Enhanced biomethane production via thermophilic anaerobic digestion of cattail amended with potassium phosphate- and magnesium-modified biochar

Biochar can effectively strengthen anaerobic digestion (AD) and improve the treatment efficiency of organic wastes. However, the types of biochar tested so far are very limited and the exact mechanism remains unclear. This paper investigated the effects of potassium phosphate- and magnesium-modified biochar and the biochar particle size on AD of cattail. The direct use of raw pine pyrolysis biochar in AD showed an adverse effect on the methane production. The addition of potassium phosphate-modified biochar with a smaller particle size (< 1 mm) was most conducive to methane production, increasing the biogas production by 18.3–20.1%. The use of biochar doped with 2 M MgCl 2 and calcined at 800 °C resulted in a 21.1% increase of specific methane productivity compared with AD without biochar. The increased buffer capacity, nutrients released by the biochar, enhanced electron transfer and better aggregation function of small particles may contribute to the improved methane production. Preliminary analysis showed that the cost of raw materials and increased product sales can be balanced, and the application of this technology may bring more profits. The knowledge obtained can be used as a guide for enhancing the performance of anaerobic digesters at the plant. Graphic abstract