Optimizing coagulant dosing for enhanced sludge settling and subsequent anaerobic digestion

Area of Science:

• Environmental Engineering
• Water Treatment Technologies
• Waste Management

Background:

• Effective sludge management is crucial for wastewater treatment plant efficiency.
• Coagulant selection significantly impacts sludge settling, dewatering, and downstream processes like anaerobic digestion.
• Optimizing coagulant dosage and type is essential for cost-effective and sustainable sludge treatment.

Purpose of the Study:

• To evaluate the efficacy of different coagulants (polyacrylamide, polyaluminum chloride, polyferric sulfate) for sludge settling and dewatering.
• To optimize coagulant dosage using response surface methodology for enhanced sludge treatment performance.
• To assess the impact of coagulant application on anaerobic digestion and overall economic feasibility.

Main Methods:

• Screening of five coagulants, followed by detailed testing of polyacrylamide (PAM), polyaluminum chloride (PAC), and polyferric sulfate (PFS).
• Application of response surface methodology to determine optimal coagulant dosages for primary and waste activated sludge.
• Evaluation of supernatant quality, sludge volume index (SVI), and methane yield in anaerobic digestion.

Main Results:

• Polyaluminum chloride (PAC) effectively reduced turbidity and suspended solids but increased sludge volume index (SVI).
• Polyacrylamide (PAM) addition mitigated SVI increase in primary sludge and reduced SVI in waste activated sludge.
• Combined PAC-PAM addition showed minimal impact on methane yield, while polyferric sulfate (PFS) significantly inhibited anaerobic digestion.
• Economic analysis indicated PAC-PAM as the optimal choice, with treatment costs of 10.35 US$/m³.

Conclusions:

• Coagulant selection and dosage are critical for optimizing sludge settling and dewatering in wastewater treatment.
• The combined use of PAC and PAM offers a balanced approach, improving sludge characteristics without significantly compromising anaerobic digestion performance.
• This study provides a practical framework for selecting and applying coagulants in integrated sludge management, enhancing treatment efficiency and economic viability.