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The current study was carried out through three main phases. In Phase I, sampling, preparation, and characterization of sludge were done. In Phase II, the recovery of aluminum from sludge was applied using hydrochloric acid. Six different parameters that affect the recovery process were studied. The optimum values of the recovery parameters were applied to obtain a solution that had the best recovery of aluminum, then characterized and tested in water clarification and compared with the virgin coagulant (aluminum sulfate). In Phase III, sequential coagulant recovery from sludge using hydrochloric acid was evaluated. To sum up the experimental work phases and experiments, Table 1 was designed to provide a summary of the experimental steps carried out throughout the research.

Table 1

Summary of experimental phases and steps

ExperimentDescription
Phase I: Sludge sampling, preparation, and characterization 
Experiment 1: Sludge sampling and preparation Includes the methods used in sampling and preparation of sludge from ESZ-WTP before recovery 
Experiment 2: Sludge characterization This section exhibits a detailed illustration of the characterization of sludge showing different analytical techniques used 
Phase II: Aluminum recovery, coagulant preparation, and characterization 
Phase II, Part I: Aluminum recovery using hydrochloric acid 
Experiment 1: Effect of hydrochloric acid concentrations Various concentrations of hydrochloric acid were used to estimate the effect of acid concentration on the recovery efficiency of aluminum with fixing other conditions to constant values 
Experiment 2: Aluminum recovery at different masses of sludge Applying fixed conditions from temperature, rotational speed, acid concentration, and time, different sludge weights were used to evaluate its impact on aluminum recovery 
Experiment 3: Effect of mixing time By using constant values for other conditions, various mixing times were used to test its effect on the aluminum recovery 
Experiment 4: Effect of temperature Three different temperatures were used with constant values for other conditions to evaluate the effect of temperature on the recovery rate of aluminum coagulant 
Experiment 5: Effect of mixing speed Different mixing speeds were used to test its effect on aluminum leaching by stabilizing other conditions 
Phase II, Part II: Testing the recovered coagulant solution 
Experiment 1: Preparation of a coagulant solution from alum sludge using hydrochloric acid In this experiment, optimum conditions obtained from the above experiments were used to prepare coagulant solution 
Experiment 2: Evaluation of the recovered coagulant solution in water clarification In this step, the recovered coagulant was applied to the raw water of ESZ-WTP to evaluate its efficiency in clarification of water versus a commercial one 
Phase III: Evaluation of sequential recovery using hydrochloric acid 
Experiment 1: Evaluation of virgin coagulant and proceeding first recovery In this experiment, fresh coagulant was applied to raw water in ESZ-WTP and the resulting water analyzed to evaluate the coagulant. Afterwards, the sludge produced underwent recovery using the optimum conditions obtained through the experiments in Phase II, Part I 
Experiment 2: Evaluation of first recovered coagulants and proceeding second recovery The same as Experiment 1, Phase III but starting with applying the first recovered coagulant to the raw water and the produced water was analyzed then the sludge used to produce the second recovered coagulant 
Experiment 3: Evaluation of second recovered coagulants and proceeding third recovery The same as Experiments 1 and 2, Phase III but starting with applying the second recovered coagulant to the raw water and the produced water was analyzed then the sludge used to produce the third recovered coagulant 
Experiment 4: Evaluation of third recovered coagulants The same as Experiments 1, 2 and 3, Phase III but applying the third recovered coagulant to the raw water and the produced water analyzed to evaluate its efficiency in clarification of water 
ExperimentDescription
Phase I: Sludge sampling, preparation, and characterization 
Experiment 1: Sludge sampling and preparation Includes the methods used in sampling and preparation of sludge from ESZ-WTP before recovery 
Experiment 2: Sludge characterization This section exhibits a detailed illustration of the characterization of sludge showing different analytical techniques used 
Phase II: Aluminum recovery, coagulant preparation, and characterization 
Phase II, Part I: Aluminum recovery using hydrochloric acid 
Experiment 1: Effect of hydrochloric acid concentrations Various concentrations of hydrochloric acid were used to estimate the effect of acid concentration on the recovery efficiency of aluminum with fixing other conditions to constant values 
Experiment 2: Aluminum recovery at different masses of sludge Applying fixed conditions from temperature, rotational speed, acid concentration, and time, different sludge weights were used to evaluate its impact on aluminum recovery 
Experiment 3: Effect of mixing time By using constant values for other conditions, various mixing times were used to test its effect on the aluminum recovery 
Experiment 4: Effect of temperature Three different temperatures were used with constant values for other conditions to evaluate the effect of temperature on the recovery rate of aluminum coagulant 
Experiment 5: Effect of mixing speed Different mixing speeds were used to test its effect on aluminum leaching by stabilizing other conditions 
Phase II, Part II: Testing the recovered coagulant solution 
Experiment 1: Preparation of a coagulant solution from alum sludge using hydrochloric acid In this experiment, optimum conditions obtained from the above experiments were used to prepare coagulant solution 
Experiment 2: Evaluation of the recovered coagulant solution in water clarification In this step, the recovered coagulant was applied to the raw water of ESZ-WTP to evaluate its efficiency in clarification of water versus a commercial one 
Phase III: Evaluation of sequential recovery using hydrochloric acid 
Experiment 1: Evaluation of virgin coagulant and proceeding first recovery In this experiment, fresh coagulant was applied to raw water in ESZ-WTP and the resulting water analyzed to evaluate the coagulant. Afterwards, the sludge produced underwent recovery using the optimum conditions obtained through the experiments in Phase II, Part I 
Experiment 2: Evaluation of first recovered coagulants and proceeding second recovery The same as Experiment 1, Phase III but starting with applying the first recovered coagulant to the raw water and the produced water was analyzed then the sludge used to produce the second recovered coagulant 
Experiment 3: Evaluation of second recovered coagulants and proceeding third recovery The same as Experiments 1 and 2, Phase III but starting with applying the second recovered coagulant to the raw water and the produced water was analyzed then the sludge used to produce the third recovered coagulant 
Experiment 4: Evaluation of third recovered coagulants The same as Experiments 1, 2 and 3, Phase III but applying the third recovered coagulant to the raw water and the produced water analyzed to evaluate its efficiency in clarification of water 

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