Sulfur flows and biosolids processing: Using Material Flux Analysis (MFA) principles at wastewater treatment plants

Area of Science:

• Environmental Engineering
• Environmental Chemistry
• Agricultural Science

Background:

• High sulfur loads in wastewater treatment plants (WWTPs) can lead to environmental issues like gaseous emissions and acid rain.
• Sulfur is a vital agricultural nutrient, making its recovery from WWTPs desirable for soil amendment.
• Current understanding of sulfur dynamics within WWTPs and their impact on biosolids quality is limited.

Purpose of the Study:

• To investigate sulfur flows through biosolids processing in six WWTPs.
• To identify how different biosolids processing configurations influence sulfur retention.
• To pinpoint data gaps and future needs for substance flow analysis.

Main Methods:

• Tracking sulfur flows across six WWTPs with varying biosolids processing configurations.
• Detailed sulfur speciation and flow analysis at one representative WWTP.
• Quantification of sulfur outflows via air, land, and ocean sinks, including odor control systems.

Main Results:

• Biosolids processing configurations prioritizing solids recovery (e.g., high-efficiency separation) retain more sulfur.
• The majority of sulfur is removed as sulfate in secondary effluent, but biosolids retain valuable sulfur content.
• Variations in incoming sulfur loads and concentrations, potentially from industrial sources and iron salt dosing, impact sulfur recovery efficiency.

Conclusions:

• Optimizing biosolids processing for solids recovery effectively enhances sulfur retention in biosolids for agricultural reuse.
• Effective management of sulfur flows in WWTPs is essential for both environmental protection and nutrient recycling.
• Further research is needed to address data limitations and refine substance flow tracking for better sulfur management.