In order to simulate the water purification system of bacterial and algal interactions before the experimental group creates the experiment, so as to better help the experimental group design the experiment and help the experimental group better understand the experimental process, which can effectively reduce the experimental cost and experimental error. Therefore, the modelling group established a biodynamic model to simulate the bacterial-algal interactions water purification system.
First of all, the team simulated the whole process, for the whole simulation process, roughly refer to Integral microalgae-bacteria model (BIO_ALGAE): Application to wastewater high rate algal ponds this literature, for which the exposure environment treatment, and plant-based bacterial and algal interaction water purification model was modified, the sub-model was changed to the experimental scenario of bacterial and algal interaction water purification model, the schematic is as follows The sub-model was changed to a model of bacterial-algal interactions for water purification in an experimental scenario, as shown in the schematic below:
The bacteria used in the experimental group were heterotrophic bacteria corresponding to the model Q. aquimaris, and the algae used were P. tricornutum. the treated effluent was the f/2 culture solution prepared by the experimental group, and the density of the bacteria and algae are shown in the Appendix for details. Experimental conditions: 12 hours of light, no other nutrients added, sealed treatment. According to the above process of treatment of wastewater by bacteria and algae using differential equations and matrixing, the specific formulas are in the annex, as follows:
By using these equations, we get 1. at the same ratio of bacteria and algae with time: curve of change in biomass of bacteria and algae, curve of removal rate of pollutants such as NH4 ,NH3 in sewage, 2. at the same time, with different ratios of bacteria and algae: curve of biomass of bacteria and algae, curve of removal rate of pollutants such as NH4 ,NH3 in sewage. The graphs are as follows, please see the attachment for the complete results.
The left graph shows the curve of change in NH4 as a function of the amount of hours, and the right graph shows the curve of change in NH3 as a function of the amount of hours.
The growth rate, biomass, oil accumulation, photosynthetic efficiency and pigment accumulation of P. tricornutum co-cultured with Q. aquimaris at different density ratios were determined as follows.
1) The addition of Q. aquimaris increased the growth rate and biomass of P. tricornutum.
2) As the concentration of Q. aquimaris in the culture system increased, the photosynthetic efficiency of microalgae showed a tendency of rapid increase and then gradual decrease; among them, the 1:1 and 1:3 microalgae:bacterium treatment groups showed the most obvious increase of FV/Fm in D1, and the 1:3 treatment group maintained a better photosynthetic efficiency in the later stage of D5.
3) The analysis of the relative pigment contents of the treatment groups revealed that the 1:1 and 1:3 treatment groups could significantly promote the pigment accumulation of P. tricornutum. by about 1.3 times, respectively, but the 1:7 treatment group had a significant inhibitory effect on the chlorophyll content of the microalgae, which was consistent with the results of the poor photosynthetic efficiency of this group.
4) In terms of lipid accumulation of microalgae in the intercropping system of P. tricornutum and Q. aquimaris, the lipid accumulation of microalgae in the treatment groups of 1:1 and 1:3 was significantly enhanced; among them, the lipid accumulation of the treatment group of 1:3 was enhanced by 60.46% compared with the control group.
Based on the above conclusions, the 1:3 co-culture ratio of P. tricornutum and Q. aquimaris was selected for the subsequent experiments, mainly to analyse the photosynthetic efficiency and lipid accumulation of the co-culture system as a reference to help the co-culture system to achieve the desired bioremediation performance.
The experimental group designed six groups of experiments, namely, algae to bacteria density ratio of 1:0, 1:3, 1:51:7, 1:9, and 0:1. In this experiment, the optimal ratio for these six groups of experiments was 1:3, which was equal to the 1:3 obtained by the modelling group, and the biomass curve of the bacteria and algae obtained from the experiments was close to that obtained by the modelling group, and the pollutant removal curve obtained by the experimental group was also close to that of the modelling group under the 1:3 algae to bacteria density ratio. At 1:3 algal density ratio, the pollutant removal curve derived by the experimental group is also close to the curve derived by the modelling group, and the experimental results are plotted below:
The left panel shows the effect of different P. tricornutum to Q. aquimaris ratios on microalgae-related metrics, and the right panel shows the visualisation and fluorescence intensity analysis of microalgal oil plastids
Through the validation of the experimental group, the model was proved to be accurate and credible, providing a complete simulation process for the experimental group to better understand the water purification system of bacterial and algal interactions, as well as saving the experimental cost for future experiments.
Through the biodynamic modelling, we derived the optimal ratio of bacterial-algal interactions for water purification, from which we were able to better design the experiments. Contribute to the development of the future team, firstly, we provide a complete simulation process, which can help the future team to better analyse the bacterial-algal interactions system, and secondly, we derive the optimal ratio the future team can use the optimal ratio to improve the experimental efficiency and reduce the experimental cost.