Box 42 Preface Of Textbook Of Appropriate Sewerage Technology For Developing Countries

"Practically all existing textbooks on planning/design of municipal sewerage systems (MSSs) are written by Westerners and tend to emulate the environmental standards and matching design criteria utilized in the affluent industrialized countries (ICs), and because these same standards and design criteria have been used for planning/design of MSSs in the developing countries (DCs), most of the MSSs built in the DCs have been dysfunctional and have not achieved their intended objectives. The new textbook is believed to be the first that is written to be appropriate for DC use, featuring use of simple rather than sophisticated approaches, thus greatly simplifying problems of O&M. The textbook of 400 pages covers all aspects of MSSs systems including institutional, economic, financing, and environmental as well as technical engineering aspects for both sanitary and industrial wastewaters. It also recognizes the need to give attention to not only the affluent urban sectors which case afford sanitary sewers but also to the problem of ensuring adequate management of excreta from buildings not connected to sewers but utilize individual on-site disposal units. It covers all components of MSSs, including the collection component (collecting sewers, interceptors, and pumping to collect and deliver the sewage to the treatment plants, plus treatment and disposal. Dr. Harvey F. Ludwig of Bangkok is Chief Author, assisted by the three co-authors. Their combined experience in MSS technology is estimated 60 man-years, about one-third in IC and two-thirds in DC systems. Dr. Ludwig is a member of the National Academy of Engineering of the U.S.

If you wish to purchase a book, please contact Mr. Kumar Vinod, South Asian Publishers at New Delhi, India. His e-mail address is <[email protected]>. Cost for persons in Industrialized Countries and International Agencies is US$32.00 (hardcover version) including surface mailing. Extra postage of US$3.00 required for airmail shipping, totaling US$35.00. A softcover version at lower price is applicable for nationals of Developing Countries. Postal address of South Asian Publishers is 50 Sidharth Enclave, P.O. Jangpura, New Delhi 110014, India." The chapters included in this textbook is as follows:


Urban Sewerage and Excreta Management

Sewage Characteristics and Flow Measurements

Sewerage System Collection Component

Onsite Sewage Disposal

Sewage Treatment and Disposal

Industrial Wastewater

Operation and Maintenance

Monitoring and Enforcement

Appropriate Standards

Environmental Impact Assessment

Sewerage Institutions

Sewerage Economics

Sewerage Financing

Other Considerations

Summary and Conclusions

Situation in Typical DCs

In contrast with the United States/ICs, the typical DC city, including even many capital cities, has yet to achieve satisfactory management of community excreta and other wastes posing public health/environmental hazards, including industrial wastewaters discharged to municipal sewers. However, in recent decades the IAAs have made many grants/loans intended to help the DCs to get a handle on this problem, but with generally ineffective results and wastage of investments. The first (and almost remarkable) finding in reviewing DC/USEM experience to date shows a lack of understanding of the three components of a comprehensive municipal sewerage system as previously described. It especially fails to recognize that the most important component is use of sewers to collect/export the sewage, not the subsequent treatment. A large number of IAA-sponsored projects of the past several decades have been formulated on the assumption that provision of treatment per se is the answer to the problem, without recognition that treatment plants are not effective without sewers to collect and transport the waste to the treatment plant.

The most comprehensive analysis of the USEM problem in the DCs known to the author is the study on "Sewerage Prioritization" in Thailand completed in 1995135. This evaluated the ongoing situation in all of the larger cities in the country (more than 100), with the key findings. These who plan/ design/manage urban sewerage systems must recognize that the DC approach must be quite different from the IC approach, as follows:

• A common notion (already noted) in both the IAAs and the DCs is that urban sewage problems can be solved simply by building a treatment plant, which receives only a portion of the area's excreta, with much of the remainder reaching the waterway without adequate treatment, without recognizing that such plants may do little good for protecting either public health or receiving water quality.

• In the ICs, virtually all buildings in the sewerage service areas are served by sanitary or combined sewers. When the public sewer system is built, all buildings connect up and existing on-site units are abandoned. Generally in the DCs, only the affluent areas (which can afford them) are served and the bulk of the population continues to depend on on-site units. Many of these on-site units do not function satisfactorily due to inadequate design and lack of periodic servicing, resulting in frequent excreta overflows into the community environment, which pose very serious disease transmission risk hazards, not only to the nonaffluent subareas but to the entire service area. Hence, the argument that is often made by IAAs that improving service to the affluent subareas can be justified in terms of protecting overall community health is hardly correct. If the planners are really interested in overall community public health protection, the project plan must include "equal attention" to the nonaffluent subareas (the same is true for provisions of improved urban water supply) if these are to be justified in terms of public health).

• Another common misconception is that treatment plants can be operated and maintained with a very low O&M budget, usually about one-third of the minimum need51, so that, even if well designed, the plant cannot be expected to function. Monitoring and acting on this problem, which is mandatory in the ICs, does not exist in the DCs. DC officials and practitioners have paid such little attention to O&M because of lack of performance monitoring and because the project feasibility studies often do not include adequate allowance in the economic analysis for O&M costs.

• A typical example is the proposed expansion in 1992 of the municipal sewage treatment plant of Chittagong (Bangladesh)8, justified on the basis of public health protection and of correcting water pollution in the river receiving the plant effluent. An evaluation showed that (1) the plant, even when enlarged, would not receive the bulk of the city's excreta, (2) the existing plant (built earlier by the British) had long since ceased to be operated properly, and, hence, was doing little if any good, and this problem was scarcely recognized in the project feasibility study, and (3) even if the old and new plants were to be properly operated, the resulting benefit both to public health and water pollution control would likely not be very meaningful. All such proposed projects need to include an EIA, which will call attention to such deficiencies and misconceptions.

