Which physical problems do you think may be caused by suspended solids?
1. They cut down light transmission through the water and so lower the rate of photosynthesis in plants.
2. In less turbulent parts of the river some of the solids may sediment out, thus smothering life on the river bed.
You may have guessed that the analysis of suspended solids is by filtration and weighing but you may not realize the laboratory skill which is required until you discover that a typical suspended solid loading for a clean looking stream would be only a few mg l-1. Even sewage discharges in the UK have to conform to conditions with a maximum of 30 mg l-1 (after 10-fold dilution of the discharge). Typically, a glass fibre filter disc with a 1.6 ^m pore size would be used with a Hartley filter funnel (Figure 3.5). The paper is clamped inside the funnel to prevent any part of the sample escaping around the side of the filter.
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