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Abstract: A simple yet relatively complete model and numerical solution method for describing the effects of osmotic pressure on the compressibility of materials bearing surface charges, and its dependence on bulk solution properties is presented. The basis of this thermodynamic model is Donnan equilibrium and surface charge regulation. The model is capable of explaining effects that were observed in with regard to the effect of salt addition on wastewater treatment sludge compressibility. The simulation results suggest that the filtrate conductivity changes with the level of compression, which was confirmed experimentally. Furthermore, the simulation results suggest a dependence of compressibility on the dewatering method, i.e. on the fate of the expelled water. In case the solution that is expelled from the compressed gel stays in contact with the gel (e.g. centrifugation), the compressibility properties can be different from the properties in case the expelled water is completely removed (e.g. filtration). [ABSTRACT FROM AUTHOR]

Abstract: Mathematical models are potentially a valuable tool for the prediction of continuous gravity thickener operation. However, experience shows that existing mathematical models underestimate dewatering in thickeners for flocculated feed materials when predictions are made of either the underflow solids concentration for a given solids feed flux density or the maximum solids feed flux density achievable for a minimum underflow solids concentration set point. One reason postulated for this discrepancy is shear enhancement of sedimentation and bed dewatering as a result of aggregate densification. This process is not taken into account in conventional 1-D thickener models. A pilot scale column, operated at low bed heights without the addition of mechanical shear, produced results that compared well with 1-D model predictions. The effect of mechanical shear and/or greater bed height was to significantly enhance thickener performance relative to model predictions (as measured by underflow density or maximum solids flux density achievable for a nominated underflow density). An experimental method was developed that enabled shear to be incorporated into the suspension dewatering characterisation. The results suggest an order of magnitude increase in solid flux density can be expected under controlled shear conditions with polymer flocculated aggregates. The results also indicate that mechanical shear is not the only factor that can enhance dewatering, since higher beds, and hence longer residence times, also improve the achievable solids flux density. This is despite the fact that the thickener is operating in a regime that is predicted to be limited by the sediment permeability and not its compressibility. This suggests an additional mechanism must be at play in full scale operation and points a direction for further experimentation. [Copyright &y& Elsevier]

Abstract: Predictive modelling of solid–liquid separation can greatly assist the design and operation of thickening and filtration equipment, improving water recovery and reducing costs. A phenomenological model describing continuous thickening has been previously developed with primary inputs being the material properties, (compressive yield stress and hindered settling function) derived from routine laboratory batch settling and filtration tests. This work aimed to validate the model by operating a pilot column continuously and measuring the underflow solids. The column was operated at two different solid fluxes and several bed heights. Additionally, the influence of flocculation conditions (polymer dosage and residence time) on thickening performance were studied. The model predicted the experimental underflow solids concentration at a given flux. For the observed underflow solids concentration, the ratio of the actual to predicted flux was observed to be between a factor of 1 (accurate) and 10. The model was most accurate for the lowest bed heights. This work confirmed the model was able to correctly predict trends for the case where minimal bed height and shear forces are present. Deviation from the model is postulated to be due to changes in the dewatering properties of flocculated aggregates over time that are not adequately captured using conventional batch sedimentation tests. The data from these tests are traditionally used as a key input to thickening models. [Copyright &y& Elsevier]

Abstract: Investigation of the response of plate and frame filter performance to changes in design and operating variables is complicated by the large matrix of potential variables and the inter-dependent kinetics of the fill, press and air blow stages. However, through some key simplifying constraints an integrated optimisation framework has been developed. An example application is presented for an iron ore fines material from the North West of Australia, which indicates an optimum filling duration exists for all conditions investigated and illustrates the throughput benefits of higher feed solids and pressing pressures and larger cavity thicknesses. Significantly, the optimum filling duration is not constant and depends on the ratio of pressing to filling pressure and cavity thickness employed, largely due to the important role of the pressing stage not from the perspective of compression, but rather from that of an increased rate of secondary filtration of unfiltered suspension remaining at the end of the filling stage. Although simplistic in the form presented and limited to incompressible systems, with the integration of more rigorous theoretical treatments of the individual filter stages, the applicability of the approach could be broadened to all types of substrates. [Copyright &y& Elsevier]

Abstract: A comparison of the dewaterability of a range of water treatment plant sludges has been completed through computation of dewatering performance indicators for a diaphragm filter press. Real parameter data, obtained from the characterisation of alum and ferric sludges, generated under precisely controlled conditions, was used for input to a phenomenological model. Comparisons of dewaterability based on throughput curves largely agree with previous analysis of the underlying parameter data. The difference in approach provides a quantification of benefit. Greater throughputs and output concentrations are predicted at the lowest coagulant doses and at pH∼6. Typical industrial cloth resistances consistently reduce throughput by a factor of 3–7, but the assessment of relative benefit is shown to be insensitive to this parameter. Quantitative agreement of the predictions with observed performance can be attained. Finally, the twin effects of solids loading and dewaterability are assessed together, showing that each has a significant influence on the required filter surface area. This quantification shows that high coagulant doses adversely affect both of these aspects, leading to filter area requirements larger than might otherwise be expected. [Copyright &y& Elsevier]

Abstract: The influence of clay dispersion method on dewatering behaviour of a run-of-mine bentonite was examined to better understand the roles of calcium–sodium ion exchange and overall electrolyte concentration on the suppression of swelling and subsequent stabilisation of the clay. As with previous work, controlled dispersion of the clay directly into a swelling suppressing environment was observed to yield order of magnitude improvements in dewatering behaviour [de Kretser, R.G., Scales, P.J. and Boger, D.V., 1997. Improving clay-based tailings disposal: a case study on coal tailings. AIChE Journal. 43 (7), 1894–1903.]. The calcium ion, even after normalisation for its valence, yielded significantly better clay stabilisation performance than the sodium ion indicating the greater benefit afforded via divalent ion-exchange driven controlled dispersion. However the results also highlighted a synergistic effect of the double layer suppression effect on the efficacy of ion-exchange mediated controlled dispersion through simultaneous swelling suppression and structure preservation during the transient process of ion exchange on hydration. Studies of controlled dispersion in dual ion, Na+ and Ca2+, systems illustrated that although the efficacy of controlled dispersion deteriorated with an increase in the Na+ to Ca2+ ratio, even small amounts of calcium character could generate significant improvements in dewaterability over the pure sodium case. This result was relevant in terms of defining an operational window for the commonly used, but sparingly soluble calcium source, gypsum where the low deliverable calcium level could be more than offset by the controlled dispersion benefits of maintaining a higher overall salinity level. Based on the results presented, the potential impact of practical implementation of a controlled dispersion framework within a mineral processing operation was illustrated via numerical modelling of the operation of a steady state thickener. [Copyright &y& Elsevier]

