Water & Wastewater Treatment Magazine
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www.wwtonline.co.uk | WWT | JUNE 2015 | 37 In the know Technically speaking: wastewater treatment T he activated sludge process may have been in existence for 100 years but that does not mean that it operates without problems. The same is true of all biological treatment processes, whether they are a new innovative design or a more traditional trickling filter. Microscopic examination of activated sludge or fixed film biomass is a technique that can be used to identify the causes of poor settlement, foaming and other operational problems, the outcome of which can threaten compliance with consent limits. A•er identifying the microbiological cause, actions can be taken to eliminate the problem. A wide range of pressures apply within the municipal and industrial sectors. Many of these are the same across both types of wastewater treatment plants – such as pressure from regulators and economic drivers to be more efficient in terms of energy, chemical and manpower levels. Municipal plants are at the mercy of new developments, the impacts of climate change (such as dealing with rainfall and flooding on a more frequent basis) and on-site sludge handling issues. Industrial plants can have the added challenge of the current wastewater having altered significantly from when the effluent plant was designed. All of these may lead to small (or large) changes in the way an effluent treatment plant is operated Under the microscope Microscopic examination of sludge or biomass can reveal the biological roots of common problems within a treatment process and can affect the delicate balance of the microbiome present within the treatment system. This could lead to poor settlement and foaming in an activated sludge plant and under or over growth of a biofilm in an attached growth process. The outcome of these could lead to consent limits being threatened due to solids carryover or incomplete treatment. Microscopic examination of the mixed liquor or biofilm can be used to identify the biotic causes of many operational issues. Once the microbiological reason has been established, actions can be taken to eliminate the underlying causes. These could be simple things like introducing or increasing balancing volume or increasing aeration capacity. On the other hand, large- scale capital schemes for plant upgrades may be required. Methodology for microscopic examination Samples of biomass are collected from the effluent treatment plant; this may be mixed liquor or scrapings from a fixed film process such as a trickling filter or a SAF media. The samples should be examined soon a•er collection, especially for high food-to-mass (F/M), low sludge-age plants. Key observations should be made of the floc structure, protozoal and metazoal populations, filamentous bacteria (Type and abundance/ length), and the clarity of the bulk liquid (space between the flocs). Filamentous identification to a type or species level is achieved with the use of Neisser, Gram and Indian ink staining where appropriate. Using these characteristics it is possible to assess the sludge age and the F/M, identify signs of insufficient oxygen and deficiencies of other nutrients as well as noting that shock conditions may have occurred. Shocks might include rapid changes in influent pH and BOD concentration, presence of chemicals or detergents from spillages and changes in temperature. The exact nature of these can be later verified through site knowledge and operating data. If possible photographs of the EMMa MorlEy SENior ProcESS SciENTiST, AqUA ENviro Filament Type 021N is a leading cause of poor settlement and is a sign of septicity in the sludge handling process