The effect of additives on the biodegradation of polyhydroxyalkanoate (PHA) in marine field trials.

The persistence of conventional fossil fuel-derived plastics in marine ecosystems has raised significant environmental concerns. Biodegradable plastics are being explored as an alternative. This study investigates the biodegradation behaviour in two marine environments of melt-extruded sheets of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) bioplastic as well as blends of PHBV with a non-toxic plasticiser (triethyl citrate, TEC) and composites of PHBV with wood flour. Samples were submerged for up to 35 weeks in two subtropical marine conditions: on the sandy seabed in the sublittoral benthic zone and the sandy seabed of an open air mesocosm with pumped seawater. Rates of biodegradation, lag times and times to 95 % mass loss (T95) were determined through mass loss data and Gompertz modelling. Mechanisms of biodegradation were studied through changes in molecular weight, mechanical properties and surface features. Results reveal a rapid biodegradation rate for all PHBV samples, demonstrating a range of specific biodegradation rates relative to exposed surface area of 0.03 ± 0.01 to 0.09 ± 0.04 mg.d-1.cm-2. This rapid rate of biodegradation meant that the subtle variations in biodegradation mechanisms across different sample thicknesses and additive compositions had little effect on overall lifetimes, with the T95 for most samples being around 250-350 days, regardless of site, highlighting the robust biodegradability of PHBV in seawater. It was only the PHBV-wood flour composite that showed faster biodegradation, and that was only in the exposed ocean site. The mesocosm site was otherwise shown to be a good model for the open ocean, with very comparable biodegradation rates and changes in mechanical properties over time.

Evaluating novel biodegradable polymer matrix fertilizers for nitrogen-efficient agriculture.

Enhanced efficiency fertilizers (EEFs) can reduce nitrogen (N) losses in temperate agriculture but are less effective in the tropics. We aimed to design a new EEF and evaluate their performance in simple-to-complex tests with tropical soils and crops. We melt-extruded urea at different loadings into biodegradable polymer matrix composites using biodegradable polyhydroxyalkanoate (PHA) or polybutylene adipate-co-terephthalate (PBAT) polymers with urea distributed throughout the pellet. These contrast with commercially coated EEF that have a polymer-coated urea core. We hypothesized that matrix fertilizers would have an intermediate N release rate compared to fast release from urea or slow release from coated EEF. Nitrogen release rates in water and sand-soil columns confirmed that the matrix fertilizer formulations had a more progressive N release than a coated EEF. A more complex picture emerged from testing sorghum [Sorghum bicolor (L.) Moench] grown to maturity in large soil pots, as the different formulations resulted in minor differences in plant N accumulation and grain production. This confirms the need to consider soil interactions, microbial processes, crop physiology, and phenology for evaluating fertilizer performance. Promisingly, crop δ15N signatures emerged as an integrated measure of efficacy, tracking likely N conversions and losses. The three complementary evaluations combine the advantages of standardized high-throughput screening and more resource-intensive and realistic testing in a plant-soil system. We conclude that melt-blended biodegradable polymer matrix fertilizers show promise as EEF because they can be designed toward more abiotically or more microbially driven N release by selecting biopolymer type and N loading rate.

Synthesis and physical properties of polyhydroxyalkanoate (PHA)-based block copolymers: A review.

Polyhydroxyalkanoates (PHAs) are a group of natural polyesters that are synthesised by microorganisms. In general, their thermoplasticity and (in some forms) their elasticity makes them attractive alternatives to petrochemical-derived polymers. However, the high crystallinity of some PHAs - such as poly(3-hydroxybutyrate) (P3HB) - results in brittleness and a narrow processing window for applications such as packaging. The production of copolymeric PHA materials is one approach to improving the mechanical and thermal properties of PHAs. Another solution is the manufacture of PHA-based block copolymers. The incorporation of different polymer and copolymer blocks coupled to PHA, and the resulting tailorable microstructure of these block copolymers, can result in a step-change improvement in PHA-based material properties. A range of production strategies for PHA-based block copolymers has been reported in the literature, including biological production and chemical synthesis. Biological production is typically less controllable, with products of a broad molecular weight and compositional distribution, unless finely controlled using genetically modified organisms. By contrast, chemical synthesis delivers relatively controllable block structures and narrowly defined compositions. This paper reviews current knowledge in the areas of the production and properties of PHA-based block copolymers, and highlights knowledge gaps and future potential areas of research.

