluent disposal drains often referred to as leach or French drains. Both of these methods of disposing of liquid waste are on-site disposal systems. They must be installed and maintained properly. In these systems, the effluent is soaked into the surrounding soil. Some soils don't allow good soakage such as clay or similar soils; if there are any problems with this disposal system a local government EHO should be consulted to talk about the problem.

On-site disposal systems cannot be installed in all situations. For example, they cannot be installed:

·         in areas that flood regularly

·         in areas that have a high water table (that is, where the underground water is close to the surface)

·         where the amount of wastewater to be disposed of is large near to drinking water supplies

Effluent (wastewater) disposal system: In this method the effluent from the community is carried by large pipes to the lagoon. These pipes serve all the houses and other buildings in the community. The sewage may be either treated in septic tanks at the houses or buildings or at the lagoon. There are no leach or French drains.

Full sewage system: All the sewage from the toilet, shower, laundry and other areas enters waste and sewer pipes directly and is pumped to a lagoon. There are three types of full sewage system:

Sanitary landfill rubbish disposal method

A sanitary landfill site is an area of land where rubbish is dumped in layers or cells. Each layer or cell is covered with sand. Disused quarries, depressions or hollows make good sanitary landfill sites. This rubbish disposal method has been used extensively around cities to fill and level areas for later development.

Care must be taken when choosing a place for this kind of rubbish tip. This is because there may be small rivers or streams underground or a high water table and contaminants in the rubbish tip could soak through the soil into the water beneath. As a result, people and wildlife drinking the water could be poisoned. It is necessary to contact an EHO to help choose a sanitary landfill site. This method also requires a reliable vehicle or machine to maintain the tip and a supply of sand, because each time the rubbish is taken to the tip it must be covered.

TYPES OF SEWAGE

1.      Combined Sewers

2.      Separate Sewers

3.      Simplified Sewers

4.      Solid free sewers

5.      Pressurised sewers

6.      Vacuum sewers

7.      Open channel drains

Combined Sewers: these are large networks of underground pipes that convey domestic sewage, industrial wastewater and storm water runoff in the same pipe to a centralised treatment facility mostly found in urban areas do not require on-site pre-treatment or storage of the wastewater Transport all their wastewater to a WWTP where it is treated and discharged to a water body. Provide a high level of hygiene and comfort for the user at the point of use the ultimate health and environmental impacts are determined by the treatment provided by the downstream wastewater treatment facility.

Separate Sewers: Separate sewer systems are designed to convey wastewater and storm water in separate pipes Sanitary sewer systems collect and transport wastewater Storm sewer systems collect and transport storm water runoff Sanitary sewer systems may also collect wet weather flow via illicit connections from house drains or storm sewers, as well as through defects in the pipes and manholes. The construction costs can be higher than for the combined sewer system because two separated networks are necessary. they provides a high level of hygiene and comfort in a properly constructed separated system the sewage is transported in a closed system directly to the treatment plant and cannot overflow into the environment.

Simplified and Condominal Sewers: describe a sewer system that is constructed using smaller diameter pipes laid at a shallower depth and at a flatter gradient than conventional sewers Allows for a more flexible design associated with lower costs and a higher number of connected households Blockages need to be removed and the system needs to be flushed periodically The pipeline system components, such as cleanouts or ventilation points should be regularly checked and maintained

Solids-free Sewers: These are similar to conventional sewer systems, except that the wastewater is pre-settled and solids removed before entering the system As solids are removed, sewer diameter can be much smaller and they can be constructed using less conservative design criteria (lower gradients, fewer pumps, less pipe depth, etc.) resulting in significantly lower investment costs Due to the simplified design, solids-free sewers can be built cheaper. They are well suited for areas where soak pits are inappropriate due to sensitive groundwater or lack of space for on-site infiltration discharge of non-pre-settled wastewater into the sewers should be prevented require a constant supply of water, although less water is needed compared to conventional sewers.

