Evaluation of leached metals in recovered aluminum coagulants from water treatment slurry

The water treatment industry consumes large quantities of coagulant and produces huge amounts of slurry. The cost of alum used in water treatment, stringent regulations and negative impacts of sludge disposal are the motive to do integrated research studies on the technical feasibility of aluminum coagulant recovery from sludge using acidification. This work studied the leaching of iron, manganese, and chromium as the most extracted metals with aluminum during sludge acidification; furthermore, these metals have a great impact on the recovered coagulants' efficiency and treated water quality. The sludge used was collected from El-Sheikh Zayd water treatment plant in Egypt, then dried and ground; afterward, the effect of acid concentration, sludge mass, temperature, mixing speed and mixing time was studied. In addition, it was noticeable that the efficiency of sulfuric acid in leaching iron, manganese and chromium is higher than that of hydrochloric acid. Also, higher leaching for the three metals was obtained in all the experiments using higher acid concentration, elevated temperature, and rotational speed. Finally, the leached metals in recovered aluminum coagulants will not limit its application to water and wastewater treatment, as their concentrations are still very low if compared with aluminum, even with the highest leaching efficiency.

High Efficiency Aluminum Coagulant Recovery from Drinking Water Treatment Plant Sludge by Using Ultrasound Assisted Acidification

In this study, a novel combination of ultrasound with acid for coagulant recovery from drinking water treatment plant sludge (DWTPS) is investigated in view of improving the coagulant recovery efficiencies. Optimal recovery conditions, a sulfuric acid concentration of 2.0 M, an ultrasonic treatment time of 30 minutes, an ultrasound power of 1000 W and stirring speed of 1000 rpm, have been found in the lab test. The aluminum recovery rates from acidification process with assistance of ultrasound increased by approximately 20% compared with that of acidification only. It was found that the synergistic effects between acid with ultrasound contribute to improving the treatment efficiency.