Peter Grant, Process Engineer at Aqua Enviro.
Treating wastewater is often an energy intensive process. The aeration of wastewater, using mechanical blowers and diffusers, is a major user of this energy. With efforts being made to decarbonise and keep energy costs down, it is important to make sure the aeration of wastewater is done efficiently.
Oxygen Transfer Efficiency (OTE) tests can be carried out to quantify what percentage of oxygen blown into an aeration basin is transferred to the wastewater as dissolved oxygen.
An aeration system operating at higher OTE values requires less air to transfer the same amount of oxygen to wastewater as a system with lower OTE values. Aeration systems can be optimised to maximise OTE and minimise costs.
OTE data can be determined during the normal everyday operation of aeration basins using off-gas testing.
How Is It Done?
A buoyant off-gas hood is positioned on the surface of the aeration basin. Gas from the liquid surface passes into the hood where it is collected. A vacuum pump is used to aspirate this gas from the hood, before the gas is tested using analytical monitoring equipment. A DO probe is simultaneously used to provide dissolved oxygen concentration data from the aerating wastewater.
Aqua Enviro has developed bespoke off-gas testing equipment which allows for the simultaneous monitoring of oxygen concentrations in both wastewater and off-gas.
The sampling procedure is repeated at multiple positions to give a representative set of results for the whole aeration basin, taking into account factors such as aeration tapering.
OTE values are calculated using molar fractions of oxygen in the inlet air and in the off-gas. Calculations are made for OTE at standard conditions and to account for contamination in the wastewater.
The data from OTE tests can then be used to inform operators of best operational practice, aeration system performance and maintenance requirements. This can help to provide both OPEX and CAPEX savings.
Aqua Enviro has over a decade of experience providing technical expertise and practical testing services in Asset Optimisation.