airlift fermenter
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The thermophilic filamentous bacterium Laceyella sacchari LP175 was cultivated in a 10.0 L airlift fermenter to produce serine protease at 50 °C. Maximal serine protease activity at 1,123.32 ± 15.8 U/mL was obtained for cultivation at 0.6 vvm aeration rate for 36 h. The crude enzyme was applied for degradation of poly (butylene succinate) (PBS), and poly (butylene succinate)/poly(lactide) blend (PBS/PLA) powders at 50 °C for 48 h with different substrates and enzyme concentrations. Results showed that serine protease produced from L. sacchari LP175 degraded PBS and PBS/PLA at 46.5 ± 2.05 and 49.8 ± 1.45 %, respectively, at an initial substrate concentration of 100 g/L with 1,200 U/mL of serine protease activity. Percentage degradation of PBS and PBS/PLA was improved to 51.4 ± 1.06 and 56.9 ± 1.42 %, respectively, when upscaled in a 2.0 L stirrer fermenter with 200 rpm agitation rate. Degradation products evaluated by a scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) confirmed that serine protease produced from L. sacchari LP175 degraded both PBS and PBS/PLA polymers. Results showed that microbial enzyme technology could be used to degrade PBS and PBS/PLA blend polymers and reduce the accumulation of waste. HIGHLIGHTS Upscaled serine protease production was achieved in a 10 L airlift fermenter by sacchari LP175 using low-cost agricultural products as substrate The crude enzyme degraded PBS and PBS/PLA powders (100 g/L) at up to 51.4 and 56.9 %, respectively in a 2.0 L stirrer fermenter under optimal conditions Degradation products of PBS and PBS/PLA by crude enzyme produced from sacchari LP175 were characterized GRAPHICAL ABSTRACT

This study involved the design and fabrication of airlift fermenters for the mass propagation of a consortium of three microorganisms  (Pseudomonas aeruginosa, Pseudomonas fluorescence and Aureobasidium pullulans). The efficacy of the blend in the bioremediation of simulated crude oil polluted water systems environments was also tested with a view to generating more data on crude oil degrading microorganisms for bioremediation purposes. The organisms were separately grown on a gyratory shaker at 120 rpm and at 30 °C until notable growths were observed. Equal volume of the grown organisms (500 ml) of mixed culture was used as inoculum for the 4.5 L of medium in the 7 L airlift fermenter. Thereafter, this was transferred into the 45 litres medium in the 70 L fermenter until significant growth was observed at room temperature. Culture broths were withdrawn at intervals for the determination of biomass and residual hydrocarbon concentrations. The product from the 70 L fermenter was introduced into simulated polluted water systems from which samples were withdrawn weekly. Analyses for residual hydrocarbon contents were carried out using appropriate analytical techniques. The results showed that 78.5% hydrocarbon removal was observed in the 7 L fermenter after 72 h, while that of the 70 L fermenter was 97.8% after 180 h of fermentation. Polluted water sample treated with the microbes experienced 96.4% removal after 10 weeks of treatment. It was observed further that the application of NPK fertilizer biostimulant aided microbial activities in the removal of petroleum hydrocarbons than urea, cow dung and poultry droppings. The study has demonstrated that effective bioremediation of crude oil polluted water systems could be achieved through the application of biostimulants with mass propagated crude oil degrading organisms using airlift fermenter systems. Keywords: Pseudomonas aeruginosa; Pseudomonas fluorescence; Aureobasidium pullulans; Airlift fermenter; Bioremediation; Biostimulation; Bioaugmentation.

A conventional external loop uniform tube airlift fermenter (UT-ALF) was modified to improve its performance. The riser part was replaced by a converging- diverging tube. The newly developed reactor system is named a converging-diverging tube airlift fermenter (CDT–ALF). The modified bioreactor (CDT–ALF) provides a unique hydrodynamic characteristic. Empirical correlation was developed to determine KLa with respect to power input per unit volume. The modified system (CDT-ALF) shows 250% higher KLa compared to conventional one.