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ispartof: ENVIRONMENTAL POLLUTANTS AND BIOAVAILABILITY vol:34 issue:1 pages:338-351 status: accepted

International audience; High energy consumption during harvesting is one of the main bottlenecks for sustainable microalgae production. Membranes can efficiently separate microalgae from liquids with low energy consumption, but membrane fouling remains an important issue. Flocculation prior to membrane filtration can increase membrane fluxes and decrease fouling, thus offering a low-cost and efficient solution to harvest microalgae. Biobased cationic cellulose nanocrystals were successfully used as flocculants for microalgae and were effective over a wide pH-range and for both freshwater and marine microalgae. Such flocculation was for the first time combined with vibration-assisted filtration using a charged, surface patterned membrane, enabling operation at very high flux (95 L/m2 h) using a vibration frequency of only 1 Hz, and even under sub-optimal flocculation conditions. Intermittent vibration decreased energy consumption further while keeping excellent filtration performance to finally achieve a record-low energy consumption for the membrane filtration of only 6.7 Wh/m3, which is andgt;25-times lower than that of normal membrane filtration. Interaction forces revealed that increasing particle size through flocculation prior to membrane filtration can significantly prevent microalgae attachment on the vibrating membrane surface. This work opens a new direction for sustainable microalgae harvesting with an ultra-low energy consumption, combined with a very high microalgae recovery, reduced use of chemicals, and lower membrane investment cost.

The increased input of nutrients into biological systems has been shown to result in altered biotic interactions through changes in food availability. The aim of this study was to test for an association between phytoplankton nutrient content and epibiont variables in natural zooplankton populations. Via a field survey, we studied how a gradient in food quantity and quality impacted host population density and epibiont variables in Daphnia pulex . We found a significant decrease in epibiont prevalence and infracommunity richness, which could mainly be attributed to a changing phytoplankton N : P ratio (caused by P‐limitation). We performed a lab experiment in which we exposed Daphnia magna to different algal nutrient ratios and the epibionts detected in the field study. P‐limitation in the algae affected D. magna performance and resulted in similar trends of food quality effects in the epibiont variables. The experiment, however, also reflected subtle differences between different epibiont species.

International audience; Microalgae are a promising resource for biofuel production, although their industrial use is limited by the lack of effective harvesting techniques. Flocculation consists in the aggregation and adhesion of cells into flocs that can be more easily removed from water than individual cells. Although it is an efficient harvesting technique, contamination is a major issue as chemical flocculants are often used. An alternative is to use natural biopolymers flocculants such as chitosan. Chitosan is a biobased nontoxic polymer that has been effectively used to harvest Chlorella vulgaris cells at a pH lower than its pKa (6.5). While the reported flocculation mechanism is said to rely on electrostatic interactions between chitosan and the negative cell surface, no molecular evidence has yet confirmed this mechanism. In this study, we performed force spectroscopy atomic force microscopy (AFM) experiments to probe the interactions between C. vulgaris cells and chitosan at the molecular scale to decipher its flocculation mechanism. Our results showed that at pH 6, chitosan interacts with C. vulgaris cell wall through biological interactions rather than electrostatic interactions. These observations were confirmed by comparing the data with cationically modified cellulose nanocrystals, for which the flocculation mechanism, relying on an electrostatic patch mechanism, has already been described for C. vulgaris. Further AFM experiments also showed that a different mechanism was at play at higher pH, based on chitosan precipitation. Thus, this AFM-based approach highlights the complexity of chitosan-induced flocculation mechanisms for C. vulgaris.

At this moment about 7.6 billion people inhabit the earth (Worldpopulation clock 2018). A sustainability revolution is necessary (WCED 1987, UNCED 1992, Rockström 2009) to avoid this huge population in striving for a luxury life depleting the resources of the planet. There are also important social issues that need to be resolved (Raworth 2017). It has been argued that even a real cultural shift is needed (Kagan 2010).This revolution can be started in education (UN 2003). The decade of education for sustainable development (UNESCO 2014a) ran from 2005 till 2014. It is being carried further in the Global Action Program (UNESCO 2014b). At the University of Leuven, the ‘Science and Sustainability’ course is a stand-alone elective course of 6 credits that specifically aims to provide master’s students in the natural sciences with education for (the benefit of) sustainability action (Ceulemans & Severijns 2018a and 2018b). Last year (2016‐2017), the course ran for the first time and insight was gained in the competences that master’s level students hold for sustainability. Based on this experience, stronger emphasis was placed in the second year (2017‐2018) on providing, and making students use, tools to approach sustainability issues. Specific attention was directed toward allowing students to get acquainted with systems thinking and deal with inter- and transdisciplinary issues by approaching problems from a multi-stakeholder point of view. The sustainability reports the student teams compiled therefore necessarily included a representation of the system map they compiled to get a grip on the sustainability issue. Also a stakeholder map needed to be drawn.Near the end of the course it became apparent that students had difficulty in deviating from the Western interpretation of sustainability, where ecological criteria strongly dominate and ecological responsible behavior is pretended to be adequate to drive the transformation for true sustainability. However, it is in the socio-political and socio-cultural dimensions that the value-laden component of sustainability is really found. Several team-tailored feedback and discussion sessions were therefore organized to make students at least consider a slightly broader view on sustainability.Three student reports of projects that were carried out within this framework are presented in the appendices to this abstract. Students were asked to focus in their reports specifically on the broader sustainability related issues. Technical and exact-scientific information related to their project topic was preferably included in an addendum. Sustainability dimensions on which a focus was laid (e.g. Social, Cultural, Politics, Economics, Communications) varied among the projects, being largely dependent on the topic addressed and in part also on the major stakeholders.

