The studied organic chemical wastewater had a high COD, 20–45 g/L, and low TSS, less than 200 mg/L, making anaerobic bio-filtration a suitable treatment method. The organic matter consisted of alcohols, amines, ketones and aromatic compounds, such as toluene and phenol. Granulated activated carbon (GAC) and a porous stone called tezontle, widely available in Mexico, were used as a bio-film support. Once inoculated, the mesophilic reactors with granulated activated carbon (GAC-BFs) reached stability with 80% COD removal in 40 days, while the reactors with tezontle material (tezontle-BF) required 145 days. Biodegradation of more than 95% was obtained with both support media: at organic loads less than 1.7 kg m−3 d−1 in tezontle-BF and with loads of up to 13.3 kg m−3 d−1 in GAC-BFs. The bio-filters with GAC allowed COD removal efficiency of 80% at a load as high as 26.3 kg m−3 d−1, while the same efficiency with tezontle was obtained at loads up to 4.45 kg m−3 d−1. The use of GAC as support material allows greater biodegradation rates than tezontle and it makes the bio-filters more resistant to organic increases, inhibition effects and toxicity. Methanogenic activity was inhibited at loads higher than 1.7 kg m−3 d−1 in bio-filters with tezontle and 22.8 kg m−3 d−1 in bio-filters with GAC. At loads lower than the previously mentioned, high methane production yield was obtained, 0.32–0.35 m3CH4/kg CODremoved. The biomass growth rates were low in the bio-filters with both kinds of material; however, a sufficiently high biomass holdup was obtained.

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