Doulaye Koné - Eawag/Sandec.“- Presentation transcript:
2 Household and neibourghood Sanitation Infrastructures: Excreta, wastewater disposal in developing countries Doulaye Koné - Eawag/Sandec
3 Objectives of a sanitation systems Structure of the presentation Objectives of a sanitation systems What are we talking about? Wastewater sources and their characteristics Pathways of domestic wastewater Household sanitation management infrastructures Realistic holistic sanitation systems
4 Tasks of sanitation systems Prevent disease - guarantee effective barriers against sanitation related diseases Protect the environment - prevent pollution, return nutrients to the soil, and conserve water. Be simple - operation of the system must be feasible using locally available resources (human and material). Where technical skills are limited, simple technologies should be preferred. Be affordable - total costs (incl. capital, operation, maintenance costs) must be within the users’ ability to pay. Be culturally acceptable - it should fit local customs, beliefs, and desires. Work for everyone - it should address the needs of children and adults, of women and men. The first question of course is: Why do we need any sanitation facility, be it a latrine, a flush toilet, a septic tank or whatever? What conditions must be fulfilled by any sanitation system? Sanitation system must…
5 What are we talking about? Blackwater toilet wastewater (faeces and urine with or without flushing water) Greywater domestic wastewater form kitchen, bath, shower (excluding faeces and urine) Brownwater Blackwater without urine Yellowwater Urine Domestic wastewater consists of different fractions, with very specific characteristics Faecal sludge Sludge accumulating in “on-site sanitation systems” (Latrines, Septic tanks, etc.)
6 The Path of Excreta and Greywater in Urban Areas The human waste system The Path of Excreta and Greywater in Urban Areas ~ 2 billion (2004) ~ 3 billion (2025) sewered sanitation (black and greywater) “on-site” sanitation (excreta, black and greywater) Latrines (trad., VIP, PF, double-pit, no-mix, …) Greywater Septic tanks Wastewater treatment plant (WWTP) Small-bore sewerage for effluent of interceptor or septic tanks Effluent to soakage or drains Septage FS treatment Plant (FSTP) Liquid to discharge into receiving waters or to co-treatment in WWTP “Faecal sludge-FS” Products from double-pit and no-mix latrines might be used on-site Effluent to agricultural use or discharged into receiving waters Biosolids to agriculture for soil conditioning and fertilization Eawag / Sandec 2004
7 Characteristics of the different wastewater sources Total Greywater Urine Faeces Volume [l/cap*a] 25’ ‘000 25’ ‘000 500 50 Nutrients Nitrogen 2-4 kg/cap*a 5% 85% 10% Phosphorous kg/cap*a 10%** 60% 30% Potassium kg/cap*a 34% 54% 12% COD 30kg/capa 41% 47% Faecal coliforms - /100ml 0 /100ml Main differences are in terms of quantities, nutrient content, and level of pathogenic contamination: Urine: Contains almost all the nitrogen and large parts of the potassium and phosphorous excreted by humans. N:P:K = 10:1:2 Urine is usually sterile (exceptions known by urinary tract infections). Contamination with pathogens occurs only if urine is exposed to faeces. Easily applicable, diluted or not, depending on the crop and crop stage. Faeces: Mainly undigested organic matter made up of carbon. Faeces contain almost all pathogens: bacteria (e.g. faecal coliforms, vibro cholerae) viruses (e.g. rota virus) protozoa (e.g. amoeba hystolitica) helminths (e.g. Ascaris eggs) Low nutrient content, but good characteristics as soil conditioner: increase the organic matter content, improve the water holding capacity. Greywater: Greywater is defined as household wastewater without input of human excreta It includes used water from baths, showers, hand basins, washing machines, dishwashers, laundries and kitchen sinks Big quantities with relatively low nutrient contents. Big reuse potential: Irrigation: Agriculture, landscape, aquaculture Municipal uses: Fire protection, street cleaning, car washing, cooling, road construction operation, … Non-potable domestic uses: Toilet flushing, laundry, floor cleaning Main issue: Toxic substances (organic compounds, metals, chlorine etc.), fats from kitchen, can affect natural treatment and disposal systems → source control very important component of greywater management system * healthy people ** can be as high as 50%, depending on washing and dish-washing powder used
8 Of course there are many more aspects! Criteria influencing the selection of sanitation systems Economic, institutional and other aspects regulations and standards (including enforcement) costs for construction, O&M willingness to pay (initial and monthly payments) self-help potential and initiative of local people and organizations local entrepreneurs, consultants, construction companies, … Existing system! …. Of course there are many more aspects! comprehensive list doesn’t exist strongly depends on local settings list of criteria has to be developed on-spot, in close collaboration with local people,organisations and institutions
