Tratamento e valorização de efluentes da bovinocultura por processos biológicos

Abstract

In this study, reactors and biological methods were tested for treatment and valorization of cattle wastewater. The waste was treated in real scale in a plug flow biodigestor followed by a stabilization pond, at ambient temperature and hydraulic retention times of 32 and 6 days, respectively. Biogas volumes between 278.5 and 2,186.1 m³ month-1 were produced, with average CH4 concentration of 65%, which enabled monthly electricity generation between 2,070 and 19,168 KWh, sufficient to supply the farm’s energy needs. The average annual removals of BOD5,20, COD, NH4 and TKN were 86, 70, 88.5 and 85.5%, respectively. The treated effluent from the pond was used as biofertilizer to grow sugarcane (Saccharum officinarum), and the results showed that this biofertilizer can replace urea as a source of nitrogen. With application of the biofertilizer, cane yields greater than 147.5 Kg ha-1 were attained, higher than the Brazilian average. Seeking to enhance the production of biogas, a hybrid anaerobic bioreactor was tested in mesophilic conditions (37 °C ± 1 ºC), operated with water retention times of 6, 5, 3 and 2 days. Methane concentrations between 69 and 75% and biogas volumes up to 1.4 m³ m-3 d-1 were obtained, the last value being higher than described in the literature over the past 15 years for this type of effluent. The removals of organic matter, with values of 60-81% (CODt) and 51-75% (CODs), allowed obtaining methane yields of 0.155-0.183 m³ CH4 Kg-1 CODt and 0.401-0.513 m³ CH4 Kg-1 CODs. The effluent treated in the hybrid reactor was submitted to sedimentation in an Imhoff cone and then sent for secondary treatment in photobioreactors, applying both batch and continuous flow methods. In the batch regime, removals of 65 to 70% of CODs, 98 to 99% of NH4+ and 69 to 77.5% of PO4-3 were recorded after 12 days. In continuous flow mode, the removals were 57 to 61% of CODs, 94 to 96% of NH4+ and 65 to 70% of PO4-3 with hydraulic retention time of 12 days. Higher volume yields of biomass of the microalga Scenedesmus obliquus were achieved in batch operation (213 - 358 mg L-1 d-1). The maximum productivity of proteins, carbohydrates and lipids were 150, 110 and 64 mg L-1 d-1. The process of bioremediation and valorization of cattle wastewater in photobioreactors can be considered promising, since besides energy generation, the biomass can be used as fertilizer, feed for ruminants and/or production of biodiesel.