Treating Waste with Waste: Using Biochar to Recover Nutrients from AD Effluent

The processing of food waste with animal manure through anaerobic digestion (AD) can be an effective waste management and energy recovery strategy. However, there is growing concern with the widespread deployment of AD, because managing its nutrient-rich effluent (digestate) has become an environmental challenge. Digestate is often separated into its solid and liquid fractions using mechanical processing such as a screw press. The solid fraction is often repurposed as cow bedding, while the liquid fraction is applied to crop fields as an alternative to synthetic fertilizers, which might lead to nutrient run-off and subsequent water contamination. We are developing a potential solution to this problem by processing the solid fraction of the effluent through thermochemical conversion (TC) to produce biochar, a porous carbonaceous material known for its adsorption capabilities. This material would be used to recover nutrients like nitrogen, phosphorus and potassium present in the liquid fraction of the effluent. The resulting nutrient-rich biochar can be applied as an alternative fertilizer that reduces potential water contamination. If an efficient integration of AD and TC processes is achieved, it can result in an enhancement of the system’s economic viability and reduction of their associated environmental impacts.