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Zero waste is a catchphrase that keeps coming up when it comes to sustainability.

What is meant is to produce as little waste as possible and to use raw materials that are available as sparingly as possible.

This should succeed by closing material and energy cycles.

The idea behind it: Products are designed with a cycle concept, can be reused and repaired in the course of their life.

And the materials used are given a new chance through recycling.

There is an urgent need to reduce the global consumption of resources. Because stocks are shrinking and greenhouse gas emissions are rising. According to the United Nations Environment Program (UNEP), the worldwide use of primary materials more than tripled between 1970 and 2017 from 27 to 92 billion tons. And by 2060 - ten billion people are likely to live on earth by then - the amount of minerals, ores, fossil fuels and biomass used should more than double again in the maximum scenario.

In Germany, raw material consumption has been largely constant for years at around 1.3 billion tons.

That is 16.2 tons per person per year or 44 kilograms per day.

“That is a long way from conserving resources.

If everyone in the world would live like us, we will continue to cross the planetary boundaries, ”says Henning Wilts, head of the circular economy at the Wuppertal Institute for Climate, Environment and Energy.

"We have to reduce our use of resources by a factor of 4."

Phosphorus from sewage

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The German Resource Efficiency Program, or ProgRess for short, was adopted in 2012 for the sustainable use and conservation of natural resources. Now in its third edition, it provides impulses, for example, with regard to waste avoidance, reuse, recycling of waste and urban mining. One of the concerns is the technical recovery of phosphorus from wastewater, sewage sludge and sewage sludge ash. The chemical element is essential for all living things and is used in agriculture as a fertilizer for plant growth.

But Germany itself has no phosphate ore deposits and has to import mineral fertilizers in the order of 131,000 tons per year, for example from China and several African countries. But Germany has treated wastewater for this. In the 50,000 sewage treatment plants in this country, 1.7 million tons of sewage sludge dry matter are produced annually. “Theoretically, around 50,000 tons of phosphorus can be obtained from this through phosphorus recycling processes and around ten percent of the current demand can be covered,” says Tabea Knickel, Managing Director of the German Phosphorus Platform.

In eight years, phosphorus recovery will be mandatory for all municipal wastewater treatment plants if sewage sludge with at least two percent phosphorus is produced.

Wastewater treatment plants that serve 100,000 or more people must start doing so by 2029.

Smaller plants with an expansion size for more than 50,000 people from 2032. Until then, these plants may still accommodate sewage sludge in agriculture.

Very small systems will still be able to do this after 2032. Many processes are currently being tested.

Sometimes engineers try to get phosphorus directly from wastewater, sometimes from sewage sludge.

Still others take the ashes of the sewage sludge after the incineration.

Two larger plants are in operation

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Knickel knows that there are currently two systems that have outgrown the pilot stage. One plant is operated by the water supplier Hamburg Wasser and the disposal company Remondis and aims to convert 20,000 tons of sewage sludge ash into 7,000 tons of phosphoric acid, which can be used in the chemical industry or processed into fertilizer. In addition, gypsum is to be extracted for the building materials industry. A good 200 kilometers as the crow flies southeast, in Haldensleben, Saxony-Anhalt, the fertilizer manufacturer Seraplant wants to recycle 35,000 tons of sewage sludge ash together with Glatt Ingenieurtechnik. The ash is converted into a suspension and then spray granulated. The result is a phosphate or complex fertilizer that can be used directly.

It is up to those responsible which procedure the respective municipality chooses.

However, a rough concept must be presented by 2023.

Many smaller municipalities are likely to wait for the results of RePhoR (regional phosphorus recycling), a measure funded by the Federal Ministry of Education and Research.

Started last year, the project focuses on processes that take into account the circumstances of wastewater treatment and sewage sludge utilization on site and want to bring all stakeholders to one table.

Make better use of organic residues

Recycling alone is not enough.

The products obtained have to be returned to the cycle.

But currently the costs of phosphorus recovery exceed the possible revenues of the recyclates.

Here she is calling on the federal government to examine economic incentives in order to facilitate market access for recyclates.

In order to become even more independent of phosphorus imports, the potential of organic residues such as digestate, liquid manure, compost, animal by-products and crop residues should also be expanded.