Pressurised Sewers: Pressurised sewers differ from conventional gravity collection systems, because they use pumps instead of gravity to transport wastewater, The primary effluent is delivered to the collection tank by gravity where it is grinded (pressed) before being transported into the pressurised system by pumps The system can be built with only shallow trenches and relatively small-diameter pipes It is an effective solution where conventional systems are impractical such as in rocky, hilly or densely populated areas or areas with a high groundwater table.

Vacuum Sewers: Vacuum sewer systems use a central vacuum source to convey sewage from individual households to a central collection station Vacuum sewers use differential air pressure (negative pressure) to move the sewage A central source of power to operate vacuum pumps is required to maintain vacuum (negative pressure) on the collection system. This is suitable in areas where a collection is needed but other options are too costly or not feasible, Flat topography: gravity systems demand installation at great depths to maintain adequate flow, areas where rock layers or a high groundwater table make deep excavation difficult, areas short of water supply necessary for operation of gravity systems, areas with obstacles to a gravity sewer route.

Open Channels and Drains: An open channel is a conveyance in which water flows with a free surface Although closed conduits such as culverts and storm drains are open channels when flowing partially full, the term is generally applied to natural and improved watercourses, gutters, ditches, and channels. An open channel or drain system generally consists of a secondary drainage system, with a network of small drains attached. These small drains bring the water to a primary drainage system, composed of main drains (also called interceptor drains), which serve large areas, The main drains are generally connected with natural drainage channels such as rivers or streams. Can be constructed in almost all types of settlements (urban or rural), but enough land area is required to build a reasonable construction. Even though they offer simple solutions for storm water drainage, they bear many risks for public health and the environment due to the risk of illegal discharge of wastewater and solid waste

FLOOR GREASE TRAPS

A grease trap is an engineered device designed to remove spent Fats, Oils and Grease (FOG) and associated solids and debris from food service establishment waste streams, preventing entry of these materials into either municipal sewer collection systems or privately owned on-site wastewater treatment facilities. The grease trap captures those wastes and contains them until a waste hauler or pumper service can properly dispose them. If you operate a food service establishment, you should have and maintain a grease trap. This fact sheet is intended to provide food service establishments with basic common misconceptions about their use; how are they cleaned and maintained; and who regulates their use.

One of the primary purposes of a properly sized grease trap is to retain high temperature spent FOG until cooling and separation of the spent FOG and water can take place. The retention of food service solids lost to the waste stream is also an important function of a grease trap. Large particle solids, with masses greater than that of water, settle to the bottom of the grease trap and are intended for removal along with the floatable spent FOG during periodic cleaning.

Types of Grease Traps

1.      In-Kitchen Passive Interceptors

2.      In-Ground Grease Traps

In-Kitchen Passive Interceptors: These units collect grease as it rises to the top of a small baffled tank when wastewater generated in the facility flows through the unit. The collected grease from these types of traps must be removed manually. Because of their relative small size (typically 20-25 gallons), these traps must be cleaned on a short periodic interval (usually ranging from daily to once a week), depending on the load at each particular food service establishment. If these small units are not cleaned accordingly, they quickly become full of grease and allow spent FOG to enter directly into the waste stream. However, if maintained properly, In-Kitchen Passive Interceptors can remove spent FOG and associated solids at a rate of 95%.

In-Ground Grease Traps: A pre-case concrete grease trap operates on the same principle as the in-kitchen type, only on a larger scale. The most common sizes of in-ground grease traps are in the range of 750 to 2,000 gallons. These larger traps are capable of handling much larger volumes of spent FOG and related material than in-kitchen types. Food service establishments using these larger grease traps must have grease-plumbing companies like AWS clean the traps periodically.

