Candidatus Accumulibacter phosphatis (Accumulibacter), which plays an important role in enhanced biological phosphorus removal in wastewater treatment plants, is phylogenetically classified into two major types (Types I and II). Phosphate concentrations affect the Accumulibacter community of the biomass enriched in treatment plants. Therefore, in the present study, Accumulibacter enrichments were conducted using a down-flow hanging sponge reactor under five conditions and a wide range of controlled phosphate concentrations in order to investigate how phosphate governs the community. We found that excessive phosphate levels inhibited Accumulibacter activity, that this inhibitory effect was greater for Type II. In addition, the affinity of Type II for phosphate was higher than that of Type I. Type IIA-B dominated at a phosphate concentration less than 5 mg P L−1, while Type IA was dominant at 50 and 500 mg P L−1. These patterns of enrichment may be explained by an inhibition kinetics model.

A combination of upflow anaerobic sludge blanket (UASB) and downflow hanging sponge (DHS) reactor has emerged as an interesting alternative wastewater treatment process. The combined system not only exhibited good organic removal performance in pilot scale experiment, moreover, several studies in the last decades also showed the good efficiency and robustness of DHS reactor in full-scale operation for wastewater treatment. This paper provides a review on the basic concept, historical process development and application of the DHS reactor for wastewater treatment. Over twenty-year development of DHS technology suggests that DHS reactor had become a viable alternative not only solving the sanitation problems in developing countries but also great further potential development in the field of resources recovery technologies from wastewater.

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