A system of falling droplets was investigated for the application of wastewater aeration as it was hypothesised that the system would not be adversely affected by elevated mixed liquor suspended solids. The concept was trialled using a device able to create droplets of different diameters, where the liquid is pumped to a height and allowed to fall through air as droplets. Oxygen transfer into the falling droplets was determined by using de-oxygenated feed water and measuring the dissolved oxygen concentration of samples collected at various fall heights. The influence of droplet diameter on mass transfer was also investigated by using four different droplet size settings. The results were compared with a theoretical model and the droplet diameters produced from both fresh water and brewery waste sludge were measured to determine the effect of a feed liquid containing suspended solids and an organic fraction. The results demonstrated that greater oxygen transfer occurs with larger fall heights however the rate of transfer is greatest at the beginning of the fall. The experimentation and modelling showed oxygen transfer per volume to be higher with smaller droplets. Analysis of the droplet diameters produced with both fresh water and brewery waste water at 10,000 mg/L indicated that the droplet size produced by a liquid containing a live culture and relatively high suspended solids was smaller than the droplet size produced by fresh water. The higher surface area to volume ratio of a smaller droplet results in more efficient mass transfer in the system and indicates that the system can achieve an alpha factor around 1.1. The advantage of the system of falling droplets applied to wastewater treatment is that the system is not negatively impacted by increased suspended solids in the liquor and therefore is able to provide consistent aeration at around 1.35 kg/kWh oxygen transfer efficiency.
Chemeca2008. Chemeca2008: Towards a Sustainable Australasia (Newcastle, N.S.W. 28 September - 1 October, 2008)