Effect of sludge type on the fermentation products

Area of Science:

• Environmental Engineering
• Waste Management
• Biotechnology

Background:

• Wastewater treatment generates significant sludge volumes, including primary sludge (PS) and waste activated sludge (WAS).
• Sludge fermentation is a potential pre-treatment process to enhance resource recovery and reduce sludge volume.
• Understanding nutrient release and organic matter solubilization during sludge fermentation is crucial for process optimization.

Purpose of the Study:

• To investigate the effects of co-fermenting PS and WAS on soluble chemical oxygen demand (COD) and nutrient release.
• To compare sludge fermentation performance from biological nutrient removal (BNR) and carbon-removal-only wastewater treatment plants.
• To assess the potential for phosphorus recovery as struvite from fermented sludge.

Main Methods:

• PS and WAS from two different wastewater treatment plants (WEWPCC and SEWPCC) were fermented individually and co-fermented at 21°C.
• Semi-continuous flow fermenters were utilized to evaluate soluble COD production, volatile fatty acids, and nutrient release (phosphate, ammonium).
• Volatile solids destruction was quantified to assess the extent of sludge stabilization.

Main Results:

• PS fermentation yielded significantly higher soluble COD than WAS fermentation.
• Co-fermentation of WAS and PS enhanced soluble COD production and increased phosphate and ammonium release.
• Volatile fatty acids constituted the primary soluble COD components, with 20-22% volatile solids destruction achieved.
• Sludge from the BNR plant (WEWPCC) released higher phosphate concentrations than the non-BNR plant (SEWPCC).
• Co-fermentation produced phosphate concentrations sufficient for struvite recovery at both plants.

Conclusions:

• Co-fermentation of PS and WAS is an effective strategy to enhance soluble COD production and nutrient recovery.
• Sludge fermentation can achieve significant volatile solids reduction, contributing to sludge stabilization.
• The phosphate concentrations achieved through co-fermentation are suitable for struvite recovery, offering a valuable resource from wastewater sludge.