FULL-SCALE ANAEROBIC TREATMENT OF BEET-SUGAR
WASTEWATER
Kees C. Pette, Engineer
Rob de Vletter, Engineer
Evert Wind, Engineer
Wim van Gils, Engineer
CSM Suiker b. v.
Amsterdam
The Netherlands
In the period from 1966 to 1972 the Centrale Suiker Maatschappij (CSM) carried out
an intensive study with respect to the wastewater situation at her beet sugar factories [ 1 ].
It was found that after internal clean-up an unavoidable more or less concentrated wastewater stream would remain. This stream originates from the washing of the beets. The most
important soluble impurities are sugar and its break-down products. A study for the most
efficient method of removing of these impurities showed that anaerobic wastewater purification offered very attractive possibilities. However, at that time this technology was still
under-developed and very few anaerobic treatment plants for purification of wastewater
were operating successfully.
The favorable perspectives which anaerobic wastewater treatment should be able to offer
also had caught the attention of Lettinga of the Department of Water Pollution Control
at the Agricultural University of the Netherlands. They were developing and testing a new
concept in digester design; the upflow anaerobic sludge blanket process (U.A.S.B.).
In 1973 CSM and Lettinga decided to continue their studies together on a pilot plant
scale for the purpose of developing an industrial sized anaerobic treatment plant. Quite
a few publications [2-6] appeared during recent years, concerning the principles and feasibilities of the U.A.S.B. process and about the research being carried out in the Netherlands.
The purpose of the present paper is to report on some of the main results in the technical
applications of this anaerobic treatment method at the CSM factories.
ANAEROBIC TREATMENT PLANTS
The basic concept of the U.A.S.B. digester design is that the wastewater is fed into the
tank from below and leaves it at the top via an internal baffle system for separation of the
gas, sludge and liquid. The presence of such a separator has been proven to oe ot
fundamental importance. It enables the sludge particles to settle back towards the digesting
zone, thus ensuring adequate sludge residence times and high anaerobic sludge
concentrations in the digester. In the method of operating the process sludge recirculation
over an internal clarifier is omitted completely and the mixing within the digester is done
by the gas production of the anaerobic sludge only. Efficient means of distributing the feed
over the bottom of the tank therefore is indispensable. In Figure 1 a schematic drawing of
the U.A.S.B. reactor is given.
Since 1974 the CSM has built, in a program towards realising full scale anaerobic
treatment at one of its factories, three pilot plants. In 1974 the scaling up work was started
by the building of a 6 m3 pilot plant, followed by the construction of two larger pilot
plants of 30 and 200 m3 volume capacity in 1976 and 1977, respectively. Some characteristic results of the operation of the pilot plants are listed in Table I.
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