The present study focuses on newer biocoagulants, bioformulations, and the understanding of coagulant behavior with biocoagulants in relation to chemical coagulants. Newer biocoagulants, seeds of Azadirachta indica (AI) and pads of Acanthocereus tetragonus, are discussed along with two known biocoagulants, Moringa oleifera and Cicer arietinum seeds. Dye removal studies were carried out using widely reported Congo red dye to facilitate easy comparison with other conventional coagulants and the effect of various parameters such as initial dye concentration, pH, coagulant dose, etc. are discussed in detail. The use of biocoagulant was found to be highly effective, and up to 99% dye removal was achieved for coagulant doses in the range of 300−1500 mg/L. It was also observed that coagulation is pH sensitive, similar to chemical coagulants. Although the biocoagulant dose is relatively higher than the conventional chemical coagulants, a good value for the sludge volume index, ∼50 mL/g for 1 h and 30 min, respectively, was obtained for the two coagulants, Acanthocereus tetragonus and Moringa oleifera. A very high particle count compared to chemical coagulants was observed using a focused beam reflectance measurement. Bioformulation with chemical coagulants such as alum, ferric, and aluminum based coagulants can, not only lower doses of biocoagulants (up to one-third) but can also result in significant improvement in the coagulation performance, up to 50% or more.
The present work provides a proof of concept for a new hybrid process, cavigulation, by combining cavitation and coagulation and its application to dye wastewater treatment. Both acoustic and hydrodynamic cavitations were evaluated. Removal of a commonly used dyes such as Congo red was investigated by cavigulation in the concentration range of 50 to 500 ppm. A broad spectrum of coagulants including two inorganic coagulants; poly aluminium chloride, iron (III) chloride, and natural biocoagulants derived from Moringa oleifera, Cicer arietinum and Acanthocereus tetragonus were employed to substantiate the concept of cavigulation. A vortex diode device employing vortex flow for cavitation, was used for the hydrodynamic cavitation (HC) -based cavigulation. Cavigulation in the form of acoustic cavitation + coagulation, showed significant improvement over individual processes; acoustic cavitation alone was largely ineffective for dye removal. Increase over conventional coagulation to the extent of 24% and 48% was observed for the two inorganic coagulantsIron (III) chloride and PAC SAB 18, while for Moringa oleifera, Acanthocereus tetragonus, and Cicer arietinum the increase was 27%, 33%, and 29% respectively. The pH has a large impact on the cavigulation process, similar to coagulation and the coagulant dose could be reduced by more than half by adjusting pH to 3. Auramine O dye removal was effective using hydrodynamic cavitation compared to coagulation. The developed cavigulation process, especially using biocoagulants, could be an effective alternative to the conventional chemical coagulation in the form of a green process in dye wastewater treatment
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