Replacing methanol with internally produced VFA-based carbon source for denitrification at the Henriksdal WWTP

Area of Science:

• Environmental Engineering
• Microbiology
• Waste Management

Background:

• Future nitrogen removal targets necessitate external carbon addition at wastewater treatment plants (WWTPs).
• Methanol, the projected carbon source, is fossil-based and contributes to greenhouse gas emissions.
• Low influent BOD/TN ratios, chemical use, and low temperatures exacerbate carbon demands.

Purpose of the Study:

• To evaluate a volatile fatty acid (VFA)-based fermentate from primary sludge and food waste as a sustainable carbon source for denitrification.
• To compare the fermentate's performance against glycerol and projected methanol use.
• To assess the impact of fermentate use on microbial communities and biogas production.

Main Methods:

• Production of VFA fermentate from primary sludge and food waste in a mesophilic fermenter.
• Batch denitrification tests comparing fermentate and glycerol.
• Pilot-scale testing in a membrane bioreactor (MBR) for 70 days, replacing glycerol.
• Microbial community analysis and methane potential tests.

Main Results:

• Fermentate achieved a 40% higher denitrification rate than glycerol in batch tests.
• Pilot trials demonstrated a 30% higher denitrification rate and 50% lower carbon consumption.
• Effluent nitrate concentrations remained below 3 mg NO3--N/L.
• No significant microbial community shifts were observed.
• Replacing methanol requires 10% of primary sludge and food waste, with only a 2% reduction in biogas production when fermentate solids are recycled.

Conclusions:

• VFA fermentate is a highly effective and sustainable alternative carbon source for denitrification.
• It offers improved performance, reduced carbon consumption, and minimal impact on microbial communities.
• Utilizing waste streams for carbon addition aligns with circular economy principles and reduces reliance on fossil fuels.