Large Flocs Research Articles

Algal-algal bioflocculation enhances the recovery efficiency of Picochlorum sp. QUCCCM130 with low auto-settling capacity

Large-scale production of microalgal biomass is still considered non-viable due to the high cost and energy required for harvesting. A fast, cost-effective, and successful harvesting technique has become widely sought after in microalgal biotechnology applications. Algal-algal bioflocculation was adopted for the current study, pH and the ratio between species were selected as two parameters to be optimised. Picochlorum sp. QUCCCM130, Nannochloris sp. QUCCCM31 and Tetraselmis sp. QUCCCM50 presenting a cell size of ∼2 μm, ∼5 μm, and ∼15 μm, respectively, were selected to be subjected to the harvesting optimisation experiments. Results showed that self-settlement capacity increased with cell size and can be indirectly related to a decreased zeta potential of larger cells which enhances the Van der Waals attractive forces. Furthermore, it was noted that pH enhanced the self-settlement capacity of small-sized cells as well that are unable to self-settle. Algal-algal bioflocculation efficiency is dependent on the ratio between species with different sizes, increasing with a higher proportion of larger size microalgal cells. Mixing three microalgae together at pH 10 led to the appearance of large flocs in which the larger cells surrounded the smaller cells. Microscopic observation confirmed that Tetraselmis sp. held the small cells inside the flocs using their flagella. Thus, we can conclude that mixing microalgal cells in a specific ratio and at a specific pH increases the recovery efficiency of small-sized microalgae that can be difficult to harvest, such as Picochlorum sp. QUCCCM130.

Destabilization of polystyrene nanoplastics with different surface charge and particle size by Fe electrocoagulation

Nanoplastics (NPs) discharged from wastewater could pose a major threat to organisms in aquatic environments. Effective removal of NPs by the current conventional coagulation-sedimentation process is not yet satisfactory. This study aimed to investigate the destabilization mechanism of polystyrene NPs (PS-NPs) with different surface properties and sizes (i.e., 90 nm, 200 nm, and 500 nm) by Fe electrocoagulation (EC). Two types of PS-NPs were prepared by a nanoprecipitation method using sodium dodecyl sulfate and cetrimonium bromide solutions to produce negatively-charged SDS-NPs and positively-charged CTAB-NPs. For both NPs, obvious floc aggregation from 7 μm to 14 μm was observed only at pH 7 with particulate Fe accounted for >90 %. At pH 7, Fe EC removed 85.3 %, 82.8 %, and 74.7 % of the negatively-charged SDS-NPs at small-, mid-, and large-sizes from 90 nm, 200 nm, to 500 nm, respectively. Small-size SDS-NPs(90 nm) were destabilized through physical adsorption on the surface of Fe flocs, while the main removal mechanism of mid- and large-SDS-NPs(200 nm and 500 nm) involved the enmeshment of large Fe flocs. Compared to SDS-NPs(200 nm and 500 nm), Fe EC performed similar destabilization behavior to two CTAB-NPs(200 nm and 500 nm), but it resulted in much lower removal rates of 54.8 % - 77.9 %. The Fe EC also exhibited no removal (<1 %) ability toward the small-size and positively-charged CTAB-NPs(90 nm) due to insufficient formation of effective Fe flocs. Our results provide insight into the destabilization of PS in nano-scale with different sizes and surface properties, which clarifies the behavior of complex NPs in a Fe EC-system.

The influence of physical floc properties on the separation of marine microalgae via alkaline flocculation followed by dissolved air flotation

