CE 264_B Latrine.pdf

1 INTRODUCTION TO ENVIRONMENTAL QUALITY ENGINEERING CE 264 Dr. H.M.K. Essandoh  Content 2  Excreta management:  Classification of excreta disposal systems  Handling of human excreta: o...

1 INTRODUCTION TO ENVIRONMENTAL QUALITY ENGINEERING CE 264 Dr. H.M.K. Essandoh  Content 2  Excreta management:  Classification of excreta disposal systems  Handling of human excreta: on-site and off-site systems  Introduction to solid waste management.  Learning outcomes 3  At the end of the lessons on excreta management you should be able to:  Classify excreta disposal systems based on water use and point of treatment  Describe on-site and off-site systems for handling excreta  Explain how these systems function  Identify advantages and disadvantages associated with each excreta management system  Introduction 4  Three main waste flows are generated by human activities  Human excreta: composed of urine and excreta (black water)  Sullage: originating from bath, laundry and kitchen (grey water), etc  Municipal solid waste: composed of domestic, commercial and industrial waste  Introduction 5  Global sanitation crisis is mainly due to:  Rapid population growth especially in developing countries  Inadequate technology selection to solve local problems at lowest unit cost  The belief that improved water supplies alone would be able to improve public health  Introduction 6  Inadequate sanitation may create environmental stress when it exceeds the natural self purification capacity of the environment  Hygienic disposal of human wastes is very important to the well being and public health of people all over the world  Most diseases occurring in developing countries are related to poor water supply and environmental sanitation (According to WHO)  Major water and sanitation related diseases (Boot, 1984) 7 Group of Infection manifestations diseases Diarrhoeas Cholera, dysentery, diarrhoea Worm infections Roundworm (ascaris), whipworm (trichuriasis), pinworm, hookworm, guinea worm and schistosomiasis (bilharzia) Skin, eye and Scabies, ringworm, yaws, trachoma, louse louse borne borne typhus or relapsing fever infections Mosquito and fly- Malaria, yellow fever, filariasis borne infections (elephantiasis), sleeping sickness, river blindness (onchocerciasis)  Introduction 8  The objective of environmental sanitation is to positively contribute to the sustainable development of a society by providing appropriate sanitation facilities that are:  Appropriate tools to improve public health  Attractive for all categories of users  Financially affordable by users  Provide acceptable solutions for environmental protection 9 Human excreta management Technology options  Sanitation technologies 10  A wide range of sanitation technologies exist world wide.  Traditional pit latrine  Ventilated Improved Pit (VIP) latrine  KVIP latrine  Pour flush latrine  Aquaprivy  Sanitation technologies 11  Urine diverting dry toilet (UDDT)  Enviroloo  Water closet with septic tank  Sewerage system etc.  Feasibility of the technology depends on technical, environmental, cultural and economic criteria.  General criteria for selection of 12 sanitation systems  Surface water should not be contaminated  Groundwater should not be contaminated (e.g. wells, boreholes, springs)  Excreta should not be accessible to flies and domestic animals  General criteria for selection of 13 sanitation systems  There should be no handling of fresh excreta  There should be freedom from odours and unsightly conditions  The system should be simple and inexpensive to construct, use and maintain  Classification of sanitation technologies 14  Sanitation technologies can be classified according to water use and according to the degree of treatment at the source of excreta generation.  Classified according to water use as:  Wet sanitation (Water dependent)  Dry sanitation (Non-water dependent)  Classification of sanitation technologies 15  Classified according to degree of treatment (partial or no treatment) at the point of generation as:  On-site sanitation (treatment occurs at the source of generation)  Off-site sanitation (excreta is disposed of/ treated away from the source where it is generated)  Wet on-site sanitation systems 16  These have water seals which prevent odours from reaching the privy room e.g.  WC + septic tank or cesspool  Pour flush  Aqua privy  Dry on-site sanitation systems 17  Examples of these are  Traditional pit latrine  Trench latrine  VIP latrine  KVIP latrine  Off-site sanitation systems 18  Wet sanitation e.g.  Vault system  WC + sewerage system  Treatment may be by conventional means such as activated sludge, trickling filter or by natural systems such as WSPs  Dry sanitation e.g.  Pan/bucket latrine Sanitation classification based on population density and water needs 19  Sanitation service levels 20  In order of increasing level of service and hygiene offered in their use:  Open field defaecation  Pan/bucket latrine  Traditional pit latrine  VIP latrine  KVIP latrine  Water seal latrines  Conventional sewerage system 21 Traditional pit latrine Dry onsite sanitation technology  Traditional pit latrine - Description 22  A pit latrine is a pit for accumulation and decomposition of excreta and from which the liquid component infiltrates into the surrounding soil.  