Análise econômica, ambiental e social de sistemas descentralizados de tratamento de esgoto doméstico para reúso na agricultura.

Abstract

This work investigated household decentralized wastewater systems related to minimal cost, and effluent quality for physicochemical and microbiologic parameters prior to reuse in cultivation of Palma forage aiming to propose an alternative of minimal total cost, thence economically feasible, linked to an appropriate removal efficiency of organic matter, suspended solids and indicator organisms for soil conservation, piping clogging effect minimization of reuse system, in addition to reducing workers risks of exposure in agricultural irrigation practices. This research was accomplished from January to December, 2014, and applied as a scenario the reality of Santa Cruz settlement in Campina Grande-PBBrazil. For economic assessment of minimal cost, it was estimated the costs for implantation, operation and maintenance of five household onsite decentralized wastewater systems, and one household wastewater reuse system. These costs added generated the total costs, brought to present value in a project timeline of twenty years. Related to environmental assessment, removal efficiency data of organic matter and solids was compared among treatment systems, selecting the most appropriate alternative in terms of pollutants removal performance. Finally, for social analysis, it was verified which system has produced the lowest risk contamination level for workers and consumers, in terms of removal of microbiological parameters like thermo tolerant coliforms and helminthes eggs, based on guidelines for agricultural reuse from the United States environmental protection agency and World Health Organization. The most appropriate treatment alternative selection has considered that three evaluated dimensions prior to identification of the prime system in terms of cost and removal efficiency. In the economic assessment, UASB Y reactor has achieved the best position (R$ 4.839,64), with respective differences regarding other investigated systems of: 33,90% (TS), 49,01% (ECO 1), 59,62% (UASBC + FAN) and 63,92% (UASBC + FaFint), making it the better choice in terms of total costs. The estimated total cost for household reuse system was R$ 59.859,38. Related to environmental criteria, the compact reactor ECO 1 has shown the better choice, reaching removal efficiencies in terms of DQO, SST and SSV, respectively of 85%, 96% and 95%, while the anaerobic-aerobic association of Conventional UASB and Intermittent Sand Filter has gotten the second better option in terms of removal efficiencies of DQO, SST and SSV, with respective amplitude of one, six and four percentage points when compared to ECO 1 system. Regarding to social assessment the ECO 1 anaerobic-aerobic compact system offered the better coliforms removal efficiency, reaching 1.72 log removals while concerning helminthes eggs removal systems ECO 1, UASB C+FaFint, and UASB C+FAN, has attained the WHO recommendation of ≤ 1 ovo/L-1, with respective results of 0, 0 and 1 ovo/L-1 showing expressive removing efficiency. Considering the three dimensions assessment, the ECO 1 system has found to be the better choice, although it has not achieved the lowest cost but highlighting under environmental and social assessment, both ordering in number one position. The utilization of decentralized treatment systems has shown to be of low cost and good appropriate efficiency option with potential for agricultural reuse, which characteristics are crucial if universalization of sanitation in rural and peri-urban areas is to be pursued.