Preparation Of Potassium Ferrate By Electrochemical Cycle And Anaerobic Fermentation Of Pretreated Waste Sludge To Produce Aci

The waste activated sludge generated during urban sewage treatment process is the main by-product that requires treatment and disposal in sewage treatment plants.The sludge production is steadily increasing.Sludge contains a large number of heavy metals and organic pollutants,and improper disposal can cause serious environmental pollution.However,sludge contains abundant resources such as proteins and polysaccharides that can be recovered during treatment.To address this,the oxidation performance of ferrates can be harnessed to accelerate sludge decomposition,enhance hydrolysis rates,improve anaerobic fermentation acid production efficiency,and facilitate resource recovery.This study is the first to use electrochemical cycling to prepare potassium ferrate,and the structural characterization of the prepared product was carried out.Experimental study on the pre-treatment and anaerobic fermentation efficiency of waste activated sludge using prepared potassium ferrate solid.Recycle the intermediate product of the electrolysis process,the ferrate anode solution（FAS）,for the pretreatment of waste activated sludge,investigate its impact on sludge settling and dehydration,and explore its effect on sludge cracking and fermentation acid production.The main research content and results are as follows:（1）The effects of alkaline concentration,electrolysis time,and current density on the electrochemical cycling preparation of potassium ferrate were investigated through a diaphragm type electrolytic cell.In a KOH solution with an alkaline concentration of 14 mol/L,with an electrolysis time of 8 hours per cycle and a current density of 6 m A/cm²,the highest current efficiency reached 73.7%,and the product purity reached 96.8%.The current efficiency initially increased and then decreased with the increase of electrolysis cycle.Overall,the first three electrolysis cycles emonstrated relatively high current efficiency.The product was qualitatively characterized through instrumental analysis.The X-ray diffraction（XRD）pattern confirmed that the prepared product was potassium ferrate.The Fourier transform infrared spectroscopy（FTIR）image exhibited a characteristic absorption peak at a wavelength of 807 cm^-1,further confirming the identification of the product as potassium ferrate.Scanning electron microscopy（SEM）images revealed that the potassium ferrate prepared in this experiment predominantly appeared as long rod or block crystal powder.（2）The effect of potassium ferrate pretreatment on the degradation of waste activated sludge under various conditions was investigated.When the dosage of potassium ferrate was 0.5g/g TSS,the concentration of soluble chemical oxygen demand（SCOD）in the sludge reached3446 mg/L,accounting for about 31.3%of the total chemical oxygen demand（TCOD）of the original waste activated sludge.The main component of organic matter in the supernatant is protein,with a maximum content of 1387 mg/L.Potassium ferrate pretreatment disrupts the extracellular polymer（EPS）structure of sludge,leading to increased extractable EPS content and accelerates hydrolysis process.（3）The effect of different dosages of potassium ferrate pretreatment on the acid production efficiency of anaerobic fermentation of waste activated sludge was investigated.After pretreatment,the anaerobic acid production efficiency of sludge was improved,and short-chain fatty acids rapidly accumulated.At a dosage of 0.2 g/g TSS,the maximum accumulation of short-chain fatty acids in the sludge fermentation broth reached 2106 mg COD/L,with acetic acid and propionic acid occupying the dominant position.Excessive potassium ferrate can have a certain inhibitory effect on acid production.Potassium ferrate pretreatment can change the community structure of microorganisms and promote the enrichment of functional microorganisms.After pretreatment,the relative abundance of bacteria related to acid production,such as Proteiniclasticum,Acetoanaerobium,Parabacteroides,Petrimonas,and Macellibacteroids,increased to 41.7%.（4）Considering that the intermediate product generated during electrolysis,the ferrate anode solution,contained a large amount of OH^-and ferrate ions,the effect of directly using the ferrate anode solution on the pretreatment of waste activated sludge was explored.The treatment of ferrate anode solution improved the settling and dewatering performance of sludge,with a reduction of 9.1%in sludge settling ratio and 9.7%in sludge cake moisture content,respectively.The pretreatment with ferrate anode solution significantly damaged the structure of sludge flocs and microbial cells.At a dose of 10 m L/L,the SCOD concentration reached 3807 mg/L,and the cracking effect was better than that of potassium ferrate pretreatment.The soluble protein and polysaccharide contents were 1490 mg/L and 418 mg/L,respectively,which were 1.63 and 2.05times higher than the control group.The pretreatment of anode solution damaged the EPS structure of sludge,promoted the diffusion of organic matter from the inner to the outer layer,and accelerated the hydrolysis rate of sludge.（5）Further exploration was conducted on the effect of pretreatment with ferrate anode solution on the anaerobic acid production efficiency of waste activated sludge.The ferrate anode solution had a promoting effect on anaerobic fermentation of sludge to produce acid at low doses（≤10 m L/L）,accelerating the hydrolysis rate of sludge and increasing the production of short-chain fatty acids.At a dosage of 10 m L/L,the production of short-chain fatty acids reached 2142mg COD/L.At high dosage（>10 m L/L）,the strong alkaline environment caused by the treatment of the anode solution inhibited the activity of acid producing bacteria,and the acid production efficiency of the remaining sludge decreased.Research has shown that the electrochemical cycling preparation of potassium ferrate can improve current efficiency and product purity within a certain period of time.The cyclic electrolysis of anode solution provides a cost-effective and continuous online production technology for the preparation of potassium ferrate.Electrochemical preparation of potassium ferrate and intermediate product ferrate anode solution as pretreatment agents has a good cracking effect on sludge,which can promote the dissolution of organic matter in sludge and accelerate the hydrolysis process,promote the rapid accumulation of short-chain fatty acids in anaerobic fermentation process,and provide technical support for resource recovery in sewage sludge.