Effect Of PH On The Anaerobic Treatment Of Sulfate Organic Wastewater

Anaerobic treatment has the characteristics of low energy consumption and clean energy recovery,has always been considered as the first choice to treat high concentration organic wastewater.A large amount of sulfuric acid is used in some chemical synthesis of various materials and pharmaceutical intermediates.So many wastewater has the characteristics of high COD and sulfate.The problem of anaerobic treatment of sulfate organic wastewater is that SRB?sulfate reducing bacteria?would compete with MPA?methane producing archaea?and it can produce sulfate reducing product such as H₂S,S^2-and HS^-in the reactor.SRB and MPA can be inhibited by H₂S and it even causes the system unstable and collapsed.The cost of gas purification increased due to the methane generated from the reactor contains high concentration of H₂S.Based on the relationship between pH and sulfide morphology,the pH value in the reactor is increased may solve the above problems,but this is still lack of systematic research.Therefore,anaerobic UASB was using to simulate the treatment of high sulfate organic wastewater,to explore purification performance,competition between MPA and SRB,sludge properties and microbial community under high pH system.The main conclusions were as follows:?1?The research about anaerobic treatment of organic wastewater under different pH?7.5,8.5?showd that methane volume produced by pH7.5 system were higher than pH8.5 system.The COD removal effiency was better while sulfate removal effiency was lower in pH 7.5 system than that of in pH 8.5 system when COD/SO₄^2–ratio changed from 10 to 2.The COD removal effiency was lower while sulfate removal effiency in pH 7.5 system was similar to pH8.5 when COD/SO₄^2–ratio was 1 and 0.5.Compared to pH 7.5 system,the gaseous H₂S in pH8.5 system was lower which can reduce the cost of gas purification.In addition,H₂S concentration in water can reach to 92.8mg/L by theory calculation which was higher than 5.5mg/L in pH8.5 system.It illustrated that high pH can remove the inhibitory effect of H₂S.It can be concluded that high pH control is feasible.?2?The electron flow show that the dominated microorganism was MPA in pH8.5 system when the COD/SO₄^2–ratio gradually decreased from 10 to 1 while SRB was dominated when the COD/SO₄^2–ratio was 0.5.MPA was still dominated in pH7.5 system.The competition between MPA and SRB related to the synergy of pH and COD/SO₄^2–ratio.They played important roles in substrate removal and maintain the stability of the system.?3?The electron microscope scanning showed that the microorganism in domesticated sludge in pH8.5 system were relatively single,which were mostly spherical.While in pH7.5 system the strains are richer,like filamentous bacteria,bacillus,short bacillus,coccus and so on.The increase of organic load rate?OLR?was beneficial for sludge gathered.The decrease of COD/SO₄^2–ratio was unfavorable to sludge growth.The MLSS increased in two reactors which suggested the accumulation of inorganic particles.The anaerobic sludge will produce more polysaccharide to cope with the pressure of low ratio of COD/SO₄^2–.The EPS concentration in pH7.5 system was higher than that in pH8.5 system.The coenzyme F₄₂₀20 was analyzed through three-dimensional fluorescence.The fluorescence intensity of coenzyme F₄₂₀20 in pH8.5 system was weaker than that in pH7.5 system when COD/SO₄^2-ratio was 10.It colud speculate that high pH had an inhibitory effect on MPA While it was stronger when COD/SO₄^2-ratio was 0.5.It colud speculate that MPA can adapt to higher pH conditions in lower COD/SO₄^2-ratio.?4?The MPA community showed that Methanosaeta sp,Methanobrevibacter and unclassified_fMethanobacteriaceae were the main MPA in pH8.5 system.It can be speculated that above MPA were alkali-resistant.The methane was produced by acetoclastic and hydrogenotrophic methanogenesis in pH8.5 system.Methanosaeta sp.was dominant in pH7.5 system and the methane was produced by acetoclastic methanogenesis.?5?The SRB community showed that the sulfate reduction was based on most Desulfomicrobium and a small amount of Desulfonatronum in pH8.5 system.It can be found that above SRB were alkali-resistant.Five different SRB played important roles in sulfate reduction in pH7.5 system in higher COD/SO₄^2-ratio.But in lower COD/SO₄^2-ratio,the dominant SRB were Desulfococcus and Desulfobulbus in pH7.5 system,while Desulfonatronum and Desulfomicrobium were major SRB in pH8.5 system.