Research Of Potassium Ferrate Pretreatment Enhanced Blue Algae Anaerobic Digestion

In recent years,blue algae blooms occurred frequently in the Taihu Lake Basin.To deal with the large-scale growth of blue algae during the outbreak period,currently blue algae fishing was considered to be the most direct and effective approach.However,the collected blue algae should be properly handled to prevent secondary environmental pollution.Anaerobic digestion of blue algae can be used as an effective means for blue algae resource utilization.It has many advantages,including environment friendly,less energy consumption,reducing the concentration of algal toxin and achieving energy recovery.However,the structure of blue algae aggregates is complex,has protective cell walls.It needs effective pretreatment methods to enhance the anaerobic digestion of blue algae.In this paper,potassium ferrate was selected as an oxidant to pretreat the blue algae to study its effect and mechanism of promoting anaerobic digestion.Clarify the double enhancement mechanism of potassium ferrate as an iron-based oxidant to enhance the wall breaking of cyanobacteria through oxidation and enhance the anaerobic reaction efficiency through the action of iron.Firstly,the decrypting effect on blue algae by potassium ferrate pretreatment was explored.The concentration of SCOD in the supernatant increased with the concentration of potassium ferrate increasing.When the potassium ferrate concentration increased from 0 to 50 mg/g VS,the concentration of SCOD in the supernatant increased from 201 to 2553 mg/L.These organic compounds mainly included proteins,polysaccharides and DNA,etc.The results of three-dimensional fluorescence analysis showed that potassium ferrate pretreatment could enhance the content of biodegradable organic compounds in the liquid phase,alonging with the increase of potassium ferrate concentration.It was found that potassium ferrate pretreatment could damage the extracellular polymer of cyanobacteria and the cyanobacteria cells.Moreover,the effects of p H and substrate concentration in the pretreatment process on the cracking effect of blue algae were also explored.The higher the p H of blue algae system in the pretreatment process,the stronger the cracking effect on blue algae,and the solubility of potassium ferrate powder in water can increase the p H.With the increase of substrate concentration,the decaying effect of cyanobacteria declined.Then,the effect of anaerobic digestion productivity of methane was analysied.When potassium ferrate was 0,10,25,50 and 100 mg/g VS,the cumulative methane production on the 30th day of anaerobic digestion was 21.3,19.5,47.4,54.6 and 26.6m LCH₄/g VS,respectively.The maximum cumulative methane production was obtained corresponding to 50 mg/g VS potassium ferrate,and achieved 2.56 times methane that of the control group.Potassium ferrate pretreatment increased the degradation of organic matter.Meanwhile,high concentration of potassium ferrate enhanced the VFAs production.According to the results of methant production model analysis,the content of biodegradable organic matter and the hydrolysis rate of anaerobic digestion were significantly enhanced.The relative abundance of acid-producing bacteria（Mesotoga）and hydrogen-producing bacteria（Hydrogenispora）increased,the relative abundance of Geobacter microorganisms competing with methanogens was decreased,and the activity of methanogens coenzyme F420improved.Finally,the effect of iron in potassium ferrate on anaerobic digestion was investigated.The results showed that iron in the digestible fluid may accelerate the recovery activity of methanogens,increase the methane production rate,and improve the methane production in anaerobic digestion of blue algae.50 mg/g VS potassium ferrate pretreatment resulted in the highest methane production（72.20 m LCH₄/g VS）,and the methane production time was 4 days earlier than that of the control group.The total iron concentration in the digestive fluid of the experimental group was the highest in all the experimental groups.The peak concentration within 1-15 days was 62.03mg/L.Compared with the control group,the content of iron bound to iron and manganese Oxides in the solid phase increased significantly in the experimental group.XRD analysis results showed that Fe O crystals were formed in the experimental group,and the abundance of Geobacter microorganism associated with interspecific electron transfer was increased.Iron may promote the methanogenesis process by enhancing the interspecific electron transfer of microorganisms.The community structure analysis showed that the addition of potassium ferrate could enhance the abundance of Methanobacterium,Proteiniclasticum and Petrimonas.In conclusion,blue algae pretreated by potassium ferrate can effectively enhance methane production in anaerobic digestion.The pretreatment process enhance the decrypting of blue algae and increase the content of biodegradable organic matter through the oxidation of potassium ferrate.In the process of anaerobic digestion,iron in potassium ferrate promote methane production by enriching methanogenic microorganisms and direct interspecific electron transfer.