Cascade Disposal Of Sludge In Microbial Electrolysis Cells With Biochar Cathode

Excessive amounts of waste activated sludge which is the byproduct of wastewater treatment plants has received increasing attention due to its environmental risks and abuntent organic.Generally,anaerobic digestion of sludge is an environmentally beneficial and previously sustainable technology,leading to destruction of pathogenic organisms,reduction of sludge volume as well as simultaneously generation of methane.Investigations have found that anaerobic digestion were limited by the slow hydrolysis rate.Yet,the microbial electrolysis cells(MECs)possess the potential to overcome such bottlenecks.But the catalyst material obstructed the application of MEC and investigation of large-scale systems was scanty..Therefore,the main purpose of this study was to utilize an easy-prepared and low cost biochar from the effluent of MEC as cathode of MEC to cascade degrade waste activated sludge.Besides,updated analysis technologies were used to deterimine the pysical as well as chemical charactristics of biochar.Last but not least,the operation parameters such as concentration,stirred speed and applied voltage were also tested to optimize the performance of hydrogen production from large sacle continuous stirred MEC(CS-MEC).This study demonstrated that sludge and corn straw biochar could be served as efficient cathode catalysts of MECs.At an applied voltage of 0.9 V and SCOD(soluble chemical oxygen demand)concentration of 1300 mg/L,the MECs with S25-C75 biochar cathode of which the mass ratio of sludge and corn straw was 1:3 showed the best performance ewith a hydrogen production rate of 1.17±0.23 m3-H2/m3/d.The performance was comparable with MECs with Pt/C(1.19±0.16 m3-H2/m3/d)and activated carbon(1.18±0.15 m3-H2/m3/d)cathodes.What's more,the energy efficency ?E of MEC with S25-C75 cathode was 120.27±12.46%,which was 11.53% and 37.91% higher,while cost of cathode was only 19.6%? 121% comparing with Pt/C and activated carbon cathode.At an influent concentration of 3000 mg/L,the hydrogen production rate of MEC with S25-C75 could be as high as 1.33±0.08 m3-H2/m3/d.The scanning electron microscope,Brunauer-Emmett-Teller and elemental analysis revealed that corn straw biochar was rich in miropores,nitrogen content as well as high surface aera.Raman spectra,X-ray diffraction and linear sweep voltammetry ananysis proved sludge biochar with a high degree of graphene carbon and catalytic activity towards hydrogen evolution reaction but poor conductivity.Crucially,the S25-C75 possessed best hydogen production performance in terms of combining the advantages form sludge and corn straw biochar.After that,CS-MEC with S25-C75 biochar cathode was used to test the production of methane from sludge under different operation conditions.The improvement of stirred speed would increase the proton transfer ability.Additionally,the increase of applied voltage would promote the thransfer and reduction of proton,thus increasing the hydrolysis rate of sludge.Third,the addition of COD concentration of influent was favor for the metabolism of microorganism as well as improving reduction of sludge.As a result,the optimal condition was achived with a COD removal of 61.7% and maximum methane production rate of 0.08 m3/m3/d when the stirred speed,applied voltage and COD concentration was 200 rpm,0.6 V and 4559±260 mg/L respectively.Thereafter,the MEC showed promising potential on a large scale to degrade waste sludge as well as produce energy,and after that the effluent was fabricated to biochar which served as the cathde of MEC.In this way,cascade disposal of sludge was achived and favor for the reduction,stabilization and reclamation of sludge.