Nitrification rates of algal–bacterial biofilms in wastewater stabilization ponds under light and dark conditions

The objective of this study was to investigate nitrification rates in algal–bacterial biofilms of waste stabilization ponds (WSP) under different conditions of light, oxygen and pH. Biofilms were grown on wooden plates of 6.0 cm by 8.0 cm by 0.4 cm in a PVC tray continuously fed with synthetic wastewater with initial NH₄-N and Chemical Oxygen Demand (COD) concentrations of 40 mg l^?1 and 100 mg l^?1, respectively, under light intensity of 85–95 μE m^?2 s^?1. Batch activity tests were carried out by exposure of the plates to light conditions as above (to simulate day time), dim light of 1.8–2.2 μE m^?2 s^?1 (to simulate reduced light as in deeper locations in WSP) and dark conditions (to simulate night time). Dissolved oxygen (DO) concentration and pH were controlled. At some experiments, both parameters were kept constant, and at others they were left to vary as in WSP. Results show biofilm nitrification rates of 945–1817 mg-N m^?2 d^?1 and 1124–1615 mg-N m^?2 d^?1 for light and dark experiments. When the minimum DO was 4.1 mg l^?1, the biofilm nitrification rates under light and dark conditions did not differ significantly at 95% confidence. When the minimum DO in the dim light experiment was 3.2 mg l^?1, the nitrification rates under light and dim light conditions were 945 mg-N m^?2 d^?1 and 563 mg-N m^?2 d^?1 and these significantly differed. Further decrease of DO to 1.1 mg l^?1 under dark conditions resulted in more decrease of the nitrification rates to 156 mg-N m^?2 d^?1. It therefore seems that under these experimental conditions, biofilm nitrification rates are significantly reduced at a certain point when bulk water DO is between 3.2 mg l^?1 and 4.1 mg l^?1. As long as bulk water DO under dark is high, light is not important in influencing the process of nitrification.     

Diel activities of antioxidant enzymes,photosynthetic pigments and malondialdehyde content in stationary-phase cells of Tetraselmis gracilis (Prasinophyceae)

The activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), as well as photosynthetic pigment contents and free malondialdehyde (MDA), were determined in senescent batch cultures of Tetraselmis gracilis (Kylin) Butcher, under a cyclic light regime. A 2.6-fold increase in SOD activity (from 53 to 137 U mg⁻¹ protein) was observed in the light phase, contrasting with a 9-fold increase in CAT (from 1 to 9 μmol H₂O₂ min⁻¹ mg⁻¹ protein) and a 1.7-fold increase in APX (from 3 to 5 μmol ascorbate min⁻¹ mg⁻¹ protein) activities, both enzymes peaking in the dark phase. The β-carotene and lycopene content did not vary significantly with the light–dark cycle. The Chl a, Chl b, lutein, zeaxanthin, violaxanthin and neoxanthin pigments exhibited the highest values in the first half (3–6 h) of the light phase, followed by a declining trend and a plateau or a slight increase 3 h from the beginning of the dark phase onwards. The highest values for prasinoxanthin were observed in the second half of the dark phase and the first half of the light phase. None of the pigments displayed any discernible cyclic trend. The possibility of the xanthophyll cycle occurring during senescence is discussed in light of the high value (∼0.9) obtained for the zeaxanthin/(zeaxanthin + violaxanthin) ratio. The free MDA content was enhanced during the experimental period, which may be an indicator of oxidative stress in aging cell cultures. Our results indicated the occurrence of an imbalance between the production of reactive oxygen species and the antioxidant defense in stationary T. gracilis cells.     

Batch and continuous fermentative production of hydrogen with anaerobic sludge entrapped in a composite polymeric matrix

