Biomass Production Rate Research Articles

Effects of Nitrogen Supplementation Status on CO2 Biofixation and Biofuel Production of the Promising Microalga Chlorella sp. ABC-001.

The use of microalgal biomass as feedstock for biofuels has been discussed for decades as it provides a sustainable approach to producing fuels for the future. Nonetheless, its feasibility has not been established yet and various aspects of biomass applications such as CO2 biofixation should also be explored. Therefore, in this study, the CO2 biofixation and lipid/carbohydrate production potential of Chlorella sp. ABC-001 were examined under various nitrogen concentrations. The highest biomass productivity and CO2 biofixation rate of 0.422 g/l/d and 0.683 g/l/d, respectively, were achieved under a nitrogen-rich condition (15 mM nitrate). Carbohydrate content was generally proportional to initial nitrate concentration and showed the highest value of 41.5% with 15 mM. However, lipid content showed an inverse relationship with nitrogen supplementation and showed the highest value of 47.4% with 2.5 mM. In consideration as feedstock for biofuels (bioethanol, biodiesel, and biogas), the sum of carbohydrate and lipid contents were examined and the highest value of 79.6% was achieved under low nitrogen condition (2.5 mM). For lipid-based biofuel production, low nitrogen supplementation should be pursued. However, considering the lower feasibility of biodiesel, pursuing CO2 biofixation and the production of carbohydrate-based fuels under nitrogenrich condition might be more rational. Thus, nitrogen status as a cultivation strategy must be optimized according to the objective, and this was confirmed with the promising alga Chlorella sp. ABC-001.

Design, Fabrication, and Performance Evaluation of Open Raceway Ponds for the Cultivation of Chlorella vulgaris Beijerinck in the Philippines

Two pilot-scale open raceway pond systems were designed and fabricated in the University of the Philippines Los Baños (UPLB) for the cultivation of Chlorella vulgaris Beijerinck to observe the biomass productivity of the alga in an open condition in the Philippines. One design was an oval track with a middle island, while the other was a multi-stage raceway pond (MSRP) consisted of several sections separated by baffles. The pond designs aimed to accommodate 1,000 L of culture. The nutrient media used was composed of urea, NPK (16-20-0), FeCl3, and Na2EDTA – a locally formulated medium that sustains the growth of the species. Paddlewheel was installed to provide mixing, which was turned on during the daytime, while aeration was continuously supplied through perforated air-distributor PVC pipes installed on the pond floor. Only natural light was utilized, and no lighting was provided during the night. The growth rate was generated by monitoring the biomass concentration in the pond through spectrophotometry at 425 nm, where optical density and biomass concentration relationship was initially established. Using the equation for first-order kinetics and taking the points from the exponential phase, the specific growth rate of Chlorella obtained from the oval raceway pond was computed to be 0.007308 h–1 with doubling time of 94.84 h. The biomass productivity rate was computed to be 308.49 g/m3-d or equivalent to 63.24 g/m2-d. On the other hand, the MSRP obtained a specific growth rate of 0.003389 h–1 with a doubling time of 204.55 h and equivalent biomass productivity of 302.19 g/m3-d or 60.44 g/m2-d. The biomass productivity obtained is comparable, even superior to other commercial open pond cultivation using C. vulgaris.

