Anaerobic Co-digestion Performance Of Chinese Cabbage Waste And Cow Manure And The Biogas Slurry Fertility

Chinese cabbage waste including residual leaves and other discarded materials which are removed during the harvesting,processing,transportation,and sales.Cow manure is typical of livestock manure.Both of them are suitable raw materials for anaerobic digestion.Anaerobic co-digestion of Chinese cabbage waste and cow manure can well regulate the water content of the system,adjust p H,increase the buffering capacity of the system,and improve system stability and methane yields by promoting synergistic effects of diverse microbial communities.The biogas slurry produced by anaerobic digestion is a good organic fertilizer.In this paper,the anaerobic co-digestion process of Chinese cabbage waste and cow manure at mesophilic and thermophilic temperatures using five different substrate ratios and the changes in the structure of the bacterial community after co-digestion were investigated by using a batch anaerobic digestion process,and the growth-promoting effect of biogas slurry on plants was studied by measuring above-ground biomass and under-ground biomass,providing a theoretical basis for the comprehensive utilization of agricultural waste.The main results are as follows:1)The anaerobic co-digestion characteristics of different wet base mixing ratios of Chinese cabbage waste and cow manure on 1:1（M1）,2:1（M2）,5:1（M3）,10:1（M4）,and 20:1（M5）at mesophilic temperatures（37±1°C）were studied.The results showed that the digestate SCOD concentration in the final stabilization period showed a decreasing and then increasing trend with the increase of Chinese cabbage waste in the co-substrate.Treatment groups M1 and M2 digestate SCOD concentrations ended up at a lower level of 16761.92 mg L^-1 and 11530.29 mg L^-1,respectively.Treatment group M2 had the lowest digestate SCOD concentration.The cumulative methane yields in the final stabilization period showed a trend of increasing and then decreasing as the content of Chinese cabbage waste in the co-substrate increased,with treatment groups M1 and M2 eventually obtaining higher cumulative methane yields and treatment groups M3～M5 having lower ultimate cumulative methane yields.The highest cumulative methane yields of 180.27 m L g^-1 VS_added was obtained for treatment group M2.The optimal ratio of 2:1 was obtained for co-digestion of Chinese cabbage waste and cow manure at mesophilic temperatures.2)The anaerobic co-digestion characteristics of different wet base mixing ratios of Chinese cabbage waste and cow manure on 1:1（T1）,2:1（T2）,5:1（T3）,10:1（T4）,and20:1（T5）at thermophilic temperatures（55±1°C）were studied.The results showed that the digestate SCOD concentration in the final stabilization period showed a decreasing and then increasing trend with the increase of Chinese cabbage waste in the co-substrate.The digestate SCOD concentrations of treatment groups T1～T4 ended up between10086.98 mg L^-1 and 17936.35 mg L^-1.Treatment group T4 had the lowest digestate SCOD concentration.The cumulative methane yields in the final stabilization period showed a trend of increasing and then decreasing as the content of Chinese cabbage waste in the co-substrate increased,with treatment groups T1～T4 eventually obtaining higher cumulative methane yields and treatment groups T5 having lower ultimate cumulative methane yields.The highest cumulative methane yields of 328.12 m L g^-1VS_added was obtained for treatment group T4.The optimal ratio of 10:1 was obtained for co-digestion of Chinese cabbage waste and cow manure at thermophilic temperatures.3)The characteristics of anaerobic digestion at mesophilic and thermophilic temperatures were compared.It was found that the change pattern of SCOD concentration of digestate in the final stabilization period was consistent,but the SCOD concentration of thermophilic digestate with the same coordination ratio was slightly higher.Comparison of biogas production at mesophilic and thermophilic temperatures revealed that the digestion reaction lag phase（λ）decreased with increasing manure content in all treatment groups,with a shorter lag phase at thermophilic temperatures.The cumulative methane yields at mesophilic and thermophilic temperatures follow the same