Climate change is increasing variability in Nordic surface waters. Tailored coagulant blends help utilities improve NOM removal, reduce chemicals and sludge, extend filter runs, and increase effective plant capacity without major infrastructure expansion.
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Across the Nordic region, drinking water utilities are facing a new operational reality. Climate change is affecting the quality and variability of surface water sources, placing increasing pressure on treatment plants that were often designed for more stable raw water conditions.
Rising levels of natural organic matter (NOM), progressive browning of lakes and rivers, more intense rainfall events, seasonal colour fluctuations and prolonged cold-water periods are making coagulation more difficult to control. For waterworks that rely on surface water, these changes can increase chemical demand, reduce process stability, shorten filter run times and increase sludge production.
For utilities, the challenge is clear:
How can drinking water treatment plants remain reliable, efficient and compliant when raw water quality is becoming less predictable?
One practical answer is climate-resilient coagulation.
Nordic surface waters are changing
Surface water is a key source of drinking water in the Nordic countries. However, many lakes, rivers and reservoirs are increasingly affected by changes in organic loading, colour and turbidity.
One of the most important trends is the increase in dissolved organic matter, often described as brownification or browning. This is caused by several interacting factors, including climate change, changes in precipitation, catchment conditions and recovery from historical acidification.
For drinking water producers, higher NOM and colour levels can create several treatment challenges:
- Higher coagulant demand
- Greater pH and alkalinity impact
- Increased risk of turbidity breakthrough
- Higher sludge production
- Shorter filter run times
- More frequent backwashing
- Greater operational workload
- More variable residual aluminium control
Extreme rainfall can make the situation even more challenging. Heavy precipitation events can rapidly change turbidity, colour, UV254 and organic loading. These sudden shifts can be difficult to manage with fixed dosing strategies or traditional coagulant programs.
At the same time, Nordic treatment plants must often operate under cold-water conditions, where coagulation reactions can be slower and floc formation can be weaker. This combination of cold water, high NOM and rapid raw water variation creates a demanding operating environment.
Why conventional alum treatment can be challenged
Aluminium sulfate, commonly known as alum, has been widely used in drinking water treatment for decades. It remains an important and well-established coagulant. However, in high-NOM waters, cold-water conditions or situations with rapid raw water variability, conventional alum-based treatment can face limitations.
Typical operational challenges may include:
- Increased coagulant dosage requirements
- Lower pH and higher need for alkalinity or pH correction
- Weaker or slower floc formation
- Shorter filter runs due to faster head-loss development
- Reduced process stability during seasonal NOM peaks
- More operator intervention during raw water events
In many plants, these challenges are managed by increasing the alum dose. However, this can also increase sludge production, pH adjustment requirements and overall chemical consumption. In capacity-constrained plants, shorter filter runs and more frequent backwashing can also reduce the net production capacity of the treatment process.
This means the issue is not only chemical performance. It is also plant capacity, operational resilience and long-term sustainability.
Climate-resilient coagulation: a practical pathway
Climate-resilient coagulation is about designing the coagulation process to perform reliably across a wider range of raw water conditions.
Instead of relying only on one standard coagulant, tailored advanced coagulant blends can be developed based on the specific characteristics of the raw water and the treatment plant. These blends may combine different coagulant and flocculant technologies to improve performance under changing conditions.
A tailored approach typically considers:
- Raw water NOM and colour
- UV254 and organic character
- Turbidity variation
- Temperature profile
- pH and alkalinity
- Existing mixing and flocculation conditions
- Sedimentation or flotation performance
- Filter design and hydraulic loading
- Sludge handling limitations
- Plant capacity constraints
This makes it possible to optimize coagulation for the actual conditions at the plant, rather than applying a one-size-fits-all solution.
The role of tailored advanced coagulant blends
Tailored coagulant blends are designed to improve destabilization of particles and organic matter, strengthen floc formation and improve downstream clarification and filtration performance.
For Nordic surface water plants, this can provide several important benefits.
1. Improved NOM and colour removal
Natural organic matter is one of the main drivers of treatment complexity in surface water plants. NOM contributes to colour, increases coagulant demand and can act as a precursor for microbial regrowth and disinfection by-products.
Tailored coagulant blends can improve NOM and colour removal by matching the coagulant chemistry to the organic character of the raw water. This is especially important during seasonal peaks, snowmelt periods, autumn turnover and heavy rainfall events.
Improved NOM removal helps utilities maintain more stable treated water quality and strengthens the overall treatment barrier.
2. Reduced coagulant dose and improved pH stability
A more efficient coagulant program can reduce the overall coagulant dose needed to achieve the same or better treatment performance.
