Within the framework of WOW! Project, the market potential and technical feasibility for production of bioplastic (PHA) from sewage with primary sludge as feedstock has been proved. However, an estimate of economic viability has shown that this requires a waste water treatment plant (WWTP) capacity of approximately 2 million people equivalent (PE).
Since in most regions in North-West Europe, the capacity of WWTPs are typically below 2 million PE, strategic placement of a centralised PHA production facility for PHA production was researched where a combination of WWTPs together would make up the required amount of sludge for delivery to the central plant. The previously in WOW created decision support tool (DST) helped for the specific site selection for three regions (Scotland, Ireland and Germany). The goal of the assessment was to let geographical information system (GIS) software pick the ideal location for a centralised PHA production facility and to show the participating WWTPs which are required to gather enough primary sludge for the production of 5,000 ton of PHA per year. All of this taking into account technical, economic and environmental aspects.
The main environmental aspect in this assessment was transport. By reducing transport distances, you can reduce environmental impact. However, since primary sludge contains a lot of water, the assessment also went into discovering if it is better to install already the first step of the process, the PHA enrichment from primary sludge, at the participating WWTPs and transport PHA-enriched biomass. This way you’d need to transport less matter, so less truck kilometres, but you do need more technical installations e.g. PHA enrichment facility, dewatering unit and drier.
From technical point of view, the assessment took into account only WWTPs with a capacity of 50,000 PE (people equivalent) or higher and having a dryer onsite only possible at WWTPs of 300,000 PE and higher.
The outcome showed that for Scotland, the ideal location for a PHA production facility would be Shieldhall, near Glasgow, including 9 WWTPs that would need to contribute their primary sludge. The total transport distance per year would be around 310,000 kilometres. When transporting only dried biomass, only 4 WWTPs would need to contribute, reducing the total transport distance to 7,000 kilometres, but additional facilities needs to be installed at all 4 WWTPs.
For Ireland, Ringsend, near Dublin, was the chosen location, requiring 3 WWTPs at roughly 20km distance to bring its primary sludge to Ringsend. For Germany, there are 8 potential locations spread around the country that could each fit a centralised PHA production facility, assuming the boundaries that a maximum of 7 WWTPs may contribute within 45km distance, each having a capacity of at least 300,000 PE and having a PHA enrichment facility, dewatering unit and drier onsite. The WWTPs with a capacity high enough on itself were not taken into account in the assessment.
From financial point of view, the scenario of transporting primary sludge would result costs of €4,87 per kg of PHA, while transport dried PHA enriched biomass would result in €6,32 per kg of PHA. The next phase of the research will be an assessment on the circularity assessment of centralised PHA production.
Detailed information of the study can be found in the following report:
Report and GIS maps about most suitable locations to realize a centralized PHA compounding and processing facility