Abstract
Abstract High nitrate concentrations in wastewater treatment plant effluents and aquifers can challenge sequential biofiltration systems in preventing nitrite and gas formation in the sand bed, as well as to achieve the regulated limit value for nitrate in potable water reuse applications. This study investigates the introduction of electron donors in the form of organic fixed bed materials as an in-situ anoxic zone into sequential biofiltration systems. Laboratory batch and column tests with straw, soft wood, peat, polylactic acid (PLA), and polycaprolacton (PCL) revealed incomplete denitrification with a hydraulic retention time below 10 h, high organic carbon leaching, especially during the first three months, and gas accumulation within the filter bed. Therefore, ex-situ denitrification prior to oxic biofilters or in a defined side-stream treatment is recommended. No enhanced transformation of trace organic chemicals was observed under nitrate reducing conditions. Peat revealed a sorption potential for 5-methyl-benzotriazole, carbamazepine, benzotriazole, and metoprolol.
Highlights
Surface water used for potable water reclamation can be influenced by upstream discharges of waste water treatment plant (WWTP) effluents (Karakurt et al )
While in the first filtration step, biodegradable DOC is removed associated with the consumption of oxygen, beneficial carbon limiting and oxic conditions are established in the second filtration step after aeration for enhanced trace organic chemicals (TOrCs) removal
With a better adjustment of HRT, influent oxygen concentrations or even temperature, this time could be decreased and PCL might be a possible substrate for long-term fixed bed denitrification
Summary
Surface water used for potable water reclamation can be influenced by upstream discharges of waste water treatment plant (WWTP) effluents (Karakurt et al ). Sequential biofiltration (SBF) systems or sequential managed aquifer recharge technologies (SMART) represent an advancement of conventional biofilters and MAR systems A further technical pilot application consists of a horizontal plug-flow reactor filled with technical sand and an in-situ introduction of oxygen (Karakurt-Fischer et al ) Since these systems are promoting oxic conditions, contaminants such as nitrate, carbamazepine, or iodinated x-ray contrast agents which are predominantly removed or dehalogenated under anoxic and anaerobic conditions
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