Sewage sludge tests

The results of sewage sludge tests (Fig. 12.7) and the soil terrarium (Fig. 12.8) were remarkably similar in form, but the sludge degradation is much more rapid. 

Figure 7. Biodegradation of various polyethylenes as measured by release of " C02 in sewage sludge test...

An official gas chromatographic method [29] is available from the determination of volatile fatty acids in sewage sludge. This method is based on gas liquid chromatographic estimation with a flame ionization detector, and is applicable up to 2000mg total volatile fatty acids per litre, while the concentrations of individual fatty acids can also be determined. Where this method is not practicable an empirical method based on the spectrophotometric determination of ferric hydroxamates can be used, giving a value for total fatty acids expressed as acetic acid. For control purposes a rapid test is described in which the volatile fatty acids are determined by electrometric titrimetry on the neutralized sludge obtained from the determination of alkalinity. 

Aerobic degradation of diethyl phthalate by acclimated soil and activated sewage sludge microbes was studied using an acclimated shake flask CO2 evolution test. After 28 d, loss of diethyl phthalate (primary degradation) was >99%, with a lag phase of 2.3 d, and ultimate biodegradation (CO2 evolution) was 95%. The half-life was 2.21 d (Sugatt et al., 1984). 

Genotoxicity is one of the most important characteristics of toxic compounds in waste. For studying genotoxicity of waste, contaminated soil, sewage sludge, and sediments the conventional Ames test with Salmonella is usually used together with SOS-Chromotest and Mutatox [11,19,50-52,165-167]. 

The examples of the attribution of the real sewage sludge formed on different treatment plants to the classes of hazard are presented in Table 7. The same approach was adopted in Russia for the attribution of the waste as a whole to the classes of hazard. The only difference is the use of the test organisms representing water life (water flea, algae, protozoa) [174]. 

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