Optimization Of Sludge Settleability And Dewaterability Using Pilot Scale Liquid State Bioconversion Process Under Non-Controlled Conditions

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.

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