Abstract
As a treatment method of sewage sludge, the hydrothermal carbonization (HTC) process was adopted in this work. HTC has a great advantage considering the economic efficiency of its process operation due to its reduced energy consumption and production of solid fuel upgraded through the increased fixed carbon and heating value. The ash of sewage sludge, however, contains up to 52.55% phosphate, which degrades the efficiency of the thermochemical conversion process such as pyrolysis, combustion, and gasification by causing slagging. In this study, three kinds of organic acids, i.e., oxalic, tartaric, and citric acid, were selected to eliminate phosphorus from hydrochars produced through the HTC of sewage sludge. The efficiency of the phosphorus removal and the properties of the corresponding HTC hydrochars were analyzed by adding 20 mmoles of organic acids per 1 g of phosphorus in the HTC sample. In addition, the phosphorus reduction effect and the applicability to an upgrading process were verified. Oxalic acid was selected as the most appropriate organic acid considering the economic efficiency of its process operation. Furthermore, the optimal conditions were selected by analyzing the efficiency of the phosphorus elimination and the characteristic property of the HTC hydrochars with the weight fraction of oxalic acid.
Highlights
Sewage sludge is generated after the anaerobic digestion of organic matter in wastewater treatment facilities [1]
The sewage sludge used as the carbonization feed was obtained from the Gongchon branch of the wastewater treatment plants (WWTP) of South Korea, and its properties were analyzed monthly by sampling over the course of the year
20 mmoles of each organic acid was added per 1 g of phosphorus [25]
Summary
Sewage sludge is generated after the anaerobic digestion of organic matter in wastewater treatment facilities [1]. The reduction and energy conversion projects of sewage sludge have been actively carried out under the government initiative, since 2013, when marine dumping of sewage sludge was banned by the London Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matters. The conventional treatments of sewage sludge are burying, drying, or burning sewage sludge on land. Requires large energy consumption for dewatering and drying because it contains high moisture content above 80 wt.%, causing the problem of low economic value. Hydrothermal carbonization (HTC) has received attention recently as a way to convert organic waste to solid fuel and to improve the bio-energy production efficiency [4,5]
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