Effect Of Organic Carbon Sources Research Articles

Effect of organic carbon sources on growth, lipid production and fatty acid profile in mixotrophic culture of Scenedesmus dimorphus (Turpin) Kützing

Due to non-renewability of fossil fuels and various environmental problems associated with their use, there is a growing interest in producing biodiesel from microalgae. Finding novel microalgal strains with desired characteristics such as rapid growth rates, high lipid productivity, and suitable fatty acid compositions is important for the production of biodiesel. Comparatively, photoautotrophic cultivation of microalgae results in low biomass yields and lipid productivities. Mixotrophic and heterotrophic cultures, in contrast, lead to higher biomass and lipid productivities but their productivities are species specific and depend a lot on the organic carbon source and culture conditions. In the present study, the potential of Scenedesmus dimorphus for biodiesel oil production under mixotrophic culture was investigated. The effects of organic carbon sources (glucose, ethanol and glycerol) on growth, biomass yields, lipid contents, lipid productivities and fatty acids compositions of Scenedesmus dimorphus in mixotrophic cultures were investigated. In comparison to photoautotrophic cultures, mixotrophic cultures produced significantly higher biomass concentration, lipid content, and lipid productivities (P≤0.05) under all the cultivation conditions investigated. The maximum biomass and lipid productivities achieved by mixotrophic culture were 83.88±0.05 and 17.11±0.04 mg L−1 day−1 respectively which are more than 2.6 and 3.1 folds higher than those obtained under photoautotrophic condition. Using glucose as the organic carbon source was better than ethanol and glycerol in terms of biomass and lipid productivities (glucose > ethanol > glycerol). The majority of the produced fatty acids were composed of C16 and C18 fatty acids. The two most abundant fatty acids in all the cultures were linolenic and palmitic acids. The values of biodiesel properties of oil obtained from S. dimorphus are within the American (ASTM D6751) and European (EN 14214) biodiesel specifications. The results show that S. dimorphus has good potentials for biodiesel oil production and that the productivity can be enhanced by mixotrophic cultivation.

Effects of Four Organic Carbon Sources on the Growth and Astaxanthin Accumulation of Haematococcus lacustris.

The microalga Haematococcus lacustris has a complex life cycle and a slow growth rate, hampering its mass cultivation. Culture of microalgae with organic carbon sources can increase the growth rate. Few studies have evaluated the effects of organic carbon sources on H. lacustris. We compared the vegetative and inductive stages of H. lacustris under autotrophic and mixotrophic conditions using four organic carbon sources: sodium acetate, glycerol, sodium gluconate, and ribose, each at various concentrations (0.325, 0.65, 1.3, and 2.6 g/L). The cell density was increased by 1.3 g/L of glycerol in the vegetative stage. The rapid transition to the inductive stage under nitrogen-depletion conditions caused by 1.3 or 2.6 g/L sodium acetate promoted the accumulation of astaxanthin. The production of astaxanthin by H. lacustris in mass culture using organic carbon sources could increase profitability.

Effects of organic carbon source and pH on growth, astaxanthin accumulation and endogenous phytohormone secretion of Haematococcus pluvialis

Effects of organic carbon source and pH on growth, astaxanthin accumulation and endogenous phytohormone secretion of Haematococcus pluvialis

EFFECT OF VARIOUS CARBON SOURCES ON THE GROWTH PROPERTIES AND MORPHOLOGY OF $SPIRULINA~PLATENSIS$

Cyanobacteria generate biomass under photoautotrophic conditions during photosynthesis. Cultivation of cyanobacteria under photoheterotrophic conditions using various organic carbon sources can increase yield of biomass. In the current study, the effect of organic carbon sources on the growth properties and morphology of cyanobacteria Spirulina platensis, as well as the production of the photosynthetic pigments: chlorophyll a, carotenoids, and phycocyanin were investigated. Carbon sources, such as glucose, fructose and succinate, caused not only an increase in the cyanobacterial growth rate, but also morphological changes in S. platensis trichomes. An increase in the amounts of photosynthetic pigments was also observed. Thus, glucose, fructose, and succinate are more efficient substrates for photoheterotrophic cultivation of these cyanobacteria.

