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

Optimization of process parameters for pilot-scale liquid-state bioconversion of sewage sludge by mixed fungal inoculation

Liquid-state bioconversion (LSB) technique has great potential for application in bioremediation of sewage sludge. The purpose of this study is to determine the optimum level of LSB process of sewage sludge treatment by mixed fungal (Aspergillus niger and Penicillium corylophilum) inoculation in a pilot-scale bioreactor. The optimization of process factors was investigated using response surface methodology based on Box–Behnken design considering hydraulic retention time (HRT) and substrate influent concentration (S0) on nine responses for optimizing and fitted to the regression model. The optimum region was successfully depicted by optimized conditions, which was identified as the best fit for convenient multiple responses. The results from process verification were in close agreement with those obtained through predictions. Considering five runs of different conditions of HRT (low, medium and high 3.62, 6.13 and 8.27 days, respectively) with the range of S0 value (the highest 12.56 and the lowest 7.85 g L−1), it was monitored as the lower HRT was considered as the best option because it required minimum days of treatment than the others with influent concentration around 10 g L−1. Therefore, optimum process factors of 3.62 days for HRT and 10.12 g L−1 for S0 were identified as the best fit for LSB process and its performance was deviated by less than 5% in most of the cases compared to the predicted values. The recorded optimized results address a dynamic development in commercial-scale biological treatment of wastewater for safe and environment-friendly disposal in near future

Liquid state bioconversion continuous bioreactor of sewage sludge treatment: Determination and evaluation of mixed fungi growth kinetics

Liquid state bioconversion (LSB), a bioremediation and biodewatering process was applied for sewage sludge treatment in this study. The LSB process is a non-hazardous, safer and environmentally friendlier method for ultimate sludge management and disposal compared to the other available technologies. The system presented in this study was developed by using mixed fungi of Aspergillus niger and Penicillium corylophilum to treat sewage sludge in a LSB bioreactor. This research was conducted in order to study the LSB process on continuous system in terms of kinetic coefficients determination. For the continuous LSB process, a mathematical model was developed from the basic principles of material balance based on Monod equation. By investigating the kinetics of substrate utilisation and biomass growth, the kinetic coefficients of growth yield coefficient (Y), specific microorganism decay rate (Kd), half saturation constant (Ks) and maximum specific growth rate (μmax) were found to be 0.79 g VSS g COD−1, 0.012 day−1, 1.78 g COD L−1 and 0.357 day−1, respectively