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•Electrocoagulation (EC) has high harvesting efficiency (E) for Chlorella vulgaris.•Charge concentration was identified as the main process parameter (q ≥ 14.4C/L)•E > 95% was ...achieved for biomass (0.2–1.8 g/L), pH 7 and phosphates < 0.15mgP/L.•Energy costs of harvesting using EC were 83–89% lower than centrifugation.•EC-harvested C. vulgaris is suitable for human consumption (iron < 4 mg/g)
Centrifugation is the most commonly used method for harvesting autotrophically produced microalgae, but it is expensive due to high energy demands. With the aim of reducing these costs, we tested electrocoagulation with iron electrodes for harvesting Chlorella vulgaris. During extensive lab-scale experiments, the following factors were studied to achieve a high harvesting efficiency and a low iron content in the harvested biomass: electric charge, initial biomass concentration, pH, temperature, agitation intensity, residual salt content and electrolysis time. A harvesting efficiency greater than 95% was achieved over a broad range of conditions and the residual iron content in the biomass complied with legislative requirements for food. Using electrocoagulation as the pre-concentration step prior to centrifugation, total energy costs were reduced to 0.136 kWh/kg of dry biomass, which is less than 14% of that for centrifugation alone. Our data show that electrocoagulation is a suitable and cost-effective method for harvesting microalgae.
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•Harvesting Chlorella vulgaris using a cooking oil-CTAB emulsion was studied.•Over 90% harvesting efficiency (HE) was achieved at pH 10 and 12.•HE ˃ 90% required 0.13–0.33% (v/v) ...cooking oil and 2.7–6.7 mg/L CTAB.•Observed harvesting mechanisms were flocculation/sedimentation and flotation.•Proteins increased the consumption of cooking oil-CTAB emulsion by up to 6 times.
In this study, a novel harvesting emulsion (HEM) consisting of cooking oil in an aqueous solution of cetyltrimethylammonium bromide (CTAB) was tested for the harvesting of a technologically important microalga, Chlorella vulgaris. The influence of HEM dose, biomass and bovine serum albumin (BSA) (model interferer compound) on harvesting efficiency (E) were studied. The HEM E was over 90% at pH 10 (0.33% (v/v) cooking oil, 6.7 mg/L of CTAB) and 12 (0.13% (v/v) cooking oil, 2.7 mg/L of CTAB). Harvesting efficiencies at pH 4 and 7 were < 73.5% due to the absence of precipitate formation. Bovine serum albumin (10 mg/L) increased the HEM dose necessary to achieve E ˃ 90% by 1.2 (pH 10), and 3 fold (pH 12). By manipulating the dose of HEM and pH, the method of harvesting (flocculation/sedimentation or flotation) was adjustable depending on the technological requirements.
•Alkaline flocculation of Chlorella sorokiniana by calcium phosphate was studied.•Influence of wastewater model compounds on alkaline flocculation was evaluated.•Proteins showed the strongest ...disrupting effect on flocculation efficiency (FE).•Negative effect of humic acids, surfactant and alkalinity on FE was partial.•Simultaneous effect of multiple substances, simulating real wastewater, was tested.
Amongst harvesting processes, alkaline flocculation stands out as a technically feasible and low cost method. The interference of model wastewater components with alkaline flocculation of Chlorella sorokiniana (pH 8–12), induced by calcium phosphate (CaP) precipitates, was evaluated. Between the compounds tested, inorganic nitrogen, sodium alginate, salinity and algal organic matter had no effect on flocculation efficiency (FE). The negative effect of humic acids, sodium dodecyl sulphate and alkalinity on FE was partial. Bovine serum albumin and bacterial organic matter (BOM) of Escherichia coli showed the strongest disruption of FE. The impact of BOM can be explained by the high protein content (65% of total organic carbon). Proteins, negatively charged at alkaline pH, interrupt microalgae flocculation by preferentially interacting with positively charged CaP precipitates. The simultaneous effects of multiple substances were tested to simulate real wastewater. The results confirm the need to investigate the composition of wastewater prior to alkaline flocculation.
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•Novel continuous electrocoagulation reactor was developed, capacity 240 L/h.•Chlorella biomass harvesting efficiency was higher than 85 %.•Harvested biomass was suitable for human ...consumption, Fe content below 4 mg/g.•Power consumption was reduced by 80 % compared to centrifugation alone.
The most frequently used method to harvest microalgae on an industrial scale is centrifugation, although this has very high energy costs. To reduce these costs, a continuous electrocoagulation process for harvesting Chlorella vulgaris was developed and tested using a pilot-scale 111 L working volume device consisting of an electrolyser with iron electrodes, aggregation channel and lamellar settler. The flow rate of the microalgal suspension through the device was 240 L/h. When using controlled cultivation and subsequent electrocoagulation, a high harvesting efficiency (above 85%), a low Fe contamination in the harvested biomass (<4 mg Fe/g dry biomass, a harvested biomass complied with legislative requirements for food) and significant energy savings were achieved. When comparing electrocoagulation and subsequent centrifugation with the use of centrifugation alone, energy savings were 80 % for a biomass harvesting concentration of 0.23 g/L. Electrocoagulation was thus proven to be a feasible pre-concentration method for harvesting microalgae.