Flocculation is a widely used technology in industry including for wastewater treatment and microalgae harvesting. To increase the sustainability of wastewater treatment, and to avoid contamination of the harvested microalgal biomass, there is a need for bio-based flocculants to replace synthetic polymer flocculants or metal salt coagulants. We developed the first cellulose nanocrystalline flocculant with a grafted cationic point charge, i.e. glycine betaine (i.e. N,N,N-trimethylglycine) grafted cellulose nanocrystals (CNCs) effective for the flocculation of kaolin (a model system for wastewater treatment), the freshwater microalgae Chlorella vulgaris, and the marine microalgae Nannochloropsis oculata. We successfully grafted glycine betaine onto CNCs using a one-pot reaction using a tosyl chloride activated esterification reaction with a degree of substitution ranging from 0.078 ± 0.003 to 0.152 ± 0.002. The degree of substitution is controlled by the reaction conditions. Flocculation of kaolin (0.5 g L-1) required a dose of 2 mg L-1, a comparable dose to commercial polyacrylamide-based flocculants. Flocculation was also successful for freshwater as well as marine microalgae (biomass concentration about 300 mg L-1 dry matter), although the flocculation efficiency of the latter remained below 80%. The dose to induce flocculation (DS = 0.152 ± 0.002) was 20 mg L-1 for the freshwater Chlorella vulgaris and 46 mg L-1 for the marine Nannochloropsis oculata, comparable to other bio-based flocculants such as chitosan or TanFloc. ispartof: NANOSCALE ADVANCES vol:3 issue:14 pages:4133-4144 ispartof: location:England status: published

Flocculation could offer a low-cost and straightforward solution to harvest microalgae in an economic and energy-efficient way. Cationically modified cellulose nanocrystals (CNCs) have been propose...

Microalgae are able to produce many valuable biomolecules, such as polysaccharides, that presents a large diversity of biochemical structures and functions as antioxidant, antifungal, anticancer, among others. Static magnetic fields (SMF) influence the metabolism of microorganisms and has been shown as an alternative to increase microalgae biomass, yield and compounds production. Especially, some studies have highlighted that SMF application could enhance carbohydrate content. This study aimed to evaluate different conditions of SMF on Spirulina and Chlorella in indoor and outdoor conditions, in order to confirm the influence of SMF on polysaccharides production, evaluating which polysaccharidic fraction could be enhanced by SMF and highlighting a possible modification in EPS composition. Starch from Chlorella and exopolysaccharides (EPS) from Spirulina were quantified and characterized. SMF increased the starch content in Chorella fusca biomass. EPS productions from A. platensis and Spirulina sp. were not significantly increased, and global composition appeared similar to the controls (constituted basically of 80–86% neutral sugars and 13–19% uronic acids). However, the monosaccharide composition analysis revealed a significant modification of composition, i.e., the amount of fucose, arabinose, rhamnose, galactose and glucuronic acid was increased, while the glucose content was decreased. SMF application led to significant modification of polysaccharides production and this study demonstrate that combining the outdoor conditions with SMF, the starch content and EPS composition was positively affected.

Membranes have a lot of potential for harvesting microalgae, but mainly membrane fouling and high harvesting costs linked to low fluxes are hampering their breakthrough. Patterned membranes can reduce fouling by enchancing local turbulences close to the membrane surface on one hand, and by increasing the active area per m2 of installed membrane on the other. Flocculation can further increase membrane permeance by increasing microalgal partical size and reducing the fraction of free organic matter in the feed. In current study, the effect of polyethylene glycol (PEG) in the casting solution of patterned polysulfone membranes was investigated to better tune the performance of the patterned membranes, together with the effects of cross-flow velocity and chitosan dosage on membrane fouling. The energy consumption and total harvesting cost, extrapolated to a full-scale microalgal harvesting, were then estimated. The patterned membrane prepared with a 28w% PEG concentration showed the highest clean water permeance (900±22 L/m2 h bar) and membrane permeance in a microalgal suspension (590±17 L/m2 h bar). Patterned membranes showed a lower filtration resistance (15% permeance decline at the end of filtration) than flat membranes (72%) at a cross-flow velocity of 0.0025 m/s. Increasing cross-flow velocity could increase membrane permeance in most cases. The highest stable membrane permeance (110±17 L/m2 h bar) and the lowest filtration resistance were achieved when combining patterned membrane filtration with flocculation at optimized chitosan dosage. A very low energy consumption (0.28 kWh/kg) and harvesting cost (0.16 €/kg) were achieved under these conditions. ispartof: WATER RESEARCH vol:198 ispartof: location:England status: published

