Sludge digestion

SoHd by-products include sludge from wastewater treatment, spent catalyst, and coke from the EDC pyrolysis process. These need to be disposed of in an environmentally sound manner, eg, by sludge digestion, incineration, landfill, etc. 

The whole proeess of sludge digestion may be likened to a faetory produetion line where one group of workers takes the raw material and eonditions it for a seeond group with different "skills" who eonvert the material to the end produets. 

Water treatment Clarification of potable water, industrial effluents, municipal waste water thickening and dewatering of sludge filtration of primary sludge, digested sludge food processing... 

Primary 400-250 Comminution, sedimentation, sludge digestion or incineration Flocculations by chemical additives, flotation... 

Surfactants such as LAS and NPEO have been found in compartments with low oxygen content, such as anaerobic sludge digesters or anaerobic continental and marine sediments [14,15,18-25]. One of the possible causes of this persistence is the inhibition of the anaerobic digestion [17,26,27]. Battersby and Wilson [27] observed inhibitory effects of NP at 50 mg CL-1 on methane formation in a survey of the anaerobic biodegradation potential of organic chemicals in digesting... 

In sludge digester startup, this condition is known as a stuck digester and can be cured by the slow addition of alkaline buffers to the mix. Strong alkalis can take the mix well out of the sludge range, where all activity stops. 

Chen et al. (1999) studied the anaerobic transformation of 1,1,1-trichloroethane, 1,1-dichloroethane, and choroethane in a lab-scale, municipal wastewater sludge digester. 1,1,1-Trichloroethane degraded via reductive dechlorination to give 1,1-dichloroethane, chloroethane, and then ethane. When cell-free extracts were used, 1,1,1-trichloroethane degraded to acetic acid (90% yield) and 1,1-dichloroethylene, the latter degrading to ethylene. 

Kirk, P.W.W., Rogers, H.R., and Lester, J.N. The fate of chlorobenzenes and permethrins during anaerobic sewage sludge digestion, Chemosphere, 18(9-10) 1771-1784, 1989. 

Plant 000012 produces 3.9 x 10" kkg/year (8.7 x lO lb/year) of emulsion crumb rubber, primarily neoprene. The contact wastewater flow rate is approximately 8.45 m /day (2.25 X 10 gpd) and includes all air pollution control equipment, sanitary waste, maintenance and equipment cleanup, and direct contact wastewater. The treatment process consists of activated sludge, secondary clarification, sludge thickening, and aerobic sludge digestion. Noncontact wastewater, with a flow rate of approximately 1.31 x 10 m /day (3.46 x 10 gpd), is used on a once-through basis and is remrned directly to the river source. Contact wastewater is also returned to the surface stream after treatment. 

TABLE 3.2 Sorption Parameters for Six Commonly Encountered Pharmaceuticals in Two Soils and with Sludge Digested Under Distinctly Different Conditions"... 

Anaerobic bioreactors have been used since the 1880s to treat wastewaters with large amounts of suspended solids. However, anaerobic reactors are sensitive to toxic pollutants and vulnerable to process upsets, and have been used mainly for municipal sludge digestion. For methane production the sequential metabolism of the anaerobic consortia must be balanced, and the methanogens in particular are vulnerable to process upsets. Recently, anaerobic-aerobic processes (Figure 1.1) have been developed for the mineralization of xenobiotics. These processes take advantage of an anaerobic reactor for the initial reductive dechlorination of polychlorinated compounds or the reduction of nitro substituents to amino substituents. If the reduced compounds are more readily mineralized in an aerobic reactor, an anaerobic-aerobic process is feasible. 

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