Response of sulfur-metabolizing biofilm to external sulfide in element sulfur-based denitrification packed-bed reactor

Dosing sulfide into the sulfur-packed-bed (S0PB) has great potential to enhance the denitrification efficiency by providing compensatory electron donors, however, the response of sulfur-metabolizing biofilm to various sulfide dosages has never been investigated. In this study, the S0PB reactor was carried out with increasing sulfide dosages by 3.6 kg/m3/d, presenting a decreasing effluent nitrate from 14.2 to 2.7 mg N/L with accelerated denitrification efficiency (k: 0.04 to 0.27). However, 6.5 mg N/L of nitrite accumulated when the sulfide dosage exceeded 0.9 kg/m3/d (optimum value). The increasing electron export contribution of sulfide a maximum of 85.5% illustrated its competition with the in-situ sulfur. Meanwhile, over-dosing sulfide caused serious biofilm expulsion with significant decreases in the total biomass, live cell population, and ATP by 90.2%, 86.7%, and 54.8%, respectively. This study verified the capacity of dosing sulfide to improve the denitrification efficiency in S0PB but alerted the negative effect of exceeded dosing.