Investigating Critical Parameters of Dissolved Air Flotation(DAF) for Solid-Liquid Separation with Different Influents as part of the LOTUSHR Project

Abstract

Many rapidly expanding cities around the world including India’s capital New Delhi face increasing potable water quality and health risks due contaminated open drains carrying the cities untreated wastewater into the adjoining river, which is also the city’s water source. To tackle this problem in a practical and holistic way, innovative wastewater treatment solutions are needed. This is the goal of LOTUSHR project - to research and build a holistic and resource-oriented wastewater treatment plant (wwtp) to treat the Barapullah drain water in New Delhi, India. To achieve this goal, Dissolved air flotation (DAF), due to its ability to withstand fluctuating flows and low area requirements was identified as a possible technology in the LOTUS wwtp scheme. This research is focused on identifying and investigating critical operating parameters of a bench-scale DAF column set up with various influents for a comparative and deeper understanding. To achieve this, different influent at the site - Barapullah drain water and anaerobic sludge from a Delhi wwtp, and their counterparts in the laboratory - canal water and anaerobic sludge from a Delft wwtp were tested with the DAF. As there were potentially many critical factors that could have an impact on the DAF performance, experiments were conducted based on the Plackett-Burman experimental design. Furthermore, to understand the effect of particle characteristics and morphology on the DAF performance, microscopic images of the influent and clean effluent samples were analyzed using ImageJ-Fiji. Finally, Particle Image Velocimetry (PIV) analysis was done to gain insight into the characteristics and behavior of the particle-bubble agglomerate and its relation to the DAF performance. Additionally, pathogen (E-coli and C.Perfringens) removal potential of the DAF was studied with Barapullah drain water. The results obtained suggest that for canal water the critical parameters are Time of Coagulation prior to the DAF, Retention Time and Influent TSS Concentration. Whereas, for drain water, it was only the Influent TSS Concentration. For anaerobic sludge from the wwtp in Delft themost significant parameter was found to be Pressure and a similar trend with higher removal was observed for anaerobic sludge from Delhi. Image analysis with canal water, drain water and sludge samples showed that for higher TSS removal runs, a general trend of average influent particle sizes of 12 um,3-5 um and 80-100 um respectively was observed. And, clean effluent particle sizes were found to be 2-3 um for drain water and canal water. Furthermore, for drain water runs with high removal, the particle-bubble agglomerate rise velocities were found similar to the theoretically calculated values of 1.69E-03 m/s. Bubble to particle ratio for high TSS removal runs was calculated to be 34 bubbles/particle for drain water and 50 times more for sludge. In terms of pathogen removal, E-coli removal for drain was found as high as 1.65 log for higher influent TSS runs. No significant correlation was found between the TSS removal and E-coli removal by the DAF. It is recommended that for future research further optimization (with experimental designs such as CCDR) of the significant parameters identified should be done. More extensive research in addition to results found in this study is suggested to be done on the effect of different coagulants
and coagulation conditions on the DAF performance. To further understand the differences observed in the significant parameters of the influents, research on the influent properties such as hydrophobicity and density is recommended. More experiments with adequate site equipment are suggested to be done to understand the removal of Giardia and Cryptosporidium to further understand their relation to the TSS removal by the DAF.