Dimorphism of Candida tropicalis and its effect on nitrogen and phosphorus removal and sludge settleability.

Candida tropicalis PNY, a novel dimorphic strain with the capacity of simultaneous carbon, nitrogen and phosphorus removal in anaerobic and aerobic conditions, was isolated from activated sludge. Dimorphism of C. tropicalis PNY had effect on removing nitrogen and phosphorous and slightly affected COD removal under aerobic condition. Sample with high hypha formation rate (40 ± 5%) had more removal efficiencies of NH4+-N (50 mg/L) and PO43--P (10 mg/L), which could achieve 82.19% and 97.53%, respectively. High hypha cells dosage exhibited good settleability and filamentous overgrowth was not observed. According to label-free quantitative proteomics assays. Up-regulated proteins involved in the mitogen-activated protein kinase (MAPK) pathway indicated the active growth and metabolism process of sample with high hypha formation rate (40 ± 5%). And proteins concerning about glutamate synthetase and SPX domain-contain protein explain for the nutrient removal mechanism including assimilation of ammonia and polyphosphates synthesis.

Advanced simultaneous nitrogen and phosphorus removal for non-sterile wastewater through a novel coupled yeast-sludge system: Performance, microbial interaction, and mechanism.

A novel coupled yeast-sludge system (CYSS) was constructed by the yeast Candida sp. PNY integrated with activated sludge to treat non-sterile mainstream wastewater. After 240-day cultivation, compared with single activated sludge, simultaneous removal efficiency of total organic carbon (TOC), nitrogen and phosphorus increased by 19.5% (176.34 mg TOC g-1 d-1), 21.3% (11.25 mg TN g-1 d-1) and 15.0% (6.95 mg TP g-1 d-1), respectively, while the amount of sludge reduced by 50%. Amplicon sequencing analysis showed that the abundance of Nitrosomonas, Nitrospira, Zoogloea, Dechloromonas, and Candidatus Accumulibacter significantly decreased to 0% on Day 200. Abundance of nirS and nirK for denitrification significantly decreased in CYSS by quantitative PCR (qPCR), and the copies of nirS and nirK were 3.37-fold and 1.71-fold decrease from Day 0 to Day 240, respectively. The results of Fluorescence in situ hybridization and co-occurrence network showed that Candida sp. PNY predominated its distribution in CYSS, and strongly connected with environmental variables based on network analysis. Furthermore, this study reconstructed the carbon, nitrogen and phosphorus metabolic pathways of the CYSS based on metagenomics.

High-concentration COD wastewater treatment with simultaneous removal of nitrogen and phosphorus by a novel Candida tropicalis strain: Removal capability and mechanism.

Aerobic and anaerobic continuous stirred-tank reactor (CSTR), up-flow anaerobic sludge blanket (UASB) were set up and inoculated with newly isolated Candida tropicalis. Reactors were operated at high concentrations of chemical oxygen demand (COD) (8000 mg/L), the modified UASB expressed better COD removal rate simultaneously removal of nitrogen and phosphate than other two reactors. Notably, under both aerobic or anaerobic conditions, large amounts of organic acids and alcohol were generated. Transcriptomic analysis showed that carbon metabolism under anaerobic conditions shared the same pathway with aerobic conditions by regulating and inhibiting some functional genes. Experiments utilizing different carbon sources proved that our strain has excellent performances in utilizing organic materials, which were verified by transcriptomic analysis. Finally, the strain was applied to treat four types of sugar-containing wastewaters. Among them, our strain exerts the best removal capability of COD (90%), nitrogen (89%), and phosphate (82%) for brewery wastewater.

Candida tropicalis prompted effectively simultaneous removal of carbon, nitrogen and phosphorus in activated sludge reactor: Microbial community succession and functional characteristics.

A new Candida tropicalis that simultaneously remove nitrogen and phosphorus, and degrade organic matters was isolated. Three continuous stirred tank reactors inoculated with C. tropicalis, activated sludge, and their co-existing system in aerobic condition were operated for 150 days. Results demonstrated that the inoculation of C. tropicalis in the co-existing system remarkably improved the carbon, nitrogen, and phosphorus removal efficiencies. The co-existing system had increased carbon, nitrogen, and phosphorus removal efficiencies (92%, 73%, and 63%, respectively); decreased biomass (reduced from 1200 mg/L to 500 mg/L); and C. tropicalis as the dominant strain. The relative abundance of traditional nitrogen- and phosphorus-removing microorganisms, such as Mycobacterium, Flavonifactor, and Devsia, increased in the co-existing system. Metagenomic analysis showed that the presence of the PCYT2, EPT1, and phnPP genes and more complexed metabolism pathways in the co-existing system might be responsible for the more activated metabolism process.

N-doped biochar from sewage sludge for catalytic peroxydisulfate activation toward sulfadiazine: Efficiency, mechanism, and stability.

Sewage sludge-derived biochar (SBC) could remove organic contaminants in environment and reuse the sludge effectively. In this study, urea-doped SBC (NSBC) was prepared, characterized, and applied as heterogeneous catalytics to peroxydisulfate (PDS) activation. Sulfadiazine (SD), a widely used antibiotic, was used as a model pollutant to evaluate the efficiency and mechanism of this system. The degradation rate of SD increased to 100% after 4 h when 1 g/L of NSBC was added to the system with a SD concentration of 20 mg/L. In this study, it was confirmed that there were two important pathways in the degradation of SD by NSBC/PDS system: the free radical on the surface of NSBC and the nonradical (1O2) in the solution. The doping of N atoms makes neighboring C atoms positively charged, thereby making the direct transfer of electrons with S2O82- and the generation of 1O2 via nonradical pathway easy. In addition, the CO functional group formed during the pyrolysis of NSBC can produce 1O2 in a similar way. A total of 22 SD degradation products were identified, and 4 possible pathways were proposed. This study provide supplement for the degradation mechanism of organic compounds by carbon-based materials.

Triclosan in contact with activated sludge and its impact on phosphate removal and microbial community.

Triclosan (TCS) is applied in a wide range of pharmaceutical and personal care products to prevent or reduce bacterial growth. In this study, the effects of TCS on phosphate removal and bacterial community shifts of activated sludge, especially on functional bacteria variation, were investigated. Compared with the control group (R-control), the treatment group (R-TCS) with 100 µg/L TCS inhibited the microbial growth. In addition, the phosphorus removal efficiency of PO43--P and total phosphorus removal rates declined by 15.99% and 7.81%, respectively. Proteobacteria gradually dominated the microorganisms. The growths of Proteobacteria and Bacteroidetes were inhibited when 150 µg/L of TCS was added. Moreover, the differences in the microbial community structures of the R-control and R-TCS groups gradually expanded, no obvious difference was observed in the final stage, and the interrelationships of microbes in the latter weakened. The long-term addition of TCS impairs the growth of polyphosphate-accumulating organisms (PAOs).