Biosolids: Composition, Treatment, and Management Options
This chapter presents information on the composition of biosolids, treatment procedures, and management options. Lester describes raw sewage as a dilute, heterogenous medium that is generally rich in nitrogen. Raw domestic sewage entering as influent into the headworks of a wastewater treatment facility is composed of 99.9 percent water and 0.1 percent total solids. The quantity and nature (composition) of biosolids depends on the character of the sewage from which it is removed, the type of treatment facility, and on the nature of the treatment process by which it is obtained. Biosolids obtained from primary settling, usually 40 percent to 60 percent of the influent solids, is essentially the settleable solids in the raw sewage and is termed raw biosolids. The proportion of solids and water in liquid biosolids depends on the nature of the solids, its source, whether derived from primary or secondary settling tanks, and the frequency of removal from these tanks.