Phosphorus Is Vital
Nitrogen and phosphorus are the most important nutrient elements for all life on earth. No life form can exist without phosphorus. Phosphorus makes up 0.099 % of the earth's crust and cannot be replaced by any other element. Unlike nitrogen, it is not part of the atmosphere. In every cell, whether bacterial, plant or animal cells, phosphorus serves, among other things, as the central element in the ATP (adenosine triphosphate) molecule - the universal currency of life. When nutrients are broken down, energy is generated and temporarily stored in the form of ATP. Now the ATP can be transported to another place in the cell where it is needed. An organism could therefore not function without phosphorus. But phosphorus is also needed in other parts of the organism: For example, phosphorus is an important factor for bone formation in humans and a central component of the genetic material of all living things.
The Battle for Phosphorus
Phosphorus was discovered in 1669 and used industrially as an essential component of matches. Today, 80 % of the phosphates extracted worldwide are used to produce fertilizers. 12 % is used in the production of detergents, 5 % in the production of animal feed and 3 % in other applications. Around 160 million tons of phosphate are extracted from natural deposits every year. The reserves are mainly concentrated in four countries, which hold 80 % of the deposits: Morocco, China, South Africa and Jordan. China, the USA, Morocco, Russia and Tunisia are the main countries involved in extraction. Europe needs 90 % of its imports from these countries.
The Chemical Sciences and Society Summit (CS3) describes in its 2011 white paper entitled "A Sustainable Global Society"that reserves will be exhausted in the next 30-100 years. Since a few countries control almost the entire supply of a raw material that is needed by all other countries, conflicts are inevitable. Limiting phosphorus affects the national security of many countries. This is because the production of crops is already at risk in many countries due to the limited supply of phosphorus.
Phosphorus Recovery Is Necessary
In view of the fact that natural phosphorus reserves are coming to an end, phosphorus recovery is absolutely essential. Wastewater contains very large quantities of phosphorus: around 70% from human and animal faeces and the remaining 30% from cleaning agents, detergents and kitchen waste. Most technical solutions therefore focus on the recovery of phosphorus from sewage sludge from wastewater treatment plants.
The German pharmacist and alchemist Hennig Brand is considered the discoverer of phosphorus. He discovered it while trying to find the philosopher's stone. This philosopher's stone was supposed to be able to transform base metals into gold and silver. Brand heated urine and obtained a white substance that glowed in the dark and could be easily ignited. Brand gave it the name "cold fire" because of the white fire when burning.
In 2012, new phosphorus deposits were discovered in North Africa and Iraq. According to estimates by the German government, this could mean that demand will still be covered for around 400 years. (Source)
The Dilemma: Good Phosphorus, Bad Phosphorus
On the one hand, phosphorus is a limited resource and must be recovered if the food supply for an ever-growing human population is to be secured. On the other hand, the phosphorus that arrives in sewage treatment plants with the wastewater is a problem. Although total emissions in Germany have fallen by 70 % since the 1980s, many bodies of water are still highly polluted today. In wastewater, phosphorus is mainly present in inorganic form (orthophosphate) and, to a lesser extent, also as organic phosphorus in undissolved and dissolved form. If phosphorus from the wastewater treatment plant enters the receiving water, it can quickly lead to eutrophication of the water. Phosphorus is usually the limiting element for microorganisms and plants. If this limitation is removed, microorganisms and plants can multiply almost unchecked. This leads to increased oxygen consumption and the development of anaerobic zones. The water body turns over and the resident fish populations die.
New, Stricter Limit Values
In order to prevent the eutrophication of water bodies, the German government has committed itself to a further reduction in phosphorus inputs as part of its sustainability strategy. This increases the pressure on sewage treatment plant operators to comply with the increased limits if they want to avoid higher charges.
Removal of Phosphates from Wastewater
There are basically two options for phosphate elimination.
Firstly, the phosphate can be chemically precipitated with the help of metal salts. Here, the metal salts of iron and aluminum form insoluble compounds with the dissolved phosphate in the activated sludge plant. These metal phosphates can then be removed from the secondary clarifier with the excess sludge.
