Use of wet oxidation for making the recalcitrant part of organic matter available for use in Danish biogas plants. Furthermore, detoxification of tar residuals formed during pyrolysis of straw in a thermophilic biogas plants

The pyrolysis condensate and the wet oxidised condensate have a biogas potential of 190 m3/ton VS, and the low amount of suspended solids is allowing the waste water to be treated in the UASB reactor as well as in the CSTR. The pyrolysis condensate could successfully be degraded in a CSTR in a 5% concentration when codigested with manure, and the wet oxidised pyrolysis condensate could be degraded when added at a concentration of 30%. The UASB reactor was preferred over the CSTR since the xenobiotic compounds present in the waste water might easily be absorbed on the co-substrate required when using the CSTR technology. Consequently, decreased degradation of xenobiotics would be observed in the CSTR. A combined anaerobic and denitrifying UASB reactor was successfully digesting 5.5% of wet oxidised pyrolysis condensate, but further loading increments deteriorated the anaerobic digestion process. However, when a UASB reactor was fed with pyrolysis condensate (up to 100%) good reactor operation was observed indicating that the waste could be used as substrate in the biogas process, even in very high concentrations. The detoxification of pyrolysis condensate was further studied and the toxicity of pyrolysis condensate was decreased more than 77 times in the UASB reactor that was operating on 100% pyrolysis condensate. Phenol, methyl and dimethylphenols along with methoxyphenols were shown to be degraded within the reactor systems. Degradation rates for phenol and substituted phenols were determined indicating that the biomass was selective towards the substrates. Maximum growth rates and half saturation constants for phenol, 4-Methylphenol and 2-Methoxy-4-methylphenol were determined in batch experiments. A UASB reactor concept was further designed for the treatment of pyrolysis condensate at the gasification plant at Harboøre, DK