Areal Productivity Research Articles

Prevention of algaculture contamination using pesticides for biofuel production

Compared to terrestrial biofuels, algal biofuels have the advantages of high areal productivity, high oil content and the ability to be cultivated using non-potable water on non-arable land. However, just like terrestrial agricultural crops, algae can be grazed by a wide variety of organisms, particularly in open pond systems. Algal grazers can be controlled using pesticides to make a more sustainable source of biofuels. In this study, we choose Chlorella kessleri as the model freshwater algal producer and select the freshwater rotifer, Brachionus calyciflorus and the freshwater ciliate, Colpoda sp. as the model algal grazers. The pesticides - quinine (QN), niclosamide (NC), 3-trifluoromethyl-4-nitrophenol (TFM), rotenone (ROT) and protons (pH) are used to inhibit algal grazers. C. kessleri is not affected by TFM and NC at concentrations up to 39 and 31 μM respectively, while inhibition of B. calyciflorus is achieved at concentrations of 18 and 14 μM respectively. Colpoda sp. is inhibited by NC at 8 μM, while, QN, TFM and ROT inhibit Colpoda sp. at 30 μM. A pH range between 8.4 and 10.3 inhibits B. calyciflorus and allows C. kessleri to grow well. Compared to previous results using ROT, the findings presented in this study demonstrate that algal grazers may be effectively controlled by using QN, NC and TFM yet may require higher doses than ROT.

Application of purple phototrophic bacteria in a biofilm photobioreactor for single cell protein production: Biofilm vs suspended growth

Single cell protein (SCP), has been proposed as alternative to effectively upgrade and recycle organics and nutrients from wastewater. Biomass recovery is a critical issue, and recovery as a biofilm is effective in comparison with sedimentation of suspended biomass. This study aims to determine the applicability of purple phototrophic bacteria (PPB) biofilm on infra-red irradiated, submerged surfaces for the treatment of pre-settled red meat processing wastewater, and SCP generation. PPB removed up to 66% of COD and 42% of TN and TP during batch operation with total areal productivities between 15 and 20 gVS m−2 d−1 achieved. More than 60% of the total biomass grew attached (as biofilm) with the remainder being suspended. The biofilm can be harvested at around 160 gTS L−1 with high protein (>96 g L−1) and low ash contents (>4.0% compared to >30% in the wastewater). The compositions of attached and suspended biomass differed significantly, where the suspended fraction resembled the wastewater composition (e.g. in terms of inert components). The PPB community was similar in the suspended and biofilm fractions while the biofilm had higher relative abundance of PPB representatives (57% vs 43%). A consistent product composition is highly relevant for the manufacturer and ultimately determines the value as feed, feed additive, or supplement.

Experimental shifts of hydrologic residence time in a sandy urban stream sediment–water interface alter nitrate removal and nitrous oxide fluxes

The sediment–water interfaces (SWI) of streams serve as important biogeochemical hotspots in watersheds and contribute to whole-catchment reactive nitrogen budgets and water-quality conditions. Recently, the SWI has been identified as an important source of nitrous oxide (N2O) produced in streams, with SWI residence time among the principal controls on its production. Here, we conducted a series of controlled manipulations of SWI exchange in an urban stream that has high dissolved N2O concentrations and where we concurrently evaluated less-mobile porosity dynamics. Our experiments took place within isolated portions of two sediment types: a coarse sandy stream bed resulting from excess road-sand application in the watershed, and a coarse sand mixed with clay and organic particles. In these manipulation experiments we systematically varied SWI vertical-flux rates and residence times to evaluate their effect on the fate of nitrate and production rates of N2O. Our experiments demonstrate that the fate and transport of nitrate and N2O production are influenced by hydrologic flux rates through SWI sediments and associated residence times. Specifically, we show that manipulations of hydrologic flux systematically shifted the depth of the bulk oxic–anoxic interface in the sediments, and that nitrate removal increased with residence time. Our results also support the emerging hypothesis of a ‘Goldilocks’ timescale for the production of nitrous oxide, when transport and reaction timescales favor incomplete denitrification. Areal N2O production rates were up to threefold higher during an intermediate residence-time experiment, compared to shorter or longer residence times. In our companion study we documented that the studied sediments were dominated by a long-residence-time less-mobile porosity domain, which could explain why we observed N2O production even in bulk-oxic sediments. Overall, we have experimentally demonstrated that changes to SWI hydrologic residence times and SWI substrate associated with urbanization can change the biogeochemical function of the river corridor.