Cell immobilization techniques were adopted to biohydrogen production using immobilized anaerobic sludge as the seed culture. Sucrose-based synthetic wastewater was converted to H₂ using batch and continuous cultures. A novel composite polymeric material comprising polymethyl methacrylate (PMMA), collagen, and activated carbon was used to entrap biomass for H₂ production. Using the PMMA immobilized cells, the favorable conditions for batch H₂ fermentation were 35 °C, pH 6.0, and an 20 g COD l⁻¹ of sucrose, giving a H₂ production rate of 238 ml h⁻¹ l⁻¹ and a H₂ yield of 2.25 mol H₂ mol sucrose⁻¹. Under these optimal conditions, continuous H₂ fermentation was conducted at a hydraulic retention time (HRT) of 4–8 h, giving the best H₂-producing rate of 1.8 l h⁻¹ l⁻¹ (over seven-fold of the best batch result) at a HRT of 6 h and a H₂ yield of 2.0 mol H₂ mol sucrose⁻¹. The sucrose conversion was essentially over 90% in all runs. The biogas consisted of only H₂ and CO₂. The major soluble metabolites were butyric acid, acetic acid, and 2,3-butandiol, while a small amount of ethanol also detected. The PMMA-immobilized-cell system developed in this work seems to be a promising H₂-producing process due to the high stability in continuous operations and the capability of achieving a competitively high H₂ production rate under a relatively low organic loading rate.     

Now you see me,now you don’t: The locomotory activity rhythm of the Asian garden dormouse (Eliomys melanurus) from Saudi Arabia

The locomotory activity rhythms of Asian garden dormice, Eliomys melanurus from Saudi Arabia were investigated under controlled laboratory conditions. Animals were maintained under different lighting conditions for a period of two weeks each. Dormice exhibited predominantly nocturnal activity during the light/dark (LD) (mean % nocturnal activity: 95.5 ± 0.9%) and dark/light (DL) (mean % nocturnal activity: 96.8 ± 0.7%) light cycles. All animals expressed free-running rhythms of locomotor activity when subjected to constant darkness (mean τ: 24h06 ± 0h09). Upon inversion of the LD cycle to DL, activity re-entrained to the new light cycle within 3 days. When the dark component of the day was lengthened to 8L:16D the active time increased significantly from 11h43 ± 0h05 to 13h43 ± 0h22. In contrast, when the dark component was shortened from 12L:12D to16L: 8D, the active time decreased significantly to 7h58 ± 0h04. No difference was apparent in the locomotor activity at 20 and 30 °C however, dormice became very inactive at 10 °C.Overall, locomotor activity patterns of the Asian garden dormouse largely resemble those of other species of dormice. However, Asian garden dormice spent long periods of time inactive both during light and darkness, when exposed to an ambient temperature of 10 °C, which may be related to the dramatic and sudden change in temperature. This period of inactivity may reflect a bout of torpor or the entering into a state of hibernation.     

Application of polyethylene glycol immobilized Clostridium sp. LS2 for continuous hydrogen production from palm oil mill effluent in upflow anaerobic sludge blanket reactor

A novel polyethylene glycol (PEG) gel was fabricated and used as a carrier to immobilize Clostridium sp. LS2 for continuous hydrogen production in an upflow anaerobic sludge blanket (UASB) reactor. Palm oil mill effluent (POME) was used as the substrate carbon source. The optimal amount of PEG-immobilized cells for anaerobic hydrogen production was 12% (w/v) in the UASB reactor. The UASB reactor containing immobilized cells was operated at varying hydraulic retention times (HRT) that ranged from 24 to 6 h at 3.3 g chemical oxygen demand (COD)/L/h organic loading rate (OLR), or at OLRs that ranged from 1.6 to 6.6 at 12 h HRT. The best volumetric hydrogen production rate of 336 mL H₂/L/h (or 15.0 mmol/L/h) with a hydrogen yield of 0.35 L H₂/g COD_removed was obtained at a HRT of 12 h and an OLR of 5.0 g COD/L/h. The average hydrogen content of biogas and COD reduction were 52% and 62%, respectively. The major soluble metabolites during hydrogen fermentation were butyric acid followed by acetic acid. It is concluded that the PEG-immobilized cell system developed in this work has great potential for continuous hydrogen production from real wastewater (POME) using the UASB reactor.     

