The rapid darkening of hydraulic oils and fluids in use has occasionally been reported. This paper summarizes the past investigations into this phenomenon, which have largely focused on the compression of air bubbles in mineral hydraulic oil. The process leads to a form of high temperature degradation known as dieseling and the probable formation of sub-micron carbonaceous particles. The importance of system design and particularly the choice of pumps, in this process, are discussed. The primary objective, however, is to examine the effects of dieseling on phosphate ester fire-resistant fluids and to clarify if an analysis of the used fluid can indicate whether this process is taking place. An investigation of samples taken from systems displaying rapid degradation suggests that the presence of certain breakdown products may infer the approximate level of temperature to which, at least, small amounts of the fluid are being subjected. The presence of carbonaceous material in the dieseling process is also confirmed. Some suggestions made for the mechanism of its formation as well as the formation of other major degradation products. Lastly, recommendations are made for ways of minimizing this form of breakdown not only in terms of system design but also with respect to fluid properties, fluid maintenance and the use of in-situ conditioning.

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Anaerobic degradation of TNT and TNB in gravel systems was rapid and similar to removal rates in parrot feather lagoons. Planted and unplanted anaerobic gravel systems were the only treatments that provided significant reduction of RDX and HMX. Planted systems with parrot feather had no effect on removal rates of explosives in anaerobic gravel systems. Reciprocating wetlands were not effective in biodegrading RDX or HMX, but were very efficient at removing COD. A scaled-up concept for bioremediating contaminated groundwater can be envisioned with the data obtained in the current study. The effectiveness of anaerobic gravel systems indicate an anaerobic subsurface-flow constructed wetland can be established as the primary treatment for remediation with C added to the influent or step fed down the length of the wetland. Another option would be to add compost as a more permanent source of C to the gravel substrate. With time, the need for C supplementation may be reduced with the C exudates and redox lowering potential of certain plants like canarygrass (Phalaris arundinacea). As a secondary treatment, a reciprocating wetland would appear to be a logical choice to quickly remove C released in effluent waters of the anaerobic wetland.

When assessing the cleanliness of industrial hydraulic fluids, current procedures focus on particles above 4 µm in size. However, the use of more sophisticated techniques has confirmed that substantial numbers of much smaller particles can be formed in use — mainly by high‐temperature degradation processes. The paper outlines the mechanisms for fine particle generation and procedures for their measurement and control. Significant quantities can adversely affect fluid surface‐active properties and hinder the operation of system components. The effect of flow electrification or applied electrical fields to assist filtration is also discussed. The paper suggests that residual charge could stabilise particle dispersions, assist the depletion of dispersed anti‐foam particles and affect foam stability. An extension of the ISO 4406 cleanliness code to quantify the presence of fine particulate is recommended as is the need for further work to investigate the limits that should be placed on their presence in different applications. Copyright © 2015 John Wiley & Sons, Ltd.