Potential microalgal strains for converting flue gas CO2 into biomass

A screening method using 15% CO2 (v/v) as screening stress and a spotting plate method was developed to isolate microalgae with the potential to convert flue gas CO2 to biomass. A total of six microalgal strains, belonging to the genera Chlorella, Heynigia, Desmodesmus, and Scenedesmus, were isolated from ponds near metallurgical/cement/power plants. The growth of these isolated strains was dramatically promoted at 5 to 15% CO2 when they were cultivated in bubble column photobioreactors aerating with 0.03%, 5%, 10%, and 15% CO2. The growth of Heynigia riparia SX01 in particular showed substantial improvement with the increase of CO2 concentrations from 5 to 15%. Furthermore, the maximum biomass, overall biomass productivity, maximum biomass productivity, and maximum CO2 fixation rate of these microalgal strains greatly increased at 5 to 15% CO2 as well. Chlorella sorokiniana GS03 showed the highest values in maximum biomass productivity (0.36 g L−1 day−1) and maximum CO2 fixation rate (0.66 g L−1 day−1) at 5% CO2. Heynigia riparia SX01 exhibited the highest values of maximum biomass (3.28 g L−1), overall biomass productivity (0.27 g L−1 day−1), maximum biomass productivity (0.39 g L−1 day−1), and maximum CO2 fixation rate (0.71 g L−1 day−1) at 15% CO2. This study provides not only an efficient screening method obtaining microalgae with wide CO2 tolerance but also microalgal strains utilizing high levels of CO2 up to 15% to produce biomass, which contributes to further exploration in converting real flue gas CO2 into biomass feedstock.

Arbuscular mycorrhizae induce a global metabolic change and improve the nutritional and health benefits of pennyroyal and parsley

This study was conducted to investigate the potential use of arbuscular mycorrhizal fungi (AMF), Rhizophagus irregularis, as an innovative cultivation procedure to improve the production and quality of two medicinal plants, pennyroyal (Mentha pulegium), and parsley (Petroselinum hortense). We elucidated the impact of AMF on soil properties and growth and metabolic profiling of pennyroyal and parsley. AMF treatment improved the availability of essential elements and phenols in the rhizospheric soil. Plant biomass production and photosynthetic rate were improved. We also recorded improved primary and secondary metabolism, where the levels of most of the detected soluble and insoluble sugars, organic acids, essential (isoleucine and valine), and non-essential (glutamine, alanine, and cysteine) amino acids, fatty acids (especially unsaturated fatty acids), phenolic acids, and flavonoids were increased. Overall, this study supports the use of AMF in the artificial cultivation, as an alternative to the chemical fertilizers, for the production of high-quality medicinal plants with enhanced levels of bioactive compounds.

CO2 biofixation and fatty acid composition of two indigenous Dunaliella sp. isolates (ABRIINW-CH2 and ABRIINW-SH33) in response to extremely high CO2 levels.

Global warming, as a result of atmospheric CO2 increase, is regarded as an important universal concern. Microalgae are considered as appropriate microorganisms for CO2 assimilation. Here we aimed to investigate carbon biofixation ability of two indigenous isolates of Dunaliella spp. (ABRIINW-CH2 and ABRIINW-SH33) under elevated CO2 concentrations of 10, 20, and 30% (v/v) as well as their lipid content, productivity, and fatty acid profile under adjusted pH conditions. The maximum biomass production and CO2 biofixation rates were obtained under 10% CO2. High CO2 concentrations were favorable for the accumulation of lipids, lipid productivity, and polyunsaturated fatty acids formation. The highest lipid content and lipid productivity was obtained at 10% CO2. The highest fraction of the fatty acids (FA) profile was allocated to omega-3 FAs at 20% CO2. Accordingly, these isolates were able to tolerate extremely high CO2 concentrations and present even enhanced growth as well as formation of valuable products.

The influence of soil warming on organic carbon sequestration of arbuscular mycorrhizal fungi in a sub-arctic grassland

A substantial portion of grassland photosynthates is allocated belowground to arbuscular mycorrhizal fungi (AMF), but controversy remains about whether this carbon (C) contributes to soil organic carbon (SOC) under warming. The goal of this study was to investigate how AMF biomass and C sequestered by AMF (CNew) are influenced by soil warming. We estimated the AMF biomass and CNew, assumed to be mostly AMF necromass, in mycelial ingrowth bags buried for 1, 2, or 3 years in soil under warming (~+0.5–16.4 °C). The AMF biomass had a positive, curvilinear response to warming gradients after one year of burial. About 107 g C m−2 of CNew accumulated over the three years and ~12% of this C was from glomalin-related soil protein. Modelling suggested the production rate of AMF biomass was 153 g C m−2 yr−1 with a rapid (36–75 days) turnover while AMF necromass turnover was much slower (1.4 ± 0.2 yr−1). Warming duration (7–9 years vs. > 50 years) did not have significant influence on AMF biomass or CNew (P > 0.05). Our results suggest that AMF are more tolerant to increases in temperature than other microbes or fine roots. The dramatic loss of soil C and stable soil aggregates under warming found earlier at this site were not attributed to a decrease in AMF biomass or CNew. Despite a low AMF standing biomass, its contribution to SOC may be substantial.

