Tratamento de águas residuárias domésticas através de sistema conjugado anaeróbio/aeróbio: alternativa tecnológica para minimização de impactos ambientais.

Abstract

The disposal of domestic sewage without or only partial treatment into receiving water bodies, causes eutrofication as a result of the high concentrations of organic material and nutrients, provoking sanitary, ecological, economical and social problems. It is therefore necessary to improve existing technologies and develop new ones to address this problem. In this research different configurations of biological reactors were evaluated for the treatment of domestic sewage. The combinations of reactors used to stimulate the nitrification/denitrification processes leading to N removal were: 1) Upflow anaerobic sludge blanket reactor (UASB) followed by Sequencial Batch Reactor systems (SBR), one with dispersed biomass and the other with adhered biomass on a support medium of Luffa cylindrica; 2) Raw sewage (RS) treatment in SBR with different operational cycles; 3) RS treatment in SBR with external carbon sources: acetate and lysed sludge; 4) RS treatment in a combination of an anaerobic reactor with dispersed biomass followed by an aerobic reactor operating in batch with adhered biomass on a synthetic support and for biological P removal 5) RS treatment in SBR operating in an anaerobic/aerobic cycles with different solids retention times. Respirometry studies were made to determine: the kinetic constants of the heterotrophic and autotrophic bacterial populations; the assimilation of organic material in the process of phosphorus removal and quantification of the soluble and particulate fractions of COD. The adhered biofilm on the Luffa cylindrica support gave higher nitrification and COD removal rates than the SBR system with disperse biomass. A SBR system operated with 3 cycles per day didn't give significantly different results (p>0.05) compared to a RBS operating with 4 cycles per day, both performed well with respective removals for COD of 86 and 85%, for TKN of 91 and 90% and TSS of 86 and 86%. SBR treating RS jointly with lysed sludge removed on average 23 and 40% more total phosphorus and orthophosphate, respectively, than the systems just receiving RS as substrate. The combination of an anaerobic reactor with dispersed biomass followed by an aerobic reactor with adhered biomass with recirculation between the reactors showed promising results in terms of N-NH4+ and N-NTK removals with efficiencies of 91 and 94%, respectively, and producing a clarified effluent with SVS mean concentrations of 8 mg.L-1. SBR with a sludge age of 5 days gave the best results for phosphorus removal with a concentration of 12.6% P in the excess sludge. For nitrogen removal via nitrification/denitrification the systems with adhered biomass gave better nitrification rates than dispersed biomass reactors, but, the addition of an external carbon source was essential for good denitrification. Better P removals were obtained in reactors with suspended biomass and again the addition of an external carbon source (lysed sludge) increased removal rates. In terms of a clarified effluent (removal of solids), the reactors with adhered biomass were better.