Due to increasing demands for microalgal biomass and products originating from microalgae, large-scale production systems are necessary. However, current microalgal production technologies are not ...cost-effective and are hindered by various bottlenecks, one of which is the harvesting of microalgal biomass. Cell separation is difficult because of the low sedimentation velocity of microalgae, their colloidal character with repelling negative surface charges, and low biomass concentrations in culture broths; therefore, large volumes need to be processed in order to concentrate the cells. Flocculation is considered to be one of the most suitable methods for harvesting microalgal biomass. This article provides an overview of flocculation methods suitable for microalgal harvesting, their mechanisms, advantages and drawbacks. Special attention is paid to the role of surface charge in the mechanism of flocculation. The novelty of the review lies in the interconnection between the context of technological applications and physico-chemical surface phenomena.
Objective
Marine actinomycetes from the genus
Salinispora
have an unexploited biotechnological potential. To accurately estimate their application potential however, data on their cultivation, ...including biomass growth kinetics, are needed but only incomplete information is currently available.
Results
This work provides some insight into the effect of temperature, salinity, nitrogen source, glucose concentration and oxygen supply on growth rate, biomass productivity and yield of
Salinispora tropica
CBN-440
T
. The experiments were carried out in unbaffled shake flasks and agitated laboratory-scale bioreactors. The results show that the optimum growth temperature lies within the range 28–30 °C, salinity is close to sea water and the initial glucose concentration is around 10 g/L. Among tested nitrogen sources, yeast extract and soy peptone proved to be the most suitable. The change from unbaffled to baffled flasks increased the volumetric oxygen transfer coefficient (k
L
a) as did the use of agitated bioreactors. The highest specific growth rate (0.0986 h
−1
) and biomass productivity (1.11 g/L/day) were obtained at k
L
a = 28.3 h
−1
. A further increase in k
L
a was achieved by increasing stirrer speed, but this led to a deterioration in kinetic parameters.
Conclusions
Improvement of
S. tropica
biomass growth kinetics of was achieved mainly by identifying the most suitable nitrogen sources and optimizing k
L
a in baffled flasks and agitated bioreactors.
Objective
Desalination of cheese whey by electrodialysis yields saline wastewater (SWW). The goal was to test this as the basis of a culture medium and to prove experimentally the concept that it was ...a suitable resource for heterotrophic cultivation of the freshwater green microalga
Chlorella vulgaris
.
Results
Optimization of glucose concentration, nitrogen source and medium salinity for microalgal growth was first carried out in defined medium (DM) and shake flasks. These results were then adopted in shake flask cultivation experiments using pre-treated SWW medium (PSWW). Subsequently, microalgal growth under optimized conditions was tested in bioreactors. Various media such as DM, PSWW and diluted PSWW (DPSWW) were compared. Volumetric biomass productivities decreased in the order DM (0.371 g L
−1
h
−1
, urea) > DPSWW (0.315 g L
−1
h
−1
, soy peptone) > PSWW (0.152 g L
−1
h
−1
, soy peptone). Although biomass productivities in DPSWW and PSWW media were significantly lower than in DM, these media required the addition of only 66 and 33% of DM N sources, respectively. No other added DM component was necessary in (D)PSWW to achieve microalgal growth.
Conclusions
Although the optimized cultivation of freshwater microalgae on alternative medium based on SWW resulted in biomass productivities lower than those on DM, the required addition of N sources was also lower. Potentially lower production costs of
Chlorella
biomass and the meaningful use of SWW are the main outcomes of this work.
Pythium oligandrum, a soil-born oomycete, is an effective biological control agent exhibiting antagonistic and parasitic activity against pathogenic fungi. This study is the first attempt to ...characterize its surface properties and to apply models of physicochemical interactions (thermodynamic, DLVO and XDLVO) to quantify its adhesion properties to a model material, represented by magnetic beads (MB). The predictions of interaction models were based on experimental data (contact angles, zeta potentials, size). Adhesion intensities (AI) were determined experimentally taking advantage of MB with different surface properties. The role of weak physicochemical interactions was estimated by comparing experimental AI with model predictions. The results revealed that the surface properties of the three Pythium spp. studied were very similar and fell within the range for hydrophilic microorganisms (ΔGTOT > 0) with a predominantly negative surface charge. The most reliable description of AI was obtained using the DLVO model, including Lifshitz-van der Waals and electrostatic interactions. The highest AI between Pythium spp. and all three MB was observed at pH 3, which was supported by the DLVO prediction. The greater agreement between the sphere-sphere geometric version of the DLVO model and experiment suggests that the surface protrusions of the oospores increase the efficiency of adhesion. The surface properties of the pathogenic fungi, characterized in this work, fell within the range defined by MB and therefore it can be expected that their physicochemical interactions with Pythium spp. will also be favourable.