International audience; Harvesting efficiency is one of the key issues restricting the further commercialization of microalgae. Traditional biofilm studies only tend to focus on enhancing biofilm formation, while neglecting the subsequent harvesting of the biofilm. In this study, a win–win strategy for high-density microalgal cultivation and low-cost harvesting through biofilm cultivation on a pH-responsive, charge-switchable, patterned membrane was investigated using a polyethylenimine (PEI)-crosslinked polyvinylidene fluoride (PVDF) membrane. The patterned membranes were prepared by spray-modified non-solvent induced phase inversion, and the effect of pattern height on biofilm formation and microalgal harvesting was investigated. The PEI-crosslinked PVDF membrane surface was positively charged below pH 8 and negatively charged above pH 9, resulting in a higher attractive energy below pH 8 and a repulsive energy above pH 9 according to the extended Derjaguin, Landau, Verwey, Overbeek model. Patterning of these membranes increased the active area for microalgal attachment, and created a low-shear area in the valleys that prevents early detachment of microalgal cells. Membranes with a higher pattern height resulted in faster biofilm development and increased final biomass accumulation. Low-energy membrane vibration was applied to enhance cell detachment. pH = 7 was found to be the optimal pH for enhanced microalgal biofilm formation on PEI-crosslinked patterned membranes, and a switch to pH = 10 was best for microalgal harvesting.

Flocculation of marine microalgae is challenging because of the high ionic strength of the culture medium. We investigated cationic cellulose nanocrystals (CNCs) as biobased flocculants for the marine microalgae Nannochloropsis oculata, and compared its performance to chitosan. Cationic CNCs induced flocculation at a low dose of 11 mg.L-1 while chitosan required a dose of 35 mg.L-1. Our cationic CNCs possess a permanent positive charge, allowing flocculation over a wide pH-range (4 to 10). The CNC maximum flocculation efficiency was 90 %, while chitosan achieved > 95 %, attributed to small flocs remaining in suspension for CNCs. However, centrifugation for 1 min at 180 g or gravity filtration using a 30 µm nylon filter after CNC flocculation resulted in the removal of these small, stable flocs (∼150 µm diam) and > 95% harvesting efficiency. Cationic CNCs can serve as a sustainable alternative natural flocculant for harvesting both freshwater and marine microalgae. ispartof: Carbohydrate Polymers vol:240 ispartof: location:England status: Published online

The assembly of host-associated bacterial communities is influenced by a multitude of biotic and abiotic factors. It is essential to gain insight in the impact and relative strength of these factors if we want to be able to predict the effects of environmental change on the assembly of host-associated bacterial communities, or deliberately modify them. The environmental pool of bacteria, from which the host is colonized, and the genetic background of the host are both considered to be important in determining the composition of host-associated bacterial communities. We experimentally assessed the relative importance of these two factors and their interaction on the composition of Daphnia magna gut bacterial communities. Bacterioplankton originating from natural ponds or a laboratory culture were used to inoculate germ-free Daphnia of different genotypes. We found that the composition of the environmental bacterial community has a major influence on the Daphnia gut bacterial community, both reflected by the presence or absence of specific taxa as well as by a correlation between abundances in the environment and on the host. Our data also indicate a consistent effect of host genotype on the occurrence of specific bacterial taxa in the gut of Daphnia over different environments., The assembly of the Daphnia magna gut microbiota is strongly influenced by the composition of the environmental bacterioplankton community, and additionally structured by the host genetic background.

Facilities for the production of microalgal biomass often suffer large losses in productivity as a result of biological contamination of cultures by ciliates, unicellular protozoans that feed on microalgae. Garlic oil is a low-cost natural product that is known to be active against several protozoans. In this study, we investigated whether garlic oil can be used to control ciliate contamination in microalgal cultures, using the ciliate Oxytricha and the microalga Chlamydomonas as a model system. Low doses of garlic oil (5–10 mg L−1) were capable of eradicating the ciliate Oxytricha from a contaminated Chlamydomonas culture within 1 day without influencing the productivity of the Chlamydomonas culture. The LD50 of garlic oil to the ciliate (3 mg L−1) was 19 times lower than the LD50 to the microalgae, which implies a low risk to the microalgal culture in case of overdosing. Analysis of the garlic oil indicated that it was composed mainly of polysulfides, with the main compound being diallyl disulfide. Diallyl disulfide had a lower toxicity to the ciliate (LD50 14 mg L−1) than garlic oil, indicating that diallyl disulfide is not the main active compound in garlic oil against the ciliate. Because garlic oil has a low cost, is already approved for use in agri- and aquacultures, has a low toxicity to humans, and is biodegradable, it may offer a sustainable solution to control biological contamination by ciliates in microalgal cultures. We would like to thank Jan Czech (Hasselt University, TANC) for execution of the GC-MS analysis. The first author would like to acknowledge the Ministry of Education and Training of Vietnam for funding the PhD program. Funding information The authors thank KU Leuven University for funding this research through grant OT/14/065.

