Describe the methods of excreta disposal and sewage treatment.

The Sanitation Problem and Methods of Excreta Disposal

• The diseases related to unsafe excreta disposal — diarrhoeal disease, cholera, typhoid and paratyphoid, dysentery, hepatitis A and E, poliomyelitis, ascariasis, hookworm, other soil-transmitted helminths, amoebiasis and giardiasis
• The route of transmission is summarised by the F-diagram — faeces reaching a new host through fluids, fields, flies, fingers and food
• The value of the diagram is that it shows where each barrier acts — sanitation is the primary barrier, blocking faeces at source; while safe water, handwashing and food hygiene are secondary barriers acting later
• The primary barrier is more effective because it blocks every subsequent route at once
• The additional harm of environmental enteric dysfunction deserves emphasis, since it explains a puzzle about Indian nutrition — chronic ingestion of small quantities of faecal organisms causes a subclinical inflammatory change in the small intestine, with blunted villi and increased permeability, impairing absorption even without any episode of diarrhoea
• This helps explain why India has higher stunting than countries that are poorer and eat less, and it means sanitation is a nutrition intervention
• Open defaecation produces a negative externality — the health of a household with a latrine still depends on whether its neighbours have one, since faecal contamination is shared through the environment
• Therefore sanitation benefits appear only when coverage and use are high, which is the rationale for aiming at whole-village open-defaecation-free status rather than at counting individual toilets
• The requirements of a sanitary method of excreta disposal are examined as a list — it should ensure that:
• The soil surface is not contaminated
• Ground water and surface water are not contaminated
• Excreta is not accessible to flies or animals
• There is NO handling of fresh excreta
• There is NO nuisance from odour or unsightly appearance
• The method is simple, inexpensive and acceptable to the community
• The methods in unsewered areas:
• Service type (conservancy) — now prohibited, since it requires manual handling of excreta
• Manual scavenging is prohibited by law under the Prohibition of Employment as Manual Scavengers and their Rehabilitation Act, 2013, and its persistence is a matter of caste and dignity as much as of public health
• Non-service (sanitary) types — bore-hole latrine; DUG-well latrine; water-seal latrines including the RCA and PRAI types; and the septic tank
• The twin-pit pour-flush water-seal latrine is the design promoted in India, and its advantages should be explained:
• The water seal (a U-trap holding about 20 mm of water) blocks odour and flies, which are the two commonest reasons a latrine is abandoned
• Two pits are used alternately — one is used while the other rests; after about two years the rested pit contains safe, odourless manure which can be removed by hand without any health risk
• That is the design’s decisive advantage, since it ends the need for manual handling of fresh excreta and gives the household a useful product
• It uses little water (1 to 2 litres per flush), is cheap, needs no sewer, and can be built and upgraded incrementally
• The siting rule must be known — the latrine pit should be at least 15 metres from any well or water source, and ideally downhill of it, with the bottom of the pit above the water table

Sewage Disposal and Programmes

• The septic tank is used where water is piped but no sewer exists
• Its principle — sedimentation of solids as sludge, flotation of grease as scum, and anaerobic digestion of the sludge, with a retention time of about 24 hours
• The effluent remains rich in bacteria and must not be discharged into open water, and is disposed of through a soak pit or dispersion trench
• Practical points — desludge periodically but leave a seed of sludge behind to maintain the bacterial population; and do not put disinfectants down the tank, since they kill the very organisms doing the digestion
• Sewage and its treatment in sewered areas:
• Primary treatment — screening, grit removal and sedimentation, removing suspended solids
• Secondary (biological) treatment — trickling filters or the activated sludge process, in which aerobic organisms oxidise dissolved organic matter
• Tertiary treatment — further removal of nutrients and disinfection
• Oxidation ponds (waste stabilisation ponds) are the method best suited to India, working by a symbiosis between algae and bacteria — bacteria oxidise the organic matter and release carbon dioxide, which the algae use in photosynthesis, releasing the oxygen the bacteria need
• They are cheap, need NO machinery or power, and achieve excellent removal of pathogens including helminth ova and viruses, but require large areas of land and abundant sunlight — both of which are more available in India than capital and electricity
• The measures of sewage strength — biochemical oxygen demand (BOD), the oxygen required by micro-organisms to oxidise the organic matter, conventionally over 5 days at 20°C; and chemical oxygen demand
• A high BOD indicates heavy organic pollution, and discharge of such sewage depletes the oxygen of a receiving river and kills its fish and aquatic life
• Sullage (waste water from kitchen and bathing) should be distinguished from sewage, and is disposed of by soakage pits, kitchen gardens or seepage pits
• The INDIAN programmes — the Central Rural Sanitation Programme, then the Total Sanitation Campaign and Nirmal Bharat Abhiyan, and since 2014 the SWACHH BHARAT mission
• The change IN approach is the substance of the topic, and it is a change from supply to demand
• The earlier programmes subsidised and built toilets, and found that many were not used — being used as storerooms, or abandoned because of smell, poor construction, lack of water, or a belief that a latrine near the house is polluting
• The lesson learned was that construction is not use, and that counting toilets built measures the wrong thing
• The later approach therefore emphasised — community-led total sanitation, which uses triggering to create collective disgust and a community decision rather than individual subsidy; declaring whole villages open defaecation free; behaviour change communication; swachhagrahis as community motivators; and Swachh Bharat Mission phase II, which addresses sustainability, faecal sludge management, greywater and solid waste
• The achievement and the caveat should both be stated — coverage rose enormously and open defaecation fell dramatically; but sustained use, maintenance, water availability, faecal sludge management and the safety and dignity of sanitation workers remain the unfinished tasks
• Sanitation is a nutrition intervention, through its effect on environmental enteric dysfunction and absorption
• Construction is not use, which is the lesson that changed Indian sanitation policy from subsidy to behaviour change
• Open defaecation harms the neighbours too, which is why coverage must be near-universal before benefits appear
• Sanitation is the primary barrier in the F-diagram, blocking every subsequent route at once
• Site a pit at least fifteen metres from a well, downhill of it, with the pit bottom above the water table
• The water seal blocks odour and flies, which are the two commonest reasons a latrine is abandoned
• Twin pits end the handling of fresh excreta, since the rested pit yields safe odourless manure after two years
• Manual scavenging is prohibited by law, and its persistence is a matter of caste and dignity as much as of health
• Leave seed sludge when desludging a septic tank, and never put disinfectant into it
• Septic tank effluent is not safe and must go to a soak pit rather than into open water
• Oxidation ponds suit India, needing land and sunlight rather than capital and electricity
• Algae and bacteria work symbiotically in a pond, each supplying what the other consumes
• Ponds remove helminth ova well, which conventional secondary treatment does less reliably
• High BOD depletes river oxygen and kills aquatic life, which is how sewage damages a water body
• Sullage is not sewage, and can be disposed of through soakage pits or used on a kitchen garden
• Community-led total sanitation uses triggering, creating a collective decision rather than an individual subsidy
• Declare villages open defaecation free, which measures the right thing where counting toilets does not
• Latrines were used as storerooms, which is the concrete form the construction-versus-use failure took
• Phase II addresses sludge and greywater, which is the unfinished business after coverage was achieved
• Sanitation workers deserve safety and dignity, and their conditions remain the least addressed part of the programme
• Polio and hookworm are excreta-related, which is easily forgotten when the list is reduced to diarrhoea and typhoid
• Enteric dysfunction occurs without diarrhoea, which is why the harm was invisible to programmes counting diarrhoeal episodes