Study On Swine Biogas Slurry Treatment By Mixed Bacteria Coupled With Microalgae Cultivation

The development of intensive swine farming industry has resulted in the excessive accumulation of swine manure,which has brought great pressure to the environment.Biogas slurry with high pollution load produced by anaerobic digestion of swine manure is one of the common problems in the industry of harmless utilization of swine manure.It is rich in organic matter,ammonia nitrogen and heavy metal ions(like Cu(?)and Zn(?)),which will cause serious environmental pollution if discharged directly without treatment.In recent years,biological treatment technology as a kind of utilization and harmless wastewater treatment technology has been widely used in the treatment of swine biogas slurry.Microorganisms dominated by photosynthetic bacteria have a strong tolerance to pollutants in wastewater.Microalgae dominated by green algae can play a highly efficient and deep treatment role in the biological purification of swine biogas slurry,effectively utilize the nutrients in swine biogas slurry and convert them into high-value microalgae biomass,which can turn waste into treasure.In order to effectively remove organic matter and heavy metals from swine biogas slurry,swine biogas slurry was taken as the research object,and the selection of strains and the optimization of culture conditions was carried out.The removal efficiency and the mechanism of high concentration of organics and heavy metals in swine biogas slurry by mixed bacteria was studied.Finally,Chlorella vulgaris was used to further purify the wastewater pretreated by mixed bacteria,trying to construct a new way of harmless and utilization of swine biogas slurry by mixed bacteria coupled with microalgae.The main results are as follows:1.The mixed strains were screened from swine wastewater including Alcaligenes,Rhodopseudomona,Tissierella praeacuta,Enterococcus mundtii,Brevundimonas diminuta.According to the analysis of 16sRNA,the proportions were 53.8%,21.3%,5.1%,4.9%and 3.1%,respectively.In addition,the selected mixed bacteria has the characteristics of inseparability,which is because the swine biogas slurry is complexity,and it is difficult for a single strain to survive independently.Therefore,in order to achieve the survival goal,the bacteria need to play a synergistic role between organisms to make full use of biodiversity.2.Through the optimization of the culture conditions of mixed bacteria,it was found that they grew best under the condition of light and oxygen.After 9 days of cultivation,the biomass increased from 68mg/L to 1758mg/L,25.9 times of the initial amount,and the removal rates of TC,TN and COD reached 58.4%,37.4%and 47.7%,respectively.The preliminary application of mixed bacteria in the treatment of synthetic swine wastewater showed that it had a good removal effect on the pollutants in the wastewater,and the removal rates of NH4+-N,COD,TP,TC and TN were 14.5%,65.4%,42.3%,46.9%and 31.6%,respectively.Therefore,it is considered as strains of swine biogas slurry pretreatment.3.The main heavy metals Cu(?)and Zn(?)were added to the synthetic biogas slurry to explore the treatment effect of mixed bacteria on wastewater.The results showed that the selected mixed bacterias could grow in the medium with high concentration of Cu(?)and Zn(?)wastewater.In the simulated biogas slurry containing 40 mg/LCu(?),after 9 days of cultivation,the biomass increased from 49 mg/L to 525 mg/L.In the simulated biogas slurry containing 100 mg/LZn(?),after 9 days of cultivation,,the biomass increased from 45 mg/L to 613 mg/L.The mixed bacteria can adsorb Cu(?)and Zn(?)in wastewater by secreting extracellular polymeric substances.The adsorption capacity of Cu(?)and Zn(?)was up to 10.1 mg/g,and that of Zn(?)was up to 95.0 mg/g,respectively.Heavy metal ions in the synthetic biogas slurry mainly interact with proteins in extracellular polymeric substances and bind to the surface of bacteria.In the mixed bacteria,Brevundimonas diminuta play an important role in the adsorption of heavy metals.4.Through the experiment of treating two kinds of different swine biogas slurry by three culture methods,it was found that the treatment effect of using mixed bacteria for 5 days and then using Chlorella vulgaris for 5 days was better than that of using only mixed bacteria or Chlorella vulgaris for 10 days.The removal rates of COD,TN,TC and TP in high-concentration swine biogas slurry by the combined treatment of bacteria and algae were 87.6%,68.3%,52.7%and 69.2%,respectively;while that of mixed bacteria alone was 84.4%,50.3%,43.5%and 57.7%;and only Chlorella vulgaris could not grow and reproduce directly in biogas slurry.The removal rates of COD,TN,TC and TP by the combined treatment of bacteria and algae in low-concentration swine biogas slurry were 87.6%,68.3%,52.7%and 69.2%,respectively;while that of mixed bacteria alone was 21.4%,31%,11.5%and 8.5%;and only Chlorella vulgaris was 42.3%,49.6%,16.6%and 63.8%.This shows that the technology of mixed bacteria coupled with microalgae can be effectively applied to the treatment of swine biogas slurry.In addition,the protein and lipid contents of chlorella were 41%and 32.3%respectively after the combined treatment,while the Cu(?)and Zn(?)contents of Chlorella vulgaris were very low,which were both less than 10 mg/kg.This shows that it has the potential to be used to develop algal feed protein,which is worthy of further study.