​Rock Phosphate Mining – Viable Industry Or Environmental Millstone?

Phosphorus and calcium are the 2 most abundant minerals in our body. Fortunately, a healthy balanced diet that contains enough protein also generally supplies enough of these 2 essential minerals. The most common dietary sources for humans include meat, poultry, fish, dairy products, and eggs. Phosphorus in particular is needed for a multitude of functions. It: 

  • produces and manages our energy storage and supply,
  • keeps our heart beating regularly,
  • keeps our muscles moving, and helps reduce 'after exercise' muscle pain,
  • helps the kidneys filter waste,
  • keeps our bones and teeth strong,
  • helps our nerves work properly,
  • is involved in cellular and tissue growth, maintenance and repair,
  • is needed for the production of DNA and RNA
  • balances and lets us correctly metabolise minerals and vitamins, notably iodine, zinc and magnesium, and group B and D vitamins,

In fact, without phosphorus we'd be in a pretty bad way! Likewise, the plants that underpin the diets of our primary sources of phosphorus would also be in a bad way without it. And plants of course get it from the soil they're grown in.

Way back when, when we were hunter-gatherers, we didn't need to pay all that much attention to where our phosphorus was coming from because it was in our primary food sources (meat, fish, poultry). When we transitioned into farmer growers around 10,000 years ago and started nurturing our food from the ground up, we discovered that sooner or later plants grown over and over in the same place run out of nutrition too. The manure from our livestock noticeably helped our plants grow better, so we made a point of using it. Eventually though our cropping outstripped our manure stockpiles and we had to start looking around for other ways to keep those plants growing. Thus, the manufactured fertiliser industry 
was invented.

Phosphorus And Fertilisers

Phosphorus is a key ingredient in fertilisers. Indeed, without it global food production will halve. Animal manures contain fair amounts of both organic and inorganic phosphorus (along with potassium, nitrogen and various other compounds) courtesy of the plants they eat. Cow manure is around 2% phosphorus for instance.

However, animal manures, although still comprising a portion of the fertiliser market, have been well and truly overtaken by manufactured fertilisers. Manufactured fertilisers predominantly contain nitrogen, phosphorus and potassium. The phosphorus needs to be dug up out of the ground as rock phosphate. However, current estimates are that if we continue to use it like we are currently, we could run out of known reserves within half a century. If not sooner.

Another issue is that over 80% of the world's rock phosphate deposits are located in just half a dozen countries, one of which is China! Should any of these countries choose to do so, they could dictate the world's food supplies. That makes phosphorus a potential political weapon. This 'situation' was considered so important that in 2014 the EU declared it a "critical raw material". This term is generally used to denote a crucial raw material whose supply is subject to risk.

So what are our options?

If we look beyond rock phosphate, there are several significant alternative sources of phosphorus sitting right under our noses. Nearly two hundred years ago a facility in Rothamsted used sulphuric acid to dissolve animal bones and turn them into phosphate fertiliser. Modern researchers have revisited this concept and found that abattoir waste (bones, blood, horns etc) is indeed a very viable alternative source of phosphorus for phosphate fertilisers. In fact, the fertilisers produced from this source worked as well as conventional phosphate fertilisers, if not better, and could potentially supply up to one quarter of the UK's fertiliser requirements.

Another potentially viable source of phosphorus comes from us! Or more precisely from the copious amounts of sewerage we produce. Notably urine. If those dietary sources of phosphorus we mentioned earlier supply us with too much of this mineral, we get rid of it via our kidneys and eventually our urine. In fact, it's normal for a healthy adult to pass between 0.4 to 1.3 grams of phosphorus in their urine over a 24-hour period. That's a lot of a valuable commodity being flushed unrecoverably down the loo!

Or is it unrecoverable?

Some countries are well on their way to sustainable phosphorus production via recycling animal and human waste. A number of waste treatment plants around the world already recover phosphorus from sewerage. Thames Water owns one.

A Swiss company has set up a mobile treatment plant (called the "Urine Express") that collects urine from sports fields and similar venues, extracts the phosphorus and binds it with magnesium oxide to create MAP (magnesium ammonium phosphate) or struvite. MAP is an excellent fertiliser. The wastewater is also not wasted. It's filtered and purified, then used for irrigation. The plant can extract 930 litres of water and 70 litres of phosphate fertiliser from 1000 litres of urine in just 2 to 3 days. Enough to fertilise and water 2000 square metres of soil.

Germany though is even further ahead of the pack. When more than half the country's rivers that were tested for phosphates and nitrates had significant, and damaging, levels of phosphorus, authorities were prompted to take action. Now not only are they producing and selling around 400 tons of MAP annually that comes from their sewage system but they also have waste management systems that extract the solids from sewage and return clean filtered water to the environment. The solids or 'sewage sludge' is either dried and burnt to produce energy or turned into fertiliser. The 'stuff' that is burnt leaves a phosphorus rich ash that is treated further to extract the phosphorus. Around 90% of the remaining phosphorus is reclaimed this way. Further work is being done to develop new ways of extracting phosphorus from the sewage sludge itself.

Germany has also mandated that all large cities (over 1000,000 people) must have systems in place to recycle phosphorus from sewage by 2029. Urban centres with over 50,000 people must have them by 2032. The rest of the world needs to catch up!

Important though it is, phosphorus nevertheless comes with some environmental problems. There is the problem of untreated effluent and wastewater still with high levels of phosphorus getting into natural water systems and polluting them. That's one issue. Another one is that in many parts of the world, fertiliser use is often a case of 'a little is good but more is better'. According to some figures, there is as much as 12 months worth of phosphorus supply locked up in the ground courtesy of over fertilisation.

Such overuse hasn't just depleted reserves. It's also contributed significantly to the destruction of water systems. The excess gets washed away and eventually ends up in creeks and rivers, where it can cause prolific algal blooms. Therefore, recycling as much as we can from those sources we have some control over, such as animal and human waste, makes a whole lot of sense. Educating phosphorus users about its correct application would also seem to be a logical action too!
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