Phosphorus recovery

Dr. Christian Adam is working on technical solutions for recovering and recycling phosphorus back into the material cycle

Source: BAM

Phosphorus is a valuable nutrient that every organism needs but cannot produce for themselves. Fossil phosphorus resources are limited, nevertheless, we are quite profligate with this precious raw material. In Germany, phosphorus-containing sewage sludge ash is still largely disposed of in landfills, with the result that the precious substance is lost.

BAM scientist Dr. Christian Adam and his team from the Thermochemical Residues Treatment and Resource Recovery Division are working on developing technical solutions for recovering and recycling phosphorus back into the material cycle. A novel fertiliser that delivers nutrients to the growing plant precisely when it is needed is a key objective of his research.

Phosphorus is essential for all living beings: they need the nutrient to store genetic information in DNA and RNA, and for building and maintaining bones. Crops that provide food for humans and animals absorb phosphorus, along with other substances, from the farmlands and missing nutrients are usually replaced by fertilising the soil. Agriculture regularly uses mineral fertilisers from fossil deposits outside Europe, especially from Africa, China, Russia and the USA. The problems are obvious: resource exploitation and environmental problems in producer countries, market dependency, price volatility and inadequate domestic recycling. In addition, fossil mineral fertilisers are often contaminated with heavy metals that accumulate in the soil or get into the food chain via the plants. Therefore, alternatives must be found and used phosphorus should be returned to the material cycle.

BAM is looking for a next-generation fertiliser

BAM scientist Dr. Christian Adam and his team are experts in thermochemical waste treatment and material recovery. Phosphorus recovery from sewage sludge ash is one of their specialties. Thermally treated sewage sludge is particularly well suited for the recovery of phosphorus as sewage sludge ash contains high phosphorus concentrations and is easy to recycle. Sewage sludge is produced in large quantities in wastewater treatment plants and can be further processed into ash by high temperature incineration. During combustion, energy can be produced and organic pollutants such as drug residues safely destroyed. Phosphorus contained in the sewage sludge remains in the ash and can be further processed into a “next-generation fertiliser”.

The aim of such new fertilisers is that nutrient release takes place in sync with the course of plant growth, as Dr. Adam explains: "This is actually a new generation of fertilisers. We believe that raw materials derived from the recycling of phosphorus-containing materials can play an important role in recycled fertilisers. These raw materials are not water soluble, unlike raw materials in conventional fertilisers. Water solubility is counterproductive in acidic soils. At the same time, these novel nutrients are highly bioavailable, that is, the fertiliser effect is the same as with conventional fertilisers."

Another advantage: one can reduce so-called pollutant loads using secondary raw materials because pollution in conventional fertilisers is sometimes rather high, e.g. with cadmium, uranium and thorium, while these pollutants are barely present in recycled fertilisers.

Dr. Adam and his team have been successfully cooperating with international partners for years. This cooperation has led to joint patents with industrial companies. BAM’s scientists are currently working on the development of a new generation of fertilisers in an international consortium within the "Closing the Global Nutrient Loop" (CLOOP) project. They perform their research together with colleagues from the University of Bonn, the technology and contracting company Outotec, the Berlin Water Competence Centre and the Universities of Sao Paolo (Brazil) and Queensland (Australia).

The aim is to develop next-generation fertilisers e.g. for sugar cane cultivation. The CLOOP project is funded within the framework of the BMBF funding measure BioEconomics International.

The deadline is coming: phosphorus recovery will be mandatory by 2029

The legislator tightened sewage sludge regulation in October 2017, which now stipulates that operators of wastewater treatment plants of more than 100,000 population equivalents must recycle a part of the phosphorus from sewage sludge into the material cycle in the future. The 12-year transitional period started running from autumn 2017, and now processes and products will have to be developed to market readiness, therefore, expertise in technology and chemistry is in high demand.

Phosphorus recycling needs acceptance

Recycled products have to face competition by currently available products. As far as recycled fertilisers are concerned, they need acceptance. They must be either cheaper than fertilisers from fossil sources or must have advantages that conventional fertilisers do not have. Next-generation fertilisers are expected to have such benefits.

But why have the plant operators been so slow to take up of these well-known and proven phosphorus recovery methods so far? The reason may be that world market price for rock phosphate varies widely but tends to be rather low. Phosphorus recovery is currently quite expensive for plant operators and investments earmarked for the construction of new facilities have been frozen. Also, an operator needs security of supply regarding the ash. However, plant operators are finding it difficult to ensure sewage sludge ash supply as they first have to win tenders. But now, the new Sewage Sludge Provision that makes phosphorus recycling compulsory, might boost technology development greatly and gain market acceptance of products.

Networks, projects, BAM expertise

Dr. Adam and his team were involved in a large EU project: P-REX. The project looked into phosphorus recycling methods that had been investigated, tested and optimised in the past. Now they have been comparatively evaluated using life-cycle analyses, cost analyses and scientific and technical comparative methods, taking into account the different levels and development statuses. P-Rex is considered one of the most important projects in the field of phosphorus recovery from wastewater in the past.

BAM’s expertise in this field plays an important role in advising politicians and is in demand by technical committees and partners from industry and science.