Cleaning & Maintaining Grease Traps

A grease trap should be checked and maintained to ensure it is working properly. Backups, odours and drainage problems are signs that the grease trap is not functioning as it should. By far, the greatest factors affecting the amount of spent FOG released to the waste stream in any food service establishment are the cleaning and maintenance techniques of the kitchen staff. The care taken by staff to dry scrape leftover food and spent FOG from cooking utensils, food preparation equipment and dishes prior to using water is key to reducing the loading of grease traps. Also, the disposing of wastes such as leftover milk and other beverages can have a major effect on the waste stream. Best Practices regarding cleaning and maintaining grease traps include:

*        Dry Clean-up – don’t use the hose as a broom.

*        Prevent spills – this reduces waste and the need for clean-up.

*        Train all staff on the location, purpose and function and proper maintenance of grease trap and interceptors on a frequent basis.

*        Assure that maintenance is conducted on a regular schedule and is written into policies and procedures for facility.

*        The most important management procedure for grease traps is that a company representative be present during any cleaning, pumping or skimming performed by a contractor. This safeguard permits management to respond appropriately to any questions about the services performed.

*        Pump out schedules should be properly established and strictly followed. It is important that these pump outs are complete; i.e., the grease caps removed, the sides scraped or hosed down and the trap refilled with water. The contractor should indicate whether the trap is refilled with clean water or water from the trap.

*        Never “hot flush” (continuously run hot water) the grease trap as the heated, liquefied grease will be flushed down the sewer. While hot flushing may divert the need for pumping, the facility is liable for any costs associated with clogs caused by the flushing.

Many people assume that the amount of spent FOG generated at a particular site is directly related to the type of food being prepared, but this is often not the case. The importance of maintaining a clean and properly operating grease trap is often unknown or overlooked by food service operators. Because spent FOG fills a grease trap from the top down, it is hard to measure the depth of ‘fullness’ of a grease trap on a visual inspection. The most important aspect to remember is that as more spent FOG is retained in a grease trap, the more the separation efficiency diminishes.

Chemical treatment: It consists of using some chemical reaction or reactions to improve the water quality.  Probably the most commonly used chemical process is chlorination.  Chlorine, a strong oxidizing chemical, is used to kill bacteria and to slow down the rate of decomposition of the wastewater.  Bacterial kill is achieved when vital biological processes are affected by the chlorine.  Another strong oxidizing agent that has also been used as an oxidizing disinfectant is ozone. A chemical process commonly used in many industrial wastewater treatment operations is neutralization.  Neutralization consists of the addition of acid or base to adjust pH levels back to neutrality.  Since lime is a base it is sometimes used in the neutralization of acid wastes. Following water and wastewater treatment chemicals:

Ø  polyelectrolytes for primary coagulation and as coagulant aids

Ø  polyelectrolytes for sludge dewatering

Ø  inorganic coagulants (e.g. aluminium sulphate, ferric chloride)

Ø  lime (quicklime and slaked lime)

Ø  soda ash

Ø  caustic soda

Ø  oxidants and disinfectants (e.g. hypochlorite, chlorine dioxide, ozone, hydrogen

Ø  peroxide, bromine)

Ø  ammonium hydroxide

Ø  activated carbon

Ø  fluoride

Chemical toilet is a special type of toilet in which chemicals are used to break down the faeces and urine. It is not often used in dwellings, but is common in caravans and small leisure boats. Chemical toilets are also used in portable (able to be moved) facilities, for example, in toilets on construction sites or at special public events, such as outdoor music festivals. The chemical toilet has a tank attached to it to which chemicals are added, where small capacity tanks are required, such as in caravans, the tanks are usually under the seat. However, where a number of toilets with a large capacity are needed, one large tank may be placed under the ground to receive the sewage from all of the toilets. The chemicals treat the sewage to break down the solid materials to a liquid. When the tank is full, the effluent is pumped out and disposed of at an appropriate site, such as a rubbish tip. The tank is rinsed out and more chemicals are added before it is used again.

CARE & MAINTENANCE OF A SEWAGE SYSTEM

A sewage system which has been properly installed, should, with proper care & maintenance provide many years of service. There are, however, some things which individuals need to be aware of which will help the system function properly.

