Application of natural zeolites for the reduction of ammonia emissions during the composting of organic wastes in a laboratory composting simulator

Abstract

Ammonia losses from composting of unchopped and chopped straw-pig slurry mixtures were studied in a laboratory composting simulator. Ammonia emissions were reduced when pig slurry was composted with chopped straw. Chopped straw was more easily degraded by the microorganisms because its surface area was higher than that of the unchopped straw. An average of 84·88% of initial NH 4-N was immobilized and incorporated into the organic-N fraction. Zeolite clinoptilolite was very effective in trapping the ammonia lost during the composting process. The zeolite sample was placed inside the composting simulator, in the spent-air stream, just after the air had passed through the composting material. Reduction in the effectiveness of ammonia adsorption in zeolites was related to their water adsorption. The connentration of ammonia in the airstream played an important role in the ammonia adsorption. The zeolite amount required to retain 80% of N-losses was 53 g kg −1 of fresh chopped straw-pig slurry mixture, while the amount was 82 g kg −1 of fresh mixture when unchopped straw was used. The combination of mixing the pig slurry with an easily degradable straw and covering the composting material with zeolite minerals is a very effective procedure for reducing ammonia emissions.