Pit latrine description 23  A circular, square or rectangular hand dug pit covered with a squatting plate or seat  Depth of pit usually ranges from 2.5 – 6 m but can be as deep as 8m  The pit is usually unlined  A superstructure to provide privacy  Pit latrines 24  Traditional pit latrine - Description 25 26  Operation 27  Excreta is deposited into the pit through the squatting hole  The pit is filled with soil and sealed once the pit is filled with excreta up to within 0.5m of the cover slab  A new pit is dug and the superstructure relocated over the pit.  Advantages of traditional pit latrines 28  Cheap to construct and operate  Quick to construct  No water needed for operation  Any anal cleansing material can be used  Disadvantages 29  Odour nuisance  Attracts flies and other disease-carrying insects which breed in the pit  Unhygienic  Often built poorly and so may pose a danger to users (superstructure easily collapses)  Possible groundwater contamination  Temporary in nature  Children may refuse to use it 30 Borehole latrine Dry onsite sanitation technology  Borehole latrine 31  Similar to the pit latrine except that the hole is bored by an auger  Average depth is about 8 m typical diameter of 400 mm  Advantages 32  The borehole can be excavated quickly if boring equipment is available  Suitable in hard ground conditions  Appropriate where only a small workforce is available  Disadvantages 33  Drilling equipment is required  Latrine lifetime is short because of small volume of pit  Greater risk of groundwater pollution because borehole depths generally result in penetration of the water table  Sides are liable to be fouled causing odour and attracting flies  There is a high likelihood of blockages  Ventilation is impossible because of depth and diameter of borehole 34 Ventilated improved pit latrine Dry Onsite Sanitation Technologies  Ventilated improved pit latrine 35  The VIP latrine is an improvement on the traditional pit latrine  It is a pit latrine with a screened vent pipe and a partially dark interior  Two important features distinguish it from the pit latrine. These are:  It is designed to be safe for the user and to last for at least two years  It has a superstructure slightly offset from the pit and a tall vertical vent pipe with a fly screen fitted on the pit and outside the latrine superstructure  VIP latrine - components 36  A pit to hold accumulated solids  A cover slab with a squat hole and a vent hole  Superstructure lightly offset from the pit  Tall, vertical vent pipe with a fly screen fitted on the pit outside the superstructure  Pit versus VIP latrine 37 38  Description – The pit 39  The top part of the pit is lined to prevent collapse of the walls  Lining materials include bricks, concrete, stone, cement mortar plastered directly onto the surface of the walls of the pit  Holes are left in the lining to allow liquid to seep out of the pit  The bottom of the pit is usually left unlined  The lining is extended to the bottom of the pit in situations where groundwater covers part of the pit  Description – The foundation 40  A foundation built of brick, stone or concrete is provided around the pit.  Functions of the foundation are:  It raises the slab above the ground to prevent stormwater entering the pit  It provides an effective seal between the pit and the slab  The slab is usually bedded onto the foundation with cement mortar  Description – The cover slab 41  A cover slab of reinforced concrete is placed over the pit.  A squat hole which is usually key shaped or pear shape is provided in the slab  A hole is also left for insertion of a vent pipe  The slab is embedded into the foundation and sealed with cement mortar  VIP - Squatting slab 42  A cover slab of reinforced concrete is placed over the pit.  A squat hole which is usually key shaped or pear shape is provided in the slab  A hole is also left for insertion of a vent pipe  The slab is embedded into the foundation and sealed with cement mortar 43  Description – The superstructure 44  The superstructure provides privacy and shade from poor weather  The inside is shaded to prevent flies from entering the privy room  The toilet should be located in an area where there is free flow of air  Adequate ventilation is provided (usually at the front of the building to ensure unrestricted flow of air through the squat hole and up the vent in order to effectively control odour  Description – The superstructure 45  The opening must face the prevailing wind  There must be no other openings at the side or back of the building to prevent short circuiting of wind and ensure that the incoming air goes into the squat hole  Description – The vent 46  The vent may be made of unplasticised PVC, bricks, concrete blocks  The vent pipe is equipped with a fly screen at the upper end. Mosquito netting is often used but aluminium or stainless steel is best.  Important functions of the vent and fly screen are:  The control of odour  Exclusion of flies  Trapping of flies  Description – The vent 47  Ventilation of the pit removes odours and also ensures that any flies are attracted to the odours escaping from the top of the vent pipe and not to the toilet.  