Leveraging Existing Assets for the Future: A Progressive Pathway forward in Biosolids Management

Last Modified: Jan 31, 2019

Authors:

  • Ruth Borgmann, Michael Bullard - Hazen and Sawyer

The City of Columbia currently manages biosolids at the 60 MGD Metropolitan Wastewater Treatment Plant via DAF thickening and centrifuge dewatering for landfill disposal. Hazen completed a Solids Handling Master Plan for the facility in 2013 which established a short-term plan to restore service to the anaerobic digesters and repair / rehabilitate thickening and dewatering equipment and a long-term plan to produce a Class A dewatered biosolids product. The recommended digester rehabilitation and upgrade project is currently under construction. With the digesters available to deliver stabilized Class B biosolids upon construction completion, Hazen was retained to update the Solids Handling Master Plan. Development of the updated Solids Handling Master Plan will be the focus of this presentation. The update was conducted to evaluate new and emerging solids treatment technologies to confirm that proposed near-term improvements from the 2013 Plan were compatible with the recommended long-term improvements.

Near-term improvements were based on condition assessments and required processing needs. The main focus of the near-term improvements were the replacement or rehabilitation of aging or deteriorated infrastructure and low-capital cost changes to improve sludge handling, staging and storage. The necessary steps to develop a Class B land application program were also evaluated.

Longer term improvements were based on evaluating advanced processing technologies, beneficial use of digester gas and co-digestion of FOG and food waste. THP, thermal drying and gasification were the advanced processing technologies considered. Biogas utilization feasibility evaluations were performed using Hazen’s Energy Balance and Analysis Tool which models the complex relationship between energy production, energy demands, and energy costs to provide accurate long-term cost/benefit assessments for multiple biogas utilization alternatives.

All of the recommendations for improvements were developed with a proactive approach for continued process performance. The near-term improvements recommended in the 2013 Plan were confirmed to be consistent with the long-term management plan for the facility. Recommendations for biosolids management included development of a Class B land application program with flexibility for future implementation of a small dryer to utilize excess biogas and to produce a Class A product suitable for marketing and distribution. This presentation will describe the evaluations conducted as part of the master planning effort and present the selected biosolids management path forward.

For more information, please contact the author at rborgmann@hazenandsawyer.com.

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