•Pythium oligandrum exerts mycoparasitism through surface interactions.•Surface properties and adhesive interactions of P. oligandrum are unknown.•Adhesion of Pythium spp. was studied theoretically and experimentally.•Pythium spp. were found to be hydrophilic with predominantly negative charge.•Pythium spp. adhesion to model materials were well described by the DLVO model.
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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.
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.
Spore-forming thermophilic bacteria of the genus
Geobacillus
and
Anoxybacillus
are frequent contaminants in dairy industry. This study is the first attempt to apply models of physicochemical ...interactions (thermodynamic, DLVO, and XDLVO) to quantify their adhesion properties to stainless steel particles (SSP). The predictions of interaction models were compared with experimental data (contact angles, zeta potentials, size) regarding interacting surfaces (cells and SSP). Adhesion intensities (AI) were determined experimentally taking advantage of the magnetic properties of particulate stainless steel. The importance of weak physicochemical interactions was estimated by comparison of experimental AI with model predictions of colloidal interactions. The results revealed that the most reliable description of AI was obtained using the XDLVO model, including Lifshitz–van der Waals (LW), acid–base, and electrostatic (EL) interactions. The AI of cells to SSP at an ionic strength of 10 mM decreased in the order
G. stearothermophilus
DSM 456 >
A
.
flavithermus
DSM 2641 >
G
.
stearothermophilus
DSM 22, and the differences were statistically significant. At a higher ionic strength (100 mM), the highest AI was observed for
A
.
flavithermus
DSM 2641, but the differences between species studied were statistically insignificant. The main driving force for bacterial adhesion to SSP at 10 mM was EL interactions, while at 100 mM, the XDLVO model predicted favorable interactions between
A
.
flavithermus
DSM 2641 and SSP due to attractive LW forces.
The biotechnological potential of
Microcystis aeruginosa
brings requirements for efficient cultivation and harvesting of biomass. Flocculation of
M. aeruginosa
at alkaline pH induced by calcium or ...magnesium precipitates was studied under model conditions, in culture medium with/without cellular organic matter (COM). The effect of independent variables (Ca
2+
, Mg
2+
, PO
4
3−
, and pH) on the zeta potential and turbidity of cells and inorganic precipitates was quantified by response surface methodology. The experimentally obtained flocculation efficiencies (FEs) were compared with predictions of physicochemical interaction (DLVO) models. The results presented here delimited the concentration ranges of Ca
2+
, Mg
2+
, PO
4
3−
, and pH, resulting in FE > 85%. The DLVO prediction model suggested that for high FE, positively charged precipitates and sufficient precipitate turbidity were required. At pH 10, alkaline flocculation was more advantageous using magnesium precipitates, since it required less phosphate. High FE with COM was achieved at pH 12 when precipitate formation was induced at a low phosphate concentration by the addition of magnesium hydroxide.
To describe temporal trends in inpatient care use for adult mental disorders in Czechia from 1994 until 2015.
Data from the nationwide register of inpatient care use and yearly census data were used ...to calculate (a) yearly admissions rates, (b) median length of stay, and (c) standardized inpatient-years for adult mental disorders (ICD-10 codes F0-F6 or G30). Segmented regressions were used to analyze age- and sex-specific temporal trends.
Admission rates were increasing in adults (average annual percent change = 0.51; 95% confidence interval = 0.16 to 0.86 for females and 1.01; 0.63 to 1.40 for males) and adolescents and emerging adults (3.27; 2.57 to 3.97 for females and 2.98; 2.08 to 3.88 for males), whereas in seniors, the trend was stable (1.22; -0.31 to 2.73 for females and 1.35; -0.30 to 2.98 for males). The median length of stay for studied mental disorders decreased across all age and sex strata except for a stable trend in male adolescents and emerging adults (-0.96; -2.02 to 0.10). Standardized inpatient-years were decreasing in adults of both sexes (-0.85; -1.42 to -0.28 for females and -0.87; -1.19 to -0.56 for males), increasing in female adolescents and emerging adults (0.95; 0.42 to 1.47), and stable in the remaining strata.
Psychiatric hospital admissions were increasing or stable coupled with considerable reductions in median length of stay, suggesting that inpatient episodes for adult mental disorders have become more frequent and shorter over time. The overall psychiatric inpatient care use was decreasing or stable in adults and seniors, potentially implying a gradual shift away from hospital-based care.
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