| A large number of livestock wastewater discharge has brought great pressure to environmental management.Taking swine wastewater as an example,there are some problems in the traditional treatment process,such as poor nitrogen and phosphorus removal efficiency,too long treatment process,and unable to effectively recover valuable resources from wastewater.Microalgae are widely used in wastewater treatment because of its strong adaptability to environment,efficient utilization of nutrients such as nitrogen and phosphorus,and resource utilization.Using aerobic bacteria and microalgae symbiosis culture in wastewater treatment can further improve the removal efficiency of organic matter in wastewater,increase the biomass and treatment load,and then strengthen the wastewater treatment efficiency.However,at present,the control of algae-bacteria symbiotic system and its influence on wastewater treatment efficiency still needs further study.In this paper,the optimization of different algae-bacteria symbiotic systems in the advanced treatment of livestock wastewater were studied.And the preliminary investigation experiment based on microalgae or activated sludge was carried out,then the optimization experiment of algae-bacteria symbiotic system was carried out.The results show that,based on 0.5 g·L-1 microalgae,adding 0.1 g·L-1 activated sludge increased the activity of microorganisms in the system.The highest concentration of DO was 8.92 mg·L-1.Especially the removal efficiency of ammonia nitrogen was obvious and final removal efficiency was 97.28%.At the end of the experiment period,the removal efficiency of TP was 86.86%,89.77%respectively.The advantages of microalgae-activated sludge(bacteria)were preliminarily verified.Based on 1.5 g·L-1 activated sludge,microalgae can increase DO concentration of the system,decrease ion concentration or salt content in wastewater,improve system environment,and make COD removal efficiency reach the peak value of 96.5%in one day.Three days before the experiment,the removal efficiency of ammonia nitrogen was over 98%,the highest removal efficiency of TN was 97%,and the highest removal efficiency of TP was 92.8%.The content of chlorophyll-a in activated sludge and microalgae group reached the maximum value of 7.5 mg·L-1 on the 6th day.For the total biomass,it showed an upward trend after the third day,the highest biomass reached 4.2 g·L-1,the increment was about 28%,which the main contribution was microalgae.The superiority of the symbiotic system of algae-bacteria was further verified.The optimization experiment of algae-bacteria symbiotic system parameters shows that response surface method can optimize the treatment process of livestock wastewater by this system.There are different optimal parameter combinations for different targeted pollutants.Such as,the results of RSM showed that the optimal conditions for COD removal were:activated sludge to microalgae IP at 6.0(w/w),AR at 2.0 L·min-1 and initial NH4+-N concentration of 750 mg·L-1 with the highest COD RE over 92%.Considering all parameters that influence the pollutant REs,the optimized parameter combination can be selected. |
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