In this study, subcritical water hydrolysis was developed to treat refractory organic waste as a pretreatment process for high-efficiency anaerobic digestion. Sewage sludge and cyanobacteria as representative refractory waste were used. Different treatment temperatures were investigated and methane fermentation from the two pretreated wastes by subcritical water hydrolysis were carried out. The results showed that the optimum treatment temperature is 180°C. 0.8 g/l of formic acid, 8.6 g/l acetic acid, 9.9 g/l propionic acid and 0.6 g/l butyric acid were produced from sewage sludge and 405.8 µg/l of microcystin in cyanobacteria was completely removed in the pretreatment process at 180°C. The cumulative methane production was 43.2 ml and 54 ml from pretreated sewage sludge and cyanobacteria, respectively. Both of them were much higher than those produced from untreated one. Therefore, efficient anaerobic digestion of refractory organic waste using subcritical water hydrolysis as pretreatment process could be achieved.
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.
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