Evaluation of the quality of drainage sludge in To Lich River basin and the proposal of suitable management solutions

Abstract

This study aims to examine the characteristics and to assess the hazardous level as well as the reusability of sewage sludge and river sediment from To Lich River (TLR) basin, which is the largest wastewater catchment in Hanoi. Sludge samples were collected from six manholes along Tran Binh Trong (TBT) and Thai Ha (TH) sewers in rainy and dry seasons. Sediment samples were collected from seven sites near principal wastewater and storm water discharging points along TLR upstream in dry season. Parameters, such as pH, humidity, total ash, zinc (Zn), copper (Cu), lead (Pb), and cadmium (Cd) in sewage sludge were examined. Trace metals in TLR sediment, e.g. arsenic (As), mercury (Hg), lead (Pb), zinc (Zn), chromium (Cr), and cadmium (Cd) were analyzed. The results of sludge and sediment analysis were then compared with national environmental regulations for hazards and aquatic life preservation, and land use purposes, including QCVN 43:2012/BTNMT, QCVN 50:2013/BTNMT, QCVN 03-MT: 2015/BTNMT. The majority of examined parameters of sewage sludge, except ash content, are higher in dry seasons than in rainy seasons. Regarding hazardous level, all the investigated heavy metals in sewage sludge in dry and rainy seasons, respectively, as followings: 644 and 598 mg.kg-1 Zn, 146.5 and 127.3 mg.kg-1 Cu, 71.2 and 69.5 mg.kg-1 Pb, and 1.51 and 1.46 mg.kg-1 Cd, are below the legislated thresholds, thus, can be considered as nontoxic. Reusability of sewage sludge, however, should be considered since Zn exceeded permissible values for all of land use purposes. The concentration of As (0.659 mg.kg-1), Hg (0.03 mg.kg-1), Pb (4.07 mg.kg-1), Zn (81.3 mg.kg-1), and Cd (0.078 mg.kg-1) meets national standards on hazardous waste, and sludge from water treatment process, as well as to protect aquatic life and to be reused in anthropogenic activities. However, Cr concentration (157 mg.kg-1) is above those legislated thresholds, thus, unsuitable to be reused as land or fertilizer. With high concentration of several trace metals and humidity, drainage sludge from TLR basins should be treated to improve its reusability.
 Article history: Received 20 March 2018, Revised 05 April 2018, Accepted 27 April 2018