Tratamento da água residuária de suinocultura utilizando processos biológicos anaeróbios e microaerobios em reatores de alta taxa

Abstract

The high demand for food has transformed the pig farming activity in the last decades into an intensive industry. This results in large quantities of swine wastewater (SWW) production. An effluent that has high levels of organic matter, suspended solids, nutrients and considerable microbial load, in addition to antibiotic and hormone residues. The upflow anaerobic sludge blanket (UASB) reactor, among technologies that use anaerobic digestion, represent a process widely used in the treatment of swine wastewater. During SWW treatment in UASB reactors, the improvement of hydrolysis is fundamental to solubilize these complex substrates into simple organic substrates for later conversion into methane. Thus, in this study, the performance of an UASB reactor and a upflow microaerobic sludge blanket (UMSB) reactor operating under the same feeding conditions (COD = 5 gO2 L-1), organic loading rates (COV = 10,4 ± 0,9 COD m-3 d-1) and HRT (12 h) in the treatment of SWW was evaluated. With a main focus on hydrolysis and volumetric production of methane. For this purpose, the removal of parameters related to particulate organic matter (CODP, BOD520°CP, VSS, CODT, BOD520°CT) were evaluated; the volume and composition of biogas produced by the reactors, production and evolution of biomass and microbiological community of sludge. In addition, SMA tests were performed in order to analyze the performance of sludge in the degradation of starch, glucose and VFAs solution, in order to evaluate hydrolytic, acidogenic and acetogenic/methanogenic activities, respectively. The study was divided in two parts. In the first part the effect of microaeration on the hydrolysis rate of the reactors was evaluated. Where the performance of a UASB reactor (called R1) and a UMSB (called R2) reactor with 11.3 mLAir min-1 (0,5 LO2 Lfeed-1 d-1) as dose of microaeration was compared during the SWW treatment. In this first part, the UMSB reactor treating SWW obtained better performance. In the stationary state, the reactor removed on average 74.5 ± 3.2 % of CODT. The main advent of the reactor was its removal of particulate organic matter due to the high removal of VSS (79.4 ± 4.6 %). In SMA tests the microaerobic sludge presented higher hydrolytic and acetogenic/methanogenic activity than inoculum and anaerobic sludge. The microbiological evaluation of UMSB reactor revealed the presence of groups such as Clostridium sensu stricto 1 and Brachymonas, important constituents of the microbiota responsible for the anaerobic digestion of complex substrates. In the second part of the experiment, using the same operational parameters (inffluent COD, OLR, HRT), the effects of different doses of microaeration on the UMSB reactor: 2.0, 3.8, 5.6 mlAirmin-1 (0,09; 0,17; 0,25 LO2 Lfeed-1 d-1, respectively) were analyzed. In this second phase, the microaerobic process showed the best results when operated with a microaeration dose of 3.8 mLAir min-1, removal of organic matter in terms of VSS, CODT, CODP, BOD520°CT and BOD520°CP of 85.0 ± 3.5 %, 83.2 ± 2.7 %, 86.9 ± 3.7 %, 85.3 ± 1.9 %, 87.8 ± 1.9 %, respectively. The microaeration dose of 5.6 mLAir min-1 provided a volumetric production of methane reaching average values of 5 LCH4 d-1. The results indicated that, with the correct microaeration dose, it is possible to obtain in a microaerobic reactor higher rates of hydrolysis of particulate organic matter, greater removal efficiency of the organic matter present (COD, BOD and VSS) and volumetric methane production, when compared to strict anaerobic process.