Technical Study On Purification Of Piggery Wastewater By Immobilized Biofilm-Attached Cultivation Of Chlorella Pyrenoidosa

Humanity is faced with difficulties as a result of polluted environment and inadequate supply of energy presently.As one of the most important energy resources,microalgae have unique advantages of not competing for food with people,not reclaiming land with cereal,and not contesting for edible with animals.As a result,algae utilization has become a topical research area for scholars.Swine wastewater is a kind of organic liquid,which has characteristics of high concentration of nitrogen and phosphorus as well as other complicated composition.In case of not being treated well,the organic and nitrogen and phosphorus substance will lead to eutrophication of water bodies and ground water.This research would make effective connection a between microalgae and the swine wastewater which was difficult to do deep purification and provide a theoretical basis for achieving algae bio-fuel production and decreasing the cost of wastewater treatment.This paper takes twelve kinds of algae strains as research subjects,to select the best algae which can tolerate the higher concentration of ammonia nitrogen,copper ions and have higher photosynthetic activity and promote faster growth rate simultaneously.Secondly,we choose Chlorella pyrenoidosa as a primary subject to study the feasibility of treating piggery wastewater with Chlorella Pyrenoidosa by immobilized biofilm-attached cultivation.In order to explore the optimal purification effect and the most suitable diluted ratio of piggery wastewater with Chlorella pyrenoidosa,the high concentration of wastewater is diluted with different times.Under the best suitable circumstance,the algae cell is harvested to be made powder after the end of cultivation period,then in which are extracted to detect and analyze the content of protein and amino along with other conventional nutrients.According to some researches above all,the main ideas are as follows:1)This article cultured 12 strains of microalgae under 16 kinds of medium with different concentration of ammonia nitrogen and copper to cultivate,observe,identify,analyze,and to carry out microscopic examination.According to the growth curve of OD₆₈₀,we generally divide the algae into copper ion sensitive and ammonia sensitive type.Algae strains sensitive to the concentration of ammonia nitrogen(200 mg·L^-1、400 mg·L^-1、800 mg·L^-1、1000 mg·L^-1、1600 mg·L^-1)are Pandorina morum,Desmodesmus insignis,Pediastrum cruentum,Closterium lunula,Staurastrum tetracerum,Chlorella pyranoidosa,Euglena gracilis,and sensitive to the concentration of copper ion(0.5 mg·L^-1、1.0 mg·L^-1、2.0 mg·L^-1)are Nostoc flagelliforme,Spirulina platensis,Scenedesmus obliquus,Chlamydomonas.sp.2)According to the determination of the photosynthetic activity of algae atrains by PAM,we found that:firstly,the algae of the highest concentration of ammonia nitrogen and copper ion(1600 mg·L^-1NH₄⁺-N+2.0 mg·L^-1Cu²⁺)treatment group of photosynthetic activity greater than the blank treatment group are:Nostoc flagelliforme,Botryococcus brauniim,Chlorella pyranoidosa,secondly,the photosynthetic activity of algae less than that of the blank control group are:Pandorina morum,Desmodesmus insignis,Pediastrum cruentum,Closterium lunula,Staurastrum tetracerum,Euglena gracilis,Spirulina platensis,Scenedesmus obliquus,Chlamydomonas.sp.Among them,1600mg·L^-1NH₄⁺-N+2.0 mg·L^-1Cu²⁺treatment group have the greatest influence on the photosynthetic activity of Spirulina platensis,while,in the photosynthetic activity of Nostoc flagelliforme,Botryococcus brauniim,Chlorella pyranoidosa are still high after 12days and greater than the blank treatment group.Therefore,these three kinds of algae can be used as an alternative to treat the high concentration of ammonia nitrogen and copper ion wastewater.3)It is feasible and highly effectively to cultivate Chlorella pyrenoidosa by immobilized biofilm-attached medium in the rich nutrient piggery wastewater.Under the condition of the intensity of illumination of 4500 Lux,the temperature of 23±1℃,the initial biomass was 8.60 g·m^-2,the algae cultivated 8 days,at the end of experiment,the biomass of 48.02 g·m^-2,the biomass productivity of 5.03 g·m^-2·d^-1 was achieved.After the nutrient in the wastewater was absorbed by Chlorella pyrenoidosa,the concentration of ammonia nitrogen decreased from initial consistency of 409.00 mg·L^-1 to 98.00 mg·L^-1,the concentration of total phosphorus decreased from initial consistency of 35.00 mg·L^-1 to10.00 mg·L^-1,and the concentration of chemical oxygen demand decreased from initial consistency of 601.00 mg·L^-1 to 152.00 mg·L^-1.Algae removed ammonia nitrogen,total phosphorus,and chemical oxygen demand by 75.9%,68.4%,74.8%,respectively.At the end of experiment,the concentration of Zn²⁺、Cu²⁺、Fe²⁺was 0.96 mg·L^-1、1.02 mg·L^-1、0.74 mg·L^-1,respectively,the removal efficiency of 65.71%、53.64%、58.89%.The lipid content of algae cells collected after the test was 35.90%and the lipid production yield was1.80 g·m^-2·d^-1.The FAMES compositions in the algae paste were mainly consisted of C18:3,C18:2,C16:0.The proportion of C18:3 and C18:2,was respectively 43.39%,37.38%.At the same time,the polyunsaturated fatty acids of algae cells were 81.17%and57.61%respectively cultivated in piggery wastewater and BG11 medium.4)The piggery wastewater was diluted with purified water by 1,2,5 and 10 times in culture medium,respectively.The thesis measured the removal efficiency of COD,ammonia nitrogen,total nitrogen,total phosphorus,and the enrichment effect of heavy metal copper and zinc and iron.Meanwhile,we investigated the lipid production of Chlorella pyrenoidosa in different diluted wastewater of 1,2,5 and 10 times.It turned out that the purification effect of COD,ammonia nitrogen,total nitrogen and total phosphorus is the best when the piggery wastewater is diluted 5 times.The removal efficiencies are86.8%,94.1%,85.2%,84.3%,respectively.Correspondingly,the lipid content is as high as32.7%,the removal efficiency of heavy metal copper,zinc,iron is of 72.9%,70.0%,73.0%,respectively.And the biomass productivity is 4.21 g·m^-2·d^-1 at the end of experiment.5)The content of protein of Chlorella pyrenoidosa in piggery wastewater of 5 times,BG11,and 1 times（raw water）were 57.30%,54.90%,53.10%,and the essential amino acids as high as 21.73%,20.04%,18.47%,respectively,which are higher than that of daily protein sounrce foods like eggs,pork,and so on.The data proved that the content of total amino acid and essential amino acid in the piggery wastewater of 5 times are slightly higher than the other two treatment groups.According to the mode of FAO/WHO,Chlorella pyrenoidosa cultivated by the three different treatment groups all had limiting acids,the first limiting acids of algae cells in 5 times diluted treatment were methionine and cysteine.6)The content of organic substance was extracted from Chlorella pyrenoidosa algae cells of 5 times diluted group was the highest,the extracellular polysaccharide of 16.87%,chlorophyll of 43.68 mg·m^-3,crude fiber of 4.08%,moisture 4.85%,ash content of 6.57%,lipid of 32.5%.Chlorella pyrenoidosa has great potential as the high-quality protein resource.