[Long-term Impacts of TiO2 Nanoparticles on the Stability of an Anaerobic Granular Sludge Bioreactor].

In the present study, the fate and long-term effect of TiO2 nanoparticles (NPs) on anaerobic granular sludge (AGS) was evaluated in an anaerobic methanogenic system. In the short-term experiment, the methane production rate decreased when the dosage of TiO2 NPs was greater than 150 mg·g-1. However, no significant difference in the products of acidification and methanation between the control and 150 mg·g-1(as VSS) of TiO2 NPs assays was observed, indicating low bacteria cytotoxicity of TiO2 NPs on AGS in dark anaerobic digestion. The operation data of the AGS bioreactor showed that acidogens was more sensitive to prolonged exposure to TiO2 NPs with the accumulation of VFAs and a decrease of biogas production in the TiO2 NPs containing reactor. The inhibiting effect of TiO2 NPs on the AGS might be attributed to the physical restraints. The average TiO2 concentration escaping with the effluent was 0.632 mg·L-1, suggesting most of the NPs were retained inside the reactor. The long-term presence of TiO2 NPs could alter the composition of the microbial communities in the AGS, since the amount of Methanosarcina increased by 115.6%. The results also indicated that the treatment of short-term sudden exposure to TiO2 NPs using batch tests might not be appropriate for interpreting their cumulative effects on the AGS, since a long time was need for the TiO2 NPs to show negative effects on the microbial populations in the AGS. Our study could supply useful proof for assessments of potential risks for TiO2 NPs on anaerobic activated sludge.

[Acute Toxic Effects of Bromate on Aquatic Organisms].

Acute toxic effects of potassium bromate, sodium bromate and potassium bromide on luminescent bacteria, water flea, green alga and zebrafish were studied using standard toxic testing methods. The results showed that the pollutants had no effect on the luminous intensity of luminescent bacteria. The 96 h EC5. of potassium bromate on Scenedesmus obliquus was 738.18 mg x L(-1), 48 h EC50 on Daphnia magna and Moina was 154.01 mg x L(-1) was 161.80 mg x L(-1), while 48 h LC50 was 198 52 mg x L(-1), 175.68 mg x L(-1), and 96 h LC50 on zebrafish was 931.4 mg x L(-1). The 96 h EC50 of sodium bromate on Scenedesmus obliquus was 540.26 mg x L(-1), 48 h EC50 Daphnia magna and Moina was 127.90 mg x L(-1), 111.07 mg x L(-1), while 48 h LC50 was 161.80 mg x L(-1), 123.47 mg x L(-1), and 96 h LC50 on zebrafish was 1065.6 mg x L(-1). But the effects of potassium bromide on the above several kinds of aquatic organisms were far smaller than those of potassium bromate and sodium bromate. The toxic effects on test organisms were due to the impacts of bromate after the comparison of different pollutants, and the effects were more obvious with the increase of exposure time. The order of sensitivity to the toxic effects of bromate was Daphnia magna, Moina > Scenedesmus obliquus > zebrafish > Chlorella vulgaris, luminescent bacteria.

[Effects of Bromate on the Growth and Physiological Characteristics of Chlorella vulgaris].

The effects of bromate on the growth and physiological characteristics of Chlorella vulgaris were investigated via the static exposure experiments and tested by flow cytometry. The results showed that when Chlorella vulgaris was continuously exposed to bromate for 96 h at 8 mmol·L-1, the specific growth rates and cell membrane integrity decreased significantly, while the esterase activity, mitochondrial membrane potential and reactive oxygen species (ROS) increased significantly. The membrane-damaged cells could be found from the scanning electron microscopy analysis. It could be identified that ROS were overproduced in presence of bromate, which could not be eliminated by Chlorella vulgaris in time through self-regulation. The excess ROS could lead to abnormal situation of cell membrane integrity, esterase activity and mitochondrial membrane potential, disorder of physiology function and damage of cell structure. It could be concluded that Chlorella vulgaris died or their growth was inhibited by the existence of bromate.

Study on the factors affecting simultaneous removal of ammonia and manganese by pilot-scale biological aerated filter (BAF) for drinking water pre-treatment.

