| Microalgae biodiesel is considered a potential biomass energy,but has not yet gained applied in Industry,mainly due to the high cost of algae cultivation.Combining microalgae culture and wastewater treatment is an effective method to reduce costs.The establishment of algae-bacteria symbiosis system can further improve the microalgae biomass and wastewater purification effect.At the same time,the papermaking wastewater has rarely study using the algae-bacteria symbiosis system for advanced treatment.Therefore,this paper isolated and purified algae symbiotic bacteria,studied the effects of commensal bacteria on the growth of microalgae,constructed and optimized algae-bacteria symbiotic system to explore the effect on the advanced treatment of papermaking wastewater.In this paper,five strains of bacteria were separated from the autotrophic culture system of Ochromonas,which were identified as A-Porphyrobacter sp.,B-Hyphomonas sp.,C-Aquimonas sp.,D-Agrobacterium sp.,E-Hydrogenophaga sp.by 16S rDNA sequencing technology.Five strains of bacteria belonged to the Proteobacteria,and accounting for 30.8%,12.0%,13.6%,18.0%,25.6%respectively.The changes in the content of chlorophyll a in the spirulina platensis indicate that the five strains of bacteria have different effects on the growth of algae:the supernatant of the Agrobacterium culture after centrifugation had no significant effect on the growth of Ochromonas,and its cell sediment significantly inhibited the growth of microalgae,which could reduce the biomass of Ochromonas by 23.6%;at the same time,the cell body of Aquamonas had a significant promotion effect on the growth of Ochromonas,which could increase the biomass by 43.58%;the other three strains bacteria had no significant effect on the growth of Ochromonas.Therefore,Agrobacterium,which has a significant effect on promoting the growth of Ochromonas,was selected as the strain for constructing algae-bacteria symbiotic system.The results of optimization of microbial nutritional sources showed that the best carbon source suitable for the growth of Aquimonas was sucrose,and the nitrogen source was peptone;the best carbon source suitable for the growth of Ochromonas was sucrose,and in addition to ammonium chloride,the other four N sources(urea,beef extract,peptone,sodium nitrate)were suitable for the growth of microalgae.Adding different doses of Aquimonas to the BG11 culture system of Ochromonas,when the dose was 3 mL(OD600?0.5 for bacterial seed solution,and 8×107 CFU/mL after inoculation),the microalgae biomass got the maximum value.The orthogonal design result showed that the concentration of sucrose and the inoculation dose of Aquimonas had significant effects on the growth of Ochromonas.The best conditions for algae-bacteria symbiotic system as follows:sucrose concentration of 5 g/L;bacterial inoculation dose of 1 mL;peptone concentration of 2 g/L.Under the optimal culture conditions,the chlorophyll a of Ochromonas could reach 13.98 mg/L,the biomass was 19.37 mg/L,and the amount of Aquimonas could reach 1.6×109 CFU/mL.Four kinds of microbial systems were used on papermaking wastewater treatment:Aquimonas,Ochromonas,Ochromonas and Aquimonas,and algae-bacteria symbiotic system.And the papermaking wastewater was been diluted(the diluted water body contains 20%,50%,80%,and 100%of papermaking wastewater,respectively).The experimental result showed that when the wastewater content was 100%,the biomass of microorganism could get the maximum value,and the the purification effect was the best.During the 7 days of processing,different microbial dosing systems had different purification effect on papermaking wastewater.The single bacteria dosing system had a poor effect on water purification.In the single microalge dosing system,the content of chlorophyll a of Ochromonas was 8.213 mg/L,and the dry weight was 12.89 mg/L.The COD,TN,and TP of wastewater decreased from 148.4 mg/L,23.61 mg/L,1.13 mg/L to 96.46 mg/L,12.51 mg/L,and 0.25 mg/L,respectively.And the removal rates were 35%,47%and 78%,respectively.In the microalgae and bacteria dosing system,the presence of bacteria increased the biomass of microalgae by 14.62%,the chlorophyll a of Ochromonas was 9.414 mg/L,the dry weight was 14.24 mg/L,and the biomass of Aquimonas was 1.02×109 CFU/mL.The purification effect of wastewater had also been improved,the concentrations of COD,TN,and TP decreased from 148.4 mg/L,23.61 mg/L,1.13 m/Lg to 74.2 mg/L,11.09 mg/L and 0.14 mg/L,respectively.The removal rates were 50%,53%and 88%.In the algae-bacteria symbiotic dosing system,the algae biomass reached maximum,increased by 43.93%,the content of chlorophyll a of Ochromonas was 11.812 mg/L,the dry weight was 16.93 mg/L,and the number of bacteria was 1.5×109 CFU/mL.Compared with single microalge dosing system.The appearance of the treated wastewater was clear,and the COD,TN,and TP concentrations of the wastewater were reduced from 148.4 mg/L,23.61 mg/L,1.13 m/Lg to 56.39 mg/L,9.92 mg/L,and 0.09 mg/L,respectively.The removal rates were 62%,58%and 92%,respectively.The results of wastewater treatment showed that in the algae-bacteria symbiotic dosing system,the microalgae biomass was the highest and the wastewater treatment effect was the best.Aquimonas became the dominant species,and gathered around the cells of Ochromonas,which promoted the growth of Ochromonas.The research results showed that the algal-bacteria symbiosis system used in this paper was suitable for the advanced treatment of papermaking wastewater,close to the discharge standard of Shaanxi Province,and had certain application prospects.The research in this paper would provide important references and data support for revealing the effects of microalgal commensal bacteria on the growth of microalgae and the application of the algal-bacterial symbiotic system in the treatment of papermaking wastewater. |
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