Triple Bottom Line (TBL) For Biosolids Management
The Water Environment Research Foundation (WERF) has published "Triple Bottom Line Evaluation of Biosolids Management Options," providing guidance on bringing environmental and social criteria into decision-making regarding biosolids management options. A NEBRA team played a large role in this project.
The TBL approach, which is a form of multi-criteria decision analysis (MCDA), is widely used in corporations, government organizations, and non-profits as a rational process for understanding the sustainability of systems and informing decisions. Several water resource recovery facilities (WRRF) have used the TBL approach in choosing biosolids management systems. This WERF study built on their experiences and experiences in other sectors, creating a spreadsheet model that integrates environmental, social, and economic criteria into common numerical units, allowing for apples-to-apples comparisons of different options. The project team carefully selected criteria that would help biosolids management planners identify those factors most important in differentiating different technologies and systems. The resulting model is populated with these criteria, but allows for users to modify them and the weightings - the impact - of each criterion.
Ultimately, a TBL model is truly useful only when there is considerable stakeholder involvement in understanding the significance of each social, environmental, and economic criterion included in the decision-making process and how each criterion is weighted. As the WERF report notes, those planning biosolids management systems will benefit from working with community members and other stakeholders in tweaking the TBL model to represent local conditions and goals.
The WERF report includes an example of running the TBL model. The project team applied its best professional judgment regarding biosolids management options available to a typical 10 MGD WRRF, entering pertinent data and weightings into the TBL spreadsheet model. Six different biosolids management scenarios were compared. The highest TBL score was for the system that included anaerobic digestion with co-digestion and combined heat & power (CHP), followed by land application. While this scenario was not the least costly in economic terms, it scored higher on environmental criteria such as net greenhouse gas emissions, net energy consumption, and resource utilization. It also scored well for social criteria that include nuisance issues and the inherent degree of public engagement inhered to the biosolids management system.