Our Phosphorus Recovery
In the pontes pabuli process, ashes containing phosphate, such as those from sewage sludge, are processed into high-quality, standardised granular fertiliser. The first step is to render the phosphate in these ashes available to crops. To this end, we combine phosphates with acids to break them down, similar to processing of crude phosphate in the fertiliser industry.
After the ash has sufficiently reacted with the acid, this mixture is further refined into high-quality fertilisers. At this stage further nutrient components are added in exact quantities, allowing us to precisely adjust the composition. The type and quantity of additional nutrients are determined by our recipe and the desired fertiliser type. This mixture, now optimally matched to the nutritional requirements of the plants, is finally granulated and then dried. The result is a ready-to-use fertiliser that is equal to the quality of mineral fertilisers used in agriculture today.
Through precise addition of raw materials, we can effectively compensate for high fluctuations in the composition of residual materials.
We regard consistent product quality as essential to success when marketing the fertilisers we produce. Variation in the exact composition of phosphate-containing waste materials is a considerable obstacle to this. For example, the chemical and mineralogical make-up of sewage sludge ashes from an incineration plant already has a large variance, which is significantly increased when ashes from different incineration plants are compared. This fluctuation margin must be effectively compensated for when processing these residues.
Our process then allows us to add various additional raw materials. This makes it possible, depending on the actual composition of the phosphate-containing residues, for our blending system to supply components as needed to guarantee consistent product quality at the end of the process. In this way we can produce standard fertilisers of consistently high quality that are ready for direct use in agriculture.
This not only enables us to flexibly react to the fluctuation range of a waste material, but also opens up the possibility of cyclically using a wide variety of waste materials. Besides sewage sludge ashes, there are also many other nutrient-containing waste materials such as ammonium sulphate solution, animal and bone meal or fermentation and slurry residues.
The key to our low processing costs is our exceptionally low energy costs. As a result, the manufacturing costs are kept well below typical market prices.
A distinguishing characteristic of our method is an innovative and exceptionally energy-efficient process management. Many methods rely on heat to separate water, requiring large amounts of energy and therefore incurring high costs. With the pontes pabuli method, our engineers have found a trick that greatly reduces the thermal energy required, limiting it to the residual drying of the granules produced.
As a further cost factor, electrical energy is also used sparingly because, for example, material is transported mechanically rather than by air. This consumes considerably less energy and lowers the amount of exhaust air, which will ultimately have to be cleaned using yet more energy.
With our process, virtually all of the phosphate-containing ash is converted into high-quality fertiliser. Without separating phosphate from ash, we simply make it accessible to plants.
Many phosphorus recycling processes result in large amounts of waste. For example, if the phosphorus is extracted from sludge ashes through leaching, a large amount of undissolved residue is left behind. This residue must then be conditioned and disposed of as expensive waste, raising questions as to both the cost-effectiveness and sustainability of this practice.
Phosphorus is not dissolved and separated from insoluble components in our phosphorus recovery process, but is instead converted into a form from which plants can extract the benefits. We add additional nutrients to the entire mixture in order to achieve the requisite nutrient combination for the fertiliser. This nutrient mixture is then granulated and ultimately forms a granular fertiliser. No waste is generated. The only residue that is discharged in our process are the separated heavy metals. Compared to other processes, however, this amount of waste is negligibly low and consists of concentrated heavy metals as a raw material for possible recovery.
Heavy metal depletion can be integrated into the process. The amount and nature of the removal can be adjusted according to requirements. This gives flexibility and legal certainty.
The question of whether the phosphorus recycling process should have the goal of separating heavy metals continues to be the subject of much debate. Aside from this fundamental issue of sustainability, legal uncertainty still remains as to whether it is sufficient for resulting fertilisers to comply with the limit values set by the Fertilisers Ordinance or whether the sewage sludge ash itself must satisfy them. In the first approach, it is argued that the recycling processes are a conversion of materials and that therefore the Circular Economy Ordnance (KrWG) applies. The second view is that dilution of pollutants is not permitted under waste legislation. Legal certainty will come in the next few years, possibly only when phosphorus recycling becomes mandatory.
The pontes pabuli process can be used for heavy metal removal. The best thing about it - this ability to remove heavy metals can be modularly integrated into the process where required. If, for example, there is a change in the heavy metal content in the ash, heavy metal removal can be activated. The extent of this can be determined according to pollutant concentration requirements and economic considerations. This offers the security of being able to react to future legal changes or increase product purity requirements if necessary.
We convert residues into high-quality fertilisers with technologies that have been tried and tested for decades. This is proven, cost-effective and reliable.
For individual steps in the process, we rely on robust and proven technologies. Most of the components have been standard in fertiliser production for decades, for example mixing and granulating equipment, dryers and straining equipment. And for good reason: They are perfectly suited, long-lasting and cost-effective, both in terms of purchase price and maintenance.
Conventional fertiliser production is similar to our phosphorus recovery. Our innovation is to combine these proven technologies in such a way that they can also be used for phosphate recycling. This is achieved through our unique process management, which enables us to dispense with expensive and failure-prone reactors and reliably manage phosphate recovery.
The steam produced is an energy source that makes us less dependent on more expensive sources of energy, cutting costs and protecting the environment.
Incineration plants typically produce large amounts of waste heat, which can for example be converted into steam. We can then use this steam in our process to dry the granulates that are produced. We find the synergies between our process and sludge incineration plants particularly interesting. The erection of the recycling plant in the immediate vicinity not only eliminates the need for long transport routes for the ash produced, but also allows readily-available, cost-effective steam to be used directly on site. This further increases the efficiency of the process and also reduces the environmental footprint. Such solutions are in line with the principle of sustainability.
Together with our contractors, we install site-specific recycling plants quickly and safely. Proven technical components combined with know-how is our recipe for success.
We are currently working with our plant constructors to prepare the first production plants. We determine the scale of the system according to customer and location requirements. And here we have a decisive advantage: All technical components required for each step of the process are already available in a range of dimensions and can be delivered on request. This eliminates the need for lengthy and risky design and assembly, saving time and minimising risk in our installations.
Of course, site-specific concerns are factored into the design and planning process. For example, the type of energy sources available on-site. Available source material flows can also be integrated if necessary.