Sludge treatment affects the environment when it is treated, with transports and in the disposal of the final product. The Freeze Dry Unit has a lower environmental impact than today’s drying methods, as it lowers energy consumption, transports and produces polymer free final products.
In the treatment of sludge, the biggest contributor to climate change is the production of energy. Transports use fossil fuels which release greenhouse gases and oxides that contribute to climate change, eutrophication and acidification. Different ways of disposal often require transports, but the sludge itself produces greenhouse gases and in some instances, contributes to eutrophication and acidification.
The Freeze Dry Unit is more environmentally friendly than today’s drying methods. This is thanks to the low energy consumption and that the process does not require any polymer. The Freeze Dry Unit can additionally dry the sludge to a desired dryness between 30 and above 95 percent. In this way, the sludge volume decreases which lowers unnecessary transports between the plant and the disposal location.
Today’s methods for sludge treatment consumes huge amounts of energy as they often use high temperatures to dry the sludge. The Freeze Dry Unit uses low temperature which lowers the amount of energy needed to only a tenth of traditional drying method and in that way, reduces greenhouse gases from energy production.
The Freeze Dry Unit uses between 20 to 50 kWh/m3 depending on which type of sludge is dried. This can be compared to today’s methods which use at least 1,000 kWh/m3 to dry to a dry substance of 95 percent.
Polymer is a microplastic that is produced chemically. Polymer consists of long chains of smaller molecules, monomers. Polymers are used to flock sludge particles together which helps the dewatering process.
The Freeze Dry Unit works both with and without polymers. This is a unique advantage with the Freeze Dry Unit. Most technologies today require polymers or great amounts of energy to dewater the sludge successfully.
Polymers are bonded with sludge particles. This means that polymers still reside in the final sludge product.
The final product from the Freeze Dry Unit can be totally free from polymers, provided no polymers has been added in a previous step. This makes the product very suited to be used as a fertilizer in agriculture. By utilizing the nutrients in sewage sludge, a circular economy can be created.
Sludge products from sewage waste often contains phosphorus and other important nutrients such as nitrogen, sulfur and magnesium. There can also be iron, boron, selenium and zinc. Through sludge products, up to 7,000 tonnes of phosphorus and 9,000 tonnes of nitrogen can be recycled every year in Sweden.
Nutrients like phosphorus and nitrogen are vital to agriculture. Today, a lot of the nutrients are extracted from minerals such as phosphate rock. The mining of phosphorus has a significant impact on the environment. Deposits of phosphorus have decreased and there is talk of a peak phosphorus, where it is too expensive to extract the remaining phosphorus from the ground.
The Freeze Dry Unit enables the recycling and utilization of existing phosphorus from, for example, the sewage system. The high dryness of the sludge after the process, above 95%, allows for effective incineration after which phosphorus can be extracted from the ash and used in fertilizer products.
The transportation of sludge is not just a monetary question, but also an environmental one. Transports often use fossil fuel which when used in a combustion engine, releases gases and substances that impact climate change, eutrophication and acidification. Studies have shown that with a decreased sludge volume, transports can be decreased up to 80 percent.
A final product with a high dry solids content, which the final product from the Freeze Dry Unit has, have a smaller volume as it doesn’t contain a lot of water. This makes the transport of the final product minimal, but as the Freeze Dry Unit does not require any polymers, these polymer transports disappear completely.
Reduced transports also lower the wear on roads and decreases the noise levels these transports would have resulted in.
Financial support from the Swedish Environmental Protection Agency
The project with the Freeze Dry Unit was approved with support from the Swedish Environmental Protection Agency. Elajo Technology Solutions got the support along with the city of Oxelösund within the agency’s project City Innovations.
The Freeze Dry Unit received about € 122 942 from the agency. The money was contributed to pilot testing of the Freeze Dry Unit process at Oxelösunds wastewater treatment plant, where the focus was to test polymer free dewatering and drying.
Altogether, City Innovations handed out € 6 309 499 to 50 projects. The projects are in many different categories of city innovation: waste treatment, buildings and building, digital tools, ecosystem services and farming, energy, transports as well as water and sewage systems.
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