Producción Científica, Microalgal-bacterial consortium can be used to upgrade biogas by removing CO2 and H2S. Photosynthetic biogas upgrading requires harvesting microalgal-bacterial biomass in order to use the biomass-free cultivation medium as scrubbing liquid in the absorption column. In this study, the efficiency of different flocculants (Zetag 8125, cationically modified cellulose nanocrystals, Tanfloc, chitosan, and FeCl3) to harvest microalgal-bacterial biomass used for biogas upgrading in alkaline medium (inorganic carbon concentration up to 1800 mg L−1 and a pH ~10) was evaluated. Zetag and cationic cellulose nanocrystals resulted in maximum flocculation efficiencies of 95% (optimal dose 30 mg g−1) and 93% (optimal dose 20 mg g−1), respectively. Low flocculation was observed with other flocculants at doses as high as 200 mg g−1, which can be ascribed to the high pH of the alkaline medium. Zetag and cationic cellulose nanocrystals were selected for harvesting the biomass during semi-continuous cultivation of the microalgal consortium. Both Zetag and cationic cellulose nanocrystals were effective in flocculating the biomass with efficiencies of over 90% during five successive harvesting cycles. Gravity settling of the flocs formed by Zetag and cationic cellulose nanocrystals resulted in low biomass concentration factors of 7.7 and 2.0, respectively. Screening of flocs using a nylon mesh screen (pore size of 180 μm) resulted in a biomass concentration factor as high as 19.8. Zetag and cationic cellulose nanocrystals could be useful in harvesting biomass under high alkaline conditions without detrimental effects on biomass growth., Junta de Castilla y León y programa EU-FEDER (CLU 2017-09) y (UIC 071), FWO-NRF cooperation project (VS00218N), European Union's Horizon 2020 research and innovation programme under grant agreement no 751637

Temperate and tropical shallow lakes differ in several fundamental aspects with respect to management of eutrophication. High altitude tropical shallow lakes are a special case, showing similarities with temperate and tropical lakes. We studied the ecology of the eutrophic high-altitude tropical lake Yahuarcocha in the Ecuadorian Andes and evaluated the potential of biomanipulation to control eutrophication. With a toxin-producing Cylindrospermopsis bloom, low Secchi depth and low submerged macrophyte cover, Yahuarcocha is clearly in a turbid ecosystem state. Relatively low nutrient concentrations should theoretically allow for a shift to a clear water state through biomanipulation. Top-down control of phytoplankton by zooplankton, however, is complicated by the (1) absence of predatory fish, (2) fish community dominated by small poecelid species, (3) lack of a refuge for zooplankton from fish predation within the macrophytes, and (4) persistent, grazing resistant bloom of the cyanobacterium Cylindrospermopsis. In these aspects, lake Yahuarcocha is more similar to tropical shallow lakes, probably because water temperature is high relative to the mean air temperature and because of the absence of a cold season. The fish and macrophyte communities consisted almost entirely of exotic species. The exotic fish species probably stabilized the turbid state in the lake.

Nitrogen (N) limitation is considered as the most efficient strategy to induce the accumulation of lipids, carbohydrates or other target compounds in microalgal biomass. However, along with biomass biochemical composition, alterations in N limitation affect the photosynthetic apparatus and result in decreased growth. In this study, Chlorella vulgaris was cultivated in semi-continuous mode with different degrees of N limitation and chlorophyll (Chl) fluorescence analyses were used to investigate the effect of N limitation on photosystem II (PSII) performance, in terms of structural and functional heterogeneity. As expected, N limitation resulted in the decrease of quantum yield and calculated OJIP parameters related to PSII performance. N limitation resulted in a significant increase of trapped energy per reaction center (RC) and subsequently to higher dissipation of excess energy. However, despite the negative effect of N limitation on the number of RCs, the electron transport beyond QA as well the capacity of reducing/re-oxidation of plastiquinone were not negatively affected, implying that performance of RCs was not affected by N limitation. Photochemical quenching (qp) increased of as N limitation increased while the curve of non-photochemical quenching (NPQ) was unimodal, i.e. increased up to a level of N limitation and then decreased as N limitation degree increased further. The overall results of the present study suggest that the decrease of PSII performance was due to a reduction of the number of RCs accompanied with higher energy dissipation a probable outcome of the decreased need for reductant by cells due to lower metabolic activity under N limitation.

The aim of the present study was to evaluate the effects of varying concentrations of different nitrogen sources (individually or in combination) on the biochemical, transcriptomic and proteomic profiles of Arthrospira sp. PCC 8005 under batch and continuous modes. In batch mode, while ammonium showed a repressive effect on nitrate-assimilation pathway of the cyanobacteria; better growth and nutrient uptake rate were observed in presence of urea than nitrate. The inhibitory effect of ammonium was further confirmed by the continuous photobioreactor study wherein the nutrient feed was transiently replaced from nitrate to ammonium (28mM turbiostat regime). The changes in lipid, exopolysaccharide, transcriptomic and proteomic profiles of cyanobacteria on transition from nitrate to ammonium indicated at an onset of nutrient stress.

Microalgae are promising sources of lipids for applications in food, fuel, pharmaceutics and cosmetics. However, these lipids are also subject to lipolysis reactions during processing and storage. Especially during wet biomass storage, substantial amounts of free fatty acids (FFA) are formed, which has negative effects on flavor and nutritional value and can cause downstream processing problems in biodiesel production. This study contributes to a better understanding of the underlying processes leading to lipolysis by focusing on cell wall differences between species. Therefore, in a first phase, a comparison was made between the lipolytic stability of Nannochloropsis oculata and T-Isochrysis lutea , two species reported to have substantial differences in cell wall structure and strength. Nannochloropsis appeared to be stable during the first days of wet storage, while in T-Isochrysis , lipolysis started immediately after harvest. In a second experiment, the influence of cell disruption by high pressure homogenization (HPH) on lipolytic stability during wet storage of Nannochloropsis was investigated. It was observed that the HPH treatment induced lipolysis, as the FFA content was rapidly increasing immediately after the treatment, in contrast to the control sample, in which the FFA content was constant during the first days of storage. The integrity of the microalgal cell was thus found to play a crucial role in lipid stability during short-term post-harvest wet storage.

