Alexandre Colzi Lopes

Hydrogen sulphide removal in the anaerobic digestion of sludge by micro-aerobic processes: pilot plant experience

H(2)S removal from biogas produced in anaerobic digestion of sludge through the introduction of oxygen under micro-aerobic conditions is studied. Research was carried out in two pilot plant reactors (working volume, 200 L each) treating sludge from WWTP with HRT of 20 days. Mixing was provided via sludge or biogas recirculation. Introduction of very low oxygen flow (0.013-0.024 L/L(reactor) d) successfully removed H(2)S content in biogas with an efficiency above 99%. Reactor performance during micro-aerobic operation in terms of biogas production, methane yield and COD removal were not affected by the amount of oxygen supplied, remaining stable and similar to the anaerobic behaviour. Sludge recirculation ( approximately 50 L/h) and biogas recirculation ( approximately 3.5 L/min) as mixing methods were found not significant in H(2)S removal from biogas while biogas recirculation reduced by 10 times dissolved sulphide concentration compared to sludge recirculation.

Molecular analysis of the biomass of a fluidized bed reactor treating synthetic vinasse at anaerobic and micro-aerobic conditions

The microbial communities (Bacteria and Archaea) established in an anaerobic fluidized bed reactor used to treat synthetic vinasse (betaine, glucose, acetate, propionate, and butyrate) were characterized by denaturing gradient gel electrophoresis (DGGE) and phylogenetic analysis. This study was focused on the competitive and syntrophic interactions between the different microbial groups at varying influent substrate to sulfate ratios of 8, 4, and 2 and anaerobic or micro-aerobic conditions. Acetogens detected along the anaerobic phases at substrate to sulfate ratios of 8 and 4 seemed to be mainly involved in the fermentation of glucose and betaine, but they were substituted by other sugar or betaine degraders after oxygen application. Typical fatty acid degraders that grow in syntrophy with methanogens were not detected during the entire reactor run. Likely, sugar and betaine degraders outnumbered them in the DGGE analysis. The detected sulfate-reducing bacteria (SRB) belonged to the hydrogen-utilizing Desulfovibrio. The introduction of oxygen led to the formation of elemental sulfur (S0) and probably other sulfur compounds by sulfide-oxidizing bacteria (γ-Proteobacteria). It is likely that the sulfur intermediates produced from sulfide oxidation were used by SRB and other microorganisms as electron acceptors, as was supported by the detection of the sulfur respiring Wolinella succinogenes. Within the Archaea population, members of Methanomethylovorans and Methanosaeta were detected throughout the entire reactor operation. Hydrogenotrophic methanogens mainly belonging to the genus Methanobacterium were detected at the highest substrate to sulfate ratio but rapidly disappeared by increasing the sulfate concentration.

Microalgae harvesting and cell disruption: a preliminary evaluation of the technology electroflotation by alternating current

Some species of microalgae have high productivity and lipid content, which makes them good candidates for biodiesel production. Biomass separation and cell disruption are important steps in biodiesel production from microalgae. In this work, we explored the fundamentals of electroflotation by alternating current (EFAC) with non-consumable electrodes to simultaneously harvest microalgae and disrupt cells from mixed microalgae obtained from waste stabilization ponds. The harvesting efficiency was evaluated using chlorophyll-a and turbidity, which reached removals of 99% and 95%, respectively, during a batch time of 140 min. Cell disruption was evaluated using lipid extraction, and the best results were achieved with a batch time of 140 min, which resulted in a 14% yield. Therefore, EFAC was shown to be an attractive potential technology for simultaneous microalgal harvesting and cell disruption.

Multivariate optimization of headspace‐GC for the determination of monoaromatic compounds (benzene, toluene, ethylbenzene, and xylenes) in waters and wastewaters

The objective of this study was to optimize, by employing a central composite rotatable design, and validate an analytical method to detect and quantify monoaromatic compounds (benzene, toluene, ethylbenzene, and xylenes) in waters and wastewaters by using headspace extraction followed by GC coupled with photoionization detection. The extraction parameters optimized were: salinity, sample volume, incubation time, and extraction temperature. The results revealed that the sample volume was the most significant parameter in the extraction process, whereas the salinity effect was negligible, which extends the applicability of the analytical method to waters with different salinities. Finally, the studied method was very selective and, at the optimal extraction conditions (15 mL sample volume, 15 min incubation time, and temperature of 70°C), presented excellent repeatability (<4%), linearity (R > 0.999 for each compound), and sensitivity, since very low LODs (0.13-0.48 μg/L) and LOQs (0.43-1.61 μg/L) were achieved.

Removal of the metal ions Zn2+, Ni2+, and Cu2+ by biogenic sulfide in UASB reactor and speciation studies

Abstract This work evaluated the effects of the chemical oxygen demand (COD)/ ratio on sulfate removal efficiency of an upflow anaerobic sludge blanket reactor inoculated with sludge from an industrial brewery. The removal of nickel (Ni2+), zinc (Zn2+), and copper (Cu2+) by precipitation with the biogenic sulfide was also studied as well as the metals speciation through the reactor height with scanning electron microscopy/energy-dispersive X-ray spectroscopy/X-ray fluorescence (SEM/EDX/XRF) techniques. Ethanol was used as organic carbon source for electron donor, the hydraulic retention time was 18 h, and the organic loading rate was 1.5 kg COD m−3 d−1. The experiment was divided in five periods, evaluating the system capacity in terms of sulfate reduction (COD/ of 2.26, 1.13, and 0.57) and metals (50 and 100 mg L−1) removal by biogenic sulfide. High removal (higher than 98.5%) of the metals was achieved in the bioreactors, which were directly related to the solubilities solubility product of NiS, ZnS, an...