This study aims to look at the effect of introducing controlled amounts of oxygen on biogas quantity and quality during anaerobic digestion. The anaerobic digestion process is studied, specifically, it’s biochemical processes, to understand the effect of addition of oxygen. Anaerobic sludge is aerated to mimic DAF (Dissolved Air Flotation) conditions, where tap water is pressurized (at 3 and 5 bar) and then depressurized in contact with the anaerobic sludge in a column reactor. During the course of this process, air micro-bubbles which were dissolved under high pressure are released due to contact with atmospheric conditions. To estimate and compare the methane production of the originally collected non-aerated sludge (anaerobic sludge not aerated in the column reactor, therefore, considered as 0 bar) and aerated sludge (anaerobic sludge subjected to high-pressure micro-air bubbles in the column reactor at 3 and 5 bar) a BMP test is conducted. Methane production was found to be lower in the aerated sludge with the BMP value for the 0 bar sludge being 296.17 +/- 45.15 NLCH4kg 1 and the value for 5 bar aerated sludge being 252.26 +/- 16.8 NLCH4 kg 1. Biogas composition of the aerated sludge was also examined with a Gas Chromatography (GC) machine and the percentage of methane, carbon dioxide and oxygen were measured for the 3 and 5 bar aerated sludge. For the 5 bar
aerated sludge, the overall percentages are averaged at 30%, 70%, and 1% respectively and for the 3 bar aerated sludge the average values are 20%, 80%, and 1% respectively. Furthermore, particle size distribution (PSD) analysis was done to compare variations for particle sizes between the aerated (5 bar) and non-aerated (0 bar) sludge. Very low variation was observed between these samples with the average size of the aerated samples being marginally smaller than the non-aerated sludge, indicating poor separation efficiency for the separation method adopted.

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.