Anaerobic stabilization of sludge

During the anaerobic stabilization of sludges from wastewater treatment plants, the buffer value of undissolved carbonates is particularly important. 

For the titration of a carbonate system, titration indices 4.5 and 8.3 are used, but for the analysis of sludge water from anaerobic stabilization of sludge the value of pH 5.78 has been recommended [18]. To determine the consumption of acid or base for neutralization of wastewaters titration to pH 7.0 is recommended. 

Currently, mechanical and biological wastewater treatment with anaerobic stabilization of sludge is used most frequently, with various modifications of the last stages of sludge disposal. 

A considerable proportion of the sludge dry matter is that ascribed to lipids (ether and petroleum-ether extractable substances), consisting of free fatty acids, their esters and substances incapable of undergoing saponification. The content of fatty acids in sludge is a value which is useful for characterizing the biochemical conditions in the anaerobic process of sludge stabilization. 

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. 

Azo dye metabolites Activated sludge Under aerobic conditions, two compounds 4,4 -thiodianiline and p-kresidine were most easily degraded, followed by 4,4 -diaminodiphenylmethane and 2-naphthylamine. Under anaerobic conditions, stabilities of the amines were totally different and compounds p-kresidine, 4,4 -diaminodiphenyl methane, and 2-naphthylamine were degraded while the 4-chloroaniline, 2,4-diaminotoluene, and 2,4-diaminoanisole were partly degraded [16]... 

Under anaerobic conditions, mirex was slowly dechlorinated to the 10-monohydro derivative by incubation with sewage sludge bacteria for two months (Andrade and Wheeler 1974 Andrade et al. 1975 Williams 1977). The primary removal mechanism for mirex was anaerobic degradation as demonstrated by the 6-month stability of the compound in nine aerobic soils and lake sediments (Jones and Hodges 1974). 

Anaerobic treatment of CP-containing liquids has been reported in fixed-film reactors (Hend riksen et al., 1991) and upflow anaerobic sludge bed reactors (UASB) with anaerobic granular sludge, resulting in less-chlorinated phenols (Hendriksen etal., 1992 Mohn Kennedy, 1992 Woods etal., 1989) or mineralization (Wu et al., 1993). WithMCPs, the UASB treatment resulted in mineralization (Krumme Boyd, 1988). UASB had better PCP removal efficiency and stability than anaerobic fixed-film reactors (Hendriksen Ahring, 1993). Anaerobic remediation always requires the addition of an external electron donor. 

Cell recycle fermentors consist of two main units a vessel where the biomass is allowed to grow, and a membrane separation unit (as in Figure 7.40). Vessels are usually designed to insure a uniform concentration of nutrients and pH throughout the whole volume. Due to complete mixing, process control and stability of the microbial slurry are not difficult to achieve.88 After anaerobic stabilization, when the biomass is well developed, the reactor biomass is pumped to the UF unit where solid-liquid separation occurs. The sludge is flushed back to the reactor. In most cases, the flow rate of nutrient feed is kept equal to the permeate flow rate thus keeping a constant liquid level in the anaerobic reactor. 

Table 3.66. Composition of primary, anaerobically stabilized and activated sludges in per cent of dry mass...

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