Effects Of Initial Biomass Concentration Research Articles

Hydrogen gas production from waste paper by dark fermentation: Effects of initial substrate and biomass concentrations

In this study, waste paper was used as the raw material for hydrogen gas production by dark fermentation at different initial substrate and cell concentrations. Glucose obtained from acid hydrolyzed waste paper was used at six different concentrations between 3.84 and 45.5 gL−1 to determine the effects of sugar concentration on bio-hydrogen production. The highest cumulative hydrogen gas was obtained at 18.9 gL−1 initial sugar concentration. Sugar concentrations above 18.9 gL−1 resulted in product inhibition. Similarly, the initial biomass concentration was varied between 0.25 and 2 gL−1 while sugar concentration was kept constant at 18.58 ± 2.45 gL−1 to determine the effects of initial biomass concentration. The highest cumulative hydrogen gas production was obtained with the initial biomass concentration of 0.5 gL−1. The highest hydrogen yield (140 ml H2 g−1 total sugar) was observed at 3.84 gL−1 total sugar concentration. Hydrogen yield decreased with increasing initial sugar concentration due to inhibition by volatile fatty acids (VFAs) produced by dark fermentation and furan derivatives produced from acid hydrolysis of waste paper.

Effect of operating conditions on Chlorococcum sp. growth and lipid production

Microalgal cultivation has attracted global attention in recent years. It is a worldwide rapidly growing business sector due to the numerous applications of microalgae biomass and the valuable natural by-products. Some of these products are used in pharmaceutical, biomedical, cosmetic, and food industries, and recently in biofuel production. The cost reduction of microalgal biomass production is an essential factor, and many studies have been focused on microalgae cultivation in wastewater. The selection of microalgae for biomass and lipid production is a very crucial factor. Chlorococcum sp. are common microalgae, found in wastewater. The aim of this study was to investigate the effect of initial biomass concentration, air supply, and type and duration of light exposure of Chlorococcum sp. cultures in a high nutrient concentration synthetic wastewater. Experiments were conducted under controlled environmental conditions in order to investigate the removal of nutrients from wastewater, the biomass growth rates, and lipids accumulation in microalgae. The results of this study demonstrated that high initial biomass concentration is more efficient for lipid production. Specifically, higher lipids content (27.7%) was observed with high initial microalgae concentration, even though the phosphorus concentration was almost zero. Biomass production was increased faster at the higher air flow rate (6L/min), without need for addition of carbon dioxide (CO2). Τhe growth rate of Chlorococcum sp. was greater under artificial light compared to sunlight exposure, as well as the CO2 biofixation, since it is directly related to the algal biomass.

Hydrogen gas production from waste paper by sequential dark fermentation and electrohydrolysis

Waste paper was evaluated for hydrogen gas production by sequential dark fermentation and electrohydrolysis. Acid hydrolysed waste paper towel hydrolysate was first subjected to dark fermentation to determine the most suitable initial biomass concentration. The effects of initial biomass concentration was investigated at constant substrate concentration by varying the biomass concentration between 0 and 6 g/L and the most suitable hydrogen production was obtained at 0.10 g/L. Then effects of initial substrate concentration was investigated at 0.10 g/L initial biomass concentration by varying the glucose concentration between 5 and 40 g/L. 21.33 g glucose/L resulted in the highest hydrogen formation yield and rate in the second set of experiments. When the effluent of dark fermentation operated at optimum initial biomass and substrate concentration was subjected to electrohydrolysis the overall hydrogen production of the sequential process was 30.12 mL H2/mL.