Abstract: The coagulation and flocculation processes in conventional drinking water treatment generate aggregates which settle to form a sludge waste. This sludge can be dewatered further by thickening, centrifugation and filtration operations in order to recover water and minimise the volume of the waste stream. A range of water treatment sludges generated in the laboratory were characterised according to a phenomenological method that is valid from the dilute free-settling regime to the concentrated cake compression stages. These were compared with plant samples. Experimental results show that raw water natural organic matter (NOM), coagulant dose and coagulation pH affected both the rate and potential extent of dewatering. Similar effects were observed for both aluminium sulfate and ferric chloride. These results suggest that increasing dose or pH leads to an increase in the proportion of rapidly precipitated material in the sludge or flocs, which form looser aggregates and hence exhibit inferior dewatering properties. [Copyright &y& Elsevier]

Abstract: The aim of gravity thickening processes is to increase the solids concentration of particulate slurries. Gravity thickening depends on the difference in densities between the solid and liquid phases. The solids settle to a more concentrated slurry zone towards the underflow at the thickener base, while relatively solids free liquid rises to the overflow at the top. Predictive modelling of gravity thickener performance from experimentally determined material properties has been shown to under predict throughput by a factor of up to 100. One phenomenon proposed to account for some of this discrepancy is aggregate densification, whereby aggregates compact and become smaller when subjected to shear forces in the thickening process. As the aggregates decrease in size, through densification, the tortuosities around the aggregates will decrease, thus leading to a significant net decrease in the resistance to fluid flow. Dewatering theory has been applied to predict the impact of aggregate densification on the material properties that describe dewatering. The anticipated decrease in aggregate size and associated increase in the density of these aggregates is expected to increase the settling rate. It is further expected on this basis that the material will settle to higher solids concentrations. The impact of these changes on gravity thickening performance is modelled and predicted to be significant. [Copyright &y& Elsevier]

Abstract: This work describes an easy methodology for assessing the compressibility of particulate suspensions at relatively low pressures. The material used in this study was an anaerobically digested waste water sludge. Using a centrifuge, the equilibrium sediment bed height was recorded as a function of rotational speed during the centrifugation. This approach avoids errors due to expansion of the sediment bed after the centrifugation is stopped, a phenomenon typically seen with waste water sludges. A straightforward numerical method was used to solve a one-dimensional centrifugation model describing the equilibrium sediment bed height as a function of rotational speed. It has been shown that this approach yields realistic results. The one-dimensional model is able to describe the compressibility of the anaerobically digested sludge. Besides yielding a close fit for the measured sediment bed heights, extrapolating these results to a different initial solids volume fraction resulted in a good prediction of the bed height as well. Different constitutive equations for the relation between solids pressure and solids volume fraction were assessed. The typical power law functions [F. Tiller, W. Leu, Basic data fitting in filtration, Journal of the Chinese Institute of Chemical Engineers 11 (1980) 61–70], often used in filtration modelling, were the most adequate for describing the compressional behaviour of the sludge. A functional relation based on the osmotic pressure within the solids network, suggested for describing the phenomenology of filtration dewatering [K. Keiding, M. Rasmussen, Osmotic effects in sludge dewatering, Advances in Environmental Research 7 (2003) 641–645], could not be used to adequately describe the behaviour of the sludge at the low pressures generated during centrifugation. [Copyright &y& Elsevier]

Abstract: The role of natural organic matter (NOM) in changing the interaction between particles and subsequently the flow properties of concentrated particulate slurries has been modelled using electrokinetic and shear yield stress measurement data. Natural organic matter from soil, coal and peat sources as well as full and fractionated samples from aquatic sources has been examined. The data shows that the majority of the humic and fulvic rich samples adsorb in a flat configuration on a model alumina surface where the interaction is driven by a combination of electrostatics and chemical contributions to the adsorption free energy. Using a DLVO based model that assumes that the rheology response of a concentrated suspension of particles at low strain is the result of the summation of pair-wise particle interactions, the assumption of either a flat or molecularly dense adsorption configuration for most of the species at high additive addition rates was found to be valid. The model showed a consistent relationship between the measured rheology and electrokinetic data in terms of colloidal stability. The same modelling exercise for selected NOM samples at low dose showed a discrepancy between the electrokinetic and rheology data. This was for the NOM samples dominated by the neutral and hydrophilic fractions. The model indicated that the measured electrokinetics were poorly representative of the colloid stability possibly due to the presence of a poorly contiguous adsorbed layer that affects the hydrodynamic flow during electrokinetic measurements. [Copyright &y& Elsevier]

Abstract: The electrokinetics and rheology of a model alumina suspension has been investigated in the presence of a series of natural organic matter (NOM) fractions from soil and aquatic sources. The role of natural organic matter in changing both the dispersed state of the solids and the rheology of concentrated suspensions has been investigated. The data shows that at high surface coverage there is a good correlation between the nature of the adsorption layer and the electrokinetic and rheology responses. The data highlights key differences between the different fractions in aiding dispersion. At intermediate surface coverage, the correlation is less robust particularly for the more hydrophilic NOM fractions. The measured value of the electrokinetic potential is no longer a good indicator of colloidal stability as indicated by a DLVO type analysis. The reason may be due to the adsorbed layer showing a different response to particle movement in electrokinetic measurements than it does in static rheology measurements. In the latter case, the behaviour is dominated by particle interaction. [Copyright &y& Elsevier]

• Systematically analyse the effects of kaolin in mineral tailings dewatering in terms of compressibility and permeability. • With the increase of kaolin content in tailings, thickener underflow at a given solids flux decreases significantly. • The predicted solid throughput, filter size and filtration time increase extensively with increasing kaolin content. Aluminosilicate clays like kaolin are commonly found in mineral ore bodies. The presence of clay negatively impacts most mineral beneficiation unit operations due to the detrimental effects of these clays on suspension rheology and sedimentation behaviour. Further, the amount of clay usually varies with location across an ore body. This causes not only poor performance in dewatering but also significant and often unpredictable process variations. In this study, the effect of clay in mineral tailings dewatering is explored and quantified via experiments and modelling using a comprehensive dewaterability analysis. Batch sedimentation and pressure filtration methods were employed for measuring the compressibility and permeability of particulate suspensions to parameterise dewaterability over a range of solids concentrations at varying proportions of clay. The variation in the clay content of tailings was simulated using a combination of fine kaolin in calcium carbonate and alumina suspensions. The dewatering properties of these simulated tailings were then used in models of thickening and filtration. The results quantify the role of increasing kaolin concentration in calcium carbonate and alumina suspensions on dewatering, and the extent to which larger filter sizes and longer filtration times are required. This combination of experimental characterisation and modelling provides the mineral industry with a method to systematically monitor and quantify the effects of clay in tailings on the final throughput and moisture content of both thickening and filtration operations. [ABSTRACT FROM AUTHOR]