The wire fly-screen prevents flies from entering the pit.  The vent – odour control 48  Odour control  The vent creates a strong draught of air that carries all foul smelling gases from faecal matter in the pit up the vent pipe  Continuous ventilation is achieved by air movement (wind, breeze) across the top of the vent pipe  Sunlight also heats the vent pipe causing a convection effect: As the vent pipe is exposed to sunlight, the air column in the pipe is warmer and thus lighter than that in the privy room  The vent –fly control 49  Fly exclusion  Flies are attracted to faecal odours moving up the vent pipe  They therefore concentrate at the top of the vent pipe but are unable to enter the pit due to the presence of the fly screen  Fly trap  Fliesthat find their way into the pit are attracted to light and try to escape through the vent pipe but are trapped.  They eventually fall back into the pit and die  Principles of operation of the VIP 50  Liquid portion of the excreta soaks away into the soil  The solid portion is broken down into simpler compounds though anaerobic digestion by microorganisms  The soluble products of biological digestion are carried into the soil by the liquid portion of the excreta  Gases produced during biological digestion of the excreta (mainly H2S and CH4) are removed by the vent  Principles of operation of the VIP 51  Continuous ventilation is achieved by air movement (wind, breeze) across the top of the vent pipe  Sunlight also heats the vent pipe causing a convection effect.  As the vent pipe is exposed to sunlight, the air column in the pipe is warmer and thus lighter than that in the privy room  Cold air entering the squat hole displaces the foul air in the pit which moves out through the vent pipe.  Principles of operation of the VIP 52  Venting the pit dries the waste which assists in natural destruction of potential pathogens, ultimately rendering a safe humus-like waste product.  The partially dark interior ensures that flies in the pit are attracted towards the light in the vent and not into the privy room.  The flies fly up towards it in an attempt to escape from the pit  The flies are trapped in the vent pipe as they escape toward the light, ultimately dying and falling back into the pit.  Types of VIP latrines 53  Single-pit VIP latrine  Alternating double-pit VIP latrines  Multiple-pit VIP latrine  Types of VIP latrines – single pit 54  Designed to be used for at least 2 years  Suitable for use in rural areas where the soil is deep and pit size is unlimited  Usually unlined  Requires re-location whenever they are full  Alternating double-pit VIP latrines 55  These are permanent structures with two pits that are used alternately  More appropriate in urban areas where people can afford to pay for a permanent structure  One pit is used until it is full (within 0.5 m of the cover slab)  Alternating double-pit VIP latrines 56  It is then sealed and the other pit put in use  When the second pit is almost full, the first pit is emptied and made ready to be put back in use  A minimum of one year is recommended for complete destruction of pathogens  Multiple pit VIP latrine 57  Have more than one cubicle  Suitable for communal institutions such as schools  The pit is divided into separate compartments by airtight walls  The walls are made airtight to ensure effective ventilation of the pit  Multiple pit 58  Each pit except the ones at the ends has two squat holes  The volume of the end pits is half that of the inner ones  The latrine is operated as a series of alternating double pit VIP latrines  At any time half the pits compartments are sealed off and half put in use. 59 Alternating double pit Multi-pit  Applications of VIP latrines 60  Suitability for applying VIP latrines in relation to the following:  Ruralareas  Urban areas  Water use  Hygiene habits  Applicability – rural areas 61  Particularly suitable for rural areas  Construction can be based on traditional house-building techniques  Most materials for building the latrine are available locally  Applicability – Urban areas 62  Can be built in urban areas if sufficient space is available on the house plot for two latrine sites, which will be used alternately  One pit is used until full and then covered with soil.  The superstructure is then relocated to the other site.  Communal facilities can be provided where space is limited or where each household cannot afford its own latrine  Applicability – Water use & hygiene habits 63  Can be used in areas where there is no water supply at the premises  Water is only needed for handwashing and for cleaning the floor of the latrine  Can be used where bulky anal cleansing material eg. Corn cobs and mud balls are used  Advantages of well maintained 64 VIP latrines  Low annual cost  Easy construction and maintenance  All types of anal cleansing materials may be used  Absence of odours and minimal fly and mosquito nuisance  Minimal water requirements  Low level of municipal involvement  Minimal risks to health  Disadvantages 65  In dense urban areas, there is a lack of space for relocating the pit  There is a potential for groundwater pollution  Difficulty of construction in rock or subsoil containing boulders  Cannot dispose of large quantities of sullage in the pit  The KVIP Latrine 66  What does KVIP stand for?  