Nitrogen transformation in food-waste composting

In this thesis research, nitrogen transformations under different conditions during food-waste composting were studied using batch-scale in-vessel composting systems. The 24-1 fractional factorial design approach was adopted to investigate various factorial effects on nitrogen transformation. Four factors (C/N ratio, aeration rate, starting culture amount and coal ash amendment) were examined through nine runs (including one quality control run) of composting experiments.;The C/N ratio of the raw materials and the starting culture amount played significant roles in nitrogen transformation during food-waste composting. There might also be a potential to use an adequate amount of matured compost as the starting culture to substantially reduce ammonia emission and nitrogen loss. Moreover, increasing the amount of seeding compost could help improve the self heating capability as it provided more desired microbial cultures; however, this would have a significantly negative effect on OM loss. Application of coal ash as an amendment could help increase the maximum temperature of the composting process; however, it would lead to a decreased OM loss. The interaction between C/N ratio and starting culture amount is found to have significant effect on ammonia emission and nitrogen loss. The interaction between starting culture amount and coal ash amendment was also significant in effecting OM loss and maximum temperature.;Based on the factorial analyses, response surface models were developed to reflect interrelationships between the system conditions and the nitrogen transformations.;The average organic matter (OM) loss in these experiments was found higher than the results based on other different composting materials. There existed a significant correlation between ammonium concentration and pH level during the pH-ascent. The increase in pH level was due to the generation of ammonia through ammonification and mineralization. In the later period of the composting process, formation of nitrate and nitrite would then be accompanied by a decrease in ammonium concentration.