Analysis of particle size distribution of organic carbon for landfill leachate-implications for sustainable treatment

BACKGROUND: Landfill leachate has a complex composition requiring experimental support to formulate a sustainable treatment strategy. This study utilized the particle size distribution (PSD) of the chemical oxygen demand (COD) content to assess the profile of biodegradable and inert COD fractions; it also emphasized the functions and benefits of ultrafiltration and nanofiltration modules coupled to an activated sludge process. The evaluation profited from the field data of a landfill site in Istanbul, where the leachate was actually treated in a membrane bioreactor (MBR) plant. RESULTS: COD and total nitrogen levels fluctuated between 10 100-31 200 mg L-1 and 1150-2800 mg L-1, respectively. PSD analysis for COD, conducted at two extremes, displayed similar results, where the majority of the COD was observed to accumulate at the low extremity of the particle size, 70-72% below 2 nm. Therefore, direct membrane filtration of leachate yielded low COD removals that were limited to 9% with ultrafiltration and to 31-35% with nanofiltration. COD fractionation indicated a ratio of 5% for the inert COD in leachate. The permeate COD of ultrafiltration in the existing plant was 2000 mg L-1, much higher than the inert fraction ratio, which was further reduced to 266 mg L-1 by nanofiltration. CONCLUSION: PSD analysis was an integral complement of respirometry for establishing the size-biodegradation relationships of different COD fractions. It located the majority of soluble COD fractions below 0.55 nm, thus implying the necessity of a biological process. PSD also identified the generation of soluble residual metabolic products, indicating that residual COD escaping treatment would be equally significant to the removal potential of the biodegradable substrate. (c) 2023 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).