Stepwise hydrolysis to improve carbon releasing efficiency from sludge

Area of Science:

• Environmental Engineering
• Biotechnology
• Wastewater Treatment

Background:

• Waste activated sludge (WAS) presents a significant disposal challenge.
• Efficient recovery of carbon and nutrients from WAS is crucial for sustainable wastewater management.
• Conventional thermal alkaline hydrolysis (TAH) has limitations in carbon releasing efficiency.

Purpose of the Study:

• To develop and evaluate a novel stepwise hydrolysis strategy for enhanced carbon recovery from WAS.
• To compare the efficiency of stepwise hydrolysis with conventional TAH.
• To assess the impact of stepwise hydrolysis on sludge dewaterability and economic feasibility.

Main Methods:

• Implementing a four-stage stepwise hydrolysis process with increasing temperature and pH.
• Analyzing released soluble chemical oxygen demand (SCOD) and its biodegradability (BOD/COD ratio).
• Measuring volatile fatty acids (VFAs) yield and capillary suction time (CST) for dewaterability assessment.
• Conducting an economic assessment of alkali demand and thermal energy consumption.

Main Results:

• Stepwise hydrolysis increased SCOD release by nearly two times (from 7200 to 14,693 mg/L).
• Released carbon showed improved biodegradability (BOD/COD = 0.47) and higher VFA yield (0.37 g VFAs/g SCOD).
• Sludge dewaterability improved, with CST decreasing from 2500 to 1600 s.
• Stepwise hydrolysis demonstrated lower alkali demand and thermal energy consumption compared to conventional TAH.

Conclusions:

• Stepwise hydrolysis is a highly effective strategy for enhancing carbon recovery from WAS.
• This method improves the biodegradability of released carbon and the dewaterability of residual sludge.
• The process is economically advantageous, requiring less alkali and energy.
• Findings support concepts for improved carbon and nutrient recovery in wastewater treatment.