Bacillariophyceae (i.e., diatoms) are an important class of algae with potential use in the production of proteins and lipids including long-chain ω-3 polyunsaturated fatty acids. Biphasic extraction of microalgae lipids using water-immiscible solvents such as hexane, can avoid the excessive energy required to distil solvents from water, but generally requires energy-intensive rupture of the cells. The unique cell structure and surface chemistry of diatoms compared to other microalgae species might allow biphasic lipid extraction without prior cell rupture. The kinetics of biphasic lipid extraction from intact Navicula sp. cells was investigated during low-shear and high-shear mixing, and with prior or simultaneous application of ultrasound (20 kHz at 0.57 W/mL). Dynamic interfacial tension measurements and electron microscopic analysis were used to investigate lipid extraction in relation to interfacial behaviour and cell structure. High yields (>80%) of intracellular lipids were extracted from intact cells over the course of hours upon low-shear contacting with hexane. The cells associated with and stabilised the hexane-water interface, allowing hexane to infiltrate pores in the frustule component of the cell walls and access the intracellular lipids. It was shown that mucilaginous extracellular polymeric substances (EPS) bound to the cell walls acted as a barrier to solvent penetration into the cells. This EPS could be removed by prior ultrasonication. Biphasic extraction was greatly accelerated by shear applied by rotor-stator mixing or ultrasound. High-shear could remove mucilaginous EPS from the cell surfaces to facilitate direct contact of the cell surface with hexane and produced smaller emulsion droplets with increased surface area. The combination of high-shear in the presence of hexane resulted in the in-situ rupture of the cells, which greatly accelerated lipid extraction and allowed high yields of neutral lipid (>95%) to be recovered from freshly harvested cells within less than 5 min. The study demonstrated the ability of shear to enable simultaneous cell rupture and lipid extraction from a diatom alga based on its cell structure and interfacial behaviour. [ABSTRACT FROM AUTHOR]

• A novel dewatering device, called High Pressure Dewatering Rolls has been developed. • Industrial sludges were tested achieving similar results as state-of-the-art devices. • Material characterisation for dewatering and shear strength properties are measured. • Material properties can be used for modelling for comparison with other devices. The optimisation of solid-liquid separation or dewatering processes for more efficient operation and reuse of material streams is of high importance. Suspension dewatering aims to increase the solids concentration and exhibits two limitations: the dewatering extent and the rate. A novel dewatering device, called High Pressure Dewatering Rolls (HPDR), has been developed. It combines shear and compression while maintaining a short filtration length between the rollers. The HPDR challenges the limitations of dewatering processes through the application of high pressures and induced shear to aid the extent of dewatering, and a short filtration length to allow fast dewatering. A prototype HPDR is described along with a performance assessment for different operating conditions as well as a comparison against state-of-the-art technology for a variety of industrial suspensions. The results demonstrate that the HPDR prototype, without any optimisation, outperforms or achieves comparable cake solids concentrations to existing equipment in a continuous mode of operation. Analysis of energy consumption and throughput remain outstanding and require further prototype development. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ruptured algae cells were fractionated and the components used to emulsify hexane. • The interfacial properties and stability of the emulsions were quantitatively compared. • A mechanistic understanding of emulsification in algal lipid extraction was developed. • Competitive interfacial adsorption of cell components affected emulsion stability. • The use of microalgae as a source of biosurfactants or bioemulsifiers was proposed. Abstract A systematic investigation of the emulsifying properties of ruptured algae cells was performed for the first time. The slurry of ruptured algae cells was separated into different biomass fractions, namely the cell debris , the delipidated debris , the serum , and the lipid. The interfacial interactions of these biomass fractions with a nonpolar solvent (e.g. hexane or hexadecane) were characterized using pendant drop tensiometry and interfacial shear rheology. The stability of the different emulsions (formed by the different biomass fractions) was tested using analytical centrifugation. The extracted lipid was an excellent surfactant that reduced the interfacial tension, however, it was not effective at stabilizing the emulsions. The protein-rich serum produced a strong interfacial film that stabilized the emulsions against coalescence during centrifugation. The cell debris stabilized the emulsions to a lesser extent by adsorbing to the droplet surface, presumably via interactions with hydrophobic extracellular polymeric substances (EPS). However, neither the serum nor the cell debris were very effective surfactants, and required the presence of the lipid fraction to produce small emulsion droplets. When present together, the components exhibited competitive interfacial adsorption, which influenced emulsion stability. In particular, the interruption of the protein film by the presence of lipid or cell debris reduced the stability of the emulsions. This study provides a new mechanistic understanding of emulsification during wet lipid extraction from microalgae that will be useful for determining strategies to improve solvent recovery. The results also suggest potential for developing effective bioemulsifiers or biosurfactants from fractionated microalgae biomass for commercial application. [ABSTRACT FROM AUTHOR]

