Effect And Mechanism Of Cetyl Trimethyl Ammonium Bromide On Short Chain Fatty Acids Production And Dewaterability Of Sludge By Anaerobic Fermentation

Waste activated sludge（WAS）is one of the main by-products in the biological treatment of wastewater,which is inevitably produced in large quantities every day,and needs to be treated and disposed effectively to avoid the threat to the ecological environment.Anaerobic fermentation technology can not only produce short chain fatty acids（SCFAs）,but also inactivate pathogenic microorganisms and reduce sludge volume.Sludge dewatering,as an essential step in the process of sludge treatment,can achieve sludge volume reduction to a great extent and reduce the environmental burden.Therefore,the development of efficient and environmentally friendly sludge anaerobic fermentation and dewatering technology has become a research hotspot in recent years.Cetyl trimethyl ammonium bromide（CTAB）,as a typical cationic surfactant,has been applied in the environmental field,but its effect on anaerobic fermentation and dewaterability of sludge has not been clearly understood.Based on this,this paper mainly studied the effect and mechanism of CTAB on sludge anaerobic fermentation to produce SCFAs and dewaterability,filling the blank of CTAB in the field of sludge physics.Firstly,we explored the effect of CTAB pretreatment on the production of SCFAs by WAS anaerobic fermentation and analyzed the underlying mechanism.On the one hand,experimental results showed that the optimal dosage of CTAB pretreatment to promote SCFAs yield was 0.03 mg/g TSS,and the accumulation of SCFAs reached 273.5 mg COD/g VSS on the eighth day of fermentation,which was 5.43 times that of the 0 mg/g TSS group.On the other hand,mechanism revelations showed that CTAB pretreatment could destroy the EPS structure of sludge and promote sludge solubilization.Then,the organic matter and enzyme bound by EPS were released to promote the hydrolysis of organic matter.In addition,CTAB increased the abundance of hydrolytic and acid-producing microorganisms which promoted the production of SCFAs,but decreased the abundance of acid-consuming microorganisms and reduced the consumption of SCFAs.In conclusion,CTAB pretreatment promoted the stage of sludge solubilization,hydrolysis and acidification,but inhibited the stage of acid consumption,and finally realized the increase of the accumulation of SCFAs in sludge anaerobic fermentation.Then,the effect and underlying mechanism of CTAB conditioning on dewaterability of anaerobic fermentation sludge（AFS）were studied.On the one hand,experimental results showed that after sludge was conditioned by 75 mg/g TSS CTAB,capillary suction time（CST）,specific resistance to filtration（SRF）,and the water content of sludge cake(WC_SC)by vacuum filtration decreased from 164.1±10.7 s,1.90±0.05×10¹²m/kg,and 97.36±0.12%to 32.1±1.4 s,0.18±0.01×10¹²m/kg,and 70.55±0.21%,respectively.On the other hand,mechanism revelations showed that CTAB reduced the viscosity of sludge and turbidity of supernatant,improved the particle size distribution and microstructure of sludge,and increased Zeta potential,which was conducive to solid-liquid separation of AFS;CTAB could also enhance the hydrophobicity and the adhesion among the sludge particles to reduce the surface energy,and CTAB could release the intracellular water by damaging the outer membrane of sludge cells.The presence of CTAB also decreased the concentrations of PO₄^3-,humic acid,and proteins in the liquid phase through electrostatic attractive or hydrophobic interactions.Consequently,all these CTAB-caused variations in either the solid or liquid phase of sludge could result in the enhancement of sludge dewaterability.Finally,the technology of CTAB treatment to promote sludge anaerobic fermentation SCFAs production and dewatering was explored.The experimental results showed that under the condition of the same dosage of CTAB,the comprehensive optimal condition of single adding 0.12 g/g TSS CTAB treatment was that SCFAs and CST were 1800.4±10.5 mg COD/L and 102.5±1.3 s,respectively.The comprehensive optimal condition of batch adding0.03+0.09 g/g TSS CTAB treatment was that SCFAs and CST were 2643.4±9.7 mg COD/L and 61.7±3.0 s,respectively.Therefore,batch adding CTAB treatment has better effect in promoting SCFAs production and dewatering of sludge.This paper provides a theoretical basis for the application of CTAB in the field of sludge treatment.These findings deepen our understanding of the impact of CTAB on sludge anaerobic fermentation and dewatering,and may guide engineers to develop promising strategies to promote sludge anaerobic fermentation SCFAs production and sludge dewatering in the future.