| With the rapid development of the economy,the continuous improvement of living standards,the rapid development of the aquaculture industry,the large amount of aquaculture wastewater was generated.The cost of traditional sewage treatment methods was high.The treatment of aquaculture wastewater with microbial method is economical and effective.Microalgae has a wide distributed range,strong environmental adaptability,fast growth and reproduction,high photosynthesis efficiency,and could effectively absorb nutrients such as nitrogen and phosphorus in wastewater.The organic matter in the wastewater could be degraded by aerobic bacteria through heterotrophic metabolism.The nitrogen,phosphorus and organic matter in the aquaculture wastewater could be removed by the algal-bacteria co-culture system.In this paper,the common green algae-Chlorella vulgaris was used to treat aquaculture wastewater.Firstly,the treatment effect of wastewater by the Chlorella in free and fixed state was compared.And the effect of different immobilized materials,the content of immobilized material and the dosage of immobilized rubber ball on wastewater treatment were compared.In order to improve the removal effect of wastewater,the co-culture systems of Chlorella with Bacillus subtilis and activated sludge were constructed.The wastewater treatment results by single algae,single bacteria and algal-bacteria co-culture system under free and immobilized were studied;The co-culture system with Chlorella and activated sludge was optimized.Finally,the stability of the optimal algal-bacteria co-culture system was investigated.The main results were as follows:?1?The removal rates of NH4+-N,TN and TP of immobilized Chlorella were 27.99%,39.66%and 27.42%higher than free Chlorella,respectively,while the COD removal rate was10.29%lower.Immobilization could improve the removal effect of NH4+-N,TN and TP by Chlorella,but not conducive to the removal of COD.The removal effect of Chlorella by sodium alginate immobilized was better than agar and polyvinyl alcohol.The ammonia nitrogen and phosphate could be adsorbed by alginate gel balls in a short time.The sodium alginate content of the ball had little effect on the removal of NH4+-N and TN by immobilized Chlorella.With the increase of sodium alginate content,the removal rate of TP was increased,while the removal rate of COD was reduced.The larger dosage of immobilized Chlorella,the greater removal rates of NH4+-N,TN and COD could be achieved.The TP removal rate was the highest with 600 per 100 mL.Based on the comprehensive experimental results,sodium alginate was selected as the immobilization material,the content was 3%,and the dosage was600 per 100 mL.?2?The co-culture systems of algal-bacteria?Chlorella and bacillus/Chlorella and activated sludge?were better than the single algae and single bacteria.The co-culture system of Chlorella and activated sludge was better than the co-culture system of Chlorella and bacillus,the removal rates of NH4+-N,TN,TP and COD were 84.14%,84.41%,50.30%and85.17%,respectively.It indicated that the co-culture of algal-bacteria had a synergistic effect and could improve the removal effect of pollutants.The removal rates of NH4+-N,TN,TP and COD in the immobilized system of Chlorella/activated sludge co-culture were 12.21%,10.99%,45.42%and 2.99%higher than that of the free co-culture system.It indicated that the immobilization of the algal-bacteria co-culture system could further improve the removal of pollutants.The removal rates of NH4+-N,TN,TP and COD by immobilized Chlorella/activated sludge co-culture system were 96.35%,95.40%,90.92%and 88.16%,respectively.?3?The different co-culture methods of Chlorella and activated sludge immobilization were compared.The time to achieve the best removal rate of different pollutants by the different co-culture systems of Chlorella and activated sludge were different.The removal rates of NH4+-N,TN and TP were increased with time in different co-culture methods.The removal rates of COD and TOC were increased with time by free Chlorella and activated sludge.But the immobilized algal-bacteria co-culture system reached the maximum removal rate at 48 h.Phosphorus could be adsorbed by alginate gel beads and reached saturation at 12h.Except the effect of adsorption by the rubber ball,the removal of phosphorus in the first 48h was positively correlated with the increase of algae cells.The free activated sludge could effectively reduce COD and TOC.The COD removal rates of free activated sludge,free activated sludge and immobilized Chlorella,free Chlorella and free activated sludge were95.24%,93.41%and 92.53%at 48 h,respectively.The best removal effect of NH4+-N,TN and TP,and the removal rates were 99.41%,97.71%and 99.21%,respectively,when the free activated sludge and immobilized Chlorella were co-cultured.The concentration was decreased to 0.46,2.33 and 0.11 mg·L-1.The co-culture method of free activated sludge and immobilized Chlorella was determined.?4?The study on the running stability of free activated sludge and immobilized Chlorella co-culture system showed that,the biomass and chlorophyll a content of the reinforced group were 1.58 and 1.56 times that of the unreinforced group,respectively.In the unreinforced group,algae cell leakage occurred in the fourth cycle,and the surface of the rubber ball appeared uneven at the fifth cycle.The removal rates of NH4+-N and TP in the first8 cycles of the reinforcement group were stable at 81.59%93.69%and 84.23%98.74%,respectively,which were 6.34%24.04%,12.01%35.42%higher than those in the unreinforced group.The removal rates of COD was stable at 79.54%91.96%.Re-reinforcement was beneficial to improve the stability of the system. |
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