6. Recommendations

6.1    The Working Party Guidelines (55) appear to be well conceived and it is considered desirable that they should be complied with as soon as is practically possible.

6.2    The Working Party Guidelines (55) should be supplemented with recommended standard methods for sampling and analysis to ensure that they are followed in an adequate and uniform manner. This would permit a body of comparable data to be accumulated, which would assist in subsequent revisions of the guidelines. It is suggested that the recommendations to follow are incorporated into the guidelines for the disposal of sewage sludge to land.

6.2.1 Methods for the sampling of soil, crops and sludges should be stated. (This could be implemented by the use of existing A.D.A.S. and Standing Committee of Analysts methods).

6.2.2    The frequency of sampling of soils, crops and sewage sludge should be stated.

6.2.3    Methods for the analysis of metals and metalloids in soils, crops and sludges, should be stated. (This could be done by the use of existing A.D.A.S. and Standing Committee of Analysts methods).

6.2.4    The frequency of analysis of the individual metals and metalloids should be stated.

6.2.5 Methods of recording and storage of data should be stated. -

6.2.6 A central body should be selected to store, collate and analyse this data (Possibly the DoE).

6.2.7    Responsibility for the sampling and analysis of each type of sample should be delegated. While it is readily accepted that the analysis of additional samples of soil and crops would impose an immense burden on the A.D.A.S., their experience in this area is paramount.

6.3    It is considered particularly important that the recommendations of the Working Party (55) on “Rates of application of elements” are followed. This states that “These total dressings of sludge need not be applied in equal annual increments, but the maximum applied in any one year should not normally exceed one fifth of the total, nor exceed the annual limits for the application of available nitrogen. Following an application of sludge which raises the average rate of application over the recommended maximum long—term average, no further sludge should be added until the running average has fallen to the recommended long—term average”.

6.4    Wherever possible, effort should be directed towards minimising the metal and metalloid content of sewage sludges so that these sludges can be applied to agricultural land with minimal risk to future agricultural production.

6.5    The farmer should be provided with analyses of the nutrient (nitrogen, phosphorus and potassium) and metallic content of sludges. The neutralising value, magnesium concentration and solids content would also be of value.

6.6    The use of cadmium should be discouraged wherever possible. If this metal is essential for an industrial process, it should be removed from any wastewater by appropriate treatment at its source.

6.7    Research into the following topics is urgently required.

6.7.1    As suggested in the Working Party Report (55): “High priority work is required to determine the states of metals in sludges for the interpretation and forecasting of the effects of metals in sludges on soils and crops. This will have to be supported by the determination of the extractability of elements using the extractants employed in soil analyses, and pot and field trials with crops to measure the uptake of elements. Research on extractability is also required to examine the effects of time, of the mixing of sludges and soils, of wetting and drying and of sludge conditioners, particularly iron and aluminium salts”.

6.7.2    Sufficient information on the agricultural value of sewage sludge is not available and it is felt that the research on manurial value suggested in the Working Party Report (55) should be undertaken. “Pot and field tests are necessary to compare the manurial values of sewage sludges, particularly those most commonly utilised, with those of standard fertilisers. The tests should include investigations of nitrogen and phosphorus, and also where appropriate the effects of iron and aluminium compound flocculents on the availability of phosphorus. Trials are required to study the effect of time of application of nitrogen in sludges”.

6.7.3    The toxicity ratios used in the calculation of zinc equivalent values should be re—examined over a period of years on a wider range of crops and on those crops which are most likely to receive a large volume of the current sludge production, namely cereal crops and grass.

6.8    In the light of the re-organisation of the water industry and the publication and general acceptance of the Report of the Working Party on the Disposal of Sewage Sludge to Land; it is recommended that the situation be kept under review and examined in depth when the recommendations of the Working Party (55) have been in operation for several years. After perhaps five years when some results from research field trial and monitoring programmes should be available, the guidelines may be revised and ultimately a code of practice produced.