Flocculation achieved by raising the pH, termed alkaline flocculation is a sustainable way of inducing flocculation in marine microalgae. Flocs formed post-alkaline flocculation have the potential to be harvested via dissolved air flotation (DAF) or sedimentation. While DAF results in faster separation and biomass with a higher solids content compared to sedimentation, it has not been tested in saline environments, particularly when combined with alkaline flocculation. DAF processes, like most separation techniques, are heavily dependent on physical floc properties. In this study, the impact of alkaline floc properties on the performance of DAF versus sedimentation was evaluated to harvest marine Nannochloropsis oculata, benchmarking against the well-studied ferric chloride flocculation. This was followed by the use of the DAF white-water model to illustrate how alkaline and ferric floc properties impact bubble-particle attachment and DAF separation efficiencies. Alkaline flocs were smaller (peakmax < 300 μm; majority flocs 130–470 μm), stronger (~70 % strength factor) and more compact (scattering exponent > 2.30) compared to ferric flocs which were larger (peakmax ~ 1700 μm; >65 % of flocs >1000 μm), relatively weaker (<40 % strength factor), less compact (scattering exponent 1.49–2.30). However, as both flocs were hydrophilic, sedimentation yielded ~15 % greater efficiency than DAF. Stoke's Law suggested that sedimentation benefited due to alkaline floc compactness and large sizes of ferric flocs. Nonetheless, maximum separation efficiencies of ~80–85 % were still obtained via the DAF process. From the white-water model, bubble-floc attachment efficiency of alkaline flocs (0.01–0.001 %) was observed to be at least an order of magnitude greater than ferric flocs (0.001–0.0001 %) despite both methods resulting in comparable DAF separation efficiencies. For alkaline flocs, elevated bubble-floc attachment efficiency compensated low hydrophilicity; for ferric flocs, low bubble-floc attachment was compensated by large floc sizes. Overall, it is suggested that the determination of floc properties post-coagulation-flocculation could be used to optimise separation processes.

Polymer-flooding produced water treatment using an electro-hybrid ozonation-coagulation system with novel cathode membranes targeting alternating filtration and in situ self-cleaning

Polymer-flooding produced water is more difficult to treat for reinjection compared with normal produced water because of the presence of residual hydrolyzed polyacrylamide (HPAM). A novel cathode membrane integrated electro-hybrid ozonation-coagulation (CM-E-HOC) process was proposed for the treatment of polymer-flooding produced water. This process achieved in situ self-cleaning by generated microbubbles in the cathode membrane. The CM-E-HOC process achieved a higher suspended solid (SS), turbidity and PAM removal efficiency than the CM-EC process. The SS in the CM-E-HOC effluent was ≤ 20 mg/L SS, which met the reinjection requirements of Longdong, Changqing Oilfield, China (Q/SYCQ 08,011–2019) at different current densities (3, 5 and 10 mA/cm2). The CM-E-HOC process greatly mitigated both reversible and irreversible membrane fouling. Therefore, excellent flux recovery was obtained at different in situ self-cleaning intervals during the CM-E-HOC process. Furthermore, alternating filtration achieved continuous water production during the CM-E-HOC process. On one hand, the effective removal of aromatic protein-like substances and an increase in oxygen-containing functional groups were achieved due to the enhanced oxidation ability of the CM-E-HOC process, which decreased membrane fouling. On the other hand, the CM-E-HOC process showed improved coagulation performance because of the increased oxygen-containing functional groups and polymeric Fe species. Therefore, larger flocs with higher fractal dimensions were generated, and a looser and more porous cake layer was formed on the membrane surface during the CM-E-HOC process. Consequently, the CM-E-HOC process exhibited better in situ self-cleaning performance and lower filtration resistance than the CM-EC process.

Effects of organic matter on the aggregation of anthropogenic microplastic particles in turbulent environments

Biofilm-coated microplastics are omnipresent in aquatic environments, carrying different organic matter (OM) that in turn influences the flocculation and settling of microplastic aggregates. In this study, the effects of chitosan, guar gum, humic acid, and xanthan gum on the flocculation of anthropogenic microplastics are examined under controlled shear through the mixing chamber experiments. The results show that all of the selected OMs have positive effects on biofilm culturing and thus enhance the growth of microplastic flocs, with more evident promoting effects for cationic and neutral OMs (i.e., chitosan and guar gum) than anionic OMs (i.e., humic acid and xanthan). No critical shear rate is observed in the size vs. shear relationship based on our measurements. In addition, the quadrature-based two-class population balance model is employed to track the development of bimodal floc size distributions (FSDs) composed of small and large microplastic flocs. The model predictions show reasonable agreement with the observed FSDs. The largest error of settling flux from the two-class model is 7.8% in contrast with the reference value measured by the camera-based FSDs with 30 bins. This study highlights the role of different OMs on microplastic flocculation and indicates that a two-class model may be sufficient to describe microplastic transport processes in estuaries.

