Removal and Transformation of Pollutants in a Two-Line Denitrifying Phosphorus Removal Process Treating Low C/N Municipal Wastewater: Influence of Hydraulic Retention Time

Abstract

A two-line denitrifying phosphorus removal process (2L-DPR) was established treating low C/N municipal wastewater efficiently in our previous studies, while hydraulic retention time (HRT) is one of the most important factors determining the substrate loading, contact time for biomass, and pollutants and further affect performance of the whole system. Removal and transformation mechanism of organic carbon (C), nitrogen (N), and phosphorus (P) were investigated together with mass balance under various HRTs (6, 9, and 18 h) in the established 2L-DPR process. The results showed that in anaerobic units, the concentration of the main storage products in activated sludge such as poly-hydroxyvalerate (PHV) and poly-hydroxybutyrate (PHB) at HRT of 9 h was higher than that under other HRTs. The highest TN and TP removal efficiency was also achieved under the HRT of 9 h with removal rates of 55.9% and 84.6% respectively. Increasing HRT from 6 to 9 h greatly enhanced TN removal in anoxic and aerobic units; however, HRTs had little influence on COD removal with effluent concentration of 48.6, 49.1, and 48.9 mg/L, respectively. HRT affected phosphorus up-taken in anoxic and aerobic units rather than on the release of phosphorus processes in anaerobic units.

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