9 Classification of Excreta and wastewater management technologies - Cesspit trucks That means that we have a whole series of sanitation concepts (all with certain strengths and limitations) which require a whole series of technological modules. Decentralised and centralised options In DC, also in urban areas, most common systems are decentralised systems. Of course historically grown, but as explained by Roland yesterday, decentralised sanitation not only because centralised systems not affordable, has its advantages:
10 Partially sewered cities Business centre of large cities with high water consumption rate Lack of treatment sites and wastewater treatment plants Discharge of wastewater into natural water bodies and open canals
11 Cities without sewers Represent more than 90% of cities in developing countries Are very heterogeneous in urban infrastructure Often lack financial and human resources for sanitation development and upgrading
12 Decentralised sanitation systems are often more suitable - why? Existing systems are decentralised (e.g. latrines) Treatment and reuse can be tailored to the specific waste stream (e.g. urine, faeces, greywater etc.) Decentralised systems are easier to plan and implement (different “independent” areas with specific needs and characteristics) Capital investments are generally less than for centralised systems (reduced investments for trunk sewers and pumping stations, lower O&M costs) Capacity expansion and thus capital requirements can track demand much more closely (incremental approach) No reason to impose a “one size fits all” approach Different strategies can be employed in various parts of the service area.
13 The Path of Excreta and Greywater in Urban Areas The human waste system The Path of Excreta and Greywater in Urban Areas ~ 2 billion (2004) ~ 3 billion (2025) sewered sanitation (black and greywater) “on-site” sanitation (excreta, black and greywater) Latrines (trad., VIP, PF, double-pit, no-mix, …) Greywater Septic tanks Wastewater treatment plant (WWTP) Small-bore sewerage for effluent of interceptor or septic tanks Effluent to soakage or drains Septage FS treatment Plant (FSTP) Liquid to discharge into receiving waters or to co-treatment in WWTP “Faecal sludge-FS” Products from double-pit and no-mix latrines might be used on-site Effluent to agricultural use or discharged into receiving waters Biosolids to agriculture for soil conditioning and fertilization Eawag / Sandec 2004
14 On-site dry systems Simple pit latrine 2 m or more in depth covered by latrine slab with or without superstructure percolation of liquids into soil partial anaerobic decomposition of solids + cheap, easily understood - unstable soils (→ lining) - not good with high water table - hazardous and difficult emptying (depth > 2 m) - odor problems, fly breathing Let’s come back to normal situations in urban and peri-urban areas. Quite theoretical material, cannot go too much into detail, many source books. Interesting would be to hear from you: expertise, experiences etc.
15 On-site dry systems
16 On-site dry systems VIP latrine (ventilated improved pit latrine) Naturally induced ventilation with screened ventilation pipe removes odor prevents escape of flies + bad smell and flies reduced - difficult to construct properly - more expensive than simple pit latrine
17 On-site dry systems Groundwater contamination If contamination potential is high –> raised pits or vaults completely over ground > 2m above highest groundwater level less –> at least 20 m to next well. But: main risk of contamination is via dug well
18 On-site dry systems Double pit systems and raised pit (vault) systems Permanent pits Filling - consolidation -emptying dehydration and hygienisation –> reuse can be an option with urine separation + “treatment” included + more hygienic emptying - O&M more complicated -/+ costs Alternative to single pit: double pit
19 On-site systems Pour flush pits Flushing of excreta with 2-3 liters Permanent pits or vaults Can be combined with double vaults + reduced smell problem with water seal - water must be available
20 Designing latrines Site Construction materials Superstructure design Distance and position relative to housing: depending on cultural habits at least 20 m from surface water sources easily accessible for all users (children, women, old people, disabled) Construction materials local availability stable and durable esthetic considerations Superstructure design depending on cultural habits (open or closed) protect from rain, stormwater runoff, … superstructure = important factor influencing the use (essential that users are involved in design) Now look closer to design of latrines, if interesting for you.
21 Designing latrines
22 Designing latrines (cont.) Slabs concrete, wood, fero-cement or plastic (local manufacturers?) keyhole shape most suitable squat hole covers (not for VIP) Ventilation pipes 15-20 cm diameter length of VIP pipe = 0.5m higher than superstructure orientation Pit excavation and lining top 0.5 m usually lined (pre-cast concrete, bricks, cement blocks, etc.) No movable parts!