Given the importance of A. platensis as a potential food protein source, we describe an affordable deodorization process that does not significantly affect the nutritional value of algae biomass.; Results: Ethanol, acetone or hexane were used to deodorize algae biomass and then to identify the profile of volatile compounds associated with its distinctive odor. Sensorial characteristics were improved in the biomass cake after the proposed solvent extraction. Panelists identified the ethanolic extract with the most pronounced algae-related odor. Gas chromatography-mass spectrometry analysis showed that a mixture of 20 different compounds derived from fatty acids and amino acids contributed to the characteristic smell of A. platensis biomass. The results of the present study show that the ethanol solvent-free A. platensis biomass contained > 600 g kg-1 protein, 65% in vitro protein digestibility, similar to the original biomass. The Fourier transform infrared spectroscopy secondary protein structure was comparable among samples, indicating that the only change after ethanol extraction was a reduction of the algae smell.; Conclusion: The various extraction procedures investigated in the present study were effective in deodorizing the algae biomass. The most effective protocol was the removal of odoriferous compounds with ethanol. This particular procedure yielded an algae biomass with an improved sensorial traits. The results of the present study should help with the identification of odoriferous compounds derived from fatty acids, pigments and proteins associated with A. platensis. © 2017 Society of Chemical Industry.; © 2017 Society of Chemical Industry.

The detection of new pollutants, stricter environmental regulations, and advancements in treatment technologies are driving improvements in bioprocesses for treating wastewater. Specifically, special concern is being placed on phosphorus and nitrogen forms, which spur eutrophication of water bodies, and emerging micropollutants such as pharmaceuticals and person-care products. Algae and cyanobacteria cultivation requirements include water and nutrient sources that currently are supplied by fertilizers, which provide poor sustainability and economics. Using wastewater as a source of nitrogen and phosphorus represents an attractive option to cultivate microalgae simultaneous with contaminant removal. Phycoremediation refers to the assimilation or disintegration of organic and inorganic compounds (carbon, nitrogen, or phosphorus), metals, and emerging contaminants in wastewater by microalgae – algae and cyanobacteria. In addition, added value comes when the microalgae are harvested to become feedstock for biofuels such as biogas. Although promising studies have been published for algal growth in wastewater while simultaneously removing contaminants, limitations in the scale-up process still have to be addressed. In this work, we summarize biological mechanisms by which nutrients and contaminants are removed by microalgae. We specifically address the interactions that the microalgae have with other microorganisms and the production of extracellular polymeric substances, a mechanism well known in the literature, but hardly studied in microalgae. Finally, we discuss different strategies reported to improve the scale up of microalgae cultivation in wastewater.

© 2016 John Wiley & Sons Ltd The tropical Andes has a high density of glacial lakes that are situated in the high-altitude páramo (3500–4500 m). Ecological information about such lakes is scant despite the fact that these lakes are an important source of water for drinking, irrigation and electricity generation and feed several major tributaries of the Amazon. In this study, we provide data on a survey of 31 lakes in Cajas National Park (Ecuador). Two of the lakes were monitored monthly during one year. In situ nutrient addition experiments were carried out in three of the lakes. Seasonal monitoring in two lakes revealed a thermal stratification of the water column between October and June, with a small temperature difference between epi- and hypolimnion (2–3 °C). Oxygen depletion of the hypolimnion towards the end of the stratification period indicated that no complete mixing of the water column occurred during stratification. There was no evidence of depletion of nutrients in the epilimnion or accumulation in the hypolimnion during stratification. There were also no clear seasonal changes in chlorophyll-a (Chl-a) concentration nor in phytoplankton community composition in the two lakes. Inputs of dissolved organic carbon (DOC) from the vegetated catchment resulted in high DOC concentrations (median 2.9 mg L−1) compared to temperate mountain lakes. Water transparency was relatively low, with a median extinction coefficient for photosynthetic active radiation of 0.50 m−1 and for UV-B radiation of 10.13 m−1. Although the thermocline was deep and water transparency was low, estimates of the critical depth for photosynthesis were deeper than the mean water depth in all lakes, suggesting that phytoplankton was not light limited. The phytoplankton community was dominated by chlorophytes (e.g. Oocystis), diatoms (small Cyclotella spp.) or small colonial cyanobacteria (Aphanocapsa, Merismopedia). The zooplankton community was either dominated by large cladocerans and cyclopoid copepods, or by the calanoid copepod Boeckella occidentalis. Total concentrations of phosphorus (P) and nitrogen (N) were comparable to those in temperate mountain lakes (4–35 μg P L−1 and 162–758 μg N L−1) while Chl-a concentrations were in the lower range (

© 2016, Springer Science+Business Media New York. This study investigated the effects of pH, salinity, biomass concentration, and algal organic matter (AOM) on the efficiency of four commercial cationic flocculants. The tannin-based biopolymers Tanfloc SG and SL and the polyacrylamide polymers Flopam FO 4800 SH and FO 4990 SH were tested for flocculation of two microalgae models, the freshwater Chlorella vulgaris and the marine Nannochloropsis oculata. Both biomass concentration and AOM presence affected all polymers evaluated, whereas salinity and pH affected only Flopam and Tanfloc, respectively. A restabilization effect due to overdosing was only observed for Flopam polymers and increasing Tanfloc dose resulted in improved efficiency. Flopam polymers showed a significant decrease in the maximum quantum yield of photosystem II as function of polymer dose for Chlorella, which supported the need for toxicological studies to assess the potential toxicity of Flopam. In overall, Tanfloc was not affected by salinity nor presented potential toxicity therefore being recommended for the flocculation of both freshwater and marine species. ispartof: BIOENERGY RESEARCH vol:10 issue:2 pages:427-437 status: published

