Effect of ozone on the performance of a hybrid ceramic membrane-biological activated carbon process

Two hybrid processes including ozonation-ceramic membrane-biological activated carbon （BAC） （Process A） and ceramic membrane-BAC （Process B） were compared to treat polluted raw water. The performance of hybrid processes was evaluated with the removal efficiencies of turbidity, ammonia and organic matter. The results indicated that more than 99% of particle count was removed by both hybrid processes and ozonation had no significant effect on its removal. BAC filtration greatly improved the removal of ammonia. Increasing the dissolved oxygen to 30.0 mg/L could lead to a removal of ammonia with concentrations as high as 7.80 mg/L and 8.69 mg/L for Processes A and B, respectively. The average removal efficiencies of total organic carbon and ultraviolet absorbance at 254 nm （UV254, a parameter indicating organic matter with aromatic structure） were 49% and 52% for Process A, 51% and 48% for Process B, respectively. Some organic matter was oxidized by ozone and this resulted in reduced membrane fouling and increased membrane flux by 25%-30%. However, pre-ozonation altered the components of the raw water and affected the microorganisms in the BAC, which may impact the removals of organic matter and nitrite negatively.

Characteristics and removal mechanism of the precursors of N-chloro-2,2-dichloroacetamide in a drinking water treatment process at Taihu Lake

N-chloro-2,2-dichloroacetamide(N-Cl-DCAM)is an emerging nitrogenous disinfection by-product(N-DBP)which can occur in drinking water.In this study,an analytical method based on liquid chromatography with tandem mass spectrometry(LC-MS/MS)was developed to validate the concentration of N-Cl-DCAM,which was found to be 1.5µg/L in the effluent of a waterworks receiving raw water from Taihu Lake,China.The changes of N-Cl-DCAM formation potential(N-Cl-DCAMFP)in the drinking water treatment process and the removal efficiency of its precursors in each unit were evaluated.Non-polar organics accounted for the majority of N-Cl-DCAM precursors,accounting for 70%of the N-Cl-DCAM FP.The effect of conventional water treatment processes on the removal of N-Cl-DCAM precursors was found to be unsatisfactory due to their poor performance in the removal of low molecular weight(MW)or non-polar organics.In the ozonation integrated with biological activated carbon(O_(3)-BAC)process,the ozonation had little influence on the decrease of N-Cl-DCAM FP.The removal efficiency of precursors by a new BAC filter,in which the granular activated carbon(GAC)had only been used for four months was higher than that achieved by an old BAC filter in which the GAC had been used for two years.The different removal efficiencies of precursors were mainly due to the different adsorption capacities of GAC for individual precursors.Low MW or non-polar organics were predominantly removed by GAC,rather than biodegradation by microorganisms attached to GAC particles.