Sandra Imaculada Maintinguer

Potential of biohydrogen production from effluents of citrus processing industry using anaerobic bacteria from sewage sludge

Citrus crops are among the most abundant crops in the world, which processing is mainly based on juice extraction, generating large amounts of effluents with properties that turn them into potential pollution sources if they are improperly discarded. This study evaluated the potential for bioconversion of effluents from citrus-processing industry (wastewater and vinasse) into hydrogen through the dark fermentation process, by applying anaerobic sewage sludge as inoculum. The inoculum was previously heat treated to eliminate H2-consumers microorganisms and improve its activity. Anaerobic batch reactors were operated in triplicate with increasing proportions (50, 80 and 100%) of each effluent as substrate at 37°C, pH 5.5. Citrus effluents had different effects on inoculum growth and H2 yields, demonstrated by profiles of acetic acid, butyric acid, propionic acid and ethanol, the main by-products generated. It was verified that there was an increase in the production of biogas with the additions of either wastewater (7.3, 33.4 and 85.3mmolL-1) or vinasse (8.8, 12.7 and 13.4mmolL-1) in substrate. These effluents demonstrated remarkable energetic reuse perspectives: 24.0MJm-3 and 4.0MJm-3, respectively. Besides promoting the integrated management and mitigation of anaerobic sludge and effluents from citrus industry, the biohydrogen production may be an alternative for the local energy supply, reducing the operational costs in their own facilities, while enabling a better utilization of the biological potential contained in sewage sludges.

Evaluation of the microbial diversity of denitrifying bacteria in batch reactor

Microbial communities in an industrial activated sludge plant may contribute to the denitrification process, but the information on the microorganisms present in denitrifying reactors is still scarce. Removal of inorganic nitrogen compounds can be accomplished by the addition of carbon sources to the biological process of denitrification. Ethanol is an economically viable alternative as a carbon source in tropical countries like Brazil, with large-scale production from sugarcane. This paper reports the successful aplication of activated sludge with nitrate and ethanol in a batch anaerobic reactor. The operation lasted 61.5 h with total consumption of nitrate in 42.5 h, nitrite generation (2.0 mg/L) and ethanol consumption (830.0 mg/L) in 23.5 h. Denitrifying cell counts by the most probable number at the start of the operation were lower than at the end, confirming the ability of the inoculum from activated sludge for the denitrification process. The samples from cell counts were identified as Acidovorax sp., Acinetobacter sp., Comamonas sp. and uncultured bacteria. Therefore, these species may be involved in nitrate reduction and ethanol consumption in the batch reactor.

Thermal characterization of anaerobic sludges from wastewater treatments applied to biological generation of H-2

A wide variety of organic residues may be used as energy source such as anaerobic sludge from wastewater treatment systems. However, due to inherent differences in composition, the proper characterization of these biomasses is essential to support their reuse through any conversion process. The aim of this study was the employment of thermal analysis techniques (TG/DTG and DTA) to perform the characterization of anaerobic sludges from different wastewater treatment plants (industrial and municipal), which were further applied for biological production of H2. The different profiles observed through thermal characterization support the application of these residues as inocula, confirming their potential for H2 production, while demonstrating the main causes for the different yields obtained (mol H2 mol−1 sucrose): 0.9 from sludge of brewery industry and 2.0 from sludge of municipal wastewater treatment plant, corresponding to the overall yields of 10.8 and 25%, respectively. These results confirm the versatility of thermal analysis techniques for biomass characterization, focused on its application for power generation. It is urgent to adopt more sustainable and cost-effective solutions for their management, considering a large amount of residues daily generated in both treatment processes addressed; therefore, biohydrogen production by anaerobic digestion may be a promising alternative for the reuse of both residues as it promotes their transformation from costly and potentially polluting waste into clean and renewable energy sources. The development of this anaerobic process is even more attractive in countries as Brazil, where the weather conditions are naturally favorable.