© 2018 Elsevier B.V. Contamination of microalgal cultures by rotifers is known to cause large losses in productivity. The factors that control population dynamics of rotifers in microalgal cultures were studied in controlled contamination experiments in laboratory cultures. These experiments revealed that rotifer growth rates increase with microalgae biomass at low rotifer population densities and declines with rotifer biomass as the rotifer population approaches a carrying capacity. Experimental results were used to construct a model that describes the impact of rotifer contamination on three types of large-scale microalgal cultures. The results of this model indicate that rotifer contamination causes a complete loss in productivity in open pond and closed photobioreactor cultivation systems. In contrast, losses in productivity are limited in thin layer cascade reactors because the rotifer population cannot achieve a sufficiently high population density to cause a crash of the culture. These results suggest that different cultivation systems respond differently to rotifer contamination. ispartof: ALGAL RESEARCH-BIOMASS BIOFUELS AND BIOPRODUCTS vol:38 status: published

The treatment of nitrogen-deficient agriculture wastewater, arising from the vegetable and fruit processing, is a significant problem that limits the efficiency of its biological treatment. This study evaluates the effectiveness of the symbiotic co-culture of Azospirillum brasilense and Scenedesmus sp., under two nitrogen levels (8.23 mg L&minus, 1 and 41.17 mg L&minus, 1) and mixing systems (aeration and magnetic stirring), aiming to simultaneously use the N-deficient media for their growth while producing biomass for biofuels. Microalgae growth and biomass composition, in terms of protein, carbohydrate and fatty acid contents, were evaluated at the end of the exponential growth phase (15 days after inoculation). Results show that the symbiotic co-culture of microalgae-bacteria can be effectively performed on nitrogen-deficient media and has the potential to enhance microalgae colony size and the fatty acid content of biomass for biofuels. The highest biomass concentration (103 &plusmn, 2 mg&middot, L&minus, 1) was obtained under aeration, with low nitrogen concentration, in the presence of A. brasilense. In particular, aeration contributed to, on average, a higher fatty acid content (48 &plusmn, 7% dry weight (DW)) and higher colony size (164 &plusmn, 21 &micro, m2) than mechanical stirring (with 39 &plusmn, 2% DW and 134 &plusmn, m2, respectively) because aeration contribute to better mass transfer of gases in the culture. Also, co-culturing contributed in average, to higher colony size (155 &plusmn, m2) than without A. brasilense (143 &plusmn, m2). Moreover, using nitrogen deficient wastewater as the culture media can contribute to decrease nitrogen and energy inputs. Additionally, A. brasilense is approved and already extensively used in agriculture and wastewater treatment, without known environmental or health issues, simplifying the biomass processing for the desired application.

Ciliates are a common but less-explored group of contaminants in microalgal cultures that feed on microalgae and can cause severe losses in productivity of cultures. The aim of this study was to evaluate the potential of biological control to eradicate ciliates from microalgal cultures. In lab-scale experiments, we used the carni- vorous cyclopoid copepod Acanthocyclops robustus as a biological control agent to eliminate the ciliate Sterkiella from cultures of the microalga Chlamydomonas. Our experiments showed that the copepod Acanthocyclops ro- bustus can consume up to 400 ciliates individual−1 day−1. Addition of 0.07 copepods mL−1 to a culture that was contaminated with 10 ciliates mL−1 resulted in a complete elimination of ciliates from the culture within 1 day and restored the algal biomass production at the level of a non-contaminated culture. Addition of copepods to a fresh Chlamydomonas culture did not cause a reduction in the microalgal biomass concentration, indicating that this copepod does not feed on Chlamydomonas. These laboratory-scale experiments indicate that copepods have potential to be used as a biological control agent to address the problem of contamination of large-scale mi- croalgal cultures by ciliates. The authors are grateful to three anonymous reviewers for their constructive comments, which helped us improve the manuscript. The authors thank KU Leuven University for funding this research through grant OT/14/065. The first author would like to acknowledge the Ministry of Education and Training of Vietnam for funding the PhD program. D. Vandamme is a researcher funded by the Research Foundation - Flanders Belgium (FWO) (2016-2019 12D8917N).

Microalgae have a great commercial potential as a source of several compounds of interest to the food, pharmaceutical, and chemical industries. The market was estimated to be around US$1.25 billion per year with more than 20 different commercial products and the genera commercially produced are mainly Chlorella, Arthrospira (Spirulina), Dunaliella, and Haematococcus, with a production of 5.000 tons of dry matter in 2004, increasing to 9.000 tons in 2010. However, despite extensive research carried out to date, harvesting is still one of the most costly processes in microalgae production. Consequently, the microalgae that are currently produced commercially are mainly indented for high value products (>$10,000 t−1). The aim of this chapter is to give an overview of the major constraints and technologies available for harvesting microalgae.