Behavioural activation to mitigate the psychological impacts of COVID-19 restrictions on older people in England and Wales (BASIL+): a pragmatic randomised controlled trial.

BACKGROUND: Older adults were more likely to be socially isolated during the COVID-19 pandemic, with increased risk of depression and loneliness. We aimed to investigate whether a behavioural activation intervention delivered via telephone could mitigate depression and loneliness in at-risk older people during the COVID-19 pandemic. METHODS: BASIL+ (Behavioural Activation in Social Isolation) was a pragmatic randomised controlled trial conducted among patients recruited from general practices in England and Wales, and was designed to assess the effectiveness of behavioural activation in mitigating depression and loneliness among older people during the COVID-19 pandemic. Eligible participants were aged 65 years and older, socially isolated, with a score of 5 or higher on the Patient Health Questionnaire-9 (PHQ-9), and had multiple long-term conditions. Participants were allocated in a 1:1 ratio to the intervention (behavioural activation) or control groups by use of simple randomisation without stratification. Behavioural activation was delivered by telephone; participants were offered up to eight weekly sessions with trained BASIL+ Support Workers. Behavioural activation was adapted to maintain social connections and encourage socially reinforcing activities. Participants in the control group received usual care with existing COVID-19 wellbeing resources. The primary clinical outcome was self-reported depression severity, assessed by the PHQ-9, at 3 months. Outcomes were assessed masked to allocation and analysis was by treatment allocation. This trial is registered with the ISRCTN registry (ISRCTN63034289). FINDINGS: Between Feb 8, 2021, and Feb 28, 2022, 449 eligible participants were identified and 435 from 26 general practices were recruited and randomly assigned (1:1) to the behavioural activation intervention (n=218) or to the control group (usual care with signposting; n=217). The mean age of participants was 75·7 years (SD 6·7); 270 (62·1%) of 435 participants were female, and 418 (96·1%) were White. Participants in the intervention group attended an average of 5·2 (SD 2·9) of eight remote behavioural activation sessions. The adjusted mean difference in PHQ-9 scores between the control and intervention groups at 3 months was -1·65 (95% CI -2·54 to -0·75, p=0·0003). No adverse events were reported that were attributable to the behavioural activation intervention. INTERPRETATION: Behavioural activation is an effective and potentially scalable intervention that can reduce symptoms of depression and emotional loneliness in at-risk groups in the short term. The findings of this trial add to the range of strategies to improve the mental health of older adults with multiple long-term conditions. These results can be helpful to policy makers beyond the pandemic in reducing the global burden of depression and addressing the health impacts of loneliness, particularly in at-risk groups. FUNDING: UK National Institute for Health and Care Research.

Integrating PET chemical recycling with pyrolysis of mixed plastic waste via pressureless alkaline depolymerization in a hydrocarbon solvent.

This study presents a proof of concept for a technology train that integrates polyethylene terephthalate (PET) recovery from mixed plastic waste and plastic pyrolysis. PET is depolymerized into terephthalic acid (TPA) by hydrolysis using a low volatility oil as medium, which enables (i) low-pressure operation, and (ii) a selective separation and recovery of TPA from the product mix by a simple process of filtration, washing, and precipitation. Full PET conversion and high TPA recovery (>98 %) were achieved at 260 °C. This technology train is demonstrated to be effective for processing mixed waste streams, leading to higher yield and quality of liquid product from thermal pyrolysis when compared with feedstock that has not been pre-treated. Further, the technology could be readily integrated with a plastics pyrolysis process, whereby a by-product from the pyrolysis could be used as the low-volatility oil.

