Abstract
In the present study, a coagulation process was used to treat paper-recycling wastewater with alum coupled with poly aluminum chloride (PACl) as coagulants. The effect of each four factors, viz. the dosages of alum and PACl, pH and chemical oxygen demand (COD), on the treatment efficiency was investigated. The influence of these four parameters was described using response surface methodology under central composite design. The efficiency of reducing turbidity, COD and the sludge volume index (SVI) were considered the responses. The optimum conditions for high treatment efficiency of paper-recycling wastewater under experimental conditions were reached with numerical optimization of coagulant doses and pH, with 1,550 mg/l alum and 1,314 mg/l PACl and 9.5, respectively, where the values for reduction of 80.02 % in COD, 83.23 % in turbidity, and 140 ml/g in SVI were obtained.
Highlights
The pulp and paper mills are among the most important industries in the world, and some of the biggest polluting agents, discharging a variety of pollutants such as gaseous, liquid and solid wastes into the environment
In the present study, a coagulation process was used to treat paper-recycling wastewater with alum coupled with poly aluminum chloride (PACl) as coagulants
The optimum conditions for high treatment efficiency of paper-recycling wastewater under experimental conditions were reached with numerical optimization of coagulant doses and pH, with 1,550 mg/l alum and 1,314 mg/l PACl and 9.5, respectively, where the values for reduction of 80.02 % in chemical oxygen demand (COD), 83.23 % in turbidity, and 140 ml/g in sludge volume index (SVI) were obtained
Summary
The pulp and paper mills are among the most important industries in the world, and some of the biggest polluting agents, discharging a variety of pollutants such as gaseous, liquid and solid wastes into the environment. To minimize the impact of effluents on the environment, several treatment technologies have been employed, little is known on their efficiency to eliminate the toxicity attributed to the presence of organic compounds. This is mainly due to the fact that it is the type of paper mills (packaging, recycling, kraft) and the water system configuration that determine the COD, toxicity and organic load of the effluent. Coagulation is one of the most used water effluent treatments It employs a cationic metal as a coagulant agent which usually promotes water hydrolysis and the formation of hydrophobic hydroxide compounds with different charges, depending on the solution pH. The coagulation effectiveness and cost depend on the coagulant type and concentration, solution pH, ionic strength as well as on
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