THE USE OF Static Mixers For WASTE Water Treatment
Table Of Contents
Introduction: How wastewater treatment is governed in the UK
Regulatory framework and standards governing UK wastewater treatment.
The Role of Static Mixers in Wastewater Treatment
Applications of Static Mixers in Wastewater Treatment
Design Considerations for Static Mixers in Wastewater Treatment Systems
Introduction: How Wastewater Treatment is Governed in The UK
Wastewater treatment is a sensitive sector in the UK, driven by the complex demands of public health, environmental protection, sustainability, and energy efficiency. Modern wastewater treatment plants have a range of regulatory standards and guidelines to adhere to, and must demonstrate the highest standards of sanitation, alongside a commitment to minimising their carbon footprint.
For many organisations, this is a delicate tightrope to walk. In this guide, we will look at the role of static mixers in wastewater treatment, explaining how static mixers can improve mixing efficiency compared to many alternatives – such as mechanical mixers – while also significantly reducing energy usage in your plant.
Implementing static mixers into your treatment plant can make it easier for you to remove harmful contaminants and pathogens from wastewater, promote resource recovery and water reuse, comply with environmental legislation, and minimise your operating overheads.
Regulatory Framework and Standards Governing UK Wastewater Treatment
Wastewater treatment applications are regulated by stringent standards that are overseen by external bodies and authorities, which in the UK may include the Environment Agency and the Water Services Regulation Authority, or Ofwat – operating under close government oversight. Again, to take the UK as an example,
Important Items Of Legislation Would Include:
- Water Industry Act 1991 (England and Wales)
- Environment Act 1995
- Urban Wastewater Treatment Directive (91/271/EEC) – despite Brexit, this key EU environmental directive has been retained in UK law and affects the way in which urban wastewater is collected and treated before discharge into public water bodies.
- Environmental Permitting (England and Wales) Regulations 2016
In other jurisdictions, different standards and regulation would apply. The goal of creating these standards is to safeguard strong standards of water quality and set out a framework for the way that sewage and industrial discharge are treated before being returned to the environment or recycled.
The Role of Static Mixers in Wastewater Treatment
The operating principle behind all static mixers is ‘continuous flow mixing’. To achieve this, each mixer uses a series of fixed elements within either a pipeline or channel to mix fluids by repeatedly dividing and recombining the flow. Static mixers differ from other mixing machinery in being devoid of moving parts, and often use gravity to feed a stream of effluent or wastewater through the mixer.
In wastewater treatment systems, static mixers facilitate the blending of treatment chemicals with wastewater, promoting the reaction kinetics necessary for effective treatment, without unnecessary energy expenditure. Many organisations employ static mixers to treat a wide array of contaminants, including suspended solids, organic compounds, raw sewage, agricultural chemicals, pathogens, and more recently, other complex contaminants such as pharmaceutical byproducts, hormones and microplastics helping to achieve both regulatory compliance and the safe discharge of treated fluid.
Advantages Of Static Mixers Over Mechanical Mixers:
✔ Improved mixing efficiency.
✔ Energy savings and reduced operational costs.
✔ Space-saving design.
✔ Lower maintenance requirements.
✔ Enhanced treatment of specific pollutants.
In this section, we’ll look at the main applications of static mixers for wastewater treatment applications, as well as the varieties of static mixers used at different stages of the process.
Applications of Static Mixers in Wastewater Treatment
Static mixers are a staple component in many wastewater treatment plants, carrying out various critical mixing processes. Their ability to achieve effective mixing with minimal external energy input, and without moving parts, makes static mixers an extremely valuable asset at several stages of wastewater treatment.
For example:
- In chemical dosing and flocculation, mixers ensure the full integration of coagulants and flocculants with the process water, promoting the agglomeration of finer particles into larger ones that can be easily separated.
- For pH adjustment, static mixers allow the uniform distribution of acids or bases throughout the wastewater stream, providing consistent pH levels for optimal treatment conditions.
- Nutrient addition, which is central to many biological treatment processes, benefits from the precise and homogenous mixing capabilities of static mixers, guaranteeing the dispersion of the essential nutrients required for microbial growth.
- Static mixers can also be used to mix additives into primary, secondary, and tertiary effluents, integrating disinfectants, dechlorination agents, and other treatment chemicals to prepare the effluent for discharge or reuse.
