possible sequence would be anaerobic pond-aerated lagoon-facultative pond- maturation pond. The economic re-use of treated nightsoil or sewage effluent ...
Proc. Instn Ciu. Engrs. Part 1, 1977, 62, Feb., 163-165
INFORMAL DISCUSSION
Water and waste water engineering for low income communities in developing countries introduced by R. Feachem, PhD, BSc and D. Mara, PhD, BSc reported by Prof. K. Ives, DSc,PhD,
MICE
Dr Feachem in his introduction restricted his comments to rural water supply in developing countries. More than loo0 million people, representing 86% of the rural population, were without adequate water supplies, and due topopulation growth, this number was increasing. The low income and lack of technical skills in rural communities posed the ‘quantity-quality dilemma’, i.e. should water of known inferior quality be supplied to a large number of people, rather than, atthe same cost, water of a good quality to a small number of people? The arguments for providing more people with inferior water were: (a) water treatment implied a maintenance problem, which cannot be met in rural areas; consequently the system breaks down and no water, or untreated water is supplied ; (b) plentiful untreated polluted water might be lessof a health risk than inadequate quantities of water. The reason for this second argument is that in the rural tropics the majority of waterrelated diseases are not water-borne, i.e. caused by drinking infected water. Rather, they are water-washed and infection is by touch, or through cooking utensil or food, which better hygienewould improve. Also, many skin and eye infections would be improved by more frequent and adequate washing, even with poor quality water. In other words, an improvement in domestic and personal hygiene far outweighs the health risk from classical water-borne diseases such as cholera and typhoid. The contrary arguments, which support the provision of water only if it is of safe quality were: (a) a piped supply could increase the number of users of a single source leading to epidemic transmission; (b) a piped supply of greater quantity might be inferior to an existing smaller supply (e.g. a local well) of better quality, thus increasing the water-borne health risk; (c) an engineer might be legally liable if there were adverse health consequences resulting from his design and installation of a low quality water supply. Dr Feachem discussed these risks, and concluded that an improvement in rural water supply was desirable, even if the best possible was not available, for often the alternative would be that nothing at all would be done. A number of speakers referred to the maintenance problem with respect to water treatment. It was pointed out that pumping and distribution implied that some level of technical maintenance would be available. Also, the main cost in water supply was distribution, not treatment. However, mechanical maintenance also seemed to be a problem, and the case was cited of one region of India where 80% of handpumps were 163
I N F O R M A L DISCUSSION broken and ineffective. Furthermore, even taps and pipes were broken (sometimes deliberately to obtain morewater) and notrepaired, as had been observed in ruralNepal. The distinction was drawn between hand powered, animal powered and wind pumps, which might need only occasional (monthly) maintenance, and diesel or petrol engined pumps which required daily maintenance. It was generally agreed that the problems were institutional rather than technical or even financial. The rural community might have, or even perceive, the need for water supply, but be incapable of organizing the social structure of the village or farms to provide and maintain it. It was even possible that the skills were available but the impetus was lacking. It was often difficult to appoint someone to carry out repairs, and an awareness of a breakdown did not bring the necessary action. Epidemics improved organization, claimed one speaker, but it was debatable whether it improved the ability to spend money wisely. It was also suggested that the current vogue of 'self-help' in fact was detrimental, as it diverted governmental agencies from their proper responsibilities towards communal facilities in rural areas. One speaker referred to the collection of rainfall and roof runoff into tanks which gave water of satisfactory bacterial quality, but it was pointed out thatrainwater systems cost $40 per capita, compared with $20 for a windpump-borehole-distribution system, and S10 for handpump-borehole-distribution system (supplying 150 persons). Experience from Nigeria suggested that a pump and piped scheme could allow for subsequent provision of a treatment stage when appropriate.Another speaker indicated the advantages of installing mechanical equipment, with simple clarification and disinfection. It was suggested that this might be feasible where a local institution existed such as a hospital, prison or school. Dr Mara introduced the topic of waste water disposal, with particular reference to urban areas. He said that sanitation in developing countries was totally inadequate: for example in Kenya, 51% of the urban population had no sanitation (40%pit latrines) and only 2% had sewer connections. Part of the problem was that ruraldwellers came to urban areas with rural sanitary ideas. Sewerage was certainly too costly, probably US$2OO/person for the capital outlay. Nightsoil collection was mainly crude, and its organization was a social rather than a technical problem. Regarding sewage treatment, a two-stage septic tank with an upflow percolating filter could provide an effluent which could be discharged to a storm drain. Also, aqua privies could be used with small flatgrade sewers discharging to waste stabilization ponds. Such ponds, with a retention time of 15-30 days, could reduce BOD partly by sedimentation with anaerobic decomposition in the sludge, and partly by an algal-bacterial system solubilizing and oxidizing the organic matter. Maturation ponds could destroy faecal bacteria in two 7-day ponds in series. Anaerobic pretreatment ponds could remove 50%-75% of the BOD acting rather like large open septic tanks. Aerated lagoons could also be incorporated to reduce BOD, but mechanical stirrers were required. A possible sequence would be anaerobic pond-aerated lagoon-facultativepondmaturationpond. The economic re-use of treated nightsoil or sewageeffluentwas important. A system devised in Papua New Guinea not only produced methane, useful sludge and algae, but also incorporated duck and fish culture, and hydroponic cultivation of cash crops. Some speakers commented that sewerage, not treatment, was still the principal problem, and that nightsoil collection was unsatisfactory. In onetown in Africa which experienced regular flooding, nightsoil vaults were at head height allowing gravity discharge into tankers. Some nightsoil collectors sold to farmers, and would oppose sewerage. Public latrines were discussed, as they had been successful in West Africa in urban areas. However, who managed such public latrines and what happened to the effluent ? The definition of nightsoil came under scrutiny, and although agreed as faeces and urine, various explanations of its origin referred to night collection, night discharges and even night trainloads departing from Manchester. 164
WATER AND WASTE WATER ENGINEERING
The discussion concluded with comments on the need for dialogues between doctors and engineers, and it was suggested that engineers usually benefited by learning from doctors, but not vice-versa. The role of the London School of Hygiene and Tropical Medicine was favourably commented upon, and some links between the Institution and the Royal Society for Tropical Medicine were suggested. The chairman remarked that the speakers’ views had not been as heretical as be had expected, but-he knew that the World Health Organization opposed the provision of dirty water supply. Nevertheless, he quoted Voltaire that ‘the best is the enemy of the good’.
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