Abstract
Hydrothermal oxidation (HTO) provides an efficient technique to completely destroy wet organic wastes. In this study, HTO was applied to treat fecal sludge at well-defined experimental conditions. Four different kinetic models were adjusted to the obtained data. Among others, a distributed activation energy model (DAEM) was applied. A total of 33 experiments were carried out in an unstirred batch reactor with pressurized air as the oxidant at temperatures of <470 °C, oxygen-to-fuel equivalence ratios between 0 and 1.9, feed concentrations between 3.9 and 9.8 molTOC L–1 (TOC = total organic carbon), and reaction times between 86 and 1572 s. Decomposition of the fecal sludge was monitored by means of the conversion of TOC to CO2 and CO. In the presence of oxygen, ignition of the reaction was observed around 300 °C, followed by further rapid decomposition of the organic material. The TOC was completely decomposed to CO2 within 25 min at 470 °C and an oxygen-to-fuel equivalence ratio of 1.2. CO was formed as an intermediate product, and no other combustible products were found in the gas. At certain reaction conditions, the formation of unwanted coke and tarlike products occurred. The reaction temperature and oxygen-to-fuel equivalence ratio showed a significant influence on TOC conversion, while the initial TOC concentration did not. Conversion of TOC to CO2 could be well described with a first-order rate law and an activation energy of 39 kJ mol–1.
Highlights
According to an estimate of the World Health Organization (WHO) for 2015, approximately 2.4 billion people worldwide have no access to hygienically safe sanitation facilities
The reaction temperature and oxygen-to-fuel equivalence ratio showed a significant influence on total organic carbon (TOC) conversion, while the initial TOC concentration did an activation energy of 39 kJ mol−1
Depending on the degree of conversion, a transparent brown-yellowish to colorless liquid reaction product was obtained
Summary
According to an estimate of the World Health Organization (WHO) for 2015, approximately 2.4 billion people worldwide have no access to hygienically safe sanitation facilities. The lack of a safe sanitation infrastructure is especially encountered in rural areas of low-income countries and in informal urban settlements (slums). Problems that arise from the lack of sanitation are, for example, contamination of drinking water, the promotion of diseases, and high infant mortalities.[1] Decentral collection and treatment of the fecal matter could provide a solution for this problem. Because a supply of electric energy might be scarce in the target regions, treatment technologies that work “off the grid” are necessary. Hydrothermal oxidation (HTO) could provide a technology that allows safe in situ sanitation of fecal matter and does not require an external infrastructure
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