Tratamento descentralizado de esgotos domésticos em sistemas anaeróbios com posterior disposição do efluente no solo

Abstract

Release of domestic sewage into environment without any treatment can cause negative environmental impacts, particularly in relation to contamination and pollution of water bodies. Current alternatives for domestic sewage treatment involve two approaches: centralized and decentralized. Centralized management is mainly applied in regions with high population density and aims to treat large volumes of domestic sewage. Decentralized systems are designed to collect, treat, allocate and still reuse the treated effluent near the point of generation, and are applied in rural and peri-urban areas not served by a sanitary sewer system. Anaerobic treatment of domestic sewage has proved suitable for decentralized management with possible effluent disposal in soil by means of septic tank followed by sinkhole, which is still often applied because of their very long useful life and ease of infiltration into soil. However, replacing the septic tank, UASB reactor is presented as an alternative to improvements in pre-treatment of domestic sewage, producing effluent also for release in soil. Given the above, this study evaluated and compared the efficiency of decentralized single-family treatment of domestic sewage using a septic tank (TS) and UASB reactor, both with disposal of effluent into soil. Experimental system was monitored in EXTRABES and consisted of two treatment units: TS followed by a sinkhole 1 (S1) and a UASB reactor followed by a sinkhole 2 (S2), intermittently fed by domestic sewage. Experimental period was conducted in two phases. First phase corresponds to operation of anaerobic systems (TS and UASB) and the second phase corresponds to departure of sinkholes. Monitored parameters were: pH, total alkalinity and VFA, COD, nitrogen and phosphorus, solid and its fractions and thermotolerant coliforms. Results obtained from first phase of experiment show that anaerobic systems presented operational stability, reaching steady state after 12 weeks of operation. Removal efficiency of COD in TS and UASB was 44% and 57%. For SSV, results showed significant variation (p-value=0.033198) between TS and UASB. In second phase, with departure of sinkholes, were observed high concentrations of nitrite (2.73mgN-NO2.L-1) and nitrate (26,19mgN-NO3.L-1) in S1. Removal of organic material in terms of COD, remained around 60% in TS and UASB. There was similar retention of ST and SS in TS and UASB. For clogging of sand in S1 and S2, variants (infiltration rate and infiltration volume) indicate tendency of fouling in S1, possibly due to the most significant contribution of SST in TS compared to UASB, showing its ability to replace TS in decentralized treatment of domestic sewage, with subsequent application of treated effluent into soil.