GB1431541A - Control of sewage treatment - Google Patents

Abstract

1431541 Photo-electric measuring method ENGLISH CLAYS LOVERING POCHIN & CO Ltd 22 March 1973 [22 Dec 1971] 59798/71 Heading G1A The settling rate of suspended solid matter in a sewage liquid is determined by introducing thoroughly mixed sewage liquid into a container, stopping the flow of liquid into the container and allowing the solid matter to settle, and measuring photo-electrically either the time taken for the interface formed between the settling solid matter and the supernatant liquid to descend a known vertical distance after the flow has been stopped or the distance descended by the interface after a predetermined period of time has elapsed from the cessation of flow. In the first alternative, the flow is stopped when the liquid reaches a first level and a horizontal beam of light is projected into the liquid at a second level, a known distance below the first level, which beam is transmitted or reflected to at least one photo-electric device, the passing of the interface through the second level producing a change in output of the photo-electric device. The time taken for the interface to fall from the first level or a known third level between the first and second levels, to the second level is measured. Alternatively, a light source and photo-electric detector are arranged above the liquid level in the container so that light reflected from the interface produces a change in output of the detector when it falls to the second level. In both embodiments, the passage of the interface through the upper level is measured photo-electrically. In the second alternative, a plurality of sources and detectors are arranged vertically relative to the container so that the distance descended by the interface may be determined. In one embodiment of the apparatus, Figs. 2a, 2b and 3 (not shown), the container is cylindrical with its axis horizontal, the container being provided with an inlet, an outlet and an overflow. Light is projected into the container through a window, reflected light being transmitted through the same window to a photo-cell. A parameter of a continuous process for treating sewage liquid is controlled by measuring, by one of the methods described, the settling rates of a series of samples of sewage liquid of known and different solid concentrations, monitoring continuously or intermittently the solids concentration of the sewage liquid during its treatment by measuring the settling rate by one of the methods described, comparing the measurements obtained with the known values, and adjusting the parameter, e.g. aeration, accordingly.