Ø  Avoid putting Fats, oils & grease, Gasoline, antifreeze, Varnishes, paints & solvents, Caustic drain & harsh cleaners, Photographic solutions, bleach, pesticides, Nail polish remover, Cat box litter, Tampons, sanitary napkins, diapers, paper towels, condoms, Plastics, Coffee grounds, egg shells & other kitchen waste  into a septic system.

Ø  Do not allow roof drains or sump water to discharge into the sewage system.

Ø  Do not allow surface water to drain towards the area of the leaching bed.

Ø  Do not direct water softener and iron filter discharge to the sewage system unless the system has been designed to accept such discharges.

Ø  Water usage in the home should be kept to a minimum. Excessive use, such as doing numerous loads of laundry in one day, could flush solids from the treatment unit (septic tank) into the leaching bed.

Ø  There should be no need to use “starters”, “bacterial feeds” or “cleaners”.

The treatment unit should be inspected at regular intervals & pumped out whenever sludge & scum occupy 1/3 of the working capacity of the tank. Because they contain deadly gases, septic tanks should only be inspected by firms specializing in this work.

Vehicular traffic (including snowmobiles) should not be allowed over the leaching bed.

The area over a leaching bed should have a good cover of grass allowing for adequate sunlight & ventilation to be maintained. Avoid planting shrubs and trees over this area.

PLUMBING HAZARDS IN FOOD ESTABLISHMENTS

Plumbing shall be so sized, installed and maintained as to prevent contamination of the water supply; as to properly convey sewage and liquid wastes from the establishment to the sewage or sewage disposal system; and as not to constitute a source of contamination of food equipment or multiuse utensils or create and un-sanitary condition or nuisance. There shall be no cross connections between the potable water supply and any non-potable or questionable water supply. Where non-potable water systems are permitted for purposes such as air conditioning and fire protection, the non-potable water must not contact directly or indirectly: food, potable water or equipment that contacts food or utensils. The piping of any non-potable water system shall be durably identified so that it is readily distinguishable from piping that carries potable water.

There shall be no cross connections between the potable water supply and any non-potable water supply. The potable water system shall be installed to preclude the possibility of back flow and back siphonage. Devices shall be installed to protect against backflow and backsiphonage at all fixtures and equipment unless an air gap is provided. The air gap must be at least twice the diameter of the water supply inlet, but not less than 1", between the water supply inlet and the fixture's flood level rim.

Cross connection: A cross connection is defined as any connection or structural arrangement between a potable water system and a non-potable source, liquid or otherwise, through which backflow can occur.

Backflow: Backflow is defined as the flow of water or other liquids, mixtures, or substances into a potable water system from any source, other than the intended source.

A connection to a sewer line may be direct or indirect:

*        A direct connection is a solid physical joining to a waste or soil line;

*        An indirect connection is other than a solid physical joining to a waste or soil line (such as a submerged inlet). An indirect connection may be one of two types:

An air gap means the unobstructed vertical distance through the free atmosphere between the lowest opening from any pipe or outlet supplying fixture, or other device, and the flood level rim of the receptacle. The vertical physical separation shall be at least two times the inside diameter of the water inlet pipe above the flood rim level, but shall not be less than one inch.

An air break is a piping arrangement in which a drain from a fixture, appliance, or device discharges indirectly into another fixture, receptacle or interception at a point below the flood level rim. The connection does not provide an unobstructed vertical distance through the free atmosphere and is not solidly connected, but precludes the possibility of backflow to a potable water source into a sink or dishwasher/or fixture being drained.

Backpressure backflow: Backpressure backflow occurs when the pressure of the non-potable system exceeds the positive pressure in the water distribution lines; that is, the water pressure within an establishment's plumbing system exceeds that of the water distribution system. For example, there is a potable water connection to a hot water boiler system that is not protected by an approved backflow preventer. Pressure in the boiler system increases to a point that it exceeds the pressure in the water distribution system, a backflow from the boiler to the public water system may occur.