Sludge treatment and disposal have become important environmental issues in China. Mechanical dewatering is widely used to reduce the amount of sludge to be disposed and relieve the rapid growth pressure of waste sludge. In comparison to traditional sludge dewatering processes, pressure electro-osmotic dewatering has many advantages on sludge dewatering efficiency, low conditioner dosage and concentrated cake are both beneficial to further recycling of waste sludge. In general, complex electrochemical effects (eg. electrochemical oxidation, ohmic heating and pH gradient effect) are accompanied by the pressure electro-osmotic dewatering process. These electrochemical effects will inevitably cause solubilization and/or degradation of key constituents of wastewater sludge - extracellular polymeric substances (EPS). In this study, the effects of voltage, pH and ionic strength on sludge electro-osmotic dewatering performance and electrochemical effects were investigated. The solubilization and degradation of EPS were analyzed by examining the variation of dissolved organic matter (DOM) in the filtrate, and the relationships between microstructural properties of sludge cake and DOM and electro-osmosis dewatering performance in electro-dewatering process was examined. It was found that electro-dewatering properties were improved by raising the operating voltage or decreasing the pH value, while dewatering rate initially increased at low ionic strength it decreases with increased ionic strength. In addition, the porous structure of cathodic cake was more plentiful than that at the anode. At the cathode, the EPS dissolution was mainly related to alkalization, while the oxidation and acidification were responsible for release of EPS at the anode. Meanwhile, electrophoresis effect was able to promote migration of EPS toward the anode. The average electro-osmotic dewatering rate at the anode (R 2 .>0.79, p < 0.02) and at the cathode (R 2 .>0.87, p < 0.03) strongly correlated with the volume of pore of sludge cake. There was no correlation between the total content of anodic DOM (R 2 <0.31, p>0.08) and electro-osmotic dewatering rate at the anode, however, the content of cathodic DOM (R 2 > 0.62, p < 0.09) negatively correlated with average electro-osmosis dewatering rate of cathode. Since cathode is the main water-permeable side in sludge electro-dewatering, and the sticky biopolymers (proteins and humic subtances) could not be converted into small molecules, higher EPS release was associated with worse sludge filterability. As for the anode, the biopolymers were degraded into small molecules due to electrochemical oxidation, which greatly reduced the impact of DOM on dewatering effect. Therefore, the operating conditions (voltage, pH and ionic strength) caused changes in electrochemical effects, which played a crucial role in compartmentalization of sludge EPS dissolution and consequently sludge electro-dewatering behavior. [ABSTRACT FROM AUTHOR]

Silica sand and quartz represent the second most common mineral in the earth's crust. The silica-water interface is central to the processing of a large number of mineral systems and the flow properties of particulate suspensions. In particular, these flow properties define the upper limit to processing of tailings suspensions in the mining industry and, ultimately, the recovery of water. In some regions of the world, the scarcity of fresh water has pushed this industry to use seawater, either as is or partially desalinated. Here we analyze the impact of monovalent alkali metal chlorides that are typical of seawater on the viscoelastic behaviour of flocculated silica sediments at concentrations typical of thickening systems. The sediment samples were subject to creep-recovery tests. All sediments exhibit nonlinear viscoelastic behaviour, deduced from the compliance-applied stress relationship. Interestingly, creep recovery was observed to be related to the Hofmeister series, Cs + < K + < Na + < Li + , with Cs + producing lower recoveries than Li + . The yield stress, critical strain, and critical strain energy of the sediments were observed to be higher in maker salts (Na + and Li + ) compared with breaker salts (Cs + and K + ), due to stronger bonds in the particle networks. Our model of viscoelastic behaviour (Goñi et al., 2015) satisfactorily reproduces all experimental strain-time curves. The work provides novel input to decisions about the use of seawater or partially desalinated seawater in minerals processing with direct implications for tailings transportation, handling and water recovery. [ABSTRACT FROM AUTHOR]

Existing population models of bacteria and phages have most commonly described single well-mixed reactors. Whilst crucial to gain an understanding of population dynamics, these models are not directly applicable to scenarios requiring multi-reactor models. Using standard approaches we have formulated these models to describe behaviour within multiple interconnected reactors. A model incorporating phage dynamics in wastewater treatment systems was then developed to investigate the potential use of phages as a tool to reduce foaming or bulking. The model couples wastewater treatment dynamics within the commercial software GPS-X (Hydromantis Inc.) with phage dynamics through a newly developed add-on called PhageDyn. Simulations predict that immediately after phage dosing there is a lag period during which no apparent changes are observed, which is followed by a sudden and quick increase in the phage concentration and reduction in foaming biomass. “Normalization” without foaming is achieved within 1–2 weeks after dosing. The system may subsequently relapse back to foaming, requiring additional phage dosing, or be “cured” such that the added phages keep the problematic foaming biomass indefinitely at bay. Kinetic parameters describing the behaviour of the phages, as well as reactor configuration, are key determinants of the final outcome. The model is useful for predicting potential behaviour and for determining the characteristics of phages that are likely to be successful, assisting in isolation and screening. [ABSTRACT FROM AUTHOR]

• A credit framework to predict the chemical removal by ozone has been established. • O 3 /TOC ratio and O 3 CT value to achieve predictive outcomes are demonstrated. • Two chemical classifications to achieve chemical removal evaluation are indicated. • UV 254 and TOC as on-line surrogates for ozone barrier integrity are demonstrated. Ozonation is an effective barrier for removing a wide spectrum of organic Chemicals of Concern (CoC) in a water treatment process. In this study, bench- and full-scale tests were conducted on a secondary treated effluent at the Eastern Treatment Plant (ETP) of Melbourne Water to probe the performance of ozonation in removing CoC in a wastewater discharge. From the secondary treated effluent as the feed to the ozone process, 58 organic chemicals were measured out of a possible 949 compounds by using the AIQS-DB analytical method. A chemical credit framework for the ozonation process has been established according to the bench-scale results. Chemical classifications based on the chemical structures (aromatics, aliphatic and halogenated aliphatic compounds) and reaction rate constants with O 3 (K O3) and the ∙OH radical (K ∙OH) and a combined O 3 /TOC ratio and O 3 CT value as operating parameters were confirmed to be useful and important in determining whether a chemical would be removed by ozone. It is shown that an O 3 /TOC ratio of >0.404 was shown to be necessary to overcome the instantaneous ozone demand (IOD) to guarantee enough ozone to oxidise CoC. For CoC with K O3 >105 M −1 s −1 and K ∙OH >109 M −1 s −1, an O 3 /TOC ratio of ≥0.461 or a measurable O 3 CT of ≥0.063 mg min/L can achieve log reduction values (LRVs) of ≥1, these are chemicals with aromatic structures; For CoC with low K O3 and high K OH , a combined O 3 /TOC ratio and O 3 CT value inclusive of a chemical structure classification is indicated as necessary criteria to evaluate the removal. UV 254 and TOC were demonstrated to be good online surrogates of ozone barrier performance in the absence of continuous O 3 /TOC ratio and O 3 CT value measurements. Full-scale operational results confirm the effective predictions of the chemical credit framework, which highlights the necessity and importance of monitoring both the O 3 /TOC ratio and O 3 CT values to predict the removal efficiency of a given chemical with a known response to O 3 or a known chemical structure. [Display omitted] [ABSTRACT FROM AUTHOR]

