8.1 Environmental challenges in energy, carbon dioxide, air, water  (Page 9/21)

The ash from these plants may contain high concentrations of various metals that were present in the original waste. If ash is clean enough it can be “recycled” as an MSW landfill cover or to build roads, cement block and artificial reefs.

Biomass

Biomass is derived from plants. Examples include lumber mill sawdust, paper mill sludge, yard waste, or oat hulls from an oatmeal processing plant. A major challenge of biomass is determining if it is really a more sustainable option. It often takes energy to make energy and biomass is one example where the processing to make it may not be offset by the energy it produces. For example, biomass combustion may increase or decrease emission of air pollutants depending on the type of biomass and the types of fuels or energy sources that it replaces. Biomass reduces the demand for fossil fuels, but when the plants that are the sources of biomass are grown, a nearly equivalent amount of CO ₂ is captured through photosynthesis, thus it recycles the carbon. If these materials are grown and harvested in a sustainable way there can be no net increase in CO ₂ emissions. Each type of biomass must be evaluated for its full life-cycle impact in order to determine if it is really advancing sustainability and reducing environmental impacts.

Solid biomass: burning wood

Using wood, and charcoal made from wood, for heating and cooking can replace fossil fuels and may result in lower CO ₂ emissions. If wood is harvested from forests or woodlots that have to be thinned or from urban trees that fall down or needed be cut down anyway, then using it for biomass does not impact those ecosystems. However, wood smoke contains harmful pollutants like carbon monoxide and particulate matter. For home heating, it is most efficient and least polluting when using a modern wood stove or fireplace insert that are designed to release small amounts of particulates. However, in places where wood and charcoal are major cooking and heating fuels such as in undeveloped countries, the wood may be harvested faster than trees can grow resulting in deforestation.

Biomass is also being used on a larger scale, where there are small power plants. For instance, Colgate College has had a wood-burning boiler since the mid-1980’s and in one year it processed approximately 20,000 tons of locally and sustainably harvested wood chips, the equivalent of 1.17 million gallons (4.43 million liters) of fuel oil, avoiding 13,757 tons of emissions, and saving the university over $1.8 million in heating costs. The University’s steam-generating wood-burning facility now satisfies more than 75 percent of the campus's heat and domestic hot water needs. For more information about this, click here

Gaseous biomass: landfill gas or biogas

Landfill gas and biogas is a sort of man-made “biogenic” gas as discussed above. Methane and carbon dioxide are formed as a result of biological processes in sewage treatment plants, waste landfills, anaerobic composting, and livestock manure management systems. This gas is captured, and burned to produce heat or electricity usually for on-site generation. The electricity may replace electricity produced by burning fossil fuels and result in a net reduction in CO ₂ emissions. The only environmental impacts are from the construction of the plant itself, similar to that of a natural gas plant.