A downstream pressure that is greater than the potable water supply pressure causes backpressure backflow. Backpressure can result from an increase in downstream pressure, a reduction in the potable water supply pressure or a combination of both. Boiler pumps, pressure pumps or temperature increases in boilers can create increases in downstream pressure. Reductions in potable water supply pressure occur whenever the amount of water being used exceeds the amount of water being supplied, such as during water line flushing, fire fighting or breaks in water mains.

Backsiphonage: Backsiphonage occurs when there is a partial vacuum (negative pressure) in a water supply system, which draws the water from a contaminated source into a potable water supply. The water pressure within the distribution system falls below that of the plumbing system it is supplying. The effect is similar to siphoning or drinking water through a straw. For example, during a large fire, a pump is connected to a hydrant. High flows pumped out of the distribution system can result in significantly reduced water pressure around the withdrawal point. A partial vacuum has been created in the system, causing suction of contaminated water into the potable water system. During such conditions, it is possible for water to be withdrawn from non-potable sources located near the fire -- for example, air-conditioning systems, water tanks, boilers, fertilizer tanks and washing machines -- into buildings located near a fire. The same conditions can be caused by a water main break.  

METHOD AND DEVICES TO PREVENT BACKFLOW

A backflow preventer is a method or mechanical device to prevent backflow. The basic method of preventing backflow is an air gap, which either eliminates a cross-connection or provides a barrier to backflow. Mechanical backflow preventers are devices that provide a physical barrier to backflow. There are four devices commonly used -- the reduced pressure principle assembly, the double check valve assembly, the pressure vacuum breaker and the atmospheric vacuum breaker. All of these devices require periodic maintenance and testing. Other types of mechanical devices, such as the barometric loop, superior pressure type device or the venturi type vacuum breaker, are used for backflow prevention.

The double check valve assembly was one of the first designs during the early 1900s to prevent backflow. Improvements in the early designs of double check valve assemblies ranged from the early metal-to-metal seats to resilient facing on the clapper assembly.

An atmospheric vacuum breaker means a mechanical device which automatically air vents a pipeline to prevent back siphonage. The device shall be located beyond the last control valve prior to the first outlet and at an elevation 6 inches higher than any source of contamination. Atmospheric vacuum breakers shall be installed so that they are not subject to backpressure or continuous operating pressure of more than 12 hours duration.

Ø  Air Gap

Ø  Reduced Pressure Principle Backflow Preventer –RPZ

Ø  Double check valve assembly

Ø  Pressure Vacuum Breaker/ Spill Proof Vacuum Breaker

Ø  Atmospheric Vacuum Breaker

Ø  Vented Double Check

Ø  Atmospheric type vacuum breaker

Ø  Barometric loop

 Air Gap: An air gap is a vertical, physical separation between the end of a water supply outlet and the flood-level rim of a receiving vessel.  This separation must be at least twice the diameter of the water supply outlet and never less than one inch. An air gap is considered the maximum protection available against backpressure backflow or back-siphonage, but is not always practical and can easily be bypassed.

Reduced Pressure Principle Assembly (RP or RPBA): An RP is a mechanical backflow preventer that consists of two independently acting, spring-loaded check valves with a hydraulically operating, mechanically independent, spring-loaded pressure differential relief valve between the check valves and below the first check valve. It includes shutoff valves at each end of the assembly and is equipped with test cocks. An RP is effective against backpressure backflow and backsiphonage and may be used to isolate health or non-health hazards. The RP may be used on all direct connections which may be subject to backpressure or backsiphonage and where there is the possibility of contamination by the material that does constitute a potential health hazard. A health hazard or high hazard is a cross-connection involving any substance that could cause death, illness, spread disease or have a high probability of causing such effects. The degree of hazard refers to a contaminant being toxic on nontoxic, whereby a health hazard involves a toxic substance.