To meet water reuse and discharge requirements in Davis Station, Antarctica, an advanced water treatment plant (AWTP) had been designed and tested for nine months. The key design factors for operating in small communities in remote areas included low maintenance requirement (low chemical inventory, minimal onsite labour), high LRVs for pathogens, robust operation, and high automation. Based on these requirements, the seven-barrier AWTP included ozonation, ceramic microfiltration, biological activated carbon, reverse osmosis, ultraviolet radiation, calcite filtration and chlorination. The nine month test demonstrated that the plant was able to provide minimum LRVs of 12.5 for virus and bacteria, and 10 for protozoa. The overall estimated chemical consumption was lower than equivalent continuous operations elsewhere due to a reduced number of Clean in Place (CIP) cycles as compared to industry. This was achieved by optimised integration of the barriers. Furthermore, there was no functional failure of major barriers and the automated online pressure decay test (PDT) validations for MF and RO were successful. Although some minor improvements, such as a reduced frequency of RO pre-filter cartridge replacement, are still needed, the new integrated plant has fulfilled the requirements of high pathogen LRVs, remote online control and validation, and relatively low chemical consumption. [ABSTRACT FROM AUTHOR]

A new empirical three-parameter viscoelastic model is proposed for describing the rheological behavior of linear and nonlinear materials. In particular, the model succesfully reproduced experimental creep curves at various constant stresses for flocculated suspensions of alumina in the presence of different types of seawater salts. The new model is compared to the classical standard linear solid model and to an extension of this, also proposed here, to represent nonlinear materials. Based on the goodness of fit, the new model is found to be the most appropriate for the experimental system studied. A sensitivity analysis of the parameters to applied stress and type of salt in the sediments reveals that the new model, originally proposed as an ansatz, has three components, constant, linear and nonlinear, as inferred from the behaviour of each model parameter with the applied stresses. The linear contribution follows a correlation with the applied stresses for salts that enhance the hydrogen network of water, so called maker salts, and another for the salts that weaken the network, so called breaker salts. Even more interesting, the nonlinear contribution is characterized by large exponential decay lengths for breaker salts and small exponential decay lengths for maker salts. The existence of linear and nonlinear components may enable applying the model to a variety of systems. [ABSTRACT FROM AUTHOR]

Quantification and comparison of the dewatering characteristics of fifteen sewage sludges from a range of digestion scenarios are described. The method proposed uses laboratory dewatering measurements and integrity analysis of the extracted material properties. These properties were used as inputs into a model of filtration, the output of which provides the dewatering comparison. This method is shown to be necessary for quantification and comparison of dewaterability as the permeability and compressibility of the sludges varies by up to ten orders of magnitude in the range of solids concentration of interest to industry. This causes a high sensitivity of the dewaterability comparison to the starting concentration of laboratory tests, thus simple dewaterability comparison based on parameters such as the specific resistance to filtration is difficult. The new approach is demonstrated to be robust relative to traditional methods such as specific resistance to filtration analysis and has an in-built integrity check. Comparison of the quantified dewaterability of the fifteen sludges to the relative volatile solids content showed a very strong correlation in the volatile solids range from 40 to 80%. The data indicate that the volatile solids parameter is a strong indicator of the dewatering behaviour of sewage sludges. [ABSTRACT FROM AUTHOR]

A model is presented for design of a thickener for solid–liquid separation where the flocs or aggregates within the solid–liquid suspension undergo an aggregate densification process due to the action of rakes. This aggregate densification facilitates suspension dewatering. The novel feature of the model is that it manages to couple together a hindered settling zone (higher up in the thickener, where the flocs are separated from one another, and the suspension cannot bear weight) and a gelled suspension zone (lower down in the thickener, where the flocs are packed together, and the suspension is able to bear weight). The model determines solids fraction profiles throughout the hindered settling zone and the gelled suspension zone, and also gives zone heights and residence times. Parametric investigations using the model are carried out for different suspension fluxes (which influence the solids fluxes and underflow solids fractions attained), and also for different specified amounts of and rates of aggregate densification. [ABSTRACT FROM AUTHOR]

This paper considers an initially networked suspension in a batch settler subjected to very slow aggregate densification. The so-called pseudo-steady state aggregate densification theory developed by van Deventer (2012) has been extended to the case of initially networked suspensions. The solids behaviour and the evolutions of the suspension height and the consolidated bed height in the batch settler have been predicted using the extended pseudo-steady state theory. Different formulae for the weight-bearing strength of the consolidated bed (so-called weak gel and strong gel formulae, which differ near the top of the bed) are considered. The suspension height approaches the consolidated bed height far more quickly when using the weak gel formula than when using the strong gel one. This paper also investigates how the initial feed solids volume fraction and the initial suspension height affect the evolutions of the heights of the suspension and the consolidated bed, as well as the determinations of the solids volume fractions obtained at the bottom of the batch settler. When the initial feed solids fraction is sufficiently large and/or the initial suspension is sufficiently tall, the densification process has little effect on the solids fraction observed at the bottom of the settler. [ABSTRACT FROM AUTHOR]

Experimental data from batch settling tests on polymer flocculated suspensions was used to determine the material properties that quantify dewatering behaviour and relate settling rate to solids concentration. These material properties were subsequently used to predict the performance of a pilot-scale gravity thickener, including the expected solids concentration profile in the thickener. Analysis of data from a novel laboratory fluidisation rig, used to simulate the hindered settling zone of a thickener, and the pilot-scale thickener, indicates that relative to simple batch settling tests, the dewatering behaviour and related material properties of flocculated aggregates change over time, even at concentrations less than the gel point of the suspension and in the absence of mechanical shear. The change is primarily attributed to the phenomenon of aggregate densification as a result of aggregate-aggregate buffeting and manifests as enhanced settling and increased thickener throughput. A fluidisation case study using calcite with no added mechanical shear (only that due to fluidisation) found that the aggregates densified to 86% of their original diameter over a period of order 4000 s. This was enhanced with the addition of mechanical shear with a further decrease in aggregate size to 76% of their original diameter. Almost identical results were observed for the pilot thickener. Laboratory data typically underestimates thickener performance, even at the pilot scale, and the agreement between laboratory and pilot results represents a novel outcome for the characterisation of material dewatering properties. The observations herein are an important step towards full-scale thickener modelling incorporating aggregate densification effects due to shear. [ABSTRACT FROM AUTHOR]

