As global pressures around limiting environmental impacts of phosphorous and availability of phosphate fertilizers to support food production continue to grow, requirements around phosphorous recovery from wastewater are emerging. Municipal wastewater facilities have a unique opportunity through the recovery of phosphorous to limit point-source and non-point source nutrient discharge that impact water bodies with the production of a market viable struvite fertilizer product.
Phosphorus has long been identified as an element that is essential to life through the food we consume. With world population continuing to grow, phosphorus fertilizer production has soared to support the food production required. This has highlighted the need to recover phosphorous to reduce dependence on imports from limited regions with highly concentrated rock phosphorus reserves. In countries like Europe, Germany and Switzerland they are taking action to require phosphorous recovery and expect this trend to continue to spread.
Phosphorous is also a known contributor to eutrophication that is impacting our local water bodies which has driven the recent increase in mandates around removal from wastewater facilities. According to the EPA, nutrient impairment prevails in 58% of the nation’s rivers and streams, 45% of our lakes, about two thirds of our coastal areas, and more than one third of our estuaries. To address this, the EPA is working to increase the adoption and tightening of discharge phosphorous limits. In the United States approximately 150 plants add new permits every year for reduced phosphorous discharge levels. Phosphorous recovery through struvite precipitation provides the opportunity to address the major global challenges we face around phosphorous.
Evoqua Water Technologies and Ostara Nutrient Recovery Solutions have partnered with a licensing agreement where Evoqua will engineer and supply the Ostara Pearl nutrient recovery system while Ostara continues to support the process design and handle the struvite offtake. This water treatment solution revolves around the treatment of the high nutrient loaded post digestion centrate line with recovery of phosphorus and nitrogen in the form of struvite. This reduces point source phosphorous eutrophication while also supporting food production with the controlled production of struvite which can then be resold as “Crystal Green®” fertilizer.
The system consists of two major components, the core piece being the Ostara Pearl® system which is designed to precipitate struvite from the centrate of filtrate streams. Also included in the equipment package is the product handling equipment. This includes dewatering, drying, and bagging equipment to prepare the Crystal Green® fertilizer to be commercially ready for shipment. The other piece of the solution is the WASSTRIP™ system, which is designed to improve internal phosphorous removal providing critical benefits to plant operations, maximizing nutrient removal and recovery in a controlled environment.
Through the controlled precipitation of struvite within the reactor, the Pearl® system reduces the phosphorous load in the recycled centrate or filtrate line by up to 85%. This additional outlet for phosphorus reduces nuisance struvite issues, lightens phosphorous load that is recycled back to the front of the plant that causes challenges for BNR treatment, and assists in achieving effluent phosphorous limits all while producing an ecofriendly, commercially viable fertilizer product, Crystal Green® fertilizer.
The WASSTRIP™ system is an anaerobic stage in the side stream that is designed to allow for phosphorous release from PAOs in WAS. This provides benefits to facilities using anaerobic digestion by releasing phosphorus and magnesium upstream in the process and bypassing the anaerobic digester system sending the stream directly to the Pearl® system. Magnesium is typically the limiting component for struvite production in municipal applications, with each ton of magnesium diverted around the digestor resulting in 10 tons less unintentional struvite production. Bypassing of Magnesium helps protect digesters, dewatering equipment, and pipes from struvite scale formation, while bypassing phosphate improves dewaterability, and reduces biosolids volume.
Studies point to the release of phosphorous from the WAS prior to dewatering, provides a more favorable monovalent to divalent cation ratio, providing up to 4% improvement in cake solids and 15% reduction in polymer use.
It can be a difficult task for a wastewater plant to identify a market and sell a product into that market as it strays off from the main vital mission of treating wastewater and meeting permit limits, especially for small to midsize plants. Fortunately, Ostara has a committed group that has worked on research, marketing the product based on this research, and selling it to the agricultural industry. This allows any plant that does implement an Ostara Pearl system to have a guaranteed buyer that will purchase the product from the end user. Ostara will pick up the product from your specific site and will pay an agreed amount based on product produced.
Crystal Green® fertilizer is only 4% water soluble versus ~90% water solubility for typical phosphorous fertilizers. This greatly reduces the runoff and leaching of phosphorous into our waterways and groundwater. The nutrients are accessible from acid release of the crop roots allowing the fertilizer to remain in the root zone longer, requiring less phosphorous application for greater crop yields.
Due to the fertilizer being produced from controlled precipitation of struvite through targeted reaction conditions, the product is >99.6% pure struvite in its final form making it a viable resource recovery product. Crystal Green® fertilizer is a registered fertilizer in US and Canada, an AAPFCO approved source of slow-release nutrients, and a USDA CSP approved input.
