Uses of biogas produced by digestion of wastewater sludge. The SIAAP's experience feedback and projects

The SIAAP, in charge of the purification of the Great Paris wastewaters (8 M inhabitants), handles 2.7 Mm3/day. Five wastewater treatment plants permit to dean these wastewaters before they are discharged into the receiving environment: 'Seine Aval' (Acheres, 1,7 Mm3/day), 'Seine Amont' (Valenton, 600 000 m3/day), 'Seine Centre' (Colombes, 240 000 m3/day), 'Seine Gresillons' (Triel-sur-Seine, 100 000 m3/day) and 'Marne Aval' (Noisy-Le-Grand, 40 000 m3/day). Biogas produced by digestion of sludge provides a part of the energy required by the five sewage treatment works. Energy recovered from biogas have been used by the SAV site since 1940. As soon as the first part of this plant started up, biogas was used as fuel to heat digester, to produce power through biogas engines and to drive blowers. In the 60's and 70's, dual-fuel engines were brought into service, and then in 1992, a gas turbine was installed. Nowadays, a combined heat and power (cogeneration) project is in progress with the installation of two gas turbines, each generating 5 MW. All of these installations had allowed a 70% energetic autonomy ratio on 'Seine Aval' site. Then, new treatment units were introduced. Thus, energy consumption has increased, with only 60 % of energy demands being covered. By 2020, a complete make-over of the 'Seine Aval' plant will be done. This should allow to cover about 70% of energy demands, partly thanks to biogas reuse. New plants are currently being constructed. All of them will include sludge digestion process providing biogas. With the 'Seine Gresillons' plant upgrading, digestion process will occur on site. Biogas will be used in a cogeneration system to produce both electricity (that would be either used on site or sold commercially, this has not been decided by now) and heat for digesters heating. The new 'Seine Moree' plant will be built in the city of Blanc-Mesnil. A partnership with the Syctom (an association in charge of treatment and reuse of the Great Paris household refuses) would permit co-digestion of organic waste from domestic refuses and sewage sludge on the same site. At last, in the 'Seine Amont' site, important works have been done to improve biogas system safety. Moreover, in this plant, with the improvement of wastewater treatment efficiency, digestion process is going to increase. (author)