Formation characteristics of an anoxygenic photosynthetic bacterial biofilm in a photorotating biological contactor for azo dye wastewater treatment

Abstract

BACKGROUND: Most photobioreactors used for wastewater treatment with anoxygenic photosynthetic bacteria (APB) are based on suspended cultures because APB have poor biofilm-forming ability. In this study, a photo-rotating biological contactor (PRBC) was applied for the culture of APB biofilm using azo wastewater, with a particular emphasis on the formation of APB biofilm and its relationship to other microorganisms and exopolysaccharides (EPS). RESULTS:The PRBC was successfully used for the cultivation of APB biofilm and in the removal of chemical oxygen demand and color. In situ analysis showed that APB biofilm formation can be divided into two distinct stages: development and differentiation. In the development stage, nonphotosynthetic filamentous microorganisms initially proliferated on a disc surface and promoted the adherence of APB. In the differentiation stage, filamentous microorganisms and their EPS matrices caged APB in the inner layer and stabilized the APB biofilm. During biofilm stratification, the biofilm biomass and APB numbers reached 24.2 ± 0.63 g L −1 and 4.8 ± 0.6 × 10 8 CFU (g dry biofilm) −1 , respectively. The dominant APB in the mature biofilm were identified as Rhodopseudomonas, Rhodomicrobium, and Chlorobium. CONCLUSION: APB with poor biofilm-forming ability formed a stable biofilm in the PRBC with the aid of nonphotosynthetic microorganisms. Light microscopy and SEMBiofilm samples were carefully collected from the disc surface in PRBC, and the outer and inner layers of the biofilm were separated and observed using a light microscope (Olympus BX50, Japan). For

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“…When the feed composition is located on the right side of both azeotropic points (segment III in Figure ), the situation is reversed; the feasible sequence changes to the low–high-pressure sequence, and the high–low-pressure sequence becomes unfeasible due to the uncross of composition profile. When the feed composition is located between both azeotropic points (segment II in Figure ), both separating sequences (the low–high-pressure and high–low-pressure sequences) are feasible, and rigorous comparisons are needed before concluding which one is better …”

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