The lack of viable solutions for the management, treatment, and safe resource recovery of faecal sludge from onsite sanitation installations results in direct disposal of the majority of untreated faecal sludge into urban environments in developing countries, and reliance on resource intensive processes in developed countries. The application of anaerobic digestion as a reliable, low-cost technology with resource recovery can provide revenue to offset treatment costs and significantly reduce the impact of faecal sludge on human and environmental health.
Anaerobic digestion is a well-developed and reliable technology that has been used to effectively treat sewage sludge for decades in Europe and the United States (Weiland et al., 2010). Anaerobic with the production of biogas has been evaluated as one of the most energy-efficient and environmentally beneficial technology for bioenergy production. The digestate containing high nutrient concentrations (e.g., nitrogen, phosphorus, and potassium) can be used as an organic fertilizer and soil conditioners, which can substitute mineral fertilizers. The operation of anaerobic digestion also contributes to the inactivation of pathogens (e.g., bacteria, viruses, protozoa, and helminths) in sludge (Aitken et al., 2005). The main factors attribute to the inactivation of pathogens are temperature, retention time, and free (i.e., nonionized) ammonia concentration (Aitken et al., 2005; Magri et al., 2015; Pecson et al., 2007). Ammonia addition in dewatered sewage sludge after anaerobic digestion was also shown to be an effective, low-cost treatment to reduce the concentration of bacterial indicators (E. coli and Enterococcus spp.) to below detection limit (i.e., 100 and 10MPN/g, respectively) (Nordin et al., 2015).
Lessons can be learned from anaerobic digestion of sewage sludge, but due to the wide-ranging characteristics of faecal sludge, they can be quite different than sewage sludge, and hence, that knowledge is not directly transferable. The characteristics of faecal sludge are typically one to two orders of magnitude higher in solid, organic and nutrient concentrations (Niwagaba et al., 2014). Faecal sludge is highly variable based on types of containment, emptying technologies and frequencies, quality of construction, and inputs into the system. Therefore, an understanding of the fundamental properties that affect inactivation mechanisms during anaerobic digestion processes would allow for the technology to be developed specifically for faecal sludge, and identify parameters that could be used to enhance inactivation. The performance of anaerobic digestion in inactivating pathogens will be predicted using a previous developed model (Fidjeland et al., 2015) with measured input data from laboratory experiments. The application of effective, low-cost post-treatment (e.g., addition of ammonia) will also be considered to provide an additional barrier of inactivation for anaerobically digested dewatered faecal sludge.
The goal of this project is to provide a better understanding of pathogen inactivation mechanisms during anaerobic digestion treating faecal sludge. Laboratory-scale experiments will be set up to determine inactivation rates and mechanisms of pathogenic indicators in faecal sludge during anaerobic digestion processes. Results will be used to estimate inactivation performance of anaerobic digestion treating faecal sludge in different designs and operational conditions. Laboratory- and pilot-scale experiments will provide inputs to improve design, operation, and maintenance practices in using anaerobic digestion for resource recovery with the focus on pathogen inactivation.
The hypotheses and objectives of this study are:
Hypothesis 1: Anaerobic digestion can provide a reliable treatment for faecal sludge to recover resources and inactivate pathogenic indicators in faecal sludge.
Objective 1: To characterize operational parameters (e.g., temperature, retention time, pH, free ammonia concentration) that have effects on inactivation of pathogenic indicators in a pilot-scale anaerobic digester treating faecal sludge.
Objective 2: To measure the inactivation performance and production of biogas of the pilot-scale anaerobic digester.
Hypothesis 2: The inactivation mechanisms of pathogenic indicators in anaerobic digestion treating faecal sludge can be determined and predicted in different designs and operational conditions.
Objective 3: To characterize the inactivation mechanisms of pathogenic indicators during anaerobic digestion of faecal sludge.
Objective 4: To predict inactivation rates of pathogenic indicators in different designs and operational conditions.
Hypothesis 3: The design and operation of anaerobic digestion can be optimized to enhance inactivation performance.
Objective 5: To determine the optimal designs and operational conditions for inactivation performance and biogas production in the pilot-scale anaerobic digester.
Dr. Linda Strande
Dr. Viet-Anh Nguyen