Application of Natural Wastes to Improve Settleability Properties of Activated Sludge

Document Type : Research Paper


1 Graduate of Environmental Eng., Dept. of Civil Engineering, Isfahan University of Technology

2 Prof., Civil Eng. Dept., Isfahan University of Technology,


Sludge volume index (SVI) and zone settling velocity (ZSV) are parameters to quantify the settleability of activated sludge. Natural wastes commonly enter the environment as useless material. The assessment of the influence these materials have on activated sludge settleability was the principal objective of this research. Natural wastes used included: maize stalk, almond shell, coconut shell, walnut shell, hazelnut shell, egg shell, peanut hull, and pine bark. The experiments were conducted in five stages and three iterations, based on the standard methods. Average values of SVI for the control (blank) sample was 823 mL/g. The optimum dosage of different natural wastes reduced SVI value to 100 mL/g (88 percent decrease). The average value of ZSV for the control (blank) sample was 1.222 m/h and different natural wastes increased ZSV of the control samples by up to 2 to 3 times. With this increase in ZSV, Surface Overflow Rate (SOR) could also be increased without losing its efficiency. Activated sludge return with natural additives caused an improvement in sludge settleability. Jar tests revealed that natural wastes typically act mainly as ballasting agents and to some extent as coagulator which causes a reduction in SVI.


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