Piloting Cost-Effective Biosolids Management Strategies for Small WAS-Only WWTPs

Presentation Description: Ironhouse Sanitary District (ISD) developed a Biosolids Master Plan (BMP) to identify the best strategy for treatment, storage, and beneficial use of the District's biosolids. As part of the BMP, ISD conducted a pilot study of the top-ranked alternatives: air drying and Ag-Bag storage. This presentation will summarize the BMP and pilot study methodology, findings, and lessons learned. This presentation should be of particular interest to wastewater agencies that operate wastewater facilities that produce waste activated sludge (WAS) only and no primary sludge, as well as to wastewater agencies interested in piloting biosolids treatment and storage processes.

The BMP started with a technology screening followed by a detailed financial and non-financial evaluation of 11 biosolids treatment and storage alternatives. The detailed evaluation identified aerobic digestion with Ag-Bag storage, facultative lagoons, and air drying as the top-ranked alternatives.

To select between these alternatives, ISD performed pilot studies to further investigate their process, odor, and operational risks. The pilot studies were operated by ISD staff at the WRF site from June to September 2022.

Ag-Bags were piloted to examine if they would tear when storing solids at a lower percent solids concentration than has been previously practiced at NapaSan and to determine their odor and emission potential. The pilot study found that the Ag-Bags do not tear at the lower solids concentration produced by ISD. However, it also identified various operational issues including increased odors and challenges with bag unloading and truck loading. The air-drying pilot was conducted to examine odor and vector attraction potential risks. The air drying pilot was easy to operate, did not have the expected odor and vector attraction issues, and provided substantial volume reduction.

Based on the BMP and pilot findings, air drying was identified as the best strategy for biosolids treatment and storage for the ISD WRF.