Effects of organic carbon sources on algal biofilm formation and insight into mechanism

Algal biofilm cultivation has great potential in producing high biomass yields and reducing harvesting costs. Organic carbon sources can promote algal growth in suspended cultivation, but their effects on algal biofilm formation and related mechanism have rarely been studied. In this study, we determined the most suitable organic carbon source and its concentration for the formation of algal biofilm, and structure/composition characteristics of extracellular polymeric substances (EPS) from algal biofilm. The results showed that the glycerol concentration of 1000 mg C L−1 in algal biofilm system was the most suitable condition to contribute to the biofilm formation and enhance attached biomass among the treatments. The algal biofilm at the glycerol concentration excreted the contents of relatively high EPS and its protein (EPS-PN), which were beneficial to forming the biofilm. The high EPS-PN content was mainly attributed to the increased hydrophobic proline and alanine contents but declined hydrophilic glutamic acid for improving algal biofilm formation. These findings enhanced our understanding of the formation mechanism of algal biofilm under the organic carbon source condition and provided the theoretical basis for algal biofilm formation.

Effects of organic carbon sources on growth and oil accumulation by Desmodesmus subspicatus LC172266 under mixotrophic condition.

Energy crisis and environmental sustainability have attracted global attention to microalgal biofuels. The present study investigated the impact of organic carbon sources on growth and bio-oil accumulation by an oleaginous microalga Desmodesmus subspicatus LC172266 under mixotrophic culture condition. Glucose and glycerol supported higher growth rates and lipid productivities than sucrose, fructose, mannitol and acetate. Each of the organic carbon source tested supported significantly (P < 0.05) higher growth rates and lipid productivities than the photoautotrophic culture (without organic carbon source). The lipid productivity obtained with a mixture of optima concentrations of glucose and glycerol (5.0gL-1 glycerol + 10.0gL-1glucose) (0.14875 ± 0.002g/L/day) was about 25% and 66% higher than the values obtained with only 10.0gL-1glucose and 5.0gL-1glycerol, respectively. When a batch culture with 5gL-1glycerol was fed with 0.5gL-1glucose daily the cell growth and lipid productivity were lower than the values obtained in a batch culture with a mixture of glucose and glycerol. The lipid productivity obtained in a 4-L photobioreactor was 94% (0.217gL-1day-1), higher than the value obtained in a flask culture with 10.0g/Lglucose (0.112gL-1day-1) and 46% higher than the value obtained in a flask culture with 5.0gL-1glycerol (0.086gL-1day-1).

Applications of Sponge Iron and Effects of Organic Carbon Source on Sulfate-Reducing Ammonium Oxidation Process.

The typical characteristics of wastewater produced from seafood, chemical, textile, and paper industries are that it contains ammonia, sulfate, and a certain amount of chemical oxygen demand (COD). The sulfate-reducing ammonium oxidation process is a biochemical reaction that allows both ammonia and sulfate removal, but its low growth rate and harsh reaction conditions limit its practical application. Due to the adsorption properties of the iron sponge and its robust structure, it provides a suitable living environment for microorganisms. To reduce the negative impact on the environment, we employed 4.8 kg of sponge iron in a 2.0 dm3 anaerobic sequencing batch reactor (ASBR). We investigated the effects of the type and concentration of carbon sources on the performance of the sulfate-reducing ammonium oxidation (SRAO) process. The results demonstrated that during a start-up period of 90 days, the average ammonium removal efficiency and the sulfate conversion efficiency of the reactor containing the sponge iron were 4.42% and 8.37% higher than those of the reactor without the sponge iron. The addition of the sponge iron shortens the start-up time of this greenhouse gas-free denitrification process and reduces future costs in practical applications. The removal of total nitrogen (TN) significantly increased after adding organic carbon sources and then declined sharply, while the most considerable reduction of ammonium removal efficiency from 98.4% to 30.5% was observed with adding phenol. The performance of the group employing glucose as the carbon source was recovered on the 28th day, with the average ammonium removal efficiency increasing from 49.03% to 83.5%. The results of this simulation study will help the rapid start-up of SRAO in the water treatment industry and can precisely guide the application of the SRAO process for wastewater containing different organic carbon sources.

