Technical
The struvite accumulates in pipework, centrifuges and pumps, thereby reducing processing efficiency and increasing wastewater processing costs markedly
A cross section of pipe showing struvite build-up ©Stewart Turkington/Thames Water
particularly in days gone by. Whilst it is not uncommon to see organic fertilisers used today, these are usually based on animal manures or recycled green wastes - both of which I am a big fan of. With that said, one source has seemingly been omitted from the fertiliser chain - human excreta. The advent of modern sewerage systems has opened up the phosphorus cycle, whereby what could be considered as a valuable, renewable phosphorus source is lost to the sea and, with that, comes significant environmental issues. Yes, it is a fact that use of human excreta has caused severe epidemics in the past; however, we now live in a time where technology is able to expel these risks. Biosolids from waste treatment plants have
proven to be a valuable source of plant available phosphorus in many areas, but concerns do exist regarding the safety of the final product, particularly in respect of the heavy metals content of the product. There is a large body of regulations and guidelines regarding the use of biosolids in the agricultural sector and, though the codes of practice could be adopted for amenity uses, it seems that conventional treated biosolids are not a realistic option. As technology has advanced, however, a more recent development has been brought to into the marketplace. Struvite is most commonly known as a
problematic by-product of the wastewater processing industry. The struvite accumulates in pipework, centrifuges and pumps, thereby reducing processing efficiency and increasing wastewater processing costs markedly. There is now technology in place to extract the elements that combine to form struvite in wastewater systems, and turn it into a highly efficient phosphate fertiliser. Canadian company Ostara currently leads the way in developing and implementing this technology - there are now several plants located around the world, including one in London, which is operated by Thames Water. In respect of the actual product which is
brought to market, there are a number of benefits over mined phosphate rock. Firstly, struvite is not water soluble - the mode of release is via citrate solubility - as plants exude citric acid, this in turn releases a given amount of plant available phosphorus from the struvite crystals. The phosphorus release pattern is aligned to the production of citric acid from the plant matter; therefore, excess levels of plant
available phosphorus are never an issue. The environmental benefits are also plain to
see - struvite is a renewable phosphorus source, which takes us away from the current over reliance on an increasingly limited finite resource. Leaching is also reduced, efficiency is much improved over traditional phosphate rock sourced products, and one point that I find to be of particular importance, is the lack of contaminants - a quick check of the data sheets shows far reduced level of contaminants and heavy metals in comparison to other sources. Throughout the course of the three articles I
have written on this subject, I have referred to the use of human excreta in ages gone by several times - it is my belief that, sometimes, we have to look backwards to move forwards - it would seem that struvite brings an accurate and timely reflection to this mantra. It would seem like Aldous Huxley may well
have been onto something when he wrote the following in his novel, Point Counter Point (1928): “With your intensive agriculture, you’re simply draining the soil of phosphorus. More than half of one percent per year. Going clean out of circulation. And then you throw away hundreds of thousands of tons of phosphorus pentoxide in your sewage! Pouring it into the sea. And you call that progress?” The issue of an ‘open’ phosphorus sink has been acknowledged by many for any number of years - perhaps it is a lack of technology that has precluded the closing of the ‘phosphate loop’, or maybe the size of the commercial phosphate rock market, along with the relatively cheap prices of phosphate rock has contributed to the suppression of technological development which has the potential to bring useable sources of excreta to our doorstep. For whatever the reasons may have been,
there are solutions to the long standing issues of our reliance of mined phosphate rock available to us now - it would be my advice to look closely at alternative sources before peak phosphorus impacts upon our budgets and supply chains. To bring closure to this series of articles, I
could only now offer my candid thoughts on the issues at hand. As a practising groundsman, my focus has
always solely been on the turf and soils that I work with. Product knowledge and selection has came from what the amenity industry ‘communicates’ to me, so the issues that I have focused on within this series of issues came as
Fertiliser pellets produced from sewage in Thames Water’s facility in Slough ©Stewart Turkington/Thames Water
PC JUNE/JULY 2015 I 131
much of a surprise to me once I started looking beyond the boundaries of the amenity industry and researching the wider subject in depth. The environmental issues are without
question, unacceptable and, to a certain extent, avoidable. The ongoing supply issues are a fact, even if timing is a subject of ongoing geological debate - one certainty is that economically driven scarcity will be relevant to all of us before long. The agronomic issues of over reliance on
inorganic fertiliser applications are once again, entirely avoidable, but this is a serious point of concern for me - a large body of misinformation is passed on to many in this industry, often driven by financial gain. I have had many examples of this in my sixteen years of practising turf management, and yes, on occasion, naivety has got the better of me, so it is a cause of immense frustration when I hear of such misinformation being peddled by a spurious few. I would encourage all to do their own
research in respect of the topics that I have covered in this series of articles. I would hope that some take up the mantle and explore the wider subject, as it will be the knowledge that is gained, the willingness to acknowledge the issues at hand, and the drive to shape the future of our industry that brings the changes that are required to our industry. Finally, if nothing else, it is my sincere hope
that this series of articles has proven to be thought provoking for some of you.
”
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