Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/742656
12 WET NEWS NOVEMBER 2016 ONSITE RENEwaBlE ENERgy The facility co-digests domestic and industrial organis waste with sludge from the wastewater treatment plant Hot off the biorefinery press • wastewater treatment plant Billund BioRefinery anaerobically co-digests domestic and industrial organic waste. Veolia water Technologies' Mike Froom takes a look at its thermal hydrolysis processes. projEcT SpEcS • generate electricity and provide district heating • Monitor and optimise the biomass feed to maximise biogas production B illund BioRefinery in Denmark is much more than a wastewater treatment facility. Yes, it treats wastewater for a 70,000 Population Equivalent (PE) community, however it also anaerobically co-digests 4,200 tonnes per year of domestic and industrial organic waste together with the surplus activated sludge from the biological wastewater treatment process. Generating electricity and providing district heating, the BioRefinery has received worldwide plaudits for innovation and sustainability: a distinction in the 2014 Global Water Awards for Water Reuse Project of the Year, a European Business Award for the Environment, and Denmark's Svend Auken Award for dedicated efforts in the environmental arena. Key to the efficiency of the project is a newly commissioned ExelysTM continuous thermal hydrolysis plant. Full-scale Thermal hydrolysis is, of course, a well-established process – Veolia's first BioTHELYS plant was installed in 2006 – and its benefits are clear. Heating thickened (15% dry solids) sludge to 150-165°C for 30 minutes causes lysis of biomass cells, enhancing the conversion of volatile suspended solids into biogas in mesophilic anaerobic digestion, improving sludge dewaterability and reducing the final biosolids volume and creating an 'Enhanced Treated Product' for disposal. What is different about Billund BioRefinery is that it now boasts Denmark's first full- scale Exelys continuous thermal hydrolysis plant. Billund BioRefinery is, indeed, innovative with an array of advanced technologies. These include ANITA Mox moving bed biofilm reactor (MBBR) which converts ammonia to nitrogen using annamox bacteria without any additional carbon substrate. Precise control of nutrients is ensured by a Hydrotech Discfilter with the option of coagulant dosing and pathogens in the sludge are killed by BioPasteur prior to digestion. Billund is taking a first step toward coordination of the municipality's treatment plants and drainage systems using STAR Utility Solutions, a smart online system that measures processes online, ensuring optimal treatment while minimising energy and chemicals use. In the event of heavy rainfall, part of the plant's treatment capacity can be switched over to treat stormwater, optimising pollution control and reducing the risk of overflow. Other controls include monitoring and optimisation of the biomass feed in order to maximise biogas production and prevent overloading of the digesters. Billund's biogas production generates about three times the energy requirements of the plant itself, with the surplus being exported to the grid. Future plans include the production of odour-free organic fertiliser, and eventually, phosphorus fertilisers and biodegradable bioplastics. Denmark's former environment minister, Kirsten Brosbøl, described Billund BioRefinery as "an example of people continuously striving to do better, develop new products and come up with solutions that improve the environment in Denmark and the rest of the world". Capital cost However, it's the new Exelys plant that is currently attracting attention amongst engineers. Thermal hydrolysis was developed as a batch process – fill, heat, react, cool discharge – which, of necessity, means that processing a continuous feed of sludge requires a large storage capacity for flow balancing and a number of batch reactors operating out of phase with each other. That means a high capital cost and large footprint. What differentiates Exelys is that it is a continuous rather The Exelys can treat three times more the amount of sludge solids