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Renewable energy from wastewater

​​​​​​​​​​​​​​​​​​Since Stora Enso’s Fluting mill at Heinola is located by the headwaters of the River Kymijoki – one of Finland’s longest rivers – in a region with thousands of lakeside summer cottages, taking care of water and the environment is particularly high on the agenda. The mill’s new bioreactor is now turning wastewater effluent into energy. ​
Heinola Mill produces premium fluting for the global container board market, used to pack products including fruit, vegetables and electronic goods. The mill withdraws annually some four million cubic metres of water for its production of which the vast majority is recycled back to the environment after being carefully purified at the mill´s own wastewater treatment plant. 
 
Like any board mill, its untreated wastewater has high concentrations of organic compounds, measured as chemical oxygen demand (COD). If left untreated, such effluent can worsen environmental problems such as toxic algal blooms in nat​ural waters.  “The acceptable levels of COD in treated wastewater releases are defined in each mill’s environmental permit. To reach the required level, our wastewater has been purified through a relatively complex process involving the use of quite high amounts of energy and chemicals – until now,” explains Heinola Mill’s Development Manager Mikael Sillfors. 
 
A new era of modern wastewater treatment technology has commenced at Heinola Mill, where since July an anaerobic bioreactor has been turning organic material in the mill’s wastewater into biogas – leading to both cost savings and environmental improvements. This is the first time this kind of water treatment technology has been introduced at a Nordic forest industry mill using virgin fibre as raw material. ​

 
Sharing best practices
The 27-metre high bioreactor tower rises into the sky next to the Mill. Inside, burbling and bubbling sounds can be heard as 50 litres of water rush through its pipes every second and biogas is formed. “Approximately half of the mill’s wastewater is piped here into the bioreactor, which is filled with natural micro-organism granules that convert the COD in the wastewater into bio-based methane that we can use to generate renewable energy for our production,” Development Engineer Jere Luukkanen enthusiastically explains. 
 
The bioreactor is a great example of how new resource efficient technology is being introduced to reflect the mill’s environmental ambitions. “Instead of patching an old, inefficient wastewater treatment process we tackled its root causes by implementing a modern concept – one that brings additional benefits,” says Sillfors. 
 
Similar technology has also been used at Stora Enso’s Central European mills that use paper for recycling as raw material, for example in Ostrołęka, Poland. “This is also a good example of sharing best practices within a large company. We have been proud to successfully introduce new technology in our industry among the first ones in Scandinavia,” Luukkanen and Sillfors add.​
 
 
Development Engineer Jere Luukkanen holding a sample of micro-organism granules​ from the bioreactor.
 
Making more from less
The bioreactor effectively lowers COD levels in Heinola Mill’s wastewater, significantly reducing the need to use chemicals such as lye and sulphuric acid in treatment processes. The new technology is also expected to halve the amount of wastewater sludge generated at the mill, with annual reductions amounting to 6 000 tonnes. The simpler treatment process is also expected to cut the wastewater treatment plant’s energy use by as much as 35%. The energy generated by the bioreactor itself is sufficient to heat 300 houses, and it is expected to reduce the mill’s annual need for fossil-based energy by some 5%. “This makes a real difference, both for the climate and for local waters,” Sillfors says. 
 
The investment is expected to result in savings of up to hundreds of thousands euros a year, while also opening doors for future developments. The bioreactor may someday additionally produce biogas for consumer markets, and heat local Finnish homes.