An experimental system was set up to study the Substrate Shuttle Process (SSP). Whey was fed to an acidogenic UASB reactor. The effluent was intermittently circulated through an Ion Exchange Unit (IEU) containing an anionic exchange resin. During a load cycle, organic acids were adsorbed onto the ion exchange resin. After completion of the load cycle, the ion exchange resin was regenerated by recirculating through it the effluent of a methanogenic UASB reactor, into which the organic acids were released, prior to returning the liquid into the reactor. The pilot system was designed to operate automatically with two IEUs operating in tandem, of which one at a time was operating in a load cycle, while the other was being regenerated. The first experimental period lasted 9 days with a cycle duration of one hour. Acids were removed from the acid UASB liquor, with a concomitant rise of pH and the production of methane in the methanogenic UASB. The acid UASB produced little gas and no methane was detected. The amount of acids circulated through the IEUs was directly proportional with the quantity of methane produced by the methane UASB. After the trial, acid binding capacity had declined to 70% of its original value. A second experiment lasted 118 days, with a cycle duration of five hours. Final conversion of all acid circulated through the IEUs into methane averaged 19%. After initial conditioning of the resin, no significant long-term deterioration of process performance was evident.

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