Effects of organic carbon sources on water quality, microbial flocs protein and performance of Macrobrachium rosenbergii post‐larvae reared in biofloc and synbiotic systems

Different strategies for supplying organic carbon in biofloc and synbiotic were tested for Macrobrachium rosenbergii port-larvae (PL). The prawn (0.01 ± 0.002 g) were stocked (0.8 PL L−1) during 35 days in an experimental design with five treatments and four replicates: Ct = control; M = molasses (BFT); Mf = molasses pre-treated with Bacillus spp. without and with aeration (synbiotic); RB = rice bran (BFT); and RBf = raw rice bran pre-treated with Bacillus spp., without and with aeration (synbiotic). The prawns were fed five times a day with a feed containing 40% crude protein. Water quality variables remained within the range considered suitable for the species, and the synbiotic reduced the mean values of settleable solids. The protein content of microbial flocs (dry weight) differed among RBf (34.07 ± 0.54%) and RB (29.77 ± 0.48%), but was higher in M (43.27 ± 0.76%). The prawns submitted to RBf presented the best combination of results for variables final weight (122.85 ± 12.50 mg) and weekly weight gain (22.26 ± 2.97 mg). Thus, RBf treatments (synbiotic) in addition to maintaining water quality variables at acceptable levels can improve growth of M. rosenbergii post-larvae.

Effect of organic carbon source and stocking densities on growth indices, water microflora, and immune-related genes expression of Litopenaeus vannamei Larvae in intensive culture

The study conducted to evaluate the effect of different stocking densities in a biofloc (BF) system, with sugarcane bagasse as an organic carbon source on growth performance, immune response-related genes, and microbial biomass of shrimp larvae in a 90-days. Litopenaeus vannamei larvae (0.002 ± 0.01 g) were cultured in 12-tanks with different stocking densities (12 or 16 larvae/l), including two controls without a carbon source (12C and 16C) and two BF treatments without a commercial diet (12BF and 16BF) in triplicates. Based on the results, the total number of heterotrophic bacteria (THB) and Vibrio spp. counts (TVC) were positively affected by BF treatment. The highest THB value was recorded in treatment 12BF, whereas the lowest TVC value was recorded in 16BF. The highest (9.85 ± 1.60 g) and lowest (7.96 ± 2.72 g) weight gains were observed in 16BF and its control.Overall, the highest growth indices, survival rate and crude protein content were recorded in BF treatments. Furthermore, the expression of immunity-related genes were positively affected by BF treatment. However, the addition of agricultural by-product sugarcane bagasse as a carbon source in BF-tanks with zero-water exchange facilitated water recycling and increased the number of THB communities which could replace the commercial diet in BF-tanks and improve the growth and health of shrimp.

Effects of organic carbon source on the performance and bacterial structure in biofilm processes for source water pretreatment

The operation performance of biofilm system is limited by the oligotrophic quality of source water, especially the bioavailable organics. In this study, two lab-scale biofilm reactors (R1 and R2) feeding different organic carbon sources (OCS) were built up using sediment in drinking water source as bacterial source. Experimental results showed that sediment in biofilm systems enhanced the NH4 +-N removal performance. Using ethanol as OCS was more beneficial to the removal of NH4 +-N with ammonia removal efficiency (ARE) of 87.0 ± 5.4%, which was higher and more stable than that of glucose with ARE of 83.9 ± 13.3%. Organic carbon source changed the bacterial structure in biofilm systems. The dominant phyla in biofilm under ethanol condition were Proteobacteria, Bacteroidetes and Firmicutes with relative abundances (RA) of 29.1%, 32.7% and 22.0%, respectively. The dominant phyla in biofilm exposure to glucose was Proteobacteria with an RA of 63.4%. At genus level, Nitrospira, Lachnospiraceae, Arcobacter and Hyphomicrobium were dominant under ethanol condition (R1) with the total relative abundance of 20.5%. Sphaerotilus was the dominant genus under glucose condition (R2) with RA of 33.72%. These dominant bacteria were basically having the ability for the removal of nitrogen and organic matter.

Effects of organic carbon sources on the biomass and lipid production by the novel microalga Micractinium reisseri FM1 under batch and fed-batch cultivation

A microalgal strain Micractinium reisseri FM1 which could assimilate organic carbon sources effectively and grow rapidly under mixotrophic condition was screened and identified through morphological and 18S rRNA gene sequence. Addition of glucose, maltose and sodium acetate at 2 and 4 g L−1 contents could promote the biomass production, lipid content and productivity significantly. Compared with batch culture (8 g L−1), fed-batch culture (fed 2 g L−1 4 times) with glucose, maltose and sodium acetate respectively, could not only enhance biomass, but also boost lipid productivity. More importantly, the composition of fatty acid could be enriched and the proportion of saturated to unsaturated fatty acids could be improved on the basis of promoting alga growth and lipid production by feeding organic carbon and regulating culture mode. M. reisseri FM1 has the potential to assimilate organic carbon sources for high-cell density cultivation and production of biodiesel or functional polyunsaturated fatty acids.

