Available online at www.sciencedirect.com Journal of Hazardous Materials 158 (2008) 157–163 COD fractions of leachate from aerobic and anaerobic pilot scale landfill reactors M. Sinan Bilgili ∗ , Ahmet Demir, Ebru Akkaya, Bestamin Ozkaya Yildiz Technical University, Environmental Engineering Department,34349 Be¸ sikta¸ s, Istanbul, Turkey Received 4 April 2007; received in revised form 23 November 2007; accepted 18 January 2008 Available online 26 January 2008 Abstract One of the most important problems with designing and maintaining a landfill is managing leachate that generated when water passes through the waste. In this study, leachate samples taken from aerobic and anaerobic landfill reactors operated with and without leachate recirculation are investigated in terms of biodegradable and non-biodegradable fractions of COD. The operation time is 600 days for anaerobic reactors and 250 days for aerobic reactors. Results of this study show that while the values of soluble inert COD to total COD in the leachate of aerobic landfill with leachate recirculation and aerobic dry reactors are determined around 40%, this rate was found around 30% in the leachate of anaerobic landfill with leachate recirculation and traditional landfill reactors. The reason for this difference is that the aerobic reactors generated much more microbial products. Because of this condition, it can be concluded that total inert COD/total COD ratios of the aerobic reactors were 60%, whereas those of anaerobic reactors were 50%. This study is important for modeling, design, and operation of landfill leachate treatment systems and determination of discharge limits. © 2008 Elsevier B.V. All rights reserved. Keywords: Landfill; Leachate; Soluble substrate; COD fractions; Inert COD 1. Introduction Sanitary landfilling plays an important role in solid waste management of various countries in the world. One of the main problems with regard to the operation of sanitary landfill is the difficulty in managing the resulting leachates, which are complex and highly contaminated wastewaters [1,2]. Landfill leachate is characterized by its generation rate and composition, both of which are affected by the age of the landfill site. In par- ticular, leachate composition and characteristics strictly depend upon various factors such as waste type, climate, organic mat- ter content, landfill hydrogeological structure, and operational conditions [3–7]. Leachate consists of many different organic and inorganic compounds that may be either dissolved or suspended and which are biodegradable and non-biodegradable [8]. In addition to this, ∗ Corresponding author. Tel.: +90 212 259 70 70x2730; fax: +90 212 261 90 41. E-mail addresses: mbilgili@yildiz.edu.tr (M.S. Bilgili), ahmetd@yildiz.edu.tr (A. Demir), ekoca@yildiz.edu.tr (E. Akkaya), bozkaya@yildiz.edu.tr (B. Ozkaya). the characteristic of the leachate varies with regard to its com- position and volume, and biodegradable matter present in the leachate with time [9–11]. For this reason, young and old landfill leachates have very different features. Calace et al. [12] reported that the young landfill leachate fractions have low molecular weight distributions (<500 Da) at the rate of 70%, while the high molecular weight distribution (>10,000 Da) is 18%. Besides, the low and high molecular weight distributions are 28 and 67%, respectively, in old landfill leachate samples. According to this result, easily biodegradable components of leachate reduce, and constituents having high molecular weights and that are non- biodegradable increase in the course of time. These factors make leachate treatment difficult and these factors needed to be taken into account when different treatment processes are considered. The treatment requirements for leachate from sanitary landfills can vary depending on the discharge limits and contaminants present. An effective method for the treatment of leachate is recirculation through the landfill. When leachate is recirculated, the constituents attenuated by biological activity and by other chemical and physical reactions occur within the landfill. At present, collection and treatment of landfill leachates are issues surrounding the operation of landfill sites [13,14]. The 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.01.055