Technical, Economical, and Microbiological Aspects of the Microaerobic Process on H2S Removal for Low Sulfate Concentration Wastewaters

Evaluation of microaeration strategies in the digestion zone of UASB reactors as an alternative for biogas desulfurization

This study aimed at evaluating the microaeration as an alternative for hydrogen sulfide removal from biogas of UASB reactors treating sewage. The set-up consisted of two pilot-scale UASB reactors, including a conventional anaerobic and a modified UASB reactor, operated under microaerated conditions. Air was supplied in the digestion zone, at 1 and 3 m from the bottom of the reactor, and three different air flows were investigated: 10, 20, and 30 mL.min^-1, corresponding to 0.003, 0.005 and 0.005 LO₂/L_influent, respectively. The main results showed that the microaeration provided a substantial decrease in hydrogen sulfide concentrations when compared to the concentrations observed in the biogas of the anaerobic UASB reactor. Hydrogen sulfide concentrations remained below 70 ppm_v throughout the experimental period, corresponding to an average removal efficiency of 98%. Although a decrease in methane concentrations in biogas was observed, the feasibility of energy use would not be affected. The effect of microaeration on the overall performance of the reactor was evaluated, however, no significant differences were observed. The feasibility of limiting aeration conditions in the reactor digestion zone as an efficient alternative for hydrogen sulfide removal from biogas was demonstrated.

Evaluation of different air dosing strategies to enhance H2S removal in microaerobic systems treating low-strength wastewaters

This study aimed to evaluate different air dosing strategies such as microaeration flow rates and air dosing points to enhance H₂S removal in microaerobic systems treating low-strength wastewaters. Efficiency and stability of the reactors, as well as biogas quality, were assessed, and microbial community changes were evaluated using the PCR-DGGE technique. The results showed that the air dosing point affected the H₂S concentration and that air dosing at the headspace promoted the highest H₂S removal efficiency. The airflow rate also affected the process, since H₂S concentration in the biogas was higher at 0.1 mL air.min^-1 than at 0.3 mL air.min^-1. The methane concentration in the biogas was also affected by both air dosing point and flow rate, since the lowest value was observed at the highest airflow rate of the headspace dosing point, due to dilution by the N₂ influx applied to the system. The highest productivity and operational efficiency were observed at this air dosing point, with this airflow (HD_0.3), which corroborates with the operational results and the ecological parameters, since the microaeration at this stage promoted high bacterial and archaeal species richness and diversity, optimum functional organization, high COD and H₂S removal efficiencies.

Anaerobic digestion of wastewater rich in sulfate and sulfide: effects of metallic waste addition and micro-aeration on process performance and methane production

This work explores the effect of two metallic wastes (mining wastes, MW; fly ashes, FA) and micro-aeration (MA) on the anaerobic digestion of wastewater which is rich in sulfate and sulfide. Two initial COD concentrations (5,000 and 10,000 mg/L) were studied under both conditions in batch systems at 35 °C, with a fixed COD/SO₄^2- ratio = 10, with 100 mg/L of S^2-. It was observed that the use of MW and FA in the assays with an initial COD concentration of 10,000 mg/L resulted in a simultaneous increase in COD removal, sulfate removal, sulfide removal and methane generation, while MA only improved the COD and sulfide removals in comparison with the control system. On the contrary, the use of MW, FA or MA in systems with initial COD concentrations equal to or lower than 5,000 mg/L did not show any improvement with respect to the control system in terms of COD removal, sulfate removal or methane generation, with only sulfide removal being positively affected by MW and FA.