杨木炭对东北黑土吸附猪粪沼液氮素特性的影响

为探究杨木炭对东北黑土吸附猪粪沼液氮素特性的影响,明晰其吸附机理,选取杨木炭和壤质、砂质两种黑土,以活性炭作为标准比较炭,系统研究活性炭、杨木炭的粒径及添加比例、初始质量浓度、振荡时间、温度对黑土吸附、解吸猪粪沼液中氨态氮、硝态氮特性的影响规律,并拟合等温吸附模型和吸附动力学模型。结果表明:黑土对猪粪沼液氮素的吸附能力随着活性炭和杨木炭粒径的减小、添加比例的增加而显著增加;当粒径为0. 25 mm、添加比例10%时,添加杨木炭的黑壤土和黑砂土的氨态氮、硝态氮的吸附量为224. 8、107 mg/kg和212. 4、104 mg/kg,比空白纯黑壤土和黑砂土提高388. 7%、296. 3%和453. 13%、333. 33%,比添加活性炭的黑壤土和黑砂土降低19. 71%、10. 08%和12. 38%、7. 14%,但添加杨木炭比添加活性炭对吸附平衡后沼液中氨态氮、硝态氮浓度变化影响的差异均不超过2. 5%;添加活性炭黑土、杨木炭黑土、空白纯黑土和纯炭对猪粪沼液中氨态氮的吸附过程为吸热反应,而对硝态氮的吸附过程为放热反应,且所有吸附过程均经历快速、缓慢、趋于平衡3个阶段,硝态氮快速吸附的时间更短; Freundlich、Langmuir模型和准二级模型均能较好描述其等温吸附过程和吸附动力学过程,Freundlich模型比Langmuir模型相对更优,吸附反应过程同时存在不均匀的多分子层表面物理吸附和均匀的单分子层化学吸附;添加活性炭、杨木炭黑土对沼液中氨态氮、硝态氮的吸附量越大,解吸率也越大,但解吸量远小于有效吸附量,添加杨木炭的黑壤土和黑砂土对氨态氮、硝态氮的有效吸附量比添加活性炭的黑壤土和黑砂土减少14. 57%、9. 19%和5. 34%、5. 74%。杨木炭在提高黑土对猪粪沼液氮素的吸附能力、减少猪粪沼液氮素损失方面的效果优良,可为杨木炭和猪粪沼液在东北黑土改良方面的深入研究提供理论依据。

Effects of Poplar Wood Biochar on Northeast Region Black Soil Adsorbing Nitrogen in Pig Biogas Slurry

Poplar wood biochar was added as adsorbent into two types of northeast region black soil (loamy and sandy) to investigate the effects of poplar wood biochar on black soil adsorbing ammonium and nitrate nitrogen in pig biogas slurry, and the adsorption mechanism was studied by using oscillation method. Commercial activated carbon was used as a standard for comparison. The effects of the particle sizes (0.25mm, 0.5mm and 1mm) and addition proportions (2%, 5% and 10%) of commercial activated carbon and poplar wood biochar, the initial mass concentration of pig biogas slurry, the oscillation time and the oscillation temperature on black soil adsorbing ammonium and nitrate nitrogen in pig biogas slurry were studied systematically. The adsorption mechanism was analyzed by different isothermal and kinetic adsorption models. The results showed that the smaller particle sizes and the more addition proportions of commercial activated carbon and poplar wood biochar led to better ammonium and nitrate nitrogen adsorption capacity of black soil in pig biogas slurry. And 0.25mm particle size and 10% solid weight ratio were optimum addition treatment for commercial activated carbon and poplar wood biochar. Under optimum addition treatment, the ammonium and nitrate nitrogen amount adsorbed by black soil with poplar wood biochar addition were higher than that by pure black soil by 388.7%, 296.3% (black loamy soil) and 453.13%, 333.33% (black sandy soil), and were lower than those by back soil with commercial activated carbon addition by 19.71%, 10.08% (black loamy soil) and 12.38%, 7.14% (black sandy soil), respectively. However, the effects of poplar wood biochar and commercial activated carbon on the ammonium and nitrate nitrogen concentration of pig biogas slurry after adsorptive stability were not significantly different, and all the differences were less than 2.5%. The ammonium nitrogen amount adsorbed by the pure black soil, the pure commercial activated carbon and pure poplar wood biochar and the black soil with commercial activated carbon and poplar wood biochar addition were all increased as the increase of temperature, posing endothermic reaction. While the nitrate nitrogen adsorption amount showed a decreasing trend as temperature was increased, posing spontaneous exothermic reaction. Furthermore, the ammonium and nitrate adsorption processes showed three stages of fast adsorption, slow adsorption and balance. The adsorption models of Freundlich, Langmuir and Pseudo second order described the isothermal adsorption characteristics and kinetic adsorption characteristics of the black soil added with commercial activated carbon and poplar wood biochar adsorbing ammonium and nitrate nitrogen in pig biogas slurry precisely. However, Freundlich was superior to Langmuir. Therefore, there were multi layers uneven physisorption reaction and monolayer chemisorption reaction during the ammonium and nitrate adsorption process, concurrently. The more adsorption amount was, the more desorption amount was, but the desorption amount was much less than the effective adsorption amount. The effective ammonium and nitrate nitrogen adsorption amount of black soil with poplar wood biochar addition were lower than those of black soil with commercial activated carbon addition by 14.57%, 9.19% (black loamy soil) and 5.34%, 5.74% (black sandy soil). Poplar wood biochar was favorable for improving the nitrogen adsorption capacity of northeast region black soil and decreasing the nitrogen loss of pig biogas slurry. The results provided good insights into improving the northeast region black soil by using poplar wood biochar and pig biogas slurry.