Search

Objective: To investigate the effect of iron on the growth, physiology and photosynthesis of cyanobacteria. Methods: A gradient of iron concentrations was employed to investigate the growth, photo-pigments (chlorophyll A and phycocyanin), and cell chemical contents (C, N, P) of Microcystis aeruginosa in response to different iron additions. Results: The specific growth rate during the exponential growth phase, as well as the cell chlorophyll A and the phycocyanin content, was limited by iron below 12.3 μmol Fe·L−1. The growth was inhibited when the iron concentration was at 24.6 μmol Fe·L−1. The cell chlorophyll A and the phycocyanin content were saturated when the iron concentration was above 12.3 μmol Fe·L−1 and declined slightly at 24.6 μmol Fe·L−1. At a low iron concentration (about 6.15 μmol Fe·L−1 and less), the cell nitrogen and carbohydrate content were iron limited, and the variation of the cell phosphorus content was similar to that of the nitrogen and carbohydrate, with a transition point of 12.3 μmol Fe·L−1. Conclusion: The variation of cynobacteria growth is synchronous with that of the photo-pigments or the cell chemical content, and there exist relationships among photosynthesis, growth and internal chemical content, which could be useful for the growth estimation from the cell characteristics. [Copyright &y& Elsevier]

In this study, the effect of zeolite powder addition on submerged membrane bioreactor (SMBR) on membrane permeability, and the removals for COD, NH_3-N, TN were investigated. Through the parallel operation of control and test systems, it was found that the zeolite powder addition could alleviate the ultra-filtration membrane fouling and enhance the membrane permeability. On the basis of experimental investigations, a concept of "protection coating layer" was proposed to illustrate the phenomenon of UF membrane fouling. In addition, the removal for COD in test system was more stable, a little higher compared to the control system. Due to the combination of nitrification and ion exchange, a more excellent removal for NH_3-N in test system was obtained regardless of influent NH_3-N loading rate. It was also found that a mean 25% higher TN removal took place in the test system, and ion exchange and simultaneous nitrification and de-nitrification were analyzed to be main factors. During the stable operation period, the SOURs of test pectively zeolite powder added sludge and control activated studge were measured to be 75mgO_2/(gML VSS·h) and 24 mgO_2/(gML VSS·h) respectively, it meant that the zeolite powder addition could enhance the microorganism activity significantly. [ABSTRACT FROM AUTHOR]

A molecular biology method, fluorescent in situ hybridization (FISH), in which the pre-treatment was improved in allusion to the media of the constructed wetlands (CW), e.g. the soil and the grit, was used to investigate the vertical distribution characteristics of ammonia-oxidizing bacteria (AOB) quantity and the relation with oxidation-reduction potential (ORP) in the Typha latifolia constructed wetlands under three different loadings in summer from May to September. Results showed that the quantity of the AOB decreased in the Typha latifolia CW with the increase of vertical depth. However, the AOB quantity was 2-4 times the quantity of the control in the root area. Additionally, ORP in the rhizosphere was found to be higher than other areas, which showed that Typha latifolia CW was in an aerobic state in summer when using simulated non-point sewage at the rural area of Taihu Lake in China and small town combined sewage. [ABSTRACT FROM AUTHOR]

In recent years, worldwide concern over global warming has been expressed. It has been reported that domestic wastewater and its treatment processes are sources of CH4 and N2O, designated as greenhouse gases, the reduction of which was noted to be extremely important at the Third Conference of the Framework Convention on Climate Change (Conference Of the Parties; COP3). Here we report a study of a field that has been unexplored until now: analytical evaluation of the properties of the emission of CH4 and N2O and methods of restricting their emission in soil-trench wastewater treatment processes, the use of which is spreading, mainly in developing nations. The results have provided the following information. A field fact-finding survey has confirmed that soil trenches emit 9.3–13.9 g CH4 m−3 and 8.2–12.2 gN2O m−3 in Japan, and 3.0–4.5 g CH4 m−3 and 3.3–5.0 g N2O m−3 in China. The emission properties widely vary according to the structure of the treatment system. The conversion ratio for nitrogen in the wastewater influent to N2O by a soil trench is between 2 and a maximum of 8%, and ranges from a few- to several 10-fold as much as that with the activated sludge method, suggesting that this can be a large source of N2O emission. It has also clearly been shown that the aerobic–anaerobic state inside the treatment system is closely related to its CH4 and N2O emission characteristics. By performing ventilation to maintain the oxidation–reduction potential (ORP) near the trench at an aerobic condition of +200 mV or more, the quantities of CH4 and N2O emitted can be reduced by as much as 50% from the levels without this ventilation, and that this can make a large contribution. [Copyright &y& Elsevier]

Abstract: To explore a method for rapid restoration and artificial regulation of submerged macrophytes in large-scale restoration of eutrophic lakes, the succession and the biodiversity changes of four communities composed of four native, common submerged macrophytes, Hydrilla verticillata, Potamogeton malaianus, Vallisneria spiralis and Najas marina, on two kinds of sediments were investigated. Under low light intensity (reduced by 99%), the plant biomass changed with seasonal changes, plant competition, and environmental stress. The competitive capability for light differed in the four species due to different shoot height and tiller number. After 405 days of transplantation, H. verticillata became dominant in all communities. The biomass of H. verticillata, with strong ability to endure low water light environment, accounted for more than 90% of the total community biomass, and P. malaianus had only weak growth, while V. spiralis and N. marina almost disappeared. Based on livability and biomass of submerged macrophytes on two sediment types, brown clay sediment appeared to be more favorable for the settlement of the plants, while fertile sludge sediment was suitable for vegetative growth. In conclusion, the improvement of habitats and the selection of appropriate plant species are of the greatest importance for ecological restoration of the aquatic ecosystem. [Copyright &y& Elsevier]

