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 H-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 H 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) or vinasse (8.8, 12.7 and 13.4mmolL) in substrate. These effluents demonstrated remarkable energetic reuse perspectives: 24.0MJm and 4.0MJm, 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.

Hydrogen-producing bacterial strains were isolated from granular sludge from a UASB reactor that treats brewery wastewater. Most of the isolated strains were related to the Enterobacter genus through a phylogenetic analysis of the 16S rRNA sequences. The strains could use various carbon sources (sugars and glycerol) to produce hydrogen. The isolated strain, identified as Enterobacter sp. based on 16S rRNA gene sequencing, produced 6.8 mmol H 2 L À1 culture medium when growing on glucose (2.0 g L À1) in anaerobic conditions at 30 C. The main liquid metabolites were acetic acid (367 mg L À1), methanol (437 mg L À1) and ethanol (1101.26 mg L À1), after 9 h of fermentation. The maximum hydrogen yield of 0.8 mol H 2 /mol glucose was observed, indicating that Enterobacter sp. isolated from brewery wastewater was an efficient hydrogen-producing bacterium under mesophilic conditions.

Biohydrogen production is a cheap and clean way to obtain hydrogen gas. In subtropical countries such as Brazil the average temperatures of 27 C can favor the hydrogen producing bacteria growth. A mixed culture was obtained from a subtropical sludge treating brewery wastewater and anaerobic batch reactors were fed with glucose, sucrose, fructose and xylose in low concentrations (2.0, 5.0 and 10.0 g L À1) at 37 C, initial pH 5.5 and headspace with N 2 (99%) to maintain the anaerobic conditions. The inoculum was a subtropical granulated sludge from UASB (Upflow Anaerobic Sludge Blanket) reactor treating brewery wastewater. The higher H 2 yields were obtained in reactors operated with 2 and 5 g L À1 of fructose and they were 1.5 mol H 2 mol À1 of fructose and 1.3 mol H 2 mol À1 of sucrose, respectively. The volatile fatty acids (VFA) generated at the end of operation were, predominantly, butyric and acetic acid, indicating the favoring of the metabolic route of hydrogen generation by the consortium of anaerobic bacteria from the brewery wastewater. Biomolecular analyses revealed the predominance of hydrogen producing bacteria from Firmicutes phylum distributed in the families Streptococcaceae, Veillonellaceae and uncultured bacteria. These results confirm future applications of subtropical sludges with agroindustrial wastewaters containing low concentrations of sugars on hydrogen generation.