Study On Typical Iodinated Contrast Media Removal By Enhanced Aerobic Nitrification In Biological Aerated Filter

Pharmaceutical and personal care products (PPCPs) are emerging trace pollutants in source water and drinking water in recent years. These PPCPs always have high biological reactivity and magnification effect, thus they have risks on human health via drinking water and food chain. The distribution and influence of iodinated contrast media (ICM), a series of PPCPs which was frequently detected in various environmental media, had drawn the attention of researchers.Iopromide (IOP) and Iomeprol (IOM) were selected as the representatives for ICM in present study to investigate the enhanced degradation of ICM by aerobic nitrification in biological pretreatment of source water. The main conclusions could be obtained as follows:(1) Enrichment culture of nitrobacteria isolated from the secondary sedimentation tank of Shanghai Songjiang WWTP was performed at room temperature, pH6.5～8.5and2mg L-1dissolved oxygen, with addition of organic carbon source and carrier. When the NH4-N concentration of influent increased to300mg L-1, and the C/N=1.7, the concentration of Nitrosomas and Nitromonas in sludge reached3.5×107and2.5×108MPN mL-1, respectively, which were117and42times more than Nitrosomas and Nitromonas concentrations without enrichment after4weeks of culture. The removal rate of NH4-N reached96.7%after30days’ culture. The nitrifying capacity and nitrification rate of nitrobacteria were67.90mg(NH4+-N) L’1h-1and9.504mg(NH4+-N) g(MLSS)-1h-1, respectively.(2) In the optimal condition of30℃, pH8.0～8.5and the initial concentration of10mg L-1 IOP, the degradation of ICM was efficiently enhanced by nitrobacteria. The influence of organic carbon on the degradation of IOP by nitrobacteria was investigated to confirm the mechanism of co-metabolism. With the addition of glucose, soluble starch and maltose, the degradation rate of IOP was efficiently increased. Especially, when in the presence of500mg L-1glucose, the degradation rate of IOP by nitrobacteria reached60.3%in3days. In the optimal conditions, the degradation rate of IOP by nitrobacteria could reach84.1%in5days. IOM, the other representative of ICM, could also be degraded by nitrobacteria.(3)Enrichment cultured nitrobacteria was inoculated to BAF packed with volcanic to start the installation to treat the source water polluted with ICM by enhanced nitrification. It was observed that the biomass was abundant in BAF after12d operation. The removal of NH4-N reached up to95.2%. The degradation rate of IOP and IOM reached94.9%and83.4%with addition of nitrobacteria after enrichment in the condition as follows:gas water ratio of4:1, hydraulic loading of0.4m3m-2h-1, HRT of3h and influent flow of3.0L h-1. When nitration reaction was inhibited, the removal efficiency for both IOP and. IOM was less than15%. Hence, it was confirmed that the degradation for ICM was enhanced by nitration reaction. The degradation efficiency for IOP and IOM in BAF with enrichment cultured nitrobacteria in8days reached84.5%and68.7%, respectively.31.2%and21.7%higher than the degradation efficiency for IOP and IOM in BAF without enrichment cultured nitrobacteria. These observations indicated that the inoculation of enriched nitrobacteria into BAF was feasible and efficient to significantly increase the degradation of ICM.(4) The distribution of ICM in BAF columns was investigated. The organic matter was removed by the filter material in the range from0-60cm after the BAF inlet, up to95.7%of total TOC removal by the BAF. The removal of NH4-N occurred in40cm of the filter, the removal efficiency was68.4%, which was82.5%of total NH4-N removal. IOP and IOM were removed slowly near the BAF inlet, and the removal rate increased rapidly from40cm to BAF outlet, IOP and IOM were removed mostly in the dominant range of40～60cm in BAF.