5. Conclusions
The results reported in this paper have shown that, even if
SBBGR treatment does not assure depurative levels sufficient for
direct discharge, it is suitable as an on-site treatment before
discharge in public municipal sewer systems. In fact, an overall
inspection of the results reveals some undoubtable points of
strength inherent in the use of SBBGR: good treatment efficiencies
can be obtained with an OLR as high as 2.4e2.6 kgCOD m3 d1 and
HRT around 20 h.
Despite the great variability in composition, stable performances
were observed for all the examined parameters. Wide
variations were reported only for colour, being removal strongly
dependent on the wastewater stock rather than on the operating
condition. However, these variations do not hinder the possibility
to discharge the treated effluent into the sewer system.
Compared with the results of previous studies with SBRs, higher
OLRs and lower HRTs can be used with SBBGR, resulting in the need
for smaller reactors and in the consequent reduction of costs.
Moreover, the possibility to adopt cycles of 6e8 h does no longer
require the presence of a post-treatment tank for the accumulation
of wastewater before discharge into the sewer system needed
to avoid peak flow discharges of treated wastewater into the
sewerage.
Another remarkable aspect is the very low sludge production. As
sludge treatment and disposal accounts for a large part of treatment
cost in a conventional wastewater treatment plant, SBBGR is
expected to be really competitive, strongly reducing global treatment
costs.