The horizontal flow state of water in R3 was homogenous,
resulting in a relatively constant accumulated removal
efficiency of CODtot and CODdis in all the three operation
phases. Most of the primary sludge added into the reactor
was carried to the second and third compartments with the
horizontal flow of water. Therefore, the individual removal
efficiencies of CODtot and CODdis in the third compartment
were lower than those in the first and second compartments
(shown in Table 2). The individual removal efficiency of
CODtot in the first compartment in R3 increased from 28%
in P1 to 51% in P3, despite the reduction in HRT. This
indicated that the anaerobic sludge was getting stable with
the operation of the reactor. It has been shown in previous
studies that the performance of a septic tank improves with
increasing periods of operation.[9]
The effluent in R2 had the highest value for
CODdis/CODtot of 94% among the three reactors in P1,
which indicated that R2 had the most effective solids
removal performance when HRT was 36 h due to the retaining
effect of the YDT carrier. However, this effect was
weakened with the decrease of HRT as reflected by the dramatically
reduced CODdis/CODtot value, which fell from to
73%and61%in P2 and P3, respectively. However, this ratio
in the effluent of R1 stabilized at approximately 80% when
HRT decreased from 36 to 12 h, indicating that the baffled
chambers were efficient and stable for solids removal even
under the shorter HRT.