Studies on the Attached Cultivation of Filamentous Oleaginous Microalga Tribonema minus

Attached cultivation is a promising method for microalgal biomass production. Filamentous oleaginous microalga Tribonema minus (hereafter T. minus ) has shown a remarkable potential for biofuel production in terms of its high lipid content. However, the strain has only been cultivated in suspended cultivation systems including open pond and closed photobioreactors. Here, we attempted to study the attached cultivation of T. minus , which might be helpful for its scale-up cultivation and industrial applications. As the results, the optimal conditions for T. minus growth in the attached biofilm are 200 μmol photons m −2 s −1 of light intensity and 5% of CO 2 , and the maximum biomass density of 223 g m −2 has been achieved under the light intensity. The non-woven fabric as substratum was found as the best substratum in thin layer attached bioreactor, on which the average biomass productivity of T. minus is about (9.73 ± 2.19) g m −2 d −1 . Furthermore, two attached bioreactor systems, rotary drum and rotation disc, were designed following the light dilution strategy and introduced into T. minus cultivation. The highest footprint areal biomass productivity of these two systems is 33 and 47.1 g m −2 d −1 , respectively, much higher than that in suspended cultivation system. The results shows that T. minus can be cultured with attached cultivation method to improve its biomass productivity.

Isolation, Identification and Biotechnological Applications of a Novel, Robust, Free-living Chlorococcum (Oophila) amblystomatis Strain Isolated from a Local Pond

Bioprospection of novel autochthonous strains is key to the successful industrial-scale production of microalgal biomass. A novel Chlorococcum strain was recently isolated from a pond inside the industrial production facility of Allmicroalgae (Leiria, Portugal). Phylogenetic analysis based on 18S ribosomal ribonucleic acid (rRNA) gene sequences suggests that this isolate is a novel, free-living Oophila amblystomatis strain. However, as our phylogenetic data strongly suggests that the aforementioned taxon belongs to the genus Chlorococcum, it is here proposed to rename this species as Chlorococcum amblystomatis. In order to characterize the biotechnological potential of this novel isolate, growth performance and biochemical composition were evaluated from the pilot (2.5-m3) to industrial (10-m3) scale. The highest maximum areal productivity (36.56 g·m−2·day−1) was reached in a 10-m3 tubular photobioreactor (PBR), as compared to that obtained in a 2.5-m3 PBR (26.75 g·m−2·day−1). Chlorococcum amblystomatis displayed high protein content (48%–56% dry weight (DW)) and moderate levels of total lipids (18%–31% DW), carbohydrates (6%–18% DW) and ashes (9%–16% DW). Furthermore, the lipid profile was dominated by polyunsaturated fatty acids (PUFAs). The highest pigment contents were obtained in the 2.5-m3 PBR, where total chlorophylls accounted for 40.24 mg·g−1 DW, followed by lutein with 5.37 mg·g−1 DW. Overall, this free-living Chlorococcum amblystomatis strain shows great potential for nutritional applications, coupling a promising growth performance with a high protein content as well as relevant amounts of PUFAs, chlorophyll, and carotenoids.