Maximizing mouse embryonic stem cell production in a stirred tank reactor by controlling dissolved oxygen concentration and continuous perfusion operation

One of the key challenges in stem cell bioprocessing is the large-scale cultivation of stem cells in order to meet the demanding meaningful cell numbers needed for biomedical applications, especially for clinical settings. Mouse embryonic stem cells [1], used as a model system herein, were cultivated on microcarriers in a fully controlled stirred tank reactor (STR) [2]. The impact of varying the concentration of dissolved oxygen (at 5%, 10%, 20% and 30% DO) and operating under a continuous perfusion mode on cell growth and pluripotency maintenance was investigated. In addition, in order to further optimize the feeding strategy of the STR operating under continuous perfusion toward maximal cell production, the influence of different medium residences times (12 h, 24 h, 32 h, 48 h and 96 h) was evaluated. Overall, the maximal cell concentration of 7.9–9.2 × 10⁶ cells/mL were attained after 11 days, with no passaging required, under a DO of 10–20% in the continuous perfused bioreactor with cell retention and medium residences times of 32–48 h. Importantly, mESC expanded under these conditions, retained the expression of pluripotency markers (Oct4, Nanog and Ssea-1), as well as their differentiation potential into cells of the three embryonic germ layers.The STR-based cultivation platform optimized herein represents a major contribution toward the development of large-volume production systems of differentiated cell derivatives for a wide range of biomedical applications.     

Seasonal variations in photosynthetic irradiance response curves of macrophytes from a Mediterranean coastal lagoon

The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Thau lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17 °C, 982 μmol O₂ g⁻¹ dw h⁻¹ and 9.1 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹, respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25 °C, 583 μmol O₂ g⁻¹ dw h⁻¹ and 2.6 μmol O₂ g⁻¹ dw h⁻¹/μmol photons m⁻² s⁻¹ respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to R_d (ranging 6.7–794 μmol O₂ g⁻¹ dw h⁻¹, respectively for Rytiphlaea tinctoria at 7 °C and for Dasya sessilis at 25 °C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of P/I curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum).     

Energy balance and greenhouse gas emissions in organic and conventional avocado orchards in Mexico

There is a worldwide growing awareness of the negative impacts of the increasing fossil fuel reliance and greenhouse gas (GHG) emissions from agriculture, in particular for intensive crop systems. We analyze the energy balances and greenhouse gas emissions from export-oriented avocado orchards in Mexico. Avocado is a very important export crop and one of the main drivers of land-use change in the country. We compared 12 avocado orchards under organic and conventional management during two production cycles (2010 and 2011) in a representative region of Central Mexico. Our analysis shows no significant differences in energy consumption and GHG emissions between organic and conventional systems with 55 and 56 GJ ha⁻¹, and 3.30 t CO₂ equiv. ha⁻¹ and 3.57 t CO₂ equiv. ha⁻¹, respectively.Organic systems show three times more use of renewable energy than their conventional counterparts. However both systems depend heavily on fossil fuel inputs, machinery and N-fertilizers (synthetic or organic). Also, there is a high heterogeneity in management practices and input application within both systems, which is reflected in a large variation of their energy-related parameters. Given that avocado production is rapidly expanding in Mexico, a move toward organic production without systematically changing toward less fossil fuel dependent agricultural practices would not be sufficient to ensure a sustainable production.     

Alkaline lipase from a novel strain Burkholderia multivorans: Statistical medium optimization and production in a bioreactor

An alkaline lipase from Burkholderia multivorans was produced within 15 h of growth in a 14 L bioreactor. An overall 12-fold enhanced production (58 U mL⁻¹ and 36 U mg⁻¹ protein) was achieved after medium optimization following the “one-variable-at-a-time” and the statistical approaches. The optimal composition of the lipase production medium was determined to be (% w/v or v/v): KH₂PO₄ 0.1; K₂HPO₄ 0.3; NH₄Cl 0.5; MgSO₄·7H₂O 0.01; yeast extract 0.36; glucose 0.1; olive oil 3.0; CaCl₂ 0.4 mM; pH 7.0; inoculum density 3% (v/v) and incubation time 36 h in shake flasks. Lipase production was maximally influenced by olive oil/oleic acid as the inducer and yeast extract as the additive nitrogen. Plackett–Burman screening suggested catabolite repression by glucose. Amongst the divalent cations, Ca²⁺ was a positive signal while Mg²⁺ was a negative signal for lipase production. RSM predicted that incubation time, inoculum density and oil were required at their higher levels (36 h, 3% (v/v) and 3% (v/v), respectively) while glucose and yeast extract were required at their minimal levels for maximum lipase production in shake flasks. The production conditions were validated in a 14 L bioreactor where the incubation time was reduced to 15 h.     

