On‐line turbidimeters are currently used for monitoring particle concentration in water and gas treatment processes. For small particle concentration, the intensity of scattered light is a linear function of the particle concentration, as long as a number of other parameters are kept constant: the refractive indexes of the particles and the surrounding medium, size, measuring angle and wavelength of the light. An international standard has been created in order to define the characteristics of the turbidimeters and the calibration suspension. The effects of the parameters are described and quantified. The special aspects of the measurement of very low turbidity values in water are treated: the zero value of water and the definition of the calibration conditions. A measuring method is presented which grants long‐term stability without recalibration.  The first industrial application for on‐line turbidimeters was the monitoring of beer filtration in breweries, which started about 50 years ago. In the meantime, turbidimeters have been used in very diversified fields such as dust measurements in stacks, visibility in road tunnels and filtration control in the chemical industry. However, their main application today is the monitoring of drinking water treatment plants: control of the flocculation process by measuring the variations in the raw water (rivers, lakes, ground‐water, sources) and the resulting properties, sand filtration survey and final quality control.

No abstract

On two occasions in 1995 the effects of severity of conditioning and pressing on the drying rate of Italian (Lolium multi¯orum Lam.; IR) and perennial (Lolium perenne L.; PR) ryegrass were assessed. The cut herbage was either left unconditioned (0C) or conditioned by passing through a laboratory scale macerator three (3C) or six (6C) times after which the herbage was placed into wire mesh trays and either left unpressed (0P) or pressed (P). The twelve treatment combinations (two species´three conditioning levels´two pressings) were replicated three times on each of the two occasions. On each occasion the trays plus herbage were weighed at hourly intervals over an »6-h period and dry matter (DM) of the herbage was estimated from the weight change. Pressing treatment gave, on average, a negative effect on the drying rate of the herbage. Conditioning signi®cantly (P < 0á001) increased the drying rate of the herbage. Compared with 0C herbage, the greatest increase in drying rate was obtained with the 3C treatment; the additional conditioning imposed by the 6C treatment produced only a small further increase in drying rate. Drying constants calculated for each treatment combination showed that IR dried 1á45 times faster than PR and that, compared with 0C, herbage drying rate was 2á18 and 2á38 times greater as a consequence of the 3C and 6C treatments respectively. Pressed (P) herbage dried at a rate of 0á90 of that of the unpressed herbage (0P).

No abstract

No abstract