Keeping on top of treatment
Eleanor Raper, senior geoscientist at Envireau Water, on the importance of reviewing your wastewater treatment system
Wastewater treatment was once an overlooked process, but increasingly stringent emission limits mean that it has become a higher priority for businesses.
Wastewater discharges are heavily regulated and failure to comply with environmental permits and licences can have severe impacts on business economics and productivity.
Whether you are treating domestic, agricultural or industrial wastewater, many common principles apply.
Treatment systems typically consist of a sequence of methods, combined to create an overall process, capable of producing a treated wastewater suitable for release into the receiving environment. This may involve any combination of physical, chemical and biological processes.
- Physical – screening, sedimentation, filtration, absorption
- Chemical – precipitation, coagulations, disinfection
- Biological – aerobic, anoxic, anaerobic
In many instances, WWTPs have changed dramatically over time to adapt to ever-changing water treatment requirements. Changes to treatment requirements can arise for numerous reasons.
Some industries have been impacted significantly by the changing UK and global markets – changes in production volumes have resulted in changes to the volumes of wastewater requiring treatment.
On the other hand, some businesses have seen changes to wastewater compositions over time due to changing production processes or changes in the source of raw materials.
Treatment processes have been modified to effectively treat such wastewaters. Industries have also been expected to meet new emission limits that have been introduced due to greater awareness of the environmental impacts of pollutants.
For example, heightened awareness of the impacts of eutrophication has led to lower emission limits for nitrogen and phosphate compounds. Better knowledge of persistent organic pollutants (POPs) and endocrine disrupting chemicals (EDCs) has led to new compounds being added to regulated lists.
While the modification of treatment processes has enabled businesses to be flexible and adapt to changing requirements, a common problem that arises relates to the loss of knowledge regarding the treatment system. This loss of knowledge causes the occurrence of treatment failures with significant costs to the business.
The transfer of knowledge over time from one generation of operators to the next can be associated with a loss of a ‘true’ understanding of the system. In many instances, current operators do not fully understand the role of different stages in the treatment system and how each relates to the treatment process as a whole.
A recurring comment across a range of businesses is “we just do it like that because that’s the way it has always been done”. This presents two problems – that treatment processes are being used that are no longer required, or processes are being operated without an understanding of what the requirements are for them to operate effectively.
It is important to step back and consider what is being done and why. A review of a business’ wastewater treatment system can lead to performance improvements through process optimisation, not necessarily requiring large capital investment.
Key considerations for a treatment process review include:
- the current wastewater characterisation
- the quality standards that need to be obtained
- the role that each stage has in a treatment system
- how these may interact with each other
- what method is the most economically and environmentally appropriate way to treat the wastewater
- the ability of the treatment system to stand the test of time
Wastewater characterisation is a very basic yet commonly overlooked consideration. If inputs are unknown, outputs cannot be accurately predicted. Businesses frequently monitor the characteristics of their treated wastewater (due to permit obligations) but fail to monitor the characteristics of their incoming wastewater.
Wastewaters can vary both over time and space and it is important to understand these changes and how a treatment system must be adapted to cope with them. In some instances, one compound may vary in response to another compound and these inter-relationships also need to be understood and considered.
An understanding of the role of each stage in the treatment process is essential to enable the production of a consistent effluent. Understanding each of the key stages allows operators to make small modifications (e.g. change the pH, carbon supply, retention time, dose rate of key chemicals) to ensure that the treated wastewater is compliant with emission limits. This enables operators to be responsive to events, such as changes in the wastewater composition, toxic shocks to bacteria and changing wastewater volumes.
Responding to these events appropriately and in good time can lead to both environmental and economic gains for the business.
The appropriateness of the applied technology should not be overlooked. Ongoing research and development means that new technology is constantly being introduced. Not all new technology requires large economic investment but it is often capable of leading to economic savings.
The application of new technology or processes may simply be a requirement due to newly introduced emission limits. Selection of appropriate technologies can also offer businesses a way in which to meet their ever-changing needs and ensure that the process is robust.
Ultimately, carrying out a review of your wastewater system does not necessarily require large capital investment. Simple changes can lead to large improvements in performance. Carrying out a review of your treatment process not only potentially enhances performance but can also increase the knowledge and understanding of operators, which in turn enables them to be more responsive to changing business needs.
This article originally appeared in the October issue of WWT
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