Microscopy and filament identification as a tool for troubleshooting biological treatment processes

Morley, E., Aqua Enviro Limited, UK



Aqua Enviro have microscopically examined thousands of activated sludge samples in the last 15 years developing an overview of conditions across a wide range of plants.  While Microthrix parvicella is still widespread in the municipal sector, increased sludge handling is leading to Type 021N becoming more common on some plants as return liquors become stronger and septicity is introduced to the head of the works.  Industrial plants have a myriad of filaments depending on their process conditions and influent types.  Legislative pressures are meaning that influents are typically becoming more concentrated and effluent limits tighter so there is more pressure on the effluent plants to perform to a high level.  Understanding the health of the biomass is vital in maintaining the effluent quality and optimising expenditure.

Keywords: Activated Sludge, Biological Treatment, Bulking, Microscopy, Microthrix parvicella, Type 021N, Wastewater Treatment


Despite the long history of activated sludge there are still operational problems which occur on occasion.  This is true for other biological treatment processes whether they are a new innovative design or a more traditional trickling filter.  All the biological systems depend on maintaining a healthy and often varied consortium of bacteria and protozoa within the process which is not always easy to do.

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.  The Environment Agency can be acting to ensure that new directives and regulations are met by municipal and industrial operators while the municipal operators can themselves be the regulator for trade effluent discharges from industry.   There are financial pressures to reduce operating costs, which can include man power, energy and chemical dosing, and to minimise capital expenditures which might be delaying asset renewal or upgrades or having wait until the next financial year or even AMP cycle.  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.  Sites could have effluents that are vastly different from original plant designs with industrial inputs being replaced by domestic sewage over the asset life.   The same applies to industrial plants in which the water usage and the manufacturing process have changed considerably over since the plant was first constructed.

These are all likely to have an impact on the microbiome that is present in the treatment plant, as operating parameters such as sludge age and F/M ratios, as well as the chemical constituents of the effluent, change.  The upshot of this could be poor settlement and foaming in an activated sludge plant and under or over growth of a biofilm in an attached growth process.   The ultimate outcome could be 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 or operating outside the ‘normal’ ranges of operation, on the other hand large scale capital schemes for plant upgrades may be required to ensure that compliance is maintained.

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