Arthrospira is the most widely cultivated strain of all microalgae and cyanobacteria. Arthrospira forms helical trichomes that, under certain circumstances, can switch to a straight morphology. This study compared harvesting using filtration and centrifugation between helical and straight Arthrospira strains. Filtration using woven nylon membranes is the most commonly used harvesting method in the industry. Gravity filtration using nylon membranes resulted in a high retention efficiency for both strains, but the filtration flux was very low for the straight strain. Pumped filtration resulted in an increase in the filtration flux for both strains (12 to 20 m3 m−2 h−1) but in a strong decline in the retention efficiency for the straight Arthrospira strain. The nominal pore size of the woven nylon membranes had only a minor influence on the harvesting efficiency. Centrifugation yielded a high harvesting efficiency and a solid pellet at relatively low g forces (4000 g) for the straight strain, but efficiency was low even at high g forces for the helical strain. These results illustrate the importance of selecting the most appropriated harvesting methodology depending on Arthrospira strains’ morphology. While the helical strain could be easily harvested using filtration, it is preferably to use centrifugation at low g force for the straight strain.

© 2019 Society of Chemical Industry BACKGROUND: The cyanobacterium Arthrospira contains proteins and the blue pigment phycocyanin that can be used as a natural colourant in the food industry. The aim of this study was to investigate a strategy for increasing the yield of phycocyanin and protein from Arthrospira cultures by shading the cultures with neutral density and red light filters. Experiments were conducted under three different irradiance conditions: (i) laboratory tests under relatively low light intensities (100 μmol m −2 s −1 ), (ii) laboratory tests under relatively high light intensities (516 μmol m −2 s −1 ) and (iii) scaled-up tests under natural conditions by cultivating Arthrospira in raceway ponds in a greenhouse. RESULTS: In all cases, shading of cultures with red filters resulted in biomass with increased phycocyanin content achieving a maximum of 134, 71 and 121 mg g −1 under low light intensity, high light intensity and natural conditions, respectively. Under high light intensity and natural conditions, shaded cultures displayed phycocyanin of higher purity and increased protein content, which reached up to 43 and 65%, respectively. CONCLUSIONS: Shading of Arthrospira cultures by low-cost polyester red light filters may be an effective way for enhancing phycocyanin production and improving its purity in outdoor ‘spirulina farms’. © 2019 Society of Chemical Industry. ispartof: JOURNAL OF CHEMICAL TECHNOLOGY AND BIOTECHNOLOGY vol:94 issue:6 pages:2047-2054 status: published

© 2018 John Wiley & Sons Australia, Ltd The high-altitude páramo grasslands of the Andes Mountains are rich in lakes that represent a source of high-quality water for the region. Páramo grasslands are mainly used for cattle grazing. The aim of this study was to investigate the influence of cattle on the trophic status of páramo lakes. In a survey of 30 lakes in Cajas National Park (NP), a semi-quantitative estimate for cattle abundance in the vicinity of the lakes was the best predictor of the chlorophyll-a concentrations in the lakes. Cattle abundance was also significantly related to phytoplankton community composition, being associated with a shift from chlorophytes to diatoms and dinoflagellates. Lake Culibrillas, a lake situated in the Sangay National Park (Sangay NP), a region with much more intensive cattle farming than Cajas NP exhibited a chlorophyll-a concentration greater than twice as much as the largest concentration measured in the Cajas NP lakes, being characterized by a dinoflagellate bloom. Although chlorophyll-a concentrations increased with cattle abundance, the concentrations in all the study lakes remained low (0.02–1.8 μg/L), indicating that extensive cattle farming does not cause severe eutrophication. The results of this study nevertheless indicate that intensification of livestock farming in páramo grasslands might result in a deterioration of water quality in the páramo lakes. ispartof: Lakes and Reservoirs: Research and Management vol:23 issue:4 pages:303-311 status: published

Key issues for membrane technology in harvesting microalgae are to reach high fluxes and to alleviate fouling by microalgal cells and extracellular organic matter. To achieve this goal, negatively charged patterned membranes were prepared from polysulfone/sulfonated polysulfone (PSf/sPSf) blends using a spray-modified phase inversion method, and the effect of sPSf on the membrane morphology and filtration performance was investigated. The patterned membrane with highest sPSf concentration exhibited the highest clean water permeance (2420 ± 260 L/m2 h bar), lowest membrane intrinsic resistance (6.1 m-1) and highest critical flux (55 L/m2 h) for harvesting microalgae. Membrane vibration could mitigate membrane fouling both for the patterned and flat membranes. The vibration system can easily achieve turbulent flow at frequencies higher than 7 Hz. The synergy between membrane vibration, surface pattern and charge thus resulted in a clearly enhanced membrane performance.

International audience; Membranes have a lot of potential for harvesting microalgae, but membrane fouling is hampering their breakthrough. In this study, the effects of charge and corrugated surface on membrane filtration performance were investigated. The clean water permeance (CWP), the microalgae harvesting efficiency and the membrane flux for a microalgal broth were determined using patterned polysulfone (PSf) membranes with different shapes of the surface patterns and containing different charge densities by blending sulfonated polysulfone (sPSf). The flow behavior near the patterned membrane surface, as well as the interaction energy between membrane and microalgae were investigated using computational fluid dynamics (CFD) simulation and the improved extended "Derjaguin, Landau, Verwey, Overbeek" (XDLVO) theory, respectively. Membrane charge and pattern shape significantly improve the membrane performance. The critical pressures of all sPSf blend patterned membranes were higher than 2.5 bar. A 4.5w% sPSf blend patterned membranes with wave patterns showed the highest CWP (2300 L/m(2) h bar) and membrane flux in the microalgal broth (1000 L/m(2) h bar) with 100% harvesting efficiency. XDLVO analysis showed that sPSf blend patterned membranes prepared obtained the lowest interaction energy and highest energy barrier for microalgal attachment. CFD simulation showed a higher velocity and wall shear on the pattern apexes.