"In this way, in theory, around 75 percent of the phosphorus requirement in Germany can be met," says Knickel.

Through phosphorus recycling and the targeted use of organic fertilizers, the valuable substance phosphorus is returned to the cycle and the import of phosphate ores is reduced to a minimum.

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A source of waste for which a solution will also have to be worked out in the next few years are wind turbines. As it says in Progress III, “some of them have already reached their design lifespan of 20 years.” According to the Federal Environment Agency (UBA), more dismantling can be expected from this year onwards. While recycling routes exist for old concrete from the towers and ballast from the foundations as well as for scrap steel, copper and aluminum scrap, the recycling of rotor blades is unclear. The older ones are made of glass fiber reinforced plastics, the newer ones are made of carbon fiber reinforced plastics. Recycling is particularly attractive for the latter. Because CFRP is a material that devours resources in production and is around six times more expensive than steel, for example:One kilogram of the so-called black gold costs around 20 euros.

Wind turbines are thrown away

The only industrial process for CFRP waste is currently pyrolysis. And the only plant is in Wischhafen, Lower Saxony, and belongs to the Mitsubishi Chemical Advanced Materials group. Specifically, the delivered material is treated at temperatures of over 350 degrees in the absence of oxygen, the plastic matrix breaks down into an energy-rich gas, leaving clean fibers ten to 100 millimeters in length. Up to 3500 tons per year can be processed in this way at the site. So far, this has mostly been production waste from the aviation industry, around 20 percent is end-of-life waste such as bicycle frames, sports equipment or parts from automobile manufacturers such as BMW. "With the dismantling of the wind turbines, the proportion will increase from 2025," says Tim Rademacker, General Manager at Mitsubishi Chemical Advanced Materials.

Experts estimate that around 1700 tons of rotor blades will then have to be recycled, ten years later more than 5000 tons. Rademacker believes that from 2025 there will also be relevant quantities from the aviation industry, such as the A320, and vehicle construction. “The inquiries are increasing.” The fibers are used as reinforcement components in the plastics industry, for example in the cover of SLR cameras or electrically conductive floors, as well as semi-finished textile products in aircraft interiors or as battery covers in e-vehicles. Other fields of application are carbon concrete - here the fibers could replace steel as a reinforcement structure - or 3-D printing.

“Increase in the proportion of recycling in the construction sector” is another heading in the German Resource Efficiency Program, because mineral construction waste represents Germany's largest waste stream with almost 219 million tons per year.

This resulted in a good 73 million tons of recycled building materials in 2018.

Interesting are, for example, those made from construction rubble that occurs when buildings are dismantled.

These are aggregates that can replace natural materials such as gravel and broken primary rock in resource-saving concrete.

Lighthouse project Bayernkaserne

A lighthouse project in this regard is the dismantling of the Bayern barracks in Munich: around 5500 apartments are to be built on an area of ​​58 hectares by 2030. Previously, there will be selective dismantling. About half of the 1.2 million tons of building rubble and soil will be processed and reused - one third as concrete, one third in road construction, one third as substrate for plant cultivation. The material is treated on site.

The trucks have to drive 3.3 million kilometers less, saving 82 laps around the world. Resource-saving concrete is to be made from 100 percent recycled material - a novelty. Currently, the standard only allows a maximum of 45 percent of the natural grain to be replaced. The product is intended to be used in landscaping as well as civil engineering and building construction. In a temporary pavilion, those interested can see how it all works in practice.

The idea of ​​using recycled concrete for building construction is not new.

This happened for the first time in the mid-1990s when the office of the German Federal Environmental Foundation was being built in Osnabrück.

After that, the subject almost came to a standstill.

Old material, some of which was processed in high quality, was more likely to be used in road and path construction.

Innovative pilot projects in building construction only started again between 2011.

However, more than lighthouse projects are necessary to sustainably transform the construction sector.

They show what is feasible, which is why recycling building materials are far from being used.

One solution: more information.

In the case of the Bayernkaserne, however, the public sector is also in demand.

She must request the material in the tender.

With the new recycling law, this has now been mandatory since the beginning of the year.