Research On The Process Optimization And Model Of Compound Metals On Anaerobic Fermentation

For the current heavy metal pollution is serious,with the difficulty of heavy metal biomass reuse and the lack of energy,in this paper,biogas production by anaerobic fermentation with Phragmites australis straw,a dominant species of wetland containing heavy metals was proposed,to study the effect of heavy metals on anaerobic fermentation performance,and the master-subordinate relationship of copper,chromium and zinc.The mechanism of composite metals and optimal process conditions on anaerobic fermentation were explored by establishing mathematical model between fermentation process parameters and gas production value.The main conclusions in this paper were as follows:(1)Zinc salt could accelerate the arrival of the daily biogas yield peak.And the effects on cumulative biogas yields the zinc salt presented a trend of promotion in low concentration and inhibition in high concentration.The results showed when the zinc salt concentration was 5 mg/L,the cumulative gas production was the largest,54.30 mL/g TS,that was higher 21.30%than the control group;when the zinc salt concentration was 100 mg/L;the cumulative gas production was the smallest.35.38 mL/g TS,that was lower 20.98%than the control group.(2)The results of orthogonal test with three factors and three levels showed that the sequence of three metals for biogas production was copper>chromium>zinc.For copper salt,when the concentration of copper was 15 mg/L.the average was the largest,and the biogas yield was 34.23 mL/g TS.For chromium salt,when the concentration of chromium was 20 mg/L.the average was the largest,and the biogas yield was 33.18 mL/g TS.For zinc salt,when the concentration of zinc is 3 mg/L,the average was the largest and the biogas yield is 30.35 mL/g TS.The optimum conditions of biogas production by anaerobic fermentation were A1B1C1.i.e.the concentration was 15 mg/L,20 mg/L and 3 mg/L for the copper salt,chromium salt,and zinc salt,respectively.Under this conditions,the biogas yield reached 43.28 mL/g TS.(3)The effects of copper salt,chromium salt,and zinc salt on the biogas production were investigated based on central composite design.According to the test of the model,it could draw the conclusion that the quadratic model is most suitable for the anaerobic fermentation data.From response Surface and Contour,the interaction between metal copper and metal Chromium was not very significant,and when the concentration of copper was about 15 mg/L and Chromium 28 mg/L,the amount of biogas production reached maximum;the interaction between metal copper and metal zinc was not very significant,and when the concentration of copper was about 15 mg/L and zinc 3 mg/L,the amount of biogas production reached maximum;the interaction between metal chromium and metal zinc was significant,and the optimum concentration was approximately chromium 20 mg/L and zinc 3 mg/L.The results of optimization by the numerical method showed that under the optimal conditions,the confidence of the predicted was 95%,when the concentration of copper added was 15 mg/L,chromium was 20 mg/L,and zinc was 3 mg/L.the biogas production of anaerobic fermentation reached a maximum value of 42.16 mL/g TS.The combination of mathematics and experiment can not only effectively reduce the number of experiments,but also establish a mathematical model to solve the present problems of adding heavy metals in anaerobic fermentation,which reduced the cost of experiments and made the operation simple and convenient.While recycling the waste,this research increased the gas production rate of biogas projects and provided scientific guidance for the promotion of optimal operation of biogas projects.