Sludge anaerobically digested

Parameter Primary influent Primary effluent Primary sludge Secondary effluent Waste activated sludge Anaerobic digester feed Centrifuge supernatant Centrifuge sludge... 

Table 2.1 Composition of landfill gas and biogas from farm plants and sewage sludge anaerobic digesters. 

Ana.eroblc Digestion. Methane can be produced from water slurries of biomass by anaerobic digestion in the presence of mixed populations of anaerobes. This process has been used for many years to stabilize municipal sewage sludges for purposes of disposal. Presuming the biomass is all cellulose, the chemistry can be represented in simplified form as follows ... 

The microorganisms grow in response to the food source suppHed in the wastewater and produce more biological sludge than is needed to maintain the process. This excess sludge must be wasted from the process and is usually treated by dewatering and aerobic or anaerobic digestion. 

Sludge Stabilization. Organic sludges need to be stabilized before ultimate disposal except in the case of incineration. This is usually achieved by either aerobic or anaerobic digestion. In aerobic digestion, the degradable volatile soHds are Hquefted and oxidized to CO2 and H2O. In anaerobic digestion the soHds are Hquefted and fermented to CH and CO2. 

Fig. 3. Process components for the activated-sludge process, with aerobic digestion at plants <473.1 m /h and two-stage anaerobic digestion at plants...

Sludge is destroyed by microorganisms and the kinetics of their life processes is temperature dependent. Short anaerobic digestion detention times are obtained at 35°C. Even shorter detention times are possible at 52—54°C, but detention in this range is costly. An increase in detention time occurs at 35—43°C and then a progressive decrease takes place until 52—54°C. This variation is caused by a change in character of the dominant process organisms. 

An anaerobic digester is a no-recycle complete mix reactor. Thus, its performance is independent of organic loading but is controlled by hydraulic retention time (HRT). Based on kinetic theoiy and values of the pseudo constants for methane bac teria, a minimum HRT of 3 to 4 days is required. To provide a safety factor and compensate for load variation as indicated earlier, HRT is kept in the range 10 to 30 days. Thickening of feed sludge is used to reduce the tank volume required... 

High-rate filtration Oxidation, see Activated sludge. High-rate filtration. Trickling filter Reduction, see Anaerobic digestion Phenol removal... 

Michalke K, EB Wickenheiser, M Mehring, AV Hirner, R Hensel (2000) Production of volatile derivatives of metal(loid)s by microflora involved in anaerobic digestion of sewage sludge. Appl Environ Microbiol 55 2791-2705. 

Hickey, R.F., Vanderwilen, J., and Switzenbaum, M.S., The effects of organic toxicants on methane production and hydrogen gas levels during the anaerobic digestion of the waste activated sludge, Water Res., 21, 1417-1427, 1987. 

Figure 26.8 Suspended growth anaerobic digestion using an upward flow anaerobic sludge blanket.

Anaerobic digesters reduce BOD levels between 40 and 70%. They can also remove nitrates.59 When two digesters are used, the first is agitated and the second is not. Less power is required than for activated sludge units. 

Juarez-Rodriguez et al. applied the sludge derived from anaerobically digested cow manure in the production of biogas (methane-air), to maize (Zea mays L.) cultivated in a nutrient-low, alkaline-saline soil with EC 9.4 dS m 1 and pH of 9.3. The results showed that the C02... 

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