Enhanced chromium and nitrogen removal by constructing a biofilm reaction system based on denitrifying bacteria preferential colonization theory.

Understanding the developmental characteristics of microbial communities in biofilms is crucial for designing targeted functional microbial enhancements for the remediation of complex contamination scenarios. The strong prioritization effect of microorganisms confers the ability to colonize strains that arrive first dominantly. In this study, the auto-aggregating denitrifying bacterial Pseudomonas stutzeri strain YC-34, which has both nitrogen and chromium removal characteristics, was used as a biological material to form a stable biofilm system based on the principle of dominant colonization and biofortification. The effect of the biofilm system on nitrogen and chromium removal was characterized by measuring the changes in the quality of influent and effluent water. The pattern of biofilm changes was analyzed by measuring biofilm content and thickness and characterizing extracellular polymer substances (EPS). Further analysis of the biofilm microbiota characteristics and potential functions revealed the mechanism of strain YC-34 biofortified biofilm. The results revealed that the biofilm system formed could achieve 90.56% nitrate-nitrogen removal with an average initial nitrate-nitrogen concentration of 51.9 mg/L and 40% chromium removal with an average initial hexavalent chromium Cr(VI) concentration of 7.12 mg/L. The biofilm properties of the system were comparatively analyzed during the biofilm formation period, the fluctuation period of Cr(VI)-stressed water quality, and the stabilization period of Cr(VI)-stressed water quality. The biofilm system may be able to increase the structure of hydrogen bonds, the type of protein secondary structure, and the abundance of amino acid-like components in the EPS, which may confer biofilm tolerance to Cr(VI) stress and allow the system to maintain a stable biofilm structure. Furthermore, microbial characterization indicated an increase in microbial diversity in the face of chromium stress, with an increase in the abundance of nitrogen removal-associated functional microbiota and an increasing trend in the abundance of nitrogen transfer pathways. These results demonstrate that the biofilm system is stable in nitrogen and chromium removal. This bioaugmentation method may provide a new way for the remediation of heavy metal-polluted water bodies and also provides theoretical and application parameters for the popularization and application of biofilm systems.

Efficacy of auto-aggregating aerobic denitrifiers with coaggregation traits for bioaugmentation performance in biofilm-formation and nitrogen-removal.

To promote efficiency nitrogen-rich wastewater treatment from a sequencing batch biofilm reactor (SBBR), three aerobic denitrifiers (Pseudomonas mendocinaIHB602, Methylobacterium gregansDC-1 and Pseudomonas stutzeriIHB618) with dual-capacities of strong auto-aggregation and high nitrogen removal efficiency were studied. The aggregation index analysis indicated that coaggregation of the three strains co-existed was better when compared with one or two strains grown alone. Optimal coaggregation strains were used to bioaugmente a test reactor (SBBRT), which exhibited a shorter time for biofilm-formation than uninoculated control reactor (SBBRC). With different influent ammonia-N loads (150, 200 and 300 mg·L-1), the average ammonia-N and nitrate-N removal efficiency were all higher than that in SBBRC, as well as a lower nitrite-N accumulation. Microbial community structure analysis revealed coaggregation strains may successfully colonize in the bioreactor and be very tolerant of high nitrogen concentrations, and contribute to the high efficiency of inorganic nitrogen-removal and biofilm-formation.

[Sexual reproduction of Filinia longiseta in Jinghu Lake of Wuhu City].

From May to November 2004, the sexual reproduction of Filinia longiseta in two areas of Jinghu Lake was studied, with its relations to the population density of F. longiseta and to the water temperature, Chl-a concentration, Secchi's disc reading, and total density of rotifers examined. The results showed that no mictic F. longiseta females were detected till the water temperature was up to 22 degrees C or the Secchi's disc reading was <95 cm in small area and <100 cm in large area. The sexual reproduction of F. longiseta occurred when its population density was > 122 ind . L(-1) and >113 ind . L(-1) in small and large areas, respectively. The density of mictic F. longiseta females was positively correlated to the population density of F. longiseta and the total density of rotifers (P <0. 01), but no significant relationships were observed between the mictic F. longiseta females density and the water temperature, Chl-a concentration and Secchi's disc reading. All the test affecting, factors had no significant effects on F. longiseta mictic and fertilization rates. The sexual reproduction of F. longiseta occurred in the early phase of population growth cycle, and the mictic F. longiseta females were produced in the patterns of punctuation and multi cycles. The maximal mictic rate occurred with the occurrence of maximal population density, while the maximal fertilization rate occurred by the end of population growth cycle.