Reclamation of urban pollution impacted groundwater by advanced treatment processes: Effect of prechlorination on the removal of metals, ammonium and NOM at pilot scale

The need for new water resources in water scarcity regions has driven the exploration of water reclamation through a variety of treatment technologies. The present study aims at reclaiming impacted urban groundwater through two different treatment routes: one based on adsorption and ion-exchange processes on consecutive pyrolusite, granular activated carbon, zeolite and Fe(oxy)hydroxide filters (route L1) and a second one relying on sorption (on pyrolusite) and RO-membrane filtration (route L2). Both routes were operated without and with prechlorination to ascertain whether NaClO, beyond inactivating undesired pathogens, affected the removal of target parameters (Mn, As, NH4+, DOC) and the formation of trihalomethanes (THMs). Results showed that route L1 was successful at removing Mn, As, pathogens and THMs at levels below those stipulated by the legislation on reuse and drinking water. Only NH4+ failed to decrease below its threshold limits for drinking water, but only in the absence of prechlorination. However, concentration of Cl- and Na+ increased during treatment due to the chemicals used, compromising reuse of the produced water in specific industrial sectors requiring low contents of these ions. Route L2 showed a consistent high removal of all targeted parameters (also NH4+) without and with prechlorination conditions, producing a finished water with high potential for reuse and production of drinking water. DOC and its fluorescent fulvic and humic-like fractions were moderately removed by route L1 but highly removed by route L2. The outperformance of route L2 in terms of produced water quality must be balanced by the associated treatment cost, as it was 8-10 % higher for route L2 than for route L1. This made evident that a trade-off between quality and cost must be faced. This study demonstrates that reclamation of urban groundwater through the proposed treatment routes has a huge potential for reuse for a wide diversity of final purposes (urban, agricultural, industrial, environmental and recreational uses) and, although it may need further exploration, likely for drinking water purposes.