Role of lake dissolved organic matter in cyanobacteria removal by cationic polyacrylamide flocculation and screen filtration

Prompt removal of densely accumulated cyanobacteria is a straightforward method to alleviate the harm of cyanobacterial blooms to lakes. In this study, a cyanobacteria harvesting ship based on flocculation and filtration was used for the removal of cyanobacteria in a bay of Dianchi Lake (Yunnan Province, China), in which the fate and influence of lake dissolved organic matter (DOM) were investigated. After flocculation with 1–3 mg/L cationic polyacrylamide (CPAM) and filtration with the 100-µm-pore-sized screens of a rotary drum filter (RDF), >90 % of cyanobacteria was removed and the DOM was slightly reduced from 7.83 mg/L to 4.61 ∼ 6.49 mg/L. Tryptophan protein-like and high molecular weight (MW) DOM was selectively removed, increasing the humification index and decreasing the biological index in the treated water. Lake DOM, especially the high MW fractions of lake DOM, played an important role in CPAM flocculation. Cyanobacteria could not be effectively flocculated in Milli-Q water while the removal efficiency increased to over 90 % when 1–3 mg/L high MW DOM of Dianchi Lake was added. Three lakes in Yunnan Province were also plagued by cyanobacterial blooms, including Erhai Lake, Qilu Lake, and Xingyun Lake. The high MW DOM (1.7–2.7 mg/L) in the lakes could also deduce the effective flocculation of cyanobacteria with CPAM. The flocculation mechanism could function by the interactions of quaternary ammonium groups of CPAM and carboxylate groups of high MW DOM that form net-like polyelectrolyte complexes (PECs), and coexisting cyanobacteria cells were encapsulated into the PECs, leading to the formation of large flocs under stirring conditions. In the lakes with high densities of cyanobacteria, there might be enough high-MW DOM to promote the flocculation of CPAM, and after flocculation-filtration treatment, both cyanobacteria and cyanobacteria-deprived DOM were effectively removed.

Uncovering the optimal structural characteristics of flocs for microalgae flotation using Python-OpenCV

Coagulation-based dissolved air flotation is generally recognized as an efficient and economical method for removal of algae from eutrophicated water, whose efficiency is directly affected by the structural characteristics of flocs. However, it is not clear which floc structures are suitable for microalgal floatation, whether large and compact flocs or small and loose flocs have good rising performance. In this study, a novel technology for dynamically tracking the growth and rising behaviors of flocs was developed based on Python-OpenCV to visually uncover the optimal structural characteristics of flocs for Microcysts aeruginosa coagulation-flotation. Different coagulation flow fields (velocity gradient, G) were adopted to artificially create flocs with various structural characteristics and floatation kinetics. Results showed that G value had significant effects on the growth and rising behaviors of flocs, thus achieving intuitively different flotation kinetics. An idea rising velocity of 91.5 m h−1 was achieved by flocs with optimal structural characteristics generated at a suitable G of 34.1 s−1, which was 29–75% higher than that of flocs at other G. The rising velocity of floc was synergistically determined by the size and fractal dimension of floc. The structural characteristics (size and fractal dimension) of flocs were introduced into the calculation model of rising velocity, which guided the principle of optimal floc structure characteristics (large and compact) suitable for Microcysts aeruginosa removal using DAF. These may provide new technology for the studies of the growth and settling/rising behaviors of flocs, and lay a theoretical foundation for the design of DAF system with high load rate and the selection of optimal operating conditions applied to cyanobacteria blooms prevention and control.

Reducing disinfection byproduct precursors through coagulation enhancement as particle weight and size control using potassium permanganate.

The widespread use of chlorine pre-oxidation in water purification has been limited in several countries owing to the production of carcinogenic byproducts when combined with naturally occurring organic matter. This study investigates the efficient use of potassium permanganate (KMnO4) pretreatment and coagulation enhancement as particle size and molecular weight distribution controlling parameters. KMnO4 pretreatment significantly reduced the apparent molecular weight of humic acid due to KMnO4 reduction and the continuous generation of manganese dioxide (MnO2) formed in situ under neutral and alkaline conditions. The MnO2 formed in situ had adsorption characteristics that enabled it to form large and stable flocs with the hydrolysis products of aluminum sulfate. However, under acidic conditions, KMnO4 pretreatment exhibited strong oxidation characteristics due to Mn(VII) reduction to Mn(II), and the mean particle floc size was the same as without KMnO4 pretreatment. Overall, KMnO4 pretreatment is a useful alternative strategy for traditional pre-oxidation using chlorine and a good coagulant enhancement agent in neutral and basic media.

