Treatment of landfill leachate through struvite precipitation and nitrogen removal bacteria and poly-phosphate bacteria (in-pots experiment)

Wastewater is usually hazardous to human populations and the environment and must be treated prior to disposal into streams, lakes, seas, and land surfaces [1]. Obligatory anaerobic treatment of domestic and agro-industrial wastewater releases large amounts of phosphorus and nitrogen into wastewater. These nutrients are directly responsible for eutrophication (extraordinary growth of algae as a result of excess nutrients in water bodies) of rivers, lakes, and seas worldwide [2, 3]. Consequently, disposal of wastewaters produces a constant threat to dwindling freshwater on a global scale [4].

Landfill leachate treatment is an important issue of the waste management system in municipal areas [5, 6, 7]. Their quantity and quality depends on a number of factors: the type of deposited wastes as well as the age of the landfill and the phase of waste decomposition. The leachates withdrawn from landfill in methanogenic phase (methanogenic leachates) are characterized by high nitrogen load and large amount of refractory organic compounds with a high chemical oxygen demand/biochemical oxygen demand (COD/BOD) ratio [7]. Landfill leachate that is collected and removed from a landfill must be managed in a suitable manner. This involves some type of treatment process whether on or off-site. The various methods and technologies tested, applied and proposed for the treatment of landfill leachate range from the recirculation of leachate through the landfill to the more sophisticated combination of physical, chemical and biological processes [8, 9, 10, 11,12]. Magnesium ammonium phosphate (MAP) precipitation is a physical/chemical technique [7, 5, 13], which produces MgNH PO .6H O by the precipitation of magnesium, ammonium and phosphate under alkaline conditions. This precipitation 4 4 2 method is advantageous due to its ability to effectively precipitate NH-N from wastewaters forming easily settleable 4 insoluble compounds, which have a potential as a binding material in cement [14].

Mg + + NH + + H PO + 6H O MgNH PO - + 6H O + 2H 2 4 2 4 2 4 4 2 2 The most promising compound for recovery from wastewater plants is magnesium ammonium phosphate hexahydrate (MgNH PO .6H O), commonly known as struvite, which precipitates spontaneously in some wastewater processes [15, 16, 4 4 2 17]. If formation and collection are controlled and cost-effective, struvite might have potential in the fertilizer market. Struvite precipitates spontaneously in wastewater treatment environments where high concentrations of soluble phosphorus and ammonium are present. Additional essential conditions are low concentration of suspended solids and pH above 7.5. Precipitation of struvite requires that its components are available simultaneously in the wastewater in the molecular ratio 1(Mg2+):1(NH +):1(PO 3). Normally, municipal wastewater and several other wastewaters tend to be rich in ammonium, but 4 4 deficient in magnesium, so supplementation of magnesium is required, and this helps to increase solution pH [18, 19, 20, 21, 22] . Similarly, addition of magnesium chloride or bittern, a low-cost magnesium, forced precipitation of phosphorus and reduced the concentration of soluble phosphorus in swine waste within a 10-min reaction time [23, 24] . The pH can also be elevated by adding NaOH, an expensive process [16], by air stripping [25], where aeration of wastewater removes CO and 2 pH increases in the process [26] or by ion using phosphate-selective sorbents [27] . This process was viewed as enhanced biological phosphorus removal (EBPR) in wastewater treatment systems [28, 29, 30].

This study investigates the following steps: (1) struvite pretreatment of raw landfill leachate, (2) applying nitrogen removal bacteria and poly-P bacteria to remove N and Pout leachate. With The objectives of this study were: (1) to investigate the effects of pH and molar ratios for magnesium, and phosphate ions on ammonia N and phosphate P removal from raw landfill leachate, (2) to apply nitrogen removal bacteria and poly-P bacteria to enhance the waste disposal process.