Who developed it and where was it developed?  Describe the system  How does it work?  Applicability  Compare to the VIP (any similarities and differences?) 67 Overhung latrine Dry on-site sanitation  Overhung latrine 68  The overhung latrine consists of a platform with a squat hole over a body of water and a superstructure which provides privacy  They are used in urban or rural situations where streams, canals or tidal areas are used for excreta disposal. 69 Overhung latrine  Disadvantages 70  The receiving water becomes heavily polluted  Children and adults using the water downstream for washing, cooking or drinking are at risk of contracting diseases from pathogens in the water  This technology is therefore not recommended because it facilitates the transmission of diseases 71 Enviro loo Dry onsite sanitation  Enviro Loo 72 73  http://www.enviro-loo.com/how.html 74  Principle of operation 75  The system separates liquid and solid waste as it enters the container via the toilet bowl.  Liquid waste drains to the bottom of the container while solid waste remains on the drying plate  Both the liquid and the solid waste are exposed to a continuous flow of air that is driven through the unit by the forced aeration ventilation system. 76  The movement of air is assisted by the ventilation extraction unit positioned on top of the outlet vent pipe with air being drawn into the container via the inlet vent pipes and toilet bowl.  The odour is vented into the atmosphere via the wind driven extractor  The negative pressure within the container prevents the escape of any odour through the toilet bowl or through the air inlet pipes. 77  As the air moves through the system, it dehydrates the solid waste as it migrates down the sloped, ridged, perforated drying plate.  The liquid drained to the bottom of the container also evaporates  At the same time, sunlight absorbed by the black inspection cover increases the ambient temperature within the container. 78  The intense heat, prolonged retention periods and oxygen-rich air drawn in via the toilet bowl and side air inlets, dehydrate and decompose the waste.  At the end of this process the human waste is converted via the stimulated bacterial and biological activity into an inoffensive dry stabilised material.  It is reduced to roughly 5% of its original volume. 79 Ecological sanitation  Ecological sanitation (Eco-San) 80  Ecological sanitation refers to excreta disposal technologies in which nutrients are recycled from human excreta for agricultural production  EcoSan is based on three fundamental principles:  Pollutionprevention rather than pollution control  Rendering the urine and faeces safe for reuse  Using the safe products for agricultural purposes  Ecological toilets use a minimum amount of water or no water at all  Eco-San 81  Dry or ‘waterless’ operation indicates that no water is used for flushing faecal material, though water must be present for hand washing and other hygiene practices following defecation and urination  Eco-San technologies include:  Urine-diverting dry toilet (UDDT)  Composting latrine  Biogas toilet  The most common Eco-San technology is the UDDT  Considerations for use of EcoSan 82  Consider the use of EcoSan where  There is interest in using digested fecal material, urine or both to fertilize land  People understand and accept the technology  Significant training and monitoring is available for the proper use of this system  Demand for the urine and compost is demonstrable and/or  A high groundwater table or very rocky soil complicate excavation below the surface. 83 Composting latrines Dry on-site sanitation  Compost latrine 84  The compost latrine is similar to the alternating VIP latrine.  Batch or double vault composters are the most common types.  The toilet is composed of two adjacent pits one of which is used until it is ¾ full.  Description 85  For efficient composting the correct balance of nutrients must be present for microorganisms which digest and degrade the waste  The addition of organic carbon in the form of leaves or grass also helps to attain suitable carbon:nitrogen ratios for the degradation process  Before first use a layer of absorbent organic material is placed in the vault  After each visit, the faeces are covered with ash, sawdust, shredded leaves or organic material to reduce smells and soak up excess moisture 86  The vaults are designed to be in use for at least one year before filling up  Urine may be collected separately because the contents of the vault should be kept relatively dry  When the pit is ¾ full it is then covered with organic matter such as grass or leaves, dry soil and sealed.  The second vault is then put into use.  