Study On The Effect Of S^2- And So₄^2- On Single-phase And Two-phase Anaerobic Digestion

The organic wastewater containing S^2-and SO₄^2-is widely generated from industrial manufacturing and processing,such as paper industry,fermentation industry,pharmaceutical industry,leather industry,food processing industry,petroleum industry and mining industry.Untreated wastewater which discharged directly into water bodies can cause serious environmental hazards.This subject applied the continuous stirred reactor?CSTR?to investigate the effects of influent COD,SO₄^2-load and C/S on the single-phase anaerobic and two-phase anaerobic system operation,respectively.The succession of microbial community structure characteristics had been analyzed in acidification and methanogenesis.The main conclusions of the project were as follows:?1?In the single-phase anaerobic system,the C/S ratio reduced from 5 to 2,with the enhancing activity of sulfate-reducing bacteria?SRB?,the effluent content of S^2-increased obviously which caused toxic effect on microorganisms.The ratio reduced from 1 to 0.67 with COD removal rate decreased from 40%to 31%.The content of S^2-in the effluent lessened sharply,and the substrate removal was unconspicuous.The sedimentation of the mud deteriorated,and a large amount of sludge was carried out in the effluent leaded to the bad performance.The overall sulfur recovery rate was about 90%,and the S^2-concentration ratio in the liquid phase was the largest in each phase.While the effluent SO₄^2-occupied the largest proportion,and the recovery rate of sulfur was lower at 0.67 and elemental sulfur and sulfur precipitation were formed.The addition of SO₄^2-had a buffering effect on organic load shock.The total amount of VFA in the reactor which SO₄^2-added was lower than that in the unadded reactor,and acetate proportion in the effluent was higher than that in the later.In this experiment,when C/S was more than 2,substrate removal effect could be a more efficient achieved,and the system operation was relatively stable.?2?In a two-phase anaerobic system,the acidification and the methanogenic phase were operated in series.The acidification loading was 10 kg/m³·d,the pH was stable at 4.3⁴.5,and the ORP value was between-400 mV and-500 mV.It was propionic-type fermentation with an acidification rate of about 45%.The COD removal rate of the two-phase system reached 90%.The sludge changed from the inoculated grayish black to yellowish and finally existed in milky white form.The scanning group observed mainly by Brevibacterium,spore and filamen-tous fungi.The pH in the methanogenic phase effluent was basically stable at around 7.2,and the ORP value was between-400 mV and-420 mV.The sludge was grayish black throughout the experiment,and the presence of Methanoocto-coccus was observed in scanning electron microscopy.According to the results of16S rDNA sequencing,the dominant genuses in the acidication phase were Enterobacteriaceae,Bifidobacterium,Clostridium sensu stricto,Corynebacterium,Bacteroidetes.The dominant genuses in the methanogenic phase were Anaerolineaceae,Aminivibrio,Mesotoga,Methanobacterium.In the present study,Enterobacteriaceae was still the dominant genus in the low pH environment,and its tolerance to low pH had improved.Thermotogae in the methanogenic phase could survive and had a high abundance in a mesophilic environment?35°C?.Anaerolineaceae had an obvious advantage?45.5%?,which was symbiotic with Methanosaeta and played an important role in the methanogenic degradation of alkanes.?3?In the acidification phase,with the decreased of C/S ratio,the varied influent pH on the system was gradually weakened.The addition of SO₄^2-reduced the content of propionic in the system,while the content of acetate increased.An appropriate amount of S^2-concentration could promote the production of VFA.When S^2-concentration increased to 500 mg/L,the effluent COD concentration was higher than the influent.The S^2-concentration increased to 800 mg/L,the system deteriorated remarkably,and there was no degradation at all pH values with the sludge continuously lost.In the system containing C and S,the addition of NO₃^-had a great influence on the operation of the system.The S/N ratio was adjusted by changing the influent NO₃^-concentration.When the S/N ratio reached5:2,the removal rate of S^2-was 30%,and the accumulation of SO₄^2-occured at a ratio of 5:5.Heterotrophic denitrification occured after autotrophic denitrification.While the continually increasing S/N ratio inhibited the systemic acid production process.