Water & Wastewater Treatment

In the know Digging deeper: aerobic treatment 34 | APRIL 2016 | WWT | www.wwtonline.co.uk (Nocardia and Microthrix); these in particular rapidly foul membranes. Type 021N and Thiothrix both like a high food - micro-organisms (F:M) ratio and produce the worst settling sludge possible, while Haliscomenobacter Hydrossis is a lover of low dissolved oxygen. In addition to bulking, many other factors can reduce the efficiency of the aeration system including the presence of surfactants, blockages in the diffusers or nozzles, an influx of solids to the aeration basin or even a worn pump. Aeration systems are designed to produce a bubble of a certain size. The smaller the bubble the greater the total surface area of the bubbles for an applied, fixed volume of air and the greater the rate of oxygen transfer from the gas to the liquid phase in clean water. Any factor that adversely affects either the bubble size or the ease with which oxygen is transferred reduces the capacity of the installed aeration system. Surfactants that coat the bubble are problematic in industrial processes, such as textile manufacturers and in the paper industry where coatings are employed. These reduce the rate of oxygen transfer. Brewing industries that use filtration media such as diatomaceous earth (Kieselgur) can wear the aeration system, whilst distilleries must cope with high copper levels from the stills that are toxic to micro-organisms at very low levels. Move to the pharmaceutical sector and toxicity is an ever present risk. Here, the challenge is to meet an ammonia consent as the microorganisms Nitrosomonas and Nitrobacter are particularly sensitive to toxic compounds. The challenge is to be able to recognize when the plant is starting to struggle, pinpoint the issue and quantify its impact. In the short term, it may be possible to manage a deficit in oxygen by simply reducing the operating mixed liquor, but this does not take away the root cause of the problem and is not without risk. Reducing the levels of biomass can, on occasion, exacerbate the problem as the increase in F:M ratio and may encourage certain filaments (especially Type 021N). This is where a controlled approach is of value, gauged through microscopic analysis of the activated sludge. The key is to measure the amount of oxygen transferred into the liquid per metre depth of the tank and to be able to quantify what is being delivered to what is required. Once you have this it can be compared to the original design and provide valuable information on the plant's true aeration capacity and the severity of the problem. Whilst this is a relatively straightforward test it does require an oxygen monitor, knowledge of the original design and fabricated gas collection system that can float on the aeration tank surface. This is a useful test, but not routinely employed. This test can also be of use for water companies wishing to identify which aeration assets to prioritise in which order. As specialist consultants, Aqua Enviro's role is to help clients understand and quantify the problem and guide them to an end solution that is practical and affordable. Operational changes can be made to address an oxygen deficit, but these must be approached in a methodical, analytical way; as changes made to improve oxygen provision can result in new species of filaments arriving, worsening the situation. In severe cases, the deficit between the performance of the installed aeration system and what is required could mean that capital expenditure is needed. In this case we can develop the process design, liaise with suppliers and oversee installation and testing of the upgraded solution. Our approach is about developing a shared understanding with the client of what is needed; engaging the wastewater treatment team in defining the problems; understanding the unknowns; developing the solution; and improving the understanding of your plant through a programme of training and development. For insights and show news visit utilityweeklive.co.uk INNOVATION CONTENT STREAM: For insights and show news visit utilityweeklive.co.uk DATA & ANALYTICS CONTENT STREAM: For insights visit utilityweeklive.co.uk For insights visit utilityweeklive.co.uk Filamentous bulking under the microscope

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