Horizontal grinders chew up demolition debris and municipal waste, making them easier to haul, discard or recycle. They also allow the processing of trees, stumps, brush, other woody feedstocks and asphalt shingles into salable products. Portable grinders are diesel powered Stationary, electric-powered models are also in widespread use. The technology surrounding feed wheels, rotors and screens have turned the problem of waste into a profitable business opportunity.