Identification of emerging contaminants and their transformation products in a moving bed biofilm reactor (MBBR) based drinking water treatment plant around River Yamuna in India
The prevalence of emerging contaminants of concern in water regimes is very common these days. High anthropogenic intervention is leading to occurrence of various types of microcontaminants of concern in drinking water systems. Their removal using conventional form of treatment systems employed in water treatment plants is not widely researched upon. Their fate in the conventional as well as advanced water treatment system needs to be focused upon for efficient and safe water disposal. Some compounds may leave the system unchanged or some might transform into much more toxic byproduct. Moreover, understanding level of occurrence of these emerging contaminants in source water bodies is also quintessential for assessing their fate in treatment plant itself as well as in the final treated water. Here in this study, the occurrence and removal of various classes of emerging contaminants were investigated in a moving bed biofilm reactor (MBBR) based advanced drinking water treatment plant (ADWTP) alongside one conventional drinking water treatment plant, both of which use River Yamuna as the source of water. Non target analysis utilizing high performance liquid chromatography combined with time of flight (HPLC QToF) identified more than 300 compounds. Pharmaceuticals accounted for a major fraction (58% of the identified compounds, followed by plasticizers and insecticides. Nine parent compound and their transformation products were additionally identified using solid phase extraction followed by analysis using gas chromatography mass spectrometry and HPLC QToF. The degradation pathway of the parent compounds in MBBR based ADWTP was also analyzed in depth. The efficiency of each unit process of MBBR based drinking water treatment plant was studied in terms of removal of few emerging contaminants. Pharmaceutical compound like diclofenac supposedly was persistent, even, toward the end of the treatment train. Semi quantitative analysis revealed ineffective removal of pyridine, hydrochlorothiazide, and diethyl phthalate in the outlet of ADWTP. ADWTP was able to remove a few emerging contaminants, but a few were recalcitrant. Likewise, it was established that although some parent compounds were degraded, much more toxic transformation products were formed and were prevalent at the end of the treatment.
Environmental Monitoring and Assessment