Aerobic domestic waste water treatment in a pilot plant with complete sludge retention by cross-flow filtration
Muller, E. B., Stouthamer, A. H., Verseveld, H. W. van and Eikelboom, D. H. 1995
Aerobic domestic waste water treatment in a pilot plant with complete sludge retention by cross-flow filtration.
Water Research, 29: 1179 - 1189.
Abstract
An aerobic wastewater treatment pilot plant with cross-flow filtration
was operated for more than 300 days to examine whether reduced sludge
production and stable treatment performance can be achieved when
sludge is completely retained. The volumetric loads ranged between 0.9
and 2.0 g COD.l-1.day-1. Technical observations
were: the oxygen transfer rate became poor at high sludge
concentrations; membrane capacities declined but could be mostly
sufficiently restored by cleaning. Sludge was hardly produced when the
mixed liquor suspended solid (MLSS) concentration had increased to
40-50 g.l-1. Then, the sludge load was only 0.021 g COD.g
MLSS -1 .day-1 and only 6% of the carbon
supplied was assimilated. Non-volatile compounds hardly accumulated as
the fraction of inorganic compounds in sludge increased from 21.6 to
23.5% during the last 200 days, whereas the carbon, phosphor and
kjeldahl nitrogen contents were stable. After 300 days the content of
polluting trace elements, such as mercury, lead and cadmium, were
similar to that of a conventional treatment plant supplied with this
wastewater. Carbon and kjeldahl nitrogen removal was always quite
satisfactory. Carbon was always removed for more than 90% and kjeldahl
nitrogen that was not assimilated was completely nitrified at all
times. The nitrification capacity at 30°C was constantly around 0.2
mmol, g MLSS-1h-1, which shows that the
viability of the nitrifying population did not cease. In addition, up
to 400 of nitrogen supplied was lost as a result of
denitrification. Hence stable treatment performance and a very low
sludge production can be achieved when complete sludge retention is
applied at high hydraulic loads.