Biological hydrogen production from CO: Bioreactor performance

This paper presents an alternative solution to the current problem faced by the world; diminishing of fossil fuel. Bioconversion of synthesis gas to hydrogen as clean fuel was catalyzed by a photosynthetic bacterium, Rhodospirillum rubrum. The clean fuel production was biologically mediated by the water–gas shift reaction in a 2 l bioreactor. The work performed was on agitation effects on hydrogen production, K_La and power consumption. The results show that 500 rpm was the suitable agitation rate to be employed. The hydrogen production was optimized at 0.44 ± 0.023 atm giving a K_La of 86.4 ± 3.5 h⁻¹. The production rate was 9.6 mmol H₂/h. The maximum light conversion efficiency at agitation speed of 800 rpm, light intensity of 500 lux (732 kW/m²) and 4 g/l inlet acetate concentration was about 10.84 ± 1.73%. At this condition, the maximum CO conversion efficiency was found to be 81 ± 5.6%. The ratio of power per volume was calculated to be 322.30 ± 12.14 kW/m³ and foaming problem was successfully avoided. The corresponding power consumption was estimated to be about 0.64 ± 0.03 kW, while the output hydrogen energy was determined to be 643.2 ± 26 kW. A prolonged operation of continuous hydrogen production employing a microsparger showed stable behaviour for a duration of 27 days.     

Specific activity and viability of Nitrosomonas europaea during discontinuous and continuous fermentation

The energy conservation and number of viable cells of Nitrosomonas europaea fluctuate dramatically during cultivation. In discontinuous culture the specific activity (SA) reaches its maximum after 9 h with about 2700 nmol O₂ (mg protein)^?1 min^?1, where the highest number of viable N. europaea cells is detectable after 21 h with 2 × 10⁸ cell ml^?1. Afterwards, both SA and viable cell number immediately start to decrease. Accordingly, the exponential growth turns into a linear growth, whereby the number of viable cells permanently decreases. The exponential growth phase can be extended from about 21 to 38 h by increasing the concentration of CO₂ or trace elements. In continuous fermentation of N. europaea, SA of about 2500 nmol O₂ (mg protein)^?1 min^?1 and viable cell number of 2.5 × 10⁸ cell ml^?1 is detectable at dilution rates between 1 and 1.8 day^?1. At dilution rates below 1 day^?1, SA and number of viable cells are reduced. The minimal doubling time is 13 and 15 h during continuous and discontinuous fermentation, respectively. Consequently, cell production of N. europaea should be performed in continuous fermentation. When bacteria are grown in discontinuous systems, they should be harvested in the early exponential growth phase.     

Operation of a bioelectrochemical system as a polishing stage for the effluent from a two-stage biohydrogen and biomethane production process

Anaerobic bioenergy production processes including fermentative biohydrogen (BioH₂), anaerobic digestion (AD) and bioelectrochemical system have been investigated for converting municipal waste or various biomass feedstock to useful energy carriers. However, the performance of a microbial fuel cell (MFC) fed on the effluent from a two-stage biogas production process has not yet been investigated extensively in continuous reactor operation on complex substrates. In this study we have investigated the extent to which a microbial fuel cell (MFC) can reduce COD and recover further energy from the effluent of a two-stage biohydrogen and biomethane system. The performance of a four-module tubular MFC was determined at six different organic loadings (0.036–6.149 g sCOD L⁻¹ d⁻¹) in terms of power generation, COD removal efficiency, coulombic efficiency (CE) and energy conversion efficiency (ECE). A power density of 3.1 W m⁻³ was observed at the OLR = 0.572 g sCOD L⁻¹ d⁻¹, which resulted in the highest CE (60%) and ECE (0.8%), but the COD removal efficiency decreased at higher organic loading rates (35.1–4.4%). The energy recovery was 92.95 J L⁻¹ and the energy conversion efficiency, based on total influent COD was found to be 0.48–0.81% at 0.572 g sCOD L⁻¹ d⁻¹. However, the energy recovery by the MFC is only reported for a four-module reactor and improved performance can be expected with an extended module count, as chemical energy remained available for further electrogenesis.     