Synoptic Spatio-Temporal Variability of the Photosynthetic Productivity of Microphytobenthos and Phytoplankton in a Tidal Estuary

Tidal estuaries are regarded as highly important ecosystems, mostly due to their high primary productivity and associated role as carbon sinks. In these ecosystems, primary productivity is mainly due to the photosynthetic carbon fixation by phytoplankton and microphytobenthos. The productivity of the two communities has been mostly studied separately, and directly comparable estimates of their carbon fixation rates in the same estuary are relatively scarce. The present study aimed to characterize the spatio-temporal variability of the productivity of phytoplankton and microphytobenthos in a tidal estuary, the Ria de Aveiro (Portugal), and to estimate the annual ecosystem-level budget for carbon fixation by the two communities. Productivity rates were determined based on synoptic in situ measurements of absolute rates of electron transport rate of photosystem II, using PAM fluorometry. Chlorophyll fluorescence indices were accompanied by measurements of salinity, temperature, water turbidity, solar irradiance, and planktonic and benthic microalgal biomass. Measurements were carried out hourly, along four spring-neap tidal cycles distributed along one year, on three sites of the estuary. The most pronounced trends in the spatio-temporal variability of the photophysiology and productivity of the two communities were the following: (i) maximum biomass and productivity were reached later for microphytobenthos (summer-autumn) than for phytoplankton (spring-summer); (ii) the absorption cross-section of PSII was generally higher for phytoplankton; (iii) the two groups showed a similar photoacclimation state, but microphytobenthos appeared as high light-acclimated when compared to phytoplankton. Biomass-specific productivity was on average higher for phytoplankton than for microphytobenthos, averaging 68.0 and 19.1 mg C mg Chl a-1 d-1, respectively. However, areal depth-integrated production rates were generally higher for the microphytobenthos than for the phytoplankton, averaging 264.5 and 140.0 mg C m-2 d-1, respectively. On an annual basis, phytoplankton productivity averaged 49.9 g C m-2 yr-1 while the productivity of microphytobenthos averaged 105.2 g C m-2 yr-1. When upscaling to the whole estuary, annual primary production rates of phytoplankton and microphytobenthos reached 4894.3 and 7534.0 t C yr-1, respectively, representing 39.4% and 60.6% of the combined total of 12428.3 t C yr-1 determined for the two communities in the Ria de Aveiro.

Nitrogen fertilization of soils fuels carbonate weathering and translocation in calcareous watersheds

In calcareous watersheds, groundwater alkalinity results largely from dissolution of carbonate minerals in soils. The alkalinity increases initially approximately in proportion to nitrate (NO3−) concentration and eventually approaches an apparent maximum of approximately 8 mmol L−1 at high NO3− concentrations. This close positive relationship between alkalinity and NO3− concentration appears to be predominantly a result of three processes: (i) mineralization of organic nitrogen fertilizer, (ii) exchange of OH− and H+ during the uptake of NO3− or ammonium by crop plants, and (iii) CO2 released by roots as a result of fertilizer-stimulated plant growth. We suggest that the asymptotic approach to a maximum groundwater alkalinity at NO3− concentrations exceeding 0.25 mmol L−1 may be caused by (i) a maximum possible areal crop production at excessive N fertilization and (ii) an increasing CO2 loss to the atmosphere due to the increasing CO2 production in the soil. Our analysis provides a general understanding and quantitative prediction of steady-state groundwater NO3− concentration, alkalinity, pH, the degree of CO2 supersaturation in the soil, and soil CO2 emissions to the atmosphere. The positive correlation between alkalinity and NO3− concentration observed in groundwaters persists in rivers and lakes. We conclude that an economically efficient agricultural practice that avoids over-fertilization might accelerate the in-soil carbonate weathering rate up to approximately threefold compared to unfertilized soils, but it will not jeopardize the use of aquifers for drinking water.

A comparative life cycle assessment of microalgae production by CO2 sequestration from flue gas in outdoor raceway ponds under batch and semi-continuous regime

