Activated carbon filters work by absorbing contaminants onto the surface of carbon particles. They can improve the taste and odor of water by removing certain industrial wastes, pesticides, decaying organic material, dissolved gases, residual chlorine and by-products of chlorination. Activated carbon effectively removes many chemicals and gases, and in some cases it can be effective against microorganisms. However, generally it will affect total dissolved solids, hardness, or heavy metals. Activated carbon is created from a variety of carbon-based materials in a high-temperature process that creates a matrix of millions of microscopic pores and crevices. It is used to remove certain microorganisms and certain organic chemicals, especially pesticides, THMs, trichloroethylene and PCBs.

Activated Sludge is a process dealing with the treatment of sewage and industrial wastewaters. Atmospheric air or pure oxygen is bubbled through primary treated sewage combined with organisms to develop a biological floc, which reduces the organic content of the sewage. The combination of raw sewage and biological mass is commonly known as mixed liquor. This is the active biological material produced by activated sludge plants and which affects all the purification processes.