A novel source of dihomo‐γ‐linolenic acid: Possibilities and limitations of DGLA production in the high‐density cultures of the Δ5 desaturase‐mutant microalga Lobosphaera incisa

The Δ5 desaturase mutant (P127) of the microalga Lobosphaera incisa is a promising organism for large‐scale production of the valuable LC‐PUFA dihomo‐γ‐linolenic acid (DGLA, 20:3 n‐6). We examined the potential of P127 for DGLA production under nitrogen (N) starvation conditions, triggering the deposition of DGLA in triacylglycerols, and developed a strategy for optimization of the DGLA productivity in high‐density cultures. Towards this end, the effects of initial biomass concentration (1, 2, and 4 g L−1) and PAR irradiance (170 and 400 µmol m−2 s−1) on DGLA and total fatty acid (TFA) production were studied. The highest DGLA and TFA percentages (10 and 38% of dry weight, respectively) were displayed by the cultures initiated at 1 g L−1 and grown under a moderate irradiance. Higher irradiances and lower starting biomass content facilitated oleic acid accumulation at the expense of DGLA. Maximum volumetric productivities of TFA and DGLA were recorded in the cultures started at 2 g L−1 biomass and grown under 400 μmol PAR m−2 s−1. We show that a sufficiently high starting culture density should be combined with a mild light stress to facilitate the production of biomass enriched in DGLA‐containing triacylglycerols.Practical applicationsThe ∆5 desaturase mutant of L. incisa, P127, is a rare green source of DGLA, a LC‐PUFA with valuable pharmaceutical and neutraceutical properties. We report on the optimization of DGLA production by the nitrogen‐starving indoor cultures of P127. Stresses, such as N starvation and/or high irradiances, promote accumulation of lipids by microalgal cells. On the other hand, excessively severe stress is deteriorative for the target LC‐PUFA accumulation. An important outcome of the present work is establishing physiological constrains of DGLA productivity and finding an approach to balance starting cell density vs. irradiance in order to maximize DGLA yields. Findings of the present work lay a foundation of the efficient production of DGLA using upscaled cultures of P127.High productivity of DGLA‐enriched biomass by P127 under nitrogen starvation is attainable by combining relatively high starting culture density with a mild light stress. By contrast, high irradiances impair DGLA accumulation in the cultures initiated at the biomass content of ≤ 1 gL−1.

Effect of initial biomass concentration on bioregeneration of 4-chlorophenol-loaded granular activated carbon: kinetic and efficiency studies

Background Information on the effects of initial biomass concentration on bioregeneration rate and efficiency is lacking as many of the bioregeneration studies were conducted at constant initial biomass concentration. The objectives of this study are: (i) to develop kinetic models incorporating adsorption, desorption, biodegradation and the irreversibility of adsorption in describing the bioregeneration of granular activated carbon (GAC) loaded with 4-chlorophenol (4-CP); and (ii) to investigate the effect of initial biomass concentration on the rate and efficiency of bioregeneration of 4-CP-loaded GAC in simultaneous adsorption and biodegradation processes. Results The bioregeneration model with Haldane biodegradation kinetics gave a better fit (R2 > 0.956) than the model with first-order biodegradation kinetics (R2 > 0.805) to the experimental data. Values of the rate constant of desorption generated from the models showed that there was no observed effect of varying biomass concentration on the bioregeneration rate. The efficiency study revealed no observed effect of varying biomass concentration on the bioregeneration efficiency provided there was no inhibition effect due to 4-CP. Conclusions Change in the initial biomass concentration had no observed effect on the bioregeneration rate and efficiency, if there was no inhibitory effect due to the substrate in the latter case. © 2012 Society of Chemical Industry.

Effect of initial biomass concentration on the growth of immobilized Nitrosomonas europaea

Effect of initial biomass concentration on the growth of immobilized Nitrosomonas europaea

Effect of initial biomass concentration on the growth of immobilized Nitrosomonas europaea

Nitrosomonas europaea was immobilized in carrageenan-gel beads with a low and a high biomass concentration (100-fold difference). Under growth conditions in a continuous air-lift loop reactor, a low initial concentration yielded a few large micro-colonies per bead, whereas a high initial biomass concentration resulted in many small micro-colonies per bead. The macroscopic consumption rate of the latter was three times higher under the circumstances applied. This is also predicted by our colony-expansion model when diffusion limitation over the micro-colonies is incorporated. This model also predicts that diffusion limitation over the ultimate colonies is negligible when the initial biomass concentration exceeds 0.5 kg·m−3 of carrageenan gel.