Phosphorus (P) recovery is currently an important topic in Western Europe. Despite it being a popular fertiliser product – it is not mined on the continent. In fact, 70% of Earth’s Phosphate reserves can be found in Morocco, with the other 30% mainly spread across China, Russia and the United States; but these reserves are not inexhaustible. Wastewater is one source of P that is readily available to us, and with the current tightening of Ofwat’s regulations as water companies go into AMP7, many alternative methods for harvesting P from wastewater for reuse, known as P recovery, are being investigated.
What do we have already?
At VWT UK, we have a number of enhanced tertiary treatment technologies that can help wastewater plants meet P removal consents in an efficient manner, namely our ballasted flocculation process (Actiflo) and our woven cloth filter system (Hydrotech Discfilter).
In terms of research into P recovery methods, we also have our research and development team working on a number of possible new technologies that would enable a plant to utilise the extracted P. In particular, they are working on the use of an absorbent material to remove P from wastewater, which can then be formed into pellets and sold as fertiliser.
VWT France has already developed a P recovery process of this kind for a number of small, rural wastewater treatment plants that required a high-efficiency, low cost solution with zero chemical usage. This solution consists of pellets made from high purity phosphate rock granules, known as apatite, used as an absorbent. However, the system has a four to five-year lifespan and requires high purity apatite, which needs to be imported from abroad and is therefore costly, as well as producing a large footprint.
What are we working on?
As such, VWT is trying to develop a new absorbent based on reused materials, which are readily available and cost effective. The properties required for a viable P recovery absorbent would include:
a high P recovery efficiency of > 90% or reaching a total (TP) of < 1 mg/L
an absorption capacity of > 5 mg of P per gram of media
compatibility with VWT’s existing technology to avoid the need to develop a new technology.
From Bauxite from the aluminium industry, to egg shell, Biochar, fly ash and bottom ash, a vast number of by-products have been considered. However, many of the applicable media tests so far have raised issues in terms of social acceptance, availability and substance inconsistency.
As such, VWT has conducted two small scale pilots using fly ash alongside VWT UK’s StruviaTM and FiltryPHOSTM technologies. Dependant on the original incinerated material, fly ash can be used directly for land application after P recovery making it ideal for fertiliser. Its high absorption capacity of 9-17 mg/L, coupled with its low cost, has made fly ash the most promising absorbent so far.
However, its fine structure can make it a challenging media to work with. Therefore, as is the case with many absorbent options, a method of pelletisation would be necessary to convert the fly ash into a usable form. The size of these pellets is crucial to effective absorption, along with the use of cost-effective bonding additives which must be considered so that pelletisation does not dramatically impact the cost.
Currently, VWT is working on a solution to allow fly ash to be used on a broad scale in municipal wastewater treatment plants. However, further experimentation with other substances are also being carried out, such as crab shell, which has proven to be a viable, low cost solution for coastal facilities in Scotland.
For more information on P removal, recovery and the technologies offered by VWT UK, click below.
