Phosphorus reduction is high on the agenda of wastewater treatment plant operators at utility and industrial sites in the UK, and innovative modular systems are meeting environmental obligations for UK sites large and small. In this Q&A, Andrew Baird, technical director at Marlowe Environmental Services, formally WCSEE, outlines the challenges and solutions with a focus on small and constrained sites.
What are the drivers for phosphorus reduction on environmental discharges in England and Wales?
Water and industrial sites in England and Wales face stricter limits on ammonia, phosphorus and effluent quality under AMP8 (2025–30) and the Environment Act 2021, which mandates an 80% reduction in phosphorus by 2038. These tighter consents respond to public concern over storm overflows and environmental pollution, with some permits as low as 0.25 mg/litre, while also accommodating population growth and rising influent loads.
Small and constrained sites face specific challenges, needing to meet strict consents in limited space, manage seasonal load fluctuations, plan for future growth and maintain high effluent standards in rural or sensitive locations.
How can the regulatory expectations on tighter consents be met, especially at small-to-medium-sized sites and rural plants?
For sites with limited space, compact, modular solutions allow fast installation and retrofits without heavy civil works. These systems can scale to handle seasonal flows, future growth and high effluent standards while reducing construction time and cost.
Operational resilience is essential to maintain compliance under variable loads, network infiltration and extreme weather events. Modular systems also support lower whole-life costs (TOTEX) compared with traditional high capital expansion models.
Key considerations for small and constrained sites include managing seasonal flows, planning for growth and maintaining high effluent standards in rural or sensitive locations.
What kinds of solutions are effective for onsite phosphorus removal and how do they work?
For Marlowe Environmental Services (MES), there are two key treatment solutions for phosphorus removal – the HiPAF – high performance aerated filter and the Flocell XFM filtration system. They can be used individually or in combination, depending on the specific site requirement. These two solutions are particularly well suited for small and constrained sites due to their compact, modular design, flexibility and scalability.
HiPAF package wastewater treatment
The integral below ground HiPAF package treatment system can serve from 1 to 2,000 population equivalent (PE). The range starts with a compact system up to 60 PE for smaller sites and its modular design options make it ideal for site retrofits and constrained spaces.
The package treatment system can serve from one to 2,000 population equivalent (PE). Its compact, modular design makes it ideal for retrofits and constrained spaces.
- Raw wastewater enters the first tank, where gravity pulls organic and inorganic solids to the bottom, preparing the liquor for biological treatment.
- Stage two is biological treatment in the patented Hybrid biozone, which is proven to outperform traditional submerged aerated filter (SAF) and moving-bed biofilm reactor (MBBR) systems.
- Stage three is final settlement, where an airlift pump automatically transfers settled humus sludge back to the primary settlement tank for co-settlement and later desludging.
Read about the HiPAF in greater depth here.
Image of HiPAF and HPC
Flocell XFM Mini filtration system
The Flocell XFM Mini can be used for both tertiary solids and phosphorus removal. The units can be operated under pumped or gravity flow and can be used inline or in a ‘dialysis’ flow mode.
Its compact design and flexible operation make it well suited for small and constrained sites.
The simplicity and robustness of the Flocell XFM system means it can be set up to be operational quickly and with limited commissioning requirements. The system can operate for extended periods without a cleaning cycle and in dialysis mode there is no requirement for a complex flow control system, which adds to the simplicity of installation.
Should onsite flow rates change, multiple units can be connected in series, or run independently on multi-pass, to treat significantly higher flows. This ensures a wide range of environmental permits can be met quickly and efficiently and provides scalable capacity to meet evolving flow demands and tighter environmental permits efficiently.
Read in-depth into the Flocell XFM Mini here.
The two technologies used in combination can achieve consents of 5mg/l biological oxygen demand (BOD), 1mg/l ammoniacal nitrogen and better than 8mg/l suspended solids. With chemical dosing, phosphorus levels as low as 0.04mg/l can be met. With added UV treatment, the effluent has the potential to reach water qualities suitable for irrigation purposes.
Flocell XFM mini
Is chemical dosing typically needed to achieve phosphorus consents?