The impact of several electrolytes present in seawater on the rheological properties of flocculated alumina suspensions was assessed by using creep testing at pH conditions both above and below the isoelectric point. Flocculated suspensions were obtained by adding a high molecular weight anionic polymer flocculant to a cylinder of alumina suspension and aggregating the suspension using the plunger method. The suspension was allowed to sediment and the supernatant liquid decanted prior to tests of the viscoelastic properties of the resulting sediment. Salts analyzed were MgCl 2 , CaCl 2 and NaCl, known as water structure makers, and KI and KCl, known as water structure breakers. A high salt concentration of 0.5 M was used to approach the ionic strength of seawater. For both pH's studied, the sediments demonstrated viscoelastic non-linear behavior observed as a non-linear relationship between yield strain and applied stress. In the absence of flocculant, it has been observed that the viscosity and yield stress of a suspension increase in the presence of structure maker salts for the case of both silica and alumina suspensions. In the presence of flocculant, new results are found: when the solid and flocculant were of opposite charge, the shear yield stress of the alumina suspensions increased with the breaker character of the salts, however when the solid and flocculant were of similar charge, then the yield stress is independent of the character of the salts. Similar water structures on the interacting surfaces lead to strong particle networks. The work demonstrates the importance of salt-surface interaction to the rheology of suspensions in the presence of polymer flocculants, as is typical of many mineral processing operations world-wide. [ABSTRACT FROM AUTHOR]

Ag salt nanoparticles were manufactured at high concentration in water in the presence of a series of copolymers of poly(ethylene glycol) and maleic anhydride (PEG-MA). The Ostwald ripening behaviour was then examined using the PEG chain length of the copolymer as a variable. The ripening rate was observed to be very slow compared to previous literature studies of bare or surfactant stabilised particles in dilute solution. Despite the hindrance to ripening caused by the presence of the adsorbed copolymer, the predicted rate was shown to fit closely to Lifshitz–Slyozov–Wagner (LSW) theory. Particle ripening decreased with increasing PEG chain length. The data highlight the important role of stabiliser chain length for the stability and shelf-life of concentrated nanoparticle dispersions. [ABSTRACT FROM AUTHOR]

Cyanobacteria and their metabolites are recognised as serious water quality issues for water suppliers around the world. Water shortages not only increase the risk of the proliferation of cyanobacteria but also necessitate the development of more effective treatment regimes. Conventional water treatment processes are considered an effective initial barrier in removing cyanobacterial cells intact and without damage. However, the cells can be exposed to a range of pH conditions during these processes. The impact of various pH conditions typical of the water treatment processes was evaluated on common bloom species, Microcystis aeruginosa , Cylindrospermopsis raciborskii and Anabaena circinalis . By using cyanobacterial metabolite analysis and cell viability assays, it was shown that low pH stress (pH below 5), which can occur during coagulation upon the application of metal hydroxide coagulants, occurs quickly and results in considerable cell lysis and metabolite release. It is demonstrated that it is critical to keep the pH of water above 5 (locally) at all times in order to reduce the risk of water contamination with problem metabolites. [ABSTRACT FROM AUTHOR]

Abstract: A model is presented for the thickening of a raked suspension. The model is based on Kynch theory (Kynch, 1952), i.e. it describes systems with solids fractions sufficiently low that the solids have not gelled into a weight-bearing network. However the model incorporates a modification to describe how raking the suspension causes flocs or aggregates within it to densify. This floc densification opens up channels between the flocs through which liquid escapes, making the suspension easier to dewater. The densification theory presented here predicts profiles of varying solids fraction vs height in the settling zone in a thickener, information which is not normally available when designing thickeners via the conventional Kynch theory. Performance enhancements for thickeners due to raking can be readily determined, either in terms of increased underflow solids fraction or increased solids flux. As underflow solids fraction is increased, thickeners operated at a specified aggregate densification rate (or equivalently at a fixed settling zone height) tend to approach a ‘fully densified’ suspension state (defined as a point at which the extent of aggregate densification ceases to change with time), with improved thickening performance. [Copyright &y& Elsevier]

Highlights: [•] Compared settling of alumina slurries in cylinders and cylinders with vertical rods. [•] Polymer flocculated solids shrank from rod and settled faster: Shear densification. [•] Salt coagulated solids clung to the rod and settled slower: Syneresis. [•] Aggregation state influences settling rate changes in presence of vertical rods. [Copyright &y& Elsevier]

Highlights: [•] Rupture of three promising microalgae by high pressure homogenization was investigated. [•] Cell counting was the only reliable method for quantifying rupture of all the algae. [•] Tetraselmis suecica was highly susceptible to rupture by homogenization. [•] Chlorella sp. had similar resistance to rupture as the yeast Saccharomyces cerevisiae. [•] Nannochloropsis sp. was highly resistant to rupture. [ABSTRACT FROM AUTHOR]

Abstract: Drying pans are used during wastewater treatment (WWT) to store, stabilise and dry residual solids. The pans are filled with sludge that dries via exposure to sunshine and wind. We propose that drying pans be operated based on dry stacking principles, a technique with proven success in the mineral processing industry. The implementation of the dry stacking technique requires very little in the way of additional engineering beyond a conventional drying pan. By applying the sludge in thin layers, the sludge naturally forms its own stack with an angle that is dependent on the consistency of the material. The benefits of dry stacking are that the slope allows instantaneous run-off of rainfall and supernatant, allowing operation throughout the year rather than seasonally. The layering approach also maximises the evaporation achieved in the available deposition area compared to filling the pans sequentially. A series of laboratory tests were carried out on samples from Melbourne Water's Western Treatment Plant in Werribee, Australia, to provide validation of the dry stacking concept for WWT sludges. Rheological tests showed that samples had appropriate flow properties to form stacks. Drying and re-wetting tests on the samples indicated that a sloped, partially dry sludge sheds rainfall, depending on the slope, cake dryness and amount of rainfall. Local rainfall data was used to estimate a potential increase in pan throughput of 65%–140% due to dry stacking. The greatest improvements were predicted to occur during wetter years. In combination, the results indicated that dry stacking has the potential to dramatically improve the performance of WWT sludge drying pans. [Copyright &y& Elsevier]

