This paper describes and discusses the main problems related to anaerobic batch and fed-batch processes for wastewater treatment. A critical analysis of the literature evaluated the industrial application viability and proposed alternatives to improve operation and control of this system. Two approaches were presented in order to make this anaerobic discontinuous process feasible for industrial application: (1) optimization of the operating procedures in reactors containing self-immobilized sludge as granules, and (2) design of bioreactors with inert support media for biomass immobilization.

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BACKGROUND: The anaerobic treatment of wastewaters is usually applied to remove the organic matter, converting it into methane. The presence of sulfate in some wastewaters produces sulphide during anaerobic biological processing, which is known as an inhibitor of biological processes. In this study, a novel anaerobic bioreactor with a fixed structured bed (ABFSB) was subjected to simultaneous sulfate reduction and organic matter removal. RESULTS: Synthetic wastewater was used as organic substrate and the bioreactor performance was studied with different COD/[SO 42− ] ratios: 0.72, 1.7, 3.5 and 6.1. The highest COD and sulfate removal efficiencies were achieved at a COD/[SO 4 2− ] ratio of 1.7 (82 and 89%, respectively). Also, in this condition a greater overall kinetic apparent parameter (0.96 h −1 ) was observed. The kinetic parameters indicate that the sulfate reducing bacteria played an important role in the organic matter removal process over a range of COD/[SO 42− ] ratios from 6.1 to 1.7.CONCLUSIONS: Concerning the organic matter removal, the best synergy between sulfate reduction bacteria and metanogenic archaea communities was achieved in COD/[SO 4 2− ] ∼1.7. The ABSFB was suitable for the simultaneous organic matter and sulfate removal, especially when the COD/[SO 4 2− ] ratio was 1.7, but demonstrating a stable and efficient process in all conditions studied.

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This paper describes a new type of anaerobic bioreactor with a fixed-structure bed (ABFSB) in which the support for the biomass consists of polyurethane foam strips placed along the length of the bioreactor. This configuration prevents the accumulation of biomass or solids in the bed as well as clogging and channeling effects. In this study, complex synthetic wastewater with a chemical oxygen demand of 404.4 mg O(2) L(-1) is treated by the reactor. The ABFSB, which has a working volume of 4.77 L, was inoculated with anaerobic sludge obtained from an upflow anaerobic sludge blanket bioreactor. A removal efficiency of 78 % for organic matter and an effluent pH of 6.97 were achieved. An analysis of the organic volatile acids produced by the ABFSB indicated that it operated under stable conditions during an experimental run of 36 days. The stable and efficient operation of the bioreactor was compared with the configurations of other anaerobic bioreactors used for complex wastewater treatment. The results of the study indicate that the ABFSB is a technological alternative to packed-bed bioreactors.

An anaerobic sequencing batch biofilm reactor (AnSBBR-total volume 7.5 L; liquid volume 3.6 L; treated volume per cycle 1.5 L) treated sucrose-based wastewater to produce biohydrogen (at 30 °C). Different applied volumetric organic loads (AVOL of 9.0, 12.0, 13.5, 18.0, and 27.0 kg COD m(-3) day(-1)), which were varied according to the influent concentration (3,600 and 5,400 mg COD L(-1)) and cycle length (4, 3, and 2 h), have been used to assess the following parameters: productivity and yield of biohydrogen per applied and removed load, reactor stability, and efficiency. The removed organic matter (COD) remained stable and close to 18 % and carbohydrates (sucrose) uptake rate remained between 83 and 97 % during operation. The decrease in removal performance of the reactor with increasing AVOL, by increasing the influent concentration (at constant cycle length) and decreasing the cycle lengths (at constant influent concentrations), resulted in lower conversion efficiencies. Under all conditions, when organic load increased there was a predominance of acetic, propionic, and butyric acid as well as ethanol. The highest concentration of biohydrogen in the biogas (24-25 %) was achieved at conditions with AVOL of 12.0 and 13.5 kg COD m(-3) day(-1), the highest daily production rate (0.139 mol H2 day(-1)) was achieved at AVOL of 18.0 kg COD m(-3) day(-1), and the highest production yields per removed and applied load were 2.83 and 3.04 mol H2 kg SUC(-1), respectively, at AVOL of 13.5 kg COD m(-3) day(-1). The results indicated that the best productivity tends to occur at higher organic loads, as this parameter involves the "biochemical generation" of biogas, and the best yield tends to occur at lower and/or intermediate organic loads, as this parameter involves "biochemical consumption" of the substrate.