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The microbial transformation of arsenic species in municipal landfill leachate (MLL) was investigated with the objective to highlight arsenic transformation in the landfill system. Across the 43 day incubation in MLL, more than 90% arsenate (iAsV) was found to reduce to arsenite (iAsIII) within 20 days, while iAsIII was comparably stable although a fraction of iAsIII was temporarily oxidated to iAsV in the first 3 days. Transformation of monomethylarsonic acid (MMAV) to dimethylarsinic acid (DMAV) in MLL was slow with only 5% MMAV methylated to DMAV after 43 days incubation. A portion of DMAV and MMAV in MLL was demonstrated to transform into thiol-organoarsenic and monomethylarsonous acid (MMAIII), which were identified to include dimethyldithioarsinic acid (DMDTAV), dimethylmonothioarsinic acid (DMMTAV) and monomethyldithioarsonic acid (MMDTAV) by HPLC–ICPMS and LC–ESI-MS/MS. The microbial formation of DMDTAV, DMMTAV and MMDTAV is postulated to relate to hydrogen sulfide generated by bacteria in MLL. Differences in arsenic transformation in sterilised and non-sterilised MLLs demonstrate bacteria play a crucial role in arsenic transformation in the landfill body. This study reveals the complexity of arsenic speciation and highlights the potential risk of forming highly toxic thiol-organoarsenic and MMAIII in the landfill environment. [ABSTRACT FROM AUTHOR]

This article reviews two interrelated areas of research: the first is the use of TiO 2 -supported adsorbent materials as enhanced heterogeneous photocatalysts and their application to various reactions for organic pollutant removal from air and water; the second is the combination of adsorbent materials with TiO 2 photocatalysts which aims to efficiently regenerate adsorbent materials using illumination. By reviewing both areas of research, the following topics are covered; (i) photocatalytic activation of TiO 2; (ii) related properties of photocatalytic TiO 2; (iii) shortcomings of photocatalytic processes; (iv) preparation methods of composite TiO 2 /adsorbent materials and their photocatalytic performance; (v) properties of common adsorbents and their applications for pollutant removal from air and water; (vi) adsorbent regeneration methods and their economic and operational issues; (vii) conclusions and future outlooks. This topic has not been previously reviewed to such an extent, and considerable knowledge can be gained from assembling the large number of studies on adsorption-photocatalysis combinations. As such, this review provides guidance for researchers working in the fields of environmental and chemical engineering focussing on organic pollutant removal and the engineering of new high performance photocatalytic TiO 2 -supported porous adsorbent materials., (Copyright © 2017 Elsevier B.V. All rights reserved.)