Responses of the seagrass Halophila stipulacea to depth and spatial gradients in its native region (Red Sea): Morphology, in situ growth and biomass production

The tropical seagrass Halophila stipulacea is the most dominant and widespread seagrass species in the Gulf of Aqaba (GoA, northern Red Sea). In light of the ecological services provided by H. stipulacea in its native regions, and its reported colonization and dispersion in non-native areas, there is a growing global interest in understanding its vegetative development and growth strategies under varying environmental gradients. Aiming to compare growth and biomass production rates in native vs. invasive regions in the near future, it is rather surprising that such baseline data hardly exists for H. stipulacea. Focusing on the northern GoA, we investigated morphological characteristics, in situ growth rates, and biomass production at three different sites (NB, TY and SB), and at each site, at two depths (5 and 14 m) during the summer months (June-July 2019). Significantly larger (11 %) rhizome internodes and longer (19 %) and wider (15 %) leaves were observed in deeper plants compared to those inhabiting shallow meadows. On the contrary, shoot and internode formation rates in shallow plants were markedly higher than in deep-adapted plants, with production values of one shoot and one internode every 5.9 ± 0.8 and 6.9 ± 0.6 days, respectively. Rhizome elongation rates did not vary significantly across sites and depth with an average value of 0.2 cm d−1. In addition, larger leaf area, number of leaves, and higher above and below-ground biomass were observed in the NB site, compared with TY and SB, suggesting that more favourable growth conditions for H. stipulacea existed at NB which is exposed to high anthropogenic pressures. Results highlight how the species is highly responsive to in situ conditions, and thus contribute to an improved understanding of its vegetative dynamics and growth strategy as a basis for future comparisons and temporal assessments.

Optimization of Rhodomonas sp. under continuous cultivation for industrial applications in aquaculture

The microalgae species Rhodomonas sp. is commonly used in aquaculture for its high nutritional value due to the eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) content. Understanding the effect of cultivation parameters on biomass production rate and composition is presently limited, however essential in further commercialization of this strain. Under nutrient replete conditions, light intensity and temperature are the main factors determining biomass growth and composition. Therefore, the combined effect of light and temperature on the biomass production rate and biomass composition of Rhodomonas sp. was studied using a statistical Design of Experiment approach. Rhodomonas sp. was cultivated under continuous (turbidostat) conditions in lab-scale reactor systems (1.8 l) under different temperature (15–20–25–30 °C) and light conditions (60–195–330–465–600 μmol m−2 s−1). Stable biomass production was observed under all conditions except experiments performed at 30 °C, which led to cell death. Under optimized growth conditions, high growth rates (>1.0d−1) and high biomass production rates, up to 1.5 g l−1 d−1, were obtained in this study. The biomass production rate reported here is >10-fold higher than values reported in literature on Rhodomonas sp. The optimal temperature for maximal growth was found at T = 22–24 °C under all light conditions. The maximum biomass yield on light (Yx,ph – 0.87 g mol−1) was found at light levels between 110 and 220 μmol m−2 s−1. The fatty acid profile was only significantly influenced by temperature, with higher EPA and DHA contents at lower temperatures (15 °C). A total fatty acid (TFA) content of 8–10% of the total dry-weight was found for all tested conditions. The EPA content fluctuated between 9 and 16% of TFA and DHA content between 6 and 9% of TFA, only affected by temperature. A maximum EPA + DHA production rate of 114 mg l‐−1 d−1 was obtained at 20 °C and high light (600 μmol m−2 s−1) conditions.