Advantages 87  Humus can be used for soil conditioning  The latrine needs no water for flushing. The composting process is more efficient when the material is moist but not wet  The compost latrine does not need to penetrate the subsoil and hence can be built on rock  Poses low risk of pollution especially where the vaults are completely sealed  Can be applied in flood prone areas, in areas of high groundwater table or in impermeable soil  Disadvantages 88  Organic waste is needed to correct the carbon-nitrogen ratio of the excreta and provide the right conditions for composting. Biodegradable organic material must therefore be available  Pathogens persist if the waste is not stored long enough posing a health risk to those handling the humus  There is the need for high user care in its operation otherwise the pit contents may easily become too wet leading to breeding of flies. Users must therefore be committed to producing and using the compost 89 Urine diverting dry toilet  UDDT 90  The UDDT is designed to keep faeces and urine separate  Urine diversion serves a number of important functions including:  Reducing odour  Simplifying the excreta management process  The UDDT allows for the source separation of urine and faeces through the use of a specially designed seat or squatting pan, generally referred to as the user interface. 91 92 93 94  UDDT 95  Components of UDDT 96  A UDDT consists of eight basic functional elements:  Urine diversion toilet seat or squatting pan;  One or two vaults, usually above ground, or one shallow pit for faeces collection and storage;  A urine piping system leading from the user interface to an infiltration or collection system;  A ventilation pipe to exhaust moisture and odours from the vault or pit;  Components of UDDT 97  An anal cleansing area with mechanisms for the separate collection and drainage of anal wash water, if required;  A toilet super-structure, unless the toilet is installed inside an existing house;  A bucket with dry cover material; and  A hand washing facility with soap and water  UDDT 98  Urine is separated at the user interface, drained through a piping system and infiltrated into the soil for disposal, or collected, stored and sanitised in containers for use as a fertiliser.  Faecal matter and anal wiping material are collected into a ventilated vault directly below the user interface. 99  Following defecation, the user covers the fresh faeces with a small volume of dry cover material eg ash or sawdust in order  To absorb moisture,  Control initial odour and  Prevent insect infestation  The faeces vaults may be located above or below ground, depending on the chosen faeces management method. 100  Advantages 101  Waterless operation  No odour when correctly used and maintained  Treated faecal matter is dry, odourless and less offensive  Does not attract flies or other vectors  Treated faecal matter is partially sanitised and safer to handle  Above ground design or use of containers in below ground vaults makes emptying simple  Advantages 102  Minimal risk of contamination of ground and surface water resources  Possibility for above ground design facilitates construction in challenging environments, such as rocky or unstable soils and high water table  Possibility for construction in close proximity to or inside of the home which adds to security and convenience for users.  UDDTs have a well-documented record of resilience during flood events. The sealed, above ground vaults can be built above the established flood line and also returned to operation quickly when affected.  UDDTs are suitable in situations where: 103  Water is scarce or costly, such as in arid or semi- arid climates  Sewerage infrastructure costs are prohibitive, such as instances of unfavourable terrain, sprawling settlement patterns or poverty  Frequent flooding would impact pit latrines and septic tank systems, resulting in inoperable toilet systems and the contamination of water resources  Unfavourable soil conditions, such as unstable or rocky soil and high water table, make pit-based sanitation difficult and expensive  Suitability 104  Groundwater is the primary source of drinking water and is likely to be contaminated by pit- based sanitation  Limited land space restricts the excavation of new pits if full pit latrines are usually not emptied  Indoor installations are preferred as they provide greater comfort and security at night thus making them more accessible for all  Local agriculture and diminishing soil fertility create demand for affordable fertiliser and soil conditioner. 105 Pour flush toilet Wet onsite sanitation  Pour-flush Toilet 106  The pour-flush toilet is a manual flush toilet  It is as hygienic to use as the cistern-flush toilet.  The toilet has a water seal, the water being retained by a shallow U- bend in the latrine pan  The water seal prevents odours from the pit from escaping through the toilet and insects from entering or leaving the pit.  Pour-Flush Toilet 107  After defaecation a few litres of water is poured by hand into the toilet bowl to transport the excreta into the pit. 1 – 3 L is often sufficient.  The latrine may be constructed directly above a pit or may be offset. Excreta therefore travels through discharge pipe to the pit or septic tank  Where the waste pipe between the U-bend and the pit is greater than 2m in length an inspection chamber is needed along its length to allow for rodding to prevent blockage 108 Latrine directly above pit Offset pit  Pit lining 109  The full depth of the pit must be lined to the prevent the possibility of collapse when saturated with water  Lining materials may be brick, stone, concrete blocks, cement stabilised soil blocks  The lining below the inlet pipe should have holes in it to allow the flush water and liquid portion of faeces infiltrate into the surrounding soil  The top 300 mm should be water tight to provide a firm foundation for the cover slab and prevent storm water from entering the pit.  