To be a sustainable energy source, a microalgal cultivation model should address important environmental challenges for its large-scale implementation. In this work, the performance of an outdoor raceway pond system was evaluated for biomass production and sequestration of flue gas carbon-dioxide under different conditions. The microalgae growth was influenced by several physio-chemical factors such as temperature, solar irradiance, carbon-dioxide in the incoming feed, cross-contamination etc. Batch microalgal cultivation, without any external carbon supplementation (0.04% CO2, v/v), exhibited lower areal biomass productivity, whereas flue gas (10 ± 2% CO2, v/v) feeding increased dissolved medium carbon concentrations, which improved carbon-dioxide fixation rate. To further improve the system’s performance, semi-continuous regime was adopted that resulted in maximum biomass density of 0.42 g/L and 3.5-fold increase in areal productivity of 11.488 g/m2.s. Next, a “cradle-to-gate” Life Cycle Assessment (LCA) was performed using SimaPro 8.3.0.14 software to identify the potential environmental impacts associated with the production of Chlorella vulgaris biomass (functional unit: 1 kg). Results showed cultivation step to have significant environmental impact (>75%) in terms of GHG emission, energy requirement and other impact categories as estimated by GWP 100 IPCC 2013, CED and ReCiPe Endpoint method. Further, sensitivity analysis assisted in identifying the effect of variables with greatest impact on systems performance in the proposed scenarios; especially with the co-location of cultivation systems and flue gas emitting point sources. The results of attributional LCA revealed that flue gas utilization by microalgae in outdoor raceway ponds has less carbon footprint when a semi-continuous cultivation is carried out and will be more suitable when raceway ponds are co-located with thermal power plants.

Light guide systems enhance microalgae production efficiency in outdoor high rate ponds

Microalgae provide a powerful solar driven biotechnology platform for the production of the increasing quantity of food, fuel, high value products, fine chemicals and clean water required to supply our expanding global population. Light capture fuels all photosynthetically driven microalgae processes and consequently, maximizing light capture efficiency at minimal cost is central to process design. Raceway-style and paddle wheel operated open ponds, also known as high rate ponds (HRP0), are widely used, easy to operate and offer low-cost evaporative cooling compared to energy intensive closed systems. Here, the concept of delivering light from the surface into greater depths of the algae solution was tested at pilot-scale, by fitting a standard HRP0 with light transmitting guides designed to allow the capture of sunlight between ~10:00 am and ~3:00 pm to improve light distribution throughout the depth of the solution (HRP+). This prototype (HRP+) was analyzed to compare light distribution and biomass production efficiency against two control systems in two separate experiments such as: 1) a standard High Rate Pond (HRP0), and 2) a standard HRP0 fitted with no light transmitting dummy guides (HRP-) to maintain comparable fluid dynamics system characteristics. Under semi-continuous cultivation, HRP+ showed a significantly improved light distribution within the culture compared to the HRP- when operated at moderate to high densities. An increased proportion of the culture in the HRP+ was kept within the desired optimal photosynthetic zones while dark zones (unfit for photosynthesis and causing biomass loss) were drastically reduced compared to the HRP-. The HRP+ system exhibited a 3.9-fold higher maximum areal productivity of 49.2 ± 8.3 g·m−2·d−1 compared to HRP- (March–April 2018). Overall, this study establishes proof-of-concept of the functionality of light guides to improve light distribution and productivities in microalgae cultivation systems compared to the control systems run at the same incident light levels.

Comparative study on attached-growth photobioreactors under blue and red lights for treatment of septic tank effluent

Attached-growth photobioreactors (AG-PBRs) employing low-cost attached-growth media were applied to treat septic tank effluent which contained abundant organic and nutrient matters as well as pathogenic microorganisms. This study investigated effects of blue and red LED lights on organic, nutrient and pathogenic removals, biomass productivity and compositions of microbial community in the AG-PBR system. The experimental results showed the blue AG-PBR to be more effective in removing chemical oxygen demand (COD), total nitrogen (TN) and ammonia nitrogen (NH3–N) and generating biomass productivity than those of the red AG-PBR (P < 0.05). Mass balance analysis indicated that the TN and total phosphorus (TP) were removed mainly by assimilation into the biomass. The TN removal rates via nitrification and denitrification processes in the blue AG-PBR were found to be higher than that of the red AG-PBR, corresponding to the observed results of bacterial biomass and abundances of nitrifying and denitrifying bacterial species in the treatment systems. The maximal areal algal biomass productivity of 47 gDW/(m2. d) in the blue AG-PBRs was found to be higher than those of other algal attached-growth systems. Although, the red and blue AG-PBR systems could effectively treat the septic tank effluent to meet the national and international discharge standards, based on treatment efficiencies and biomass productivity, the blue AG-PBR is recommended for treatment of septic tank effluent.

