Mine activities leaked heavy metals into surrounding soil and may affected indigenous microbial communities. In the present study, the diversity and composition of the bacterial community in soil collected from three regions which have different pollution degree, heavy pollution, moderate pollution, and non-pollution, within the catchment of Chao River in Beijing City, were compared using the Illumina MiSeq sequencing technique. Rarefaction results showed that the polluted area had significant higher bacterial alpha diversity than those from unpolluted area. Principal component analysis (PCA) showed that microbial communities in the polluted areas had significant differences compared with the unpolluted area. Moreover, PCA at phylum level and Matastats results demonstrated that communities in locations shared similar phyla diversity, indicating that the bacterial community changes under metal pollution were not reflected on phyla structure. At genus level, the relative abundance of dominant genera changed in sites with degrees of pollution. Genera Bradyrhizobium, Rhodanobacter, Reyranella, and Rhizomicrobium significantly decreased with increasing pollution degree, and their dominance decreased, whereas several genera (e.g., Steroidobacter, Massilia, Arthrobacter, Flavisolibacter, and Roseiflexus) increased and became new dominant genera in the heavily metal-polluted area. The potential resistant bacteria, found within the genera of Thiobacillus, Pseudomonas, Arthrobacter, Microcoleus, Leptolyngbya, and Rhodobacter, are less than 2.0 % in the indigenous bacterial communities, which play an important role in soil ecosystem. This effort to profile the background diversity may set the first stage for better understanding the mechanism underlying the community structure changes under in situ mild heavy metal pollution.

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 energyintensive because of aeration and relatively poor cathode performance. To overcome these disadvantages, a novel EC system was proposed using an air cathode to generate H 2 O 2 in situ for improved energy efficiency of As(III) removal. With the air cathode, the H 2 O 2 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.

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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) contents were 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 À1 of DDBAC were added, W B in sludge decreased to 1.64 g g À1 , 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.

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The potential benefits of surfactant-conditioned sludge dewatering treatment with acid/alkali pretreatment were investigated in this study. The water content of dewatered sludge (W C ) and specific resistance of filtration (SRF) were used to evaluate sludge dewaterability. Extracellular polymeric substance (EPS) content, bound water content, zeta potential, and rheological properties were measured to explain the change of dewaterability observed in the conditioning process. By introducing dodecyl dimethyl benzyl ammonium chloride (DDBAC), the EPS content of the sludge supernatant changed, and bound water content, charge strength, and apparent viscosity decreased simultaneously. Although DDBAC-conditioned sludge in strong alkaline had low bound water content, W C and SRF increased rapidly because of the dramatically increasing of EPS in sludge supernatant. Remarkable decrement was observed in bound water content and W C in DDBAC-conditioned sludge which was in weak acid environment for comparison. The results indicated that 75 mg/g of DDBAC at pH 4.84 was the optimum under which W C and SRF were at their lowest point in sludge, 58.22 % and 0.521×10 13 m/kg, respectively.

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