Occurrence and behaviour of colloidal silica and silica-rich nanoparticles through stages of reverse osmosis treating coal seam gas associated water.

Reverse Osmosis (RO) membrane filtration is a very common process for treating a wide range of groundwater types including produced water from coal seam gas (coalbed methane) wells. Mineral scaling limits water recovery for RO membranes and costs money in terms of treatment and downtime. Silica scaling can be particularly troublesome as it is often irreversible. Mitigating silica scaling requires an understanding of its occurrence, speciation mechanism and its interdependency with other operation factors. This study uses a range of techniques to show that silica colloids form during later stages of an RO process with very high recovery. This happens at silica concentrations above the solubility that would normally indicate high risk of silica scale. However, instead of scale, colloids preferentially formed which means the process can operate at high recoveries with RO performance maintained by regular cleaning cycles. The concentration of the colloidal silica through the RO stages was measured through the difference in total and dissolved silica. Once the existence was established with this technique, the particles were trapped and their size, morphology and composition were investigated with Scanning Electron Microscopy (SEM) in conjunction with Energy Dispersive X-Ray Spectroscopy (EDS). This revealed the particles to be predominantly silica with limited other elements involved.

Synthesis and Characterisation of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-b-poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Multi-Block Copolymers Produced Using Diisocyanate Chemistry.

Bacterially derived polyhydroxyalkanoates (PHAs) are attractive alternatives to commodity petroleum-derived plastics. The most common forms of the short chain length (scl-) PHAs, including poly(3-hydroxybutyrate) (P3HB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), are currently limited in application because they are relatively stiff and brittle. The synthesis of PHA-b-PHA block copolymers could enhance the physical properties of PHAs. Therefore, this work explores the synthesis of PHBV-b-PHBV using relatively high molecular weight hydroxy-functionalised PHBV starting materials, coupled using facile diisocyanate chemistry, delivering industrially relevant high-molecular-weight block copolymeric products. A two-step synthesis approach was compared with a one-step approach, both of which resulted in successful block copolymer production. However, the two-step synthesis was shown to be less effective in building molecular weight. Both synthetic approaches were affected by additional isocyanate reactions resulting in the formation of by-products such as allophanate and likely biuret groups, which delivered partial cross-linking and higher molecular weights in the resulting multi-block products, identified for the first time as likely and significant by-products in such reactions, affecting the product performance.

Hazardous state lifetimes of biodegradable plastics in natural environments.

Plastic pollution is a critical problem that has the potential for long-lasting impact. While all plastics eventually break down to at least some degree, they can remain in different transition states, such as microplastics and nanoplastics, for extended periods of time before reaching complete mineralisation to non-hazardous end products. Each of the transition states represents different types of hazards, so it is critical to understand the factors driving the lifetimes of plastics within these states. To do this, we propose a framework for assessing plastic lifetimes in natural environments based on the flow of material through potentially hazardous states: macroplastic and mesoplastic, microplastic, nanoplastic and soluble products. State changes within this framework are underpinned by three key processes: fragmentation, depolymerisation, and bioassimilation, with the pathways for generation of the different plastic states, and the lifetimes within these states, varying widely for individual materials in different environments due to their dependence on polymer material type, form and properties, and environmental factors. The critical factors driving these processes can therefore appear complex, but molecular weight, crystallinity, oxygen and water diffusivity, and inherent polymer chain reactivity (including to enzymes) are key to our understanding. By analysing currently available data that take factors such as these into consideration, we have generated information on the most likely states in which a range of plastics with different environmental degradation behaviour may exist over time in natural environments. Polyethylene (PE), for example, should be expected to fragment and accumulate in the environment as microplastic and nanoplastic. Interestingly, the state-profile for the biodegradable plastic polylactic acid (PLA) is similar, albeit over shorter timeframes. PLA also likely fragments, but then the relatively slow process of abiotic depolymerisation results in accumulation of microplastic and nanoplastic. By contrast, the state-profile for the biodegradable plastic polyhydroxyalkanoate (PHA) would be expected to be very different. The bulk material is less susceptible to embrittlement and fragmentation as a primary path to biodegradation, since the rapid enzyme catalysed depolymerisation of exposed surfaces proceeds in conjunction with bioassimilation.

