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Water treatment


5. COST OF MULTI-STAGE FILTRATION PLANTS 5.1 Introduction Lack of systematic information about investment and recurrent costs of MSF technology have limited its use, as absence of data makes it impossible to compare the costs of different MSF systems with other water treatment options. Information concerning the total life cycle cost associated with a technology is essential for effective technology selection, establishing financing arrangements, managing the system and above all, involving the community and institutions in decision making. This chapter presents an approach that permits the estimation of the total cost of MSF systems. It includes models that have been developed for different MSF alternatives to assess the construction requirement of the items that have greatest individual cost. For the application of these models, basic information is needed about unit costs of materials and labour, as these will differ between areas where MSF systems will be constructed. The chapter also includes preliminary information about time and staff requirements for operation, maintenance and administration. It concludes with a general discussion including considerations about cost distribution and economy of scale. 5.2 Background Little information is available about the cost of water treatment systems in Colombia, particularly in the case of systems providing water to small and medium-sized municipalities and rural communities. In the beginning of the 80’s, Arboleda (1982) compared the investment cost of conventional treatment plants with capacities between 0.025 m 3 s -1 and 4.0 m 3 s -1 in the USA with those in Latin America. The comparison showed that significant cost reductions were the result of innovations in the adaptation of the technology to the Latin American conditions. The Instituto Nacional de Fomento Municipal (INSFOPAL) in Colombia developed models to predict the investment cost for conventional water treatment systems that included coagulation, flocculation, sedimentation, rapid filtration (RF), disinfection, and pH adjustment (INSFOPAL, 1982). Three models were developed for different regions of Colombia based on information provided by water companies linked to the Institute. The models were limited to systems with production capacities of less than 2600 m 3 d -1 (30 ls -1 ) and presented the cost as a function of the plant capacity. The models however, are not very reliable because of the wide dispersion of data and the large differences in unit cost of local labour and materials. 1. National Context C = 142,198 Q -0.43 r = -0.4 (5.1) 2. Northern Zone C = 122,112 Q -0.42 r = -0.3 (5.2) 3. Central-Southern Zone C = 142,540 Q -0.42 r = -0.4 (5.3) In which C is construction cost in Col$/m 3 /d at 1982 prices; Q is the plant production capacity in m 3 d -1 ; and r is a correlation coefficient. 177

In 1988, The Cinara Institute with the support of the International Water Supply and Sanitation Centre (IRC), developed cost models for SSF systems on the basis of experience with full-scale demonstration projects in the hilly areas of the Cauca Valley (Galvis et al., 1989). The study included models for estimating the construction quantities and the construction cost of SSF systems with production capacities between 2 and 30 ls -1 , using filtration rates of 0.15 mh -1 . The study also assessed the economy of scale and the effect of the height of the filter box on the initial investment cost. In a provisional manner it also included the cost of coarse gravel filtration (CGF), estimated at 75 percent of the cost of SSF. This estimate was based on the very first full-scale experiments with CGF technology in Colombia. The resulting cost model was applied to SSF systems operating at 0.15 mh -1 with surface areas between 48 and 720 m 2 . Equations 5.4 and 5.5 present cost models with respect to filtration area (A) and supply capacity (Q) C = 0.2801 A 0.8533 (5.4) C = 4.2166 Q 0.8533 (5.5) In which, C is construction cost, in thousands of US$ at 1988 prices; A is filtration area, in m 2 ; and Q is supply capacity, in ls -1 Comparing these models (equations 5.4 and 5.5) with equation 5.3, it was found that the initial investment cost for systems that included SSF and CGF were more favourable than for conventional systems for plant capacities up to 6,000 m 3 d -1 or 70 ls -1 (Galvis et al, 1989). Comparative studies between SSF and conventional systems in India (Sundaresan and Paramasivan, 1982) indicated that SSF could be more economical in terms of initial investment for plant capacities up to 50 ls -1 . When operation and maintenance costs are also taken into account, the break-even point increases to 286 ls -1 . The model obtained for the initial investment cost in India was: C = 0.132 A 0.86 (5.6) In which, C is construction cost, in thousands of US$(1982) and A is filtration area, in m 2 . Most studies on water treatment costs are concentrated on initial capital investment with less attention to the Operation, Maintenance, and Administration (OM&A) costs. Besides, most of these studies concentrate on alternatives related to RF technology. Considering the potential of the MSF technology to treat Andean surface (river) water sources, the Colombian government decided to support the Cinara Institute to improve its developmental work on capital (construction) and running costs of MSF technology. The following sections reports part of the of the work with IRC (Galvis et al, 1989) and preliminary results of the project with the Colombian government (Cinara, 1998), in which some undergraduate and MSc students are now participating (e.g. Aristizabal, 1999; Rojas, 1999). Construction costs considerations are based on the design and field experience in the Cauca Valley with the technology. Running costs considerations however are still difficult to estimate in a methodological way since community-based organisations are just starting to 178

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