Arthrospira platensis (A. platensis), one of the successfully commercialized microalgae, can generate abundant extracellular polysaccharides (EPS). Separating the EPS from the culture medium is important to recycle the medium and further process the polysaccharide resource. To separate EPS from spent Arthrospira platensis culture medium, a negatively charged polysulfone (PSf) membrane was prepared by lending PSf with sulfonated PSf (sPSf), and was optimized using the response surface methodology. The optimal preparation conditions were found to be a PSf concentration of 12.5 w%, sPSf of 1.9 w% and PEG of 5.5 w% in N,N-dimetylacetamide. The hydrophilicity, porosity, mean pore size, infrared absorption spectrum, water uptake (WU), thickness and clean water permeability (CWP) were determined to characterize the membrane, and critical pressure was used to evaluate the fouling resistance of the membrane. The results show that sPSf was successfully incorporated in the optimized PSf/sPSf, and it had higher hydrophilicity, porosity, larger mean pore size, WU, CWP, thickness and higher EPS retention and lower protein retention than the pristine PSf membrane. The final EPS retention of the optimized membrane was higher than 96%.

Flocculation holds great potential as a low-cost harvesting method for microalgae biomass production. Three flocculation methods (ferric chloride, chitosan, and alkaline flocculation) were compared in this study for the harvesting of 9 different freshwater and marine microalgae and one cyanobacterium species. Ferric chloride resulted in a separation efficiency greater than 90% with a concentration factor (CF) higher than 10 for all species. Chitosan flocculation worked generally very well for freshwater microalgae, but not for marine species. Alkaline flocculation was most efficient for harvesting of Nannochloropsis, Chlamydomonas and Chlorella sp. The concentration factor was highly variable between microalgae species. Generally, minimum flocculant dosages were highly variable across species, which shows that flocculation may be a good harvesting method for some species but not for others. This study shows that microalgae and cyanobacteria species should not be selected solely based on their productivity but also on their potential for low-cost separation. publisher: Elsevier articletitle: Flocculation properties of several microalgae and a cyanobacterium species during ferric chloride, chitosan and alkaline flocculation journaltitle: Bioresource Technology articlelink: http://dx.doi.org/10.1016/j.biortech.2016.08.080 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved. ispartof: Bioresource Technology vol:220 pages:464-470 ispartof: location:England status: published

Previously, it has been observed that lipolysis occurring during (even short term) wet storage of microalgal biomass causes high free fatty acid (FFA) concentrations in the biomass. These FFA have a negative impact for different applications of microalgal lipids, e.g. downstream processing problems in biodiesel production, off-flavors and loss of nutritional value for food applications. However, it is not clear which factors influence lipolysis in microalgal biomass and which lipid class are more susceptible to lipolysis. In this study, wet biomass of T-Isochrysis lutea was stored at 20°C, 4°C and -20°C during 3 weeks. The extent of lipolysis was followed by analyzing the lipid classes distribution by ultrahigh-performance liquid chromatography−accurate mass mass spectrometry (UHPLC-amMS) and the FFA content. It was observed that FFA were formed very rapidly during post-harvest storage of wet biomass at 20°C and 4°C, the rate of this process being faster at 20°C than at 4°C, while almost no lipolysis was observed at -20°C. However, the FFA content levelled off after several days of storage because FFA reacted with alcohols to form fatty acyl esters. publisher: Elsevier articletitle: Lipolysis in T-Isochrysis lutea during wet storage at different temperatures journaltitle: Algal Research articlelink: http://dx.doi.org/10.1016/j.algal.2016.07.003 content_type: article copyright: © 2016 Elsevier B.V. All rights reserved. ispartof: Algal Research vol:18 pages:281-287 status: published

The biosorption of phosphorus in the form of orthophosphate (Po) from wastewater using biomass as the sorbent is of potential importance because the Po-loaded biomass could be applied in the agricultural sector as fertilizer and soil conditioner. However, biomass generally displays a very low affinity for Po sorption and therefore biomass surface modification is required. In the present study, the biomass (as model grinded leaves of Phragmites sp. were used) was pretreated with Ca(OH)2 to enhance Po biosorption capacity (qe). The results indicate that the alkaline pretreatment resulted in a modification of surface functional groups. It was concluded that the main sorption mechanisms were ligand exchange and electrostatic attraction. A series of experiments were conducted to investigate the performance of the pretreated biomass for Po uptake under various conditions. Isotherm and thermodynamic studies were also applied and analyzed. The biosorption process was best described by the pseudo-second order kinetic model and Langmuir isotherm, which gave a qmax of 12.27mgP/g at 25°C and pH7. The Ca(OH)2 treated Phragmites biomass applied in this study for Po recovery may present some potential advantages in terms of costs and environmental impact.