Effects of polyferric sulfate and polyacrylamide on algal mud-based hydrochar and their application potential
WANG Yi-meng1,2, LIANG Yun-yi2,3, CHEN Bing-fa2, MA Ya-xin1,2, ZHOU Zi-yu1, HE Shi-ying2, XIE Hui-fang1, XUE Li-hong2, FENG Yan-fang2
1. School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing 210094, China; 2. Key Laboratory of Agro-Environment in Downstream of Yangtze Plain, National Agricultural Experiment Station forAgricultural Environment, Ministry of Agriculture and Rural Affairs, Institute of Agricultural Resources and Environment, JiangsuAcademy of Agricultural Sciences, Nanjing 210014, China; 3. Material Science and Engineering College, Nanjing Forestry University, Nanjing 210037, China
Abstract：Using Taihu algal mud as the research subject, two common flocculants, polymeric ferric sulfate (PFS) and polyacrylamide (PAM), were selected to prepare different hydrochars at 180℃, 220℃, and 260℃. The results demonstrated that as the hydrothermal temperature increased, the carbon content in the algal mud hydrochar increased, while the hydrogen and nitrogen contents decreased. Decarboxylation and hydrolysis reactions were identified as the dominant processes during the hydrothermal conversion. The incorporation of PFS significantly enhanced the iron content in the hydrochar by 519.6% to 748.3%, and the rise in hydrothermal temperature facilitated the transformation of iron from Fe(III) to Fe(II), thereby improving its reducibility. PAM exhibited degradation at lower temperatures, generating oxygen-containing functional groups, while PFS promoted the degradation and carbonization of organic matter. The hydrochar prepared at 180℃ showed higher nutrient retention. Rice cultivation experiments indicated that the application of algal mud-based hydrochar did not adversely affect rice growth; notably, PAM-based hydrochars increased rice plant biomass by 9.0%. Based on field survey data, it was estimated that converting Taihu algal mud into hydrochar could annually recover 3077.7 tons of total nitrogen and 776.7 tons of total phosphorus. The recovered total phosphorus accounted for 43.1% of the external phosphorus load input into Taihu Lake.
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