It was demonstrated that simultaneous removal of ammonia and manganese could be accomplished by biological aerated filter (BAF) with low-cost lava as media. Long-term operation performance and impact factors were systematically studied. DGGE analysis demonstrated that ammonia oxidizing bacteria (AOB), manganese oxidizing bacteria (MOB) and simultaneous ammonia and manganese oxidizing bacteria (SAMOB) co-existed in the bio-film. Ammonia and manganese concentration profiles along the height of BAF column, including that in the influent and effluent, were investigated with varying hydraulic loadings, aeration intensities and feed ammonia concentrations. It was inferred that AOB and MOB may have different spatial distribution in vertical direction, and AOB and MOB may compete for oxygen capture or be present on different layers of the bio-films. Further work should focus on the distribution of AOB, MOB and SAMOB in the reactor and optimize it for more efficient mass transfer and better system performance.

[Removing efficiency study on Cyclops cooperating with water treatment process by alternative oxidants].

The synergic removal effect on Cyclops was studied with 4 kinds of dosages of pre-oxidants such as chloramines, chlorine, O3 and potassium permanganate composite followed by different sets of clarification treatment process pilot systems. The removal mechanisms of Cyclops in different treatment units were analyzed. The experiments results show that the inactivation rate of chlorine (25%) is the highest compared with the chloramines (21%), potassium permanganate composite (8%) and O3 (9%) in the pre-oxidation stage, while the removal rate is changed after the filtration and the sequence is chloramines (90%) > chlorine (88%) > O3 (83%) > potassium permanganate composite (80%). Only chloramines can remove Cyclops by 100% of removal rate with the treatment process with the conventional active carbon unit. The 100% of removal effect doesn't depend on the highest inactivation rate,but the reasonable cooperation between the pre-oxidation and the clarification treatment process. The size of Cyclops and its life activity are the important influencing factors. The individual removal rate of filtration unit is the highest with no lower than 50%. The removal effect of air-flotation unit is influenced by the size of Cyclops and its life activity.

[Effectiveness and characteristics of treating algae-laden raw water by stocking silver carp].

To reduce the negative effect of algae on conventional water treatment, a full-scale research of removing algae from algae-laden raw water by stocking filter-feeding silver carp was processed. After the pretreatment in a presedimentation tank with silver carp, the concentration of phytoplankton, the biomass of cyanobacteria and Microsystis flos-aquae in algae-laden raw water with Microsystis flos-aquae its dominant species decreased 61.8%, 76.1% and 78.2% respectively. This effective decrease of algae load on conventional process created favorable conditions for water treatment. Analysis indicates that food habit of silver carp and algae size are two causes of different removal efficiency between cyanobacteria and green algae. The results show that biomanipulation of silver carp is applicable for treating algae-laden raw water in which colonial cyanobacteria is dominant.

Biological control experiment of excess propagation of Cyclops for drinking water security.

Cyclops of zooplankton propagated excessively in eutrophic water body and could not be effectively inactivated by the conventional disinfections process like chlorination due to its stronger resistance to oxidation. In this study, an ecological project was put forward for the excess propagation control of Cyclops by stocking the filter-feeding fishes such as silver carp and bighead carp under the condition of no extraneous nutrient feeding. The results of experiments with different stocking biomass showed that the propagation of Cyclops could be controlled effectively, and the water quality was improved simultaneously by impacting on nutriment level and plankton community structure at proper stocking density of 30 g/m3 of water. The growth of Cyclops may not be effectually controlled with lower biomass of fish (10 g), and the natural food chain relation may be destroyed for Cyclops dying out in water while the intense stocking of 120 g per cubic meter of water. In addition, the high predator pressure may accelerate supplemental rate of nutrients from bottom sediments to water body to add the content of total nitrogen and phosphorus in water.

[Inactivation and removal of chlorine dioxide on cyclops of zooplankton].

