Surfactants as Bubble Surface Modifiers in the Flotation of Algae: Dissolved Air Flotation That Utilizes a Chemically Modified Bubble Surface (original) (raw)
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Water research, 2018
Algae and cyanobacteria frequently require separation from liquid media in both water treatment and algae culturing for biotechnology applications. The effectiveness of cell separation using a novel dissolved air flotation process that incorporates positively charged bubbles (PosiDAF) has recently been of interest but has been shown to be dependent on the algae or cyanobacteria species tested. Previously, it was hypothesised that algal organic matter (AOM) could be impacting the separation efficiency. Hence, this study investigates the influence of AOM on cell separation using PosiDAF, in which bubbles are modified using a commercially available cationic polyelectrolyte poly(N, N-diallyl-N,N-dimethylammonium chloride) (PDADMAC). The separation of Chlorella vulgaris CS-42/7, Mychonastes homosphaera CS-556/01 and two strains of Microcystis aeruginosa (CS-564/01 and CS-555/1), all of which have similar cell morphology but different AOM character, was investigated. By testing the cell s...
Investigating dissolved air flotation performance with cyanobacterial cells and filaments
Water Research, 2010
Natural organic matter Coagulant demand Microcystis aeruginosa Planktothrix rubescens a b s t r a c t Dissolved air flotation (DAF) performance with two different naturally occurring cyanobacterial morphologies was investigated with respect to the biomass removal efficiency, the toxin release to water and the coagulant demand by different water background natural organic matter (NOM). Coagulation (C)/Flocculation (F)/DAF bench-scale experiments (2 min coagulation at 380 s À1 with polyaluminium chloride (0.5e4 mg/L Al 2 O 3 , the dose depending on the water NOM content); 8 min flocculation at 70 s À1 ; 8 min DAF with 5 bar relative pressure and 8% pressurised recycle) were performed with single cells of Microcystis aeruginosa and Planktothrix rubescens filaments spiked in synthetic waters with different NOM contents (hydrophobic vs. hydrophilic NOM; moderate (2e3 mgC/L) vs. moderate-high concentration (ca. 6 mgC/L)). For both morphologies, the results show no apparent cyanobacterial damage (since the water quality did not degrade in dissolved microcystins and the removal of intracellular microcystins matched the removal of chlorophyll a) and high biomass removal efficiencies (93e99% for cells and 92e98% for filaments) provided optimal coagulant dose for chlorophyll a removal was ensured. Charge neutralisation by the polyaluminium chloride was the main coagulation mechanism of the M. aeruginosa cells and most likely also of the P. rubescens filaments. The specific coagulant demand was severely affected by NOM hydrophobicity, hydrophobic NOM (with a specific UV 254nm absorbance, SUVA, above 4 L/(m mgC)) requiring ca. the triple of hydrophilic NOM (SUVA below 3 L/(m mgC)), i.e. 0.7 vs. 0.2e0.3 mg Al 2 O 3 /mg DOC. ª (M.R. Teixeira). A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / w a t r e s w a t e r r e s e a r c h 4 4 ( 2 0 1 0 ) 3 3 3 7 e3 3 4 4 0043-1354/$ e see front matter ª
Flotation of blue-green algae using methylated egg ovalbumin
Chemical Engineering Journal, 2009
Removal of blue-green algae by dispersed gas flotation was conducted. Methylated ovalbumin (MeOA) was used as frother and flocculant, which is a biodegradable substance. The continuous flotation experiments were conducted at different feed mass flow rate of the blue-green algae cells and MeOA. The operating variables were the mass flow rate of blue-green algae cell and MeOA, the initial concentration of the cells and MeOA, and superficial gas velocity. The results showed that the mass flow rate of MeOA was most dominant variable affected to the removal efficiency and that the removal efficiency achieved ca. 0.85 when a ratio of the mass flow rate of MeOA and that of the cells was over 0.3. A proposed flotation model considering the adsorptions of MeOA to the cells, MeOA to bubble surface and the cells bearing with MeOA to bubble surface was applied to explain the experimental removal efficiency. The experimental and the calculated removal efficiency agreed well within error 19 %, indicating that the proposed model was valid fundamentally.
