Condition Optimization Of Spirulina Platensis Cultivation Using Municipal Wastewater In A Photobioreactor

Microalgae,as a new renewable energy materials,has the advantages of fast growth,high photosynthetic efficiency and environmental adaptability.A lot of nitrogen and phosphorus nutrients and water resourcesare were necessary for microalgae culture process,so the production costs in large scale are high.Microalgae cultivation with wastewater is attracting the attention of researcher,the nitrogen and phosphorus elements in wastewater could be used by microalgae growth.The wastewater is purified and the microalgae biomass is produced simultaneously,which have the great economic and environmental benefits.In this paper,the spirulina platensis was selected as the research object,and the municipal wastewater was chosen as spirulina platensis culture medium.Photobioreactor and membrane photobioreactor were made as spirulina platensis culture and separation reactors.The suitable cultivation conditions of spirulina platensis in municipal wastewater was studied.The carbon source,HRT,algae density and other operating conditions and batch,semi-continuous,continuous cultivation methods were also optimized.At the same time,based on the analysis of the pollutants of membrane,the suitable membrane pore size and membrane cleaning method were determined.Finally,the experimental results and kinetic methods were used to compare the operation effects of PBR and MPBR.The main results were as follows:?1?Municipal wastewater added 0.80 g/L Na HCO₃ could be used for the cultivation of spirulina platensis.?2?The highest biomass concentration was 1.51 g/L when Spirulina platensis was batch cultured in wastewater with the conical flask for 12 days.?3?The suitable HRT was 20 d and the algae density in the reactor was maintained at1.00 g/L-1.20 g/L when spirulina platensis was continuously cultured in PBR.The harvest biomass was 0.42 g/d.And the wastewater treatment capacity was 0.35 L/d.The removal efficiency of nitrogen and phosphorus was similar under different HRT.The removal rates of NH₄⁺-N,TN and TP were 98.52%-99.03%,90.43%-95.22%,88.25%-96.81%,and the effluent concentrations of NH₄⁺-N,TN and TP met level A of Discharge Standard of Pollutant for Municipal Wastewater Treatment Plant?GB 18918-2002?.?4?The shorted HRT was 1.75 d and the algae density in the reactor was 1.80 g/L-2.00g/L when spirulina platensis was semi-continuously cultured in MPBR.HRT was 1.75 d,MRT was 20 d and the harvest biomass was 0.69 g/d when microalgae was continuously cultured.The components of protein,carbohydrate and chlorophyll of algae cellular cultured in wastewater were similar to those in the medium.The removal rates of NH₄⁺-N,TN,TP and COD were 93.54%-98.97%,77.06%-90.24%,48.37%-66.91%and 23.37%-47.28%respectively.The effluent concentrations of NH₄⁺-N and TN met level A,TP concentration met level B.Contents of a variety of metal ions in effluent were lower than those in influent.About 93.15%of the N element and 95.57%of the P element were absorbed by the microalgae to transform into cells composition.?5?The analysis results of scanning electron microscopy?SEM?,three dimensional excitation emission matrixes?EEM?fluoresce spectroscopy and X-ray energy dispersive spectroscopy?EDX?demonstrated that the cake layer of influent side on membrane was mainly caused by organic matter,such as EOM.While Ca-based inorganic components were attached to the effluent side of the membrane,thus also causing the blocking of membrane pores at some extent.The membrane pore size was 0.45?m when the algae were havested.The contaminated membrane was cleaned by ultrasonic flutter for 0.50 h then submerged in HCl solution of p H 2 and 200 mg/L Na Cl O solution for 2 h separately.After membrane cleaning,the flux was recovered to 94.29%.?6?Compared with PBR,energy consumption and costs of MPBR were higher.But MPBR had obvious advantages in improving algal density and wastewater treatment capacity.Besides,the reactor operating conditions were more flexible so the system was more stable and efficient in MPBR The results showed that the microalgae density in MPBR were about twice as much as PBR and the harvest biomass was increased from 0.42 g/d to 0.69 g/d.HRT was significantly shortened,wastewater treatment capacity was 11 times as much as PBR.The influent N load was increased from 7.70 mg/d-8.05 mg/d to 122.28 mg/d-137.96 mg/d and P load was increased from 0.44 mg/d-0.50 mg/d to 7.57 mg/d-8.21 mg/d.The removal amount of N and P in MPBR was 14-15 times and 9-11 times as much as in PBR.The kinetic analysis proved the effectiveness of MPBR in Spirulina platensis culture.