pattern,but the same mix ratio has higher cumulative methane yields at thermophilic temperatures.4)The microbial community structure and composition in the digestate of Chinese cabbage waste and cow manure with different wet base mixing ratios of 1:1,2:1,5:1,10:1,and 20:1 at mesophilic and thermophilic temperatures were studied.The results showed that after anaerobic digestion at both temperatures,the abundance and uniformity of bacteria and archaea in the digestate decreased with decreasing cow manure content in the co-substrate.The mesophilic digestate had a more diverse population of bacteria and archaea than the thermophilic one.5)The bacterial phylum level and genus level in the digestate of each treatment group at mesophilic and thermophilic temperatures were analyzed.The results showed that the dominant bacterial phylum in the mesophilic digestate were Firmicutes,with an abundance of 30.30%～44.31%,Bacteroidetes with an abundance of 36.14%～47.89%,and Synergistetes with an abundance of 2.62%～15.24%.The dominant bacterial genus in the mesophilic digestate were Proteiniphilum with an abundance of 2.84%～46.77%,Aminobacterium with an abundance of 2.35%～15.64%,and Ruminofilibacter with an abundance of 0.09%-19.06%.The dominant bacterial phylum in the thermophilic digestate were Firmicutes with an abundance of 60.21%～83.53%,Thermotogae with an abundance of 0.23%～31.24%,and Actinobacteria with an abundance of 0.13%～6.82%.The dominant bacterial genus in the thermophilic digestate were Bacillus with an abundance of 1.81%～34.51%,and Defluviitoga with an abundance of 0.22%～32.23%.6)The archaeal phylum level and genus level in the digestate of each treatment group at mesophilic and thermophilic temperatures were analyzed.The results showed that the dominant archaeal phylum in both the mesophilic and thermophilic digestate was Euryarchaeota,with an abundance of 75.45%～99.95%.The dominant archaeal genus in the mesophilic digestate were Methanosarcina with an abundance of4.54%～29.43%,Methanofollis with an abundance of 1.41%～41.53%,and Methanocorpusculum with an abundance of 0.24%～51.74%.The dominant archaeal genus in the thermophilic digestate were Methanosarcina with an abundance of16.81%～54.04%,Methanothermobacter with an abundance of 0.53%～26.51%,and Methanoculleus with an abundance of 0.24%～28.42%.7)The characteristics of the anaerobic co-digested biogas slurry of Chinese cabbage waste and cow manure at different mixing ratios at mesophilic and thermophilic temperatures were studied.The results showed that the p H of the biogas slurry produced by each treatment group was between 7.36～8.02.The p H of the biogas slurry produced by treatment groups T1～T4 was between 8.51～8.73 at thermophilic temperatures.High total nitrogen（TN）content(1122.67 mg L^-1～1588.33 mg L^-1)was showed in both mesophilic and thermophilic biogas slurry.The potassium content(1144.57～3679.10mg L^-1)in the mesophilic and thermophilic biogas slurry decreased with the decrease of cow manure content in the co-substrate.The humification degree of the biogas slurry produced by the mesophilic treatment group was higher than that of the thermophilic treatment group.8)The promoting effect of the anaerobic co-digested biogas slurry on maize seedling growth of Chinese cabbage waste and cow manure at different mixing ratios at mesophilic and thermophilic temperatures were studied.The results showed that biogas slurry with different ratios of substrates can promote the growth of maize seedlings.The results were observed in the mesophilic biogas slurry treatment group with a substrate ratio of 1:1 of Chinese cabbage waste and cow manure,with 73.40%and 32.95%increased in aboveground dry weight and underground dry weight compared to the unfertilized control group.In the thermophilic biogas slurry treatment group with a substrate ratio of 1:1 of Chinese cabbage waste and cow manure,with 43.30%and 29.53%increased in aboveground dry weight and underground dry weight compared to the unfertilized control group.The promoting effect of biogas slurry on plant growth increased with the increase in cow manure content in the co-substrate.The mesophilic biogas slurry treatment group had a better promoting effect on plant growth than the thermophilic biogas slurry treatment group.