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.