Effect of treated sewage characteristics on duckweed biomass production and microbial communities

Duckweed biomass production in a duckweed pond fed with three differently treated sewage (i.e. sewage treated by primary sedimentation (PS); conventional activated sludge process (CAS); and downflow hanging sponge process (DHS)) was evaluated in order to assess the effects of water quality on biomass yield. Higher and stable biomass production was observed when the duckweed pond was fed with PS or DHS-effluent than with CAS-effluent, evidently due to the difference in nutrient loads. Availability of nutrients, especially phosphorus, affected the biomass production rate: higher the nutrient, faster the production. Microbial community analysis revealed that the members of Rhizobiales were likely to contribute to stable and high biomass growth. From the results of the study, a sewage treatment system consisting of a primary sedimentation followed by a duckweed pond and a tertiary treatment unit can be proposed to maximize biomass production without compromising treatment objectives. Size and operational parameters of the duckweed pond should be determined primarily based on the nutrient availability in the influent water to maximize duckweed growth.

Evaluation of accessions of vetch species for agronomic performance under nitosol and vertisol conditions in the central highlands of Ethiopia

Vetch is an annual forage legume and accessions of its species performed differently under different soil conditions. Twenty accessions of five vetch species were evaluated for their agronomical differences at Holetta and Ginchi in the central highlands of Ethiopia. The rate of DM accumulation was similar during the initial growth stage. However, after the second sampling (74 DAS), aerial DM accumulation varied widely across the testing sites due to the difference in temperature, rainfall, and soil fertility conditions. The average stretched plant height was higher at Ginchi compared to Holetta, which could be attributed to higher and extended rainfall and favorable growing conditions during the experimental period. In addition to genetic variability, soil fertility and environmental conditions could also contribute to the difference in height. On average, about 10 and 20 more days were required to harvest forage and seed yield, respectively, at Ginchi compared to Holetta. Days to forage harvest ranged from 80.7 to 113.0 and 94.3 to 126.0 days after the emergence of the seedlings at Holetta and Ginchi, respectively. The difference in maturity is an important agronomic trait to select companion crops for maximum production. The higher biomass production rate was recorded at Ginchi than in Holetta. Accessions of early maturing vetch species had a comparatively higher biomass production rate, while late-maturing accessions had lower biomass production rates at both locations. Intermediate-to-late-maturing accessions of vetch species gave relatively better forage DM yield than early maturing accessions at both locations. The highest grain-filling period was recorded for accession 2424 (Vicia villosa) at Holetta and accession 64266 (Vicia sativa) at Ginchi. Vetch accessions showed higher seed yield and thousand seed weight at Ginchi than Holetta. The 20 accessions of vetch species were grouped into three clusters based on major measured parameters.

English

Currently under production, thirty-eight Ethiopian maize varieties released majorly for three agro-climatic zones over the past thirty-nine, twenty-nine and twelve years for the high altitudes, mid–altitudes and low altitudes, respectively, were conducted at three different research center’s field trials, using randomized complete block design with three replications in 2015 main cropping season to estimate the genetic gains made on yield and yield related traits. The regression analysis indicated average annual and annual relative genetic gains of 62.3 (0.19%), 59.0 (0.57%) and –2.64 (–0.16%) in kg ha–1 yr–1 for grain yields, respectively, at Ambo Plant Protection Research Center (APPRC), Bako National Maize Research Center (BNMRC) and Melkassa Agricultural Research Center (MARC). Correlational analysis on the field studied traits indicated positively significant associations of grain yields with grain filling rate, ear length, number of kernels per row, number of ears per plant, biomass production rate, biomass yield and harvest index; also, negatively significant associations were shown for days to anthesis and days to silking at APPRC. Grain yield showed positively significant associations with ear length, plant height, grain filling rate, thousand kernel weight, biomass production rate and harvest index at BNMRC, while those only with harvest index were shown at MARC. Relatively considerable genetic gains and inconsiderable genetic reductions due to grain yields, grain yield related traits and grain yields associations with the other studied maize breeding traits had been observed across the released maize varieties from the three agro–ecological zones of Ethiopia. Key words: Annual genetic gains, annual relative genetic gains, correlational analysis, highland maize, lowland maize, mid–altitude maize, regression analysis.

