Non conventional sewerage in developing countries

This thesis reports the findings of a search of the literature on non conventional sewerage (NCS) systems in developing countries. The thesis also contains information obtained by personal communication with people and institutions having first hand experience of such systems. The opening chapter surveys the range of sanitation systems that have been implemented in low income urban areas in developing countries. It summarizes the problems associated with them, paying particular attention to those reported in connection with so-called "conventional" sewerage schemes. The various sewerage systems put forward in the literature as being unconventional are introduced. It is noted that many of them have yet to be implemented. In the second chapter the technical design of NCS systems is examined in relation to the range of design values and practices used in conventional sewerage schemes. This leads to four broad conclusions. Firstly, the primary objective of nearly all NCS design has been the reduction of costs. Secondly, NCS systems may be divided into two categories according to whether or not they incorporate interceptor tanks designed to prevent the bulk of the solids contained in excreta and sullage from entering the sewer lines. Thirdly, both NCS and conventional systems have been designed according to a wide range of specifications, although the latter appear never to have used interceptor tanks. Fourthly, there is a substantial amount of common ground between NCS and conventional design practice, and in particular between NCS designs without interceptor tanks and conventional sewerage. The third chapter reports the social, institutional and financial aspects of NCS projects, although conSiderably less information was found on these matters compared with that available on technical design. A shared feature of many systems is the emphasis on the importance of achieving a high level of community involvement in one or more of the four stages of project planning, building, maintenance and financing. The penultimate chapter focuses on NCS costs and on how successful implemented NCS systems have been. Success is defined in terms of: - how widely they have been utilized; - how well they have functioned; and - their health and other impacts. For many systems, the available information is inadequate, particularly in relation to functioning and impact. The only places where NCS appears to have been at all widely utilized are Orangi Town, a large squatter settlement near Karachi in Pakistan, and the States of Rio Grande do Norte and Sao Paulo in Brazil. The final chapter contains conclusions abcrut NCS design and about the relative success and failure achieved by the different NCS systems. Suggestions for further research are made in the light of the information gaps and the varied design, implementation and operating practices revealed during the course of the study.