Comparative experiments on the inactivation of cyclops by chlorine dioxide and chlorine were conducted. Batch experiments were performed in order to analyze the influence of pH value, organic precursor concentration on the rate of inactivation of cyclops with chlorine dioxide. In addition, the synergistic effect of different pre-oxidation followed by coagulation process on removal of cyclops in raw water was evaluated. It was found that chlorine dioxide possessed better inactivation effect than chlorine. Cyclops can be completely inactivated after 30 min of contact time by low dosage of chlorine dioxide (1.0 mg/L). The rate of inactivation was essentially the same at pH 5.7 and 8.0, and pH 9.8 resulted in the 10% of decrease in inactivation rate of cyclops than pH 5.7 - 8.0 in same contact time. The organic precursor concentration had negative effects on inactivation, and the higher the organic precursor concentration was, the lower inactivation rate of cyclops was achieved. The coagulation jar test showed that cyclops in the raw water could be completely removed by synergistic effect of chlorine dioxide pre-oxidation followed by coagulation process at chlorine dioxide dosage of 0.9 mg/L.

[Study on the technology of treating low temperature and low turbidity water by membrane bioreactor].

For the purpose of solving the problem of low temperature and low turbidity water treatment, a pilot study was made on the treatment of Songhuajiang River raw water with low temperature and low turbidity by using membrane bioreactor (MBR) process, and the removal effects of organic pollutants and turbidity and membrane filtration period were also investigated. The results showed that the effluent turbidity was lower than 1 NTU and its removal efficiency was over 90%. The removal efficiency of permanganate index and UV254 were about 40% - 50% and 30% - 45%, respectively. The operation time of the MBR was as long as 60 - 70 hours. Adding powder activated carbon (PAC) has increased the organic pollutant removal efficiency but it has no significant influence on the membrane permeability. Therefore, the MBR was capable of effectively treating waters typically used for drinking water supplies, particularly when the low temperature and low turbidity water are treated. The effluent water quality of MBR was better than that of conventional process. PAC-MBR combined process can be used to enhance organic pollutants removal efficiency when raw water was polluted severely.

[Preparation of a composite coagulant from fly ash and its application in domestic wastewater treatment].

Fly ash was investigated as a raw material for the preparation of a composite coagulant with sulfuric acid. Types of acid solution, H2SO4 concentration, ratio of H2SO4 to fly ash and stirring time were respectively examined as factors that influenced the efficiency of converting the iron and aluminum components into a composite coagulant and coagulation performance on domestic wastewater. The coagulant was attained at the condition of H2SO4-fly ash ratio of 5 mL/g, H2SO4 of 2 mol/L, stirring time of 4h and stabling time of 30 min, and contained Fe3+ of 0.010 8 mol/L with conversion efficiency of 11.4% and Al3+ of 0.035 4 mol/L with conversion efficiency of 4.3%. Removal efficiencies of COD and SS by this type of coagulant reached 70.4% and 91.9% respectively when treating domestic wastewater. This study provides a promising means to utilize fly ash for coagulation, which possibly makes wastewater treatment more economical and more sustainable.

[Toxicity and influencing factors of chlorine dioxide to chironomid larvae].

The toxic effect of chlorine dioxide to the different instar larvae of chironomid was studied using raw water as test sample. Furthermore, the effect of temperature and contact time on toxicity of chlorine dioxide was observed. It was found that chlorine dioxide possessed significantly toxic effect, and the LC50 value of chlorine dioxide to the 4th instar larvae was 0.41 mg/L(24 h). The toxicity of chlorine dioxide declined with the development of instar larvae. The 1st instar larvae was most sensitive to chlorine dioxide among the four instars, and the LC50 value of chlorine dioxide to the 4th instar was 1.78 times of that of the 1st instar larvae. Temperature was proved to have significant positive effect on chlorine dioxide toxicity, and the toxicity at 30 degrees C was 2.16 times of that at 15 degrees C. The toxicity of chlorine dioxide was significantly improved with the contact time increasing from 12 h to 24 h, while it did not make much difference with the contact time increasing to 36 h.

Inactivation of Chironomid larvae with chlorine dioxide.

