Abstract: A sensor module for monitoring chemical properties of oil well fluids comprises at least one electrochemical sensor for a chemcal species, for example to detect pH and chloride ion concentration. A micro-porous barrier separates the electrochemical sensors from the environment of the module, the micro-porous barrier being of a material which is readily wetted by water. Periodic application of a current pulse between the barrier and a counter electrode enables fouling material to be removed from the micron barrier.

Abstract: A filter which can be cleaned in situ consists of a filter membrane (33), and fluid permeable electrodes (34, 35). The membrane may be one of the electrodes, or may be electrically non-conducting but integral with or in contact with one of the electrodes (34). The electrodes (34, 35) are separated from each other only by a fluid permeable electrically insulating sheet. This sheet may be less than 1 mm thick, and may be the filter membrane (33). The filter is cleaned by periodic brief applications of electric current between the electrodes (34, 35) so that gas is generated electrolytically, and the close spacing of the electrodes (34, 35) reduces the electric power required.

Abstract: A radioactive waste stream (12) is of high pH and contains a wide variety of different fission products and also organic materials which act as complexants. Technetium and/or ruthenium are removed by first electrolytically oxidising the organic materials at an anodically stable anode (26), and then electrolytically reducing the technetium and/or ruthenium at a porous fluid-permeable cathode (42). The cathode (42) might for example be of lead wool.