Study on the Influence Mechanism of Biomass Pyrolysis Derived Wood Vinegar on Treatment of Sewage by Activated Sludge Process

Author:Zhang Fang

Supervisor:chen han ping shao jing ai


Degree Year:2019





In recent years,the scale of biomass pyrolysis industry has gradually expanded with the development of biomass pyrolysis technology,but the resulting wood vinegar(WV)has not been fully utilized.The development of sewage treatment technology has improved the treatment status of domestic sewage,but the effluent quality of traditional activated sludge process is difficult to meet the increasingly stringent requirements of environmental standards.Improving the treatment effect of activated sludge process is of great significance for alleviating water environmental pollution.The complex organics in WV can promote the growth and activity of microorganisms in activated sludge.Based on the effect of WV on pollutant removal efficiency and sludge performances of activated sludge process,this paper studied the influence mechanism of main components of WV on treatment of sewage by activated sludge process,the influence mechanism of WV on kinetics of activated sludge process and sludge activity,and the action mechanism of extracellular polymer substances on the pollutant removal effect under the action of WV.The process conditions including the dosage of WV were optimized.The purpose of the study is to provide a new utilization way for biomass pyrolysis derived WV and a new method for improving the treatment effect of activated sludge process.Firstly,the effects of WV on pollutant removal and sludge performances of activated sludge process were studied by adding two kinds of biomass pyrolysis derived WV(1 # and 2 #)to sequencing batch reactor(SBR)system and continuous operation activated sludge system for domestic sewage treatment.The results showed that WV diluted 1000 times could significantly improve the removal efficiency of chemical oxygen demand(COD),total nitrogen(TN),ammonia nitrogen(NH3-N)and total phosphorus(TP)in domestic sewage and simulated domestic sewage by activated sludge system.WV increased the sludge quantity and caused negative impact on the flocculation,sedimentation and dewatering performances of sludge.During the long-term operation of the system,the sludge quantity continued to increase,and the flocculation and dewatering performances of the sludge gradually improved.Secondly,acetic acid,phenol and hydroxyacetone were used to represent the acid,phenol and ketone in WV,and the mechanism of the concentration,proportion and the interaction of the main components in WV to affect the treatment effect of SBR was studied.The mixing experiment was designed and the mixing ratio was optimized.The results showed that in single component,acetic acid had the best effect on improving the removal rate of organics,nitrogen and phosphorus pollutants.In two components,acetic acid-phenol had the best effect on improving the removal rate of organics,and acetic acid-hydroxyacetone had the best effect on improving the removal rate of nitrogen and phosphorus pollutants.The interaction of main components had significant effect on concentration of TP in effluent,had more significant effect on BOD5 than on COD,and had more significant effect on NH3-N than on TN.The concentration of acetic acid,phenol and hydroxyacetone decided by the optimum mixing ratio was 12.73%,2.50% and 1.86%,respectively,and the expected value was 0.858.The validation experiments showed that the prediction results were reliable.Afetr that,the process of sludge growth and pollutant degradation in SBR was studied,and the kinetic parameters of sludge growth and substrate degradation were solved based on Lawrence-McCarty model.The effects of WV on the activity of enzymes,respiration and degradation of nitrogen-containing pollutants were discussed,and the improvement mechanisms of WV on the treatment effect of SBR was explained from the point of view of activated sludge kinetics and sludge activity.The results showed that WV could increase both the microbial yield and the endogenous metabolic coefficient,and increase the microbial yield more obviously,thus increasing the sludge quantity of the system.It could also reduce the saturation constant and increase the specific degradation rate of substrate,and increase the dehydrogenase activity,specific oxygen uptake rate,ammonia oxidation rate and nitrite oxidation rate of sludge.Therefore,the difficulty of substrate degradation by microorganisms was reduced,and the removal rate of pollutants in the system was increased.Then,the effects of WV on the concentration of extracellular polymer substances(EPS)and its main components protein(PN),polysaccharide(PS)and deoxyribonucleic acid(DNA)in SBR were studied.The mechanism of the effect of WV on the treatment efficiency of activated sludge process was discussed through the variation of EPS concentration under the action of WV.The results showed that WV increased the concentration of EPS components and different layers of EPS,and decreased PN/PS.Increase of the concentration of EPS and its components could enhance the adsorption performance of the sludge and the mass transfer of hydrophobic substances,increase the concentration of enzymes,and enhance the absorption of nitrogen and phosphorus pollutants,and thus enhance the removal efficiency of pollutants.When the concentration of PN and PS increased and PN/PS decreased,the flocculation,sedimentation and dewatering performance of the sludge became worse through electrostatic action and hydrophobic and hydrophilic action of groups.Among all layers of EPS,LB-EPS has the most significant effect on sludge performance,and the increase of its concentration also caused deterioration of sludge flocculation,sedimentation and dewatering performance.Finally,the coupling effect of WV concentration and process conditions of activated sludge process on effluent quality and sludge performances of SBR system was studied,and the independent variables were optimized.The fitted model could well describe the relationship between response index and variables.The objective of optimization was to minimize the concentration of pollutants in effluent,and the results were as follows: temperature was 32.76℃,pH was 8.86,dissolved oxygen concentration was 3.28 mg/L,sludge concentration was 199.97 mL/L,WV dosage was 4.15 μL/L,and the expected value was 1.000.The validation experiments show that the prediction results are reliable.Further optimization was carried out at the temperature of 20℃.According to the further optimized scheme,only a small increse in the cost caused by addition of WV was necessary to the domestic sewage treatment by activated sludge process,and better environmental and economic benefits could be achieved by reducing the concentration of pollutants in the effluent.