Abstract: A knowledge of the properties that quantify the rate and extent of particulate suspension dewatering through sedimentation and consolidation is critical to the prediction of dewatering performance for industrial processes such as gravity settling, centrifugation and filtration. The strength of a network of particles in compression is quantified as a compressive yield stress or modulus, P y (ϕ). The rate of dewatering is inversely related to the hindered settling function, R(ϕ), which is a measure of hydrodynamic resistance. Dewaterability characterisation over a broad range of solids concentrations is a challenging task requiring tests including batch settling and pressure filtration. Unfortunately, for many systems, these tests are prohibitively slow and an alternative such as centrifugation is useful in accelerating the characterisation. This paper validates algorithms for the characterisation of dewaterability from centrifugal sedimentation data obtained in a laboratory centrifuge with interface height detection and provides guidelines for obtaining accurate results over a broad range of solids concentrations. Typical dewaterability data for a flocculated industrial mineral slurry and a biological sludge are used as inputs for the numerical prediction of centrifugal sedimentation behaviour. Equilibrium centrifugation at a range of rotation speeds has been simulated and P y (ϕ) data determined using a method described by Buscall and White (1987). The result is shown to be accurate to within 10% of the expected values. Transient centrifugation data has been simulated and R(ϕ) determination using a new algorithm is shown to be accurate over a broad range of solids concentrations extending beyond the gel point, provided a new data rejection criterion is utilised. In addition, errors at low concentration in R(ϕ) data, caused by dilution, are described. It is shown that currently available analysis techniques are unlikely to quantify these errors. [Copyright &y& Elsevier]

Abstract: The presence of coarse particulate components in tailings streams poses significant challenges to the mineral processing industry. Suspensions with fast-settling coarse fractions make traditional rheological measurements tedious and inaccurate. These measurements are critical to the design and operation of mixing, dewatering, pumping and tailings equipment and operations. A methodology for predicting the gel point, close packing fraction and shear rheology of particulate slurries containing a binary mixture of fine and coarse material is presented. The model has validity subject to the constraint that the particle size of the coarse material is sufficiently distinct from that of the fine material. The model enables calculation of the gel point and close packing fraction of the mixture based on the gel points and close packing fractions of the pure fine and coarse materials in the suspension. The model predicts that the gel point (and close packing fraction) of the fine material increases with increasing coarse fraction until a maximum value is attained before decreasing to the gel point (or close packing fraction) of the coarse material. This relationship provides a subsequent basis for a yield stress model to accurately predict the yielding behaviour of binary mixtures of fine and coarse material. The model is useful in determining whether a sample exhibits yield stress behaviour through knowledge of the gel point and close packing fraction of the constitutive fine and coarse components. The model is exemplified using particulate mixtures containing coagulated aluminium oxide, calcium carbonate and coarse sand. [Copyright &y& Elsevier]

Abstract: The sedimentation behaviour of particulate slurries in laboratory scale batch settling experiments is important to the prediction of full-scale gravity thickening behaviour. However, the material throughput predicted by modelling of thickener performance from material properties derived from conventional batch experiments has been shown to be up to 100 times less than observed (at full-scale). Such discrepancies have been attributed to various shear and compression-induced effects (prevalent at full-scale) that modify flocculated aggregate structure, including aggregate densification. Standard Kynch batch settling analysis has been modified to incorporate the effect of aggregate densification behaviour on material properties. Based on this modification, a semi-analytical method is presented, which provides improved real-time predictions of batch sedimentation behaviour. This method can produce a slurry–liquid interface height versus time profile up to the end of the fan region, based on a functional form of aggregate densification behaviour. Additionally, aggregate densification theory incorporated into the compressive yield stress is used to predict the final equilibrium bed height. A functional form is proposed that incorporates parameters which describe the rate and the extent of densification. Validations of this method are presented against theoretical numerical simulations and experimental data. [Copyright &y& Elsevier]

Abstract: In this work, we investigated the importance of osmotic pressure in the overall dewaterability behaviour of a biotic sludge. Biotic sludges, such as activated or digested sludge from waste water treatment, are known to be difficult to dewater, due to their high compressibility and their gel-like water retention capacity. These properties are partly attributed to the presence of surface charges, which are due to the biological nature and the presence of weakly charged extra-cellular polymeric substances. Both in filtration and centrifugation experiments, charge related effects were partly neutralised through a controlled increase in the bulk ionic strength by the addition of NaCl. It was observed that an increase in the bulk ionic strength brings about an increase in the final solid volume fraction upon constant pressure filtration or centrifugation. Increasing the ionic strength did not result in a more classical filtration behaviour, however. The results further suggested that with increasing total pressure, the relative importance of the osmotic pressure in the total resistance against compression diminishes, and that more structural effects dominate the solid stress at high pressures. [Copyright &y& Elsevier]

Abstract: The prediction and optimisation of the performance of dewatering devices such as filters and thickeners requires the laboratory measurement of fundamental material characteristics. This work presents the application of recently developed methods for the extraction of meaningful phenomenological properties from filtration and sedimentation testing of wastewater sludges, which has previously been limited due to theoretical and experimental constraints. The results for a sample of digested wastewater treatment sludge described a material with weak network strength that was quite permeable at low solids concentrations and the gel point was about 1v/v%. The sample compressed to high solids concentrations at moderate pressures (up to 40v/v% at 400kPa) but became extremely impermeable at these high concentrations. The solids concentration dependencies of the material characteristics had a form that was expected for highly compressible materials such as wastewater sludges, but had not been reported previously. The extracted material characteristics were then used to predict the test results to show that the characterisation was valid. [Copyright &y& Elsevier]

• Filamentous algae have promise for wastewater treatment. • The literature is reviewed in relation to species selection and engineering design. • The size of filamentous algae provides advantages over microalgae. • Filamentous algae can be readily harvested and retained to control solids residence time. • Future research is needed to understand algae-bacteria interactions and techno-economics. Wastewater treatment using algae is a promising approach for efficient removal of contaminating nutrients and their conversion into useful products. Monocultures of filamentous algae provide easier harvesting compared to microalgae, and better control of biomass quality than polyculture systems such as algal turf scrubbers. In this review, recent research into wastewater treatment using freshwater filamentous algae is compiled and critically analysed. Focus is given to filamentous algae monocultures, with key relevant findings from microalgae and polyculture systems discussed and compared. The application of monocultures of filamentous algae is an emerging area of research. Gaps are identified in our understanding of key aspects important to large-scale system design, including criteria for species selection, influence of nutrient type and loading, inorganic carbon supply, algae-bacteria interactions, and parameters such as pond depth, mixing and harvesting regimes. This technology has much promise, however future research is needed to maximise productivity and wastewater treatment efficiency. [ABSTRACT FROM AUTHOR]

Wastewater surveillance has played a pivotal role in monitoring SARS-CoV-2 transmission worldwide. However, developing and implementing the methods underpinning these programmes in regions with prolonged periods of low community transmission has proven challenging. In Victoria, Australia, wastewater surveillance provided early warning of unknown community infections and informed timely public health decisions to limit their spread when case numbers were low. To achieve this, we developed a methodological approach sensitive to extremely low viral loads and could readily identify false positives within short turnaround times. Here, we describe the successful development, implementation, and evaluation of analytic methods using Reverse Transcriptase Quantitative Polymerase Chain Reaction (RT-qPCR) and amplicon sequencing in tandem with CRISPR DETECTR in an ongoing, large-scale surveillance programme to detect SARS-CoV-2 in wastewater in Victoria, Australia. Our study covers ten months, from July 2020 to April 2021, and includes all state-wide health districts and prolonged periods with no known, active community cases among the ∼6.7 million population., Competing Interests: The authors declare there is no conflict., (© 2025 The Authors This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/).)

