Abstract
Abstract This study is focused on the effect of biogas recirculation with hydrogen sulfide removal on anaerobic treatment of sulfur-enriched synthetic wastewater in a UASB reactor. The presence of hydrogen sulfide in biogas causes problems in its further energy recovery while sulfides inhibit the anaerobic process. The reactor was gradually loaded with sulfates and their effect on the reactor operation was monitored. At the same time, external absorption of hydrogen sulfide from biogas with absorbent regeneration was operated. The results show that low concentrations of added sulfates support biogas production. At the sulfate concentration of 125 mg l−1, biogas production increased by approximately 2 l d−1. However, further increasing of the amount of sulfates in the substrate led to the opposite effect. At twice the amount of sulfates, the biogas production decrease by 1 l d−1 and its adverse effects on the removal of N-NH4, NC and P-PO4 were observed. Biogas recirculation through the absorption column ensured a decrease in the hydrogen sulfide concentration from 19 960 ppm to 4 030 ppm and an increase in the methane content from 59.2 % to 83 % and also a decrease in the sulfides concentration in the reactor. From the measured data it can be concluded that this method reduces sulfides inhibition.
Highlights
Anaerobic digestion is the decomposition of bio mass by microorganisms under anaerobic condition, i.e. without oxygen
Recirculation was provided by a peristaltic pump that pumped biogas through a counter-current absorption column packed with plastic tubes to increase the surface for the phase transfer of hydrogen sulfide from biogas to water, which was used as the absorption agent
Start-up of UASB reactor was initiated at the organic load rate (ORL) of 0.5 kg (COD)·m–3·d–1
Summary
Anaerobic digestion is the decomposition of bio mass by microorganisms under anaerobic condition, i.e. without oxygen. Biogas consists of 50—70 % of methane (CH4) and 30—50 % of carbon dioxide (CO2) and of a small portion of other compounds, such as 0—3 % of nitrogen (N2), 5—10 % of water vapor (H2O), 0—1 % of oxygen (O2), 0—20 000 % of hydrogen sulfide (H2S) depending on the feedstock origin (Angelidaki et al, 2018) Industries, such as paper, textile and pharmaceutical, produce sulfate-rich wastewater which is reduced to sulfides, including gaseous hydrogen sulfide (H2S), during anaerobic treatment and causes process inhibition due to toxicity to methanogens (Pokorna-Krayzelova et al, 2017). H2S inhibits protein production, deactivates various coenzymes in the cell and interferes with the assimilative metabolism of sulfur To reduce this impact, in situ methods as microaeration and precipitation, dilution with water and a co-fermentation with a low sulfur content substrate to increase the C:N ratio can be used (Hutňan et al, 2016; Krayzelova et al, 2015). In situ methods as microaeration and precipitation, dilution with water and a co-fermentation with a low sulfur content substrate to increase the C:N ratio can be used (Hutňan et al, 2016; Krayzelova et al, 2015). Hutňan et al (2016) used precipitation to control sulfide inhibition in anaerobic treatment of waste biomass from the production of cystine with high sulfur content — about 6% of total dry matter. Chávez Fuentes J.J. et al (2015) investigated the possibility of using dilution of waste biomass from cystine production to reduce sulfide inhibition
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