The potential contributions to organic carbon utilization in a stable acetate-fed Anammox process under low nitrogen-loading rates.

The unique ability of Anammox bacteria to metabolize short-chain fatty acids have been demonstrated. However, the potential contributions of active Anammox species to carbon utilization in a mixotrophic Anammox-denitrification process are less well understood. In this study, we combined genome-resolved metagenomics and DNA stable isotope probing (DNA-SIP) to characterize an Anammox process fed with acetate under COD/TN ratios of around 0.30-0.40 and low nitrogen-loading rates. A draft genome of "Candidatus Jettenia caeni" and a novel species that was phylogenetically close to "Candidatus Brocadia sinica" were recovered. Essential genes encoding the key enzymes for acetate metabolism and dissimilatory nitrate reduction to ammonium were identified in the two Anammox draft genomes. The DNA-SIP revealed that Ignavibacterium, "Candidatus Jettenia caeni," Thauera, Denitratisoma, and Calorithrix predominantly contributed to organic carbon utilization in the acetate-fed Anammox process. In particular, the "Candidatus Jettenia caeni" accounted for a higher proportion of 13C-DNA communities than "Candidatus Brocadia sinica." This result well confirmed the theory of maintenance energy between the interspecies competition of the two Anammox species under low nitrogen-loading rates. Our study revealed its potential important role of the Anammox genus "Candidatus Jettenia" in the treatment of wastewater containing low organic matter and ammonia.

Dissolving the high-cost with acidity: A happy encounter between fluidized struvite crystallization and wastewater from activated carbon manufacture.

Production of wood-based activated carbon (WAC) generates large volume of highly acidic and phosphate-rich wastewater. Currently, the routine treatment (i.e. lime precipitation) creates significant secondary pollution, leading to extra economic and environmental burdens. Here, by exploiting the strong acidity of WAC wastewater, we successfully demonstrate fluidized struvite crystallization as a low-cost treatment alternative. Based on a 12 m3/d on-site pilot-scale system, four different fluidized struvite crystallization scenarios are evaluated from technical, economic, and environmental perspectives. The results show that using MgO with MgCl2 supplement saves 42.8% of the reagent cost when treating phosphate-rich wastewater (i.e. P = 3125.2 mg/L), and also maintains ideal P removal rate and struvite product purity. Meanwhile, the internal circulation mode exhibits higher P recovery (99.2%) than the external mode (55.3%-89.3%), while also demonstrates superior economic and environmental benefit because of less chemical consumption. In addition, the struvite morphology can be turned between pellets with strong crushing strength (external mode) to powder (internal mode). By Life cycle cost (LCC) analysis, we find that, on a treatment scale of 500 m3/d, struvite-based technology saves up to 31.33 million Chinese Yuan (CYN) during a 20-year lifespan, with relative payback period of 2.60 year. The technical, economic, and environmental assessments confirm that the struvite technology is a promising alternative in solving the bottleneck of WAC wastewater treatment.

Combined genome-centric metagenomics and stable isotope probing unveils the microbial pathways of aerobic methane oxidation coupled to denitrification process under hypoxic conditions.

Obligate aerobic methanotrophs have been proven to oxidize methane and participate in denitrification under hypoxic conditions. However, this phenomenon and its metabolic mechanism have not been investigated in detail in aerobic methane oxidation coupled to denitrification (AME-D) process. In this study, a type of hypoxic AME-D consortium was enriched and operated for a long time in a CH4-cycling bioreactor with strict anaerobic control and the nitrite removal rate reached approximately 50 mg N/L/d. Metagenomics combined with DNA stable-isotope probing demonstrated that the genus Methylomonas, which constitutes type I aerobic methanotrophs, was the dominant member and contributed to methane oxidation and partial denitrification. Metagenomic binning recovered a near-complete (98%) draft genome affiliated with the family Methylococcaceae containing essential genes that encode nitrite reductase (nirK), nitric oxide reductase (norBC) and hydroxylamine dehydrogenase (hao). Metabolic reconstruction of the selected Methylococcaceae genomes also revealed a potential link between methanotrophy and partial denitrification.