Chapter 2 - Physical and Chemical Treatment Processes for Leachate

Abstract

COD and NH3-N or TN in leachate are the two predominant pollutants that are most difficult to be removed, using physical chemical or biological means. Magnesium ammonium phosphate (MAP) method, also called the struvite precipitation, has been widely used for the chemical precipitation of NH3-N by addition of magnesium chloride hexahydrate, ammonium chloride, and anhydrous disodium hydrogen phosphate at a molar ratio of 1:1:1. The struvite is heated to regenerate magnesium phosphate for recycling so that the costs can be reduced. It is found that the struvite can be recycled over 5 times after pyrolysis with little decrease of NH3-N removal efficiency. More recyclings will lead to decreasing NH3-N removal efficiency from leachate. Air stripping can decrease NH3-N concentrations in leachate efficiently after adjusting pH to alkalinity with a removal up to 99%. Important sequence of factors that influence air stripping process follows pH value> temperature> air stripping time> gas liquid ratio. Flocculants and Fenton reagents are used for COD removal for concentrated liquid from reverse osmosis (RO) system with biological treatment. The main composition of low concentration refractory leachate treated by biological treatment is humus that can be oxidized by oxidants like potassium permanganate and sodium hypochlorite. Both magnetized super fine iron powder-activated carbon microelectrolysis and Venturi vacuum negative pressure Fe-C microelectrolysis can imorove reaction efficiency for the oxidization process. Hydration reaction and membrane treatment processes such as ultrafiltration (UF), nanofiltration (NF), membrane bioreactor (MBR), RO, and their combinations should be used after the biological treatment for effluents from aerobic tank. Mechanical Vapor Compression (MVC) process used in leachate treatment is a physicochemical separation process. The raw leachate is fed into MVC equipment after filtration, and the resulted evaporated leachate is condensed and further treated through DI ion exchange system to remove ammonia. A resin is used for the selective separation of humic acids and its contribution to the COD value in landfill leachate is determined. It is found that the percentage of HSs contributes to 40% of the COD value in leachate influent, and to 35.9% of the COD value in the effluent.