Start Circles pilot project for reuse of mineralised sewage sludge

Sewage sludge occurs in wastewater treatment process, regardles the wastewater technology applied. It presents up to 40% of wastewater treatment costs and therefore impacts every household water bill.

Sludge drying reed beds are a natural technology for sludge mineralisation, dewatering and stabilisation. The main benefits of the technology is its' low energy consumption and low operating costs. The technology is GHG emission-free. The case was contributed by LIMNOS Ltd.

The material obtained is humus, but in case of heavy metal containment, the material can be recycled for bioplastics.

For the compatibilization of humus into thermoplastic matrix the recycled polypropylene was chosen. To achive good distribution of humus inside the composite and also to prevent thermal and oxidative degradation lubricant, antioxidant and compatibilizer were added. Tests were done with addition of 15 wt.% and 30 wt.% of humus into the composite. The stiffness rise for 2 % and 13 %, the strength decreases for 15 % and 21 %, also the elongation at break decreases for 79 % and 87 % for the composites with 15 wt.% and 30 wt.% of humus respectively.

The sewage sludge can be used as filler for thermoplastic matrix for the static loaded parts with low deformation or low load. 

Further efforts will be required to demonstrate the industrial application (company selected) and cost efficiency defined. Next step is to build a business model around the case.

More info about Start Circles HERE.

Picture 1: Compounding of a bioplstic composite (extruder die for two filaments (above) and water bath (below)

Picture 2: Bioplastic composite with 15 wt.% humus (lower part of the picture) and 30 wt.% of humus (upper part of the picture)