Effect of biochar on migration and biodegradation of 4-n-nonylphenol (NP) during river-based groundwater recharge with reclaimed water

摘要

To investigate how biochar affects coupled migration-biodegradation of NP, a lab-scale column was set up to simulate the recharge process. The filler media of the two columns was mainly composed of silty clay (SC) and biochar amendment silty clay (BCSC). The results showed that the attenuation effect of NP in the BCSC system was 3.3% higher than that in the SC system. The attenuation rate constants of NP in the SC and BCSC systems were 0.20 and 0.24m(-1), respectively, which followed first-order kinetics. The two turning points of NP concentration with depth in the leachate were 0.15 and 0.45m as a result of fast sorption and biodegradation, respectively. The primary metabolites were not the only hydroxylated 4-nonyl-4-hydroxycyclohexa-2,5-dienone and 4-hydroxyphenyl-nonanoic-acid; detached branched alkyl moieties were also produced during the biotransformation process. The accumulation of NP in the soil was higher in BCSC soils than in the SC system. The bacterial community in the upper layer was more diverse than in the bottom layer, which was related to oxygen concentrations in the water-soil system. Five known bacterial classes (Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Sphingobacteria, and Bacilli) and 15 known bacterial genera (six major genera: Methylobacillus, Azotobacterium, Sphingomonas, Pseudomonas, Bacillus, and Hyphomicrobium) were considered to be NP-degradation-associated bacteria. The bacterial community diversity and percentage of NP-degradation-associated bacteria in the BCSC system were marginally greater than those in the SC system. The higher bacterial diversity and adsorption capacity in the BCSC system were able to mitigate the migration of NP into groundwater.