Effects of recycled materials on biological drying of food industry sludge
ZHU Zi-han1,2, LIU Yi-si1,3, SUN Xiao-ting1,2, ZHOU Zi-an1,2, HUANG Yan1,2, DONG Li-ming1,2
1. Key Laboratory of Cleaner Production and Integrated Resource Utilization of China National Light Industry, Beijing Technology and Business University, Beijing 100048, China; 2. State Environmental Protection Key Lab of Food Chain Pollution Control, Beijing Technology and Business University, Beijing 100048, China; 3. Sichuan road navigation construction engineering Co., LTD, Chengdu 610041, China
Abstract：The sludge from the bio-drying of dewatered sludge from food industry using hot air system was used as the recycled materials to explore the effect of utilizing different ratios of recycled materials on the effect of sludge bio-drying under the same conditions. The results showed that the best bio-drying effect was achieved when the ratio of recycled materials: straw: sludge = 1:1:4 (mass ratio), the high temperature period could be maintained for 72h and the daily cumulative temperature TD was 30.96℃/d, and the unit water removal was 287.45g/kg WM, but the bio-drying cycle was prolonged an the sludge treatment load was reduced. Three-dimensional fluorescence spectrum analysis showed that in the experimental group of reutilization, humic acid and fulvic acid substances increased in the high temperature stage of biological drying, and TC decreased from 243.8~264.2g/kg WM before biological drying to 191.7~224.9g/kg WM after biological drying, which could increase the retention of TC. The CO2 emissions generated by unit water removal ranged from 168.7L to 226.9L CO2/kg H2O.It indicated that the use of recycled materials could increase the free airspace of the mixture, increase the oxygen content in the ventilated bio-drying process, and thus reduce the CO2 emission per unit of water removal. The TN of the experimental group without adding recycled materials did not show significant changes before and after the bio-drying process, whereas the TN under the recycled materials utilization condition increased continuously from the initial 29.4~31.1g/kg WM to 31.6~31.8g/kg WM, which was mainly due to the concentration effect of TN caused by the evaporation of water and the mineralization of organic matter during the drying process. The results of energy balance analysis showed that the use of recycled materials could effectively reduce the heat dissipation brought by the turning pile and experimental process, and the heat used for water evaporation at recycled materials: straw:sludge=1:1:4 had the largest value but the percentage decreased, accounting for 78.25% of the total consumed heat. The addition of recycled materials can effectively improve the moisture removal and carbon and nitrogen retention, and also increase the degree of decomposition of the materials after bio-drying and reduce the amount of rice straw conditioner, which indicates that the use of recycled materials has an optimized role in the bio-drying of dewatered sludge from the food industry in the hot air system.
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