2) Incinerators

In incinerators of conventional design, refuse is burned on moving grates in refractory-lined chambers; combustible gases and the solids they carry are burned in secondary chambers. Combustion is 85 to 90 percent complete for the combustible materials. In addition to heat, the products of incineration include the normal primary products of combustion is carbon dioxide and water as well as oxides of sulfur and nitrogen and other gaseous pollutants; nongaseous products are fly ash and unburned solid residue. Emissions of fly ash and other particles are often controlled by wet scrubbers, electrostatic precipitators, and bag filters.

Composting operations of solid wastes include preparing refuse and degrading organic matter by aerobic microorganisms. Refuse is presorted, to remove materials that might have salvage value or cannot be composted, and is ground up to improve the efficiency of the decomposition process. The refuse is placed in long piles on the ground or deposited in mechanical systems, where it is degraded biologically to a humus with a total nitrogen, phosphorus, and potassium content of 1 to 3 percent, depending on the material being composted. After about three weeks, the product is ready for curing, blending with additives, bagging, and marketing.

Waste from the garden, yard, and table does not have to be thrown away. It may be condensed and reused as a fertilizer through a process called composting. A compost pile may be built by layering different kinds of waste in a bin, leaving space between the layers for air to circulate. Nitrogen is added to the pile in the form of manure, meal, or greenery to generate heat. Heat facilitates rotting and kills all undesirable organisms. Once the pile is slightly dampened, it is covered. As heat and steam build up, the waste decomposes over time into a nutrient-rich substance called compost. The compost is then applied to plants as a fertilizer.