For WwTP operators with tight phosphorus consents to meet, chemical dosing is usually required. This can be done through several means, including electro-coagulation and two-point chemical dosing using aluminium, ferric or an organic coagulant.
Both the HiPAF and Flocell XFM systems can be upgraded for tighter future phosphorus limits by adjusting chemical dosing in the future, which can be supported by technicians from the MES team.
How does HiPAF performance hold up under diurnal flows and seasonal fluctuations?
The HiPAF primary tanks with forward feed have a buffering capacity that can run at 150% of design load for two hours. It is also designed to run at a minimum of 10% of the design load.
Its reliability for seasonal or fluctuating flows makes it well suited for small sites needing consistent performance year-round such as SSI sites and leisure and tourism facilities.
Can the HiPAF and XFM Flocell Mini be retrofit onto existing works?
Both the HiPAF and XFM Flocell Mini systems have been specifically designed for retrofit onto existing WwTPs without the need for heavy civil engineering works.
Retrofit with HiPAF repurposes existing vessels, saving space while maintaining performance for seasonal flows and variable loads. This makes it highly suitable for small and constrained sites including campsites, leisure facilities and rural installations.
The Flocell XFM Mini can be retrofitted to the rear of a septic tank or packaged treatment plant and is ideally suited for tertiary treatment and phosphorus removal.
Technicians at MES work closely with customers to undertake a holistic assessment of the plant to ensure retrofits can be done robustly and to the highest standard without risking plant functionality or safety.
How does energy and water consumption compare between the two systems?
Both the HiPAF and Flocell XFM Mini offer high energy efficiency systems that align with water company net zero ambitions.
The patented HiPAF system comprises combined SAF and MBBR technologies, proven to treat wastewater with higher energy efficiency when compared to other submerged hybrids. Timers are fitted to the blowers as standard, and existing systems can be easily retrofitted by MES technicians making it ideal for small or constrained sites while cutting energy use by up to 50 percent.
The Flocell XFM Mini, which has 3l/s capacity, does not require a blower at all, as sufficient air is drawn into the bed to fully scour the media. With no moving parts, energy consumption is significantly reduced and, unlike other technologies, the system requires no process water to operate.
Only the volume of the filter unit itself is discharged when cleaning, with prolonged periods of operation possible due to a high retention capacity and low maintenance requirement. This makes the Flocell XFM filtration system over 99.9% water efficient.
More importantly, the solids content of the water from the cleaning cycle can be very high, but typically comprises 0.8 to 1.2% dry solids. This means the throughput can go directly to onsite sludge storage or be returned to the head of the works for co-settlement with incoming effluent, without adding significantly to the hydraulic load.
These energy and water efficient designs are especially useful for small sites where utilities footprint and operational simplicity are critical considerations.
How much operational intervention is needed on site?
Neither the HiPAF nor the Flocell XFM technology requires ongoing onsite operator intervention, except for desludging and annual filter changes.
The Flocell XFM Mini only requires checks every one-to-two weeks and depending on the criteria for each site, customers can also opt for a bolt-on to make the Flocell fully automated, with the use of telemetry to extend time between checks. For small or constrained sites, minimal operational demands help reduce staffing and complexity on site.
For both technologies it is recommended that checks are carried out every two weeks on average to ensure longevity and continued functionality.
What about spare parts?
The HiPAF has no electrical or mechanical moving parts and includes a 25-year-plus lifespan guarantee on the tank. The Flocell XFM Mini also has no moving parts in the filtration system and no replacement parts, consumables or lubricants needed, with a 20-year lifespan on average. Long-lasting, low-maintenance systems are ideal for sites with limited onsite support.
How easy is installation?
The HiPAF can be easily installed above or below ground, and both the HiPAF and Flocell XFM Mini have a compact modular design to suit any size of WwTP. Both systems are scalable to fit any population equivalent and are built off-site and delivered in self-contained units to reduce onsite installation time. This modularity and offsite construction make them particularly suitable for small and constrained sites, reducing installation footprint, complexity and risk.
To learn more about how we can support you visit www.marlowe-es.com or reach out to Andrew Baird via andrew.baird@marlowe-es.com or 0782 594 2923.