Improved capsular polysaccharide production by Streptococcus pneumoniae serotype 14 using continuous cultivation

The capsular polysaccharide (PS) is the most important pneumococcal virulence factor and is currently used as antigen in all pneumococcal vaccines. Despite its physiological and epidemiological importance, meager studies have been devoted to improve PS production and understand its relationship with pneumococcal central metabolism. In this study, kinetics of growth and production of PS by Streptococcus pneumoniae serotype 14 (PS14) in batch and continuous cultivation were investigated. Strong cell lysis was observed in batch cultivation, while accumulation of organic acids and autolysis was avoided in continuous cultivation. In the continuous cultivation was possible to achieve higher concentration of biomass and PS14. Calculation of kinetic parameters demonstrated that PS14 is a cell-associated product. The coefficients for growth-associated stoichiometric true yield and maintenance were determined as 0.25 g_glucose g_biomass⁻¹ and 1.24 g_glucose (g_biomass h)⁻¹, respectively. The maximum productivity of PS14 released in the supernatant (PS14_R) and cell-bound PS14 (PS14_C) were obtained at a dilution rate of 0.8 h⁻¹, respectively, 85 and 122 mg  (g_biomass h)⁻¹. Compared to batch fermentation, both PS14_R and PS14_C productivities were increased by about 300% in the continuous process. These findings demonstrate that continuous cultivation is a promising strategy for PS production to be used in pneumococcal vaccines.     

Comparative diel oxygen cycles preceding and during a Karenia bloom in Sarasota Bay,Florida, USA

The diel change in dissolved oxygen concentrations were recorded with an automated incubator containing a pulsed oxygen sensor in Sarasota Bay, Florida. The deployments occurred during a ‘pre-bloom’ period in May to June 2006, and during a harmful algal bloom dominated by Karenia brevis in September 2006. The diurnal (daylight) increase in dissolved oxygen concentrations varied from 16 to 104 μmol O₂ l⁻¹ with the corresponding nocturnal decrease in oxygen varying from 16 to 77 μmol O₂ l⁻¹. Nocturnal respiration consumed 42–113% of the diurnal net oxygen production with the minimum and maximum during the pre-bloom period. Hourly production rates closely followed fluctuations in irradiance with maximum rates in the late morning. Hourly oxygen utilization rates (community respiration) at night were highest during the first few hours after sunset.     

Role of calcium in alleviating effect of salinity on germination of Phragmites karka seeds

Phragmites karka (Retz.) Trin, ex. steud, a perennial reed with creeping rhizome from the family Poaceae, is distributed as pure population in brackish water swamps. Populations primarily propagate using ramets but also produce numerous seeds which form part of the seed bank after dispersal and are exposed to extremes of temperature, drought, and salinity stress. Seeds were germinated under a range of salinity (0, 100, 200, 300, 400, 500 mM NaCl) and temperature (10/20 °C, 15/25 °C, 20/30 °C, 25/35 °C, night/day) regimes in 12 h light:12 h dark photoperiod or in complete darkness with 0, 5, 10, 25 mM CaCl₂. Salinity, absence of light and high temperature (25/35 °C) reduced germination while calcium generally reversed this effect, more so at cooler temperature regimes. Calcareous soil around Karachi would help alleviate the salinity effect on the germination of P. karka and facilitate its survival.     

Modelling and simulation of continuous L (+) lactic acid production from sugarcane juice in membrane integrated hybrid-reactor system

Modelling and simulation was done for a two-stage membrane-integrated hybrid reactor system for continuous production of L (+) lactic acid under non-neutralizing conditions. The model captures microbial conversion of sugar cane juice to lactic acid under substrate–product inhibitions with downstream purification by nanofiltration. All the major phenomena and the governing parameters like fluid flow, feed dilution, substrate–product inhibitions, Donnan and steric effects during micro and nanofiltration for cell recycle, product separation and purification have been reflected in the modelling. The model describes a green, integrated continuous process of direct lactic acid production starting with a cheap, renewable carbon source. The highest lactic acid concentration achieved after the final stage of nanofiltration was 66.97 g/L at 13 kg/cm² operating pressure when the overall productivity reached 12.40 g/(L h). The developed model could successfully predict production, purification and transport of lactic acid through two stage membrane modules. Performance of the model was very good as indicated in the high overall correlation coefficient (R² > 0.980) and the low relative error (RE < 0.1).     

