Removal of tetracyclines and estrogens with simultaneous ammonia retention in swine wastewater by aerobic treatment under short sludge retention time.

The removal of tetracyclines and estrogens with simultaneous ammonia retention provides a feasible path for the resource utilization of treated swine wastewater for farm irrigation. This study therefore investigated the optimal conditions of the aerobic process for swine wastewater treatment by adjusting two important parameters, i.e., sludge retention time (SRT) and hydraulic retention time (HRT). The conventional aerobic process with an SRT of 10∼30 d had the COD removal efficiency of 77 %-91 % and the ammonia nitrification rate of 99 %, while only 61 %-74 % and 78 %-86 % for that with an SRT of only 5 d, indicating the significant impact of SRT on COD removal and ammonia nitrification. Similarly, the overall removal efficiency of tetracyclines and estrogens was generally increased with SRT, i.e., increased from 76 %-77 %-94 %-95 % for tetracyclines and from 90 %-91 %-96 %-97 % for estrogens when the SRT was increased from 5 d to 30 d at HRT = 10 d. The impact of treatment efficiency by HRT was less significant compared to that by SRT. To achieve a better ammonia retention efficiency, aerobic process with a shorter SRT of 3 d was further investigated. The results show that the COD removal efficiency was 64 %-69 % and the ammonia nitrification rate was <1 % under SRT = 3 d. It indicates that this strategy effectively hindered ammonium nitrification with a nitrification inhibition rate of >99 %. In addition, the overall removal efficiency of tetracyclines and estrogens under SRT = 3 d was 75 % and 87 %, respectively. The aerobic process with a short SRT results in the absence of nitrifying bacteria and the decrease of sludge concentration, leading to the inhibition of ammonia nitrification and the decrease of pollutant removal. These findings also indicate that nitrification inhibition and pollutant removal (both conventional and emerging) are two trade-off aspects during swine wastewater treatment by aerobic process.