Anisotropic flocculation in shear thickening colloid-polymer suspension via simultaneous observation of rheology and X-ray scattering

A shear thickening fluid, showing a significant increase in viscosity under shear stress, is a promising material for shock absorption applications. Colloidal dispersions of silica nanoparticles and polyethylene oxide polymers with large molecular weights also exhibit a shear thickening phenomenon, which is manifested by a transformation from liquid to gel, called shake-gel. To understand the gelation mechanism, small-angle X-ray scattering (SAXS) and ultra-small-angle X-ray scattering (USAXS) were performed with an X-ray transmission cell, which was used as a Couette cell in a rheometer. This setup enables simultaneous rheological measurements with SAXS and USAXS, providing real-time observation of the change from liquid to gel. An anisotropic increase of the scattering spectra indicated the formation of aligned floc structures. This result implies that a polymer chain recombined the network and transformed into the large flocs aligned in the flow direction. Additionally, the shifted peaks from the silica cluster indicated that the aligned flocs were compressed by the shear stress. The present work paves the way for the advanced design of shake-gel materials.

Enhancement of biosludge dewatering using proteins through dual conditioning

AbstractIn pulp and paper mills, effective biosludge dewatering is essential in wastewater treatment to reduce the large volume of biosludge that needs to be treated and disposed. The dewatering process normally requires the use of polymers from petroleum‐based sources. This study explores the potential of using cationic proteins such as protamine for biosludge dewatering through dual conditioning with a small amount of a synthetic anionic polymer such as anionic polyacrylamide (APAM). The results show that dual conditioning provides substantial synergistic enhancements in dewatering. The maximum cake solids content of biosludge achieved by adding protamine (7.5%) alone was 12%. By dual conditioning with a small amount of APAM (0.1%), not only the cake solids content was increased to 16%, but also the amount of protamine addition was substantially lowered to 2%. These results, coupled with the change in zeta potential of the particles in the biosludge samples, suggest that the cationic protamine reduced the negative charge of the particles, allowing smaller particles to agglomerate and providing a positively charged framework for the subsequent addition of the negatively charged APAM. After adding APAM, substantial floc‐bridging occurred, allowing smaller flocs to aggregate into larger flocs. These synergistic effects can lower the wastewater treatment cost by reducing the amount of synthetic polymer and by applying low‐value proteins from natural sources.

Influence of nitrogen species and biomass retention time on nutrient removal and biomass productivity in a microalgae-based bioreactor

This study examined the effects of nitrogen species (NH 4 + N/NO 3 − N ratio) and biomass retention time (BRT) on nutrient uptake and biomass productivity in Chlorella sp . In batch photobioreactors (PBR), microalgae were cultivated with varied nitrogen species ratios (100% NH 4 + N, 50% NH 4 + N:50% NO 3 − N, and 100% NO 3 − N). It was observed that a medium containing 100% NO 3 − N boosted algae growth, with a maximum biomass concentration of 3188 mg/L. However, the lowest nutrient removal rates were obtained under the 100% NO 3 − N condition, according to the reverse logistics model. In contrast, the highest removal rates occurred for substrate containing 100% of NH 4 + N species based on first-order decay models, although yield biomass was lower (2940 mg/L). The presence of the ammonia nitrogen resulted in the flocculation of the microalgae into large flocs, suggesting that ammonia nitrogen was rapidly consumed to produce flocculation-related metabolic products rather than for biomass production. Using the 100% NH 4 + N medium, different BRT values (7, 5, 3, 2 days) were examined under continuous operation using a membrane photobioreactor (MPBR). At 3-day BRT, the maximum biomass productivity, nitrogen, and phosphorous removal rates were 214 ± 4, 63.1 ± 4.1, and 2.1 ± 0.6 mg/L d, respectively. The biomass yield increased as the BRT decreased, leading to an increase in pollutant removal rates. Finally, this study provides some essential information for improving the operating conditions of membrane photobioreactor system under different biomass retention times and various nitrogen sources in the feed. • The highest biomass productivity was achieved in the 100% NO 3 − N medium. • The highest nutrient removal occurred in the 100% NH 4 + N medium. • The highest biomass productivity and nutrient removal was observed at 3-day BRT. • Lower fouling rates were achieved at higher BRTs.