The Effect of Organic Carbon Source on Performance of Liti(PO4)3/C Composite Electrodes in Aqueous Solutions

The spherical LiTi(PO4)3/C composites were prepared through spray drying method followed high-temperature calcination and used as anodes for aqueous lithium ion batteries. The effect of different organic carbon source based on different coating mechanisms and carbon content on the electrochemical properties of LiTi(PO4)3/C composite anodes were investigated. Results show that the amount of carbon coating is too low to prevent water from eroding. In contrast, if the amount of carbon coating is too high, the resistance of lithium ion diffusion will be high; the optimal carbon coating amount of LiTi2(PO4)3/C electrodes is 13%. The uniformity of carbon coating and the thickness of coating layer are the two main factors affecting the performance of coated electrodes. The coating mechanism has critical influence on the uniformity of carbon coating. The most uniform carbon coating was obtained by using polydopamine as the carbon source, followed by using the organic macromolecule, glucose as the carbon source. Polyacrylonitrile containing both carbon and nitrogen exhibits no special effect of nitrogen doping. (The two main factors affecting the performance of the carbon coated electrode are the uniformity and the thickness of the carbon layer.) The best performance is achieved by LiTi2(PO4)3/C anodes with the carbon amount of 13% prepared by using polydopamine as the carbon source. But, from a viewpoint of mass production and scale-up, it is more suitable to use low-cost and water-soluble glucose as carbon source.

Effect of Organic Carbon Source on Pyrite Biooxidation by Moderately Thermophilic Acidophilic Microorganisms

Iron- and sulfur-oxidizing auto-, mixo- and heterotrophic bacteria and archaea dominate in the bioleaching of pyrite from sulfide ores and concentrates both in natural conditions and in biohydrometallurgical processes. The goal of the present work was to study the oxidation of pyrite, the most widespread sulfide mineral, by representatives of microbial groups predominant in biohydrometallurgical processes (mixotrophic iron- and sulfur-oxidizing bacterial strain Sulfobacillus thermosulfidooxidans VKMB1269T, autotrophic sulfur-oxidizing bacterial strain Acidithiobacillus caldus MBC-1, and heterotrophic iron- and sulfur-oxidizing strain of archaea Acidiplasma sp. MBA-1) to evaluate the potential importance of different groups of microorganisms, and to determine the role of interspecies interactions in the population during pyrite oxidation. It was shown that pyrite was most actively leached by the strain of the mixotrophic bacterium S. thermosulfidooxidans VKMB 1269T, in the case when the medium was supplemented with organic substrates. In the experiment with a pure culture of strain VKMV 1269T in a medium with 0.02% yeast extract, 17% of pyrite was leached in 30 days, while in experiments with pure cultures of A. caldus MBC-1 and Acidiplasma sp. MBA-1, less than 1.5% of pyrite were leached. Significantly better results were obtained using mixed cultures of iron-oxidizing strains and A. caldus MBC-1: the rate of pyrite leaching was 26–28%. Moreover, in experiments with a mixed culture of S. thermosulfidooxidans VKMB 1269T and A. caldus MBC-1, addition of an organic carbon source (yeast extract) did not affect the rate of pyrite leaching (25–26%). The highest (38%) leaching rate was in the experiments with a pure culture of S. thermosulfidooxidans VKMV 1269T with periodic addition of yeast extract to the medium: 0.02% at the beginning of the experiment, as well as on days 10 and 20. Thus, in laboratory conditions it was shown that the greatest role in the process of pyrite oxidation was played by the bacterial strain of the genus Sulfobacillus, but its activity was largely dependent on availability of an organic carbon source in the medium, which may be represented by yeast extract or exometabolites of autotrophic bacteria present in the community of microorganisms performing pyrite leaching from sulfide ores and concentrates.