Improving membrane photobioreactor performance by reducing light path: operating conditions and key performance indicators

Microalgae cultivation has been receiving increasing interest in wastewater remediation due to their ability to assimilate nutrients present in wastewater streams. In this respect, cultivating microalgae in membrane photobioreactors (MPBRs) allows decoupling the solid retention time (SRT) from the hydraulic retention time (HRT), which enables to increase the nutrient load to the photobioreactors (PBRs) while avoiding the wash out of the microalgae biomass.The reduction of the PBR light path from 25 to 10 cm increased the nitrogen and phosphorus recovery rates, microalgae biomass productivity and photosynthetic efficiency by 150, 103, 194 and 67%, respectively.The areal biomass productivity (aBP) also increased when the light path was reduced, reflecting the better use of light in the 10-cm MPBR plant. The capital and operating operational expenditures (CAPEX and OPEX) of the 10-cm MPBR plant were also reduced by 27 and 49%, respectively.Discharge limits were met when the 10-cm MPBR plant was operated at SRTs of 3–4.5 d and HRTs of 1.25–1.5 d. At these SRT/HRT ranges, the process could be operated without a high fouling propensity with gross permeate flux (J20) of 15 LMH and specific gas demand (SGDp) between 16 and 20 Nm3air·m−3permeate, which highlights the potential of membrane filtration in MPBRs.When the continuous operation of the MPBR plant was evaluated, an optical density of 680 nm (OD680) and soluble chemical oxygen demand (sCOD) were found to be good indicators of microalgae cell and algal organic matter (AOM) concentrations, while dissolved oxygen appeared to be directly related to MPBR performance. Nitrite and nitrate (NOx) concentration and the soluble chemical oxygen demand:volatile suspended solids ratio (sCOD:VSS) were used as indicators of nitrifying bacteria activity and the stress on the culture, respectively. These parameters were inversely related to nitrogen recovery rates and biomass productivity and could thus help to prevent possible culture deterioration.

Simultaneous removal of pollutants and high value biomaterials production by Chlorella variabilis TH03 from domestic wastewater

Cultivation of microalgae in the domestic wastewater is an alternative approach over conventional activated sludge processes for simultaneous pollutants removal and biomaterials production for biorefinery. This study was aimed at growing a Chlorella variabilis TH03 in domestic wastewater using various closed photobioreactors and open-reactor systems for evaluation of the algal growth, pollutants removal efficiency, biomass productivity and characterization of the biomass. Results indicated that the C. variabilis TH03 exhibited an outstanding growth, achieving maximum biomass concentration of 1.52, 1.67, 1.54 and 1.72 g/L, with specific growth rate of 0.32/day, 0.27/day, 0.22/day and 0.34/day in PBR-5-R, PBR-5-S, T-50 and RW-500 reactor systems, respectively. Remarkably, additional supplement of CO2 significantly enhanced areal biomass productivity of C. variabilis TH03 grown in RW-500 from 13.1 to 38.5 g/m2 day. Pollutants in term of COD, total nitrogen and total phosphorous were removed by 74.8–89.8%, 93.8–96.1% and 97.1–99.9%, respectively, during 14–17 days cultivation of the C. variabilis TH03. The fatty acid methyl esters of the algal biomass was determined as 22.55–26.12% with the most abundant fatty acids of C16:0 (26.13–27.67%), C16:3n4 (20.07–22.24%) and C18:3n3 (34.83–36.79%) which were desirable fatty acids for biodiesel and bio-jet fuels synthesis. Moreover, total carbohydrates and proteins in the algal biomass were accumulated up to 31.56–35.23% and 33.67–37.34%, respectively. Our preliminary results demonstrated the cultivation technology of C. variabilis TH03 can sustainably replace the conventional activated sludge technologies for domestic wastewater treatment.

