Bolnhurst Water Recycling Centre in Bedfordshire is undergoing a significant upgrade to comply with new phosphorus discharge limits under the UK Water Industry National Environment Programme. The requirement to meet a 0.5 mg/L consent has prompted Anglian Water and its @one Alliance to adopt a non-traditional approach centred on algae phosphorus removal.
Rather than relying solely on chemical dosing or energy-intensive tertiary processes, the project integrates an algae-based photobioreactor between the primary and final settlement stages. The objective is twofold: secure compliance and demonstrate a lower-carbon pathway for nutrient management.
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Why Bolnhurst required a new treatment model
Bolnhurst previously had no dedicated phosphorus removal capability and operated with ageing rotating biological contactors and lagoon settlement. Meeting the new consent required a full rethink of treatment, not simply a bolt-on tertiary unit.
The site presented additional constraints. Limited footprint, ageing assets, the need to maintain operational continuity during construction, and alignment with Anglian Water’s net-zero 2030 target shaped the solution selection.
Through a multi-criteria assessment covering cost, carbon footprint, and operability, an innovative algae-based photobioreactor was selected as the preferred option.
How the ALGAESYS system works
The central feature of the upgrade is a 200 m² modular photobioreactor system supplied by ALGAESYS S.A. The process harnesses naturally occurring algae to assimilate dissolved phosphorus and nutrients from secondary effluent.
As the algae grow, they capture phosphorus within their biomass, enabling removal without chemical precipitation. The system operates within modular tanks, supported by LED lighting and controlled aeration to maintain biological activity throughout seasonal variations.
Once established, algal biomass can be harvested with potential for beneficial reuse in agriculture, aligning with circular economy principles. The broader treatment train also includes tertiary sand filters, new inlet screening and pumps, bespoke motor control centres and SCADA integration.
A temporary lamella clarifier with ferric dosing was installed to ensure compliance ahead of full commissioning, reducing the risk of permit breaches during the transition.
Expected outcomes from algae phosphorus removal
The scheme is expected to deliver consistent compliance with the 0.5 mg/L phosphorus limit, more than 50 per cent reduction in carbon emissions relative to baselines, and significantly lower energy consumption compared with conventional systems.
The modular configuration allows future expansion and adaptation, addressing footprint constraints typical of small rural works. Lessons learned at Bolnhurst are intended to inform wider phosphorus removal planning across Anglian Water’s AMP8 programme.
From ALGAESYS’ perspective, Bolnhurst represents a milestone in embedding decentralised, nature-based wastewater treatment within a major national utility framework. For Anglian Water, it demonstrates how regulatory drivers can catalyse innovation while progressing carbon and resilience objectives.
Once fully commissioned, Bolnhurst is expected to become one of the first UK sites to achieve phosphorus consent through a large-scale, chemical-free algae phosphorus removal process.
ALGAESYS will be participating in Connected by Water 2026, joining sector leaders to discuss algae phosphorus removal and nature-based wastewater treatment solutions.