Study On The Treatment Of Swine Wastewater And Coupled To Cultivate Energy Microalgae By Algae-Bacteria Symbiotic System

With the rapid development of pig breeding industry,a large number of high concentration wastewater has caused a series of environmental risk problems,which has become a bottleneck restricting the development of pig breeding industry.On the other hand,due to the aggravation of the energy crisis,microalgae production of biodiesel technology is increasingly concerned,but the high cost of microalgae culture restricts the development of the technology.The application of swine wastewater in the cultivation of microalgae can not only reduce the concentration of pollutants in wastewater,but also benefit the utilization of wastewater resources,reduce the cultivation cost of microalgae,and have good economic and environmental benefits.The concentration of pollutants in swine wastewater is relatively high,and the treatment effect of microalgae is not ideal.The algae-bacteria symbiosis system can effectively improve the removal effect of carbon,nitrogen,phosphorus and other pollutants,and improve the utilization rate of swine wastewater.Its research has important practical significance.In this paper,aiming at different water quality of pig wastewater,the purification rule and the effect of microalgae culture by algae-bacteria symbiosis system were studied.Porous starch（PS）was used as adsorbent to improve the immobilization method and optimize the immobilization conditions.In addition,the application effect of suspended and immobilized algae-bacteria symbiosis system in swine wastewater was investigated.The specific research contents are as follows:（1）Under the condition of different C/N,N/P and p H of pig wastewater,the growth,oil production characteristics and water purification effect of algae-bacteria symbiosis system were investigated.The results showed that when C/N was between 3:1 and 17:1,the growth and oil accumulation of microalgae could be promoted by increasing C/N appropriately.When C/N was 9:1,the biomass(0.65g·L^-1),total lipid(0.235g·L^-1)and neutral lipid yield(0.149g·L^-1)of microalgae reached the maximum value.The removal rates of NH₄⁺-N and TP increased with the increase of C/N,the maximum removal rates were 54.68%and 84.12%respectively.The removal rates of COD under each C/N were higher than those under each C/N The average removal rate was 88.52%.When N/P is between 5:1 and 36:1,N/P is about 17:1,which is the most favorable for the growth of algae and the accumulation of lipids;with the increase of N/P,the removal effect of TP is obviously improved,up to 89.98%;with the increase of N/P,the removal efficiency of NH₄⁺-N increases first and then decreases.When N/P is 10:1,the removal efficiency of NH₄⁺-N is the highest,which is 51.14%;under different N/P,the degradation efficiency of COD is good,and the removal efficiency of COD is above 80%.When the initial p H of wastewater is controlled within 5-10 and the p H is between 6-9,the algae bacteria symbiosis system can metabolize normally.The neutral and weak alkaline environment is conducive to the growth of algae,the accumulation of lipids and the removal of pollutants.It can be seen that the water quality characteristics of swine wastewater can be kept within a certain range,and the goal of wastewater treatment and microalgae culture can be achieved simultaneously.（2）Porous starch was used as adsorbent to improve the immobilization method of algae.The effects of the contents of sodium alginate（SA）,polyvinyl alcohol（PVA）,Porous starch（PS）and Ca Cl₂ on the mass transfer,stability,embedding rate and growth rate of algae were investigated.On this basis,the immobilization conditions were further optimized.The results of single factor test show that the content of SA,PVA,PS and Ca Cl₂ can significantly affect the properties of rubber balls.L₁₈（2¹×3⁴）mixed orthogonal table was used to optimize the immobilization conditions.The results showed that when SA content was 1.4%,PVA content was 9%,PS content was 0.4%,Ca Cl₂ content was 3%,the comprehensive properties of the rubber ball were the best.（3）The application effect of suspended and immobilized algae-bacteria symbiosis system in the actual piggery biogas slurry was explored.The two systems can metabolize normally in the biogas slurry with different dilution ratio（R）.Properly increasing the biogas slurry ratio can promote the growth of Chlorella and increase the lipid production.The difference of the biomass of suspended and immobilized algae is small,and the maximum biomass is 0.80g·L^-1 and 0.86g·L^-1respectively when R=75%and R=50%.The yield of total lipid and neutral lipid were highest when R=100%in the suspended algae-bacteria symbiosis system,while the yield of these lipids were highest when R=75%and R=100%in the immobilized algae-bacteria symbiosis system.Compared with suspended system,the yield of total lipid and neutral lipid were increased by 8.20%and8.73%respectively in the immobilized system.The removal efficiency of NH₄⁺-N and TN is similar in the two systems.The increase of biogas slurry ratio is not conducive to the degradation of NH₄⁺-N and TN,When R=25%,the removal rate of NH₄⁺-N and TN is the highest,which were 55.92%and 54.17%respectively;the increase of biogas slurry ratio can promote the removal of TP,and the removal rate of TP can be significantly increased by using immobilized system.The highest removal rate of TP is 89.63%when R=100%.The removal effect of suspended system of COD is better,and the removal rate of COD is above 80%,while immobilized system is not conducive to the degradation of COD.