• An additional finding from the USEM experience in the DCs so far is the need for standardization in design of facilities for the USEM system, to standardize practices for all system components, but especially for treatment plants. As it has been, individual designers use a variety of treatment systems that are in the same ballpark in terms of costs135 but that, because of their differences in terms of parts replacement, go unrepaired for months or even years. Replacement parts often takes months or even a year or two to get, and finding people who are trained to make the repairs is another problem. With standardization, parts replacement can be readily managed and training requirements greatly simplified. Unfortunately, few if any DCs have as yet adopted such standardization and, accordingly, O&M is usually very inadequate.

• Infiltration into sewers in the ICs used to be a serious problem but this has been virtually eliminated over the past half-century by use of new pipe jointing methodology. But jointing in existing DC sewers is often old-style (bell and spigot pipes), which can result in significant infiltration, which must be taken into account in the design.

• Selection of treatment/disposal design criteria depends on the environmental standards to be met, and the appropriate standards suited to the DC use may be quite different from the IC standards. Care must be given to selecting treatment levels that are appropriate/affordable.

• Attention must be given in the project feasibility study to the institutional and financial aspects—that is, the relationship between the central, provincial, and local governments and their relative responsibilities. Common practice in many DCs has been for the central government to build the plant, then "abandon" it to the local government to be managed without provision for funding of O&M. The ADB study of 19907 on "Economic Policies for Sustainable Development" stresses the need to decentralize so that the local governments have both responsibility and authority for planning/building/operating, with ability to raise their own funds, with the central government in an assisting role.

• The role of the EIA in the project feasibility report is very important for helping ensure attention to all of the issues already noted. The manual on EIA for USEM prepared for use in Thailand in 19976 serves this need and, as such, can be very helpful to all parties concerned including project proponents, regulatory officials, and design engineers.

Brief discussions some of the problems already noted are given next. Details

are given in135.

Sewerage-cum-Sanitation Systems for 100 Percent Excreta Management

The first effort to plan and implement a comprehensive USEM system that provides for management of all excreta in the study area, so that its public health protection target will actually be achieved, is the World Bank-sponsored Jakarta Sewerage and Sanitation Project, which was constructed in the 1980s152. It covers one selected area in the overall Jakarta region. The project includes both (1) a system for collecting and treating sewage from those portions of the area capable of paying for this service (the affluent portion), with the interceptors planned for ready expansion eventually to cover all areas, and (2) provisions for satisfactory use of on-site disposal units for buildings not connected to the sewerage system.

The recommended on-site disposal is provided by use of dual leaching pits, which receive the discharges from pour-flush toilets, including establishment by the municipality of a special pit desludging service dedicated to servicing only these nonaffluent areas, with use of special desludging trucks designed to be narrow enough to enable access to buildings on narrow streets/lanes, with long desludging hoses. These units give satisfactory service for most of the premises for which the ground permeability and groundwater levels enable them to function as designed, and for these desludging is needed only every several years, with the premise owner paying for this service. For the relatively small percentage of the houses/buildings where permeability is not adequate and/or groundwater levels are too high, more frequent desludging is needed, with these extra costs subsidized by the municipality.

Sewage Treatment Systems

Evaluation of the accumulated experience in numerous DCs showed that the tendency is for each municipal system to be designed on its own, employing a wide variety of treatment systems, each costing about the same to construct but each posing separate needs for parts replacement (which may take many months in many cases) and for O&M training. The economic answer is for each DC to standardize the design of treatment units so that one of several parts depots can readily service all plants in the country and so that O&M training is greatly simplified. The recommended procedure is to utilize a system of four types of plants, proceeding from the first to the fourth progressively as land prices increase, as shown in Figure 4.7. Note that three options (A, B, C) are indicated for System (i) and 2 options (A, B) for System (iii). The selection depends on the particular situation. For example, for System (iii), Option B will often be adequate for very small plants, as for schools in rural areas and for large plants discharging to open (unconfined) ocean water. See105 for details on the selection process.

Experience indicates that the IAAs will generally be quite willing to give grants to international DCs who wish to follow these guidelines to prepare a national sewerage system plan, including provisions for collection as well as treatment, to be progressively implemented as the country's urbanization and industrialization continue to grow and land prices correspondingly increase. The same study can also examine potentials for achieving regional pollution control systems for protecting affected waterways.

Sewage Collection (Including Interceptors, Pumping, Transmission)

The most important design consideration here is to recognize that many DC municipalities will not be able to afford immediate construction of sanitary sewers for servicing the entire community area, which will have to be achieved progressively with a series of stages, so that use is made of the existing storm drainage conduits for the collection role on an interim basis. Again, the national agency responsible for sewerage facilities should standardize use of materials and equipment for simplifying parts replacement and O&M training, including sewer-cleaning equipment.

Pumping Stations An especially difficult problem is design of pumping plants (which have always been a headache in sewerage history everywhere), but fortunately a design manual produced by Robert Sanks et al.130 is available that is invaluable for helping the designer with this problem. Another important design aspect for collecting sewers is to utilize not the old-fashioned bell and spigot pipe lengths, which generally result in entry into the sewers of large amounts of unwanted groundwater, but instead the modern type of joint (now generally available) using rubber rings, which virtually eliminate groundwater infiltration.

Curved Sewers Another valuable change in design of sewers applicable to both ICs and DCs was development in the United States following World War II of curvilinear sewer alignments, thus greatly reducing sewer construction costs,

System (i): Oxidation Pond Treatment Systems

System (i): Oxidation Pond Treatment Systems

System (ii): Aerated Lagoon Treatment System


Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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