| Nitrogen and phosphorus pollutants of piggery wastewater effluent are still abundant after current regular wastewater treatment. It has a large impact on water environment, such as leading to eutrophication of lake or river. Therefore, advanced treatment of nitrogen and phosphorus pollutions in modern livestock industry is a burning problem to be solved. It is very popular that microalgae wastewater treatment can realize the reutilization of nutrients during wastewater purification for advanced removal of nitrogen and phosphorus. Thus, in view of the coupling of wastewater deep purification with resource reuse, piggery wastewater treatment by microalgae will have great potential for development and application.This research took removal of of nitrogen and phosphorus in piggery wastewater by microalgae as main purpose. The research content was as follows:1) Denitrification pretreatment; 2) Microalgae screening; 3) The effect of N/P and nonutritional factors on the removal of nitrogen and phosphorus pollutants by microalgae; 4) Flocculation harvest condition of Desmodesmus sp. CHX1 was optimized.5) An air-lift photo bioreactor was designed for wastewater deep purification of nitrogen/phosphorus based on previous study, and the optimum gas flow rate was determined. The main results were as follow:1. The ammonium tolerance of Chlorella vulgaris 1068?BBotryococcus braunii 765 and Desmodesmus sp. CHX1 was lower than 150 mg/L,150 mg/L and 100 mg/L, respectively. It took more than 42 h for the pretreatment of piggery wastewater was by stirring with aeration 1.5 L/min.2. After comparing nitrogen/phosphorus removals of wastewater and the recycling products of Chlorella vulgaris 1068?Botryococcus braunii 765 and Desmodesmus sp. CHXl, our study found that the microalgal biomass, removal efficiency of ammonia nitrogen and total phosphorus of Desmodesmus sp. CHXl were higher than other two species of mcioalgae which reached 0.855 g/1,78.46% and 91.66%, respectively. Also, the content of chlorophyll?carotenoid, protein and lipid of Desmodesmus sp. CHX1 were the higest which reached 8.89 mg/L,3.19 mg/L, 0.510 g/L and 13.295 g/L, respectively. Therefore, Desmodesmus sp. CHX1 was the dominant microalgae.3. The results of the effect of N/P on removal of nitrogen and phosphorus pollutants by Desmodesmus sp. CHX1 showed that the removal rate of ammonia nitrogen and phosphorus in treatments were all high. The removal rate of ammonia nitrogen in N/P groups of 33:1,23:1,17:1,14:1,12:1 were 93.58%,94.95%, 95.43%,96.21% and 97.36%, respectively. The removal rate of phosphorus were 74.67%,77.73%,79.87%,80.40% and 81.89%, respectively. The removal rate increased while the ration of N/P decreased. However, lower N/P of wastewater need to add phosphorus, so based on cost considerations,Using Desmodesmus sp. CHX1 to treat piggery wastewater without adding phosphorus while the N/P was 33:1.4. The results of the effect of nonutritional factors on the removal of nitrogen and phosphorus pollutants by Desmodesmus sp. CHX1 showed that the best light intensity was 7000 lux, the best light-dark ratio was 24h:0h, the best temperature was 35?, The best microalgae density was 10%. The results of single factor experimental showed that 35? was best for microalgae to do some purification, the ammonia nitrogen and total phosphorus removal rate was 77.26% and 95.06% respectively for the time being.5. Flocculation harvest condition of Desmodesmus sp. CHX1 was optimized which showed that flocculation harvest with calcium hydroxide had good flocculation whose recovery efficiency reached 90.53%. It had lowerest cost compared with aluminum sulfate and ferric chloride. On this basis, our futher study found that the best dosage was 0.8 g/L and the best flocculation time was 90 min.6. An air-lift photo bioreactor was designed for wastewater deep purification of nitrogen/phosphorus whcih showed that microalgal biomass, removal efficiency of ammonia nitrogen and total phosphorus in aeration group with 160 mL/min were higest which reached 1.872 g/L,95.00% and 96.99%, respectively. Also, the recovery efficiency of the content of chlorophyll, carotenoid were higher than others which was 96.44%,11.259 mg/L and 3.444 mg/L, respectively. Therefore, the best aeration rate was 160 mL/min. |
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