Heterotrophic Denitrification Using Peanut Shell As Carbon Source For Groundwater Bioremediation

Groundwater contaminated by nitrate requires efficient remediation to prevent adverse environmental impacts and negative health effects.Biological denitrification is often employed for nitrate removal in the study of groundwater efficiently and cost-effectively comparing with other conventional techniques.However,the lack of carbon source in groundwater often leads to low nitrate efficiency.Herein,peanut shell were utilized as the carbon source in heterotrophic denitrification system of nitrate-contaminated groundwater.The adsorption characteristics of peanut shell on nitrate without the presence of microbial were investigated through the analysis of physicochemical properties and batch adsorption experiments.It aims to explore the feasibility of peanut shells as carbon source through the comparison of three carbon source(peanut shell,corncob and sawdust)based heterotrophic denitrification system and the dynamics changes of microbial communities involved in the process.Besides,batch experiments with different reaction parameters were designed to determine the optimal conditions of peanut shell baced denitrification system.Finally,the sequencing batch experiment was used to simulate the denitrification process in actual groundwater,and the bio-filled bed reactor was designed to explore the nitrate degradation law in actual groundwater.The results showed that the nitrate removal was efficient(100%)as well as a lower nitrite production(11.2%)with peanut shell system which added activated sludge compared with the absence of microbial.Therefore,peanut shell could be used as the carbon source for heterotrophic denitrification due to its carbon leaching can support microbial-led denitrification.Compared to corncob and sawdust system,higher nitrate removal efficiency(~100%),larger treatment capacity(11.1 mg N/(L·d))and lower ammonia accumulation and carbon residues were observed in peanut shell system.The carbon release rate of three materials matched for second-order kinetics(R~2>0.9).Microorganism analysis indicated that biodegradation(Sorangium,Cloacibacterium and Cellulomonas)and biodenitrifying bacteria(Alicycliphilus and Terrimonas)were coexisted in peanut shell system.The results of conditional optimization experiments showed that there was no accumulation of nitrite and ammonia nitrogen when peanut shell dosage was between 3~5 g/L,the optimum pH of nitrate-reducing bacteria were 7.0,and the nitrite-reducing bacteria were more sensitive to changes of pH,The diameter of peanut shell dose not have a significant effect on the denitrification effect.For the sequencing batch experiments,the maximum mass of nitrate that can be reduced was approximately 28.5 mg with per gram of peanut shell,the only products of protein degradation was ammonium.In addition,the results of continuous flow experiment demonstrated that the capacity of nitrate reduction was 39.17 mg/(L·d),but carbon release capacity of peanut shells was gradually weakened,and the organic carbon loss was faster in continuous flow experiments.Therefore,when constructing a continuous flow reactor using peanut shells as carbon source,the reactor structure and filling method(such as step filling)should be studied to ensure the effective use of peanut shell carbon sources.The results indicated that peanut shell as carbon source can improve the denitrification performance of groundwater.