Energy-Efficient Oxidation and Removal of Arsenite from Groundwater Using Air-Cathode Iron Electrocoagulation

Arsenic contamination of groundwater has affected many countries, especially in Southeast Asia. Although aerated electrocoagulation (EC) provides an effective way to remove arsenite, this process is energy-intensive because of aeration and relatively poor cathode performance. To overcome these disadvantages, a novel EC system was proposed using an air cathode to generate H₂O₂ <i>in situ</i> for improved energy efficiency of As­(III) removal. With the air cathode, the H₂O₂ production rate was 3.7 ± 0.1 mg L^–1 h^–1, which indirectly promoted As­(III) oxidation by interaction with Fe­(II). At a current density of 4 A m^–2, the average cell voltage during air-cathode electrocoagulation (ACEC) was 1.0 V, compared to 1.9 V in the EC and aerated EC systems. Energy consumption in the ACEC system was 17.0 ± 0.7 Wh log^–1 m^–3, much lower than those in the EC (67.8 ± 0.9 Wh log^–1 m^–3) and aerated EC (65.1 ± 0.8 Wh log^–1 m^–3) systems, which can be attributed to effective As­(III) oxidation, no need for aeration, and improved cathode performance with the air cathode. These results showed that the ACEC system is a promising technology for energy-efficient removal of arsenite from contaminated groundwater

Effect of surfactant on bound water content and extracellular polymers substances distribution in sludge

In this study, the effect of surfactant conditioning on bound water and extracellular polymers substances (EPS) in sludge was investigated. Results showed that by adding dodecyl dimethyl benzyl ammonium chloride (DDBAC), loosely bound EPS (LB-EPS) and slime layer EPS (S-EPS) contentswere increased, while tightly bound EPS (TB-EPS) and bound water contents (W-B) were reduced. As a result, the dewatering performance of sludge was enhanced. When 75 mg g(-1) of DDBAC were added, W-B in sludge decreased to 1.64 g g(-1), and the water content of dewatered sludge (W-C) dropped to 66.61%. EPS partially hydrolyzed into small molecular organics under DDBAC conditioning. Moreover, the quantity and species of organic functional groups in S-EPS were increased obviously. The TB-EPS content accounted for the majority of EPS in sludge, and the protein and polysaccharide in TB-EPS had a significant positive correlation with bound water, which was the main factor affecting W-B in sludge