Ammonium-nitrogen-contaminated groundwater remediation by a sequential three-zone permeable reactive barrier (multibarrier) with oxygen-releasing compound (ORC)/clinoptilolite/spongy iron: column studies
2015
Huang, Guoxin | Liu, Fei | Yang, Yingzhao | Kong, Xiangke | Li, Shengpin | Zhang, Ying | Cao, Dejun
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 NH₄⁺–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 NH₄⁺–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. NH₄⁺–N of 4.06∼10.49 mg/L was depleted and NO ₓ ⁻–N (i.e., NO₃⁻–N + NO₂⁻–N) of 4.26∼9.63 mg/L was formed before 98 PVs in the ORC zone. NH₄⁺–N of ≤4.76 mg/L was eliminated in the clinoptilolite zone. NO ₓ ⁻–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 NH₄⁺–N removal in the ORC zone. Ion exchange was majorly responsible for NH₄⁺–N elimination in the clinoptilolite zone. Chemical reduction and hydrogenotrophic denitrification both contributed to NO ₓ ⁻–N transformation, but the chemical reduction capacity decreased after 21 PVs in the spongy iron.
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