In this paper, comparative experiments on the inactivation of Chironomid larvae by chlorine dioxide and chlorine were conducted. In addition, batch experiments were performed in order to analyze the influence of pH value, organic precursor concentration and temperature on the inactivation efficiency of Chironomid larvae with chlorine dioxide. Based on it, removal effect of different pre-oxidation followed by coagulation process on Chironomid larvae in raw water was evaluated. The results showed that chlorine dioxide possessed better inactivation performance than chlorine, and complete inactivation of Chironomid larvae was obtained at CT value of 37.5 mg min/L (dose of 1.5mg/L and exposure time of 25 min). The pH in the range of 6-8 did not affect the inactivation efficiency of chlorine dioxide, whereas pH 10 resulted in around 10% decrease in inactivation rate. Meanwhile, the organic precursor had negative effects on inactivation, indicated by the decreased inactivation rate from 100% at TOC concentration of 0mg/L to 62.2% at 8 mg/L when the CT value was 45 mg min/L. With regard to the temperature, the inactivation efficiency of Chironomid larvae was significantly improved with the temperature increasing within the range investigated of 10-25 degrees C. The inactivation rate was reduced by 68.9% when temperature reduced from 25 degrees C to 10 degrees C. The coagulation jar test showed that Chironomid larvae in the raw water could be completely removed by chlorine dioxide pre-oxidation in combination with the coagulation process at CT value of 24.8 mg min/L.

Study of removal effect on Mesocyclops leukarti with oxidants.

Cyclops of zooplankton propagates prolifically in eutrophic waterbody and it cannot be exterminated by conventional disinfection process. The mutagenicity of Mesocyclops leukarti and its extermination with oxidants in a drinking waterworks in China were studied. Among five oxidants for use in bench-scale, chlorine dioxide is the most effective and the potassium permanganate is the weakest against Mesocyclops leukarti under the same conditions. Full-scale results showed that Mesocyclops leukarti could be effectively removed from water by 1.0 mg/L chlorine dioxide preoxidation combined with conventional removal physical process. After filtration, chlorite, a by-product of prechlorine dioxide, is stable at 0.45 mg/L, which is lower than the critical value of the USEPA. GC-MS examination and Ames test further showed that the quantity of organic substance and the mutagenicity in water treated by chlorine dioxide preoxidation are obviously less than those of prechlorination.

Removal effect on Mesocyclops leukarti and mutagenicity with chlorine dioxide.

Mesocyclops leukurti of zooplankton propagates excessively in eutrophic water body and it cannot be effectively inactivated by the conventional drinking water treatment process. In order to tackle this problem, a study of removal effect on Mesocyclops leukarti with chlorine dioxide in a waterworks was performed. The results showed that Mesocyclops leukarti could be effectively removed from water by 1.0 mg/L chlorine dioxide preoxidation combined with the conventional drinking water treatment process. Higher oxidizability and molecular state of chlorine dioxide in water is the key to the inactivation of Mesocyclops leukarti. The chlorite, disinfection by-products (DBPs) of chlorine dioxide, was stable at 0.45 mg/L, which is lower than that critical value of the USEPA. GC-MS examination showed that the quantity of organic substance in the water treated by chlorine dioxide obviously decreased. Ames test further revealed that the mutagenicity was reduced by chlorine dioxide with respect to prechlorine. The propagation of Mesocyclops leukarti can be inactivated effectively and safely by chlorine dioxide pre-oxidation.

[O3/H2O2 oxidation processes of cyclops of zooplankton inactivation in water].

The inactivation effects of ozone, hydrogen peroxide, O3/H2O2 processes on Cyclops of zooplankton were discussed. It was found that O3/H2O2 possessed more favorable inactivation effect on Cyclops compared with the others, in distilled water with 1.0 mg/L of O3 and 4 mg/L of H2O2 the inactivation effect was 100% after 30 min contacting; ozone also had favorable inactivation effect, the inactivation effect is 80% by 1.0 mg/L of ozone alone; while hydrogen peroxide didn't, there was almost no inactivation effect by 4 mg/L of H2O2. The best inactivation condition for O3/H2O2 processes, that was, two oxidants were added sequentially with interval in range of 30 to 60 seconds, for them ozone at first. And the influencing factors under various conditions such as the dose of hydrogen peroxide, organic substance content, pH value, etc. were researched and reported. It was found that the effect didn't changed largely with H2O2 on the range of 4 mg/L to 10 mg/L, and inactivation effects on Cyclops of O3/H2O2 were not sensitive to pH value, while it declined obviously as the organic content increased. Finally, synergic removal effect on Cyclops with O3/H2O2 preoxidation followed by clarification process was investigated. The results show that the removal effect on Cyclops is further strengthened by clarification processes after O3/H2O2 pre-oxidation.

