The Removal Efficiencies By The Effect Of Chromium On Anaerobic Bacteria

Many wastewaters contain high concentrations of sulfate and organic matter, especially, in Leather wastewater. In this case, The anaerobic digestion technology has been used to dispose the wastewater. In this passage, our emphasis is on research existing in wastewater hexavalent chromium to reactor under the condition of ions in the system of the influence of the toxicity flora. Hexavalent chromium is a highly toxic heavy metal ions, it can influence all the flora of system, such as sulfate-reducing bacteria, producing acid bacteria AB, methanogens MPB. Base on the different niche characteristics of sulfate-reducing bacteria (SRB), acidogenic bacteria (AB) and methane-producing bacteria (MPB), this experiment used two-stage anaerobic treatment with circular gas stripping. Soluble starch were used as organic substrate (COD=4000 mg·L-1), and the sulfate level is about 1500mg/L. Through the experimental analysis, the main results are as follows:(1) In the Start-up phase, As the concentration of sulfate is from 300 to 1500mg/L, The COD removal is also corresponding improvement, the COD removal efficiencies of the total system increased from46.78% to 93%, and the flora in start-up period has good biological activity. The SO42- reduction efficiencies of the total system increased to 92%-97%, sulfide and sludge also are in a stable stage, all in the activity of processing for flora.(2) Hexavalent chromium ion will have a great influence to the flora. As in the process of chrome ion rise from 0 to 40mg/L, when the concentration of chrome is below 35mg/L, flora processing efficiency is higher, the inhibit by the chrome is also lower. the COD reduction efficiencies of the total system increased to 91%-95%, and the efficiencies of the first stage anaerobic reactor increased to 61.%-64%. and SO42-reduction efficiencies is about 86%-91%.(3) In the first stage anaerobic reactor, when the concentration of chromium is below 35mg/L, SRB is in the high efficiency. Otherwise, the removal rate is decreased obviously, this means the maximum tolerance of sulfate-reducing bacteria for chromium is about 35mg/L; for the same reason, the maximum tolerance of methane-producing bacteria for chromium is about 30mg/L.(4) The composition in the reactor, because the existing of sulfide, will have a multiple relationship. When the concentration of chrome is close to 25mg/L, the reaction of sulfide and chromium is faster, under the interaction of SRB. the COD reduction efficiencies of the total system increased to 83.8%. As the concentration of chrome is more than 35mg/L, COD removal bacteria have dropped sharply.(5) After recycle ratio changed from 1.0 to 0.5, the COD removal efficiencies of the total system decreased by 8-13 percentage points, Along with the increase of chrome concentration, The gap between the removal rate has continued to expand. The SO42-reduction efficiencies decreased by 10-25 percentage points. After recycle ratio changed from 1.0 to 1.5, the COD removal efficiencies decreased a little, The gap between the removal rate also has continued to expand. But the SO42- reduction efficiencies increased tinily. The concentration of effluent sulfide increasing accompany.