Production and optimization of polyhydroxybutyrate (PHB) from Bacillus megaterium as biodegradable plastic

Among biodegradable plastics polyhydroxy alkanate and its polymers have received more attention than other biodegradable polymers because of their complete degradability, flexibility, water resistance and also the ease of production process. Polyhydroxybutyrate is one of the types of polyhydroxy alkanates that is seen as a storage granule in many microorganisms. In this study, Bacillus megaterium was prepared from Iranian microbial collection. Glucose and yeast extract were used as the main components of the medium in seed media 9 and 2.5 g/l and in fermentation medium 30 and 7.5 g/l respectively. GC-MASS and FTIR were used to identify the PHB produced. The results showed that the highest amount of biomass (0.221 g/l) and PHB (0.080 g/l) were obtained with glucose at 37°C and shaker speed of 150 rpm for 72 h incubation. The results of GC MASS and FTIR showed the production of PHB by Bacillus under investigation. Based on the mean of data on total cell growth conditions, the rate of cell biomass and PHB production in B. megaterium were 0.0869 and 0.0171 respectively. According to the results of the experiments, temperature had the greatest effect on biomass production and PHB production. The bioplastics produced by microbes are also highly degradable in the environment, and due to their specific chemical structure, they have been widely used in various fields of the food, pharmaceutical and chemical industries and are likely to replace today's plastics in the near future. DOI: http://dx.doi.org/10.5281/zenodo.3711400

Effect of fluorescent dye positioning and concentration on the growth parameters and lipid content of Chlorella sp. in a flat panel photobioreactor.

In this study, two different concentrations of fluorescent dye Rhodamine 6G (R6G) with two different strategies were used in a double layer flat panel photobioreactor (PBR) for investigation of its effect on growth parameters of microalgae Chlorella sp. Results showed that in the first strategy, when the light passed through the dye before reaching the broth, biomass productivity rate (P) and maximum specific growth rate (µmax) relative to control case, were increased up to 60 and 23% respectively. Increasing in these parameters were more, for the low dye concentration. Also, in the second strategy, when the light passed through the microalgae before reaching the dye solution, P and µmax for lower concentration increased about 9 and 15%, respectively. But using high dye concentration growth of the algae was decreased. Furthermore, using R6G caused increase in the lipid and chlorophyll content of the microalgae Chlorella sp.

Selection of low nitrogen demand yeast strains and their impact on the physicochemical and volatile composition of mead.

Mead is an ancient alcoholic beverage produced through the fermentation of a diluted solution of honey. Due to the peculiar and varied composition of honey, mead production faces several problems, such as slow or stuck fermentations mainly due to the low nitrogen concentration, lack of uniformity of the final product and the production of unpleasant aromas. In this context, this work aimed to select low nitrogen-demand yeast strains and evaluate their potential for the production of mead. Therefore, among 21 commercial wine yeast strains, 5 were selected based on their fermentative behavior at low assimilable nitrogen concentrations. The selected strains were further evaluated for their contributions in meads produced with limited nitrogen availability, and the results showed significant differences on some physicochemical parameters like biomass production, residual sugars, glycerol concentration, and fermentative rate. Moreover, meads obtained with selected strains differed in the concentration of several volatile compounds. The volatile compounds concentration and the principal component analysis based on odor activity values allowed separating strains into three groups. In general, S. cerevisiae var bayanus strains (QA23, Spark, and AWRI-R2) were the largest producers of aromatic compounds, particularly those with floral and fruity descriptors. The selection of yeast strains with low nitrogen-demand and different volatile compounds production can be explored by mead makers to limit fermentation problems and obtain characteristic products.

Microbial synergy and stoichiometry in heap biooxidation of low-grade porphyry arsenic-bearing gold ore.

