Preliminary study of a suspended growth predenitrification system

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Abstract
A laboratory study has been conducted to obtained preliminary process information of a suspended growth Predenitrification (SGPDN)system. System performance was evaluated, in terms of chemical oxygen demand (COD) removal, NH3–N removal, system biomass yield and inventory, and effluent qualities, at different solids retention times (SRTs) and recycle ratios. Chemical oxygen demand removal in an SGPDN system occurs mainly in the anoxic reactor, which accounts for 94% of total COD removal. The overall COD removal rate is independent of recycle ratio (ranging from 2–5) used in this study; however, effluent COD increase with increasing recycle ratio. The observed anoxic and aerobic COD removal rates decrease with increasing SRT. The NH3–N removal in an SGPDN system is induced by two mechanisms: assimilatory NH3–N requirement for biomass production in the anoxic reactor and nitrification in the aerobic reactor. The observed anoxic NH3–N removal rate relates directly to the anoxic COD removal rate and agrees fairly well with the assimilatory NH3–N requirement theoretically predicted. The overall NH3–N removal rate is independent of SRTs and recycle ratios used in this study. Biomass yield in an SGPDN system occurs mainly in the anoxic reactor. However, uniform distribution of biomass throughout the entire system is obtained because of the high recycle rate used. The observed biomass yield (YO) decreases with increasing STR. Tertiary treatment efficiency can be achieved in an SGPDN system. More than 90% reduction in feed COD., feed NH3–N, and NO2 + NO3–N is obtained at all SRTs and recycle ratios used in this study. Higher MLVSS loading rates can be applied to a final clarifier without impairing its separation efficiency because of the excellent settleability of the Predenitrification activated sludge.

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