Novel ozonation treatment to enhance anaerobic digestion of WAS: scale-up challenges and sanitary potential
Notice bibliographique
Résumé
Society recognises the impact of greenhouse gases on the climate, which has encouraged operators and the government to combine forces to develop more sustainable waste management practices. To enforce these essential changes, waste management laws have been reformed and improved methods for waste handling are urgently required. The Government of Quebec announced the ban of incineration and landfilling of municipal organic waste by 2022, which directly affects the wastewater treatment industry. Activated sludge treatment of wastewater produces waste activated sludge (WAS), which is treated and dewatered to produce carbon and nutrient-rich biosolids. Many wastewater treatment plants (WWTPs) are opting for anaerobic digestion (AD) of WAS to recover energy, reduce biosolids management costs and disinfect biosolids. However, in cold-climate countries, approximately a third of the energy produced during digestion is used to heat the digesters to an operation temperature of 35 °C, as temperatures of wastewater can be lower than 10 °C for large portions of the year. The goal of this thesis was to reproduce at pilot-scale using a different source of WAS, experiments conducted previously in our laboratory that evidenced the capacity of ozone pretreatment to enhance suspended solids destruction and methane production during anaerobic digestion. The project to which this thesis contributes intends to develop a process operating at either 20 or 35 °C. However, this thesis reports on a one-year pilot-scale digester experiment performed only at 35 °C, and a series of lab-scale complementary experiments performed at both temperatures.In the pilot-scale experiment performed with Victoriaville WAS, ozone treatment of the recirculating digestate solubilized chemical oxygen demand (COD) and improved the destruction of volatile suspended solids (VSS), however enhanced methane production rates were not observed. To further explore this result and assess the benefits and limitations of ozone pretreatment of WAS on AD with adequate replication, several 500-mL serum-bottle semi-continuous digester experiments were conducted. They confirmed that ozone pretreatment had a significant positive impact on VSS destruction and methane production, as they increased linearly with the dose of ozone transferred to the WAS. However, comparison of Victoriaville and La Prairie WAS suggested that the La Prairie WAS reacted more readily to treatment than Victoriaville, which resulted in higher process enhancement. Therefore, the origin of the sludge has a significant impact on the efficiency of the pretreatment. Finally, the effect of the ozone pretreatment and AD on pathogen inactivation was studied to evaluate the sanitation potential of the pretreatment. The results from this last experiment revealed that ozone inactivated approximately 1 log of E. coli, but the surviving population was more resistant to inactivation during anaerobic digestion than the original population
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|---|---|---|
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