Cyanobacterial production of 1,3-propanediol directly from carbon dioxide using a synthetic metabolic pathway

Production of chemicals directly from carbon dioxide using light energy is an attractive option for a sustainable future. The 1,3-propanediol (1,3-PDO) production directly from carbon dioxide was achieved by engineered Synechococcus elongatus PCC 7942 with a synthetic metabolic pathway. Glycerol dehydratase catalyzing the conversion of glycerol to 3-hydroxypropionaldehyde in a coenzyme B₁₂-dependent manner worked in S. elongatus PCC 7942 without addition of vitamin B₁₂, suggesting that the intrinsic pseudovitamin B₁₂ served as a substitute of coenzyme B₁₂. The highest titers of 1,3-PDO (3.79±0.23 mM; 288±17.7 mg/L) and glycerol (12.62±1.55 mM; 1.16±0.14 g/L), precursor of 1,3-PDO, were reached after 14 days of culture under optimized conditions in this study.     

Enhancement of growth rate and β-galactosidase activity,and variation in organic acid profile of Bifidobacterium animalis subsp. lactis Bb 12

The behavior of Bifidobacterium animalis subsp. lactis Bb 12 under batch cultivation, after continuous culturing for up to 12 d, was monitored in skim milk-based media. Previous continuous culture for longer than 6 d affected the physiology of said microorganism. The minimum inhibitory concentrations of lactic and acetic acids increased from 18 to 26 g/l, whereas the molar ratio of acetic to lactic acid increased from 0.8 to 1.55, when the previous continuous culture increased its duration from 1 to 12 d. The specific lactose consumption rate decreased from 0.94 to 0.77 g_lactose/g_{cell dry mass}/h within the batch culture timeframe; this was concomitant with greater amounts of acetic and formic acids, and lower amounts of lactic acid produced. The β-galactosidase activity increased as continuous culturing time increased, and reached 446 units/ml by 12 d; however, the rate of enzyme synthesis decreased concomitantly. Succinic acid was produced during the exponential growth and stationary phases of the batch culture, but the former at exponential growth phase was higher as the continuous culturing time was longer. For comparison purposes, batch cultivation of samples taken from continuous cultures by 1 and 12 d was done using a semi-synthetic medium with glucose as carbon source; a pattern similar to that observed when using skim milk-based media was observed.     

Biohydrogen production using mutant strains of Chlamydomonas reinhardtii: The effects of light intensity and illumination patterns

Biohydrogen production from microalgae still remains to be discussed and examined more specifically, given that it is one of the most important energy carriers possessing environmental-friendly and sustainable characteristics. Although microalgae species capable of biohydrogen production do exist, Chlamydomonas reinhardtii is considered to be one of the most promising eukaryotic H₂ producers, and can serve as a model organism for such studies. Unfortunately, even if the metabolic basis and environmental conditions for this process are well defined, the sustainability of biohydrogen production is not straightforward. At this point, genetic engineering tools must be efficacious in order to enable mutant strains to reach desired amounts of biohydrogen. In this study, different light intensities, illumination patterns and Chlamydomonas strains such as CC124 and D1 protein mutant strains (D240, D239-40, D240-41) were investigated for the production of biohydrogen. The results showed that an increase in the light intensity shortened the lag phase of hydrogen production. With some minor differences, biohydrogen production was also found to be affected by the illumination pattern. On the other hand, maximum biohydrogen production was reached with a double-deletion mutant strain of D239-40, which attained a total production of 490 ± 10 mL L⁻¹ hydrogen and was followed by the other double-deletion mutant D240-41 that attained a total production of 388 ± 10 mL L⁻¹.     

Improving the lactic acid production of Actinobacillus succinogenes by using a novel fermentation and separation integration system

This work describes the development of a novel integrated system for lactic acid production by Actinobacillus succinogenes. Fermentation and separation were integrated with the use of a microfiltration (MF) membrane, and lactic acid was recovered by resin adsorption following MF. The fermentation broth containing residual sugar and nutrients was then recycled back into the fermenter after lactic acid adsorption. This novel approach overcame the problem of product inhibition and extended the cell growth period from 41 h to 120 h. Production of lactic acid was improved by 23% to 183.4 g L⁻¹. The overall yield and productivity for glucose were 0.97 g g⁻¹ and 1.53 g L⁻¹ h⁻¹, respectively. These experimental results indicate that the integrated system could benefit continuous production of lactic acid at high levels.