Pressure Type Vacuum Breaker (PVB): A PVB is an assembly consisting of an independently operating, internally loaded check valve and an independently operating, loaded air-inlet valve located on the discharge side of the check valve. The device includes tightly closing shut-off valves on each side of the check valves and properly located test cocks for the testing of the check valve(s). PVBs may be used as protection for connections to all types of non-potable systems where the vacuum breakers are not subject to backpressure. These units may be used under continuous supply pressure. They must be installed above the usage point. This type of vacuum breaker can be used for lawn sprinkler systems under continuous pressure. Therefore, if properly installed, it will protect the potable water supply. The device shall be installed 12 inches above the highest sprinkler head.

Atmospheric Type Vacuum Breaker (AVB): The purpose of the AVB is to prevent a siphon from allowing a contaminant or pollutant into the potable water system. They do not prevent backflow from backpressure. The most commonly used atmospheric type antisiphon vacuum breakers incorporate an atmospheric vent in combination with a check valve. Its operation depends on a supply of potable water to seal off the atmospheric vent, admitting the water to downstream equipment. If a negative pressure develops in the supply line, the loss of pressure permits the check valve to drop, sealing the orifice, while at the same time the vent opens, admitting air to the system to break the vacuum. AVBs can be used on most inlet type water connections which are not subject to backpressure, such as low inlet feeds to receptacles containing toxic and nontoxic substances, valve outlet or fixture with hose attachments, lawn-sprinkler systems and commercial dishwashers.

Barometric Loop: A barometric loop is a looped piping arrangement 35 feet (11 meters) in height in which the water flow goes over the loop at the top. This method of backflow prevention is only capable of protecting against backsiphonage, since backpressure could drive water backward over the loop.

DRAINS: A direct connection may not exist between the sewerage system and any drains originating from equipment in which food, portable equipment, or utensils are placed, except if otherwise required by state plumbing codes. When a ware-washing machine is located within 5 feet of a trapped floor drain, the dishwasher waste outlet may be connected directly on the inlet side of a properly vented floor drain trap.

SUMMARY

Sewage is a major carrier of disease (from human wastes) and toxins (from industrial wastes). The safe treatment of sewage is thus crucial to the health of any community. Sewage wastes can attract insects and rodents, encourage the growth of disease causing bacteria and pollute the environment. Therefore, proper disposal of sewage wastes is an essential part of health protection and disease prevention. If you live in an area where a public sewage disposal system is not available, the responsibility for proper disposal rests with you. The hotel industry can reduce the amount of waste produced by implementing and following a waste management system that is modelled around the concepts of reduce, reuse and recycle called 3R of waste disposal (Green hotelier, 2004). Approximately 54% of a hotel’s solid waste can either be recycled or reused (Alexander 2002). A study by Bohdanowicz (2005) identified that “a large proportion (50-60 %) of the waste materials in an accommodation facility can be recycled or reused”. Sewage treatment plants create an artificial environment to speed up the natural process of breaking down the pollutants in sewage. The treated effluent can then be safely discharged into a local watercourse or soak away system. There are three main process types: Rotating biological contactor (RBC), Aerated filter, Submerged aerated media (SAM). Grease traps are simple primary separation devices that are designed to retain spent FOG and solids long enough for them to be manually or automatically removed. Grease traps are not systems that treat wastewater. Most spent FOB released to the waste stream in food Service kitchens is generated from equipment associated with dishwashing. All sewage including liquid waste shall be disposed of by a public sewage system or by a sewage disposal system constructed and operated according to law. If used, a grease trap shall be located to be easily accessible for cleaning. At least one utility sink or curbed cleaning facility with a floor drain shall be provided for cleaning mops and for the disposal of mop water or similar liquid wastes. The water supply must be properly protected against backsiphonage. A properly sized mop and broom rack shall be provided. All toxic materials including cleaning compounds, pesticides, sanitizers, etc. must be stored in an area away from food preparation. Sewage requires treatment and must be channelled to a wastewater treatment plant. Sewage originates in places of business, industries, and residences. From this source, the sewage flows through a main line into the collection system.  The collection system channels the water from the source to the treatment plant. This system must be entered by operators from time to time for maintenance and inspection.  Manholes and lines between manholes are used to access the collection system. The water flows from one manhole to the next down the line, all the while picking up sewage from service connections.  The sewage in the collection system is either carried directly to the sewage treatment plant or is carried to a pumping station. 

