Chen, Si (2015)

Theme

Evaluating the performance of blending raw sludges by variable application of flocculation agents

Subject

The thickening of raw sludges (i.e. primary sludge, waste activated sludge) is an important process of sludge treatment in a waste water treatment plant especially by operating a digestion according to heat transfer and residence time. It is most common to use filter belts for thickening waste activated sludge. For decreasing the solids of the sludge the usage of polymeric flocculants is necessary. The subject of this study is to optimize the process of thickening by blending primary sludge and waste activated sludge.

The graduating student is assigned to the task of designing the experimental setup in the lab, executing the experiments and evaluating the results. This includes the development of a method to compare the results of different investigations according to the variation of the ratio between primary sludge and waste activated sludge and the application of different flocculation agents. Additionally the impact of changing operation parameters, i.e. the specific amount of chemicals and the concentration of the solution of the flocculation agent, have to be determined. The graduating student has to identify the best application of conditioning the blended sludges. Based on these results digestion investigations have to be realized to describe the dewatering behavior of the conditioned sludges.

Abstract

The objective of this study was a basic evaluation of several polymers as flocculation agents used in wastewater treatment plant and determining their effectiveness in conjunction with different blends of raw waste activated sludge and primary sludge. Total dry solids content is one of the initial parameters which should be considered during the study. Results of settling and filtration experiments on a lab-scale were used to determine thickening efficiency as well as optimal flocculant dosages. Furthermore, the final supernatant or filtrate turbidity was determined as an indicator of suspended solids remaining in the liquid phase.

The performance of some polymers used as coagulants in flocculation processes of wastewater treatment plants were experimentally investigated. The complex polymers were prepared with the commercially available products Praestol K222 L, Praestol 822 BS, Praestol 835 BS, Praestol 855 BS and Praestol 857 BS. The flocculation process was studied for the primary and waste activated sludge of the wastewater treatment plant in Dresden, Germany. Different polymer types showed various performance results with regards to the settling velocity, sludge volume and specific resistance to filtration.

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