Effect of Toxic Phthalate-Based Plasticizer on the Biodegradability of Polyhydroxyalkanoate.

While new biodegradable materials are being rapidly introduced to address plastic pollution, their end-of-life impacts remain unclear. Biodegradable plastics typically comprise a biopolymer matrix with functional additives and/or solid fillers, which may be toxic. Here, using an established method for continuous biodegradation monitoring, we investigated the impact of a commonly used plasticizer, dibutyl phthalate (DBP), on the biodegradation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) in soil. The presence of DBP delayed the initial stage of PHBV biodegradation but then accelerated subsequent rates of biodegradation. Furthermore, it led to significant increases in total bacterial and fungal biomass and altered the composition of microbial communities with significant increases in the relative abundances of Thauera (gammaproteobacterial) and Mucor circinelloides (fungal) populations. It is proposed, with evidence from biodegradation behavior and microbial analysis, that the presence of DBP likely stimulated a microbial community shift, introduced higher proportions of more readily degradable amorphous regions from the plasticizing effect, and facilitated access to the bulk polymer matrix for microorganisms or at least their associated enzymes. These effects in combination overcame the initial inhibition effect of the DBP and resulted in a net increase in the rate of biodegradation of PHBV.

Utilisation of Paunch Waste as a Natural Fibre in Biocomposites.

Paunch is a fibrous solid residue consisting of partially digested feed from the stomachs of processed cattle. It is the largest untapped solid waste stream from animals at meat processing plants, and potentially a valuable source of fibres for the production of sustainable and potentially higher-value natural biocomposite materials. Paunch was obtained from the waste effluent of a red meat processing plant, and the fibre characteristics of the as-obtained material were studied and benchmarked against wood flour and ground buffel grass, with a view to evaluating the potential of paunch as a fibre for polymer composites. The ground paunch possessed a rough fibrous surface and fibre-like characteristics that were comparable to both wood flour and ground buffel grass, demonstrating their potential for use in composites. Without any pre-treatment or compatibilisation, composites of a representative biopolymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and ground paunch were successfully produced for the first time via extrusion, with up to 50 wt% paunch content. Mechanical property analysis showed that, at 30 wt% content, PHBV/ground paunch composites yielded mechanical properties that were comparable to those of composites with ground buffel grass.

Tailored production of lignin-containing cellulose nanofibrils from sugarcane bagasse pretreated by acid-catalyzed alcohol solutions.

In this study, sugarcane bagasse was pretreated with acid-catalyzed alcohols, i.e., ethanol (AE), ethylene glycol (AEG) and glycerol (AG) to prepare pulps for producing lignin-containing cellulose nanofibrils (LCNF) with tailored properties, such as hydrophilicity/hydrophobicity and dispersion stability. The results showed that AG-LCNF had the highest lignin content of 16% but relatively low hydrophobicity while AE-LCNF had a low lignin content of 11% but the highest hydrophobicity. LCNF diameter distribution, crystallinity, zeta potentials and thermal stability were also determined to understand the effects of pretreatment solvent. NMR analyses revealed that alcohols modified lignin at α-position by etherification and γ-position by esterification of aliphatic chains, subsequently affecting lignin oxidation by TEMPO in the LCNF production processes, LCNF properties and LCNF dispersion in different solvents. This study provided fundamental information in the design and tailored production of LCNF for various applications, such as manufacturing polymer composites and Pickering emulsions.

The HPK1 Inhibitor A-745 Verifies the Potential of Modulating T Cell Kinase Signaling for Immunotherapy.

