Southern Water Purchases Phosphorus Filtration Technology

Trial of an innovative phosphorus removal technology at a Sussex wastewater treatment plant (WwTP) has led to the purchase of two Flocell XFM20 filtration units by UK utility Southern Water.

Wastewater treatment specialist WCS Environmental Engineering (WCSEE), now Marlowe Environmental Services (MES), initially hired out the equipment for use at Storrington WwTP in June 2025. Following a successful trial period, Southern Water took the decision to approve the units for permanent ongoing use.

The two Flocell XFM20 units, comprising four modular filters, can process flows up to 40l/s collectively. Installed and delivered in a 6m container with no requirement for additional civil engineering, the system is enhancing existing tertiary treatment, enabling Storrington WwTP to consistently achieve its 0.5 mg/litre phosphorus consent, with a peak flow of 47l/s, serving a population equivalent of approximately 8,000.

Stringent permits
The Environment Act 2021 mandates an 80% reduction in phosphorus from treated wastewater by 2038, with interim targets for water companies to invest in upgrades. Water companies in England and Wales face ongoing challenges to meet the stringent phosphorus permits, some as low as 0.25mg/litre.

For Storrington WwTP managers this meant identifying a robust, space-efficient, solution capable of enhancing current treatment performance without extensive civils and on a short lead time, while ensuring site compliance to meet a permit of 15mg/l biological oxygen demand (BOD), 20mg/l total suspended solids, 0.5mg/l phosphorus, 4mg/l iron, and 10mg/l ammonia.

Connor Sandalls, senior processing engineer at Southern Water, said, “I discovered Flocell XFM at the European Wastewater Management Conference in 2024 and immediately saw the potential for implementation at several Southern Water WwTPs.

“Following the hire which began in June 2025, the two Flocell XFM20 units have been approved as one of a range of treatment options for Southern Water to use at appropriate wastewater treatment works. The engagement and collaboration have been fundamental to the success of the hire period.”

Adaptable technology
Flocell XFM can be used for both tertiary solids and phosphorus removal. The open-cell media is designed to efficiently reduce difficult-to-manage flocs, retaining particulates without increasing pressure within the filter or reducing flow. The units can be operated under pumped or gravity flow and can be used inline or in a ‘dialysis’ flow mode.

Monica Rodrigues, utilities sales manager at MES, said, “It is great to collaborate with Southern Water and to see the process through from initial enquiry, hiring, installation, and final purchase. MES is proud to be trusted to deliver tight phosphorus consents at Storrington and other WwTPs.”

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 backwash, and in dialysis mode there is no requirement for a complex flow control system, which adds to the simplicity of installation.

Water efficiency
Flocell XFM uses air to clean the filters - low-energy blowers agitate the media pack, removing contained solids during the short cleaning cycle. With no moving parts, the Flocell XFM significantly reduces energy consumption and unlike other technologies, requires no process water to operate, substantially reducing the volume of backwash water required for cleaning.

Only the volume of the filter unit is discharged when cleaning, with prolonged periods of operation possible due to a high retention capacity and low maintenance requirements. This makes the Flocell XFM filtration system over 99.9% water efficient.

More importantly, the solids content of the backwash can be very high, but typically 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.

Rodrigues said, “Achieving low phosphorus results, while maintaining over 99.9% water use efficiency, removes the need for backwash tanks and associated infrastructure. The system also maintains operational hydraulic loading in a small and compact footprint, which requires only a level base, and can be delivered to site and brought online within a few hours of deployment.”

Ease of use
Should the 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.

Sandalls said, “Once Southern Water had approved the use of the Flocell XFM units, the process was very smooth and there has been direct and on-going collaboration with WCSEE during installation, set-up, and operations. Engineers from MES attended onsite to train operations teams and processing engineers from a number of WwTPs, with the intention that Southern Water will expand use of Flocell XFMs at other sites in the future.”