Most digesters in industrial-scale operate in deficient level and almost nominal due to inefficient process. Optimization of the process may rectify the issue but required a valid method that does not just improve the process yet able to unravel the eventuality of the intricate process if the adjustment needed. A proper tool is required. The central composite design (CCD) was implemented in this study to investigate the suitability of this tool for optimization of anaerobic digestion (AD) process. The main effect of pH and HRT studied in CCD acquired from the screening process show the importance of having neutral pH value and long retention period for a better biogas yield. The process with pH 7.0 and HRT 15.7 days, IP 33%, TS 4% and FR 4% found to be the optimum setting for the process. The new setting successfully improved the production output up to 60% compared with baseline (existing setting), while allowing 50% more sludge to be processed. The X2 goodness-of-fit test indicates that the mathematical model applied in this study is valid at 95% of confidence level with R2 of 0.9. The results presented in the paper demonstrate the reliability of CCD as optimization tools for AD process in the industrial scale sewage treatment plant (STP).
There are countless attempts on applying banana stem waste (BSW) as a feedstock for renewable energy, the materials are also known to be excellent substrate for various bioproducts. Ferulic acid happens to be one of the bioproducts that can be produced from BSW recognized to be great anti-oxidant compound and desired by pharmaceutical and food industries around the globe. This study employed enzymatic hydrolysis of feruloyl-polysaccharide from banana stem waste (BSW) by soil mixed culture (SMC) to produce ferulic acid (FA) using 25 full factorial design (FFD) to investigate the effect and interaction of these five factors affecting FA production: fermentation temperature (A; oC), agitation (B; rpm), water-to-BSW ratio (C;v/v), substrate-to-inoculums ratio (D;v/v), and inoculation time (E; days). The linear model was well fitted at R2=0.8019 with factors contribution percentages in the order of E > C > A > D > B. Inoculation time had 27.37% contribution indicating the importance of cell growth activities. The interaction of DE was highest since the SMC needs sufficient time for substrate utilization to get a high FA yield. The most FA output produced was 1.2187 mg FA/g BSW with parameters at ambient temperature, 150 rpm agitation, 1:1 water-to-BSW ratio, 1:1 substrate-to-inoculums ratio, and one day of inoculation. The hydrolysis process applied in this study found to be affected by various factors yet could be great option for production of ferulic acid. Meanwhile, BSW is proven feasible and great for producing ferulic acid naturally.