Hematopoietic progenitor kinase 1 (HPK1) is an MAP4K family member within the Ste20-like serine/threonine branch of the kinome. HPK1 expression is limited to hematopoietic cells and has a predominant role as a negative regulator of T cell function. Because of the central/dominant role in negatively regulating T cell function, HPK1 has long been in the center of interest as a potential pharmacological target for immune therapy. The development of a small molecule HPK1 inhibitor remains challenging because of the need for high specificity relative to other kinases, including additional MAP4K family members, that are required for efficient immune cell activation. Here, we report the identification of the selective and potent HPK1 chemical probe, A-745. In unbiased cellular kinase-binding assays, A-745 demonstrates an excellent cellular selectivity binding profile within pharmacologically relevant concentrations. This HPK1 selectivity translates to an in vitro immune cell activation phenotype reminiscent of Hpk1-deficient and Hpk1-kinase-dead T cells, including augmented proliferation and cytokine production. The results from this work give a path forward for further developmental efforts to generate additional selective and potent small molecule HPK1 inhibitors with the pharmacological properties for immunotherapy.

Adaptation and evolution of freshwater Anammox communities treating saline/brackish wastewater.

The most common way to apply Anammox for saline wastewater treatment is via salt adaptation of freshwater Anammox bacteria (FAB). To better apply this process in practice, it's essential to understand the salt adaptation process of FBA, as well as the underlying mechanisms. This study investigated the long-term salt adaptation process of a fixed-film FAB culture in three reactors (namely R1-R3), under salinities of 2, 8, and 12 NaCl g/L, correspondingly. All three reactors were under stable operation and achieved 80-90% total inorganic nitrogen removal efficiency throughout the 425-day operation period. R1 servers as a blank control, based on the clear microbial community shifts in R2 and R3, the operation period was divided into 2 phases. During Phase 1, all FAB in the three reactors belonged to Ca. Brocadia sp.. The Anammox activity (AA) and the ratio of nitrite/ammonium (NO2--N/NH4+-N) consumption in R2 and R3 decreased with the increase of salinity and did not recover to the initial levels. During Phase 2, the relative abundance of Ca. Kuenenia sp. in R2 and R3 increased from nearly 0 to about 60 and 77%, respectively. With the growth of Ca. Kuenenia sp., the AA and stoichiometry of R2 and R3 gradually recovered. AA of R2 and R3 both reached 1.0 g NH4+-N/L/day at the end of this phase, which was about 80% of that in R1. These results indicated that the salt adaptation of FAB culture was achieved by species shift from a low salt-tolerance one to a high salt-tolerance one.

Salinity effect on freshwater Anammox bacteria: Ionic stress and ion composition.

The biggest challenge to apply Anammox to treat wastewater with elevated salt content is the inhibitory effect of salinity on freshwater Anammox bacteria (FAB). Most of the research into salinity inhibition has focused on the osmotic pressure effect, while the inhibitory effect and its mechanisms induced by ion composition are poorly understood. In this study, the individual and combined effect of NaCl, KCl and Na2SO4 on FAB (>99% belonging to Ca. Brocadia genera) were systematically investigated by batch tests. The corresponding responses of mRNA abundance of three functional genes (including nitrite reductase gene (nirS), hydrazine synthase gene (hzsB) and hydrazine dehydrogenase gene (hdh)) under different salt conditions were analyzed. The results indicated that NaCl, KCl and Na2SO4 have different inhibition effects, with the 50% inhibition at 0.106, 0.096 and 0.063 M, respectively. The combined inhibition of NaCl+KCl and NaCl+Na2SO4 on FAB were both synergistic; while the combined inhibition of NaCl+KCl+Na2SO4 was additive. The responses of mRNA (of genes: nirS, hzsB and hdh) suggested NaCl inhibited the transport of ammonium; Na2SO4 inhibited both nitrite and ammonium transport; high salinity inhibited functional enzyme activity. These results suggest both ionic stress and ion composition contributed to the observed inhibition.

Foveal macular pigment dip in offspring of age-related macular degeneration patients is inversely associated with omega-3 index.

