Abstract

Waste management and renewable energies are both major environmental concerns related to the largest global issue of today, climate change. Anaerobic digestion (AD) systems are able to reduce greenhouse gases (GHGs) that lead to climate change by producing biomethane gas to use as renewable energy, while treating organic waste. AD systems can also serve as carbon sinks because they are able to biologically convert excess carbon dioxide dissolved in the culture, into additional methane gas. Continuous experiments were conducted with five-litre UASB reactors that focused on simulating full-scale operating parameters at a Cascades’ paper recycling plant, and employed recycling waste streams as substrates. Experiments compared conditions of single and 2 phase anaerobic digestion (2-PAD), liquid and granular sludge beds, influent wastewater and deinking sludge substrates, temperatures between 25-45 °C, hydraulic retention times between 1 to 5 days and organic loading rates between 0.5-5.0 kg COD/m3-d. Methane yields across all conditions averaged 0.15 m3 CH4/kg CODrmv for total COD and 0.24 m3 CH4/kg CODrmv for soluble COD. Removal efficiencies consistently averaged 90% for all conditions. After feeding 2-PAD systems CO2 infused wastewater, successful bioconversion for soluble COD was observed in all organic loading rate conditions, showing between 5-21% higher methane yields for CO2 conditions, compared to control. Heavy metals from deinking sludge were monitored though no inhibition was observed. Cost analysis showed that adopting AD as a pretreatment could result in up to 1,733,100 CAD/year in additional revenue. Results of this research provide a solid guideline to pursue developing a pilot scale system.