Lithium Tracer Testing
Lithium Tracer testing is a method for determining the performance of tanks with contents that are actively mixed or agitated. It is used most commonly to assess grit accumulation in anaerobic digestion (AD) reactors but can also be applied to sludge thickening tanks, chlorine contact tanks (treating potable water) and activated sludge processes. Implemented in a series of discrete phases, tracer testing can be used to determine mixing efficiency, and through the application of standard hydrodynamic equations also provides data on active volume, dead zones and short-circuiting.
Lithium Tracer testing is used to monitor and manage grit accumulation in AD reactors, to maximize renewable energy production and minimize digester down-time for periodic de-gritting. The accumulation of grit reduces the effective operating volume of a tank, and if all other aspects remain the same, this will reduce biogas production. Timely identification of grit accumulation and mixing issues allows operators to make informed choices around planned maintenance within and upstream of reactors.
A Lithium Tracer test works by introducing a calculated quantity of lithium chloride into a reactor tank. Samples are then taken from the outlet and recirculation lines and analyzed for Lithium concentration. The difference in dose concentration and that measured in the samples is used to derive mixing efficiency, active volume and short circuiting in the tank.
The technique forms a long-established component of take-over and routine resilience tests in the water industry, but has recently been recognized as appropriate for performing the annual tank capacity and sediment assessments that are now required at all AD facilities operating under a permit from the UK Environment Agency – whether they are processing sewage sludges, food waste, or animal manures and other farm residues.
References
https://www.youtube.com/watch?v=0FDhehBwQvM
https://conferences.aquaenviro.co.uk/wp-content/uploads/sites/7/2018/08/Capon-N.-Monsal.pdf
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