BACKGROUND: Offspring of parent(s) with age-related macular degeneration (AMD) have a 45% lifetime risk of developing the disease. High foveal macular pigment optical density (MPOD) is protective, whereas individuals with a "foveal macular pigment dip" (FMPD) are at increased risk. Shortage of the dietary carotenoids lutein, zeaxanthin as well as fish consumption are reported AMD risk factors. This Early Biomarkers of AMD (EBAMD) study evaluates serum factors that protect foveal MPOD architecture in Caucasian offspring of parent(s) with AMD. METHODS: N = 130 subjects [mean (SD) age 62.8 (8.6) years; 36/94 male/female] were recruited from Scripps Health/ Scripps Memorial Hospital/ Scripps Mericos Eye Institute between 2012 and 2017. Macula pigment 3D topography was evaluated using specular reflectance. Buccal genetic cheek swab, circulating serum dietary carotenoids and long-term RBC omega-3 fatty acid status, as well as common secondary clinical structural and vision function parameters were obtained. RESULTS: 41 % of offspring of AMD parent(s) presented with FMPD. These offspring were about 4 years younger than those without FMPD (controls; P = 0.012) and had thinner foveas (P = 0.010). There were no differences in gender, BMI, % body fat, visual acuity or contrast sensitivity between those with and without FMPD. % RBC membrane docosahexaenoic acid (DHA) was reduced in FMPD offspring vs. control offspring (P = 0.04). The Omega-3 Index was significantly decreased in the FMPD group (P = 0.03). CONCLUSIONS: The percentage of FMPD in AMD offspring is nearly twice that reported for the general population in the scientific literature. Offspring presenting FMPD had similar AMD genetic risk, but significantly reduced % RBC membrane omega-3 fatty acids and thinner foveas compared with those without FMPD. Our data supports the importance of 'essential fatty' acids as an independent AMD risk factor.

Designing for effective controlled release in agricultural products: new insights into the complex nature of the polymer-active agent relationship and implications for use.

BACKGROUND: Various active chemical agents, such as soil microbial inhibitors, are commonly applied to agricultural landscapes to optimize plant yields or minimize unwanted chemical transformations. Dicyandiamide (DCD) is a common nitrification inhibitor. However, it rapidly decomposes under warm and wet conditions, losing effectiveness in the process. Blending DCD with an encapsulating polymer matrix could help overcome this challenge and slow its release. Here, we encapsulated DCD in a biodegradable matrix of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and investigated the effects of DCD crystal size and loading rates on release rates. RESULTS: Three DCD crystal size fractions (0-106, 106-250 and 250-420 µm) were blended with PHBV at 200, 400, 600 and 800 gkg-1 loadings through extrusion processing and release kinetics were studied in water over 8 weeks. For loadings ≥ 600 g kg-1 , more than 95% release was reached within the first 7 days. By contrast, at 200 g kg-1 loading only 10%, 36% and 57% of the DCD was mobilized after 8 weeks in water for 0 to 106 µm, 106 to 250 µm and 250 to 420 µm crystal size fractions, respectively. CONCLUSION: The lower percolation threshold for this combination of materials lies between 200 and 400 g kg-1 DCD loading. The grind size fraction of DCD significantly affects the quantity of burst release from the surface of the pellet, particularly below the lower percolation threshold. The results presented here are likely translatable to the encapsulation and release of other crystalline materials from hydrophobic polymer matrices used in controlled release formulations, such as fertilizers, herbicides and pesticides. © 2020 Society of Chemical Industry.

Individual and combined effect of salinity and nitrite on freshwater Anammox bacteria (FAB).

