Effects of C/N, C/S and S/N ratios on TOC and nitrogen removal in the sulfate reduction-sulfur denitrification process

Abstract

Effects of C/N, C/S and S/N ratios on TOC and denitrification removal were examined in the sulfate reduction-sulfur denitrification process using the two upflow biological filter reactors. High TOC and nitrogen removal ratio was obtained at C/N=2.2 and S/N=0.7 through the reactors. In the first reactor, sulfate reduction occurred predominantly. SRB mainly produced acetate at C/S=3.1. However, acetate was decomposed in the first reactor at C/S=1.6. In the second reactor, sulfur denitrification and heterotrophic denitrification occurred simultaneously. Sulfur denitrification occurred in the lower part of the reactor in S/N=0.7, and all sulfide produced in the first reactor was re-oxidized. On the other hand, sulfur denitrification also occurred in the upper part of the reactor in S/N=1.3, and 35 mg/gSS of sulfur granules were accumulated in the biofilm. The sulfur granules played an important role on denitrification. The activity of SDNB in the second reactor was about 3-4 times lower than the activity of DNB. When the S/N ratio increased, the activity of SDNB increased and those of DNB decreased. The number of SDNB was greater than those of DNB. The activity of SRB in the first reactor increased, when S/N ratio increased. SRB also grew in the anoxic second reactor, and the activity of SRB in the second reactor was relatively high. The sulfur cycle consist of sulfate reduction and sulfur denitrification in the second reactor might be established in the reactor.