Study On The Process Of The Cultivation Of Spirulina Using Food Wastewater Based On The Absorption Of Nitrogen And Phosphorus

Microalgae, as a new renewable energy raw materials, has the characteristics of fast growth rate, less land occupation and high carbon fixation capacity. However, the production costs in large scale are high because of the great demand of the necessary chemical reagents for culture medium, such as nitrogen and phosphorus. Producing microalgae in wastewater could make full use of nitrogen and phosphorus elements for the purpose of obtainning biomass, which is causing more and more attention.Based on the previous research, we studied the growth of Spirulina platensis under different nitrogen and phosphorus species and concentrations as well as the Spirulina platensis culture methods in food wastewater in this study. Coupling the microalgae production with water treatment, we aim to fix CO₂ and remove the nitrogen and phosphorus from wastewater at the same time. The main results are as follows:（1）The effects of different nitrogen and phosphorus species and concentrations on the growth of Spirulina platensis were investigated. Results showed that when NaNO₃ was used as the nitrogen source, the growth of Spirulina platensis was not inhibited in our experimental range（210⁸40 mg/L）. When NaNO₂ and NH₄ Cl were chosed as the inorganic nitrogen sources, the growth of Spirulina platensis was inhibited at high concentrations, and was limited at low concentrations. The inhibition and limitation concentration of NaNO₂ were 280 mg/L and 70 mg/L and were 140 mg/L and 70 mg /L for NH₄ Cl. When urea used as organic nitrogen source, Spirulina platensis could only survive in low concentration of 35 mg/L. It also appeared inhibition under high concentrations. When K₂HPO₄ was used as the phosphorus source, the maximum biomass was got under the concentration of 9.3 mg/L, and the growth of Spirulina platensis was not inhibited at high concentrations.（2）The effects of different dilution ratios and whether sterilization or not of the food wastewater on the growth of Spirulina platensis were investigated. Results showed that when Spirulina platensis was cultured in 6 times diluted food wastewater, we got the highest biomass of values 1.341 g/L and 1.276 g/L, respectively whether the food wastewater was sterilized or not. So, the food wastewater was diluted 6 times and non-sterilized before inoculation.（3）The effects of different CO₂ supplemental intervals on the growth of Spirulina platensis using 6 times diluted non-sterilized food wastewater in a 10 L homemade photobioreactor（PBR） were investigated. Results showed that while supplemental interval was 4 h, we got the highest biomass of value 1.260 g/L, higher than 8 h supplemental interval of value 1.129 g/L. The uptake of TN and TP were 39.732 mg/L and 1.585 mg/L, higher than 24.401 mg/L and 0.957 mg/L, which were got when supplemental interval was 8 h. However, the adherent growth of Spirulina platensis was serious during batch culture.（4）The semi-continuous culture of Spirulina platensis in PBR was researched. Results showed that the adherent growth of Spirulina platensis could be alleviated. The biomass productivity of the semi-continuous culture was 0.770 g/d, higher than the batch culture of value 0.513 g/d. The absorption rates of nitrogen and phosphorus were 26.798 mg/d and 0.905 mg/d, which is better than the batch culture of value 19.866 mg/d and 0.792 mg/d.（5）The three-stages culture was studied. First, Spirulina platensis was cultured in mixtrophic to improve biomass in stage I. Then the nitrogen was deprived for one day in stage II, which could improve the nitrogen utilization of food wastewater in stage III. In this protocol, the trophic mode conversion from mixtrophic to autotrophy, then to wastewater culture, which would facilitate the accumulation of biomass.