Membrane Technique for Leachate Treatment- A Literature Review

Rapid increase in population and industrialization leads to huge generation of solid waste throughout the country with landfilling as the most common practice for management of these solid waste. It is estimated that out of 3267 MLD of sewage is generated in Delhi. Concentrations of COD, BOD5, heavy metals, NH4AN, low BOD5/COD ratio and the lack of nutrients in the methanogenic phase have restricted the application of biological treatment processes like aerated lagoons, activated sludge, sequence batch reactors, trickling filter, rotational biological contactors, thereby membrane technology is now days being used. Membrane filtration can be defined as the separation of solid immiscible particles from a liquid or gaseous stream based primarily based on size difference. It includes processes such as reverse osmosis (RO), nanofiltration (NF), ultrafiltration(UF) and microfiltration (MF). MF cannot be use alone in leachate treatment, used as pre-treatment for other membrane processes e.g. UF, NF or RO. MF alone, the COD removal is between 25-35%. Using the UF step alone 50% of organic matter can be separated. Nanofiltration removes up to 60-70% COD as well as about 50% ammonia from leachates while its combination with physicochemical methods further improves leachate treatment bringing the COD removal (refractory COD inclusive) to a range of (70-80%). Reverse Osmosis process has been reported to be a very efficient and promising method for leachate treatment. RO membranes can remove more than 99% organic macromolecules and colloids from feed water and up to 99% of the inorganic ions. Due to high rejection ability, reverse osmosis membranes retain both organic and inorganic dissolved in water with rejection rates of 98 99% thus being useful for purifying of liquid Arpita Anand & Shashank Shekhar Singh 34 wastes, i.e. leachate. Permeate generated from the reverse osmosis unit is low in inorganic and organic contaminants which meet the discharge standards.