P-Recovery

P-recovery

The element phosphorus (P) is essential for all life on earth, from micro-organisms and plants to animals and man. Every cell of every living organism contains phosphorus. Furthermore there is no alternative for phosphorus. Phosphorus is essential for live and irreplaceable.

Phosphorus is an essential raw material in fertilizers and animal feed. Fertilizers are needed to grow food. It is well-known that a world without fertilizers can generate food for not more than 2 billion people whereas the current world population is already over 7 billion, and is expected to grow to over 9 billion in 2050.

Phosphate Rock is mined to produce fertilizers, animal feed and other P-containing derivatives. The world phosphate rock reserves are depleting. The European committee estimates that we used all our natural P sources in 70-90 years. Locally the situation is even worse. Europe, for example, hardly has any phosphate rock reserves and is totally depending on imports.

Contradictionary enough we lose hundreds of thousands of tons phosphorus per year in Europe only. The throughput of Phosphorus in animals and people is huge. Only a small part of the phosphorus is kept by the body in the cells and, mainly, in bones. Most of the eaten P will leave the body in animal and human excrements (“pee and poo”). The main streams of phosphorus are animal manure (around 1800 Million tons is generated every year in the EU), waste water (sewage systems) and bone meal. And strangely enough we waste almost all of this today or use it in non-fertilizer, non-food applications. For example, flow analyses from France show that 50% of the total phosphorus used there is lost – around 20% in waste water, the same through erosion and leaching and 10% in the form of food waste and other bio waste. Furthermore, intensive animal production is concentrated in specific areas close to ports, major population centers and available labor and expertise. This concentration has led to an oversupply of manure into these regions, with a gradual build-up of the phosphate content of soils and increased risks of water pollution. Likewise the growth of major cities means that phosphorus containing sewage and food waste is increasingly distant from the arable farms where it might be used.

Hence, there is no global scarcity of phosphorus, there is a lack of proper management and high-tech application (technologies) of phosphorus streams.

With proper P management, i.e. P-recycling, Europe and other P-rock deficient areas can be self-sufficient in phosphorus, and in food supply. Waste of today will generate food for tomorrow, with other word WASTE = FOOD, the slogan for the Cradle-to-Cradle concept of chemist Michael Braungart and architect William `O Donough. We should find ways to valorise our waste, to make our waste the mines for the future; the European Committee speaks about ´Urban Mining´.

Apart from these ´Urban Mines ´ that still have to be created the fastest way to expand the availability of phosphorus is to find ways to economically and ecologically process the lower end of the natural phosphate rock, i.e. phosphate rock with low P content, or in short “low grade rock”. U.S. Geological survey (2010) estimates the economically feasible resource 16000 million tons. However the reserve base is 47000 million tons, containing the reserves with specified minimum physical and chemical criteria related to current mining and production practices.

Moreover, both high grade and low grade rock contain elements like Cadmium and radioactive Uranium Once present in the soil (transported through fertilizers) Cd cannot be easily removed, but can migrate and accumulate in plants. Certain plants (sunflowers, colza, tobacco, etc.) tend to accumulate larger amounts of cadmium. In terms of health impact, the EU Risk Assessment Report on cadmium (oxide) found that the major risk of cadmium is kidney damage through food consumption and smoking. On the basis of this allowed Cd levels in fertilizers will decrease.

The radio-activity ends (Uranium), with the use of conventional industrial processes and technologies, in fertilizers and therefore in food (see att05). The vast majority of Radioactivity in human bodies originates from fertilizers.

Applying the right technology for valorising these ´Urban mines´ and ´low grade rock´ into radio-activity free fertilizers is of key importance.

P-RECOVERY POLICIES

Measures have been taken at national, EU and international level, but at first mainly to address water pollution problems from phosphorus and to reduce the waste of materials such as food or other biodegradable waste that also contain phosphorus.  However, these actions were devised with the prevention of water pollution in mind or for other policy objectives, rather than for the purpose of recycling and saving phosphorus. Initiatives that are directly focussed on phosphorus efficiency and recovery remain scattered, and are rarely considered in policy development.  An exception is Sweden, where a national interim target was established: “By 2015, at least 60% of phosphorus compounds present in waste water will be recovered for use of productive land. At least half of this amount should be returned to arable land”. In March 2003, Germany followed by announcing the objective to develop new technologies in the branch of phosphorus recovery, and in 2004 a German funding programme “Recycling Management of plant nutrients, especially phosphorus” was launched. The fund included 7 projects:

 

PhoBe

Recycling of Phosphorus – Ecological and Economical Evaluation of different Processes and Development of a Strategical Recycling Concept for Germany

Göttingen

Phosphorus Recycling – characterization of the effect of recycled phosphate fertilizers by field and pot experiments

PASCH

Recovery of Plant nutrients, especially phosphorus from ash of sewage sludge as well as meat and bone meal

Phoxnan

Optimized phosphorus recycling from waste water sewage sludges by the combination of low pressure wet oxidation and nanofiltration.

