A pilot study of three-stage biological–chemical treatment of landfill leachate applying continuous ferric sludge reuse in Fenton-like process

• Published in: Clean technologies and environmental policy 2017-03, Vol.19 (2), p.541-551
• Main Authors: Klein, Kati, Kivi, Arthur, Dulova, Niina, Zekker, Ivar, Mölder, Erik, Tenno, Toomas, Trapido, Marina, Tenno, Taavo
• Format: Article
• Language: English
• Subjects: Activated sludge; Catalysts; Chemical oxygen demand; Chemical treatment; Combined treatment; Earth and Environmental Science; Efficiency; Environment; Environmental Economics; Environmental Engineering/Biotechnology; Environmental policy; Hydrogen peroxide; Industrial and Production Engineering; Industrial Chemistry/Chemical Engineering; Landfills; Leachates; Lignin; Nitrogen; Original Paper; Oxidation; Phenols; Pilot projects; Pollutants; Pretreatment; Reagents; Reuse; Sludge; Studies; Sustainable Development; Waste disposal sites; Waste treatment; Wastewater treatment; Water exchange; Water pollution treatment; Water treatment
• ISSN: 1618-954X; 1618-9558
• DOI: 10.1007/s10098-016-1245-5

This pilot study describes a three-stage continuous process for treating landfill leachate containing significant concentrations of recalcitrant organic substances. The proposed technological scheme consisted of an activated sludge pre-treatment combined with a Fenton-like process enhanced by continuous sludge reuse and followed by an activated sludge post-oxidation. Biological pre-treatment removed >99, 86, >99, 83 and 86 % of BOD 7 , COD, NH 4 + –N, phenols and the sum of lignin and tannins, respectively. Operational conditions in the ferric sludge-catalysed Fenton-like process stage were carefully adjusted in order to maintain the efficacy and practicability of combined treatment scheme. Although the application of ferric sludge as a catalyst in the Fenton-like oxidation reduced COD removal efficiency by 32 % as compared to the conventional Fenton process, lower process efficiency was compensated by reducing the water exchange ratio to 50 % without increasing the consumption of reagents. Moreover, an intermittent addition (added to every second treatment cycle) of fresh ferrous iron catalyst at a H 2 O 2 /Fe 2+ w/w ratio of 20/1 increased the BOD 7 /COD ratio from 0.04 to 0.32 and resulted in 60 % COD removal. A cyclic addition (added to every treatment cycle) of the same amount of catalyst increased the BOD 7 /COD ratio from 0.09 to 0.32, and a 10 % higher COD removal efficiency as compared to intermittent catalyst addition was achieved. Finally, biological post-treatment of the leachate resulted in more than 95 % removal of each measured parameter. Overall, the combined technological scheme with continuous ferric sludge reuse in the Fenton-like stage proved promising alternative for landfill leachate treatment.