[Toxicity and influencing factors of liquid chlorine on chironomid larvae].

The excessive propagation of Chironomid larvae (red worm) in the sedimentation tanks is a difficult problem for the normal function of waterworks. The toxic effect of liquid chlorine on the different instar larvae of Chironomid was studied using distilled water as test sample. Furthermore, the effect of pH value, organic matter content, ammonia nitrogen, and algae content on toxicity of liquid chlorine was observed. The results show that the tolerance of Chironomid larvae to liquid chlorine is strengthened with the increase in instar. The 24h semi-lethal concentration (LC50) of liquid chlorine to the 4th instar larvae of Chironomid is 3.39 mg/L. Low pH value and high algae content are helpful to improve the toxic effect of liquid chlorine to Chironomid larvae. In neutral water body, the increase in organic matter content results in the decrease in the death rate of Chironomid larvae. The toxicity of liquid chlorine differs greatly in different concentrations of ammonia nitrogen. The death rate of the 4th instar larvae of Chironomid in raw water is higher by contrast with that in sedimentation tanks water for 24h disposal with various amount of liquid chlorine.

Removal of disinfection by-products formation potential by biologically intensified process.

The removal of disinfection by-products formation potential (DBPFP) in artificially intensified biological activated carbon (IBAC) process which is developed on the basis of traditional ozone granular activated carbon was evaluated. By IBAC removals of 31% and 68% for THMFP and HAAFP were obtained respectively. Under identical conditions, the removals of the same substances were 4% and 32% respectively only by the granular activated carbon (GAC) process. Compared with GAC, the high removal rates of the two formed potential substances were due to the increasing of bioactivity of the media and the synergistic capabilities of biological degradation cooperating with lactivated carbon adsorption of organic compounds. A clear linear correlation (R2 = 0.9562 and R2 = 0.9007) between DOC HAAFP removal rate and Empty Bed Contact Time (EBCT) of IBAC process was observed, while that between THMFP removal rate and EBCT of GAC was R2 = 0.9782. In addition certain linear correlations between THMFP, HAAFP and UV254 (R2 = 0.855 and R2 = 0.7702) were found for the treated water. For IBAC process there are also more advantages such as long backwashing cycle time, low backwashing intensity and prolonging activated carbon lifetime and so on.

Full-scale study of removal effect on Cyclops of zooplankton with chlorine dioxide.

Cyclops of zooplankton propagated excessively in eutrophic water body and could not be effectively inactivated by the conventional disinfections process like chlorination due to its stronger resistance to oxidation. In this paper, a full-scale study of chlorine dioxide preoxidation cooperating with routine clarification process for Cyclops removal was conducted in a waterworks. The experimental results were compared with that of the existing prechlorination process in several aspects: including the Cyclops removal efficiencies of water samples taken from the outlets of sedimentation tank and sand filter and the security of drinking water and so on. The results showed that chlorine dioxide might be more effective to inactivate Cyclops than chlorine and Cyclops could be thoroughly removed from water by pre-dosing chlorine dioxide process. The GC-MS examination and Ames test further showed that the sort and amount of organic substance in the treated water by chlorine dioxide preoxidation were evidently less than that of prechlorination and the mutagenicity of drinking water treated by pre-dosing chlorine dioxide was substantially reduced compared with prechlorination.

Study on coagulation property of metal-polysilicate coagulants in low turbidity water treatment.

In order to remove the low turbidity present in surface water, a novel metal-polysilicate coagulant was used to treat the raw water taken from Tanjiang River in Guangdong Province. This study on the effects of Al/Fe molar ratio on the performance of a complex compound formed by polysilicic acid, aluminium and ferric salt (PAFS) showed that PAFS with Al/Fe ratio of 10:3 seemed to have the best coagulation performance in removing turbidity and color. Experimental results showed that under the conditions of polymerization time of 15 d, sedimentation time of 12 min, and pH of 6-8, PAFS with Al/Fe molar ratio of 10:3 had the best coagulation efficiency and lowest residual Al concentration. The turbidity decreased from 23.8 NTU to 3.23 NTU and the residual Al concentration was only 0.165 mg/L in the product water. It could be speculated that colloidal impurities and particulate Al were removed by adsorption bridging and electrical neutralization of long chain inorganic polymer coagulants.