Safer sewage sludge disposal
The implementation of European directives for wastewater has led to an improvement in wastewater quality across Member States. However, it has generated an increasing amount of sewage sludge, which needs to be disposed of properly. More than 60 % of Europe's wastewater treatment plants (WWTPs) serve small municipalities and require a cheap and simple disposal solution for their sewage sludge. Such a system has been developed by the PYROCHAR (Pyrolysis based process to convert small WWTP sewage sludge into useful biochar) project. The PYROCHAR system dries the dewatered sludge and then uses slow pyrolysis technology to convert the material into useful by-products, namely synthetic gas (syngas) and biochar. The technology is based on heating the sludge in the absence of oxygen (pyrolysis) and its reuse of energy and resources offers a realistic solution for small municipalities, with low operation and maintenance costs. Researchers conducted an in-depth analysis of municipal waste in several European countries, including a study of pyrolysis by-products. They also analysed syngas contaminants and investigated gas cleaning technology. In addition, industrial catalysts were developed for tar decomposition, which enable impurities to be removed and more syngas to be produced. A new control system was developed to optimise energy efficiency and process performance by monitoring key parameters. This means the biochar produced contains a limited and acceptable amount of heavy metals, thereby enabling its reuse. BIOCHAR's ground-breaking technology will enable small municipalities to manage their sewage sludge cheaply and effectively. It will help reduce the cost of sludge treatment, storage and transport to composting and incineration, farms or larger waste treatment plants for further treatment. Moreover, useful nutrients such as nitrate, phosphorus or potassium will not be lost; instead, they will be held in a stable and economically valuable by-product, the biochar. The system will also enable compliance with EU directives for waste water treatment and sludge management.
Keywords
Sewage sludge, wastewater, wastewater treatment plants, PYROCHAR, pyrolysis, syngas
