Effect Of Zinc Cadmium Ion On Biological Denitrification And Microbial Activity And Community Of Aquaculture Wastewater

Zn²⁺and Cd²⁺are the most common heavy metals in aquaculture effluent discharged by livestock and poultry into biological wastewater treatment systems,high concentrations of Zn²⁺and Cd²⁺severely inhibit the life activity of microorganisms and thus affect the efficacy of biological wastewater treatment.The change in the efficacy of biological wastewater treatment is on the one hand the change in the composition of the microbial community and on the other the change in the electronic transmission system and the activity of various enzymes that maintain the physiological function of the microbes.Therefore,the study of microbial enzyme activity,electron transfer system,and community composition is important.The experiment used Zn²⁺and Cd²⁺as pollutants and designed Zn²⁺,Cd²⁺,and their binary mixtures with different concentrations.The direct homogeneous ray method was used to construct three different concentrations（P1、P2、P3）.A binary mixture of Zn²⁺and Cd²⁺.The effects of Zn²⁺and Cd²⁺and their mixtures on biological denitrification performance and microbial activity were investigated.The effects of Zn²⁺and Cd²⁺and their mixtures on microbial community structure were investigated by high throughput sequencing.This dissertation is organized as follows.（1）When the concentration of Zn²⁺is less than 10 mg/L,it supports the formation of aerobic terminal nitrogen and the removal of COD.The formation of aerobic terminal nitrogen,COD,and total nitrogen removal are clearly inhibited when the concentration of Zn²⁺is high.The activity of microbial dehydrogenase and the activity of the electron transfer system showed a similar law with an increasing trend when the content of Zn²⁺was less than 10 mg/L.The microbial dehydrogenase and electron transfer system activities gradually decreased when the Zn²⁺concentration was higher than 10 mg/L.With increasing Zn²⁺concentration and time,the activity of microbial hydrogenase decreased according to time and concentration.（2）Biological denitrification and microbial activity were significantly affected by Cd²⁺.With the increase of Cd²⁺concentration,the nitrogen concentration at the aerobic end showed a gradual decrease,and the total nitrogen concentration in the effluent and the COD concentration in the effluent showed a similar pattern.The inhibition of microbial dehydrogenase,microbial electron transfer system,and microbial oxidoreductase was significantly increased and time-dependent with increasing Cd²⁺concentration and time of effect.（3）The denitrification properties of Zn²⁺and Cd²⁺binary mixtures with different concentration ratios show different tendencies.Aerobic terminal nitrogen generation and COD removal showed some improvement when the P1-P2 ratio was low.Total nitrogen removal was not significantly affected.In the case of a lower concentration of P3,the generation of nitrogen at the aerobic end and the removal of COD were not significantly inhibited.The generation of aerobic terminal nitrogen,total nitrogen,and COD removal was significantly inhibited in a time-and concentration-dependent manner when the P1,P2,and P3 ratio concentration was higher.Different trends in microbial activity are observed for binary mixtures of Zn²⁺and Cd²⁺at different concentration ratios.The microbial dehydrogenase activity is similar to that of the electron transfer system when the P1-P2 ratio is low.Both show an initial increase and later decrease under the P3 ratio.As Zn²⁺and Cd²⁺binary mixtures increased in concentration and time of action,the activity of microbial dehydrogenase and microbial electron transfer system gradually decreased.Zn²⁺and Cd²⁺binary mixtures with three different concentrations inhibit the activity of microbial hydrogenase peroxide and are time-and concentration-dependent.（4）The microbial community structure was affected differently by Zn²⁺,Cd²⁺,and their binary mixtures.Under the action of single Zn²⁺,the relative abundance of Thauera,Terrimonas,Nitrospira,and other microorganisms with denitrifying functions all maintained the trend of first increasing and then decreasing.The relative abundance of Terrimonas,Nitrospira,and Denitratisoma showed a gradual decrease under the effect of a single concentration of Cd²⁺.A similar effect on the denitrification of functional microbes can be observed for different concentration ratios of Zn²⁺and Cd²⁺binary mixtures.The above-mentioned nitrogen-removing functional bacteria appear to first increase and then decrease as the concentration of Zn²⁺and Cd²⁺binary mixtures increases.The relative abundance of denitrifying microorganisms decreases significantly as the Cd²⁺content increases.Figure[42]Table[13]Reference[140]...