Anaerobic ammonium oxidation (Anammox) based technology has potential for nitrogen removal from wastewater with high salinity, but both salt and nitrite (a substrate for Anammox) have negative effect on microbial activity. In order to achieve Anammox in saline wastewater treatment, it is essential to understand the combined effect of these two components. In this study, the individual and combined effect of salinity and nitrite on fixed film freshwater Anammox bacteria (FAB, mainly belonging to the Ca. Brocadia genus), enriched on carriers from a 1500 L pilot scale one-stage (PN/Anammox) moving bed bioreactor (MBBR), were systematically investigated by 57 pre-designed batch tests. The combined inhibition of nitrite and salinity was determined by comparing with additive and independent inhibition models. With salinity only, the specific Anammox activity (SAA) decreased with increasing salinity: 14.6 mS/cm (about 9.1 g NaCl/L) of salinity caused 50% inhibition (IC50). With nitrite only, SAA started to decrease when nitrite concentration was above 450 mg N/L (threshold) and decreased with increased nitrite (IC50 = 666 mg N/L) thereafter. Significantly, when both salinity and nitrite were elevated, both the threshold and IC50 of nitrite were reduced, with inhibition enhanced. Analysis showed that at high salinity (>14.6 mS/cm) and nitrite concentration (>666 mg N/L), inhibition was close to that predicted by simulation of additive and independent inhibition models. Within a salinity range of 4-14.6 mS/cm and nitrite concentration range of 50-666 mg N/L, the combined inhibition was more severe than prediction (p < 0.05) based on the additive and independent inhibition models and therefore it was determined to be synergistic inhibition.

Silica fouling during groundwater RO treatment: The effect of colloids' radius of curvature on dissolution and polymerisation.

Silica fouling during groundwater reverse osmosis (RO) treatment can have a significant impact on filtration performance. To better understand this phenomenon, the equilibrium kinetics of amorphous colloidal silica were studied at conditions relevant to RO of silica-rich alkaline groundwater. The impact of particle size was investigated using synthetic monodisperse silica nanoparticles. Bench scale experiments were conducted by monitoring dissolved silica concentration of aqueous suspensions of colloids of 100 and 300 nm diameter and pH 8.5 to 9.5. The equilibrium data was determined from existing established rate law equations. This study concluded that surface energy has a major impact on silica dissolution rate constant, particularly for colloidal silica. Observations of Ostwald ripening in bidisperse silica dispersions further confirmed these results, which indicate that dissolution and redeposition is responsible for the problematic silica fouling behaviour during RO treatment. 2D modelling based on inferred equilibrium data allows visualization of scale layer growth in agreement with cross-sectional scanning electron micrographs of autopsied membranes.

Thermophilic production of poly(3-hydroxybutyrate-co-3-hydrovalerate) by a mixed methane-utilizing culture.

The production of polyhydroxyalkanoates (PHAs) from methane is limited to mesophiles and thus suffers from high energy requirements for cooling. To address this issue, the use of thermophilic processes is gaining interest, as this strategy may deliver improved economic feasibility for PHA production. This study reports the first thermophilic PHA-producing culture grown on methane at 55 °C in fill-and-draw batch reactors. Harvested cells were incubated with various combinations of methane, propionic acid and valeric acid to assess their capacity for the synthesis of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Only PHB was produced when fed with methane alone. The addition of odd-carbon-number fatty acids resulted in higher PHA content with 3 HV fractions in the range of 15-99 mol%, depending on the types of fatty acids added. Acetic acid addition enhanced the synthesis of 3HB monomer, but not of 3 HV. On increasing the temperature to 58 °C, PHA productivity was not significantly affected.

The rate of biodegradation of PHA bioplastics in the marine environment: A meta-study.

There is a reasonably extensive body of literature recording mass loss of polyhydroxyalkanoates (PHAs) (a class of biodegradable plastics) in the natural marine environment. However, to date, this research has been very disparate. Thus, it remains unclear what the timeframe for the biodegradation of such marine biodegradable plastics actually is. The aim of this work was to determine the rate of biodegradation of PHA in the marine environment and apply this to the lifetime estimation of PHA products. This provides the clarification required as to what 'marine biodegradation of PHA' means in practicality and allows the risks and benefits of using PHA to be transparently discussed. It was determined that the mean rate of biodegradation of PHA in the marine environment is 0.04-0.09 mg·day-1·cm-2 (p = 0.05) and that, for example, a PHA water bottle could be expected to take between 1.5 and 3.5 years to completely biodegrade.