Experiences with development of organic fertiliser products at the IVAR IKS in Stavanger have shown that thermally dried biosolids have potential to provide an important alternative to mineral fertilisers as well as meeting future demands for agricultural recycling of biosolids in Norway. The development has been accomplished over the past 3 years in co-operation with the HØST Valuable Waste Company. The main objectives have been to develop organic fertiliser products based on IVAR’s thermally dried biosolids by utilising the phosphorous content present within the sludge and with the addition of nitrogen and potassium compounds.
Trials and field experiments have demonstrated that it is possible to produce sludge-based organic fertilisers with a consistency, particle size and nutrient composition very similar to mineral fertilisers. The successful trials have concluded with a product called MINORGA with a N-P-K format of 10-2-5. The product is regarded as more environmentally friendly compared with similar mineral fertilisers leading to less run-off and prolonged fertilising effect. In that context, the products will also offer a much better balanced phosphorus supply of approximately 10-20 kg P per hectare (ha) per year which is close to the latest requirements in most Norwegian catchment areas.
This paper provides an overview of the background, planning and accomplishment of the development of the products. In addition, the paper summarizes results and experiences from trials, future challenges and the way forward involving a new fertiliser factory as an integrated part of the Regional Waste Water Treatment Plant (SNJ).
Keywords: Biosolids recycling, legislation, MINORGA, organic fertilisers, nutrient recovery, thermal drying and pelletising
The IVAR IKS company is an inter-municipal organisation responsible for the provision of drinking water and wastewater treatment in the Jæren region of Norway. In addition IVAR is responsible for the treatment and disposal of domestic waste in the region.
The Regional Wastewater Treatment Plant of North Jæren, receives and treats wastewater from the densely populated Stavanger region. The design capacity is equal to a population equivalent of approximately 240,000 based on PEB60 a). Following conventional grit and screenings removal, the current wastewater treatment comprises a primary precipitation process using ferric chloride as a coagulant.
a) Population equivalent according to EU Urban Wastewater Directive ( 91/271/EEC).
The existing sludge treatment facility includes anaerobic digestion, centrifuge dewatering, thermal drying and pelletising of dried sludge. Annual sludge production is approximately 5000 tonnes of biopellets at 85 % DS (dry solids) . The biogas is upgraded to natural gas standards and distributed in the adjacent natural gas pipeline for heating purposes or as fuel for vehicles. The biogas upgrading plant provides about 30 GWh of green energy to the natural gas system. In return IVAR is supplied with natural gas to cover the heating requirements of the entire plant.