II. Main Subjects
1. Definition of Terms ( Adapted,in part, from Crites and Tchobanoglous, 1998 and U.S. EPA, 1997)
2. Solids source, Characteristics, and Quantities
3. Solids processing flow diagrams
III. Closing Remarks
The constituents removed in wastewater-treatment plants include screenings, grit, scum, solids, and biosolids (sludge). The solids and biosolids resulting from wastewater-treatment operations and processes are usually in the form of a liquid or semisolid liquid, which typically contains from 0.25 to 12 percent solids by weight, depending on the operations and processes used. The term biosolids, as defined by the Water Environmental Federation (WEF 1998), reflects the fact that wastewater solids are organic products that can be used beneficially after treatment with processes such as stabilization and composting. The term sludge is generally used in conjunction with a process descriptor, such as primary sludge, waste-activated sludge, and secondary sludge. In cases where it is uncertain whether beneficial use criteria have been met, the term solids is used.
The problems of dealing with solids and biosolids are complex because (1) they are composed largely of the substances responsible for the offensive character of untreated wastewater; (2) the portion of biosolids produced from biological treatment requiring disposal is composed of the organic matter contained in the wastewater but in another form, and it, too, will decompose and become offensive; and (3) only a small part is solid matter (Metcalf and Eddy, 2003).
Conventional techniques of sludge digestion have many weak points; difficulties in reducing of sludge quantity, hard operations, and overload of N, and P with return sludge into wastewater treatment processes. Actually, the cost of sludge treatment occupies 40% of total wastewater-treatment (Ahn et all, 1999).
We have to accurately know the characteristics of sludge before studying operations and processes of wastewater treatment. With correct knowledge of it, we can also understand the mechanism of wastewater-treatments and solve the problems of dealing with sludge. As a result, to design solids processing, reatment, and disposal facilities properly, the sources, characteristics, and quantities of the solids to be handled must be known. So, in this paper, we’ll look into the characteristics of sludge.
1. Metcalf & Eddy, Wastewater Engineering (4th ed.), Chapt. 14, McGraw-Hill, 2003.
2. Lee, C.H., Na, Y.S., Kim, D.H., Lee, S.W., Song, S.K., Changes of physico-chemical properties of the activated sludge with anaerobic storage time, J. of Envi. Sci., vol.11(4), 339 ~ 346, 2002.
3. Ahn, K.H., Cha, H.Y., Characterization of sludge lysis using ozonized gas and aerobic digestion of waste activated sludge, 대한환경공학회 ’99 추계학술연구발표회 논문집(II), 1999.