Moderate thermal, alkaline and thermal-alkaline pretreatment of cattle manure: effects on methane production and economic feasibility
摘要
Anaerobic digestion (AD) of livestock manure stands out as a sustainable approach for energy generation and nutrient recovery while mitigating greenhouse gas emissions and reducing potential contaminants. However, the recalcitrant lignocellulosic content in cattle manure poses a challenge to methane (CH4) production, requiring pretreatments to enhance biodegradability. While previous studies have investigated manure pretreatment using various alkali agents and temperature conditions, the effects of Ca(OH)2 as an alkaline source combined with moderate-temperatures over extended durations still need to be explored. This study evaluated the effects of alkaline, thermal, and combined thermal-alkaline pretreatments on CH4 production from cattle manure and assessed the cost–benefit associated with the implementation of these strategies. Pretreatments were conducted at moderate temperatures (55 °C and 70 °C) to minimize energy consumption. The highest CH4 yields were achieved with the combined thermal-alkaline and alkaline (9% Ca(OH)2 based on dry matter) pretreatments, increasing methane production by up to 15.2 ± 3.3% and 10.6 ± 2.5%, respectively, compared to raw manure. In contrast, thermal pretreatment alone did not significantly enhance CH4 production. The economic assessment indicated that the net revenue for the thermal-alkaline pretreatment was negative, whereas alkaline pretreatment showed financial feasibility, surpassing conventional AD without pretreatment. These findings highlight alkaline pretreatment as a promising strategy for enhancing CH4 production while maintaining economic feasibility in biogas systems.