Sistema UASB/FBP submetido a hidrograma típico de vazão: avaliação do uso de meio suporte baseado em espuma de poliuretano e operação sem decantadores secundários

Abstract

The research consisted in the investigation of UASB systems followed by trickling filters (TF) subjected to typical sewage flow hydrograph, to evaluate (i) the use of lamella settler in improving the effluent quality of UASB reactor, (ii) the influence of the physical characteristics of polyurethane sponge in removing organic matter and fecal bacteria indicators in pilot-modules post-UASB reactors and (iii) the performance of a demonstration scale UASB/TF system, without secondary settlers and support media developed for industrial production. The experimental apparatus was comprised of UASB/TF systems, wherein the UASB reactor has been modified by including a high rate settler (parallel plates) in one of its settling compartments. Even with the increase in anaerobic sludge mass, the parallel plates provided an additional solid retention of about 30%, with less variability in concentrations of COD and sedimentable solids. However, in condition of high sludge accumulation in the digestion compartment, there may be flaws in reducing solids concentrations at peak flow. In the second stage investigations (post-treatment) effluent from the UASB reactor with parallel plates was directed to pilot-modules respectively composed of three different types of polyurethane sponge. The results led to the selection of the sponge with 0,5 mm pore size for the development and industrial production of the support media. For the imposed operating condition (HLR: 11,5 m³.m-2.d-1; OLR: 3,18 kgCOD.m-3sponge.d-1), high overall removal efficiency of organic matter were observed in terms of BOD (86 89%) and TSS (88 91%). The low loss of solids (31 mgTSS.L-1) in the effluent indicated perspectives for elimination of secondary settlers even if high organic load conditions are applied. The concentration of total coliforms and E. coli were similar between the sponges with pores equal or smaller than 0,5 mm, confirming one of the hypotheses associated with this research. To the stage of research with demonstration scale UASB/TF system (equivalent population: 220 inhabitants), it was possible to identify an operating limit for the removal of ammonia. The operational conditions imposed on TFs post-UASB (HLR: 10 - 12 m³.m-2.d-1; OLR: 1,9 kgDQO.m-3espuma.d-1) allowed the attendance to discharge standards for COD, BOD and TSS with failure probability 1%, but with effluent ammonia concentrations near the discharge limit of 20 mgN.L-1. The other hypotheses associated with this research were confirmed in part or with restrictions. The use of parallel plates contributed to improving the quality of UASB reactor effluent at peak flows only when the mass of anaerobic sludge was not in excess in the UASB reactor. The UASB/TF systems without secondary clarifiers, undergoing typical sewage hydrograph flows were able to meet the discharge standards of organic matter and ammonia, although the results of research suggests reducing the organic load applied to the TF for a higher nitrifying activity.