Factors affecting pollutants removal and biomass production capability of Chlorella variabilis TH03 in domestic wastewater

Cultivation of microalgae in wastewaters and co-production of algal biomass have been considered as a sustainable approach for wastewater treatment. To achieve desirable biomass productivity and pollutants removal efficiencies, microalgal strain, cultivation mode and culturing conditions should be optimized. This was firstly aimed at examining growth characteristics of Chlorella variabilis TH03 strain under phototrophic, heterotrophic and mixtrophic cultivations using BG-11 medium as the sole of nutrient source. Secondly, the culturing variables such as aeration rate, percent dilution, N/P ratio and supplemented CO2 concentration were optimized to maximize biomass production and nutrient removal efficiencies of the algal strain in domestic wastewater. Thirdly, growth and nutrient removal capability of C. variabilis TH03 were investigated in an outdoor reactor system using domestic wastewater as a culture medium. Data showed that C. variabilis TH03 grew well under phototrophic and mixtrophic conditions but completely inhibited under heterotrophic conditions. In mixtrophic conditions, optimal aeration rate, percent dilution, N/P ratio and supplemented CO2 concentration achieved for the maximum growth and nutrient removal efficiencies were 0.2 vvm, no dilution, N/P = 15:1 and 15% CO2, respectively. Moreover, C. variabilis TH03 also exhibited an outstanding growth and nutrient removal capability in the outdoor reactor system, reaching areal biomass productivity of 39.5 g/m2∙day. Pollutants including COD, TN and TP were removed at efficiencies of 73.9, 97.1 and 99.8%, respectively. Nutrient levels in the effluent dropped below those required by the national technical regulation on domestic wastewater QCVN 14:2008/BTNM and QCVN 14-MT: 2015/BTNMT. The obtained results are useful for further study in large scale cultivation of C. variabilis TH03 for the production of high volume and low price biomass, helping to obtain returns from treatment of the waste stream, which is currently considered as a major source of water pollution in Vietnam.

Size matters – Microalgae production and nutrient removal in wastewater treatment high rate algal ponds of three different sizes

High rate algal ponds for coupled wastewater treatment and resource recovery have been the focus of much international research over the last 15 years. Microalgal biomass productivity reported in full-scale studies (1-ha or greater) have often been substantially lower than that reported from smaller scale ponds in similar climates, regardless of the season or the dominant microalgal species used. The disconnect between smaller-scale and full-scale productivity is unclear and uncertainty remains regarding the applicability of smaller scale studies to full-scale systems. In order to better understand the differences in reported productivity, the performance of three different size wastewater treatment high rate algal ponds (5 m2, 330 m2 and 1-ha) were assessed with respect to nutrient removal and microalgal productivity over three seasons. Both daily areal nutrient removal and biomass production were affected by the size of the pond. NH4-N removal via nitrification/denitrification decreased with increasing pond size, with the highest removal rate in the 5 m2 pond and the lowest in the 1-ha. Microalgal areal productivity was maximal in the 330 m2 pond, suggesting that a combination of mixing frequency and higher photosynthetic potential under low light conditions were the main drivers of enhanced productivity in this pond compared to the 5 m2 (mesocosm) and 1-ha (full-scale) ponds. The lowest daily nutrient removal and biomass production occurred in the 1-ha (full-scale) pond. Our results suggest that, based on the current design and operation of high rate algal ponds, the optimum size for maximum productivity is considerably smaller than the current full-scale systems. This has implications for commercial scale systems, with respect to capital and operational costs.

Outdoor pilot-scale raceway as a microalgae-bacteria sidestream treatment in a WWTP

This study aims at demonstrating the feasibility of using microalgae-bacteria consortia for the treatment of the sidestream flow of the supernatant from blackwater dewatering (centrate) in an urban wastewater treatment plant in Northern Italy. A 1200 L raceway reactor was used for the outdoor cultivation of a diverse community of Chlorella spp., Scenedesmus spp. and Chlamydomonas spp. in continuous operation mode with 10 days hydraulic retention time. During the trial, an average daily areal productivity of 5.5 ± 7.4 g TSS m−2 day−1 was achieved while average nutrient removal efficiencies were 86% ± 7% and 71% ± 10% for NH4-N and PO4-P, respectively. The microalgal nitrogen assimilation accounted for 10% of the nitrogen in the centrate while 34% was oxidized to nitrite and nitrate. The oxygen produced by microalgae fully covert the oxygen demand for nitrification. This suggests that the proposed process would reduce the aeration demand for nitrification in the water line of the plant, while producing algal biomass to be further valorized for energy or material recovery.

