Sweden's Linkoping University discovers way to produce biogas using wastewater from pulp and paper mills; eventually, the technology might be used to cut mills' costs to aerate sludge ponds, and biogas produced could power their smaller operations

, June 27, 2014 () – Biogas is a renewable form of energy, which is usually formed out of anaerobic digestion or fermentation of biodegradable materials. Generating biogas from waste reduces the amount of disposable waste and also kills disease-causing pathogens. While extensive research on generation of biogas from waste is underway in various universities, Linkoping University, Sweden has discovered a way to produce biogas from wastewater produced by pulp and paper mills.

In a project funded by Swedish Research Agency, Linkoping University and various industrial partners, researchers have found that wastewater from pulp and paper mills has a large quantity of organic content that can be converted into biogas. They have taken samples from 70 wastewater streams from seven mills and have calculated the total potential of biogas generation could amount to 70 million normal cubic meters of biogas. They have developed two anaerobic technologies to generate biogas from this wastewater, which has been tested successfully in the laboratory. Now they are ready to implement and test it in the industry on a large scale. After the research is fine-tuned they hope to produce 100 million normal cubic meter of biogas.

The first technology is UASB (Up Flow Anaerobic Sludge Blanket), which is a digestion chamber used to clean water. In this chamber, water flows from the bottom and gets accumulated at the middle of the tank and forms granules or balls and over which a layer of microorganism responsible for methane production forms. Through the blanket of granules the water flows upwards for cleaning, leaving out the organic material captured in the bottom part. In this chamber, water cleaning and methane formation take place simultaneously.

The second technology is CSTR (Completely Stirred Tank Reactor), which can recirculate the sludge. The sludge in this reactor gets stirred and digested, later the water and sludge get separated. The fiber and microorganism in the sludge will remain in the reactor so the microorganism can yield maximum methane.

The researchers are also testing if they can reduce the residing time of the sludge, which is stored in a large sedimentation pool to increase the nutrient content and biodegradability. If this is achieved, sludge and fibers can be digested together--this will reduce the cost of dewatering and aerating in ponds, and also enhance the quantity of biogas generation.

Once UASB and CSTR are successfully implemented in pulp and paper mills, they will help the mills to reduce the aerating cost of sludge ponds. In addition, the generated biogas can be used for smaller operations in the mills thereby reducing the cost for power. Moreover, the biogas can be utilized in the form of LPG (liquified petroleum gas). These advantages will help the innovation to get adopted on a large scale.

Details: Bo Svensson, Professor, Water and Energy Studies, Linkoping University, 581 83, Linkoping, Sweden. Phone: 13-28-22-80, 70-528-22-81. E-mail: bosseh@tema.liu.se.

(c) 2014 Frost & Sullivan

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