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| Benign treatment of biogas slurry and improvement in lettuce quality using hydroponics |
| Received:September 15, 2017 |
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| KeyWord:biogas slurry;slurry treatment;lettuce hydroponics;ammonium nitrogen removal |
| Author Name | Affiliation | E-mail | | LIANG Fei-hong | College of Engineering, Huazhong Agricultural University/Key Laboratory of Agricultural Equipment in Mid-lower Yangtze River, Ministry of Agriculture, Wuhan 430070, China | | | CUI Qiu-fang | College of Engineering, Huazhong Agricultural University/Key Laboratory of Agricultural Equipment in Mid-lower Yangtze River, Ministry of Agriculture, Wuhan 430070, China | | | TU Te | College of Engineering, Huazhong Agricultural University/Key Laboratory of Agricultural Equipment in Mid-lower Yangtze River, Ministry of Agriculture, Wuhan 430070, China | | | YU Ge | College of Engineering, Huazhong Agricultural University/Key Laboratory of Agricultural Equipment in Mid-lower Yangtze River, Ministry of Agriculture, Wuhan 430070, China | | | WANG Wen-chao | College of Engineering, Huazhong Agricultural University/Key Laboratory of Agricultural Equipment in Mid-lower Yangtze River, Ministry of Agriculture, Wuhan 430070, China | | | YAN Shui-ping | College of Engineering, Huazhong Agricultural University/Key Laboratory of Agricultural Equipment in Mid-lower Yangtze River, Ministry of Agriculture, Wuhan 430070, China | yanshp@mail.hzau.edu.cn |
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| Abstract: |
| Determining the most effective and low-cost method for treating biogas slurry is one of the biggest issues for large-scale biogas projects. This study aimed to treat biogas slurry for farmland irrigation water and cultivate lettuce of high quality at low cost using hydroponic technology to reduce the concentration of pollutants, including total ammonium nitrogen(TAN), chemical oxygen demand(COD), and total phosphorus(TP). Effects of the dilution ratio of water on the removal of pollutants and lettuce quality were investigated, and the appropriate dilution ratios for biogas slurry were calculated. Prior to the experiments, ammonium nitrogen was partly removed from the raw biogas slurry using vacuum distillation. The part-treated biogas slurry was then CO2 saturated to reduce the pH to about 6.7. Finally, CO2-rich biogas slurry was diluted using water by 5~30 times as the hydroponic solution for cultivation. Lettuce cultivated in the typical chemical nutrient solution was used as the control. Results showed that after 35 d the water quality of the treated biogas slurry fully met the requirements of farmland irrigation standards, and the concentrations of TAN, COD, and TP were reduced by 98.25%~99.34%, 83.68%~96.04%, and 65.94%~80.00%, respectively. In addition, 5~15 dilution ratios are recommended for higher purification of pollutants and water savings for biogas slurry. After TAN removal, the treated slurry was used to replace the chemical nutrient solution to cultivate lettuce of higher quality. Compared to the nutrient solution, the relative growth of lettuce cultivated in biogas slurry with 5~10 dilution ratios increased by more than 60%, the leaf width increased by 4~5 cm, and the average number of leaves increased by about 2. Furthermore, the difference in the carotenoid and nitrate nitrogen concentrations between lettuce cultivated in biogas slurry and the chemical nutrient solution was significant. However, the differences in the reducing sugar and vitamin C content were not significant. More specifically, when cultivated in biogas slurry with 5~10 dilution ratios, the carotenoid content in lettuce increased by up to 20.40%, and the concentration of nitrate nitrogen was only 2.11%~4.02% that of lettuce cultivated in the chemical nutrient solution. In addition, the reducing sugar content increased by 7.79%~10.39%, and the vitamin C content only decreased by 3.60%~15.40%. |
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