Principles of operation 110  Two important actions that take place in the pit are:  Percolation of flush water and liquid portion of excreta into the surrounding soil  Biological digestion of solids in excreta  This significantly reduces the rate of accumulation of solids in the pit.  Soluble compounds in the digested excreta percolate into the surrounding soil  Gas formed through by digestion diffuses into the soil  Types of pour-flush toilets 111  There are two general types:  Single-pit pour-flush toilet  The water seal is built into the underside of a concrete slab placed directly over the pit  Double-pit pour-flush toilet  Builtwith two pits with only one in use at a time  Excreta is transported from the toilet compartment to a nearby leach pit  No interruptions in the use of the toilet for pit emptying  Applications 112  In-house  Very hygienic for installation inside homes due to the water-seal  Urban areas  The layout of the toilet is very flexible and the toilet compartment can be at a distance away from the pits. The toilet can therefore be used in densely populated urban areas.  Advantages 113  Inexpensive  Much cheaper to build than the conventional cistern- flush toilet  Involve easy construction and maintenance  Offer a long-term and appropriate solution for excreta disposal  Use low volumes of water for flushing  Advantages 114  Eliminate odour, insect and fly breeding  Can be upgraded to connect to a sewer system  Low level of municipal involvement required  There is the possibility of in-house location  There is a potential for resource recovery  Disadvantages 115  Require separate sullage disposal system  Water must be available throughout the year (at least 4 litres/person/day)  Clog easily where bulky anal cleansing materials are used  Construction is difficult and expensive in areas with high groundwater, shallow soil overlying hard rock or impermeable soil. 116 Aqua-privy Wet onsite sanitation  Aqua-privy 117  This is a latrine constructed directly above a septic tank.  The tank must be water tight to maintain a constant level of liquid in the tank  A drop pipe extends below the liquid level in the tank to form a water seal  Aqua-privy 118  Excreta is deposited directly into the tank via the drop pipe where they are decomposed anaerobically  The tank is desludged when two thirds full (about every 2 – 3 years)  To prevent odour, fly and mosquito nuisance in the toilet, the water seal is maintained by adding water per visit via the drop pipe to replace any losses.  The self-topping aqua-privy washing incorporates a washing sink with the aqua-privy. Sullage from the sink provides the necessary volume of water to maintain the water seal.  Communal aqua-privy 119  Advantages 120  Less likelihood of clogging by bulky anal cleansing materials compared to the WC and pour flush  Possible location inside the house  Low odour and insect problems  Minimal health risks  Potential for upgrading  Potential for sullage disposal  Disadvantages 121  In practice, the water seal is often broken  Small but significant amounts of water are required for the aqua-privy to be a successful sanitation technology  User education on operation and maintenance of the aqua-privy is needed  The tank requires desludging every 2 – 3 years  More expensive sanitation option than simple pit latrines because of the expensive water tight tank needed to maintain the water seal.  Skill is required for construction of the tank. 122 The Biofil Toilet Wet Onsite Sanitation The Biofil Digester  Microorganisms and macro-organisms are enclosed within the digester.  Wastewater and faecal matter enter at the top of the Biofil digester  Rapid separation of solids and liquid contents of the waste occurs. 124  The toilets have been installed in Senegal, Bangladesh, India, Liberia, Sierra Leone, South Africa and in few locations in Ghana Biofil technology  The design is  Simple  Replicable  Affordable  Operates on very low maintenance requirements  Space requirement is small  Can be installed in a day  It does not need any waste removal unlike the septic tank 127 Septic tanks Wet onsite sanitation  Septic tank description 128  These are small rectangular or cylindrical watertight chambers usually located below ground level for the collection and treatment of excreta and flush waste from toilets as well as sullage  Wastes from toilets and sometimes kitchens and bathrooms pass though pipes into the tank where they are partially treated  Septic tanks may have one, two or three compartments with multi compartment tanks providing better effluent quality 129 Single compartment septic tank 130 Double compartment septic tank  Septic tank description 131  The septic tank is suited to systems involving high water use especially where water is used for flushing and