Comprehensively understanding fouling properties of cake and bulk sludge in an anammox membrane bioreactor: Focusing on the composition, interfacial thermodynamics and microbial community

A more comprehensive investigation into fouling properties of cake and bulk sludge played an essential role in better understanding membrane fouling caused by the bio-cake formation in an anammox membrane bioreactor (MBR). In this work, the cake and bulk sludge from a stable anammox MBR were analyzed with the composition, interfacial thermodynamics and microbial community. Physicochemical analysis indicated that cake sludge agglomerated into larger flocs with a denser structure and a higher protein/polysaccharide (PN/PS) ratio as compared with bulk sludge. It also revealed that cake sludge was found to have looser protein secondary structures and more hydrophobic components than those of bulk sludge, which means the differences in surface hydrophobicity between two sludges might play a key role in revealing anammox sludge aggregation and further cake layer formation process. The dominant role of hydrophobic attraction energies between cake sludge and membrane surface at a shorter separation distance (< 2 nm), after the analysis of the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) method, confirmed cake layer formation process related with surface hydrophobicity. Furthermore, biological analysis demonstrated that the relative microbial abundances of Candidatus_Brocadia and Candidatus_Kuenenia in cake sludge were much greater than those of bulk sludge, implying a higher biofouling potential for them. Overall, this study fills the gap in understanding the mechanism between anammox sludge properties and cake formation, which provides basic knowledge for membrane fouling control in anammox MBR.

One-pot production of a graft copolymer of cationic starch and cationic polyacrylamide applicable as flocculant for wastewater treatment

A newly developed, high-performance, and environmentally friendly flocculant, i.e., a graft copolymer of cationic starch and cationic polyacrylamide (SC-CPAM), is synthesized via a single-step pathway in which the cationic agent is incorporated onto the starch backbone and into the polyacrylamide grafted branch simultaneously. One-pot preparation method is quick, reproducible, and easily scalable, which yields high-quality products with better flocculation performance than conventional cationic starch (SC) and starch-graft-polyacrylamide (S-PAM). The synthesized samples are characterized by physicochemical techniques, namely Fourier Transform Infrared Spectroscopy (FTIR), elemental analysis, H1 Nuclear Magnetic Resonance (H1NMR) Spectroscopy, Zeta Potential (ZP), and Dynamic light scattering (DLS). The application as a flocculant for wastewater treatment is investigated by flocculation of kaolinite suspension and analysis of turbidity (UV-Vis and NTU), ZP, and floc size in neutral pH. A high clarification of 97.8%, low turbidity of 1.97 NTU, and large floc size of 136 µm, obtained by SC-CPAM, are believed to result from dual flocculation mechanisms, i.e., polymer charge patch and particle bridging, enabled by the cationic high molecular weight branched bio-based flocculant for wastewater purification applications.

Impact of the Salt Concentration and Biophysical Cohesion on the Settling Behavior of Bentonites