Heap biooxidation method was used to evaluate the availability of Paodaoling gold ore in Anhui province, China. 15,000 tons of gold ores (≤ 10mm in diameter) were bioxidized under mesophilic conditions. Under the synergistic effect of microbial community, arsenic and sulfur were oxidized by 42% and 38% after 80 days. Relatively, leaching of gold was improved from 36 to 78% after heap biooxidation. The sequencing results showed there were 28 operational taxonomic units identified the microbial community in the heap. The main genera were Acidithiobacillus, Ferroplasma, Acidiferrobacter and Nitrospira. According to stoichiometry, the content of microorganisms with various functions tended to be balanced. The biomass production rate was 10g/s, the CO2 fixation rate was 18g/s, and the oxygen consumption rate was 60g/s. This study provides a good basis for the further design and application of heap biooxidation technology.

Improvement of Thermosynechococcus sp. CL-1 performance on biomass productivity and CO2 fixation via growth factors arrangement

The enormous attraction on CO2 biofixation using photosynthetic microorganisms such as cyanobacteria has been risen due to its promising efficiency and valuable by-products production. In this study, an isolated cyanobacterium from hot spring in Taiwan, Thermosynechococcus sp. CL-1 (TCL-1) was evaluated for its growth factors arrangement effect on the biomass productivity and CO2 biofixation. The initial biomass concentration, and nutrient supply level variation influenced TCL-1 biomass productivity and CO2 biofixation rate while the adjusted and controlled pH value gave an insignificant difference on its performance. The initial biomass concentration of 3 g L−1 gave the best result on biomass productivity and CO2 fixation which reached 143.4 mg L−1 h−1 and 224 mg L−1 h−1 respectively. Regarding to the result of this study, controlled pH value by the CO2 supply inside the reactor, produced an insignificant difference in TCL-1 performance compared to those with the uncontrolled pH value. The variation of nutrient supply level was achieved by the variation of macronutrient and micronutrient supply inside the medium. The G-solution contains metals and other micronutrient elements which are necessary for the growth of TCL-1. The combination between 5–folds MF medium as the macronutrient, and 3-folds G-solution as the micronutrient supply, present the best TCL-1 performance on biomass productivity and CO2 fixation rate.

Growth, Biomass Production, and Yield Potential of Quinoa (Chenopodium quinoa Willd.) as Affected by Planting Techniques Under Irrigated Conditions

Quinoa is gaining importance globally owing to its nutritional quality and its adaptability under variety of conditions. However, limited information is available on the impact of planting techniques on growth, morphology, and yield and biomass accumulation under irrigation conditions. To the date, no ideal planting technique (sowing method) has been reported for the flat irrigated land for better adjustment of quinoa in a crop rotation. To test the hypothesis, a two-year field study (2013–14 and 2014–15) was carried out at University of Agriculture, Faisalabad, Pakistan. The experiment comprised of four planting technique bed sowing (BS), ridge sowing (RS), flat line sowing (FLS), and sowing in standing water (SSW) in main plots, and two quinoa accession (A7 and A9) in subplots. The results showed that BS method improved the morphological attributes viz. stem thickness, main panicle, main panicle, thousand grain weight, grain yield, and harvest index as compared to SSW. Regarding the quinoa accessions, A9 performed better than A7 for morphology, biomass, and yield. Panicle number per plant was positively correlated with harvest index and main panicle weight in 2013–14, while 1000-grain weight and harvest index had a stronger correlation during 2014–15. The average and maximum biomass production rate of A7 in BS plants were relatively higher than other sowing techniques either for A9 or A7. Our data suggest that the BS method is a relatively better planting technique and A9 quinoa accession is a suitable genotype to obtain a high targeted grain yield under irrigated conditions.

