Methanogenic activities of sulfide and nitric oxide amended mesophilic, methanogenic culture: role of nitrososufides complex

Genomic studies on natural and engineered aquatic denitrifying eco-systems: A research update

Excess nitrogenous compounds in municipal or industrial wastewaters can stimulate growth of denitrifying bacteria, in return, to convert potentially hazardous nitrate to inorganic nitrogen gas. To explore the community structure, distributions and succession of functional strains, and their interactions with other microbial communities, contemporary studies were performed based on detailed genomic analysis. This mini-review updated contemporary genomic studies on denitrifying genes in natural and engineered aquatic systems, with the constructed wetlands being the demonstrative system for the latter. Prospects for the employment of genomic studies on denitrifying systems for process design, optimization and development of novel denitrifying processes were discussed.

The bio-chemical cycle of iron and the function induced by ZVI addition in anaerobic digestion: A review

Zero-valent iron (ZVI) is known to be an additive in facilitating waste treatment and improving biogas production in anaerobic digestion (AD) systems. This review concentrates on the chemical cycle of iron as well as the function of the iron cycle in the removal of four kinds of pollutants: organic carbon, nitrogen, sulphur and phosphorus, which are commonly encountered in waste treatment. In recent studies, the addition of ZVI to an AD system promoted the in-situ production of CH₄ from CO₂, enabling carbon capture through biotechnology. Additionally, using iron-carbon microbial electrolytic cells in AD systems in order to accelerate electron transport, as well as specific pollutant degradation mechanisms, are illustrated in the present study. Particularly, the main factors affecting the removal efficiency of contaminants in a ZVI-AD system such as pH, VFA/ Alkalinity (ALK), oxidation-reduction potential and particle size are reviewed. According to the above characteristics, combined with technical model and economic analyses, an AD system based on ZVI was considered to be an economical, efficient and carbon-neutral pollutant treatment technology. Accordingly, Iron-based AD is suggested to be a promising and sustainable approach orientated to a circular economy, which may be applied to many waste treatments fields.

Denitrifying sulfide removal and nitrososulfide complex: Azoarcus sp. NSC3 and Pseudomonas sp. CRS1 mix

Denitrifying sulfide removal (DSR) process simultaneously removes nitrate, sulfide and organic matters in the same reactor. This study applied Azoarcus sp. NSC3 and Pseudomonas sp. CRS1 mix for DSR tests in autotrophic, heterotrophic and mixotrophic growths. Negligible NO-compounds were noted in heterotrophic or mixotrophic growths, while most cells were damaged and bound with NO-compounds in autotrophic growth. Nitroprusside (SNP) ions were applied as model compound to reveal the formation of nitrososulfide complex (RSNO) by nitroso (NO(+)) and excess sulfide (S(2-)), rather than the previously proposed mechanism by direct reaction between nitric oxide (NO) and S(2-). We speculated that RSNO was then abiotically decomposed to NO and elemental sulfur in the presence of biological cells. A revised nitrogen cycle considering interactions with sulfur compounds was proposed. We also speculated that SNO and NO were inhibitory to the functional strains, whose efficient removals were essential to reach high-rate DSR performance.

Denitrifying sulfide removal by enriched microbial consortium: kinetic diagram

Denitrifying sulfide removal (DSR) process simultaneously removes nitrate, sulfide and organic matters in the same reactor. This study isolated eight DSR strains and composed a microbial consortium to reveal the stoichiometry and kinetics of autotrophic, heterotrophic and mixotrophic denitrification (DSR). A novel kinetic diagram based on mass and electron balances was proposed to graphically interpret the system kinetics and identify the accessible regime where DSR reactions can be applied. Demonstration of the use of the proposed diagram showed the easy assessment of DSR system performance by the status on the diagram.