DEFINITIONS FOR TERMS

3R: reduce, reuse and recycle.

Earth Day – Held on April 22 each year to promote awareness of environmental issues, the first Earth Day was in 1970.

Ecology – The scientific study of the relations of living things to one another and to their environment.

Blackwater - Water from toilets carrying human waste.

Liquid Effluent: Generic term for wastewater leaving the septic tank where it is separated from the solid waste material and sent to the drainfield for absortion into the soil.

CSO: Combined Sewer Overflow Outfalls.

Marine debris: Trash or litter in the water.

Sewage Effluent - Sewage that has been separated, solids from liquids, the effluent being the liquid sewage that will be released from the septic tank into the drainage field.

Litter –Waste thrown away in a inappropriate place; improperly stored waste that has escaped from its container; misplaced solid waste.

Pit toilets: Any toilet in which the faeces and urine go directly into a hole in the ground is called a pit toilet. Pit toilets are also called latrines, drop-hole toilets and bore-hole toilets.

VIP latrines: An enhanced version of the pit is the vented improved pit (VIP) latrine. This is a dry drop-hole toilet which has been specially designed so that any flies which enter the hole and crawl over the sewage cannot escape and carry disease-causing germs to people and food. Odours (smells) are reduced and any that do occur are directed away from the community by choosing the right site for the toilet. The VIP latrine has a special snail-shape design. The walls meet the roof and the floor allowing no light into toilet area except through a special air-vent pipe which lets some light into the pit under the seat.

Pan closet toilets: Pan closet toilets were once common in Australian towns. However most, if not all, have been replaced by septic tank and leach drain or full sewage or effluent systems. Pan closet toilets had a bucket under the toilet seat. These toilets were also called bucket latrines. The buckets containing the sewage were taken away once a week or more often if necessary, and a clean, empty bucket put in its place. Special contractors were employed by local authorities to do this work in towns. To stop flies getting into the bucket the toilet seat had a lid on it. To keep the contents in the buckets during transport, lids were put on them. The buckets were then emptied into a special trench at the local rubbish tip. They were washed immediately with phenol or some other disinfectant ready for use again.

EHO: Environmental Health Officers (also known as Public Health Inspectors) are responsible for carrying out measures for protecting public health, including administering and enforcing legislation related to environmental health and providing support to minimize health and safety hazards. They are involved in a variety of activities, for example inspecting food facilities, investigating public health nuisances, and implementing disease control. Environmental health officers are focused on prevention, consultation, investigation, and education of the community regarding health risks and maintaining a safe environment.

Sewage Water or Sewage Effluent - Sewage that has been separated, solids from liquids, the effluent being the liquid sewage that will be released from the septic tank into the drainage field.

References: Principles of Food Sanitation (Fifth Edition) Norman G. Marriottand Robert B. Gravani, food sanitation (Rufus K. Guthrie) www.health.ny.gov/regulations/nycrr/title_10/part_14/subpart_14-1.htm, www.healthunit.org, FOOD ESTABLISHMENT PLAN REVIEW GUIDELINE (fda), Energy and Environment Cabinet Department for Environmental Protection  Kentucky Kentucky.gov

TEST YOURSELF

Think and answer the Questions:

1. Define wastewater treatment.
2. Describe wastewater collection systems.
3. Identify the sources and types of wastewater.
4. Describe the appearance of wastewater.
5. Describe the composition of wastewater.  
6. Identify various sources and types of wastewater.
7. Describe the composition of wastewater.
8. Describe the types of sewage.