| Energy shortage and environmental pollution have become a serious problem restricting the current economic development and human life in the world.Microalgae as an excellent raw material for renewable energy,the new high-density microalgae immobilized culture technology has the potential to overcome the disadvantages of traditional suspension system like low cell density,high cost and difficulty in promoting industrial development.Algae can use nitrogen and phosphorus compounds in livestock and poultry wastewater for growth,and therefore provide an excellent solution for deep treatment of wastewater.As the light and nutrients absorption of immobilized microalgae culture is very different to suspension culture,the photobioreactor design and working mechanism also have profound difference.Therefore,this study aims to improve the biomass and oil production of microalgae in immobilized culture,to improve the removal rate of nitrogen and phosphorus in immobilized microalgae and to reduce the energy consumption of reactor system,specific aspects of the study were as follows:(1)In order to optimize the immobilized culture conditions of microalgae,the effect of CO2 flow rate,culture period and light dilution ratio on the biomass and total nitrogen removal rate were analyzed.Experiments were performed using the Central Composite Design(CCD)parameters in Response Surface Methodology(RSM).Results showed that the quadratic regression equation of microbial biomass yield and total nitrogen(TN)removal of wastewater was good,the correlation coefficient of the model was more than 97%.The optimum combination of productivity and decondamination conditions are:CO2 flow rate 0.04L/min,culture period 124.86 h,substratum light dilution ratio of 1.33.Under this condition,the productivity of C.vulgaris reached 34.81 g/m2/day,TN removal rate was 95.64%,which is in good agreement with the theoretical predicted value.(2)In this thesis,a porous substrate biofilm reactor(PSBR)was proposed,multiple adhesion substrates were installed vertical to the ground for less foot area.The light dilution rate of 17.8 can effectively use the light energy as well as to avoid photoinhibition.The feasibility of attached culture C.vulgaris in this reactor,for simultaneously wastewater treatment and biofuels production was investigated.The characteristics,including algal biofilms growth,lipid yield,nutrient removal and energy efficiency of the outdoor culture were investigated under the influence of both inoculum densities and submerging rates.A maximum biofilm productivity of 57.87 g/m2/d with adhesion rate of 81.9%was achieved under optimal conditions(inoculum density of 18 g/m2 and submerging rate of 5.7%).The lipid content and lipid yield were 38.56%and 22.31 g/m2/d,respectively.Meanwhile,the algae removed ammonia,total nitrogen(TN),and total phosphorus(TP)by 99.59%,96.05%and 99.83%,respectively.Further,an energy life cycle for the PSBR was analyzed.The biomass productivity per unit irradiance was 7.2 g/MJ.The photosynthetic efficiency was up to 10.65%.The PSBR was considered to be economically feasible due to the net energy ratio of 1.3(>1).(3)Waste microalgae biomass,one of the most abundant residues from biodiesel production,can be used as a low-cost biosorbent for heavy metal removal.The ability and mechanism of Pb(Ⅲ)removal by lipid-extraction residue of C.vulgaris were investigated.The effects of initial pH,initial heavy metal concentration,adsorbent concentration and adsorption time on the effect were studied.Experimental results show that:with pH value equal to 3,adsorbent concentration 2 g/L,initial heavy metal concentration 454.06 mg/L,balance was basically reached after 30min adsorption.The maximal biosorption capacity of waste C.vulgaris biomass for total Pb2+ was 226.28 mg/g. |
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