减压浓缩对沼液CO_2吸收性能和植物生理毒性的影响

Effect of Vacuum Concentration on CO_2 Absorption Performance and Phytotoxicity of Biogas Slurry

利用减压浓缩试验装置在50℃和2 k Pa下对沼液进行浓缩,分别测试了沼液、沼液浓缩相及冷凝回收稀相的CO2吸收性能和植物生理毒性。结果表明,沼液减压浓缩到4倍时,沼液浓缩相p H值升高至8.73,其饱和CO2吸收负荷增加26.70%,氨氮去除率为86.41%。浓缩相中的大部分氨氮以自由氨的形式转移到沼液稀相中,使稀相p H值达到10.05,饱和CO2吸收负荷达0.075 mol/L。但浓缩相和稀相的净CO2吸收容量之和比原沼液降低21.3%,其主要原因在于减压浓缩过程中自由氨的挥发损失。用原沼液、浓缩沼液及稀相的富CO2溶液育种时,大白菜种子的发芽指数(GI)均大于0.8,表现出较低的植物生理毒性,说明减压浓缩可降低消纳沼液所需的农田面积。试验中也对不同类型CO2吸收强化添加剂的性能进行了比较。在相同的CO2吸收强化性能要求下,钠盐添加剂组富CO2沼液的植物生理毒性低于氨水添加剂组,其主要原因在于添加氨水导致了沼液氨氮含量的大幅增加。

Raw biogas slurry（ RBS） was concentrated to obtain the concentrated biogas slurry（ CBS）and the diluted phase（ DP） condensed by the gas phase under the conditions of 50℃ and 2 k Pa in vacuum concentration device. CO2 absorption performances of RBS,CBS and DP were investigated,and the germination index（ GI） values of Chinese cabbage seeds germinated by these solutions after CO2 absorption were evaluated as well. Results showed that when the concentration degree of RBS was about4,the p H value of CBS was increased from 7. 87 to 8. 73,and its saturated CO2 loading was increased by about 26. 70%. Additionally,the removal efficiency of ammonium nitrogen was up to 86. 41% due to the conversion of ammonium nitrogen into free ammonia and then extracted from biogas slurry by vacuum operation. Most of the free ammonia was condensed and collected into the DP. Therefore,DP＇s p H value and CO2 loading were up to 10. 05 and 0. 075 mol / L,respectively. However,the net CO2 absorption capacity contributed by CBS and DP was 21. 3% lower than that of RBS due to the volatile loss of ammonia during concentration. Results from the germination of Chinese cabbage seeds by the CO2-rich solutions of RBS,CBS and DP showed that all the GI values were higher than 0. 8,implying their low phytotoxicities. The result implied that concentrating RBS may result in the decrease of the cropland area required to dispose the biogas slurry. Moreover, CO2 absorption enhancement by adding different additives was investigated and compared as well. Aiming at the same saturated CO2 loading value,adding sodium salts into biogas slurry was superior to adding ammonia additives in terms of low phytotoxicity,which may be attributed to the great increase of ammonium nitrogen concentration in the latter solutions.