Maximering av slam och biogasproduktion för att motverka global uppvärmning / Maximizing sludge and biogas production for counteracting global warming

Can wastewater treatment contribute to counteract global warming? Increased biogas production for substituting fossil fuel is one possibility. However, an active sludge process with biological nitrogen and phosphorus removal consume organic material, gives a sludge with less digestibility and need energy for aeration. The amount of produced sludge corresponds to half of the organic material in the sewage water. If the degree of digestion is 40 % it means that 20 % of the organic content have been transformed to biogas. Anaerobic digestion of the sewage water can give 60 to 80 % conversion of organic material in the sewage water to biogas and thereby 3 to 4 times larger biogas production. However, if maximum amount of the carbon source is used for biogas production there will be no carbon source for biological nutrient removal. Therefore new methods for nutrient removal without carbon source has to be developed, for which struvite precipitation and can anammox be used. The pilot plant Hammarby Sjöstadsverk is a unique resource owned by KTH and IVL Swedish Environmental Institute, which can be used for these studies. Also the possibility to use sewage sludge to counteract global warming by recycling carbon to deep see sediments should be studied