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Abstract
A hybrid system of flocculation–photocatalysis (HSFP) was applied to evaluate the color removal from simulative dye wastewater. The decolorization performance of HSFP was investigated considering four key factors: flocculant dosage, pH, turbidity, and ionic strength. Compared with flocculation alone, HSFP showed better decolorization effectiveness for simulative Crystal Violet–Reactive Red X-3B dye wastewater (CV-RR) and simulative Crystal Violet–Acid Orange II dye wastewater (CV-AO). The dosage of flocculant was determined by the molecular structure of target dyes. A higher dosage was required for the color removal of dyes with a lower molecular weight and less sulfonic acid groups. The dominant decolorization mechanism was different with different initial pH values of simulative dye wastewater, which influenced the decolorization efficiency of flocculation and photocatalysis. For dyes with a lower molecular weight and less sulfonic acid groups, better decolorization performance was achieved under neutral conditions, mainly depending on strong charge neutralization and adsorption bridging capacity. For dyes with a higher molecular weight and more sulfonic acid groups, decolorization efficiency was improved with an increase in pH, due to stronger deprotonation. An increase of turbidity reduced the dye removal efficiency of flocculation alone and HSFP. The presence of NaCl, CuCl2, and CrCl3 led to a different decrease in the flocculation efficiency and photodegradation efficiency.
Highlights
Removing dyes from industrial wastewater is an important and urgent environmental issue
The main objectives of the present study are to (1) investigate the decolorization performance of flocculation alone and in conjunction with photocatalysis; (2) explore the enhancement of the decolorization efficiency using the photocatalytic process as a post-treatment; and (3) analyze the effect of flocculant dosage, pH, turbidity, and ionic strength on flocculation and photocatalysis
A much higher dosage of polyaluminum chloride (PAC) was added for the treatment of Crystal Violet−Acid Orange II dye wastewater (CV-AO)
Summary
Removing dyes from industrial wastewater is an important and urgent environmental issue. Many industries, such as printing and dyeing, textile, plastic, pulp, and paper, produce dye wastewater.[1] The existence of various and complex dyes represents esthetic influence and reduces the transmittance of the water body and causes health threat.[2] The biochemical oxygen demand/chemical oxygen demand ratio of dye wastewater is usually lower than 0.30. Low biodegradability of dye wastewater is one of the major challenges in removal of dyestuff because of the azo group and aromatic ring exhibiting stable and resistant characteristics.[3,4] In addition, aromatic amines, such as aniline, toluidine, benzidine, and naphthalene, are possibly produced during the biological degradation process.[5] an effective chemical degradation method is significant and imperative for the purpose of discharge or water reuse
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