Optimal proteome allocation strategies for phototrophic growth in a light-limited chemostat

BackgroundCyanobacteria and other phototrophic microorganisms allow to couple the light-driven assimilation of atmospheric text {CO}_{2} directly to the synthesis of carbon-based products, and are therefore attractive platforms for microbial cell factories. While most current engineering efforts are performed using small-scale laboratory cultivation, the economic viability of phototrophic cultivation also crucially depends on photobioreactor design and culture parameters, such as the maximal areal and volumetric productivities. Based on recent insights into the cyanobacterial cell physiology and the resulting computational models of cyanobacterial growth, the aim of this study is to investigate the limits of cyanobacterial productivity in continuous culture with light as the limiting nutrient.ResultsWe integrate a coarse-grained model of cyanobacterial growth into a light-limited chemostat and its heterogeneous light gradient induced by self-shading of cells. We show that phototrophic growth in the light-limited chemostat can be described using the concept of an average light intensity. Different from previous models based on phenomenological growth equations, our model provides a mechanistic link between intracellular protein allocation, population growth and the resulting reactor productivity. Our computational framework thereby provides a novel approach to investigate and predict the maximal productivity of phototrophic cultivation, and identifies optimal proteome allocation strategies for developing maximally productive strains.ConclusionsOur results have implications for efficient phototrophic cultivation and the design of maximally productive phototrophic cell factories. The model predicts that the use of dense cultures in well-mixed photobioreactors with short light-paths acts as an effective light dilution mechanism and alleviates the detrimental effects of photoinhibition even under very high light intensities. We recover the well-known trade-offs between a reduced light-harvesting apparatus and increased population density. Our results are discussed in the context of recent experimental efforts to increase the yield of phototrophic cultivation.

Annual outdoor cultivation of the diatom Thalassiosira weissflogii: productivity, limits and perspectives

Diatoms are a promising source of renewable biomass for production of energy and functional ingredients and food products. The eurythermal diatom Thalassiosira weissflogii shows great resistance and robustness, and can be considered a suitable candidate for outdoor cultivation. In this study we investigated the resilience of one strain of this species during one-year outdoor experimentation in inclined tubular photobioreator with a working volume of 40 L. Cells of T. weissflogii overcome temperature and irradiance fluctuations by adapting their growth rate at the different environmental conditions. Calculation of areal biomass productivity based on 30 cultures along the year showed a median value of 3.83 g m−2 day−1 with maximal values of biomass (6.8 g m−2 day−1) and lipids (1.2 g m−2 day−1) reached in February and July, respectively. We observed a decline in biomass productivity with temperature increase, whereas lipid content (10–20% of dry biomass) was not significantly affected by the environmental conditions as far as a high concentration of nutrients was maintained. The outdoor experimentation successfully proved one year-round production of biomass from a single diatom species in closed photobioreactor, making T. weissflogii a suitable candidate for guaranteeing stable annual productive cycles in outdoor plant.

Design and Construction of Microwave-Assisted Pyrolysis of Waste Coconut Shell for the Isolation of Pyroligneous Acid

