Effects of Age of Inoculum, Size of Inoculum and Headspace on Hydrogen Production using Rhodobacter sphaeroides

Assessing the effect of multiple variables on the production of bioflocculant by Serratia marcescens: Flocculating activity, kinetics, toxicity, and flocculation mechanism

Bioflocculants gain attention as alternatives to chemical flocculants because they are more environmentally friendly and highly biodegradable. This study aims to improve the bioflocculant production by Serratia marcescens using one-variable-at-a-time (OVAT) analysis and analyze its flocculating activity performance, toxicity, and the flocculation mechanism. The effect of multiple variables including initial inoculum size, pH, mixing speed, temperature, growth medium, and incubation period was assessed through OVAT. Flocculating activity was then determined via jar test analysis, and toxicity test was performed using Daphnia magna and Daphnia pulex. The flocculation mechanism was determined via particle size distribution and zeta potential analysis. The optimum conditions for the improved bioflocculant production were as follows: 10% v/v initial inoculum size, pH 7, mixing speed of 150 rpm, room temperature, nutrient broth medium, and 72 h of incubation period. Scanning electron microscopy showed flake-like intact structure with coarse surface. The produced bioflocculant showed flocculating activity of 48% in 5227 ± 580 NTU initial kaolin turbidity with 1 mg/L concentration and 5% v/v dosage of bioflocculant, following the second-order kinetics. Toxicity test to D. magna and D. pulex showed the 48 h LC₅₀ values of 8.06 and 6.42 g/L, respectively; these values are greatly higher than the fabricated chemical flocculants. The flocculation process using bioflocculant produced by S. marcescens was suggested to occur via bridging mechanism because it greatly affected the particle size distribution. Results indicated that bioflocculant produced by S. marcescens is much environmentally friendly and has great potential for turbidity removal in water/wastewater.

Effects of different operating parameters on hydrogen production by Parageobacillus thermoglucosidasius DSM 6285

Hydrogen gas represents a promising alternative energy source to dwindling fossil fuel reserves, as it carries the highest energy per unit mass and its combustion results in the release of water vapour as only byproduct. The facultatively anaerobic thermophile Parageobacillus thermoglucosidasius is able to produce hydrogen via the water–gas shift reaction catalyzed by a carbon monoxide dehydrogenase–hydrogenase enzyme complex. Here we have evaluated the effects of several operating parameters on hydrogen production, including different growth temperatures, pre-culture ages and inoculum sizes, as well as different pHs and concentrations of nickel and iron in the fermentation medium. All of the tested parameters were observed to have a substantive effect on both hydrogen yield and (specific) production rates. A final experiment incorporating the best scenario for each tested parameter showed a marked increase in the H₂ production rate compared to each individual parameter. The optimised parameters serve as a strong basis for improved hydrogen production with a view of commercialisation of this process.