RECOVERY OF WATER AND ALUM FROM SURFACE WATER TREATMENT SLUDGE

Most of surface Water treatment plants in Egypt discharge its residual sludge into waterways. Such disposal is restricted by the environmental authorities. This study provides an assistance to prevent pollution of waterways by offering a complete treatment of sludge; i.e. reducc, recycle, recover of alum). Giza water treatment plant is the source of raw water and sludge investigated in this study. Composition of sludge depends mainly on raw water quality and dose of coagulants used for treatment. The results of sludge composition analysis indicated that 90 to 95 % of sludge is water. The settled sludge contains 94 to 96 % water while dry solids ranged from 1.5 to 4.3 g/1 with an average 2.86 g/1 sludge. Volatile organic matter ranged from 37.4 to 49.6% with an average 44% from dry solids. Fixed in-organics ranged from 31.5 to 79.6%. Acidification process was applied to the collected sludge in order to recover the consumed alum. The acidified supernatant of wet sludge was used successfully in treating raw water and secured 94.7% of turbidity removal (12 ml equivalent to 29 ml alum). Estimation of sulphuric acid needed to liberate alum from settled sludge showed that 1 m3 of settled sludge requires approximately two liters of 112 So4 (sp-gr-1.8). A recovery process was designed for saving 90 to 95 % of water in sludge by a small thickener. This water (supernatant) could be direc :ed cither to filters or to clarifiers. The settled sludge is directed to a reactor to apply the acidification process. The acidified liquor is then collected, stored, or added as assisting dose to the clariflocculators. The remaining of settled acidified sludge cake is withdrawn and transferred either to landfills, bricks factories, or to alkaline land reform. The cake may be treated for adjusting its pi I for further utilization saving water and money to the limit which may enforce water work authorities to initiate a program in some water treatment plants and stop illegal discharge of sludge.