This study examines the use of Pythium oligandrum as a biological control agent to suppress Fusarium culmorum growth and mycotoxin production during the malting of wheat (Triticum aestivum L.). The ...optimum application phase and dose of P. oligandrum were studied. The effect of P. oligandrum on F. culmorum-infected wheat was quantitatively evaluated through RT-PCR along with deoxynivalenol (DON) and deoxynivalenol-3-glucoside (D3G) content in wheat malt (WM). In addition, the effect of P. oligandrum treatment on WM quality was quantified by European Brewery Convention standard methods. Treatment by P. oligandrum in the steeping stage (2 g P. oligandrum/kg wheat) yielded optimal suppression of Fusarium contamination (20%) and mycotoxin content (17% DON and 21% D3G) relative to untreated WM. Treatment dose showed a maximum effect between 0.6 and 1 g P. oligandrum/kg of wheat, resulting in 12–14% Fusarium contamination, 13–14% DON, and 15–18% D3G, relative to untreated malt. Wheat malts treated with P. oligandrum showed no deterioration of malting or brewing quality.
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•Biological control of fungal contamination in malting is desirable.•Pythium oligandrum was used to combat Fusarium culmorum in infected wheat.•P. oligandrum was effective against fungal growth and mycotoxin production.•Optimum application (steeping) and dose (0.6–1 g/kg wheat) were established.•The brewing quality of wheat malt was not affected by P. oligandrum.
In eukaryotic green microalgae, manipulation of metabolic pathways by altering the culture medium and/or culture conditions represents a powerful tool for physiological control and is usually more ...practicable than metabolic or genetic engineering. Strategies for nutrient-induced shifts in biomass composition are generally cost-efficient, environmentally friendly, applicable on a large scale and flexible for various industrially attractive microalgae species. In addition, processes, such as nutrient limitation/deprivation, can be readily scheduled and optimised to achieve high levels of productivity for the desired target compound(s). These strategies are currently used in microalgae to achieve overproduction of metabolites such as lipids, polysaccharides and pigments. This paper presents an overview of the species and strain-specific responses of eukaryotic, green microalgal cells that are triggered by variations in selected macronutrient and micronutrient availability. Individual and mutually associated physiological responses to nutrient supply status are described at the molecular level as well as discussed from the perspective of potential biotechnological applications.
A yeast strain secreting endopolygalacturonase was used in this work to study the possibility of continuous production of this enzyme. It is a feasible and interesting alternative to fungal batch ...production essentially due to the specificity of the type of pectinase excreted by
Kluyveromyces marxianus CCT 3172, to the lower broth viscosity and to the easier downstream operations. In order to increase the reactors’ productivity, a cellulosic carrier obtained from barley spent grains was tested as an immobilization support. Two types of reactors were studied for pectinase production using glucose as a carbon and energy source — a continuous stirred tank reactor (CSTR) and a packed bed reactor (PBR) with recycled flow. The highest value for pectinase volumetric productivity (
P
V=0.98 U ml
−1 h
−1) was achieved in the PBR for
D=0.40 h
−1, a glucose concentration on the inlet of
S
in=20 g
l
−1, and a biomass load in the support of
X
i=0.225 g g
−1. The results demonstrate the attractiveness of the packed bed system for pectinase production.
Acidothermophilic bacteria of the genus
Alicyclobacillus
are frequent contaminants of fruit-based products. This study is the first attempt to characterize the physico-chemical surface properties of ...two
Alicyclobacillus
sp. and quantify their adhesion disposition to model materials diethylaminoethyl (DEAE), carboxyl- and octyl-modified magnetic beads representing materials with different surface properties used in the food industry. An insight into the mechanism of adhesion was gained through comparison of experimental adhesion intensities with predictions of a colloidal interaction model (XDLVO). Experimental data (contact angles, zeta potentials, size) on interacting surfaces (cells and materials) were used as inputs into the XDLVO model. The results revealed that the most significant adhesion occurred at pH 3. Adhesion of both vegetative cells and spores of two
Alicyclobacillus
sp. to all materials studied was the most pronounced under acidic conditions, and adhesion was influenced mostly by electrostatic attractions. The most intensive adhesion of vegetative cells and spores at pH 3 was observed for DEAE followed by hydrophobic octyl and hydrophilic carboxyl surfaces. Overall, the lowest rate of adhesion between cells and model materials was observed at an alkaline pH. Consequently, prevention of adhesion should be based on the use of alkaline sanitizers and/or alkaline rinse water.
The majority of algal cells can interact with a wide range of nano- and microparticles. Upon interaction the modified cells usually maintain their viability and the presence of foreign material on ...their surfaces or in protoplasm can provide additional functionalities. Magnetic modification and labeling of microalgal biomass ensures a wide spectrum of biotechnological, bioanalytical and environmental applications. Different aspects of microalgal cell magnetic modification are covered in the review, followed by successful applications of magnetic algae. Modified cells can be employed during their harvesting and removal, applied in toxicity microscreening devices and also as efficient adsorbents of different types of xenobiotics.
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