ProPhos

Phosphorus Recovery from waste water, sewage sludge and sewage sludge ashes

RECYPHOS

Phosphorus recycling – Sustainability contribution at the decentral wastewater treatment

PHOSIEDI

Phosphorus Recovery using Ion-Exchange and Electrodialysis

 

The recovered products should be usable as fertilizers or in fertilizer industry without further treatment, containing phosphorus and other nutrients (N, K) in a plant available form, and heavy metal and organic pollutant levels under limit values.

The Netherlands has put in place a phosphate value chain agreement, in which a range of stakeholders have committed themselves to targets such as using a set percentage of recycled phosphorus in their manufacturing process. Germany is working (following non-EU member Switzerland) on legislation planned to reduce the waste of phosphorus and use it for fertilizer and/or animal feed applications. Following the first European Conference on Sustainable Phosphorus, a European Phosphorus Platform has been set up by stakeholders in order to create a European recycled phosphorus market and to achieve a more sustainable use of phosphorus.

The European Commission underlined the importance of P-recycling by initiating a Consultative communication on the sustainable Use of Phosphorus  in 2013 that has been announced in the Roadmap to a Resource Efficient Europe and should be seen as part of the overall drive to improve resource efficiency in the EU and worldwide. The accompanying document states, amongst others the following:

“The complete replacement of phosphate mined in the EU by recycled phosphorus is neither feasible nor necessary in the foreseeable future. However, greater recycling and use of organic phosphorus where it is needed could stabilise the amounts of mined phosphate required and mitigate the soil contamination and water pollution issues. This will then put on track to close the phosphorus cycle in the long term, when the physical limitations of the resource will become increasingly important”

P RECOVERY TRENDS & POSSIBILITIES (“Urban Mining”)

It is logical to valorise those waste materials that have the highest P-content and are most readily available. In this perspective Bone meal and Sewage sludge have the highest potential. Animal manure is also an option, but is logistically more difficult.

In Europe more than 10 million tons of sewage sludge (dry mass) arises every year. One fifth of this quantity in Germany.  47% of the German sludge is used in farming and landscaping whereas 53% is currently incinerated, 45% thereof in mono-incinerators (220 kt ash/year), 55% in co-incineration.

Only in Germany around 80.000 tons of phosphorus (P) in Meat and bone Meal (MBM) (24.000 ton) and sewage sludge (55.000 ton) is treated. Germany is one of the leading countries to study valorisation of these streams. However, the conclusion of the so-called PhoBe-Study states that today no single process to recycle P from waste streams is economically viable! We, as EcoPhos know, that this is an untrue statement.

Since the BSE crisis we differentiate MBM sources in 3 categories. Category 2 and 3 are allowed to be used as animal feed or fertilizers, whereas cat. 1 (high risk) material must be incinerated. Unfortunately this incineration occurs today mostly in cement kilns or in power plants as high calorific substitute. This simply means that proteins and phosphorus are lost for ever! Mono-incineration of these materials would lead to a high quality P-source (35-40% P2O5, no heavy metals, no Uranium).

Several processes are known to recover P from waste water systems.
The Phosphorus can be regained from :

the sludge liquor

Although precipitation (most often Calcium Phosphate or Struvite (=MAP)) from the sludge liquor is relatively easy the main disadvantage of this approach is the fact that most of the P is separated from the liquor in an earlier stage of the waste water treatment process. Therefore the overall recovery potential is low. These products are generally low in heavy metals and other pollutants and have a reasonable plant availability, making them suitable for agricultural use as slow release fertilizer. Draw back of the product is, that it is NOT KNOWN and NOT ACCEPTED by the end user, the farmer.

the digested sludge

As the sludge contains organics (a.o. antibiotics, pathogens) these compounds will contaminate the recovered P-precipitate. Depending on the specific process heavy metals contamination can occur. Purification processes are complex and costly or insufficient.

the sludge ash

Sludge incineration has advantages such as energy integration and high Mercury removal. Organic pollutants including PCB´s, dioxins, hormones and POP´s, are destroyed.