Study on the Characteristics of Pyrolysis Gas and Oil from Corn Stalk Pyrolysis

In this paper, stem-skins, stem-pith, stem-leaves of corn stalks were separated and pyrolyzed to produce pyrolysis gas and oil on the temperature-controlled slide tube furnace. The gas yield, the gas component and the oil-producing rate of the skins, pith and leaves of corn stalkspyrolysis were studied under the different pyrolysis temperatures and residence time. The results show that the pyrolysis gas yield and the oil production rate wereeffected significantlyby the temperature. With the increase of pyrolysis temperature, the gas yield of the skins, pith and leaves of corn stalks increased, while the oil production rate decreased. The maximum pyrolysis gas yield isthestem-leaves, the second is the stem-pith, andthestem-skin was the smallest. When the temperature increased from 550 °C to 750 °C, the content of CO and H2increased with the increase of temperature, while the content of CO2 in pyrolysis gas decreased. The contents of C2H4and C2H6did not change obviously, and the total content was about 2%. When thepyrolysis residence time was extended from 10 min to 60 min at 650 °C, the pyrolysis gas production rate of biomass increased gradually. When residence time was 10min and 60min, the gas production rate of the stem-skin was 34.32% and 38.92%, respectively. The component of the gaseous product is affected by the residence time, while the effect of oil yield is not significant.

Biodiversity, ecosystem functioning, and the environmentalist agenda: a reply to Odenbaugh

Among the instrumental value defenses for biodiversity conservation is the argument that biodiversity is necessary to support ecosystem functioning. Lower levels of biodiversity yield lower levels of ecosystem functioning and hence the inference that we should conserve biodiversity. In our book Defending Biodiversity: Environmental Science and Ethics, we point out three problems with this inference. (1) The empirical support for such an inference derives from experiments conducted on a very small set of ecosystem types (mainly grasslands and fresh water aquatic) and ecosystem functions (mainly nutrient uptake, biomass production, and decomposition rates). These experiments suffer from a number of largely unavoidable logistical constraints making the generality of their results questionable. (2) Even if the experimental results were unequivocal, their lack of external validity would still raise significant questions about how (if at all) these results apply to real world conservation problems. And (3) even if the experimental results were unequivocal and completely applicable to conservation problems, relying on such defenses implies other rational policy commitments that are at odds with other positions that environmentalists commonly take. Odenbaugh and I disagree largely about what inferences follow from these points rather than about the points themselves. I think that what follows is that if environmentalists want to use instrumental value defenses, then we need to accept that not all biodiversity is useful to us, and parts that are useful are not necessarily more useful than alternatives that might threaten biodiversity. I also think that the unpalatable implied commitments need to be taken seriously. This may mean that we environmentalists have to accept that biodiversity should not always be conserved, and that parts of the environmentalist agenda are little more than strong personal preferences that others need not respect. If environmentalists are willing to accept these conclusions, then there are no problems with relying on these instrumental value defenses, but I suspect that environmentalists are likely to be unhappy with such conclusions.

The Effect of Light Wavelength on CO2 Capture, Biomass Production and Nutrient Uptake by Green Microalgae: A Step Forward on Process Integration and Optimisation

Microalgae have drawn the attention of several researchers as an alternative to the traditional physicochemical CO2 capture methods, since they can convert CO2 and water into organic matter and release oxygen into the atmosphere. Microalgal growth can be improved by changing light supply, such as light intensity, wavelength, and photoperiod. In this study, the effect of different light wavelengths on CO2 capture, nutrient removal from a synthetic effluent and biomass production of Chlorella vulgaris, Tetradesmus obliquus and Neochloris oleoabundans was studied. The experiments were conducted with light-emitting diodes (LEDs) with different wavelengths: 380–750 nm (white), 620–750 nm (red) and 450–495 nm (blue). The maximum specific growth rate was obtained by N. oleoabundans with white LEDs (0.264 ± 0.005 d−1), whereas the maximum biomass productivity (14 ± 4 mgdw L−1 d−1) and CO2 fixation rate (11.4 mgCO2 L−1 d−1) were obtained by C. vulgaris (also with white LEDs). Nitrogen and phosphorus removal efficiencies obtained under white light conditions were also the highest for the three studied microalgae.