Effect of organic carbon source and nutrient depletion on the simultaneous production of a high value bioplastic and a specialty pigment by Arthrospira platensis

Many studies have shown enhanced production of single high value products from microalgal cultivation can be achieved by employing nutrient limitation and/or organic carbon supplementation. The possibility of exploiting multiple high value microalgal biosynthetic products has rarely been examined, even though it is widely acknowledged that such systems are likely to improve the economics of chemical production from this source. The co-production of two high value microalgal products, phycocyanin and polyhydroxybutyrate (PHB), was investigated under photoautotrophic and mixotrophic conditions, with and without nutrient limitation, in Arthrospira (Spirulina) platensis MUR126 cultures. Cultures accumulated PHB under nutrient replete phototrophic conditions while maintaining phycocyanin levels. Supplementing Arthrospira platensis cultures with additional CO2 increased PHB (33% at day 14), biomass (23 %) and phycocyanin productivity (30%). The results from cultures grown mixotrophically using organic carbon sources commonly found in agricultural and industrial waste streams (acetate, formate, glycerol and oxalate), and under nutrient limitation, did not show a definitive trend. When Arthrospira platensis was cultured in media devoid of both N and P, supplementing with glycerol and acetate led to a significant increase in biomass productivity compared to a photoautotrophic reference culture, but negatively affected both phycocyanin and PHB production. The poor co-production results for Arthrospira platensis under mixotrophic conditions suggest that a minimum level of N is required to maintain phycocyanin levels and a greater concentration of the organic C source is needed to create a redox balance within the cells that enhances PHB production.

Effect of organic carbon sources and environmental factors on cell growth and lipid content of Pavlova lutheri

The present study aimed to investigate the effects of organic carbon sources, cultivation methods, and environmental factors on growth and lipid content of Pavlova lutheri for biodiesel production. In the 250-mL flask bioreactors, P. lutheri was cultivated in the modified artificial seawater (ASW) medium containing glucose, glycerol, sodium acetate, or sucrose as an organic carbon substrate. The effects of different growth conditions (phototrophic, mixotrophic, and heterotrophic) and environmental factors such as photoperiod, light intensity, and salinity were evaluated. Growth of P. lutheri was inhibited under heterotrophy but was enhanced in mixotrophy as compared to phototrophy. Biomass and lipid content of P. lutheri were significantly (p < 0.05) affected by changing photoperiod, light intensity, and salinity. Higher biomass concentration and lipid content were observed at a light intensity of 100 ± 2 μmol photons m−2 s−1, 18 h photoperiod, and 30% salinity, in a modified ASW medium supplemented with 10 mmol sucrose. An increase in biomass concentration from 320 ± 25.53 to 1106 ± 18.52 mg L−1 and high lipid content of 31.11 ± 1.65% (w/w) were observed with the optimized culture conditions, demonstrating a significant (p < 0.05) enhancement in biomass and lipid content due to the improved culture conditions. The present study emphasizes the possible use of sucrose for biomass and lipid production with P. lutheri under the optimized culture conditions. Using low-cost and relatively easy accessible feedstock such as sucrose would be a valuable alternative for growing microalgae with enhanced lipid content.

Effect of Organic Carbon Source on Start-up and Operation of the CANON Granular Sludge Process

The effect of organic carbon on the start-up and operation of the CANON granular sludge process was investigated in two SBR reactors with different strategies:gradually increased organic carbon concentration (R1) and without organic carbon (R2). The results showed that adding 50 mg·L-1 organic carbon accelerated the start-up of the CANON granular sludge process. R1 and R2 were started up in 23 d and 32 d, respectively. Moreover, the appropriate organic carbon enhanced the activity of AOB, AnAOB, and denitrification, increasing the ammonia removal rates and total nitrogen (TN) removal rates. The maximum ammonia removal rates and total nitrogen removal rates of R1 were 92% and 88%, respectively. The maximum ammonia removal rates and total nitrogen removal rates of R2 were 89% and 80%, respectively. Further tests showed that excessive organic carbon concentration decreased the activity of AOB and AnAOB and reduced the removal efficiency of ammonia and total nitrogen. Adding organic carbon promoted denitrification activity and increased nitrogen removal efficiency.

Nitrogen Removal and N2O Emission During Low Carbon Wastewater Treatment Using the Multiple A/O Process

