Integrated waste to energy and nutrient production system (IWENPS) for renewable methane production and fertilizer-grade digestate recovery

Anaerobic digestion converts organic waste into renewable methane.  Biogas generated from anaerobic digestion has a high concentration of CO₂ (35 – 50 %) decreasing its heating value, reducing the likelihood of beneficial use, therefore increasing the risk of fugitive methane emissions.  Furthermore, the available biogas cleanup and upgrading techniques are very cost-intensive for widespread adoption in AD industry. We developed a novel in situ bioprocess where both biogas production and cleanup take place in the same reaction vessel to produce renewable methane.  We use multivalent minerals present in porous biochar, a co-product of biomass pyrolysis, to react in situ with CO₂ to form insoluble carbonates.  The porous biochar also adsorbs H₂S from the biogas. We deliver a biogas containing > 90% CH₄ and < 5 ppb H₂S; close to fungibility. The biochar addition also enhances the process stability of the digester thereby boosting methane production rate (~28%).  Analysis of the digestate shows that this process can produce a fertilizer-grade soil amendment with highly desirable amount of macro and micro nutrients (N increase 23%, P increase %30, K increase 4-30X, Ca increase 50%, Mg increase 2-18X). Therefore, this novel process paves a path towards a new paradigm of energy and resource recovery from organic waste, including sludge, food waste, agricultural residues, manure and municipal solid waste. The nationwide adoption of IWENPS can produce a total potential energy of 2.5 billion gasoline gallon equivalents per year and reduce emissions by 6.5 million metric tons of CO₂ equivalent per year in the US.