Anaerobic treatment of inuline effluent in an internal circulation reactor

Sensus Operations C.V. is a 100 percent subsidiary of the Dutch Sulker Unie group (Cosun). At the site in Roosendaal it operates an inuline and fructose production line, using chicory beet as raw material. Inuline is a product which is gaining more and more popularity as a structural improver in food, as a low calory replacement in ice-cream and chocolate bars and as moisturizer to improve the spreadability of cleaning products. It consists of a polyfructose fibre which is hardly degraded in the human body. The cleaning and chipping process of the chicory beet is similar to the sugar beet preparation process and so is the effluent. The production process itself is different and the effluent released, also contains the effluent from a demineralisation plant, which results in an additional high COD and salt loaded effluent, During the first two years of inuline production the ''heavy water'' (high GOD, salty effluent) was simply added to one of the existing UASB reactors, because the inuline factory was running at a very low capacity. However since 1995 the production could be increased drastically to 1500 tpd so that an extra anaerobic treatment unit had to be installed. The third reactor would require enough capacity to convert 30 tons of COD per day (GOD load 37.5-40 tpd). However, the investment was quite high and the reactor volume would be of such a size that it would be more difficult to operate, considering the sludge weight and the important ground surface. At the moment the size of the reactor was known, the idea was born to consider the installation of an Internal Circulation (IC) reactor. This reactor was 25% lower in investment cost and space occupation was only 55 m(2) instead of 450 m(2). This paper reveals the performance of the IC reactor during the first campaign in 1995. (C) 1997 IAWQ. Published by Elsevier Science Ltd.