Energy Recovery Potential of Suspended Solid Particles in Wastewater at Primary Sedimentation by Heating Value Distribution

Abstract

 Suspended solids (SS) formed from various sized particles in wastewater contain organic matter that can be used as energy resource. Since the removal of SS at primary sedimentation process can be regarded as an energy recovery, the heating value distribution by particle sizes would become important.

 In this study, particle size fractionaton for wastewater and sludge samples around primary sedimentation tanks at two wastewater treatment plants (WWTPs) in Japan was performed. Then, the particle size and the organic element (CHN) distributions were clarified. The heating value distributions were elucidated by thermo gravimetry-differential thermal analysis (TG-DTA) and also CHN analysis. Finally, the energy recovery ratio at primary sedimentation tanks in two WWTP.

 As a result, it was confirmed that particles of 250 μm or more were almost recovered in the primary sedimentation tanks. The heating value distributions by particle size showed that the heating value tended to increase as the particle size fraction became smaller, but it was contrary to the tendency of the ignition loss, and the effect of high oxygen content such as toilet paper was observed. The energy recovery ratios in the primary sedimentation tanks were calculated to be 87% and 74%, respectively, but the influence of the particle size distribution itself was more dominant than the heating value distribution according to the particle size.