Publication Summary

The earlier collaborative effort between Washington State University (WSU) and the Washington Department of Ecology (Ecology) (www.ecy.wa.gov/pubs/0507047.pdf) has identified municipal solid waste as a major biomass in the state. With directed funding from the State, WSU and Ecology established a new partnership under Inter Agency Agreement C-0700136 to explore the beneficial uses of the waste material. This project was proposed to produce fuel and fertilizer from the organic fraction of municipal solid waste (OFMSW) through the application/development of anaerobic digestion technology. The purpose of this project is to develop a design of an effective high solids anaerobic digestion (HSAD) system that is ready for pilot test. The design will be tested on a bench scale to demonstrate the potential of biogas and nutrients recovery from various types of organic municipal wastes. This project includes five objectives: (1) evaluation and review of existing HSAD designs, (2) bench scale trials and validation, (3) development of modeling tools for evaluation and development of high solids digestion systems, (4) developing a technology for enhancing the anaerobic bacterial population in the high solids digestion, and (5) design of a pilot digester. This report is the first deliverable of the project.

In this report, a complete literature review of existing anaerobic digestion in general and High Solids Anaerobic Digestion (HSAD) technology in particular is presented. A general comparison of strengths and weaknesses of current designs was made using reported performance data and model simulation as well as through consideration of the technical, biological, and economical aspects of their applications. The primary performance indicators used are biogas production per unit of volume of the digester and capital cost per ton of waste treated. This review covered all HSAD types as well as required pre- and post-treatment. Different full-scale plant types were classified according to types of anaerobic reactors. Major manufactures as well as full scale applications were listed. Most of the full scale installations are in European countries. A new design was proposed with its main features illustrated in comparison with the most efficient existing systems defined. A new modeling methodology was developed to define the plant feedstock composition using practical analytical parameters. The usefulness of the methodology was illustrated by two simulation studies. The first study was for treating a mixture of two waste types. The second study was for comparison of three reactor designs. The modeling work was extended by reviewing the computational fluid dynamic concepts to model HSAD mixing and energy balance since they were found to be of great importance during the HSAD review.