The different approaches to chemical phosphorus removal across the UK wastewater industry

Water companies in the United Kingdom are currently facing unprecedented tightening of phosphorus discharge consents, which will only become stricter in the near future. Historically, the most widely applied method of phosphorus removal has been chemical precipitation through the addition of iron or aluminium salts. Although more sustainable options, such as biological processes, are already being implemented at key sites, data shows that chemical removal is likely to remain an integral part of wastewater treatment-whether as the main method in small or problematic works or as a trim for meeting consents below 1 mg/L, not achievable through biological removal alone. All sewage treatment providers in the United Kingdom have developed asset standards (internal design and operation guidelines) for the design and management of chemical precipitation at existing works. However, the approach has not been consistent throughout the sector, with wide variations of criteria, brackets and rules of thumb. This paper collates and compares these approaches, looking at asset standards from most of the water companies in the United Kingdom. The methods stated in these standards have been applied for the sizing of chemical phosphorus removal on four simulated sites, to meet theoretical consents based upon the future discharge requirements set by the Environment Agency under the Water Industry National Environment Programme. The study compared the various design guidelines for chemical phosphorus removal from across the water industry in the United Kingdom.This brought to light wide disparities in the design approach.This results in vastly different outputs, potentially oversized equipment and exaggerated forecasts for chemical consumption.Historical site experience, dealing with existing phosphorus permits, has been a key factor for the development of the more streamlined designs by some water companies.