In the Table below estimates for available volumes of (mono-incinerated) ash are given:

Sewage Sludge and mono-incineration (%)

 

Sludge (DS)

Ash

% mono-inc.

ash (mono)

as P2O5

 

t/a

t/a

 

t/a

t/a

Europe

8330000

3165400

20

633080

107624

Germany

2450000

931000

28

260680

44316

Austria

245000

93100

31

28861

4906

Switzerland

203000

77140

47

36256

6163

           

USA

8200000

3116000

22

685520

116538

Japan

3000000

1140000

50

570000

96900

TOTAL

22428000

8522640

 

2214397

376447

 

Most of the recycling processes are costly, between 3-12 € per mt recycled P and, moreover, lead to new (not known and/or accepted) products with (too) low crop accessibility (water solubility).

Moreover the market for P-fertilizers in Germany is only 10%, the majority are NPK-fertilizers. It is therefore economically preferable, if not, necessary, to aim for NPK-fertilizer production out of waste materials.

This calls for a flexible economically and ecologically feasible new technology that is able to produce several types of P-compounds that can be used either as such or in an NPK-formulation out of both low grade phosphate rock and/or MBM- or SS ashes. Such a process exists. The patented EcoPhos-process!

Again, this calls for a flexible economically and ecologically feasible new technology that is able to produce several types of high purity animal feed products or high tech (no Cd, no Uranium, highly soluble or already liquid) fertilizers than can be applied as such or in NPK-formulations out of both low grade phosphate rock and/or MBM- or SS ashes. The EcoPhos-process fits into all these requirements, let us promote this.

CONVENTIONAL INDUSTRIAL PRACTICES

In order to understand the huge advantages of the EcoPhos process it is useful to have a short introduction into the basics of the conventional industrial processes:

Industrially the Apatite in Phosphate Rock is made accessible for crops by acid attack. Conventionally most often sulphuric, phosphoric or nitric acid is used. Water soluble Calcium Di hydrogen phosphate is produced, for example:

[ Single Super Phosphate, SSP]
Ca3(PO4)2 + 2 H2SO4 à Ca(H2PO4)2 + 2 CaSO4

[Triple Super Phosphate, TSP]
Ca3(PO4)2 + 4 H3PO4 à 3 Ca(H2PO4)2

Drawback of these processes is that the acid-attack also solubilises heavy metals (such as Cadmium) and e.g. Uranium as unwanted contaminants in the end product.

Conventional phosphate mining is mostly carries out in open cast mines. This type of mining requires large areas of land. As well as the land that is mined, land is also needed for spoil heaps and for clay settling ponds. The quantities of total solid waste produced can be high, but they vary significantly between plants – one study reports findings where, for one tonne of phosphoric acid produced, 9.5 tonnes of phosphate ore are required and 21.8 tonnes of diverse wastes and 6.5 tonnes of tailings are produced. Phosphoric acid plants also produce large quantities of a by-product called phosphogypsum. In some countries phosphogypsum is stored at large stacks due to regulation of radioactivity levels or because the alternative (natural gypsum and flue gas gypsum) are more competitive. In a few countries such as Brazil and china, however, it is increasingly being used in construction and agriculture. It should be noted that natural radioactivity levels in phosphate rock can differ widely, depending on the geology of the mine. The conventional mining process is also water use and energy intensive.

Another industrial route for Phosphate Rock is to produce elemental phosphorus via the so-called thermal route in an electric arc furnace. Phosphate is reduced with cokes and the calcium oxide reacts with gravel (SiO2) to form liquid slag, calcium silicate:

2  Ca3(PO4)2 + 6 SiO2 + 10 C à 6 CaSiO3 + P4 + 10 CO

This process has the advantage to produce very pure P4, which is the basis for high quality  phosphoric acid (thermal acid) or other P-derivatives such as PClx, POCl3, P2S5, P2O5, being raw materials for Flame Retardants, Crop Protection Agents, Food Additives, Lubricating Oil additives, Water treatment additives, etcetera.

The heavy metals (partly) and Uranium end in the slag, which dramatically reduce the application possibilities for this large volume by-product. Another disadvantage is the high (electricity) costs for this process. Approximately 14 MWh per ton of P4 is needed.  So with an average price of 50 € per MWh already 700 € per ton of P4 is involved.