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A novel sequential permeable reactive barrier (multibarrier), composed of oxygen-releasing compound (ORC)/clinoptilolite/spongy iron zones in series, was proposed for ammonium-nitrogen-contaminated groundwater remediation. Column experiments were performed to: (1) evaluate the overall NH-N removal performance of the proposed multibarrier, (2) investigate nitrogen transformation in the three zones, (3) determine the reaction front progress, and (4) explore cleanup mechanisms for inorganic nitrogens. The results showed that NH-N percent removal by the multibarrier increased up to 90.43 % after 21 pore volumes (PVs) at the influent dissolved oxygen of 0.68∼2.45 mg/L and pH of 6.76∼7.42. NH-N of 4.06∼10.49 mg/L was depleted and NO-N (i.e., NO-N + NO-N) of 4.26∼9.63 mg/L was formed before 98 PVs in the ORC zone. NH-N of ≤4.76 mg/L was eliminated in the clinoptilolite zone. NO-N of 10.44∼12.80 mg/L was lost before 21 PVs in the spongy iron zone. The clinoptilolite zone length should be reduced to 30 cm. Microbial nitrification played a dominant role in NH-N removal in the ORC zone. Ion exchange was majorly responsible for NH-N elimination in the clinoptilolite zone. Chemical reduction and hydrogenotrophic denitrification both contributed to NO-N transformation, but the chemical reduction capacity decreased after 21 PVs in the spongy iron. [ABSTRACT FROM AUTHOR]

A novel fully passive permeable reactive barrier (PRB) with oxygen-releasing compound (ORC) and clinoptilolite was proposed for the removal of ammonium-nitrogen from groundwater. The PRB involves a combination of oxygen release, biological nitrification, ion exchange, and bioregeneration. A pilot-scale performance comparison experiment was carried out employing three parallel columns to assess the proposed PRB. The results showed that the PRB achieved nearly complete NH 4 + - N depletion (>99%). NH 4 + - N of 5.23–10.88 mg/L was removed, and NO 2 − - N of <1.93 mg/L and NO 3 − - N of 2.03–19.67 mg/L were generated. Ion exchange and biological nitrification both contributed to NH 4 + - N removal, and the latter played a dominant role under the condition of sufficient oxygen. Biological nitrification favored a delay in sorption saturation and a release of exchange sites. The ORC could sufficiently, efficiently supply oxygen for approximately 120 pore volumes. The clinoptilolite ensured a robust NH 4 + - N removal in case of temporary insufficient biological activities. No external alkalinity sources had to be supplied and no inhibition of aerobic metabolism occurred. The ceramicite had a negligible effect on the biomass growth. Based on the research findings, a full-scale continuous wall PRB was installed in Shenyang, China in 2012. [ABSTRACT FROM AUTHOR]