SummaryIn recent years considerable effort has been made in the Netherlands toward the development of a more sophisticated anaerobic treatment process, suitable for treating low strength wastes and for applications at liquid detention times of 3-4 hr. The efforts have resulted in a new type of upflow anaerobic sludge blanket (UASB) process, which in recent 6 m3 pilot-plant experiments has shown to be capable of handling organic space loads of 15-40 kg chemical oxygen demand (COD).m-Yday at 3-8 hr liquid detention times. In the first 200 m3 full-scale plant of the UASB concept, organic space loadings of up to 16 kg COD.~n-~/day could be treated satisfactorily at a detention time of 4 hr, using sugar beet waste as a feed. The main results obtained with the process in the laboratory as well as in 6 m3 pilot plant and 200 m3 full-scale experiments are presented and evaluated in this paper. Special attention is given to the main operating characteristics of the UASB reactor concept. Moreover, some preliminary results are presented of laboratory experiments concerning the use of the USB reactor concept for denitrification as well as for the acid formation step in anaerobic treatment. For both purposes the process looks feasible because very satisfactory results with respect to denitrification and acid formation can be achieved at very high hydraulic loads (12 day-') and high organic loading rates, i.e., 20 kg COD.~n-~/day in the denitrification and 60-80 kg C O D~r~/ d a y in the acid formation experiments.

The influence of the sludge loading rate, the addition of a small amount of granular sludge to the seed sludge and the effect of the NH4+- and Ca2+-concentration in the influent on the pelletization-process of anaerobic methanogenic sludge in UASB-reactors were studied. Two different types of sludge granules can be obtained with VFA's as feed-solution.

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This paper aims to contribute to the assesment of a (more) optimal design and operation of a high rate anaerobic waste water treatment process. The discussion will be made on basis of available information of modern anaerobic waste water treatment processes, such as the Anaerobic Filter Process and the Upflow Anaerobic Sludge Blanket process and of recently introduced Attached Film processes.

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