The study of microbial treatment of domestic wastewater treatment plant (DWTP)
sludge, by liquid state bioconversion (LSB) process, was conducted using several
approaches under sterilized controlled conditions in a bench scale with co-substrate
supplementation. For this purpose, the mixed strains (P/A) of two selected
filamentous fungi SCahmA103 (Aspergillus niger) and WWZP1003 (Penicillium
corylophilum) were used to evaluate the performance of the LSB process in the
bench scale and pilot scale, under optimized non-controlled conditions without cosubstrate
in terms of biodegradation, bioseparation, biosolid accumulations, settling
and dewatering of the DWTP sludge.
Three numerical parameters, namely sludge concentrations TSS (w/w %), inoculum
sizes (v/w %) and inoculum feeding intervals (hrs.), with three levels statistical
design under the response surface methodology (RSM), were optimized with and
without co-substrate supplementation to evaluate the performance of the process in
terms of acclimatization and biodegradation of the DWTP sludge, under non controlled (natural) conditions. The optimum process parameters of the TSS (w/w
%), inoculum size (v/w%) and inoculum feeding interval (hrs.) were observed to be
1% w/w, 5 %v/w and 11 hrs, respectively, without any co-substrate supplementation
to get the maximum predicted values of adaptation, and the COD removal of 98%
and 96.7%, respectively, in the fungal-treated sludge by LSB under the noncontrolled
(natural) conditions in shake flasks.
Another three-level statistical design under RSM was used to optimize the process
parameters of aeration rates (vvm) and mixing rate (rpm) in a 100 L pilot-scale using
the optimized value obtained from the shake flasks. This design was selected to
evaluate the bioconversion performance, using the mixed culture P/A, under natural
conditions in the pilot-scale in terms of biodegradability and biodewaterability of the
DWTP sludge. The optimum aeration rate (vvm) and mixing rate (rpm) of 0 vvm
and 10.5 rpm were respectively used to obtain the maximum predicted COD and
SRF responses of 98.9% and 98%, respectively in the fungal-treated sludge by the
LSB, under the natural conditions in the pilot-scale.
In terms of biodegradation, bioseparation and biosolid accumulations of the DWTP
sludge, the validation results gathered from the statistical models in the shake flasks
and pilot-scale showed that the LSB efficiency was higher in the pilot-scale than in
the shake flasks. Consequently, the optimized values obtained from the two
statistical models were used at a 200 L pilot-scale to investigate the settleability and
dewaterability characteristics in fungal treated with DWTP sludge, under natural
conditions. The results for settleability suggested that 65% of the sludge was settled
after one minute of settling period, with a maximum TSS reduction of 99%. The
sludge volume index (SVI) reduction of 86% for the treated and untreated sludge was 10 minutes and 180 minutes, respectively. Specific resistance to filtration (SRF) was
found to decrease by 98% in the treated sludge after 3 days of fungal treatment, as
compared to the untreated sludge. This suggested that the settleability and
dewaterability of the DWTP sludge, in the developed LSB process, were highly
influenced by the fungal mycelial entrapment under the non-controlled (natural)
conditions in the pilot scale