The environmental impact of using biomass is mixed in its good and bad effects. Burning crops such as wood or switchgrass is simply a recycling of CO2. It has a net zero effect on the presence of most greenhouse gasses. On the other hand, burning such products can produce smoke with pollutants that can cause harm. Also, if the growth of vegetation, such as wood, cannot keep up with the use of it as fuel, then depletion of the vegetation (e.g. deforestation) can produce considerably negative impacts on the local population.
Burning animal or human waste in disposal plants can result in the release of chemicals hazardous to both local people and the environment in general. These types of problems can be solved, but only by installing and maintaining expensive removal processes for the hazardous compounds emitted in the smoke from the burning or the ash remains of the combustion process.