The flocculation behavior of clay minerals in aquatic environments is an important process in estuarine and riverine dynamics, where strong gradients in salinity can locally occur. Various contradicting observations have been reported in the literature on the impact of salt concentration on the settling process of cohesive sediments. To address this issue in a systematic manner, we investigate the settling behavior of clay minerals as a function of the salt concentration of the ambient water. Specifically, we focus on montmorillonite as a prototype clay mineral with a high cation exchange capacity (CEC). To this end, we study suspensions of Wyoming bentonite (Volclay SPV) as a very important constituent for many constructional and industrial purposes. We perform an experimental campaign to study the settling behavior of moderately turbid montmorillonite concentrations in monovalent salt solutions with different salinities (sodium chloride) to represent different environments ranging from deionized to ocean water, respectively. The subsequent settling process was monitored by taking pictures by a camera in regular time intervals over a total observation time up to 48 h. In addition, a modified hydrometer analysis is conducted to determine the grain size distribution (in terms of an equivalent diameter) of the flocculated clay suspension in salt water. Despite the rather high cation exchange capacity of the investigated clay (CEC=88.1), our results show that the settling speed drastically increases within a range of 0.6–1.0 PSU and stays approximately constant for higher salinities. This critical salt concentration is defined here as the critical coagulation concentration (CCC) and lies well below the salinity of natural open water bodies. The hydrometer analysis revealed that 60% of the agglomerates exceed the equivalent grain size of 20 μm. Finally, the findings of this study are supplemented with experiments studying the effect of Extracellular Polymeric Substances (EPS) on the flocculation behavior of bentonite in salt water. Our results demonstrate that salinity is the original trigger for flocculation, whereas EPS allows for even larger floc size but it does not play a significant role for the settling processes of bentonite in estuarine environments.

Cactus Cladode Juice as Bioflocculant in the Flocculation-Thickening Process for Phosphate Washing Plant: A Comparative Study with Anionic Polyacrylamide

In the phosphate industry, the thickening process is vital to increasing the solid slurry concentration and to recovering water that is as clear as possible. The performance of the thickening process depends mainly on the coagulation–flocculation effect. The thickening process is based on flocculant agents to concentrate particles: flotation and washing plant rejects as large flocs, which accelerate their sedimentation velocity. The phosphate industry worldwide uses synthetical flocculants such as polyacrylamides. These flocculants are non-biodegradable, limiting the process efficiency regarding cost and harmful effects on the environment. This study proposes cactus cladodes juice as an eco-friendly alternative to industrial flocculants. The particle size of the phosphate samples ranges from 0 μm to 160 μm, with a solid concentration of 8%. This bioflocculant allowed for an increase in sedimentation velocity of 95% compared with the case without flocculant. The optimal amount of cactus bioflocculant for decanting 1 tonne of phosphate pulp at pH 7–8 is 1.12 kg. Special attention is paid to understanding the flocculation mechanism. The results of the physicochemical characterization show that the flocculant biopolymers have similar characteristics to anionic polyacrylamide. This work indicates the promising application of the cactus juice bioflocculant in phosphate washing plants.

Influence of HPMC and SF on buildability of 3D printing foam concrete: From water state and flocculation point of view

Due to the intrinsic high flowability of foam concrete (FC), it is challenging to achieve good buildability for 3D printing of FC. In this paper, the effects of hydroxypropyl methylcellulose (HPMC) and silica fume (SF) on the rheological properties and buildability of 3D printing FC (3DPFC) were studied from the evolvement point of the flocs and the state and distribution of water in the mixture. Flocculation structural models of 3DPFC doped by SF and HPMC were proposed. HPMC improves the yield stress and the buildability of FC by agglomerating cement particles into large and ultra-large flocs. SF does not significantly increase the proportion of ultra-large flocs, but considerably reduce the free water movement due to its adsorption on the surface and the formation of flocs composed of SF particles or SF and cement particles. In addition, the re-flocculation ability of SF flocs can significantly contribute to the thixotropy and buildability of 3DPFC.

Particle Nonresolved DNS‐DEM Study of Flocculation Dynamics of Cohesive Sediment in Homogeneous Isotropic Turbulence

AbstractA two‐phase Euler‐Lagrangian framework was implemented to investigate the flocculation dynamics of cohesive sediment in isotropic turbulence. The primary particles are modeled as sticky soft spheres using the discrete element method (DEM). The attractive van der Waals forces are modeled by the DLVO theory and the JKR adhesive contact theory. The near steady state equilibrium floc size distribution (FSD) strongly depends on the ratio of the turbulent shear to the floc strength (or particle stickiness). When turbulence is strong, a single peak around the Kolmogorov length scale appears in the FSD, and the distribution fits the Weibull distribution well. A power‐law floc size distribution develops when the floc strength is greater than the destabilizing effect of turbulent shear. Sediment concentration does not significantly affect the shape of FSD or the average floc size. The average apparent floc settling velocity Ws increases with the average floc size. Fractal dimension of flocs decreases with the floc size following a power‐law relation for large flocs. Settling velocity of flocs as a function of floc size also follows a power‐law relation. Deviation from the power‐law relationship is found for large flocs because of their porous nature. At equilibrium stage, the construction by aggregation is balanced with the destruction by breakup, and the construction by breakup is balanced with the destruction by aggregation. The aggregation kernel by turbulent shear and power‐law breakup kernel can describe the dynamics reasonably well for the flocculation of cohesive sediment in homogeneous isotropic turbulence.

