conventional activated sludge systems, and
especially extended aeration systems;
• thanks to the lower sludge production in
anaerobic systems and to their better dewaterability, sludge volumes to be disposed of from
anaerobic/aerobic systems will be much lower
than those from aerobic systems alone.
According to studies carried out by Pontes
(2003), a 30% VSS destruction can be reached
when secondary sludge produced in a trickling
filter is returned to a UASB reactor. When the
mass balance is performed, the total sludge
production in a combined UASB/Trickling Filter system can be 30–50% lower than in a conventional trickling filter system.
• the construction cost of a treatment plant with
UASB reactor followed by aerobic biological
treatment usually amounts 50–80% of the cost
of a conventional treatment plant (20–50%
investment savings). In addition, due to the simplicity, smaller sludge production and lower
power consumption of the combined anaerobic/
aerobic system, the operational costs also represent an even greater advantage. Savings on
operation and maintenance costs are usually in
the range of 40–50% in relation to a conventional treatment plant (see Table 4 and von
Sperling & Chernicharo 2005).