Study On Degradation Of Excess Sludge By Microbial Fuel Cell Assisted By Ultrasonic And Aerobic Granular Sludge

The excess sludge contains high amount of organic compounds,but they have a low biodegradability which makes it difficult to be degraded by microorganisms to achieve energy recovery.In this study,ultrasonic pretreatment and aerobic granular sludge?AGS?were combined with microbial fuel cells?MFC?for sequencing batch treatment of excess sludge and bioenergy recovery.The research contents and results are as follows:?1?The start-up of MFC reactors under different conditions.It was feasible to start dual-chambers MFC with excess sludge as the only fuel without any chemical reagent addition.The MFC reactor needed 28 days to start using raw sludge as fuel without ultrasonic pretreatment and without the addition of AGS in cathode chamber.And the start-up time for the MFC reactor successfully shortened to 14 days when ultrasonically pretreated sludge was used as fuel and AGS was added to the cathode chamber.?2?The power generation performance of MFC reactors under different conditions in two cycles.After running for 24 hours with external load resistance of 1000?,the output voltage of MFC reached 0.10V with untreated sludge as fuel without AGS addition and the output voltage increased to 0.15V when sludge was ultrasonically pretreated and AGS was added in cathode chamber,which indicates that ultrasonic pretreatment and AGS promoted the output voltage of MFC.After running for two weeks,the maximum output voltage of MFC just reached 0.24V without AGS added in the cathode chamber and the output voltage reached0.28V when AGS were applied,which indicates that adding AGS improved the output voltage of MFC.The MFC reactors continued to operate in sequencing batch mode for two cycles.In the second cycle,the maximum output power of MFC treating sludge without ultrasonic pretreatment and AGS addition reached 21.13mW/m²,and the internal resistance of the reactor was 2600?.While,when both ultrasonic pretreatment and AGS were used,the maximum power output of MFC reached 28.38mW/m²,and the internal resistance of the reactor was 1750?.It could obviously improve the power density as well as reduce the internal resistance of MFC when MFC was assisted by ultrasonic and AGS.This is related to the effects of ultrasound pretreatment and AGS on two aspects.First,ultrasonic pretreatment could destroy sludge EPS structure,the microorganism cells were broken down and released cell fluid,which caused the increase of sludge conductivity,and decrease of the internal resistance of MFC.Second,microorganisms of AGS contains numerous microorganism species and could both enhance the biocathode function,increasing the electrochemical reactivity on cathode surface,and quickly adapt to the environment to degrade the sludge.?3?Both the ultrasonic pretreatment and the addition of AGS could promote sludge degradation efficiency of MFC after two cycles.Sludge in dual chamber MFC was treated under sequencing batch mode,and the sludge passed through anode chamber and cathode chamber successively in two cycles.Based on the analysis of the changes of total chemical oxygen demand?TCOD?,extracellular polymeric substances?EPS?,polysaccharide?PS?and protein?PN?during the treatment process,it is reveal that the EPS of the sludge were gradually destroyed,tightly-bound EPS?TB-EPS?gradually transformed into loosely-bound EPS?LB-EPS?and then further transformed into soluble EPS?S-EPS?which was finally degraded by microorganisms.After running for two cycles,the removal rates of TCOD,SCOD,PS and PN of the excess sludge reached 26.8%,25.1%,23.0%,23.2%respectively without sludge ultrasonic pretreatment and AGS addition in MFC reactor.While,the removal rates of TCOD,SCOD,PS and PN of the excess sludge increased to 32.9%,49.0%,42.6%,42.6%respectively when the MFC reactor was assisted by the ultrasonic pretreatment of excess sludge and the addition of AGS.?4?The concentration of Ammonia Nitrogen?NH₄⁺-N?,Nitrate Nitrogen?NO₃^?-N?,Nitrite Nitrogen?NO₂^?-N?were analyzed to determine the effect of MFC on the denitrification of sludge.NO₂^?-N was detected in the MFC cathode chamber with the presence of AGS under the aerobic condition.It is speculated that there was a certain level of nitrogen nitrification and denitrification,which was probably a result of the special structure of AGS containing abundance of microorganisms.