Preparation and evaluation of biocide-loaded particles to control the biofouling zebra mussel, Dreissena polymorpha

The freshwater zebra mussel Dreissena polymorpha is a powerful biofouling bivalve, which has tremendous impact on industrial facilities whose operation depends on the intensive use of freshwater, such as waterworks and power stations. The control of the pest in industrial environments remains a major challenge due to low selectivity over non-target organisms and the expense of the large quantities of biocides required. A novel delivery technique involving the encapsulation of a toxin within hundred micron-sized particles, edible for the bivalves, has been recently proposed. This strategy exploits the mussels’ filtration activity and minimises their avoidance responses to certain chemicals, resulting in an increase of their susceptibility to the biocide. In the present paper, which further develops this approach, a new, promising toxin-loaded particulate formulation is presented. The effectiveness of the product as a molluscicide has been demonstrated in laboratory bioassays. Encapsulation was observed to reduce the amount of biocide required to achieve 90% mortality in a 12-h treatment by a factor of approximately three. The dependence of the biocide-loaded particles’ molluscicidal activity on their physical characteristics is also illustrated in this paper by comparing the features of the promising formulation to those of an unsuccessful particulate product.     

THE INCREASING EFFECTS OF ZEBRA MUSSELS ON WATER INSTALLATIONS IN ENGLAND

The zebra mussel, Dreissena polymorpha, is a major biofouling pest of water treatment works, irrigation systems and power stations in Europe and North America. This paper documents current problems associated with zebra mussels in English waterworks. Questionnaires and manual surveys conducted between 2001 and 2003 have revealed that over 30 water treatment works in England suffer problems associated with zebra mussels. Hundreds of tonnes of mussels are being removed each year from raw water intakes, pipelines and reservoirs. Problems have increased in. the last five years, due to a spread in the range of zebra mussels around England and the cessation of chemical treatment at the intakes of many treatment facilities during the 1990s. The importance of taking control of zebra mussels into account in planning new water supply schemes is highlighted.     

通过化工产品工程开发可持续的技术来控制斑纹蚌种群

The zebra mussel is an important aquatic pest that causes great damage to freshwater-dependent industries, due to biofouling. The main goal of the project discussed here is to develop improved solutions to control this species. Three approaches have been explored in an attempt to design innovative application strategies for existing biocides： （i） encapsulation of toxins; （ii） combination of toxins; （iii） investigation of the seasonal variation of the species＇ tolerance to toxins. In this paper, the principles behind these approaches and the major results on each topic are presented. The benefits of adopting a chemical product engineering approach in conducting this project are also discussed.     

Evolution of cake batter bubble structure and rheology during planetary mixing

The incorporation of air into a high ratio cake batter by planetary mixing was studied using two bench mixers, a Kenwood KM250 and a Hobart-N50. Power draw (expressed as specific mechanical power input) and air volume fraction, ?, were monitored over time for batters prepared in each mixer for heat-treated and un-treated cake flours. The two flour types gave very similar results, indicating that the benefit of heat treatment for cake manufacture is manifested during the baking step. Both mixers gave a rapid initial increase in ? up to ～0.50 followed by a gradual decay. Bubble size distributions of batters prepared in the Hobart showed the initial aeration stage to be accompanied by the formation of a large number of small bubbles, with diameters around 5 μm: the average bubble size increased and number of bubbles decreased with extended mixing. Batters prepared without emulsifier exhibited a steady increase in ? to a plateau at ～0.2 and contained larger bubbles which did not change in average size significantly over time. All batters exhibited power-law shear-thinning behaviour with power law indices and consistency strongly dependent on ?. At low shear rates, the apparent viscosity showed the non-linear dependency on ? expected for dense suspensions. At higher shear rates, elastic forces generated by the bubble phase became significant. The non-Newtonian nature of the liquid phase and the elasticity generated by the bubbles meant that shear-thinning and bubble break-up could not be predicted by analyses based on the capillary number. The results support a qualitative model of bubble formation and break-up caused by extensional deformation generated by shearing these bubbly liquids: the bubbles cream out slowly owing to the high viscosity of the continuous phase at rest.     

Biofouling by bryozoans, Cordylophora and sponges in UK water treatment works

In recent years biofouling from native (bryozoans, sponges) and non-native (Cordylophora) animals has increased in UK water treatment works (WTW). A survey of six UK water companies and eight WTWs revealed that these taxa were more widespread and abundant than previously recognised. Primary problems related to the occlusion of underfloor nozzles and tailpipes in rapid gravity filter beds (RGFs). These cost the UK water industry pound 1.49 m between 2005 and 2009. Additional impacts came from skin irritation to operatives from sponge spicules and the potential for elevated bacterial pathogen levels. Sponges penetrated the furthest through the water treatment process, reaching the point of final chlorination at one WTW. A monitoring plate study showed pronounced seasonality in fouling, with most taxa peaking in mid to late summer before a winter die-off. Control options, including the use of chlorine, and the importance of resistant stages for each taxon are discussed.     

Solid–liquid transitions in the rheology of a structured yeast extract paste, Marmite™

The rheology of Marmite™, a popular yeast extract spread, was studied using a range of techniques. Steady-state data indicated a structured, thixotropic material at ambient temperature; the extent of breakdown and restructuring exhibited a dependence on both stress and strain. At higher temperatures the extent of thixotropy decreased and behaviour approached Newtonian. Non-steady-state data indicated a period of shear-thickening at shear rates below those at which shear-thinning occurs. Creep tests indicated a transition between solid and liquid regimes at a critical stress that is a strong function of the solids content of the sample. A ‘true’ yield stress was not found although this may be related to the limits of the region which could be accessed experimentally.     

The impacts of ‘run‐of‐river’ hydropower on the physical and ecological condition of rivers

This paper synthesises published literature on run‐of‐river hydropower, highlighting its potential to affect both the physical and ecological conditions of river systems. The paper considers the limited number of direct studies and reviews a wider literature on the two principal impacts of such schemes on river systems: the introduction or maintenance of in‐channel barriers and water abstraction/flow regime alteration. We outline how river systems are likely to be impacted by such schemes and identify the key issues arising from their continued development. Potential mitigation approaches are highlighted and the areas of future research required to adequately address current knowledge gaps are identified.     

Prediction of binary diffusion coefficients in non-ideal mixtures from NMR data: Hexane–nitrobenzene near its consolute point

Pulsed field gradient nuclear magnetic resonance was used to measure the tracer diffusivity of the species in mixtures of nitrobenzene and n-hexane close to the consolute point. Measurements are reported over the full range of composition at 21 °C (the consolute temperature is 19.4 °C), and at several compositions including the consolute composition (x₁=0.422) over the range 21–35 °C. These NMR-derived tracer diffusivities are compared with literature values for the binary diffusion coefficient under the same conditions. It is shown that it is possible to calculate the binary diffusion coefficient, even very close to the consolute point, from the NMR-derived tracer diffusivities using a fairly simple thermodynamic correction factor, of a form similar to those reported in the literature based on critical point scaling laws. The necessary thermodynamic parameters are calculated by fitting vapour–liquid equilibrium data for the system under the same conditions, which is available in the literature. The ability to predict binary diffusion coefficients from NMR measurements has significant potential, for example in studying mass transport in porous solids or packed beds, situations where conventional diffusion measurements are impossible to make.