Microflotation performance for algal separation
Biotechnology and Bioengineering, 2012
The performance of microflotation, dispersed air flotation with microbubble clouds with bubble size about 50 mm, for algae separation using fluidic oscillation for microbubble generation is investigated. This fluidic oscillator converts continuous air supply into oscillatory flow with a regular frequency to generate bubbles of the scale of the exit pore. Bubble characterization results showed that average bubble size generated under oscillatory air flow state was 86 mm, approximately twice the size of the diffuser pore size of 38 mm. In contrast, continuous air flow at the same rate through the same diffusers yielded an average bubble size of 1,059 mm, 28 times larger than the pore size. Following microbubble generation, the separation of algal cells under fluidic oscillator generated microbubbles was investigated by varying metallic coagulant types, concentration and pH. Best performances were recorded at the highest coagulant dose (150 mg/L) applied under acidic conditions (pH 5). Amongst the three metallic coagulants studied, ferric chloride yielded the overall best result of 99.2% under the optimum conditions followed closely by ferric sulfate (98.1%) and aluminum sulfate with 95.2%. This compares well with conventional dissolved air flotation (DAF) benchmarks, but has a highly turbulent flow, whereas microflotation is laminar with several orders of magnitude lower energy density.
SPE Production & Operations, 2020
SummaryFlotation is an important segment of water treatment. Bubbles are generated and dispersed in water where they capture oil and solids residuals and lift them up to the surface. Bubbles are generated either mechanically by agitation or hydraulically by induced gas ejectors. The bubble size has a crucial role in this kind of separation. In general, the smaller the bubbles, the better separation. Water chemistry has an important role in bubble formation and size. A laboratory scale flotation unit was developed to generate the microbubbles with diameters of 10 to 100 µm. The effects of salinity, coagulant, temperature, and ethanol on bubble size were investigated. The addition of 5000 mg/L of sodium chloride (NaCl) affected mainly bubble size with 50 µm diameter, whereas bubble size reduced and diameter decreased by one-half with the addition of NaCl. The bigger bubbles (100 µm size) were affected only at a salinity of 40 000 mg/L, whereas the smaller bubbles (20 to 30 µm) remaine...
2014
Dissolved Air Flotation (DAF) is a well-known coagulation-flotation system applied at large scale for microalgae harvesting. Compared to conventional harvesting technologies DAF allows high cell recovery at lower energy demand. By replacing microbubbles with microspheres, the innovative Ballasted Dissolved Air Flotation (BDAF) technique has been reported to achieve the same algae cell removal efficiency, while saving up to 80% of the energy required for the conventional DAF unit. Using three different algae cultures (Scenedesmus obliquus, Chlorella vulgaris and Arthrospira maxima), the present work investigated the practical, economic and environmental advantages of the BDAF system compared to the DAF system. 99 % cells separation was achieved with both systems, nevertheless, the BDAF technology allowed up to 95 % coagulant reduction depending on the
The success of flotation operation depends upon the thriving interactions of chemical and physical variables. In this work, the effects of particle size, bubble size, and collector dosage on the bubble loading in a continuous flotation column were investigated. In other words, this work was mainly concerned with the evaluation of the true flotation response to the changes in the operating variables in column flotation. Two bubble sizes of 0.8 and 1.8 mm, three size fractions of 63-106, 106-150, and 150-300 μm, and three different dosages of dodecylamine, as the collector, were tested. According to the results obtained, the particle size fraction of 106-150 μm had the maximum bubble loading for bubble diameter of 1.8 mm, while the particle size of 63-106 μm had the maximum bubble loading for bubble diameter of 0.8 mm. It was also shown that increasing the bubble diameter from 0.8 to 1.8 mm increased the bubble loading in all the particle size fractions and collector dosages. However, the mass loading of air bubbles was strongly related to the collector dosage (contact angle), especially for coarse particles. The amount of collector dosage had an upper limit due to the clustering event, which significantly affected the bubble loading. The clustering was found to be more important in the presence of small particles due to a higher number of particles attached to the bubble surface. It was shown that such interactions of variables of true flotation could reasonably be monitored by the bubble loading measurement.