• The sewer water can be treated, the ground scraps extracted and either burned or deposited in land fill. Likewise the solid matter collected can either be burned or buried.

• Fuel quality is a very important determinant of the eventual impact on air quality. Coal, for example, contains various impurities and chemical components, such as minerals, metals, volatile matter and sulfur.

• The chemical interactions that lead to the formation of sulphate, nitrate and secondary organic aerosols are complex and, when a change in emissions of SO2, NOx, or VOCs occurs, the resulting change in the concentration of fine particulate matter is dependent on many factors