The influence of nitrogen and sludge age change in reactor performance and biopolymer production in activated sludge

Abstract

This study investigated the influence of nitrogen and sludge age change in reactor performance and biopolymer production in activated sludge systems. The qualitative and quantitative analyses of the naturally occurring biopolymers were performed and the results were correlated to sludge a settling characteristic and effluent quality.

In order to obtain the sludge samples for the analyses, two completely mixed, continuous flow activated sludge systems were maintained during this research. Raw wastewater from the Celanese Fiber Plant located at Narrows, Virginia was utilized as the influent. Nitrogen was added in the feed solution as ammonium sulfate. The sludge age was changed from ten to five days for both systems.

Biopolymers were extracted from the sludge floc matrix using pH-adjustment technique followed by centrifugation. The total biopolymer contents were analyzed for protein and carbohydrate concentrations. High molecular weight biopolymers were also analyzed following gel filtration. The sludge settling characteristics were measured in terms of Sludge Volume Index and effluent quality in terms of effluent turbidity.

The results indicated that the relationship between total biopolymer concentrations and sludge settling characteristics is culture specific. No consistent relationship was observed between total biopolymer concentrations and effluent turbidity and/or SVI.

Additional nitrogen in a reactor system promoted production of high protein content biopolymers. However, no significant improvement in effluent quality of the reactor was noticed by the additional nitrogen. Deficiency of nitrogen in a reactor system promoted the production of high carbohydrate content biopolymers. The high concentration of carbohydrate biopolymers seemed to correspond directly to the high effluent turbidity.