Conversion of various organic wastes into valuable materials using subcritical water treatment reactors

Abstract

The “Basic Law for Promoting a Recycling-based Society” was promulgated as a framework for the formation of a recycling-oriented society in 2000 with the aim of creating economic sustainable development while striving for both environmental preservation and social equity. Sewage sludge, animal fecal matter as well as garbage are difficult wastes for any developing or developed society to process. In order to solve these waste problems, the subcritical water treatment (SCWT) technology was developed. In this study, pilot experiments with sewage sludge, livestock manure and fishery waste were undertaken using the SCWT reactor by varying the temperature from 100°C-200°C, the pressure 1.0 MPa-2.0 MPa and limiting the time of operation to 60 minutes. The chemical analysis of the treated samples gave results appropriate for a fertilizer. For example, the resulting analysis for the treated sewage sludge was: water content 60.97%, pH 4.16, organic content 87.33%, T-N 0.69%, P2O5 0.705%, K 3,150 mg/kg, Ca 70,500 mg/kg, Mg 3,090 mg/kg, and Na 1,150 mg/kg. These results indicate good elements for a general organic fertilizer as it was verified to be pathogen free, as well as free of hazardous chemicals for continuous applications on agricultural lands. Thus, it was verified that the SCWT technology is useful for producing valuable resources from organic wastes.