Removal Of Haloacetic Acid From Tap Water By Activated Sludge Process Coupled With A Zero-valent Aluminum System

Haloacetic acids?HAAs?had been continually identified as the by-product of chlorine or chloramine during disinfection process in city water,swimming water and etc.,with a high concentration of hundreds of?g/L.From the current research it had been found there are two main types of HAAs in water which can be classified to five elements,chlorinated HAAs?including TCAA,DCAA,MCAA?and brominated HAAs?MBAA,DBAA?.These HAAs are bad for human health and take along potential risk for the environment because of their different levels of genetic and carcinogenic toxicity.The control of HAAs has always been a hot topic in water treatment in recent years dehalogenation is considered to be one of the most efficient ways to control HAAs.In this paper,which based on the good degradation effect of TCAA,by treating HAAs with powdered zero-valent aluminum,beginning the research of removal HAAs by granular zero-valent aluminum column filtration and its combination with activated sludge process,as well as studying its main influencing factors.pH has a pronounced effect on the removal of TCAA by zero-valent aluminum.With the initial concentration of 200?g/L,TCAA can be completely degraded in 30min at pH=3.The degradation efficiency is obviously reduced along with the increasing pH level.TCAA cannot be degraded by zero-valent aluminum in neutral or alkaline conditions.Susceptibility of HAAs to zero-valent aluminum reduction normally follows the order of tri-HAAs,di-HAAs,and lastly mono-HAAs.Di-and mono-HAAs were usually observed as the dehalogenation intermediates.Both DCAA and MCAA can be partially degraded with a low degradation rate constant by zero-valent aluminum.HAAs degradation followed the pseudo-first-order reaction,and the first-order rate constant?k value?was 0.008 min^-1,0.043 min^-1and 0.215min^-1 for MCAA,DCAA and TCAA,respectively.The temperature has a significant effect on the degradation of TCAA,the k value was 0.215 min^-1,0.063 min^-1and0.027 min^-1 at 45?,35?and 25?,respectively.All the five HAAs can be partially degraded by zero-valent aluminum and the k value was following the order of TCAA>DBAA>MBAA>DCAA>MCAA.pH has a significant effect on TCAA removable by zero-valent aluminum column filtration and contact reduction.Almost no TCAA can be detected after zero-valent aluminum column filtration when pH<2.However,the removal efficiency dramatically decreased to less than 15%when pH increased to 5.High TCAA removal efficiency obtained even at 25?when pH<2.The empty bed contact time?EBCT?is a key parameter for zero-valent aluminum column filtration.The TCAA degradation rate increased with increasing EBCT,more than 98%of the TCAA degraded with an EBCT at 120 min.Even at a very high level of TCAA degradation,the total HAAs removal rate is very low,because the degradation only transfer TCAA into DCAA and MCAA.In contrast,to the order of HAAs dehalogenation by zero-valent aluminum,it has generally been found that while mono-and di-HAAs are relatively easily biodegradable,and tri-HAAs are recalcitrant to biodegradation.However,total HAAs removal efficiency could be more than 90%after the combination treatment with zero-valent aluminum column filtration followed by activated sludge biodegradation.Less than 10?g/L of DCAA could be detected after the combination treatment at the initial concentration of TCAA or DCAA 200?g/L.