Secondly, the phosphates can also be absorbed by microorganisms, which are also removed with the excess sludge. Ultimately, the phosphorus in the excess sludge is either biologically bound (in the microorganisms) or chemically bound in the form of metal phosphates.
The Natural Potential of Biological Phosphate Removal
The so-called Bio-P organisms are specialized polyphosphate-accumulating microorganisms (PAO) that store phosphate in their cells in an aerobic environment and thus biologically remove it from the wastewater. They are in direct competition with glycogen-accumulating organisms (GAO), which compete for the same carbon sources in an anoxic environment. Every wastewater treatment plant has a natural potential for biological phosphate elimination. Approx. 35 % of the phosphorus is stored in the sludge. This figure can fluctuate depending on the conditions in the wastewater treatment plant. There is therefore a high natural potential which helps to reduce the phosphorus load.
Synonyms: Biological phosphate elimination is also referred to as biological phosphorus elimination, biological phosphate removal or Bio-P.
Bio-P Process for Enhanced Biological Phosphate Removal
If the natural potential of a wastewater treatment plant is not sufficient to comply with the required limit values, biological phosphate removal can be enhanced using a special process. This involves generating non-aerated zones and aerated zones through which the microorganisms are passed. This encourages them to store additional phosphate in the cells, which serves as an energy store. This is a natural protective mechanism of the PAO in order to be sufficiently supplied with energy even under poor conditions. This results in an increased removal of phosphorus.
Monitoring of PAO/GAO
VIT® gene probe technology and the VIT® PAO/GAO test kit or the Bio-P laboratory analysis can be used to check the presence of polyphosphate-accumulating organisms (PAO) in wastewater treatment plants. It is therefore possible to quickly test the basic potential of the plant for biological phosphate elimination. Furthermore, the ratio to the competing glycogen-accumulating organisms (GAO) can be measured and thus the effectiveness of biological phosphate elimination can be specifically increased through adapted process control. The process can either be used directly at wastewater treatment plants or commissioned as a laboratory service.
Phosphorus Recovery
The phosphorus bound in the excess sludge subsequently enables the recovery of this vital element. Direct use of the sewage sludge is not recommended due to the pollutant load and is also prohibited by law in many countries.
There are numerous methods of phosphorus recovery. There are basically three groups: firstly, recovery from sewage sludge mono-ash, which is, however, quite costly. Secondly, direct recycling from sewage sludge and thirdly, recycling from sludge treatment process water. As up to 90 % of the P feed loads are bound in the sewage sludge and process water only contains up to 25 % of the feed loads, recovery from the sewage sludge by digestion or crystallization is the method of choice.
Recovery makes it possible to return the phosphorus to the cycle because, unlike carbon or nitrogen, phosphorus cannot be removed from the wastewater via the gas phase.
The Battle for Phosphorus Has Already Begun
Phosphorus is one of the most important raw materials and is only available to mankind in limited quantities. If it is not recovered, it will be lost to the phosphorus cycle. The battle for this limited raw material has already begun. Europe must reduce its dependence on the few phosphorus-producing countries by increasing recovery. At the same time, the discharge of purified but still phosphate-containing sewage water into receiving waters leads to the eutrophication of water bodies. Although the situation has improved in recent years, the limit values will be further reduced in the coming years, making it more difficult for sewage treatment plant operators to comply with the limit values. VIT® PAO/GAO analysis is an important tool for wastewater treatment plants to monitor biological phosphate elimination and enables the control of the main microorganisms involved in biological phosphate elimination. Both the prevention of water contamination with phosphate and the recovery of the raw material should go hand in hand. This is because phosphorus is only available for recovery in the form of excess sludge if it is removed from the wastewater.
Further links:
The fate of mankind depends on phosphorus (German): https://www.welt.de/dieweltbewegen/article13585089/Am-Phosphor-haengt-das-Schicksal-der-Menschheit.html
The stone of light - elementary history of phosphorus (German): http://www.spektrum.de/magazin/der-stein-des-lichtes-elementargeschichte-des-phosphors/822157
The Phosphorus cycle (English): https://en.wikipedia.org/wiki/Phosphorus_cycle
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