9 october 2017

Canal de Isabel II

Spain's first phosphorus recovery plant.

In 2016, Canal de Isabel II commissioned Spain’s first industrial scale plant for the recovery of phosphorus in the form of struvite at the Sur de Madrid Wastewater Treatment Plant (WWTP). It is sized to extract up to 260 kg of phosphorus per day from the WWTP’s two return streams. Canal de Isabel II has invested €2.3 million in this initiative, which is in line with the company’s commitment to the circular economy, environmental care, sustainable management and investment in R&D&i.
Canal de Isabel
The Sur de Madrid WWTP is located on the left bank of the River Manzanares and receives wastewater from the Sur sewer. The existing sewer network enables the wastewater from other plants situated upstream from the Sur WWTP to be diverted there in the event that further treatment is necessary to guarantee the quality of the water returned to the receiving waterway. This also endows the system with flexibility.
What is struvite?
Uncontrolled struvite precipitation is a problem at wastewater treatment plants because it causes clogging of pipes, generally in the sludge line, downstream from anaerobic digestion.
Struvite is a crystal made up of magnesium, ammonium and phosphate (NH4MgPO4·6(H2O)) which forms when these three ions are present in the solution above their saturation points. Magnesium is the limiting reactant in wastewater treatment and it must be provided in the form of magnesium chloride or magnesium oxide in order to balance the concentration of phosphorus, generating a product that can be used at industrial level for certain applications. Eliminating this compound significantly reduces struvite precipitations in sludge line pipes.
Project objective and scope
This project saw the implementation of a struvite production system. Struvite is generated at different points of the sludge line, hindering operation of the facility.
The Sur WWTP has suffered from periodic episodes of uncontrolled struvite precipitation in the digested sludge outlet pipe, in the elbows of the centrifuge feed pipes and inside the anaerobic digesters.
The rate of struvite formation is controlled in the process in such a way as to obtain a high-quality product with the desired physical properties.
Phosphorus removal efficiencies of around 90% in the treated stream can be achieved and the product obtained is sold as fertilizer.
The technology adopted removes a large portion of the dissolved orthophosphate from a liquid stream, along with a small percentage of the ammonium, in order to obtain a product of higher quality for subsequent sale. For this purpose, a crystallization reactor with continuous recirculation is implemented, where magnesium chloride and caustic soda are dosed.
The reactor can be fed by either the dewatering overflows or the flotation overflows, which are sent separately to the feed chambers. The overflows from dewatering have a much higher concentration of phosphate and ammonium than the overflows from flotation. Therefore, the former stream is predominantly used to feed the reactor.
Struvite crystallized into granules in a controlled manner using magnesium chloride has been certified as an extremely pure, pathogen-free inorganic fertilizer. It has a number of features that differentiate it from conventional fertilizers and enable it to be positioned as a high added-value product. Chief amongst these features are: low release of nutrients, a beneficial magnesium content and a fully sustainable production source.
This product has been certified as a fertilizer in the United States, Canada and Europe.

Veolia Water Technologies opens door to phosphorus circular economy in Spain

The Sur de Madrid WWTP project, undertaken by the Spanish subsidiary of Veolia Water Technologies, included the design of the plant based on the OSTARA process, turnkey construction and commissioning of the facility, and commercialization of the struvite produced.
Sized for a phosphorus treatment capacity of up to 260 kilograms per day, the facility enables controlled struvite formation. One of the main features and benefits of the Ostara process is the ability to control the spherical grain size of the struvite. Moreover, these grains undergo a drying process to ensure a pathogen-free end product, thus guaranteeing safe application from a health perspective.
Phosphorus is as scarcely available in nature as it is essential to human life. Apart from the environmental benefit of its recovery, the process also has significant economic benefits: spontaneous struvite formation is controlled, thus preventing the problems and costs associated with clogged pipes; there are considerable savings in chemical reagent consumption for phosphorus removal; and less sludge is produced, so sludge disposal costs are lower.
This project is a perfect example of the circular economy. It enables the recovery of phosphorus, a valuable resource, from wastewater for reuse.
This promotes and fosters the sustainable use of this element and helps to offset Europe’s phosphorus production deficit.
Its strong involvement in the circular economy has motivated Veolia to develop its own technology, called Struvia™, for the recovery of phosphorus in sewage water treatment plants. Veolia obtained its first reference with Struvia on an industrial site in Denmark in 2016.