- For the removal of emerging substances – a range of new contaminants making modern wastewater treatment more challenging than ever before, including microplastics, hormones and pharmaceutical byproducts and residues.
Types of Static Mixers:
For wastewater treatment applications, there are three main types of static mixer that are used.
1) Non-Ragging Pipe and Channel Mixers:
‘Ragging’ or ‘clogging’ are common issues in wastewater treatment plants, where entangled fibrous materials can impede mixer operation or block pipes. These mixers are available in both pipe and channel variants, depending on your system, and each features smooth and streamlined mixing elements that minimise the areas where debris can catch and build up. This helps promote continuous and successful mixing even in wastewater applications dealing with high levels of solids and fibrous materials. Typically, these non-ragging mixers are used within primary treatment stages – where the wastewater is almost certain to contain debris which would cause a “normal” static mixer to block – but they can be used in secondary and tertiary treatment stages too, to help avoid any blockages in the event that some of this debris remains in these stages.
Find out more about our range of non-ragging static mixers by clicking here.
2) Static Pipe Mixers:
These cylindrical pipe -shaped mixers are designed to be installed within your pipeline infrastructure, and work by generating controlled turbulence that mixes treatment chemicals with the wastewater flow. Pipe mixers feature a series of baffles within the pipe, which blend the incoming fluids with the chemicals without the need for moving parts. Different static pipe mixers are optimised for different flow rates and pressure drops, making them applicable to a variety of chemical dosing and mixing applications within your treatment process. Typically, this type of mixer should only be placed after screening/filtration steps have already taken place – ie. Where there is little to no chance of debris being present which could block the mixer. They are commonly used in secondary and tertiary treatment stages.
Find out about our range of static pipe mixers here.
3) Static Channel Mixers:
Designed for open channels, or closed duct, water treatment systems, static channel mixers are well suited for large-scale sewage and wastewater treatment operations in which pipelines are not used. The mixers are installed in your water flow channels, using a series of strategically placed mixing elements to induce efficient mixing as the effluent or water flows over them. The design makes it easy to treat high volumes of wastewater with a uniform distribution of treatment chemicals across wide open areas, without the constraint of enclosed piping. Typically, this type of mixer should only be placed after screening/filtration steps have already taken place – ie. Where there is little to no chance of debris being present which could block the mixer. They are commonly used in secondary and tertiary treatment stages.
Our range of channel and duct static mixers can be viewed here.
Design Considerations for Static Mixers in Wastewater Treatment Systems
In this section, we will look at the major design considerations for incorporating static mixers into a wastewater treatment plant. If you’ve got any questions that aren’t covered here, call +44 (0)1625 920864 and we can talk you through the details of the implementation process as it pertains to your application.
1) Flow Rates, Velocities and Reynolds Number
The primary design considerations for static mixers used in wastewater treatment systems are flow rate and velocity. These are vital to achieving your required mixing and treatment outcomes.
- Flow Rate: The static mixer should provide good quality mixing across the entire flow rate range of your wastewater treatment process, so that the mixer can effectively blend chemicals with the wastewater for optimal reaction kinetics, without consuming excess energy or causing unwanted pressure drops. Most static mixers can operate across a wide range of flow conditions and accommodate the variable in-flow rates characteristic of wastewater treatment systems.
- Velocity/Reynolds Number: The velocity of the fluid through your mixer should be able to sustain enough turbulent flow – ie. Produce a high Reynolds number – for effective mixing, but not so high as to damage your mix elements.
Striking the delicate balance between flow rate and velocity will facilitate more precise dosing, better use of chemicals, and more consistent treatment quality – while maintaining operational efficiency and cost effectiveness.
2) Material Selection
Static mixers are used in various hazardous applications and are available in several materials. The right choice for your application will be influenced by considerations of chemical compatibility, cost, and durability. Importantly, the material must be capable of resisting corrosion and chemical degradation caused by the substances found in wastewater, especially raw sewage, as well as the harsh chemicals used in the treatment processes. The operational environment of the plant will also affect material choice, including temperature range, pressure, and the pH levels of the wastewater.
Stainless steel is a common choice because of its durability, easy maintenance and cleaning, and strong resistance to corrosion. Various high-grade polymers, including PVC and polypropylene, can also offer a long and reliable service life. Some materials are more costly than others. However, specifying the appropriate material during the system design phase is essential to guarantee the performance and lifespan of your plant, without mounting up costs in repairs and maintenance. Matching your choice of materials to the environmental conditions of your wastewater plant will help you balance your investment with your long-term sustainability goals and maintenance needs.
