Mechanism Of As (V) Removal With Ferric And Transformation Of Arsenate Affected By The Aerobic Bacterium

Arsenic makes up about 1.5 mg·L-1(0.00001%) of the earth's crust, making it the20 th most abundant element. Soil contains 1-10 mg·L-1of arsenic. Seawater has only1.6 ?g·L-1 arsenic. In recent years, arsenic catastrophes are resulting in serious health problems in many countries. This phenomenon aroused more and more people's attention. Many relevant scholars have paid attention to arsenic removal method and the secondary pollution problems resulted in common methods of removing arsenic.Studies showed that ferric chloride flocculation precipitation could remove arsenic effectively. This method is low-cost and easy to operate. So, it has been widely used in the drinking water treatment. However, there is no systematic study about the adjustment of the operation parameters, the establishment of cleaning system and the treatment of solid residue, which seriously affects the removal of As in groundwater and the improvement of water treatment systems. On the other hand, there is secondary pollution problem existing in the common arsenic removal methods-lime precipitation.All of the above has become the focus of many scholars research, and there is controversy in some mechanism research.On the basis of previous theories, this paper mainly completed two works. Firstly,ferric flocculation and direct filtration system was applied to groundwater As(V)removal using batch, field pilot tests, extended X-ray absorption fine structure(EXAFS) spectroscopy, and charge-distribution multisite complexation(CD-MUSIC)model. The results showed that arsenate [As(V)] was the dominant As species in thegroundwater with a concentration of 44 ?g·L-1. The treatment system could supply 64984 L As-safe drinking water(<10 ?g·L-1) using 1.5 mg-Fe·L-1. The results of toxicity characteristic leaching procedure(TCLP) demonstrated that the leachate As was 3.4?g·L-1, much lower than the EPA regulatory concentration(5 mg·L-1). EXAFS and CD-MUSIC model indicated that As(V) was adsorbed on ferric hydroxide via bidentate binuclear complexes in the pH range of 3 to 9.5, while formation of precipitate dominated the As removal at pH>9.5. Secondly, the batch and column experiments were applied to investigate the adsorbed arsenic mobilization affected by an aerobic bacterium Bacillus sp. SXB. The results showed that in the batch experiment, strain SXB could reduce the arsenate adsorbed on the goethite. In the soil column experiment, the arsenic speciation in the effluent was arsenite in the treatment with and without strain SXB. It's because that the arsenic speciation in the raw soil was arsenite. The iron began to leach when the pore volume was larger than 100. The addition of strain SXB to the soil could slightly enhance the release of arsenic from the soil and had no significant effect on the Fe release.