Preparation Of Electrophilic And Redox Mediator Suspended Biofilm Carriers And Their Application In Wastewater Treatment

In recent years,the biological wastewater treatment technology based on the suspended biofilm carriers has drawn much attention in the upgrading of the existing wastewater treatment plants(WWTPs)and the newly-built WWTPs.Currently,most commercial suspended biofilm carriers are made of polymer materials,such as polyethylene(PE)or polypropylene(PP)due to their water-approximate density and stable physico-chemical properties.However,these carriers are negatively charged,as are the microorganisms in water,leading to poor biocompatibility due to the electrostatic repulsion between the biofilm carriers and microorganisms.The poor biocompatibility results in relatively slow biofilm formation rate,hence a slow start-up for the biofilm carrier based-reactors.Except for the poor biocompatibility,the performance for the removal of refractory organic pollutants is not satisfying in these biofilm carrier based-reactors.In present work,two kinds of modified suspended biofilm carriers were developed aiming at accelerating the start-up of biofilm carrier based-reactors,and enhancing the removal efficiency of refractory organic pollutants.One is electrophilic suspended biofilm carrier,and the other is redox mediator suspended biofilm carrier.The modified carriers have excellent biocompatibility,and achieve good performance in the pilot-scale and full-scale applications for wastewater treatment.The main research contents and conclusions are as below:(1)As microorganisms are usually negatively charged in water,a certain amount of polymers with positive charges,polyquaternium-10(PQAS-10)or cationic polyacrylamides(CPAM),were blended into the high-density PE suspended biofilm carriers to enhance electrophilic property and further accelerate biofilm formation and shorten start-up period.The experiment results indicated that the high-density PE suspended biofilm carriers modified with PQAS-10 or CP AM presented good electrophilic property with zeta potential increasing from-45.7?-30.7 mV to 5.7?19.6 mV(PQAS-10)and 2.1?13.7 mV(CPAM),respectively.Their hydrophilicity was also improved with the water contact angles decreasing from 94° to around 60° for both of the modified carriers.The PQAS-10 modified biofilm carriers with more positive charges,although with similar hydrophilicity as CPAM modified biofilm carriers,presented faster biofilm formation,higher relative content of nitrifiers and denitrifiers,and better nitrogen removal.Both of the electrophilic suspended biofilm carriers(ESBCs)achieved a higher biofilm growth rate and the biofilm growth rate of PQAS-10 modified biofilm carriers was 2.4 times as much as that of unmodified carriers,and the attached biomass increased by nearly 20%.According to the analysis of fluorescence in situ hybridization(FISH),the relative content of nitrifiers and denitrifiers on PQAS-10 modified biofilm carriers increased by 25%and 11%,respectively,compared with those on the unmodified carriers.The removal efficiencies of NH4+-N and TN increased by 41%and 23%,respectively.Meanwhile,the mechanical strength of modified biofilm carriers was significantly improved,with 20%higher tensile strength and 10%higher anti-impact strength.(2)The extracellular electron transfer rate of microorganism is one of the limited factors that influence biodegradation of refractory organic pollutants.Redox mediator,known as the electron carrier can accelerate the extracellular electron transfer rate of microorganism for enhancing the biodegradation of refractory organic pollutants.As a typical non-dissolved redox mediator,carbonylated graphene oxide was blended into suspended biofilm carriers to enhance the removal of refractory organic pollutants.The biodegradation experiment results indicated that the removal efficiency of refractory organic pollutants was significantly improved due to the presence of non-dissolved redox mediator suspended biofilm carriers.When the concentration of pollutants increased to 800 mg/L,the removal efficiencies of phenol and methyl orange in the non-dissolved redox mediator suspended biofilm carriers-based reactor reached to 88%and 97%,respectively under the anaerobic condition,which increased by 32%(phenol)and 43%(methyl orange)compared to the activated sludge-based reactor,and 22%(phenol)and 29%(methyl orange)compared to the unmodified biofilm carrier-based reactor.The high-throughput sequencing analysis results indicated that the relative content of functional bacteria increased by nearly 15%on the non-dissolved redox mediator biofilm carriers,suggesting an strengthened anti-impact load of biological wastewater treatment system,and enhanced removal of refractory organic pollutants in the biological wastewater treatment process.(3)The ESBC-based integrated floating fixed-film and activated sludge(IFFAS)process was applied to improve the removal efficiencies of COD and nitrogen in pilot-scale and full-scale applications for treating pigment production wastewater.The pilot results indicated that the COD,NH4+-N and TN removal efficiencies reached to 95%,91%and 85%,respectively,in the ESBC-based IFFAS process,which increased by 9?10%,22?36%and 18?20%in comparison with those of the original activated sludge(AS)process.The effluent COD,NH4+-N and TN concentrations could meet the non-direct discharge standards before being discharged into the industrial park WWTP(DB21/1627-2008)(COD<300 mg/L,NH4+-N<30 mg/L,TN<50 mg/L).Compared to the original AS process,the relative content of nitrifiers and denitrifiers on ESBCs increased by 14%and 11%,respectively.The full-scale application results showed that the effluent COD,NH4+-N and TN concentrations in ESBC-based IFFAS process were 91?291 mg/L,10.6?28.7 mg/L and 18.9?48.6 mg/L,respectively(influent COD of 1744?3456 mg/L,NH4+-N of 48.7-95.0 mg/L and TN concentrations of 100.2?208.8 mg/L),which could meet the non-direct discharge standards before being discharged into the industrial park WWTP.(4)The ESBC-based IFFAS process was applied to remove COD and nitrogen in pilot-scale and full-scale applications for treating industrial wastewater in an industrial park.The pilot results showed that the start-up period of ESBC-based IFFAS process was reduced by around 10 days,compared with that of conventional biofilm carrier-based IFFAS process.The removal efficiencies of COD,NH4+-N and TN in the ESBC-based IFFAS process increased by 11%,67%and 51%,respectively,and the values of effluent COD,NH4+-N and TN could meet the requirement of the first-class A of"Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant"(GB18918-2002)(COD<50 mg/L,NH4+-N<5 mg/L and TN<15 mg/L).The FISH analysis results indicated that the relative content of nitrifiers(56%)and denitrifiers(24%)in ESBC-based IFFAS process was higher than those in the original AS process(only 13%of nitrifiers,and 5%of denitrifiers).The full-scale application results showed that the effluent COD,NH4+-N and TN concentrations in ESBC-based IFFAS process could also meet the first-class A of the discharge standards(GB18918-2002)at the hydraulic retention time of 22 h,which was 11 h less than that of original AS process.The effluent COD,NH4+-N and TN concentrations were reduced to 30?48 mg/L,0.2?2.1 mg/L and 8.7?14.8 mg/L,respectively(influent COD of 182?720 mg/L,NH4+-N of 14.9?62.1 mg/L and TN of 35.8?56.9 mg/L).