Sustainable and Cost Effective Biosolids Management Planning at OCSD

摘要

The Orange County Sanitation District (OCSD) in Southern California recently identified the need for a new Biosolids Master Plan (BMP). The BMP technical evaluations are complete, and a preferred biosolids management alternative has been identified. This paper presents the findings and recommendations associated with the offsite and onsite biosolids management evaluations, alternatives screening, life cycle cost analysis, and triple bottom line selection process that led to the recommended alternative. The lessons learned for this BMP will be useful for utilities that are considering updating their residuals treatment, reuse, and disposal program. The planning effort began with the biosolids end use in mind to ensure that any product generated, whether onsite or offsite, has an associated reliable, cost-effective, and sustainable end use market. In order to better define available markets for the potential biosolids products and onsite processing options, as well as determine the product's value and marketability, comprehensive market research on the regional horticultural (lawn/garden), agricultural, and fertilizer industries was completed. This included overall industry data evaluations coupled with telephone surveys and a series of in-person meetings with companies in the local targeted outlets. Two sets of evaluation criteria were developed - one market-based set for the evaluation of product-market pairs and a second set for evaluation for products only (and associated processing technologies). A total of 20 final product alternatives and 10 final market options were evaluated using predetermined evaluation criteria and weighting values. The project team then identified potential onsite processing alternatives for solids digestion and post dewatering that met the preferred product/markets that had been identified. An initial screening of these technologies was performed using the pre-established evaluation criteria noted above. The technical evaluation team then performed concept designs for the preferred onsite alternatives identified. The offsite (end-use) and onsite evaluations were merged to form end-to-end alternatives and 26 alternatives were identified. The final stage in the decision-making process consisted of a Solids Water Energy Evaluation Tool (SWEET) life cycle cost evaluation followed by a comprehensive triple bottom line evaluation using Criterium Decision Plus™ (CDP). This paper focuses on the evaluations performed and the recommendations made for OCSD Plant No. 2, one of two wastewater treatment plants (WWTPs) owned and operated by OCSD.