Disposal of Arsenic Filter Sludge in Soil and its Consequences

Incubation, macrocosm and field studies were carried out to observe any increase in the concentration of arsenic （As） in soil and its subsequent uptake by plants due to disposal of As-filter sludge into soil from two different arsenic removal media. One of the media was iron based and the other was activated alumina based. For the incubation study, sludge @ 1 T.ha^-1 and 0.5 T.hal from the two sources wer applied to soils and incubated for 180 days with five individual incubation periods viz., 15, 30, 60, 90 and 180 days. At the end of each incubation period the soils were extracted with 1M HCI. For the macrocosm study, a leafy vegetable-lpomoea aquatica L. and rice （Oryza sativa L.） were grown in pots treated with sludge @ 1 T·ha^-1 and 0.5 T·ha^-1 soils. For the field study, two leafy vegetables viz., red amaranthus （Amaranthus gangeticus L.） and Kalmi （Ipomoea aquatiea L.） were grown on soils treated with the sludge @ 1 T.ha^-1 in plots of 1 m^2 sizes. Arsenic was found to have increased under upland and lowland conditions that contributed to an increased accumulation of the element in the plants. The increase of As was found to be relatively higher under upland condition than under submerged condition. Arsenic accumulation in plants was found to be the highest in the roots followed by straw and grain. Similar observation has been made under field condition too. Increased concentration of Fe an AI has also been observed which could be a new environmental hazard. The study reveals that the filters used for making As-safe drinking water cannot be safely disposed of to the soil, particularly to the agricultural soils.

Biogeochemical reductive release of soil embedded arsenate around a crater area (Guandu) in northern Taiwan using X-ray absorption near-edge spectroscopy

This study investigates biogeochemical reductive release of arsenate from beudantite into solution in a crater area in northern Taiwan,using a combination of X-ray absorption near-edge structure （XANES） and atomic absorption spectrometry.Total arsenic （As） concentrations in the soil were more than 200 mg/kg.Over four months of laboratory experiments,less than 0.8% As was released into solution after reduction experiments.The 71% to 83% As was chemically reduced into arsenite （As（III）） and partially weathering into the soluble phase.The kinetic dissolution and re-precipitation of As,Fe,Pb and sulfate in this area of paddy soils merits further study.

Microbial reduction and migration of As/Fe mediated by electron shuttle:Differences between incorporated and adsorbed As(V)

Metal-reducing bacteria play a central and important role in the biogeochemical cycle of arsenic(As)and iron(Fe).Research on As/Fe migration from arsenic-containing iron minerals mediated by electronic shuttles is of significance to groundwater protection and human health.Further,the redox activity and bioavailability of goethite with differing occurrence and distribution of arsenic have not been studied clearly.In this study,the function of electron shuttle AQDS in Fe(III)bioreduction was determined.It was found that acidic conditions were conducive to the growth and reproduction of strain D2201,which was beneficial to the reduction of As(V)/Fe(III).The OD600nm value of the bacteria at pH 6 exceeded twice that at pH 8.Then,three types of goethite,namely pure goethite(Gt),coprecipitated As(V)-goethite(Gt-As),and adsorbed arsenic-goethite(Gt*As),were compared for microbial reduction reactivity.X-ray photoelectron spectroscopy analysis illustrated the proportion of OH-content in Gt-As was much lower than that of Gt and Gt*As,indicating Gt-As carried more surface defects and had higher bioavailability.The Fe(II)content released from AQDS-mediated bioreduction of Gt-As was two-fold higher than that of Gt and Gt*As at pH 7.In addition,pH significantly affected goethite bioreduction efficiency and arsenic migration degree.The dissolved Fe(II)concentration for Gt-As was 0.98,0.133,and 0.139 mM at pH 6,7,and 8,respectively;corresponding to dissolved As(T)content of 3.51,1.48,and 1.31μM within 9 days of culture.This study highlights the significant influence of AQDS and mineral structure on the As/Fe biochemical cycle,which will help further develop the bioremediation of arsenic-contaminated sediments.