Hydraulic retention time and pH affect the performance and microbial communities of passive bioreactors for treatment of acid mine drainage

Abstract

For acceleration of removing toxic metals from acid mine drainage (AMD), the effects of hydraulic retention time (HRT) and pH on the reactor performance and microbial community structure in the depth direction of a laboratory-scale packed-bed bioreactor containing rice bran as waste organic material were investigated. The HRT was shortened stepwise from 25 to 12 h, 8 h, and 6 to 5 h under the neutral condition using AMD neutralized with limestone (pH 6.3), and from 25 to 20 h, 12 h, and 8 to 7 h under the acid condition using AMD (pH 3.0). Under the neutral condition, the bioreactor stably operated up to 6 h HRT, which was shorter than under the acid condition (up to 20 h HRT). During stable sulfate reduction, both the organic matter-remaining condition and the low oxidation–reduction potential condition in lower parts of the reactor were observed. Principal coordinate analysis of Illumina sequencing data of 16S rRNA genes revealed a dynamic transition of the microbial communities at the boundary between stable and unstable operation in response to reductions in HRT. During stable operation under both the neutral and acid conditions, several fermentative operational taxonomic units (OTUs) from the phyla Firmicutes and Bacteroidetes dominated in lower parts of the bioreactor, suggesting that co-existence of these OTUs might lead to metabolic activation of sulfate-reducing bacteria. In contrast, during unstable operation at shorter HRTs, an OTU from the candidate phylum OP11 were found under both conditions. This study demonstrated that these microorganisms can be used to monitor the treatment of AMD, which suggests stable or deteriorated performance of the system.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-017-0440-z) contains supplementary material, which is available to authorized users.

A Cross-Sectional Study of the Gut Microbiota Composition in Moscow Long-Livers

“…We suppose that this should be due to the different dietary patterns between countries. Typical sulfate reducer Desulfovibrio could reflect a higher consumption of seafood by Italians and Japanese [22], while Roseburia could be a sign of a large amount of cereal grains in the Russian diet [23]. In addition, Russian LL microbiome had more similarities with the Italian cohort, which is geographically closer.…”

System Performance Corresponding to Bacterial Community Succession after a Disturbance in an Autotrophic Nitrogen Removal Bioreactor

“…In previous studies, variability in microbial community and system functioning was attributed mainly to selective pressures of external deterministic parameters (such as temperature, substrate concentration, and hydraulic retention time) of bioreactors ( 16 – 18 , 23 ), overlooking the direct effect of microbial community dynamics on system functioning. Thus, even though some associations between microbial community and bioreactor performance have been revealed ( 16 , 17 , 19 , 24 ), it is still unclear whether these associations are driven by shared operational conditions, microbial influence on system functioning, or a combination of the two.…”

“…Then, after a period of operation in a controlled setting, the bioreactor can be considered to reach a steady state when biomass concentration and system performance approach a constant ( 29 – 31 ). However, secondary succession of microbial communities might occur due to disturbances, such as overloading ( 32 ), adding new substrates ( 33 ), or modifying operational parameters ( 23 ). In this study, we focused on secondary succession of microbial communities within a bioreactor, after it had been considered to reach a steady state, and examined the responses of microbial community succession and system performance following an artificial disturbance which consisted of homogenizing all microbial consortia (including biofilm and suspended sludge) and resuspending the mixture in the bioreactor.…”

Descoloração de efluente têxtil em reatores anaeróbios de leito estruturado e de biomassa livre

“…No trabalho de Chen et al (2007), foi observado que SBR metanogênicos mantidos em pH alcalino tiveram concentração de ácidos orgânicos crescente no decorrer do ciclo operacional. Aoyagi et al (2017) relataram tendência semelhante ao variar o TDH de 25 a 5 horas em reator acidogênico e verificar que as concentrações de ácidos acético propiônico decresceram, respectivamente, de 1,4-1.8 e 0,7-0,8mM, até tornarem-se indetectáveis sob TDH de 5 horas. Logo, é possível que a redução na concentração de ácidos efluente decorra de limitações cinéticas nas etapas de acidogênese, levando a taxas de conversão de ácidos orgânicos progressivamente menores.…”

“…Sabe-se que sistemas com TDH muito curto podem não permitir tempo adequado para mineralização completa de matéria orgânica, enquanto que TDH longos podem esgotar substratos ou favorecer o acúmulo de material celular ou minerais precipitados, diminuindo a condutividade hidráulica ou provocando curtos-circuitos no sistema de tratamento. No presente estudo, porém, a mudança do TDH no decorrer da operação parece não ter exercido impacto significativo sobre BRS, que obtiveram níveis de eficiência semelhantes para todos TDH avaliados.A estabilidade na remoção de sulfatos, para diferentes valores de TDH, também foi avaliada porAoyagi et al (2017). Os autores estudaram a eficiência de remoção de sulfatos emreator de leito empacotado, sob condições de pH próximas à neutralidade.…”