Ammonium removal from landfill leachate by chemical precipitation

Abstract

 the landfill leachate in Hong Kong usually contains quite high NH 4 + -N concentration, which is well known to inhibit nitrification in biological treatment processes. A common pre-treatment for reducing high strength of ammonium (NH 4 + -N) is by an air-stripping process. However, there are some operational problems such as carbonate scaling in the process of stripping. For this reason, some technical alternatives for NH 4 + -N removal from leachate need to be studied. In this study, a bench-scale experiment was initiated to investigate the feasibility of selectively precipitating NH 4 + -N in the leachate collected from a local landfill in Hong Kong as magnesium ammonium phosphate (MAP). In the experiment, three combinations of chemicals, MgCl 2 6H 2 O + Na 2 HPO 4 12H 2 O, MgO + 85% H 3 PO 4 , and Ca(H 2 PO 4 ) 2 . H 2 O + MgSO 4 . 7H 2 O, were used with the different stoichiometric ratios to generate the MAP precipitate effectively. The results indicated that NH 4 + -N contained in the leachate could be quickly reduced from 5,618 mg/l to 112 mg/l within 15 minutes, when MgCl 2 6H 2 O and Na 2 HPO 4 12H 2 O were applied with a Mg 2+ :NH 4 + :PO 4 3mole ratio of 1:1:1. The pH range of the minimum MAP solubility was discovered to be between 8.5 and 9.0. Attention should be given to the high salinity formed in the treated leachate by using MgCl 2 6H 2 O and Na 2 HPO 4 12H 2 O, which may affect microbial activity in the following biological treatment processes. The other two combinations of chemicals [MgO + 85% H 3 PO 4 and Ca(H 2 PO 4 ) 2 . H 2 O + MgSO 4 . 7H 2 O ] could minimise salinity after precipitation, but they were less efficient for NH 4 + -N removal, compared with MgCl 2 6H 2 Oand Na 2 HPO 4 12H 2 O. COD had no significant reduction during this precipitation. It was found that the sludge of MAP generated was easily settled within 10 minutes to reach its solids content up to 27%. The other characteristics including capillary suction time (CST) and dry density (DD) of the MAP sludge were also tested. The experimental results indicate that the settled sludge is quite solid and can be directly dumped at a landfill site even without any further dewatering treatment.

Using ammonium‐tolerant yeast isolates: Candida halophila and Rhodotorula glutinis to treat high strength fermentative wastewater

“…From Figure 2 (a), it was found that the mixed yeast strains grew at the maximum rate before 24 h when the concentration of (NH 4 ) 2 however, has often been reported. Anthonisen et al [1] found that methane-forming bacteria were inhibited in spite of pH control when the total ammonia was over 3000 mg I" 1 .…”

Semi-aerobic stabilized landfill leachate treatment by ion exchange resin: isotherm and kinetic study

“…Generally, biological treatments such as aerobic, anaerobic, sequencing batch reactor, aerated lagoons, and activated sludge are effective in removing organic matters in the early stages (from young leachate) when the BOD 5 /COD ratio is greater than 0.4 (Kurniawan et al 2006;Renou et al 2008). On the contrary, biological treatment is inefficient when it comes to the treatment of stabilized leachate due to the narrow range of biodegradable components in leachate, the presence of substances toxic for the microorganism and the limited availability of necessary nutrients for microbial growth (Li et al 1999). Therefore, physico-chemical processes usually applied to treat persistent refractory compounds in stabilized leachate (Kamaruddin et al 2014).…”

Repeated use of MAP decomposition residues for the removal of high ammonium concentration from landfill leachate

“…While new biological techniques like short-cut nitrification/denitrification and anaerobic ammonium oxidization have demonstrated potential in solving the above problems, they are still under study and it is not yet possible to constantly control the nitrification process in the nitrite-formation dominating step Strous et al, 1997). Formation of magnesium ammonium phosphate (MAP), a crystal with a solubility as low as 0.0023 g per 100 ml H 2 O, has been considered to be an effective method for the removal of ammonium because of its high reaction rate and low residual ammonium concentration (Li et al, 1999). The method of MAP precipitation has been extensively studied to treat wastewater with high NH þ 4 content (Altinbas et al, 2002;Ozturk et al, 2003) of 1:1:1 for treating landfill leachate (Li and Zhao, 2001).…”