anal cleansing  They are usually best suited to single households or institutions such as hospitals or schools but can also serve communal facilities for up to 300 people  Functions of the tank 132  The tank must perform the following functions:  Provide quiescent conditions for settlement of sludge  Allow development of anaerobic conditions for decomposition of organic matter  Have adequate volume for storage of digested sludge  Operation of the septic tank 133  Wastewater enters the tank through pipes and is retained in the tank for 1 – 3 days  Settleable solids settle to the bottom of the tank where they accumulate and undergo anaerobic digestion  A layer of scum consisting of light weight materials including fats and grease rises to the top. This helps to maintain anaerobic conditions in the tank.  The clarified liquid flows out of the tank through an outlet structure just below the scum layer 134  The contents of the septic tank may therefore be demarcated into three distinct zones  Scum layer A floating layer on the surface of the liquid in the tank  Wastewater zone  From which solids are deposited  Sludge zone  Solids are deposited in this zone and undergo anaerobic digestion  Septic tank effluent disposal 135  The effluent from the septic tank is an obnoxious liquid containing high concentrations of organic matter, nutrients and enteric microorganisms  It should not be discharged into surface drains, streams or lakes without prior treatment  The effluent is therefore usually treated through a subsurface soil absorption system e.g. soak away, absorption field/trenches  Septic tank effluent disposal 136  Disposal is difficult in areas where:  The soil is compact resulting in low infiltration rates  High groundwater tables prevail  Population density is high and therefore there is limited space for infiltration of effluent  Desludging 137  Over time the digested sludge accumulates in the tank creating the need for occasional removal from the tank (i.e. desludging)  Desludging is required usually every 1 to 5 years depending on the design size of tank and number of users  Sludge taken out of the tank is known as septage  The septage must be further treated before final disposal  Advantages of septic tanks 138  Septic tanks are flexible and adaptable to a wide variety of household waste disposal requirements  It has no moving parts. Hence little mechanical maintenance is required and no operator is needed for its operation  Sullage can be disposed of in the tank  It is hygienic and free from odour and insect nuisance  Disadvantages 139  There is a potential for contamination of surface or groundwater if the subsoil structure is too permeable  Space is required for the construction of drainage fields  Piped water supply is needed  All drinking water must be set away from the septic tank  Disadvantages 140  Septic tanks have high cost.  They are more expensive than other onsite waste treatment systems  As the effluent is not fit for open channel discharge, a permeable subsoil structure is required for its treatment and disposal  There is potential for groundwater pollution in areas with high water table or high soil permeability 141 Vault systems Wet off-site sanitation  Description 142  The vault system uses a watertight vault located either offset from or beneath a water seal device for storage of excreta over a period of 2 weeks to 1 month  Applicability 143  Vault systems are suitable for use:  Indensely populated urban areas where on-site sanitation systems cannot be used  Where water borne sewerage is too difficult and expensive to install  Where institutional ability to organise and maintain a collection system exists  Advantages 144  The vault can be conveniently located in the house  Suitable for densely populated areas  There is minimal risk of groundwater pollution  There is high potential for resource recovery.  The night soil an excellent source of nutrients , energy or fertilizer and may be used for agriculture after treatment or for biogas production  Advantages 145  Initial cost is lower compared to the septic tank and aqua privy because the tank is smaller  Water requirements are minimised because the user is conscious of saving on vault emptying charges  Disadvantages 146  A high degree of organisation is needed for efficient and hygienic running of the collection service  There is health risk to workers who collect the excreta manually  High operating cost  Sullage disposal in the vault is not possible since it is not designed to handle sullage 147 Off-site wastewater treatment and final disposal  Wet off-site sanitation 148  Wastewater is carried through sewers to a treatment plant e.g. conventional sewerage system.  