This paper presents experiences with a full scale UASB-reactor in a fruit juice factory. The focus is on demonstrating that a UASB-reactor is as suitable for campaign industries running only 2 months a year with higher concentrated wastewater as well as for the time outside the campaign when the wastewater concentrations are very low (average COD 1000 mg/l). A number of operating results and recommendations are given, resulting from the experiences in order to show solutions for handling these very different situations. Examples of recommendations are: discontinuous feeding 8 hours a day outside the campaign, removal of pellet sludge at the end of the campaign. These frame conditions provided a COD removal efficiency in the UASB-reactor consistently above 80% throughout the year. Furthermore, it is shown that the anaerobic pre-treatment of industrial wastewater is the cheapest way in regard to the running expenses.

Another point of research was the co-fermentation of the kieselguhre-sludge-mixture. Although only 10% of the load was based on this substrate at a volumetric loading rate of 3 kg COD/(m3 · d), there was a quick drop in pH to a level of 3.5 and the pellet structure of the biomass got lost.

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