Controlled water washing mitigates slagging in cattle manure combustion by altering ash chemistry and mineral transformations

The global livestock industry generates approximately 3.7 billion tons of cattle manure annually, creating both an environmental management challenge and an underutilized bioenergy resource. However, large-scale combustion of cattle manure is hindered by severe slagging associated with alkali-rich, low-melting ash. This study evaluated controlled water washing as a simple and low-cost pretreatment to improve the fuel quality of cattle manure under practically relevant conditions. Water washing effectively removed alkali metals, with performance was determined mainly by the water-to-solid ratio and further improved by temperature. As a result, slagging severity was reduced from severe to mild. Mineralogical analysis showed that suppressing potassium- and sodium-rich aluminosilicate phases and promoting the formation of more thermally stable minerals achieved this improvement. These results demonstrate that slagging control can be achieved through a readily implementable pretreatment that directly modifies ash chemistry before combustion. From an engineering perspective, the most promising deployment route is as a front-end pretreatment for manure-combustion systems in which wash water can be recycled and drying can be assisted by low-grade or waste heat. In such settings, the principal benefit is improved operational stability through reduced slagging, rather than stand-alone fuel upgrading.