Stratified ecology techniques in the startup of an anaerobic downflow fixed film percolating reactor

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Abstract
A two-column pilot scale downflow percolating fixed film (DPFF) anaerobic reactor treating deproteinized cheese whey (DPW) was used in this study. The system was operated at one-third of the maximum working volume in an attempt to avoid mass transfer limitations of the gas products (since two-thirds of the immobilized microbial culture was unsubmerged), as well as to minimize the effects of localized high volatile fatty acids (VFA) levels and low pH on its methanogenic activity. A new method to shorten the start-up period was used by growing methanogenic and acetogenic (H2-producers) bacteria on a synthetic medium until reaching a stable methane production rate and then switching the reactor over to DPW and allowing acidogenic growth. The start-up period was reduced to 35 days as a result of this operational mode. The reactor was able to handle 8 kg COD/ m3·d after 35 days of operation.