Abstract
In this study, the raw wastewater (RW), and effluents from the acidogenic phase (AP) and methanogenic phase (MP) in a swine wastewater treatment plant were collected to investigate the occurrence and transformation of arsenic (As), as well as the abundance of As metabolism genes during the anaerobic digestion (AD) process. The results showed that total concentrations of As generally decreased by 33–71% after AD. Further analysis showed that the As species of the dissolved fractions were present mainly as dimethylarsinic acid (DMA), with arsenite (As(III)) and arsenate (As(V)) as the minor species. Moreover, real-time PCR (qPCR) results showed that As metabolism genes (arsC, arsenate reduction gene; aioA, arsenite oxidation gene and arsM, arsenite methylation gene) were highly abundant, with arsM being predominant among the metabolism genes. This study provides reliable evidence on As biotransformation in swine wastewater treatment process, suggesting that AD could be a valuable treatment to mitigate the risk of As in wastewater.
Highlights
With the rapid growth of the swine industry, pig farms discharge a large amount of wastewater, which usually contains nutrients, such as nitrogen and phosphorus, and harmful components, such as antibiotics and heavy metals [1]
The increase of pH in methanogenic phase (MP) can be explained by the volatile fatty acids (VFA), converted to CH4 and CO2
Biodegradable organic substances converted into methane and CO2 resulting in Chemical oxygen demand (COD) decrease in the digester
Summary
With the rapid growth of the swine industry, pig farms discharge a large amount of wastewater, which usually contains nutrients, such as nitrogen and phosphorus, and harmful components, such as antibiotics and heavy metals [1]. Organoarsenic additives have been extensively used in chicken and swine feeds. Most of the supplemented Arsenic (As) is excreted with the feces, further discharging into the wastewater through washing. It subsequently enters the soil through manure land application, eventually being biodegraded to the more toxic inorganic As [2]. Microbially-mediated As metabolic processes play a major role in As cycling, including arsenite (As(III)) oxidation, arsenate (As(V)) reduction, and As(III) methylation [3], as speciation, bioavailability, toxicity, environmental behavior, and their fate in the environment are changed through these processes.
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