Flocculating and dewatering of lake sediment: An in-situ pilot study comparing synthetic polymers and biopolymers for restoring lake water quality and reusing phosphorus

Dredging of lake sediment is a method to remove accumulated phosphorus and nitrogen in lakes and thereby reducing the risk of eutrophication. After dredging, the sediment is dewatered to reduce the volume. It is important to get a high dry matter content and ensure that the filtrate does not contain harmful compounds so it can be returned to the lake. A pilot-scale belt filter and flexible intermediate bulk containers (FIBC) were used for dewatering lake sediment with the sediment treated with a synthetic polymer or three different biopolymers. The goal of the study was to retain the phosphorus in the filter cake while returning the filtrate to the lake with a minimal phosphorus content. Results showed dry matter content of up to 16 % in the dewatered sediment and the sediment retained 96–99 % of the phosphorus. Furthermore, nitrogen was reduced by 27–71 % in the filtrate water. Toxicity tests found low ecotoxicity for most biopolymer filtrates, whereas synthetic polymer showed the highest potential ecotoxicity. Consequently, biopolymers provided satisfactory results, proving more environmentally friendly despite requiring longer filtration time.