| The increasing production of municipal biowaste and crop straw waste has been a direct treaten to environmental quality and social harmonious due to the fast developing of the economies, changes of the living ways and lack of feasible treatment technologies in China. According to the statistical data, there was about 25% of crop straw was directly burned in the field and only 50% of the municipal biowast was safely disposed. Therefor, the increasing of bio-waster production and limited ability of safety treatment technologies have been a bottleneck to Chinese ecological civilization construction. The pyrolysis technology that covert the bio-waste into biochar has been consided as a new tool for waste biomass management. Lots of studies have confirmed that the benefits of biochar for soil amendment including an increase in soil organic matter content, reducing soil green housegas emission, promotion of plant growth and immobilization of soil heavy metals. Rice paddies from South China has been increasingly polluted with heavy metals. Moreover, rice in these regions has been grown in acid soils that poor in organic matter, increasingly of hybrid rice cultivars, which had been considered enhancing Cd bioavailability to rice grains.Therefore, to analyze the long-term effect of biochar on soil toxic metals immobilization would be important for biowaste and heavy metal polluted soil treatment. In order to evaluate the potential of the feasible approaches of crop straw biochar application in China’s croplands, a cross sites field experiment with biochar soil amendment in different Cd polluted rice fields was conducted across South China and analyze the effect of biochar on soil Cd immobilization and rice grain Cd accumulation. A four years field experiment was operated in order to envaluate the long term effect of biochar on soil Cd immobiation and rice grain yield, we also measured the changes in green house gases emission under biochar treatmend and try to investigate the co-benefits of biochar on rice grain Cd and greenhouse gas reduction. Then, we extracted the aged biochar particles from the experiment soil and analyzed the effect of ageing prosess on biochar’s surface character and try to understand the mechanisms of biochar reaction with soil heavymetals. We also analized the heavy metal adsoption capacity of wheat straw biochar and modified it with sodium alginate into a stable capsule for heavy metal polluted water treatment. The main results were as follows:1. A biochar-alginate capsule (BAC) was successfully synthesized by dropping a mixture solution of biochar and alginate into calcium chloride solution. The adsorption curves of Cd2+, Pb2+ and Cu2+ by biochar and BAC could be described by Langmuir model and Freundlich model. The maximum adsorption capacity of Cd2+, Pb2+ and Cu2+ by biochar was 4.71,32.12 and 8.04 mg g-1. The maximum adsorption capacity of Cd2+, Pb2+ and Cu2+ by biochar was 8.66,31.34 and 16.95 mg g-1. BAC contains the porous structure of biochar, meanwhile, the solidi ication process of sodium alginate also form more micro-pores on biochar surface. The BAC heavy metal adsorption process was fast and reached equilibrium in 1 h.2. In order to determine the consistent effect of wheat straw biochar on Cd polluted soil remediation. A four years field experiment with biochar soil amendment at rates of 0,10,20,40 t ha-1 in Cd polluted rice field in Jiangsu provience was conducted from 2010. Soil organic carbon and pH were significantly increased across all biochar treatments over the four years and the rate of soil pH increase declined over time. Biochar soil amendment significatntly reduced soil CaCl2 and H2O extractable Cd over four years. Compare with the control, soil CaCl2 extractable Cd was significantly decreased by 54.5%-70.9%,53.5%-64.8%, 28.2%-58.7% and 30.3%-40.6% over the four years (2010-2013). Soil H2O extractable Cd was reduced by 33.7%-44.2%,12.8%-30.7% and 30.1%-36.5% from 2011-2013. However, a significant reduction in DTP A extractable Cd was only observable in the third and fourth year, by 11.99%-20.9% and 15.0%-42.7%, respectively.Biochar soil amendment did not affect rice grain yield but significantly decreased rice grain Cd accumulation. Compare with the control, rice grain Cd was decreased by 18.1-43.1%,32.9-48.7%,45.0-62.5% and 15.3-54.6% over the four years. The Cd concentrations of rice grains under biochar application at 40 t ha-1 were 0.40,1.21,0.30 and 0.38 mg kg-1 over the four years, which was 2-10 times higher than China state guidance limitation (0.2 mg kg-1). But the rice grain Cd content under 40t ha-1 in 2010,2012 and 2013 was close to the limit value(0.4 mg kg -1 )proposed by CCFAC.3. A cross site field experiment was conducted in different sites of South China in order to evulate the effect of biochar on soil Cd immobilization, rice grain yield and rice grain Cd accumulation,. The results indicated that biochar soil amendment did not affect rice grain yiled but significantly increased soil pH and soil organic matter content and the increase rates were 4%-26% and 8%-103%. Biochar soil amendment significantly decreased soil CaCl2 extractable Cd, but there was no significantly changes in soil DTPA extractable Cd. Biochar soil amendment induced increasing