JWSS - Journal of Water and Soil Science

The goal of this study was to evaluate tannic acid as a coagulant in turbidity removal. Tests were designed using Taguchi method and carried out on the synthetic and natural turbid samples. In order to optimize turbidity removal by tannic acid, seven factors including pH, coagulant dosage, rapid mixing rate, slow mixing rate, slow mixing time, sedimentation time and initial turbidity were investigated. The results revealed that in optimum conditions,  tannic acid could n remove up to 71 percent of synthetic turbidity and 66 percent of natural turbidity; also, tannic acid showed more coagulation activity in the lower initial turbidities. ANOVA analysis showed that initial turbidity and slow mixing time were the most important parameters in the turbidity removal by tannic acid. In general, this study showed that tannic acid was capable of removing turbidity and could be used instead of common coagulants in the preliminary treatment.

The application of coagulation processes for the treatment of stone quarrying wastewater has increased considerably in recent years. However, limited information is available regarding the appropriate coagulant type, optimum dosage, and pollutant removal efficiency. This study aimed to evaluate the performance of several organic and inorganic coagulants, including polyaluminum chloride (PAC), aluminum sulfate (alum), ferric chloride, zeolite, anionic polyacrylamide (APAM), and cationic polyacrylamide (CPAM), for the treatment of wastewater generated from different stone-processing industries (granite, marble, and travertine) located in Mahmoudabad Industrial Town, Isfahan, Iran. In this experimental study, the effects of coagulant dosage and mixing conditions on the treatment of four types of raw wastewater were investigated using the Response Surface Methodology (RSM). The results indicated that the optimum dosages of zeolite, ferric chloride, and PAC were 200 mg/L, while the optimum dosage of aluminum sulfate was 100 mg/L. For both anionic and cationic polyacrylamide, the optimum dosage was 0.5 mg/L. APAM, CPAM, and PAC exhibited the highest treatment performance among the tested coagulants, respectively. Zeolite showed the lowest removal efficiency (16.5%) for white travertine wastewater, whereas APAM achieved the highest removal efficiency (98.1%) for marble wastewater. Furthermore, analysis of the operational parameters demonstrated that mixing speed and coagulant dosage had the greatest influence on turbidity removal, whereas mixing time showed a comparatively lower effect. Overall, polymer-based coagulants, particularly APAM and CPAM, proved to be highly effective for the treatment of stone-processing wastewater