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Chemical precipitation for controlling nitrogen loss during composting

¹ College of Resource and Environmental Science, China Agricultural University
² Heinrich von Thunen-Institute
³ Beijing Environmental Sanitation Engineering Research Institute

^* To whom correspondence should be addressed. E-mail: rettlee{at}yahoo.cn.

	Abstract

Aimed at controlling the nitrogen loss during composting, the mixture of magnesium hydroxide (Mg(OH)₂) and phosphoric acid (H₃PO₄) (molar ratio 1:2) were utilized as additives to avoid increasing total salinity. In trial TA, the additives were put into absorption bottles connecting with a gas outlet of fermentor (ex situ method); in trial TB, the additives were directly added to the composting materials (in situ method). During the 26 day composting period, the temperature, pH, total organic carbon (TOC), total nitrogen (TN), ammonium nitrogen (NH₄⁺-N), total phosphorus (TP), available phosphorus (AP) and germination index (GI) were measured. The experimental results show that the additives reduced the pH, while NH₄⁺-N and TN were obviously improved. NH₄⁺-N was 11.9 g kg^–1 and 3 g kg^–1 in amended compost trial (TB) and unamended compost trial (TA), respectively; TN increased from 26.5 g kg^–1 to 40.3 g kg^–1 in TB and increased from 26.5 g kg^–1 to 26.8 g kg^–1 in TA. Analysis of the TOC and carbon mass revealed that absorbents accelerated the degradation of organic matter. The germination index test showed the maturity of TB (102%) was better than TA (82%) in final compost. Furthermore, TP and AP were also obviously improved. X-ray diffraction analysis of precipitation showed that the precipitation in absorption bottle of TA was newberyite (MgHPO₄ 3H₂O), however, the crystal in the TB compost was struvite (MgNH₄PO₄ 6H₂O: magnesium ammonium phosphate). These results indicated that Mg(OH)₂ and H₃PO₄ could reduce the ammonia emission by struvite crystallization reaction. Optimal conditions for struvite precipitation should be determined for different systems.

First published on October 6, 2009
Waste Management & Research 2009, doi:10.1177/0734242X09336546


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