DEWATERING OF URBAN LAKE SEDIMENTS USING CONSTRUCTED WETLANDS: A CASE STUDY IN HANOI, VIETNAM

Abstract

Over the past two decades, the large volume of dredged sediments with high water content from urban lakes pressurize the landfill site's area requirements and environmental sanitation in Hanoi, Vietnam. This paper evaluated the dewatering efficiency of sludge treatment wetlands (STW) with or without Cyperus alternifolius and aeration for dredged sediments from Bay Mau Lake (Hanoi). Three pilots simulated different conditions of STWs were conducted in the batch condition, pilot-scale within six months. The supernatant and leachate volumes were recorded daily, while sludge samples were collected from different sludge depths twice per month. Characteristics of sludge samples, including water contents (WC), total solids (TS), and the ratio of volatile solids to dry solids (% VS/DS), were analyzed to assess dewatering efficiency over time and end of experiments. Plant height and biomass were measured before vegetation and after harvesting to evaluate the growth of C.alternifolius in the sediment matrix. The optimum result was obtained in the aerated planted wetland with WC, sludge volume reduction, TS, and VS/DS of 36.2%, 33.6%, 63.8%, and 6.5%, respectively. After the adaptation period, C.alternifolius grew well and contributed to the dewatering process in STWs. Those results implied the possibility of using STWs for urban lake sediment treatment with C.alternifolius, aeration, and batch condition.