Dipesh Das

Date of Award

January 2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

First Advisor

Charles Moretti

Abstract

The Grand Forks Waste Water Treatment Plant (GFWWTP) is currently sending its waste activated sludge (WAS) from the activated sludge treatment process to an existing on-site wastewater treatment lagoon which has been in operation since 2003. The plant produces approximately 65,000 gallons of WAS per day. Because of this high level of loading, the existing lagoon system is no longer considered as a treatment option for the produced sludge. The Plant Authority is trying to find a sustainable solution for sludge disposal and for this reason the GFWWTP is interested in introducing screw press system for the dewatering process. As a part of this upgrade plan, the existing lagoon will be decommissioned. Biosolids from this lagoon will be dewatered and will be used beneficially. Polymers are used for coagulating sludge solid particles for better dewatering and bear a major part of cost associated with the dewatering process. So, choice of the appropriate polymer for dewatering and determining the optimum dose is very important from an economic point of view. Two bench top tests- Time to filter (TTF) and Air Pressure Cell Test were performed for determining the best usable polymer and optimum polymer dose. Polymers of four cationic concentrations(C 6210, C 6237, C 6257 and C 6285) were used as polymer samples. Sludge samples were collected from the Primary Cell 2 (PC2). From both test results, it was determined that C 6257 with cationic concentration of 50% is the best usable polymer out of the four. From these tests it was recommended that polymer concentration of 0.1% and solid concentration of 4.5~5.5% be used while dewatering sludge obtained from decommissioned lagoon. Polymer required from TTF test was 7.5~8.5 lbs/dry ton of solids and 4~5.5 lbs/dry ton on solids for air pressure cell test. Maximum cost for polymer associated with decommissioning of PC2 was estimated to be approximately 1.1 million USD.

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