This can also reduce the need for pH adjustment chemicals. Compared with conventional alum treatment, optimized blends can often have less impact on pH and alkalinity, depending on the chemistry and plant conditions.
For operators, this can mean:
- Lower chemical consumption
- More stable coagulation pH
- Reduced use of acid, caustic or alkalinity correction chemicals
- Simpler process control
- Lower operating costs
- Improved treatment consistency
This is particularly relevant in Nordic surface waters, where alkalinity may be low and pH control can be a critical part of coagulation performance.
3. Lower sludge production
Coagulation performance has a direct impact on sludge production. Higher coagulant doses typically increase the amount of chemical sludge generated.
By improving coagulation efficiency and floc formation, tailored blends can help reduce sludge volumes. This can lower the burden on sludge handling, thickening, dewatering and disposal systems.
Lower sludge production also supports sustainability goals by reducing transport, handling costs and resource use.
4. Longer filter run times and increased plant capacity
Filtration is often one of the key capacity-limiting steps in drinking water treatment. When coagulation is not optimized, weaker flocs and higher solids loading can cause faster head-loss development in filters. This leads to shorter filter runs and more frequent backwashing.
Tailored coagulant blends can improve floc strength, reduce solids carryover and slow head-loss development. This allows filters to operate for longer periods between backwashes.
Longer filter runs reduce backwash frequency, lower water and energy use, and increase net production time. In capacity-constrained plants, this can directly increase effective treatment capacity and improve operational flexibility during peak demand or extreme raw water events without expanding physical infrastructure.
This is one of the most important operational advantages of optimized coagulation. It links chemistry directly to plant capacity, resilience and capital efficiency.
5. More stable turbidity and residual aluminium control
Stable turbidity and residual aluminium control are essential for drinking water quality and regulatory confidence.
During cold-water operation or rapid raw water changes, conventional coagulation can become more difficult to control. Tailored blends can support stronger and more predictable floc formation, helping maintain more consistent clarification and filtration performance.
This can reduce the risk of process disturbances and make the treatment plant less sensitive to sudden changes in raw water quality.
Supporting compliance and risk-based drinking water management
The EU Drinking Water Directive places strong emphasis on safe drinking water, risk-based thinking and preventive control throughout the water supply chain.
For treatment plants, this means that process robustness and operational control are becoming increasingly important. Coagulation is a critical treatment barrier for many surface water systems, especially where NOM, turbidity and colour fluctuate over time.
A more resilient coagulation strategy can help utilities strengthen barrier performance, improve process documentation and reduce the risk of water quality deviations.
Sustainability benefits for Nordic utilities
Climate resilience and sustainability are closely linked.
Optimized coagulation can support sustainability by reducing:
- Chemical consumption
- pH adjustment chemicals
- Sludge generation
- Backwash water use
- Energy consumption
- Transport and disposal requirements
- Need for premature infrastructure expansion
A practical approach to implementation
A successful transition to tailored coagulant blends normally begins with a structured assessment of the existing treatment process.
This can include:
- Raw water characterization
- Review of historical plant data
- Jar testing under different seasonal conditions
- Evaluation of pH, alkalinity and dose response
- Assessment of floc formation and settling performance
- Filter performance review
- Sludge production assessment
- Full-scale plant trial
- Monitoring and dose optimization
- Continuous follow-up and adjustment
This practical, data-driven approach ensures that the solution is matched to the plant’s real operating conditions.
Why this matters for Nordic surface water treatment
Nordic drinking water utilities are expected to face increasing pressure from climate-driven raw water variability. Higher NOM, more colour, extreme rainfall and cold-water operation will continue to challenge conventional treatment processes.
Tailored advanced coagulant blends offer a practical pathway to stronger climate resilience. By improving NOM and colour removal, reducing chemical consumption, lowering sludge production, extending filter run times and increasing effective plant capacity, utilities can improve both performance and sustainability without major infrastructure expansion.
For many waterworks, the future of climate-resilient drinking water treatment will not depend on one single technology. It will depend on combining strong process knowledge, optimized chemistry, online monitoring and close cooperation between utilities and treatment specialists.
Alumichem’s role
Alumichem works with water utilities to develop tailored treatment solutions for complex and changing water quality conditions. By combining advanced coagulant technology, application expertise and plant-specific optimization, Alumichem helps drinking water producers improve process stability, reduce operating costs and strengthen climate resilience.
As Nordic surface waters continue to change, adaptive coagulation strategies will play an increasingly important role in safeguarding reliable, sustainable and high-quality drinking water production.
