Disinfection byproduct formation from algal organic matters after ozonation or ozone combined with activated carbon treatment with subsequent chlorination

Algal organic matter(AOM),including extracellular organic matter(EOM)and intracellular organic matter(IOM)from algal blooms,is widely accepted as essential precursors of disinfection byproducts(DBPs).This study evaluated the effect of ozonation or ozone combined with activated carbon(O_(3)-AC)treatment on characteristic alternation and DBP formation with subsequent chlorination of Chlorella sp..The effects of p H and bromide concentration on DBP formation by ozonation or O_(3)-AC treatment were also investigated.Results showed that the potential formation of DBPs might be attributed to ozonation,but these DBP precursors could be further removed by activated carbon(AC)treatment.Moreover,the formation of target DBPs was controlled at acidic pH by alleviating the reactions between chlorine and AOM.Besides,the bromide substitution factor(BSF)value of trihalomethanes(THMs)from EOM and IOM remained constant after AC treatment.However,THM precursors could be significantly decreased by AC treatment.The above results indicated that O_(3)-AC was a feasible treatment method for algal-impacted water.

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.

Activated carbon enhanced ozonation of oxalate attributed to HO·oxidation in bulk solution and surface oxidation: Effect of activated carbon dosage and pH

Ozonation of oxalate in aqueous phase was performed with a commercial activated carbon（AC）in this work. The effect of AC dosage and solution pH on the contribution of hydroxyl radicals（HOU） in bulk solution and oxidation on the AC surface to the removal of oxalate was studied. We found that the removal of oxalate was reduced by tert-butyl alcohol（tBA） with low dosages of AC,while it was hardly affected by tBA when the AC dosage was greater than 0.3 g/L. tBA also inhibited ozone decomposition when the AC dosage was no more than 0.05 g/L, but it did not work when the AC dosage was no less than 0.1 g/L. These observations indicate that HOUin bulk solution and oxidation on the AC surface both contribute to the removal of oxalate. HOU oxidation in bulk solution is significant when the dosage of AC is low, whereas surface oxidation is dominant when the dosage of AC is high. The oxalate removal decreased with increasing pH of the solution with an AC dosage of 0.5 g/L. The degradation of oxalate occurs mainly through surface oxidation in acid and neutral solution, but through HOUoxidation in basic bulk solution. A mechanism involving both HOUoxidation in bulk solution and surface oxidation was proposed for AC enhanced ozonation of oxalate.

Comparison of different combined treatment processes to address the source water with high concentration of natural organic matter during snowmelt period

The source water in one forest region of the Northeast China had very high natural organic matter（NOM） concentration and heavy color during snowmelt period. The efficiency of five combined treatment processes was compared to address the high concentration of NOM and the mechanisms were also analyzed. Conventional treatment can hardly remove dissolved organic carbon（DOC） in the source water. KMn O4pre-oxidization could improve the DOC removal to 22.0%. Post activated carbon adsorption improved the DOC removal of conventional treatment to 28.8%. The non-sufficient NOM removal could be attributed to the dominance of large molecular weight organic matters in raw water, which cannot be adsorbed by the micropore upon activated carbon. O3＋ activated carbon treatment are another available technology for eliminating the color and UV254 in water. However, its performance of DOC removal was only 36.4%, which could not satisfy the requirement for organic matter. The limited ozone dosage is not sufficient to mineralize the high concentration of NOM. Magnetic ion-exchange resin combined with conventional treatment could remove 96.2%of color, 96.0% of UV254 and 87.1% of DOC, enabling effluents to meet the drinking water quality standard. The high removal efficiency could be explained by the negative charge on the surface of NOM which benefits the static adsorption of NOM on the anion exchange resin. The results indicated that magnetic ion-exchange resin combined with conventional treatment is the best available technology to remove high concentration of NOM.

Liquid phase heterogeneous photocatalytic ozonation of phenol in liquid-solid fluidized bed:Simplified kinetic modeling

The isotherms of original AC （activated carbon） and photocatalysts （TiO2-AC） calcined at 500 ℃ for phenol were measured. The results showed a reversible adsorption of phenol onto both kinds of particles at 25 ℃, and could be fitted well to the Freundlich adsorption equation for the dilute solution. Five oxidation processes, namely O3, O3 [UV, O3/UV/AC, O2/UV/TiO2 and O3/UV/TiO2, for phenol degradation in fluidized bed were evaluated and compared, and the photocatalytic ozonation was found to give the highest phenol conversion because of the combined actions of homogenous ozonafion in the liquid phase, heterogeneous ozonation on the surface of the catalyst support, i.e. activated carbon, and heterogeneous photocatalytic oxidation on the TiO2 catalyst surface. With the simplified kinetic model, photolytic ozonation was confirmed to predominantly take place on the particle surface in comparison with the heterogeneous and homogeneous photolytic ozonation. Additionally, the heterogeneous photocatalytic oxidation constant was found to be enhanced by 3.73 times in photocatlaytic ozonation process with ozone as the scavenger compared to the photocatalytic oxidation process with oxygen as the scavenger.

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.