SEWAGE SLUDGE & DIGESTATE

HOW SEWAGE SLUDGE IS DEALT WITH TODAY: A WASTE OF RESOURCES!

The Swedish sewage treatment plants produce about one million tonnes of sludge every year. This sludge contains a large amount of phosphorus, nitrogen and potassium – all of which are important plant nutrients. If all sludge was used as fertiliser, up to 7,000 tonnes of phosphorus and 9,000 tonnes of nitrogen could be added to arable land each year. However, only a small part of the sludge, about a quarter, is currently being recycled. This is because the sludge contains a number of undesirable substances, including heavy metals, drugs, viruses and bacteria.

WHY MAKE BIOCHAR OUT OF THE SEWAGE SLUDGE?

Phosphorus is currently extracted from mines in a few places around the world. The maximum production of the mines is expected to be reached within 50 to 100 years. At the same time, the world’s population continues to grow. Therefore, being able to reuse phosphorus is vital for ensuring our future food production. If we could recycle all the phosphorus from Swedish sewage treatment plants, it would correspond to 60 per cent of the phosphorus currently being purchased for Swedish agriculture in the form of commercial fertilisers.

WHAT WE DO IN THE PROJECT REST TILL BÄST

Within the project Rest Till Bäst, we will produce biochar from sludge that contains different amounts of carbon and energy, and we will develop energy budgets for the conversion of each sludge type into biochar. We will also evaluate how the various properties of sludge, such as water, energy and iron content affect the energy budgets. Preliminary studies and theoretical calculations indicate that the energy content of most sludge types is sufficient to fuel both the drying of the sewage sludge and the biochar furnace. The goal is to optimise the pyrolysis process so that the costs and energy consumption are kept as low as possible, while at the same time making the biochar as clean as possible.

COMMITTED PROJECT PARTNERS

CONTACT

Markus Paulsson
markus.paulsson@lund.se
+46 (0) 46-359 53 36
City of Lund, City Office
221 00 Lund, Sweden

REST TILL BÄST

Rest till Bäst is a Vinnova-funded project whose purpose is to develop solutions for managing society’s organic residues and create a much needed beneficial product, while at the same time minimising environmental and climate impact.