Isotopic studies have shown that many of the world’s coalbed natural gas plays are secondary biogenic in origin, suggesting a potential for gas regeneration through enhanced microbial activities. The generation of biogas through biostimulation and bioaugmentation is limited to the bioavailability of coal-derived compounds and is considered carbon positive. Here we show that plant-derived carbohydrates can be used as alternative substrates for gas generation by the indigenous coal seam microorganisms. The results suggest that coalbeds can act as natural geobioreactors to produce low carbon renewable natural gas, which can be considered carbon neutral, or perhaps even carbon negative depending on the amount of carbon sequestered within the coal. In addition, coal bioavailability is no longer a limiting factor. This approach has the potential of bridging the gap between fossil fuels and renewable energy by utilizing existing coalbed natural gas infrastructure to produce low carbon renewable natural gas and reducing global warming.
In situ remediation of ammonium-contaminated groundwater is possible through a zeolite permeable reactive barrier (PRB); however, zeolite's finite sorption capacity limits the long-term field application of PRBs. In this paper, a pilot-scale PRB was designed to achieve sustainable use of zeolite in removing ammonium (NH(4)(+)-N) through sequential nitrification, adsorption, and denitrification. An oxygen-releasing compound was added to ensure aerobic conditions in the upper layers of the PRB where NH(4)(+)-N was microbially oxidized to nitrate. Any remaining NH(4)(+)-N was removed abiotically in the zeolite layer. Under lower redox conditions, nitrate formed during nitrification was removed by denitrifying bacteria colonizing the zeolite. During the long-term operation (328 days), more than 90% of NH(4)(+)-N was consistently removed, and approximately 40% of the influent NH(4)(+)-N was oxidized to nitrate. As much as 60% of the nitrate formed in the PRB was reduced in the zeolite layer after 300 days of operation. Removal of NH(4)(+)-N from groundwater using a zeolite PRB through bacterial nitrification and abiotic adsorption is a promising approach. The zeolite PRB has the advantage of achieving sustainable use of zeolite and immediate NH(4)(+)-N removal.
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 NOx(-)-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. NOx(-)-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 NOx(-)-N transformation, but the chemical reduction capacity decreased after 21 PVs in the spongy iron.
Nitrogen as ammonium (NH 4 þ -N) is one of the most common nitrogen contaminants in groundwater; this is particularly true in the industrial and agricultural regions of northern China, where rapid population growth and economic development have stressed public water supplies and reduced groundwater quality. In this study, we report the performance of a zeolite permeable reactive barrier (PRB) designed to remove ammonium from contaminated river water that infiltrates to a groundwater aquifer that serves as a drinking water supply for the city of Shenyang. Groundwater monitoring data obtained over 5 months of operation indicate that ammonium concentrations in the groundwater decreased from 2-10 mg/L to <0.5 mg/L after the PRB was installed in the vicinity. Data suggest that ammonium removal was mainly due to sorption and ion exchange, with NH 4 þ exchanged with Na þ and K þ in the zeolite. After more than 1 year of continuous operation, there is no evidence of microbial ammonium oxidation. To our knowledge, this was the first field-scale demonstration of a PRB in China.
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