A system of falling droplets was investigated for the application of wastewater treatment as it was hypothesised that the system would not be adversely affected by elevated mixed liquor suspended solids.
The concept was tested with de-oxygenated water, using an impinging jet where liquid impacts underneath a horizontal plate, spreads radially and trickles from prongs as droplets.
The recirculating system was investigated where exit water was discharged into the feed water bucket to simulate the practical application of the device. Falling droplets were also analysed to determine the influence of fall height and droplet diameter on oxygen transfer.
The results were compared with a theoretical model and the droplet diameters produced from different sized prongs were also analysed. Models of the mass transfer and energy requirement of droplet and bubble systems were used to evaluate the impact of varying alpha value on the systems.
The results demonstrated that the recirculating system transferred oxygen to the water with a logarithmic concentration profile. A k_La value of 0.0037 /s was achieved for a flow rate of 35 L/min. It was also shown that greater oxygen transfer occurs with larger fall heights however the rate of transfer is greatest at the beginning of the fall. The testing and modelling showed oxygen transfer per volume to be higher with smaller droplets.
When compared to bubble aeration, the falling droplet method was more energy efficient when the bubble system alpha factor decreased below about 0.7.
Operation of the apparatus with wastewater is currently under investigation.