Characterization of tuna dark muscle protein isolate

Fish protein isolate (FPI) was extracted from tuna dark muscle (TDM) using the pH-shift method that improves significantly its sensory quality and nutritional value. The amino-acid composition of the FPI was close to that of TDM, but the total protein content was higher. The solubility of FPI in water was higher than 85% at pH ≥ 6 and pH ≤ 3, but it dropped to about 10% at pH values close to the isoelectric point pI ≈ 5.0. The soluble FPI was present in the form of aggregates that were characterized by light-scattering. The microstructure of FPI solutions on larger length scales was probed by confocal microscopy, large protein flocs formed at pH close to pI. SDS-PAGE indicated that a significant fraction of myosin heavy chains was broken down into smaller chains. The viscosity decreased with decreasing of pH, which correlated with the decreasing size of the aggregates. Novelty Impact Statement Tuna dark muscle (TDM) represents a significant fraction of industrially processed tuna and it is currently considered a low value by-product because of its poor sensory qualities, but TDM has a high protein content that does not suffer from sensory defects if it is extracted by dispersing TDM at pH 12 and precipitating the dissolved protein at pH 5.5. The protein isolate is highly soluble (> 85%) in water at pH > 6 and pH < 3, where it is present in the form of small aggregates with average radii between 90 and 250 nm, depending on the pH. The characterization of the composition of TDM protein isolate and its properties in water show that it is a viable product for use in industrial applications.

Insights into the dewatering of excavated landfill sludge conditioned by polyferric silicate sulfate

Large quantities of landfill sludge (LS) with higher water content (WC) were stored underground, and excavation and re-dewatering of LS is a sustainable and economic strategy to save landfill space and reduce the leaching of contaminants. In this study, polyferric silicate sulfate (PFSS) was first applied in the conditioning of excavated LS, and the effects of the Si/Fe mass ratio and PFSS dosage on physicochemical properties, dewaterability and rheological properties were investigated. At the best Si/Fe of 0.18, PFSS conditioning obtained compact aggregates with the strongest internal structure, thus achieving the lowest WC. Large sludge flocs were formed, and slime and loosely-bound extracellular polymeric substances were effectively removed with the PFSS dosage above 100 mg/g dried solids, which made the WC to be lower than 51.4%. The whole mechanical compression process of conditioned LS can be described by the modified Terzaghi-Voigt model, and increasing the PFSS dosage induced the release of bound water and migration of the consolidation stage from ternary to secondary. PFSS is an economically sustainable conditioner for LS, integrating multiple functions such as charge neutralization, particle aggregation, interparticle bridging and skeleton building in one chemical.

Gravimetric selection of activated sludge for settling properties improvement and granular sludge formation – full scale case study

Abstract With an increasing frequency of extreme weather events wastewater treatment plant operators face a need to increase plant hydraulic capacity while continuing to comply with effluent quality requirements. An economically attractive way to meet this challenge is to significantly improve secondary settling tank performance and therefore assure safe wet weather plant operation. The objective of this study was to evaluate gravimetric selection technology conducted in hydrocyclones as a way for improving activated sludge settling characteristics in continuous flow BNR with a long sludge retention time and assess its ability to form granular sludge. Long term operational data and sludge morphology monitoring data were analysed. A significant drop in sludge volume index (SVI) (to values under 50 ml/g) and increase in return activated sludge solids concentration (to values above 20 g/L) was observed. Hydrocyclone installation consistently, selectively retained denser, larger flocs in the system and after a start-up phase large granules begin to appear. Gravimetric selection did not prevent the seasonal filamentous biomass outgrowth and temperature drop at the beginning of winter resulted in rapid rise of SVI and SST sludge blanket height especially after heavy rain. Technology under study proved to be effective under certain process conditions but it needs further research to consistently maintain low SVI values throughout the whole year.