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 kPa in vacuum concentration device. CO 2 absorption performances of RBS, CBS and DP were investigated, and the germination index (GI) values of Chinese cabbage seeds germinated by these solutions after CO 2 absorption were evaluated as well. Results showed that when the concentration degree of RBS was about 4, the pH value of CBS was increased from 7.87 to 8.73, and its saturated CO 2 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 pH value and CO 2 loading were up to 10.05 and 0.075 mol/L, respectively. However, the net CO 2 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 CO 2 -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, CO 2 absorption enhancement by adding different additives was investigated and compared as well. Aiming at the same saturated CO 2 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.