6 months ago


Water treatment

epresents the risk the

epresents the risk the community has to overcome in relation to, for example, its water supply. The risk-analysis helps to establish and prioritise actions to reduce the risks, as illustrated in figure 6.1. Science and technology reflected in the knowledge, the culture, the infrastructure and the tools that “actors” in development can use to reduce the environmental risks the community is facing. The interface between environment and technology represents actions that can be taken to reduce the contamination in the water sources or reduce or eliminate them by treatment, after applying the multiple barriers strategy summarised in section 1.2. In the interface between the community and the environment, priority activities can be identified that focus on changes in behaviour in relation to, for example, management of the watershed areas and personal hygiene. It encompasses discussions with the community concerning the best possible water sources (rain water, groundwater, or surface water) possibly combining them to ensure effective use. The interface between technology and community deals with the type of solutions the community is expecting, willing and able to manage, and sustain, and that are in line with the technical, social, economical and environmental conditions and capacities of the community. The activities related to risk reduction could only be sustainable if the community adopts the solution and gains ownership of it. MSF treatment plants introduced in the coffee region of the Cauca Valley were overdesigned due to the absence of information about the sanitary risks that communities (Ceylan, Restrepo, and La Marina) were facing and the lack of experience in dealing with this technology in Colombia. They perform well but at a higher initial cost than necessary. All MSF plants are contributing to reduce risks associated with drinking water within the guidelines recommended by Lloyd and Helmer (1991) and WHO (1993). Local community based organisations have developed ownership of WS systems including MSF technology and now they take care technically and financially of their infrastructure. The author expects that this thesis will contribute to bringing this experience, as part of the interdisciplinary working group of Cinara, closer to other researchers and facilitators supporting students, local government or community water leaders. It is considered that solutions matching the three interfaces and the overall political, legal and institutional framework summarised in figure 6.5 are most promising in terms of sustainability. This requires joint problem solving with the different “ actors” involved and a clear role of the community in decision-making (Garcia et al, 1997; Galvis et al, 1999). The conceptual framework presented in figure 6.5, is a simplification of the elements involved in the process and serves to illustrate the diversity of the variables. The complexity of reaching sustainable solutions is often underestimated because of lack of information, restrictions in the interdisciplinary approach and difficulties in introducing research and development activities in the sector. Although scientific or technically oriented institutions may not be able to provide immediate solutions in a specific project environment, they should provide tools and techniques to initiate the search for them and ensure quality results. The resulting benefits of such research activities, if properly shared with sector agencies and communities, may far outweigh the investment required to undertake them. 209

7 CONCLUSIONS AND RECOMMENDATIONS Based on the research activities described in this study, the following major findings are highlighted, before more specific conclusions are made. Furthermore, recommendations are also presented, aiming to improve the development of this technology and its impact in public health and wellbeing of communities having to rely on polluted surface water sources for their water supply. The results obtained during this study clearly show that appropriate combinations of coarse gravel filtration (CGF) alternatives in series with slow sand filtration (SSF) units, made it possible to produce low sanitary risk water from surface water sources with a wide range of contamination levels in the Andean Cauca Valley. They also seem to be promising for other regions of the world with similar surface water sources. This multistage filtration (MSF) technology has proved, both at pilot and full scale, to be highly effective in reducing acute risks associated with waterborne diseases. It has also proved to have a good potential for reducing the concentration of surrogate indicators of natural organic matter related to the formation of oxidation byproducts during terminal chemical disinfection. Terminal disinfection of MSF effluents should require only a low-dose of chlorine, which should also contribute in reducing potential acute risk associated with this safety barrier against waterborne diseases. This research also contributed to enriching the available information about the strengths and weaknesses of each filtration stage in a MSF plant and in the identification of more rational procedures for selecting and designing MSF alternatives. The results also show that Operation, Maintenance, and Administration (OM&A) requirements of MSF technology are within the technical and managerial capabilities available in Andean rural and urban human settlements. The introduction and development of innovative combinations of two gravel filtration stages reduce the levels of suspended solids (SS) during the rainy periods bringing many surface water sources within the range of SSF treatment capacity. Most of the SS are removed in the first filtration stage (DyGF stage, which is the easiest and least costly to operate and maintain of all treatment stages included in MSF plants). SSF units can therefore be operated for longer periods of time without cleaning activities, making coarse gravel filtration more economically feasible. This research contributed to improving existing O&M procedures of MSF plants by introducing and testing new partial cleaning procedures of coarse gravel filtration units. Small water supply systems, including MSF plants developed and monitored during this study, are now fully under the control of community based organizations and local level institutions. All of them are covering at least the running costs of the systems. This study contributed in clarifying some of the initial (capital) and continuous (running) costs related to the application of the MSF technology in the Andean Cauca Valley. The applied methodology to implement this exploratory analyses, based on quantities of construction materials and time requirements for OM&A, should be useful during preliminary analyses when introducing MSF technology to other regions with similar surface water sources to those reported in this study. 210