| 摘要 |
<p>In order to convert sewage sludge into fertilizer it is first dehydrated in settling-tanks to a water content of about 70 to 80 per cent, then in the air or by admixture with drying substances, such as peat, wool dust, hair waste, straw, plant refuse or the previously prepared finished product, to a water content of about 40 to 50 per cent, and then stacked loosely in heaps so that it becomes heated to 90 DEG C. and dried to a water content of 6 to 10 per cent, the product being finally finely disintegrated. Fresh layers of the sludge are superposed in the heaps in such a way that no compression of the fresh layers preventing abundant access of air takes place. The bottom of each settling-tank is formed on a gradient and covered with a layer of porous sand, below which clarified water is drawn off through a slide plate or gate. Water which separates above is drawn off over a slide plate acting as a weir. The liquid in the settling-tanks is covered with dry peat mould which sinks as it becomes saturated, the covering being renewed daily.</p> |
