In Austria as well as in Germany, several ideas have been put forward on how to describe the biological activity of waste. Gas-generation potential, respiration activity and analysis of material groups ('Stoffgruppenanalysen' according to Van Soest, 1963) and eluate parameters like TOC, NH4-N, COD and BOD were discussed. The use of the Incubation Test (developed by the Department of Waste Management of the Universität für Bodenkultur Wien (University of Agricultural Sciences, Vienna) -ABF-BOKU) as an experimental determination of gas generating potential is very well suited for assessing the reactivity of wastes. Large sample sizes (> 1 kg DS) and robust test conditions ensure good reproducibility of results. Due to the very long testing time (an incubation test lasts approx. 3-8 months) alternative methods were to be developed. Therefore we undertook practical tests to describe the reactivity of mechanically-biologically pre-treated (MBP) residual wastes from different treatment plants (Binner et al., 1997; Binner and Zach, 1998). Our research showed that gas production in 90 days (GS90) and respiration activity in 7 days (AT7) are the best suitable parameters for determining the biological reactivity of waste. We suggest limit values for GS90 < 20 Nl/kg DS and a correlating AT7 of about 11 mg O2/g DS. This results in a decrease of potential releasable landfill gas volume of more than 90% compared to untreated waste.
Because of a shorter test duration, the AT4 and GB21 are favoured in Germany. In September 1998 we started a research program in order to compare the incubation test (GS90) and the fermentation test (GB21) by testing low reactive samples.