at high surface loads (8 m/h) and contained up to 50 % CaC03, but were rather
unstable. Zoetemeijer and others (1981 ) observed granulation in the acidification
of glucose in an USB-reactor at residence times shorter than 1 hour at a glucose
concentration of 10 kg/m3 and shorter than 6 hours at 50 kg glucose/m3. The
granules formed were about I mm in diameter and were unstable under unfed
conditions. The fact that 'methanogenic' granulation takes place at higher
residence times and that far more stable granules are formed with anaerobic
wastewater treatment (granular methanogenic sludge remains well conserved under
unfed conditions for several years) gives evidence that the mechanism of the
formation of methanogenic granules differs from that of denitrifying and
acidifying bacteria.
Through the increasing practical experience with UASB-reactors, it became
obvious that the composition of the wastewater plays a rather dominant role.
Wastewaters as indicated in Table I gave good results, while problems arose
with rendering waste, distillery waste and corn-starch waste. However, with all
these types of waste ultimately granulation of the sludge occurred.