3) Installation and Maintenance
Two core design considerations when implementing any new equipment are installation and ongoing maintenance requirements. Correct installation – in full adherence with your manufacturer guidelines – will lay the foundations for low routine maintenance requirements and a minor risk of critical failure and downtime, reducing your lifetime cost of ownership. From a design perspective, the installation procedure should ensure the correct positioning of your static mixers within your wastewater pipelines, to prevent operational inefficiencies or damage.
Ongoing routine maintenance can be dramatically reduced by considering your choice of static mixer at the design stage.By ensuring the correct static mixer selection at the start, you can minimise your overall repair bill and reduced unscheduled process interruptions.
Static mixers are designed for low maintenance due to their lack of moving parts – however, it’s crucial to monitor your plant for signs of corrosion or material degradation that could affect your mixing efficiency or the safety of your process.
Routine troubleshooting can include checking for obstructions or build up around your mixing elements, which can impede flow and reduce efficiency.
4) Compatibility with Existing Treatment Infrastructure.
Integrating static mixers into your existing wastewater treatment plant requires careful attention to compatibility and process controls. Important considerations include the physical dimensions of the mixer relative to your existing pipelines and channels – which will determine whether modifications need to be made to your pipes. Ideally, you’ll want to avoid major changes in order to keep your implementation costs and project timeframe down. Static mixers can be easily retrofitted into existing processes, meaning modifications are kept to a minimum.
5) Compliance with Environmental Regulations
The environmental regulatory landscape is complex and rapidly evolving, with different standards being implemented and constantly revised throughout the world. In the UK, for example, The Environmental Permitting (England and Wales) Regulations 2016, in particular, establish an extremely strict framework for mitigating the environmental risks associated with water discharge, waste operations, and other ‘regulated facilities’.
Environmental compliance rests on two principles: environmental safety and energy efficiency. Static mixers, by design, can support compliance on both fronts. For example, the low energy and chemical consumption associated with static mixers contribute to a reduced environmental footprint, ticking the boxes for energy efficiency. Also, with a more efficient chemical dosing and mixing process, the environmental risk associated with wastewater treatment is reduced, allowing you to meet the safety aspect of compliance – reducing levels of contaminants within discharged water below the required consent levels, using the minimum amount of treatment chemicals. Static mixers can help you align your wastewater treatment processes with your organisational sustainability goals, as well as reduce its industrial impact on local ecosystems.
6) Cost-Benefit Analysis:
Before investing in static mixers, we recommend conducting a cost benefit analysis to map out your long-term operational savings against the initial capital investment. The cost of a static mixer varies according to need, scale and materials of construction, and we can’t make generalisations for your business. However, in general, the efficiency of static mixers in mixing processes usually leads to a substantial reduction in both energy and chemical use, translating into lower operating costs and a positive long-term ROI.
As well as this, the durability of static mixing systems further enhance their financial appeal by minimising your repair and replacement expenses over time. To discuss costs and returns with one of our team, please send us a message by [clicking here].
7) Future Trends and Innovations:
Considering the improvements in wastewater treatment processes over the past few years, it’s interesting to speculate what trends and innovations could transform the sector over the coming decade. One critical aspect which will affect future treatment methods is the ever-changing complexion of wastewater – with new, complex contaminants being identified and requiring removal in the modern age. More research on the effects of these contaminants is emerging and as we understand the environmental and biological impacts of them, new treatment methods will be required. Emerging technologies include the integration of computational fluid dynamics (CFD) modelling to enhance mixing efficiency and reduce energy consumption. This ties directly into the sustainability agenda, and the need for wastewater systems to reduce their carbon footprint.
Other innovations, such as self-cleaning mechanisms and modular designs also promise increased sustainability and adaptability for diverse water treatment applications. The integration of smart sensors and IOT connectivity into static mixers could also enable more real-time monitoring and automation, further optimising performance and lowering operating costs.
Case Study 1:
Non Ragging Static Mixers Reduce Cost of Ownership
THE PROBLEM
More and more chemicals are being dosed into today’s modern wastewater treatment plants. Including polymers, ferric sulphate and ferric chloride increasing cost for the operating companies.