23 Designing latrines (cont.) Round pits are more suitable to distribute evenly earth pressure (natural arching effect) Hand-washing facilities must be provided!
24 Designing latrines (cont.) Pit sizing V: pit Volume (m3) N: no. of users S: sludge accumulation rate (litres/cap year) D: design life (years) 2-3 years for single pits (where emptying required) 1-2 years for double pits year for double pits with urine separation F: Infiltration area (m2); (water depth = F / pit circumference) W: Amount of water used for flushing (liters/cap day) I: Infiltration rates (liters/m2 day) Sand 40 Sandy loam 25 Silt loam 20 Clay loam 8 Clay unsuitable V = N x S x D / 1000 and F = N x W / I Volume depends on number of users design life/emptying frequency sludge accumulation role of pit as infiltration pit (e.g. greywater disposal) If infiltration required: provide infiltration area at the top, in order to guarantee that when full still infiltration possible
25 Sludge accumulation rates Designing latrines (cont.) Sludge accumulation rates S depends on biodegradability of anal cleaning material (paper, stones, leaves, corncob, water) environment in which material is stored (moisture content) In emergency situations (rapid accumulation) these rates have to be multiplied by %
27 Urine diversion latrines Faeces and urine are separated before they come into contact Urine is collected in tanks and is reused as liquid fertilizer Faeces are dehydrated in the chambers and used as soil conditioner + reduced stench problems + easier handling of dried material + reduced chamber volume + no waste, but fertilizer - special squatting pan - 2 separate fractions Now to a very specific case of dry sanitation: UD Very “in” at the moment Many projects in China, Africa (South Africa, Uganda, Kenia, …), Latin America (Mexico, Guatemala) Mainly in peri-urban areas, where urban agriculture still dominant role
28 Urine diversion latrines 2 chambers, m3 each 2 doors, access normally from outside 1 urine pipe with jerry can, normally outside Squatting pan with cover
29 Urine diversion latrines Operation: Addition of ash: to increase pH and to reduce moisture In addition: lime, sawdust, dry soil,… Toilet paper separation: Toilet paper will not decompose in the chamber (only dehydration process) → separate collection in a bucket. If the toilets are well operated and maintained, no smell problems will occur. Vent pipe and window ensure a sufficient aeration
30 Urine diversion latrines Processing chambers: Always 2 chambers Above ground level, sealed Access to the chambers should be possible from outside the house Volume according to accumulation rate and number of users; → guide value: l/year/user and chamber
31 Emptying urine divertion toilet
32 Household / neighbourhood treatment systems Septic tank most frequent on-site treatment unit worldwide sedimentation tank settled sludge partially stabilised by anaerobic digestion 1-3 compartments Almost no removal of dissolved and suspended matter + simple, little space required (underground) + high institutional acceptance - low treatment efficiency (COD removal approx. 50%) - O&M often neglected (desludging) or unkown!! → look for national design standards!
33 Septic tank design V=V1 + V2 + V3 V3=F*h V3: scum layer F: surface of the tank h: height of the scum layer h=20-30cm V1 and V3 can also be estimated based on existing figures:
34 Household / neighbourhood treatment systems Anaerobic baffled reactor (baffled septic tank) Improved septic tank 2 to 3 chambers in series (up to 5) Intensive contact between resident sludge and fresh influent Treatment efficiency: 65 to 90% COD removal HRT = 2-3 days + simple, high treatment efficiency, hardly any blockages + high removal efficiencies, also for suspended and dissolved solids - construction and maintenance more complicated than conventional septic tank
35 Septic systems
36 Household / neighbourhood treatment systems Anaerobic filter Used for pre-settled domestic wastewater with low SS concentrations (e.g. greywater) Principle: close contact of wastewater with active bacterial mass on filter media filter material surface: 90 to 300m2 per m3 Treatment efficiency: 70 to 90% COD removal Volume: m3/cap for domestic wastewater + simple and durable if well constructed and wastewater properly pre-treated; high treatment efficiency; little space requirements - high construction costs (filter media); blockage of filter possible - maintenance costly and difficult
37 Faecal sludge - underestimated problem 2-2.5 billion urban dwellers on on-site sanitation ! Number and share growing !
38 Thick and yellow ……. Thin and black ……. Types of faecal sludge Sludges from unsewered public or family toilets emptied at weeks’ intervals “unstable” Thin and black Sludges from septic tanks emptied at years’ intervals partially “stable”