As a country with a large amount of natural resources, Indonesia should be able to convert this material into more value added product. However, most of the natural resources were sold as a raw material. Process system engineering research center is one of the solution to overcome this problem by developing an integrated and systematic technology. Through this research center, output of the research can be scaled up for large scale production and also can be commercialized to increase the community welfare. One of natural resources which has not been optimally utilized is waste coconut shell (WCS). Indonesia is the largest coconut producer in the world with areal production of 3.88 ha and 3.2 million ton of coconut products. Several problems arefacedbycoconutagroindustry,i.e.thelackofcoconutbasedproductdiversification and also the large number of WCS. WCS is one of organic waste, however it is quite hard to be decomposed by the microorganism due to its hard texture. This problem may gave high potential in the environmental pollution. In this research, WCS is going to be used as a raw material for pyroligneous acid through pyrolysis process. Pyrolysis is a method that is usually used to convert a biomass waste sources into a valuable product through thermal decomposition process without the presence of oxygen. This process will produce solid (char), liquid (bio-oil, tar and pyroligneous acid) and gas. Pyroligneous acid is commonly obtained as a side product from the production of active carbon and to date it has not been utilized economically. In the other hand, pyroligneous acid can be used as an anti-oxidant, antimicrobial, antifungal, anti-biofilm and also as an anti inflammatory. This properties are available due to the presence of organic matter and phenolic compound in the pyroligneous acid. This characteristics showedthatpyroligneousacidishighlypotentialasrawmaterialindrugsandpharmacy industries. Pyrolysis process requires high temperature which has range between 500 – 600 ∘C. In this paper, it will be discussed a pyrolysis equipment design and productionofpyroligneousacidfromWCSbyusingmicrowave-assistedpyrolysis(MAP).

Design scenarios of outdoor arrayed cylindrical photobioreactors for microalgae cultivation considering solar radiation and temperature

Advancing microalgae biotechnologies requires the design of high efficiency, large scale outdoor photobioreactor systems. Here we present a predictive biomass productivity model to define system design parameters yielding high biomass productivities for a facility encompassing arrays of cylindrical photobioreactors (PBRs) in a sub-tropical location (Brisbane, Australia). The model analyses the temperature and the light distributed through the culture medium as a function of PBR height, diameter, spacing distance between reactors, biomass concentration and cultivation regime (continuous vs. batch; fixed vs. capped temperature control). Temporal changes in light and temperature were used to predict volumetric and areal productivities (Pvol and Pareal respectively) for three Chlorella strains (C. vulgaris, C. sp. 11_H5 and C. pyrenoidosa). A simple empirical relationship was derived to rapidly predict Pvol in PBR arrays based on the ratio of spacing distance and reactor height (L/H) if the Pvol of a single, unshaded PBR was known. For C. vulgaris under a continuous operation and variable temperature (within its maximum growth threshold), the highest Pvol in the range analysed was obtained at the smallest diameter (0.1 m), highest biomass concentration (1.5 g L−1) and largest L/H, (Pvol ~0.3 g L−1 d−1). In contrast, the highest Pareal (~50 t ha−1 yr−1) was found at higher diameters (0.15 and 0.3 m), a lower biomass concentration (0.3 g L−1) and low L/H (0.2–0.4); this was attributed to a higher overall culture volume per PBR and per area. Our predictions, based on light and temperature effects on productivity, suggest that attaining a high Pvol could reduce costs, energy and materials associated with water usage, harvest loads and PBRs; whereas attaining a Pareal toward its maxima could reduce costs associated with land. The model supports effective PBR array design and process optimisation to help minimise production cost.

Maximising the productivity of the attached cultivation of Ulva tepida in land-based systems

The viability of land-based seaweed cultivation is linked to high areal productivity of biomass and best suited for species that grow vegetatively and unattached. To develop optimised strategies for cultivation in land-based systems for attached species characterised by short growth cycles with periodic reproduction, ropes were seeded with zoids of the green seaweed Ulva tepida and stacked vertically in the water column from one to four layers deep. The layers spanned a culture depth from 50 to 350 mm below the surface of the water. After an initial grow-out period of 10 days, the biomass was continuously harvested on a rolling 4-day cycle which maintained the biomass in an actively growing state, over the 62-day cultivation period. Compared with the single layer treatment the vertical stacking of seeded ropes, in combination with frequent harvesting, increased the areal productivity of U. tepida by 40% with productivities >20 g dw m−2 day−1. Notably, productivities were similar between stacking treatments with two, three, or four layers due to a decreasing availability of light with an increasing number of layers and an increasing depth in the water column. Consequently, the most effective method of cultivation was to stack two layers of ropes in combination with the vertical movement of the layers through the water column with frequent harvesting to reduce the onset of reproduction.