When chemicals are not mixed correctly and efficiently over dosing occurs increasing cost of ownership. Many traditional mixing solutions including static mixers designed for clean, fibre and rag free process are not suitable as they will quickly block in wastewater applications causing plant down time and increased maintenance costs.
Wastewater treatment plants are also very sensitive to increased pressure drops within the system so often retrofitting equipment to existing plants is very difficult.
THE SOLUTION
Figure 1
Figure 2
When it comes to phosphorous removal, polymer dosing for sludge preconditioning and other wastewater chemical dosing applications, the Statiflo Non-Ragging (NR) Pipe (Figure 2) and Non-Ragging Channel (Figure 1) static mixers offer significant advantages and cost savings to plant operators.
Consistently proven to avoid ragging/blocking issues caused by the build-up of fibrous solids on mixer elements and virtually maintenance-free; these innovative mixers are designed for adaptable application, efficient performance and easy installation in pipes and live open channels.
In open wastewater channels there can be huge variations in flow levels so, alongside blocking, headloss is often a problem. Using variable angle control vanes, the NRC static mixer gives a high degree of mix with extremely low headloss. This unique variable geometry enables the unit to cover an exceptionally wide range of wastewater velocities and all channel depths found across a wastewater plant. The variable angle concept (Figure 1) allows operators to ‘tune’ the mixer to match and maximise the amount of mixing to the available head.
The mixer’s highly efficient performance further lowers energy consumption and offers plant operators considerable cost savings due to lower chemical usage. Compared with dosing using an open ended pipe, the mixer can improve environmental performance with decreased biochemical oxygen demand (BOD) load and reduced iron concentration levels in the final effluent – minimising unsightly channel staining.
When it comes to wastewater pipes, installing a traditional static mixing element can result in blockage within a matter of hours. The Statiflo NR pipe static mixer offers a very different solution that is specifically designed for use by the wastewater industry. This mixer has been well proven to remain clean and free flowing; resulting in efficient, consistent mixing performance over prolonged periods without blocking.
The NR static mixer (Figure 2) uses a series of static elements that are uniquely placed and angled to avoid leading edges where fibrous material would otherwise attach and build up. These elements force fluid from the outside to the centre of the device, creating a more rotational mixing effect rather than the traditional radial mixing and flow division generated by clean water static mixers. Further down the pipe more elements repeatedly reverse the flow rotation. As well as having nowhere for fibres to attach to the elements, the mixer design also provides clear space for any obstructive materials to pass easily through the mixer while they are being rotated and mixed. A simple concept which is highly effective.
Available in a wide range of diameters and materials, and with optional dosing points, the resulting performance of the NR static mixer provides greater mixing efficiency than orifice plates, sludge mixing valves or direct dosing into sludge pumps without creating the typical blocking issues commonly associated with static mixers in wastewater pipes. This leads to better mixing performance without the need for a power supply and can significantly reduce the consumption of chemicals, such as polymers, needed across the plant.
Figure 3
Figure 4
Case Study 2:
Replacing an Inefficient Dynamic Mixer
PROBLEM
As part of their policy of constant improvement and updating, Southern Water had identified that an opportunity existed to improve consistency of performance, energy consumption and maintenance costs at their Testwood Works. These changes called for the replacement of an existing dynamic flash mixer to ensure improved process performance together with reduced running costs.
SOLUTION
Southern Water’s engineers decided to replace the outdated machinery with state of the art static mixing technology from Statiflo. Incorporating a 600mm NB Statiflo Motionless Mixer at the inlet works ensured the total and efficient distribution of dosed coagulant uniformly throughout the treated water. The mixer also substantially enhanced coagulation by applying a regular and controlled shear to the raw water which improved the flocculation process thereafter. A streaming current detector was also incorporated to control coagulant dosage.
RESULT
The installation of the Statiflo Motionless Mixer was a spectacular success. Excessive chemical consumption was vastly reduced, as were the substantial energy and maintenance costs. The Statiflo Mixer operates with no moving parts, no spare parts requirements and no maintenance whatsoever. The small head loss penalty of 130mm WG (at 20 MLD) equated to an actual power consumption of a mere 0.3kW as opposed to the 15kW required by the original dynamic flash mixer. Substantially improved process performance was also achieved producing water of previously unseen quality. The reduction in chemical consumption alone would have resulted in a payback of the mixer capital cost within one year, but the high level of energy savings recorded meant that payback was in fact achieved in a matter of weeks.
