Effects of Cd(II) and cu(II) on microbial characteristics in 2-chlorophenol-degradation anaerobic bioreactors

Cadmium effects on net N2O production by the deep-sea isolate Shewanella loihica PV-4

Deep-sea mining may lead to the release of high concentrations of metals into the surrounding seabed, which can disturb important ecosystem functions provided by microbial communities. Among these, the production of N2O and its reduction to N2 is of great relevance since N2O is an important greenhouse gas. Metal impacts on net N2O production by deep-sea bacteria are, however, currently unexplored. Here, we evaluated the effects of cadmium (Cd) on net N2O production by a deep-sea isolate, Shewanella loihica PV-4. We performed a series of Cd exposure incubations in oxic conditions and determined N2O fluxes during induced anoxic conditions, as well as the relative expression of the nitrite reductase gene (nirK), preceding N2O production, and N2O reductase gene (nosZ), responsible for N2O reduction. Net N2O production by S. loihica PV-4 exposed to Cd was strongly inhibited when compared to the control treatment (no metal). Both nirK and nosZ gene expression were inhibited in reactors with Cd, but nirK inhibition was stronger, supporting the lower net N2O production observed with Cd. The Cd inhibition of net N2O production observed in this study poses the question whether other deep-sea bacteria would undergo the same effects. Future studies should address this question as well as its applicability to complex communities and other physicochemical conditions, which remain to be evaluated.

Challenges and opportunities for the biodegradation of chlorophenols: Aerobic, anaerobic and bioelectrochemical processes

Chlorophenols (CPs) are highly toxic and refractory contaminants which widely exist in various environments and cause serious harm to human and environment health and safety. This review provides comprehensive information on typical CPs biodegradation technologies, the most green and benign ones for CPs removal. The known aerobic and anaerobic degradative bacteria, functional enzymes, and metabolic pathways of CPs as well as several improving methods and critical parameters affecting the overall degradation efficiency are systematically summarized and clarified. The challenges for CPs mineralization are also discussed, mainly including the dechlorination of polychlorophenols (poly-CPs) under aerobic condition and the ring-cleavage of monochlorophenols (MCPs) under anaerobic condition. The coupling of functional materials and degraders as well as the operation of sequential anaerobic-aerobic bioreactors and bioelectrochemical system (BES) are promising strategies to overcome some current limitations. Future perspective and research gaps in this field are also proposed, including the further understanding of microbial information and the specific role of materials in CPs biodegradation, the potential application of innovative biotechnologies and new operating modes to optimize and maximize the function of the system, and the scale-up of bioreactors towards the efficient biodegradation of CPs.

Impact of copper on the diazotroph abundance and community composition during swine manure composting

Biological nitrogen fixation is a major pathway in ecosystems. This study investigated the effects of adding Cu at different levels (0, 200, and 2000 mg kg^-1) on the diazotroph community during swine manure composting. Quantitative PCR and high-throughput sequencing were used to analyze the abundances of diazotrophs and the community composition based on the nifH gene. The nifH gene copy number was relatively high in the early stage of composting and Cu had a significant inhibitory effect on the nifH copy number. Furthermore, Cu decreased the diversity of nifH and changed the microbial community structure in the early stage. The nifH genes from members of Firmicutes and Clostridium were most abundant. Co-occurrence ecological network analysis showed that the Cu treatments affected the co-occurrence patterns of diazotroph communities and reduced the associations between different diazotrophs. Interestingly, Cu may weaken symbiotic diazotrophic interactions and enhance the roles of free-living diazotrophs.

Toxicants inhibiting anaerobic digestion: a review

Anaerobic digestion is increasingly being used to treat wastes from many sources because of its manifold advantages over aerobic treatment, e.g. low sludge production and low energy requirements. However, anaerobic digestion is sensitive to toxicants, and a wide range of compounds can inhibit the process and cause upset or failure. Substantial research has been carried out over the years to identify specific inhibitors/toxicants, and their mechanism of toxicity in anaerobic digestion. In this review we present a detailed and critical summary of research on the inhibition of anaerobic processes by specific organic toxicants (e.g., chlorophenols, halogenated aliphatics and long chain fatty acids), inorganic toxicants (e.g., ammonia, sulfide and heavy metals) and in particular, nanomaterials, focusing on the mechanism of their inhibition/toxicity. A better understanding of the fundamental mechanisms behind inhibition/toxicity will enhance the wider application of anaerobic digestion.

p-Cresol mineralization and bacterial population dynamics in a nitrifying sequential batch reactor

The ability of a nitrifying sludge to oxidize p-cresol was evaluated in a sequential batch reactor (SBR). p-Cresol was first transformed to p-hydroxybenzaldehyde and p-hydroxybenzoate, which were later mineralized. The specific rates of p-cresol consumption increased throughout the cycles. The bacterial population dynamics were monitored by using denaturing gradient gel electrophoresis (DGGE) and sequencing of DGGE fragments. The ability of the sludge to consume p-cresol and intermediates might be related to the presence of species such as Variovorax paradoxus and Thauera mechernichensis. p-Cresol (25 to 200mgC/L) did not affect the nitrifying SBR performance (ammonium consumption efficiency and nitrate production yield were close to 100% and 1, respectively). This may be related to the high stability observed in the nitrifying communities. It was shown that a nitrifying SBR may be a good alternative to eliminate simultaneously ammonium and p-cresol, maintaining stable the respiratory process as the bacterial community.

Performance of an aerobic granular sequencing batch reactor fed with wastewaters contaminated with Zn2+

The main aim of this study was to investigate the performance of an aerobic granular sludge sequencing batch reactor (AGS-SBR) receiving water streams supplied with different loads of Zn(2+) (50 and 100 mg L(-1)) during an operation of 866 cycles (ca. 109 days). When the metal was not fed, chemical oxygen demand (COD), PO4(3-) and NH4(+) were efficiently removed, with efficiencies of 56, 23 and 72% respectively. DGGE profiles showed that Zn(2+) supply negatively affected the bacterial diversity and community structure of the granules. Consequently, the shock loadings with Zn(2+), particularly at the higher levels (100 mg L(-1)), affected the nutrient removal in the AGS-SBR, although the reactor still generally complied with admissible legal values concerning organic matter, nitrogen and Zn. Simultaneous removal of PO4(3-) and TSS in such conditions needs further refining but the application of aerobic granular SBR in the treatment of Zn(2+) contaminated wastewaters seems viable.