The results shown that at DO higher than mg/L, COD and TN removal efficiencies were higher than 90 % and 60 %, respectively. However, low DO (less than mg/L) lead to poor sludge flocculation which deteriorate the membrane filterability. The TMP increased dramatically at different DO levels. | Vietnam Journal of Science and Technology 55 (4C) (2017) 251-257 STUDY ON LEACHATE TREATMENT AFTER ELECTROCOAGULATION PROCESS BY BIO-FILTER SYSTEM: A CASE STUDY IN NAM SON LANDFILL, HA NOI Le Cao Khai1, *, Le Thanh Son2, Trinh Van Tuyen2, Doan Thi Anh2 1 Department of Chemistry, Hanoi Pedagogical University Number 2, 32 Nguyen Van Linh, Phuc Yen, Vinh Phuc 2 Institute of Environmental Technology, VAST, 18 Hoang Quoc Viet, Cau Giay, Ha Noi * Email: lecaokhaimt@ Received: 30 June 2017; Accepted for publication: 17 October 2017 ABSTRACT One of the major pollution issues caused by the municipal solid waste landfill is leachate, which creates a huge risks to contaminate groundwater, surface water as well as surrounding land quality. The leachate of Nam Son landfill contains high concentrations of pollutants such as COD, BOD5, NH4+-N. Hence, this study focused on setting up a bio-filter system and investigating its performance on Nam Son landfill leachate after pre-treatment by electrocoagulation (EC). The characteristics of raw leachate for bio-treatment were as following: pH = - , COD = 1391 – 1492 mg/L, NH4+-N = 661 - 818 mg/L. The experimental system was set up with use volume of 20 lit (dimension: l = m, w = m and h = m) in conditions: room temperature (25-32oC) flow rate from 2 – 6 L/day, bio-media had a specific surface of 200 m2/m3. The experimental results were found that COD treatment efficiency from 78–96 % with input COD load from – kg/m3/day. The NH4+-N treatment efficiency from 98– % with input NH4+-N load from ÷ kg/m3/day. The research results indicated that the leachate treatment by combination of electrocoagulation and bio-filter system can promise as a potential method in practice. Keywords: bio-filter, leachate, NH4+-N treatment, COD treatment. 1. INTRODUCTION Landfilling is one of the most popular methods of municipal solid waste disposal because of its relative simplicity and low cost [1]. .