Filamentous algae (FA) can form readily harvestable floating mats or attached turfs that facilitate their application in wastewater treatment systems. However, large-scale implementation is hindered by our inability to predict performance as a function of key operational parameters. A predictive mathematical model would be a valuable tool for designing efficient FA-based systems. Developing accurate models is challenging due to dynamic environmental conditions and the spatial complexities of FA cultures. In this work, a model was developed to mathematically describe the biomass productivity of static FA cultures (mats and turfs) in relation to the incident light intensity and temperature. The model was validated against published data to investigate the influence of time-dependent inhibition (inhibition from sustained light exposure) on productivity. When time-dependent inhibition was included in the model, predictions were within ~10% of experimental values, however, without including time-dependent inhibition there was a sixfold overestimation of biomass productivity. The model could also generate predictions of the effects of time-dependent inhibition during diurnal light fluctuations using experimentally determined rate constants. The model represents a powerful tool for optimizing the design and operational parameters in FA cultures that could be further expanded to incorporate the influence of nutrient and CO 2 availability., (© 2025 The Author(s). Biotechnology and Bioengineering published by Wiley Periodicals LLC.)

The performance of individual reverse osmosis (RO) systems varies significantly with different contaminants of emerging concern (CECs). As such, log reduction values (LRVs) of the concentration of these chemicals cannot be arbitrarily credited in water treatment and water recycling. This study looks to present an approach to the management of chemical risks by providing a systematic validation of RO barrier performance with respect to LRV credits for various classes of CECs. In this work, a one-off sampling campaign across five treatment barriers (strainer filtration, ultrafiltration, RO, ion exchange, chlorination) of a full-scale water recycling plant was conducted, followed by a systematic sampling campaign for a period of six weeks across just the RO barrier. The CECs screening methodology used GC-MS for quantification of 948 trace organic chemicals along with specific 44 per- and polyfluoroalkyl substances (PFAS) screening using LC-MS/MS to demonstrate the removal credits of the RO barrier to a wide spectrum of CECs. The work was used to validate an LRV barrier credit framework so as to predict the performance of a polyamide RO membrane for removal of a range of chemical classes, under typical operational conditions. Conductivity was validated as an efficient surrogate for membrane integrity and RO performance, along with specified operational conditions associated with permeate flux and recovery rate. A bioassay method (photobacterium test) showed good potential to be used as a quick measure to indicate the general toxicity of a sample caused by chemical contamination, because of its high detection sensitivity and time and cost efficiency., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

This study investigated a novel and sensitive analytical method based on a simple heat-based derivatization using 3-bromoacetyl coumarin as the reagent and analysis with a HPLC-UV system or just a UV-vis spectrometer to allow the sub-ppm determination of PFCAs in water solution with the potential for utilization in simple laboratories and field laboratory scenarios. A Strata-X-AW cartridge was used for the solid phase extraction (SPE) procedure and higher than 98% recoveries were obtained. The derivatization condition showed that a high efficiency of peak separation was obtained with obviously different retention time among various PFCAs derivatives using HPLC-UV analysis. The derivatization stability and repeatability showed favorable results with stable derivatized analytes for ≤12 h and a relative standard deviation (RSD) of <2% for all repetitions. The limit of detection for the HPLC-UV analysis was between 0.1 ppm and 0.5 ppm. A satisfactory linearity response was found with R 2 >0.998 for all individual PFCA compounds. The limit of detection for simple UV-Vis analysis was <0.0003 ppm to measure the presence of PFCAs. Contamination of standards with humic substances and measurement of industrial samples in a complex wastewater matrix showed no adverse effects on the accuracy of PFCA determination by using the developed methodology.

The reuse of water in a range of potable and non-potable applications is an important factor in the augmentation of water supply and in improving water security and productivity worldwide. A key hindrance to the reuse of water is the cost of compliance testing and process validation associated with ensuring that pathogen and chemicals in the feedwater are removed to a level that ensures no acute or chronic health and/or environmental effects. The critical control point (CCP) approach is well established and widely adopted by water utilities to provide an operational and risk management framework for the removal of pathogens in the treatment system. The application of a CCP approach to barriers in a treatment system for the removal of chemicals is presented. The application exemplar is to a small community wastewater treatment system that aims to produce potable quality water from a secondary treated wastewater effluent, however, the concepts presented are generic. The example used seven treatment barriers, five of which were designed and operated as CCP barriers for pathogens. The work demonstrates a method and risk management framework by which three of the seven barriers could also include a CCP approach for the removal of chemicals. Analogous to a CCP approach for pathogens, the potential is to reduce the use of chemical analysis as a routine determinant of performance criteria. The operational deployment of a CCP approach for chemicals was augmented with the development of a decision tree encompassing the classification of chemicals and the total removal credits across the treatment train in terms of the mechanistic removal of chemicals for each barrier. Validation of the approach is shown for an activated sludge, ozone and reverse osmosis barrier., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Nitrogen deprivation (N-deprivation) is a proven strategy for inducing triacylglyceride accumulation in microalgae. However, its effect on the physical properties of cells and subsequently on product recovery processes is relatively unknown. In this study, the effect of N-deprivation on the cell size, cell wall thickness, and mechanical strength of three microalgae was investigated. As determined by analysis of micrographs from transmission electron microscopy, the average cell size and cell wall thickness for N-deprived Nannochloropsis sp. and Chlorococcum sp. were ca. 25% greater than the N-replete cells, and 20 and 70% greater, respectively, for N-deprived Chlorella sp. The average Young's modulus of N-deprived Chlorococcum sp. cells was estimated using atomic force microscopy to be 775 kPa; 30% greater than the N-replete population. Although statistically significant, these microstructural changes did not appear to affect the overall susceptibility of cells to mechanical rupture by high pressure homogenisation. This is important as it suggests that subjecting these microalgae to nitrogen starvation to accumulate lipids does not adversely affect the recovery of intracellular lipids.