Integration of Anaerobic Digestion and Composting Facilities

• Author / Creator

  Arab, Golnaz

• Interest in organic waste treatment has increased in recent years due to growing rate of organic waste generation. Implementing biotransformation technologies helps to divert organic waste from landfill, reduce greenhouse gas emission, and produce valuable final products. This research was conducted in two parts. The general goal of the first part was to extend the overall knowledge in organic waste characterization, generation rate, sources, and sampling. While in the second part, which is the main part of the dissertation, the focus was on anaerobic digestion and composting processes and integration of these two biotransformation technologies. In the first part (Chapter 2), a sampling methodology was proposed for higher education institutions (HEI’s), as one of the main generators in institutional, commercial, and industrial (ICI) sectors. Representative organic waste was collected according to the proposed methodology and characterized in terms of their physical, chemical, and biological properties. In the second part, different options of digestate post treatment were investigated in an integrated anaerobic digestion and composting system. Co-composting of digestate and organic fraction of municipal solid waste (OFMSW) was studied in terms of physicochemical parameters and microbial population dynamics in Chapter 3 and 4, respectively. Digestate was prepared by running a high solid anaerobic digestion (HSAD) reactor with the working volume of 500 L. Then it was mixed with OFMSW in eight different mixing ratios; 0, 10, 20, 30, 40, 50, 75, or 100% (wet mass). Composting reactors with working volume of 25 L were monitored for 100 days including 30 days of aeration and 70 days of curing. Monitored parameters were temperature, mass changes, total solids, organic matter, pH, and electrical conductivity. Stability and maturity endpoints were also quantified by running respirometry, C:N ratio, ammonium to nitrate ratio, and Solvita® tests. The results revealed that the reactors with 20 to 40% (%ww) digestate had better performance in terms of organic matter (OM) removal, temperature evolution, and also stability time. Results also showed that total ammonia nitrogen (TAN) available in the digestate could be an effective parameter in organic matter degradation and composting performance. Concentration above 5000 TAN mg.kg-1 DM found to be unfavorable for the biological activities where the improvement in composting performance was observed in the lower concentrations of TAN. OFMSW could also enhance the physicochemical properties of the digestate by balancing free air space, moisture content, and C:N ratio parameters. Simpson index calculated from pyrosequencing results also showed that microbial diversity was higher in the reactors with better performance. Proper mixing ratio of the digestate and OFMSW, 20 to 40%, (%ww) probably provided the most favourable condition for bacteria and fungi activities. Higher relative abundance of the two bacterial phyla, Thermoactinomycetaceae and Actinomycetales, in the reactors with 20 to 40% digestate indicated a potential of high efficient and rapid composting. In the fungal community, Galactomyces, Pichia, Chaetomium, and Acremonium were the four genera probably involved in higher OM degradation in the reactors with better performance. In Chapter 5, co-composting of polished digestate and composted OFMSW was studied as another option for further treatment of digestate. 8-day aerated digestate was mixed with composted OFMSW in eight different mixing ratios; 0, 20, 30, 40, 50, 60, 80, or 100% (wet mass) as feedstock for the curing process. Curing process was monitored during 100 days, with the same physicochemical analyses applied in the previous options. The results demonstrated that the two main feedstocks could not take advantages of each other and composting performance decreased when the digestate portion increased. This could be due to loss of N during aeration of the digestate and/or inappropriate inoculation time. Overall, comparing all the investigated options demonstrated that co-composting of the digestate and OFMSW with the mixing ratio of 20 to 40% was associated with higher OM degradation, higher temperature generation, and shorter stability time. Therefore co-composting of digestate with the OFMSW is suggested as a reliable and robust method for further treatment of the digestate.

• Subjects / Keywords

  • Composting
  • Anaerobic digestion
  • Composting anaerobic digestate
  • Integration of anaerobic digestion and composting

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3QN5ZQ19

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.