Anaerobic Co-digestion of Municipal Sewage Sludge with Selected Commercial and Industrial Organic Wastes

  • Author / Creator
  • The overall goal of this research was to investigate the anaerobic co-digestion of municipal sewage sludge with selected organic wastes in three main areas: (1) to determine the maximum feasible loading of co-substrate, (2) to calibrate the ADM1 model for co-digestion system at steady state, and (3) to evaluate the linkage between microbial community dynamics and reactor performance and stability during steady state and overloading co-digestion. In this study, restaurant grease waste (GTW) as a commercial waste and biodiesel glycerin waste (BGW) as an industrial waste were co-digested with municipal wastewater sludge (MWS) in separate trials. In the first part of this research, the maximum feasible loading of each of the organic wastes with MWS with respect to the reactor performance and stability were investigated in the separate pilot-scale experiments. In each run, two 1300L completely mixed reactors were operated under mesophilic temperature (37°C) and a solids retention time (SRT) of 20 days. Throughout the pilot experiment, one reactor served as control and received only MWS and the other was assigned as the test digester and fed with the mixture of MWS and the co-substrate (GTW or BGW) in various organic loadings. GTW co-digestion with MWS was found to be feasible up to a maximum loading of 23% VS or 58% COD relative to the total 1.6 kg VS/m3•d or 4.0 kg COD/m3•d loadings, respectively. At this loading, test digester biogas production was 67% greater than that of the control. The test digester biogas production declined markedly when the percentage of VS from GTW in its feed was increased to 30% of its total VS loading. Causes of the reduced biogas production were investigated and attributed to process inhibition due to long chain fatty acid accumulation. The maximum safe limit of BGW co-digested with MWS was found at 23% and 35% of the total 1.04 kg VS/ (m3•d) and 2.38 kg COD/ (m3•d) loadings, respectively. At this loading, the biogas and methane production rates in the test digester were 1.65 and 1.83 times greater than of those in the control digester which received only MWS, respectively. Process instability was observed when the proportion of BGW in the test digester feed was 31% and 46% of the 1.18 kg VS/ (m3•d) and 2.88 kg COD/ (m3•d) loadings, respectively. In the second part of the research, the ADM1 model was calibrated for co-digestion of MWS and GTW at steady state using anaerobic respirometric test with substrate characterizations. Initial biomass concentrations and distributions were estimated using methane production rate curves together with effluent values from full-scale anaerobic digesters. Two separate datasets obtained from steady state mesophilic bench-scale experiments were used to calibrate and validate the model. The modified model was able to predict reasonably well the steady-state results of biogas production, CH4 and CO2 contents, pH, alkalinity, COD and VSS observed within the evaluated GTW loading. The calibrated model predicted well the bench and pilot scale co-digesters performance. The last part of the study was to investigate the relationships between microbial population (bacteria and archaea) dynamics and reactor performance and stability during the co-digestion of MWS with GTW or BGW in two separate trails. Pyrosequencing analysis revealed that Methanosaeta and Methanomicrobium were the dominant acetoclastic and hydrogenotrophic methanogen genera, respectively, during stable reactor operation. The roles of syntrophic bacteria such as Candidatus Cloacamonas¬ and hydrogenotrophic methanogens were found to be substantial at overloading conditions in both experiments.

  • Subjects / Keywords
  • Graduation date
    Fall 2014
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • 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.