The effect of impeller clearance and liquid level on the critical impeller speed (Njs) for various radial and axial flow impellers in 0.29 m ID agitated vessel has been studied. Five types of radial impellers: Rushton turbine (RT), Straight blade (SB), Curved blade (CB), Curved blade with disc (CBWD) and R130 impeller and four types of axial impellers: Rushton turbine 45 o angle (RT 45), Pitched blade (PBT), A320 and HE3 impeller were used. Tap water and resin particle of 0.506 mm were used as liquid and solid phases, respectively. The impeller clearance to vessel diameter (T) was varied between 0.17 and 0.41. The liquid level (H) was also varied as H/T=0.5, H/T=0.75 and H/T=1. The R130 impeller and A320 impeller was found to be more efficient among radial and axial impellers respectively. A new expression for Zwietering constant 'S' was developed to predict critical impeller speed, considering impeller clearance and liquid level for all the impellers. The results obtained here show that the 'S' values increase with increase in clearance, and decrease with liquid level for all impellers and it also depends on the type of impeller.

Background: Reusing waste water by appropriate treatment is an effective method for substantiating the ever increasing water demand for construction, irrigation, domestic and industrial purposes. The greywater is the domestic waste water that does not contain the toilet effluent and it is converted and used for non-potable purpose through coagulation and flocculation by using natural coagulant. Objective: The main objective of this work is to evaluate the coagulating efficiencies of various natural coagulants on synthetic greywater by varying pH, mixing speed, mixing time and coagulant dosage. Methods: Powdered coagulants obtained from tamarind seeds, moringa oleifera, banana peels and fly ash were compared with conventional commercial coagulants like alum for synthetic and real greywater. Results: The natural coagulants have shown significant performance compared to chemicals like alum. Conclusion: The turbidity removal efficiency for tamarind seeds, moringa oleifera, banana peels and fly ash were found to be 61.33%, 85.75%, 90.42%, 94.27% against 96.49% obtained from alum on treating with synthetic grey water under identical conditions.

There is a significant need for high-performance catalysts capable of degrading harmful petrochemical waste for wastewater treatment. The biosynthetic approach is employed here for preparing ZnTiO 3 nanospheres. In the present investigation, lemon extract was used for synthesizing the above nanospheres. ZnTiO 3 nanospheres were further characterized by XRD, UV-Vis DRS, PL Spectra, BET, SEM-EDAX, TEM, AFM, and Zeta Potential techniques. The photocatalytic activity of the prepared photocatalyst was tested against real wastewater samples from the petrochemical industry. 96.74% wastewater degradation was observed with ZnTiO 3 nanospheres. Moreover, GC-MS was employed for identical analysis of organic pollutants before and after petrochemical treatment. This study shows how to make cost-effective and environmentally friendly catalysts that can be used to use UV light for wastewater treatment more effectively.

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