Construction And Optimization Of Chlorella-bacterial Consortia For Wastewater Advanced Treatment

With the great progress of human society and the rapid development of the economy,a large amount of industrial and agricultural wastewater had been discharged into the water,resulting in the destruction of the water ecological environment.In order to maintain the sustainable development of the environment,it was necessary to develop the effective advanced wastewater treatment technology to reduce nutrients in wastewater.Microalgae wastewater treatment system had attracted more and more attention as an emerging wastewater treatment method.However,due to the low stability of the single microalgae system and microalgal-bacterial consortia could significantly improve the stability,the use of the algal symbiosis system to treat sewage had shown great advantages.In fact,the microalgal-bacterial consortium itself had the problem of coordination between the algae and bacterial.For this purpose,this paper focused on the relationship between different bacteria and microalgae,as well as different environmental conditions.The effect of advanced treatment efficiency on wastewater and the use of biological methods for algae water separation of microalgae were also discussed.The main research of the thesis included the following four aspects:（1）This study mainly explored three bacteria which were commonly used in current wastewater treatment（Bacillus licheniformis,Bacillus subtilis and Rhodopseudomonas palustris）,evaluated the effects of on the growth of Chlorella pyrenoidosa and the wastewater treatment efficiency of different microalgal-bacterial consortium.The results showed that Bacillus licheniformis could promote the growth of Chlorella pyrenoidosa.The removal rates of TN and TP of the wastewater on the 2nd day were80.28%and 70.94%,which was significantly higher than that of the Chlorella pyrenoidosa alone system（P<0.05）.Bacillus subtilis had a certain inhibitory effect on the growth of Chlorella pyrenoidosa;Rhodopseudomonas palustris had no significant effect on the growth of Chlorella pyrenoidosa,but the growth of Rhodopseudomonas palustris was significantly inhibited by Chlorella pyrenoidosa（P<0.05）.（2）This study investigated the effects of different carbon sources（glucose,acetate and citrate）on the wastewater treatment effect on Chlorella pyrenoidosa and Bacillus licheniformis consortium.The results showed that under the condition of single carbon sources culture,the citrate was the most suitable carbon sources for growth of Bacillus licheniformis,and glucose was the most suitable carbon source for the growth of Chlorella pyrenoidosa.However,in the microalgal-bacterial consortium,the wastewater treatment efficiency was the highest when glucose was used as the carbon source,and the removal rates of TN,TP and TOC reached to 86.05%,93.71%and 82.19%,and the wastewater reached up to the discharge standard one day earlier.The results showed that the carbon source had a significant effect on the advanced treatment of wastewater in the microalgal-bacterial consortium.Glucose was a suitable carbon source for Chlorella pyrenoidosa and Bacillus licheniformis consortium.（3）In order to improve the nitrogen and phosphorus removal efficiency of Chlorella pyrenoidosa and Bacillus licheniformis consortium,glucose was used as the carbon source.This study investigated the effects of different C/N and the initial inoculum of algal and bacteria on nitrogen and phosphorus removal of the microalgal-bacterial consortium.The results showed that the maximum biomass of Chlorella pyrenoidosa gradually increase with the increase of C/N.In the microalgal-bacterial consortium,when the C/N ratio was 5:1,the effluent purification capacity of the microalgal-bacterial consortium was the best,and the removal rate of TN and TP was 84.19%and 91.23%,respectively.Next,based on C/N=5:1,the effects of initial inoculum size of different algae and bacteria on nitrogen and phosphorus removal of algal symbiosis system were investigated.The results showed that when the algal and bacteria ratio was less than 3:1,Bacillus licheniformis had no growth promoting effect on Chlorella pyrenoidosa.When the ratio of algal bacteria was 1:3,the nitrogen and phosphorus removal efficiency of the algal symbiosis system was the best.（4）The effective microalga harvest was a key process in the biological treatment ofwastewater.In order to improve the efficiency of microalgae recycling,the bioflocculation method was used to harvest Chlorella pyrenoidosa.A Box-Behnken designs（BBD）optimization experiments were carried out to achieve optimal microalgae harvesting process conditions.The result showed that the concentration of Fe³⁺,Ca²⁺and the dosage of bacterial fermentative solution had significant influence on the efficiency of the Chlorella pyrenoidosa flocculation.The maximum flocculating efficiency was 88.66%,with the condition of the concentrations of Ca²⁺and Fe³⁺was11.54 mM and 0.64 mM,the amount of bacteria liquid was 2.86%（v/v）,the pH was 8,and the precipitation time was 20 min,respectively.According to the research,a suitable microalgal-bacterial consortia was constructed to confirm the stability and high efficiency of Chlorella pyrenoidosa and Bacillus licheniformis consortium,and the operating parameters of the operation were optimized.The research provided basic data and operating parameters for the production application of the symbiotic system.It helped microalgal-bacterial consortia to play a role in wastewater treatment and ecological restoration engineering.