High-quality fiber and fertilizer as co-products from anaerobic digestion

Excerpt

On-farm anaerobic digesters are a commercially available technology that captures emissions of methane from stored animal manure, provides renewable energy, and opens new opportunities for nutrient management on confined animal feeding operations (CAFOs). The high capital costs for digesters have traditionally been offset through public subsidies and the sale of electricity generated from the biomethane. Extremely low electrical power prices in the Pacific Northwest have proven to be a substantial obstacle to digester projects in the region. Reduced costs and increasing revenues are essential for adoption of digesters as a dairy waste management strategy in the region. Recovery of nutrients from digested manure is a critical need for compliance with increasingly strict environmental regulations facing CAFOs.

FINANCIAL & BIOPHYSICAL ANALYSIS

Through a USDA NRCS Conservation Innovation Grant, our team completed a financial and biophysical analysis of the Vander Haak Dairy digester project. The project was designed for the manure from 1,500 cows, but actual loading rates during the study period fluctuated between 800 and 1,100 cows plus co-digestion of up to 15% food waste by mass.

The financial analysis confirmed that electrical production from dairy manure alone provides insufficient return on investment to justify a dairy digester project …