OTHER STATIFLO FEATURES
- Minimal space requirement
- Completely sealed system
- Predictable blending and dispersion formation
- Eliminates radial gradients
- Approaches deal plug flow
- Self cleaning
- Improved process control & product quality
- Processes all pumpable material in laminar or turbulent flow
- Available in small and large diameters
- Manufactured in all commercially available materials
- Designs available for open channel and rectangular duct systems
- Can be installed in bends to save space
- Custom designs to meet special specifications
- Manufactured to meet all levels of QA/QC
- Low installed weight
STATIFLO MOTIONLESS MIXER FEATURES OF PRIMARY IMPORTANCE IN THIS CASE STUDY
- No moving parts for virtually maintenance-free operation
- Low energy consumption
- Low capital cost
- Eliminates overdosing
- Chemical injection rates reduced to a minimum
Case Study 3:
Gas Dispersion Systems
PROBLEM
The inline dispersion of gases into large volumes of liquids is often performed using complex equipment, usually involving large compressors, pressurised gas containers and fine bubble diffusers. In many cases in the water treatment industry, this type of approach is a complicated and extremely expensive method of simple gas dispersion – a classic example being the oxidation of soluble iron in water using air or oxygen.
SOLUTION
The use of a combination of Statiflo Mixers has resulted in an extremely simple, cost effective and efficient alternative solution. The Statiflo inline gas dispersion system consists of a large diameter gas contacting static mixer, supplied as a flanged pipework component designed to bolt directly into the existing pipework system. Attached to this, as part of an integral package, Statiflo provide a small motive water pump, a small diameter gas dispersion static mixer, interconnecting pipework, valves and gauges for a self contained system. The motive water pump withdraws a small flow of untreated water from the inlet of the gas contacting static mixer and passes it through the small predispersion static mixer, where gas is injected at ideal dispersion velocities. This results in an intimate mixture of fine gas bubbles and water which is then injected into the large diameter gas contacting static mixer. The two phase flow is uniformly dispersed into the main water stream, ensuring optimum gas/liquid contact and highly efficient mass transfer.
RESULT
Efficient continuous mass transfer is achieved with low installed and operating costs and with minimal maintenance. As the gas bubble size is a function of the predispersion mixer flowrate and not the mainstream water flowrate, the systems maintains high efficiency at low flowrate conditions. Whether the application is oxidation of soluble iron with air, the aeration of potable water with oxygen or ozone treatment, the Statiflo gas dispersion system provides the ideal combination of cost and efficiency.
FEATURES OF PRIMARY IMPORTANCE IN THIS CASE HISTORY
- Competitive price compared with traditional methods of gas dispersion and mass transfer
- Extremely simple installation procedure
- Economic operating costs
- Consistent and predictable performance
OTHER STATIFLO MIXER FEATURES & BENEFITS
- Minimal space requirement
- Completely sealed system
- Self cleaning
- Available in all sizes
- Available in any material
- Custom designed
- Meets all QA/QC levels
- Available worldwide
Next Steps
Statiflo International are market leaders in static mixing solutions, with a wide range of static mixers designed for various applications, including wastewater treatment, petrochemical processing, food, drink, and pharmaceutical manufacturing, and more. With a global reputation for excellence and quality, our static mixing machinery helps our customers deliver efficient and consistent results, in full compliance with UK, EU and international water treatment standards.
To find out how our innovative product range can help improve your mixing efficiency, reduce your energy costs, and enhance the overall effectiveness of your equipment, please explore our website, or contact one of our team in our various offices using the details below:
Statiflo Office & Contact Details:
✔ Statiflo International Ltd
Wood Street, Macclesfield, Cheshire SK11 6JQ, United Kingdom
Tel: +44 (0)1625 920864
Fax: +44 (0)1625 511376
✔ Statiflo Corp
75 South Church St, 6th Floor, Pittsfield, MA 01201, USA
Tel: +1 (413) 684-9911
Fax: +1 (413) 464-8239
E-mail: [email protected]
✔ Statiflo Inc
2175 Sheppard Ave E, Suite 203, Willowdale, Ontario M2J 1W8, Canada
Tel: +1 (416) 756-2406
Fax: +1 (416) 490-6937
E-mail: [email protected]
