Reliability analysis of low-cost, full-scale domestic wastewater treatment plants for reuse in aquaculture and agriculture

The current paper assesses the reliability coefficients of fifty six low-cost, full-scale wastewater treatment plants, including nine different treatment technologies for wastewater reuse in aquaculture and agriculture in northeast Brazil. This was carried out with the aim to evaluate alternatives for sustainable wastewater reuse in communities experiencing water scarcity. The technologies evaluated include septic tanks (ST); septic tanks + anaerobic filters (ST + AF); septic tanks + anaerobic filters + chlorination (ST + AF + Cl); facultative ponds (FP); facultative + maturation ponds (FP + MP); anaerobic + facultative + maturation ponds (AP + FP + MP); facultative aerated ponds + facultative + maturation ponds (FAP + FP + MP); upflow anaerobic sludge blanket reactors (UASB); and upflow anaerobic sludge blanket reactors + chlorination (UASB + Cl). The parameters used for the analysis include chemical oxygen demand, total suspended solids, Escherichia coli and biochemical oxygen demand. By applying an 80% reliability level for standard compliance, the study aimed at presenting relevant, realistic and achievable targets for the evaluated parameters. Discharge limits for agriculture and aquaculture were obtained from a compilation of international and Brazilian guidelines. Performance data showed, in some cases, great variability among wastewater treatment plants of the same type, highlighting the importance of good management and operation. The technologies that presented the highest reliability for wastewater reuse were AP + FP + MP systems (waste stabilization ponds), followed by ST + AF + Cl and FAP + FP + MP. UASB and UASB + Cl performed similarly to ST + AF systems whilst the worst performances were observed for ST, FP + MP and FP. Results have shown that low-cost, full scale wastewater treatment plants are able to provide a suitable effluent for wastewater reuse in agriculture and aquaculture when an 80% reliability standard is applied.