The conventional sewerage system consists of the sewer network, structures, devices, equipment and appurtenances for the collection and transport of sewage  Wastewater should be treated before its disposal into a receiving water body to:  Reduce the spread of communicable diseases caused by the pathogenic organisms it contains  Prevent the pollution of surface and ground waters  Wastewater treatment 149  Treatment is achieved by physical, chemical and biological means  Physical unit operations: treatment in which application of physical forces predominate  Chemical unit processes: removal or conversion of contaminants is achieved by chemical addition or other chemical reactions  Biological processes: treatment occurs through biological activity (for the removal of colloidal or dissolved biodegradable organic substances and nutrients  Degree of wastewater treatment 150  Municipal wastewater can be treated even up to drinking water standards  This is however expensive  Required degree of treatment will depend on cost that can be afforded by the community, municipality or national government  Degree of wastewater treatment 151  Treatment processes can be classified according to degree of pollutant removal as:  Primary  Secondary  Tertiary  Quartenary  Primary or preliminary treatment  Physical removal of floating materials from sewage to improve its aesthetic appearance  Secondary treatment 152  Thisincludes many biological processes to biodegrade organic matter  Physico-chemical treatment methods can also be used  Tertiary treatment 153  To eliminate pollutants which are not removed by primary or secondary treatment  Involves processes that can achieve high N and P removal  Further polishing of wastewater by removing suspended solids and organic matter  Disinfection processes  Elimination of biodegradable micro pollutants  Quartenary treatment 154  To produce high quality effluents that can be re- used for potable and non-potable supplies  Involved reverse osmosis and membrane technology  Used in Namibia  Physical unit operations: e.g. Screening, mixing, flocculation, Wastewater treatment processes sedimentation, flotation, filtration, gas transfer, centrifugation, reverse osmosis, micro-filtration. Chemical processes: e.g. Precipitation, adsorption, disinfection, neutralisation, oxidation-reduction, ion-exchange, ozonation. Biological processes: e.g. Biological filtration, activated sludge, stabilisation ponds, 155 anaerobic digestion.  Conventional treatment 156  Conventional treatment of wastewater consists of the following unit processes and operations  Screening  Grit removal  Primary sedimentation  Biological treatment  Secondary treatment  Sludge treatment 157  Common biological treatment systems include:  Waste stabilisation ponds  Trickling filter  Activated sludge process  Either a trickling filter or activated sludge process is employed in conventional treatment  Sewage treatment scheme (conventional) Primary treatment Influent Grit Primary Biological Secondary treatment wastewater Screening separation settlement treatment Screenings for Grit for Primary sludge disposal disposal for disposal Secondary Final effluent settlement Secondary sludge for disposal 158  Screening 159  Screening is carried out to remove coarse pollutants such as rags, maize cobs, pieces of wood etc. that may otherwise  damage downstream operations or  clog V-notch weirs, pipes and valves.  Physical damage to pumps, weirs, aerators will  reduce treatment plant efficiency or  negatively affect aesthetics of the treatment plant. 160  Screens can be manually operated or  Mechanically driven devices Manual bar screen Typical cross section of a manually operated screen  Grit removal 161  Grit is the heavy inorganic fraction of sewage solids  Consists of particles such as sand, gravel, eggshells, ashes, charcoal  It however also includes organic solids like bone chips, coffee grounds, seeds  Grit removal may be achieved using  Open grit channels  Grit chambers Open grit channel  Importance of Grit Removal 162  To prevent wear and tear of pumps and other mechanical equipment (abrasion and abnormal wear).  To reduce formation of heavy deposits and consequent clogging of downstream unit operations and transport pipes, channels and conduits.  To reduce frequency of cleaning of sludge digester caused by excessive accumulation of grit. Accumulation of grit in the digester occurs as a result of its deposition during primary sedimentation  Sedimentation 163  The aim of sedimentation is to remove suspended organic solids from the wastewater so as to reduce the load to the subsequent biological treatment units  Solids settle to the bottom of the tank.  The sludge is periodically removed from the tank for further treatment  The effluents exits the tank for biological treatment  Biological treatment 164  Trickling filter  Activated sludge  Trickling filter 165  The trickling filter consists of a bed of highly permeable media surrounded by a tight wall  Media may be crushed rock, gravel, lava stone, plastic  Cross section of a typical trickling filter 166 1. Filter floor to support the filter materials 2. Underdrain to collect the wastewater and allow ventilation 3. Retaining wall to support air draft drafts in the filter 4. Filter media to provide surface area for biomass 5. Distributor to uniformly distribute the hydraulic load  Plastic random packing Plastic cross-flow packing Mineral Filters Advantages of trickling filter  Low energy requirement  Low sludge production rates  Simplicity in operation and consequently low running cost  Low capital investment cost  Secondary sludge is easily dewatered Disadvantages  Poor performance if high quality effluent is required (BOD