A STUDY OF THE INFLUENCE OF CRACKING ON WASTEWATER SLUDGE DRYING BEHAVIOUR / Sprickbildningens inverkan på slamtorkningsförloppet
Aerobically digested mixed biological and aluminium precipitated sludge with an initial total solids content of ca 5 % was tested on 5 pilot sand drying beds indoors. The test run continued for 84 days in a controlled environment, with a relative humidity of 30—40 % and a temperature of 24-27°C. The results showed that:
— Dewatering to a final Total Solids content of 50 % could be performed in 5 to 8 weeks depending on the initial sludge layer thickness.
— Spontaneous or artificial vertical sludge layer cracks down to an 0.15 • 0.15 m grid size did not increase the rate of evaporation from the horizontal upper sludge layer.
— The specific dewatering rate measured as grams of water per m2 of sludge and day dewatered to 50 % total solids was constant at initial sludge layer thicknesses between 187 and 335 mm. Thus, optimizing the initial sludge thickness must be based on local conditions.
— The inner diffusion resistance of the sludge layers was probably of minor importance during most of the drying time.