title: Subcritical water treatment of landfill leachate: application of response surface methodology.
abstract: BACKGROUND
  Leachate is the liquid formed when waste breaks down in the landfill and water filters through that waste. This liquid is highly toxic and can pollute the land, ground water and water ways. It is mandatory for landfills to protect against leachate in most countries worldwide. Controlling the pollutant loading, means reducing its quantity by containing or treating the waste to comply with certain discharge characteristics which are compatible with the receptor medium.
  
  
  OBJECTIVE
  This paper describes the reduction of the organic load of a mature landfill leachate using a novel experimental set-up that employs hydrogen peroxide under subcritical conditions and aims to establish this method as an effective alternative to currently used options. Response surface methodology was applied to optimize the treatment process and determine which of the following there parameters - temperature, residence time and hydrogen peroxide concentration - played the most important role.
  
  
  METHODS
  The method employed is based on the use of laboratory-scale, stainless steel reactors, filled with the leachate and appropriate quantities of hydrogen peroxide. Under subcritical conditions (temperature in the range of 100-374 °C and enough pressure to maintain the liquid state of water), hydrogen peroxide produces hydroxyl radicals which are highly reactive and oxidize the organic molecules of the leachate.
  
  
  RESULTS
  The highest COD decrease of 85% was experimentally observed at 300 °C, 500 mM H2O2 and 180 min residence time. It was determined that the combination of oxidant concentration and temperature is the rate-determining factor, whereas residence time has a lesser effect on the process.
  
  
  CONCLUSIONS
  A simple, quick, effective and environmentally-friendly method for the treatment of the organic load of landfill leachate was developed and optimized at laboratory scale.
authors.affiliation: Department of Environmental and Natural Resources Engineering, School of Applied Sciences, Technological and Educational Institute of Crete, Chania, Crete 73100, Greece.
authors.forename: P
authors.initials: P
authors.lastname: Kirmizakis
authors.affiliation: DEDISA S.A., Chania, Crete 73100, Greece.
authors.forename: C
authors.initials: C
authors.lastname: Tsamoutsoglou
authors.affiliation: Department of Chemistry, Arts and Sciences Faculty, Aksaray University, Aksaray, Turkey.
authors.forename: B
authors.initials: B
authors.lastname: Kayan
authors.affiliation: Department of Environmental and Natural Resources Engineering, School of Applied Sciences, Technological and Educational Institute of Crete, Chania, Crete 73100, Greece. Electronic address: dkalderis@yahoo.com.
authors.forename: D
authors.initials: D
authors.lastname: Kalderis
mesh_terms: D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D013696:Temperature; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D014876:Water Pollution / Q000517:prevention & control*; D018508:Water Purification / Q000379:methods*
chemical_list: D014874:Water Pollutants, Chemical; D006861:Hydrogen Peroxide
keywords: Central composite design; Hydrogen peroxide; Landfill leachate; Response surface methodology; Subcritical water; Superheated water