With the organic carbon of acetate (SBR-A) and propionate (SBR-P), the effect of organic carbon sources on nitrogen removal and nitrous oxide (N2O) emission in the multiple anoxic and aerobic process was investigated. The nitrogen removal percentages in SBR-A and SBR-P reactor were both 72%, and the phosphate removal percentages were 97 and 85.4%, respectively. During nitrification, both the NH4 +-N oxidation rate in the SBR-A and SBR-P had a small change without the influence of the addition of nitrite nitrogen (NO2 −-N). With the addition of 10 mg/L NO2 −-N, the nitrate nitrogen (NO3 −-N) production rate, N2O accumulation rate and emission factor had increased. At the same time, the N2O emission factor of SBR-A and SBR-P reactors increased from 2.13 and 0.87% to 4.66 and 2.08%, respectively. During exogenous denitrification, when nitrite was used as electron acceptor, the N2O emission factors were 34.1 and 8.6 times more than those of NO3 −-N as electron acceptor in SBR-A and SBR-P. During endogenous denitrification with NO2 −-N as electron acceptor, the accumulation rate and emission factor of N2O were higher than those of NO3 −-N as electron acceptor. High-throughput sequencing test showed that the dominant bacteria were Proteobacteria and Bacteroidetes in both reactors at the phylum level, while the main denitrification functional bacteria were Thauera sp., Zoogloea sp. and Dechloromonas sp. at the genus level.

Nitrogen Removal Performance of ANAMMOX with Different Organic Carbon Sources

Anaerobic ammonium oxidation (ANAMMOX) has been regarded as an efficient process to treat high-strength wastewater without organic carbon source. To investigate the nitrogen removal performance of ANAMMOX in the presence of organic carbon source can broaden its application in organic wastewater treatment. In this work, an anaerobic sequencing batch reactor (ASBR) was used to study the effect of organic carbon source on ANAMMOX process. The experimental results indicated that the activity of anaerobic ammonia oxidizing bacteria (AAOB) decreased by 84.2% when 200 mg·L-1 COD of glucose was added. When sodium acetate was added, the activity of AAOB was affected little. Besides, it even promoted the activity with COD less than 120 mg·L-1. The effect of sucrose on ANAMMOX process was similar to that of sodium acetate and the maximum specific ANAMMOX activity (SAA) increased by 25.0% with 80 mg·L-1 COD. When citric acid was added, the maximum SAA peaked with 80 mg·L-1 COD. The order of ANAMMOX promotion resulted from organic carbon source was sucrose, sodium acetate, citric acid and glucose. With addition of organic carbon source, nitrate could also be removed through the synergy of ANAMMOX and denitrification, and the total nitrogen removal efficiency increased.

Extracellular polymeric substances (EPS) and surface properties of activated sludges: effect of organic carbon sources.

The study aims to clarify how the type of organic substrate in a wastewater affects the production and composition of extracellular polymeric substances (EPS) and hydrophobicity and surface charge of activated sludges. For this purpose, three activated sludge reactors were operated in parallel with feeds composed of the organics (i) peptone, glucose, and acetate and (ii) peptone and (iii) glucose. EPS extracted from sludges were fractionated into very loosely bound, loosely bound, and tightly bound fractions and analyzed for protein and polysaccharide. Also, molecular weight distribution of proteins was determined by using high-pressure size exclusion chromatography (HPSEC). Regardless of the type of organic substrate, in each sludge, tightly bound EPS (TB-EPS) prevailed. The type of organic substrate affected the relative proportion of protein and polysaccharide and had an impact on hydrophobicity and surface charge. The sludge fed with peptone was distinctly more hydrophobic and had a lower negative surface charge than others. HPSEC fingerprints revealed that the variety and size of proteins were dependent on the type of feed. HPSEC also pointed to a shift of high molecular weight (MW) proteins from TB-EPS to others. In addition, results of a parallel study examining the inhibitory effect of Ag(+) on three sludges were interpreted along with feed composition, EPS, and surface measurements. The response of each sludge to toxic Ag(+) ion seemed to change with the type of feed.

Effects of cell density, carbon dioxide and molybdenum concentration on biohydrogen production by Anabaena variabilis ATCC 29413

This paper aims to determine the effects of cell density, carbon dioxide, and molybdenum concentration towards hydrogen production rate. Batch cultures of Anabaenavariabilis sp. were incubated in anaerobic environment under continuous indoor illumination of 70μEm−2s−1 at 35°C. The optimal volumetric hydrogen production rate obtained was 44μmolH2mgchl a−1h−1 occurred at cells density of 110mgL−1, 5% carbon dioxide headspace concentration, and molybdenum concentration of 1.6mM. The effect of organic carbon source (glucose) was also evaluated in the present study and it was found that the additional carbon produced the highest hydrogen production rate in all conditions. An increased concentration of molybdenum significantly enhanced the hydrogen productivity rate almost to that of glucose-supplemented culture at 49μmolH2mgchl a−1h−1. However, further increase in molybdenum concentration beyond 1.6mM showed no further improvement in the amount of hydrogen produced.