Abstract
Hydrothermal carbonization (HTC) is a promising technology used for bioenergy conversion from bio-wastes such as sewage sludge, livestock manure, and food waste. To determine the optimum HTC reaction temperature in maximizing the gross energy recovery efficiency of poultry slaughterhouse sludge cake, a pilot-scale HTC reactor was designed and operated under reaction temperatures of 170, 180, 190, 200 and 22 °C. During the HTC reaction, the gross energy recovery efficiency was determined based on the calorific value of the HTC-biochar and ultimate methane potential of the HTC-hydrolysate. The poultry slaughterhouse sludge cake was assessed as a useful source for the bioenergy conversion with a high calorific value of approximately 27.7 MJ/kg. The calorific values of the HTC-biochar increased from 29.6 MJ/kg to 31.3 MJ/kg in accordance with the change in the reaction temperature from 170 °C to 220 °C. The ultimate methane potential of the HTC-hydrolysate was 0.222, 0.242, 0.237, 0.228 and 0.197 Nm3/kg-CODadded for the reaction temperatures of 170, 180, 190, 200 and 220 °C, respectively. The potential energy of feedstock was 4.541 MJ/kg. The total gross energy recovery (GERtotal) was 4318 MJ/kg, of which the maximum value in the HTC reaction temperature was attained at 180 °C. Thus, the optimum temperature of the HTC reaction was 180 °C with a maximum GERtotal efficiency of 95.1%.
Highlights
In Korea, meat consumption has steeply increased, with food consumption patterns changing with economic growth
The sludge cake generated from the wastewater treatment plant of the poultry slaughterhouse was a useful source for bioenergy conversion due its high calorific value of approximately 27.7 MJ/kg
The solid yield of the Hydrothermal carbonization (HTC)-biochar decreased from 75.9% to 66.8% with the increase of reaction temperature from 170 ◦ C to 220 ◦ C, while the calorific values increased from 29.6 MJ/kg to 31.3 MJ/kg, and the energy densification increased from 1.07 to 1.13
Summary
In Korea, meat consumption (e.g., beef, pork, and poultry) has steeply increased, with food consumption patterns changing with economic growth. Due to the growth of the poultry industry, several environmental problems have occurred relating to the disposal of wastewater treatment sludge and various poultry processing residues (e.g., blood, feathers, bones) generated from the poultry slaughterhouse [1]. The interest in energy conversion of sludge waste is increasing due to high sludge disposal costs and limited alternative disposal methods. Poultry slaughterhouses sludge cake is characterized by a high solid content that is composed of protein and fat [3,4,5]. Sludge cake is considered an effective substrate for anaerobic digestion. High ammonium nitrogen produced from protein degradation and long chain fatty acids from fat degradation can cause inhibition during the anaerobic digestion process [6]
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