Comparison of chemo-, hetero- and mixotrophic denitrification in laboratory-scale UASBs

Abstract

This study investigated removal of sulfide and p-cresol linked to denitrification in laboratory-scale upflow anaerobic granular sludge bed (UASB) bioreactors. Three parallel denitrification bioreactors were run for nine months, which were operated under chemolithoautotrophic conditions (i.e., using sulfide as electron donor -e-donor- and bicarbonate as C source); heterotrophic conditions (with p-cresol as e-donor and C source), and mixotrophic conditions (utilizing both sulfide and p-cresol as electron donors), respectively. The average hydraulic retention time and nitrate load applied to the bioreactors was 13.4 h and 1,240 mg N-NO3/l/day, respectively. The nitrate removal efficiency was 89, 95 and 99%, respectively, for the chemo-, hetero- and mixotrophic reactors. The mixotrophic UASB removed both sulfide and p-cresol almost completely, indicating that simultaneous removal of the inorganic and organic e-donors occurred. Nitrite was seldom observed as an intermediate. N2O gas and methane concentrations in the biogas were also negligible. These results indicate that mixotrophic denitrification with phenols and sulfide is feasible in high rate UASB reactors.

Sulfide oxidation under chemolithoautotrophic denitrifying conditions

“…These results indicate that addition of small amounts of organic carbon to the feed of chemolithotrophic denitrification bioreactors could be advantageous to enhance treatment and maintain a more robust bioreactor system compared to strict autotrophic denitrification. Biological treatment systems promoting simultaneous autotrophic and heterotrophic denitrification have interesting applications in the combined removal of nitrogen, sulfur, and organic contamination from wastewaters (Oh et al, 2003;Sierra-Alvarez et al, 2005). …”

“…In wastewaters containing both N and S contaminants, nitrates generated after nitrification can be recirculated to anaerobic stages of the treatment process to promote the simultaneous oxidation of sulfides and denitrification of nitrates. The concept has been investigated for industrial wastewater treatment (Gommers et al, 1988;Reyes-Avila et al, 2004;Sierra-Alvarez et al, 2005). Microbial transformation of hydrogen sulfide to elemental sulfur offers interesting opportunities for the removal of this contaminant.…”

Kinetic limitations during the simultaneous removal of p-cresol and sulfide in a denitrifying process

“…These industrial effluents contain large amounts of nitrogenous, sulfurous and aromatic pollutants [1][2][3], which demand suitable technologies to achieve their simultaneous removal. Denitrification has lately been proposed as a suitable treatment process to achieve the simultaneous removal of these contaminants [2][3][4][5][6][7]. This dissimilatory process involves four enzymatic steps in which nitrate is reduced to nitrite, nitric oxide (NO), nitrous oxide (N 2 O) and nitrogen gas (N 2 ) [8].…”

“…Denitrification can also be linked to the oxidation of a wide variety of organic compounds including volatile fatty acids, alcohols and phenolic compounds [2,4]. Therefore, denitrifying processes can potentially achieve the simultaneous removal of nitrogenous, sulfurous and aromatic pollutants from industrial effluents.…”

“…Several studies have described an inhibitory effect of sulfide on the last steps of denitrification consequently causing release of NO or N 2 O [4,[15][16][17]. Dalsgaard and Bak [18] reported inhibition of nitrate reduction (from 37 to 71% compared to the control without sulfide) in a wide range of sulfide concentrations (46-152 lM).…”