of soil pH could accout for the reduction of soil CaCl2 extractable Cd. Biochar soil amendment by 20-40 t ha’1 significantly and consistently decreased rice grain Cd content across the experiment sites and the reduction rate was 20-90%. It is worthy to note that rice grain Cd content under biochar soil amendment at 40 t ha-1, in all sites with Cd<5 mg kg-1 could meet the guideline limit of 0.4 mg kg-1 proposed by CCFAC. Furthermore, the Cd concentrations in rice grains under biochar treatment in Jiangsu Yixing, Hunan Yueyang and Sichuan Guanghan were 0.07,0.24 and 0.16 mg kg"1 which were even less than 0.2 mg kg-1, the guidance limit of China state standard of rice Cd. A very significantly positive correlation was found in this study between rice grain Cd content and soil CaCl2 extractable Cd in soils under BSA treatmens. This suggested that the great reduction in rice Cd was largely due to the Cd immobilization in soil affected by the pH up-rise, a well-known "liming effect" by biochar.4. In order to evulate the synergistic effect of biochar on soil Cd immobilization and greenhouse gases emission a three year field experiment with municipal bio-waste biochar (MBB) treaement was conducted in Jiangsu provience. The experiment results incated that 40 t ha-*1 MBB treatment did not affect rice and wheat grain yield but significantly increased soil pH and organic carbon. The rate of pH increase declined over time. Compare with the soil before the experiment, MBB application at 40 t ha-1 significnatly increase soil Pb, Cu and Zn content in the fourth year of the experiment and the increase rates were 23.9%,22.7% and 9.4%, respectively, but there was no significant changes in soil total Cd concentration. In addition, all of the four metals in soil treated with biochar was below the national standard for the soil and environment quality. MBB soil amendment significantly increased soil CaCl2 extractable Cu and Zn by 28.6% and 25.5% respectively, during the first rice season, there was no changes in soil Pb mobility. Soil CaCl2 extractable Cd was significantly decreased over the three years. MBB soil amendment significantly decreased rice and wheat Cd accumulation, compare with the control, the reduction rates of rice grain Cd concentration during 2010-2012 were 50.0%,68.2% and 33.0%, and the reduction rates of wheat grain Cd concentration during 2010-2012 were 22.7%,23.3% and 35.4%. No significant changes was obserived in rice and wheat grain Pb and Cu accumulation with MBB treatment. A significantly increase of wheat grain Zn content was found in the first wheat season and the increase rate was 40.0%.The static chamber method was used to analyze the effect of MBB on soil and ecosystem greenhouse gas emissions in rice-wheat season. Compare with the control, MBB soil amendment didn’t affect rice and wheat season total CO2 emission but significantly increased rice season total soil and ecosystem CH4 emission and the increase rates were 45.0% and 19.5%. Furthermore, total N2O emission of soil and ecosystem was greatly decreased by 50.3% and 60.1% for rice season and 55.6% and 56.7% for wheat season, respectively. MBB amendment decreased annual net exchange of CO2 between rice-wheat ecosystem and atmosphere. Compare with the control, the reduction rates of rice-wheat ecosystem GWP and GHGI were 44.8% and 43.7%.5. Aged biochar particles were extracted from the experiment field in the third year. The character and elements content on biochar surface was determined. The results from FTIR indicated that aged biochar particles conent less glycolipids but more aromatic, carboxyl and hydroxyl functional groups than fresh biochar particles. The results from XPS analysis indicated that the aged biochar surface content less C and C-C but more O,0=C-0 and nitrogen functional groups. Compare with fresh biochar particles, the concentrations of Mg, K and P on aged biochar particles surface were decreased by 77.3%,96.2% and 77.6%. The total concentrations of Cd, Pb, Cu and Zn were 9.6,6.8,4.7 and 3.3 times higher than the polluted paddy soil which indicated that the metals adsorption capacity was much high than the soil. The microscopic analysis of the aged biochar indicated that biochar react with soil minerals and orgamic matters and form organic-inorganic complex structure. The main elements content on this structure were C, O, Si, Al, P, K, Fe, Pb, Ca, As and Mg, and the main element content in biochar nano-pores was Fe.Overall, this study demosnstrated that biochar soil amendment could be an option to tackle the Cd-tained rice in South China and the effect of biochar on soil Cd immobilization could be sustainable over the four years. Meanwhile biocahr soil amendment also decreased annual net exchange of CO2 between wheat-rice ecosystem and atmosphere. The increasing of O and N groups on biochar surface could keep biochar active year on year to continue to absob heavy metals. BAC could be used to adsorb heavy metals in the polluted water. Therefore, the pyrolysis technology that convert agricultural and municipal biowaste into biochar could be applied into Cd polluted rice paddies and ensure crop production and benefit for agriculture soil carbon sequestration and reducing greenhouse gases emission. |
PDF Full Text Request