Site Surveys

A complete survey of industrial operations is essential for any individual site before an economical waste-treatment programme can be planned. It is desirable to divide the facility into as many units as possible, as knowledge of the various material streams may show unexpected losses of finished product, solvent wastage, excessive use of water or unnecessary contamination of water which might be recycled, recovered or reused within the site. The factors, and concentrations where appropriate, listed in Table 11.1 ought to be known at all production rates under which an individual unit may operate in a representative time period.

The survey may indicate a need for better control of water usage and should identify sources of uncontami-nated and contaminated water that might be reused in the factory. Concentrated waste streams should be kept separate if they contain materials that can be profitably vercd. It is also often more economical to treat a ^ncentrate rather than a large volume of a dilute Affluent because of the saving on pumps and settling ^nk capacities, provided that concentrations do not reach toxic or inhibitory levels in biological treatment processes.

The various wastes may be tested in a laboratory and on a pilot scale to assess the best potential methods of chemical and biological treatment. Once the pHs of the Affluents are known, samples may be mixed to see if a neutral pH is reached. A variety of tests may be used to establish methods for reducing salt concentrations, coagulating suspended particles and colloidal materials, and for breaking emulsions.

The commonly used biological tests include respirometry, aeration-flask tests (Otto et al., 1962) and continuous-culture experiments. Small flask respirome-ters (Warburg or Gilson) and oxygen electrodes are used initially to establish the conditions to use in bio-oxidation of the effluent, and to test for the presence of toxic materials. Large respirometers (Simpson and Anderson, 1967) are useful for predicting effluent treatment rates and oxygen requirements. The residues in the flasks can be analysed to see if there are any recalcitrant materials. The use of laboratory continuous-culture vessels fitted with sludge-return pumps and settling tanks can provide detailed information (Ramathan and Gaudy, 1969). Proposed large-scale operating conditions for feed and aeration rates can be tested and their effectiveness assessed. The results from all these experiments may help in the design of a full-scale plant.

If the survey is comprehensive it should be possible to plan an overall treatment programme for a site and to establish:

1. Water sources which can be combined or reused.

2. Concentrated waste streams which contain valuable wastes to be recovered as food, animal feed, fertilizer or fuel.

3. Toxic effluents needing special treatment, or acids or alkalis needing neutralization.

4. The effluent loading expected under maximum production conditions.

5. The effluent(s) which might be discharged directly, without treatment, on to land or to a watercourse and not cause any pollution.

6. The effluent(s) which might be discharged into municipal sewers.

When all the relevant information has been obtained one can predict the size and type of effluent treatment plant required, and thus its capital and operational costs. This can then be compared with water company charges to treat the waste at an STW with and without on-site treatment. It should be remembered that the water company may insist on on-site treatment before a waste is discharged to the sewer, and will in most cases set consent limits for maximum flow rates and concentrations of specific analytes.

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