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Sewage Sludge (Use In Agriculture)

Volume 387: debated on Tuesday 16 March 1943

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asked the Minister of Agriculture whether he is now able to issue a statement on the production and use of sewage sludge as compost or otherwise?

I have now received, through the Agricultural Improvement Council for England and Wales, an interim report from the Agricultural Research Council based on investigations that have been in progress for the last two or three years. The present position may be summarised as follows: Certain types of sewage sludge, when not contaminated with injurious industrial effluents, have definite, though limited, value as a form of organic manure. Their main value is as a source of nitrogen, since most of the potash and phosphate in the raw sewage is inevitably lost. Sludges also have value on account of their content in organic material, but it is less than that of farmyard manure. The use of these sludges for manurial purposes has greatly increased during the war: but there are still large supplies in many districts of which no agricultural use is being made, and it is clearly desirable that this waste should be avoided provided that the limitations of the material are realised. It may therefore be concluded that the production and use of suitable types of dried sewage sludge—that is to say, of sludge free from injurious constituents—should be encouraged within the limitations imposed by the difficulties of transport: and supply of materials for the construction of sewage disposal plants other than those of a relatively simple character.

Consideration has also been given to the use of composts prepared from sludge and town refuse. Composts of this kind have been tested in a large number of trials, and have sometimes, though by no means invariably, given promising results. One of the great difficulties is that town refuse is a very variable material; and the more efficient our wartime salvage becomes the less does the final refuse contribute to plant nutrition. In these circumstances, it is clearly not desirable, at the present time, that material and labour should be devoted to the construction of new plants that would be required to make composts of this type available on an extended scale. The Agricultural Research and Improvement Councils have called attention to the possibility of composting sewage sludge with straw; and, at my request, they are actively pursuing inquiries along these lines. If this procedure proves successful, either by composting at the sewage works or on the farm, it would have the great advantage of returning the surplus straw to the land, together with its natural content of potash and lingnin. Similar trials are in progress using sawdust in place of straw; but it seems probable that the advantages will lie with straw. Any practical conclusions from these inquiries will be issued as and when they become available, but no results can be expected until after the end of the present cropping season.