Screening optimisation for indirect potable reuse

摘要

An automatic backflush pre-filter used for pre-treatment for secondary wastewater re-use wasnevaluated and optimised at two different mesh sizes over an 18 month period. The filter was initiallynrun with a 500 μm rating mesh size, as recommended by the supplier of the downstreamnmembrane filtration process, and then at 100 μm to investigate any change in water qualitynproduced and associated improved membrane performance. With the 500 μm mesh in place, thenfilter fouling rate was low and a backflush was initiated every 3.5 h. For the 100 μm mesh thenfouling rate was extremely rapid. Fouling was found to be caused by reverse side blockage ofnthe pre-filter due to biofilm growth, and not by improved solids capture; there was nonimprovement in water quality with the smaller mesh size, since particle unloading fromnthe biofilm took place. The pre-filter fouling rate was found to be related to turbidity. At a turbiditynof 5 NTU the filter backflushed around 200 times per day, while at 10 NTU this increased tonover 300 times. Further analysis enabled the backflush water volume to be decreased bynreducing the backflush duration and increasing the backflush cycle time (i.e. the time betweennbackflushes).