Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | APRIL 2016 | 33 In the know Digging deeper: aerobic treatment 'Fixing' the aerobic treatment plant Problematic micro- organisms, blockages and the presence of surfactants are amongst the most common challenges in the aerobic treatment process Matthew SMyth AssocIATe TechnIcAL DIRecToR AquA envIRo O ver the past eighteen years, I have visited hundreds of domestic and industrial effluent treatment plants; many of these sites have at their core an aerobic treatment process, with this most oen being an activated sludge plant. When problems are encountered the most common root cause is the aeration system. Be it poor settling sludge, a breach of consent limits for BOD or ammonia, reduced throughput or high energy consumption, this part of the plant is the first area to investigate. Unfortunately, it is also oen incredibly difficult to access, on occasions being under up to eight metres depth of mixed liquor. Question marks over the capacity of the aeration system are more common in the industrial, rather than the domestic, wastewater sector. This is due to the greater variability (composition, flow, characteristics) in the nature of the wastewater to be treated, as well as sites oen increasing their production capacity over time without considering the implications on the effluent plant. Industrial effluent plants are also particularly prone to filamentous bulking. Bulking is where micro- organisms grow that reduce the settlement rate (or filtration in membrane plants) of the activated sludge. More importantly, bulking affects the transfer of oxygen from the gas phase to the bubble phase. Herein lies the problem. Microscopic analysis of the activated sludge is a key weapon in the operator's armoury. Problematic organisms appear under the microscope well in advance of them manifesting themselves as a problem, giving the operator a window of opportunity to take proactive action before the sleepless nights begin. Analysed at 1000 times magnification under a phase contrast microscope, and stained to identify if the organism is gram/neisser negative or positive, it can be noted whether the cells are oval, barrel or discoid shaped; one can see the diameter of the cells, and whether they contain sulphur, motile/ immotile, or if branching is present; this is how filaments are identified. Once known, the filaments are then quantified and described in terms of the ability to bridge between flocs and disrupt the separation of final effluent from the bulk, 'mother' liquid. Common filaments that cause problems are those that produce a 'chocolate mousse' type foam Retrofitting an aerobic system in a treatment plant

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