2.4 Chemical precipitation
Chemical precipitation process is used extensively as pre-treatment to reduce high concentration of ammonium nitrogen (NH4 ± N) in leachate. As well, the COD reduce of 79 to 95. Then, ammonium concentration reduced from 5600 to 110 mg L−1 in 15 minutes by the same method (Yangin et al., 2002). Altinbas et al., (2002), studied the behaviour of magnesium ammonium phosphate (MAP) precipitation (precipitated ammonium ions as magnesium ammonium phosphate) after anaerobic process pre-treatment of domestic wastewater and landfill leachate mixture. They found the maximum ammonia reduction was 66% at a pH of 9.3.
2.5 Adsorption using Activated Carbon
The adsorption of pollutants using Activated Carbon either in columns or in powder form ( Kargi et al., 2003, Kargi et al., 2004, Zamora et al., 2000) gives good reduction in COD levels than the chemical processes. The main disadvantage is the requirement for repeated renewal of columns or high utilization of powdered activated carbon (PAC). The color, inert COD and the Non-biodegradable organics may be decreased to suitable levels for biological treatment landfill leachate.
Rodriguez et al., (2004), studied PAC and many other resins to decrease the non-biodegradable organic matter from landfill leachate. He found that Activated Carbon offered the highest adsorption capacity which was about 85% COD decrease (Kargi et al., 2003; Kargi et al., 2004). Heavey et al., (2003), used a pre-treated peat as the treatment medium. Almost 100% elimination of both ammonia and BOD, and 69% of COD were achieved. Finally, limestone has been confirmed successful in removing metals from wastewaters. Aziz et al., (2004), indicated that 90% of Fe could be removed from semi-aerobic landfill leachate by limestone filter.
2.6 Chemical oxidation
The chemical oxidation method is used for the treatment of effluents consisting refractory compounds like landfill leachate. Currently, more interest has been focused on advanced oxidation processes (AOP). Nearly all of them with the exception of simple ozonation (O3), use a combination of strong oxidants, e.g. H2O2, irradiation, e.g. ultrasound (US), ultraviolet (UV), or electron beam (EB), and some catalysts, e.g. transition metal ions or photocatalys.
However, recent studies have confirmed that AOP is efficient for treating old or well - stabilized leachate in order to improve the biodegradability of refractory organic pollutants (Wang et al., 2003). On the other hand, this method (AOP) has some disadvantages such as using a lot of energy which is necessary for devices such as UV lamps, ozonisers and ultrasounds (Lopez et al., 2004). Also, Renoua et al., (2008) confirmed that AOP, adapted to well-stabilized or old leachate, are applied to develop the biodegradability of recalcitrant organic pollutants and oxidize organic substances.
2.7 Air stripping
Recently, it has been found that the best method for removing a high concentration of NH4±N in wastewater treatment technologies is air stripping. The leachate usually contains high levels of ammonium and nitrogen, and both of them can be eliminated by using the air stripping method (Marttinen et al., 2002). This method is efficient at a high pH value because Marttinen et al., (2002) confirmed that about 89% ammonia was reduced at pH 11 within 24 hours retention time. However, this method has a disadvantage which is emission of NH3 into the air which can cause air pollution if ammonia cannot be properly absorbed with either H2SO4 or HCl.
2.8 Membrane Filtration
Membrane filtration process is defined as a separation process using semi permeable membrane to remove the suspended particles from the leachate. The size of particles that pass through the membrane is used to classify the membrane filtration. The membrane filtration includes many types such as micro filtration (MF), ultrafiltration (UF), Nano filtration (NF), and reverse osmosis (RO). However membrane filtration has some disadvantages, for example membrane fouling easily, while the life of membrane is very important for eliminating the suspended solid particles and colloidal materials from the leachate before filtration (Zhou & Smith, 2001)