Natural zeolite and expanded clay were used as filter media for biological aerated filter (BAF) to treat municipal wastewater in parallel in whole three test stages. The stage one test results revealed that zeolite BAF and expanded clay BAF have COD and NH3-N removals in the range of 84.63–93.11%, 85.74–96.26%, 82.34–93.71%, and 85.06–93.2%, respectively, under the conditions of water temperature of 20–25°C and hydraulic load of 2–3m3/(m2 h). At the following stage two, the influent NH3-N concentration was increased to about double value of the stage one, and it was investigated that the effluent NH3-N of expanded clay BAF increased significantly and then gradually restored to normal condition in 2 weeks, while the effluent NH3-N of zeolite BAF kept stable. At stage three, the low reactor temperature has also different effects on these two BAFs, under conditions of water temperature of 7–10°C, hydraulic load of 2–3m3/(m2 h), zeolite BAF and expanded clay BAF have COD and NH3-N removals in the range of 74.5–88.47% (average of 81.57%), 71.73–88.49% (average of 81.06%), 71.91–87.76% (average of 80.49%), and 38.41–77.17% (average of 65.42%), respectively. Three stages test results indicated that the zeolite BAF has a stronger adaptability to NH3-N shock load and low temperature compared to expanded clay BAF. In addition, the detection of the amounts of heterobacteria and nitrobacteria of two biological aerated filters in three stages also showed the zeolite filter media was more suitable to the attached growth of nitrobacteria, which is helpful to the improvement of nitrification performance in zeolite BAF. [Copyright &y& Elsevier]

Two types of operation means “SBR reactor alone (control reactor)” and “adding zeolite powder into SBR reactor (test reactor)” were used to treat municipal wastewater. The test results revealed that zeolite powder addition could improve the activity of the activated sludge. It was investigated the specific oxygen utilization rate (SOUR) of the tested zeolite sludge were about double times that of the control activated sludge, and the nitrification rate and settling property of zeolite-activated sludge were both improved. Due to the combination of zeolite adsorption for NH4 +-N and enhanced simultaneous nitrification and de-nitrification (SND), a higher nitrogen removal was observed in test reactor compared to the control reactor, and the addition of zeolite powder is helpful to inhabit sludge bulking. In addition, through long-term parallel shock load test, it was found that the zeolite powder addition could enhance the ability of activated sludge in resisting the shock load of organics and ammonium. Compared to the control activated sludge, zeolite powder added activated sludge could remove COD, NH4 +-N, TN and TP significantly in a shorter cycle time. At the same operational time period, the test SBR could treat wastewater quantity 1. 22 times that treated in control SBR. [Copyright &y& Elsevier]

Abstract: Zeolite synthesized from fly ash (ZFA) without modification is not efficient for the purification of NH4+ and phosphate at low concentrations that occur in real effluents, despite the high potential removal capacity. To develop an effective technique to enhance the removal efficiency of ammonium and phosphate at low concentrations, ZFA was modified with acid treatment and the simultaneous removal of ammonium and phosphate in a wide range of concentration was investigated. It was seen that when compared with untreated ZFA, only the treatment by 0.01 mol/L of H2SO4 significantly improved the removal efficiency of ammonium at low initial concentrations. The behavior was well explained by the pH effect. Treatment by more concentrated H2SO4 led to the deterioration of the ZFA structure and a decrease in the cation exchange capacity. Treatment by 0.01 mol/L H2SO4 improved the removal efficiency of phosphate by ZFA at all initial P concentrations, while the treatment by concentrated H2SO4 (> 0.9 mol/L) resulted in a limited maximum phosphate immobilization capacity (PIC). It was concluded that through a previous mild acid treatment (e.g. 0.01 mol/L of H2SO4), ZFA can be used in the simultaneous removal of NH4+ and P at low concentrations in simulating real effluent. [Copyright &y& Elsevier]

Abstract: Few studies have dealt on the evaluation of volatilization and decomposition reactions of dioxins from sediment by oxygen free pyrolysis. In this study, the performance of pyrolysis on the removal of dioxins from sediment was investigated. Dioxin concentrations of the raw sediment and the solid residues after pyrolysis were analyzed at different conditions. Results showed a removal efficiency of 99.9999% for total dioxins at 800°C and retention time of 30 min. All the polychlorinated dibenzo-furans (PCDFs) have been removed and were not formed in the solid residues at the retention time range of 30–90 min at 800°C. Close to 100% removal of polychlorinated dibenzo-p-dioxins (PCDDs) was also achieved. Only trace PCDDs were detected in the solid yields at a retention time of 60 min. The highest removal efficiency of polychlorinated biphenyls (PCBs) was more than 99.9994% at a retention time of 30 min. During cooling period following pyrolysis, however, the concentration of total dioxins in solid residues increased 130 times as compared to that of the raw sediment under air atmosphere. This confirmed that some complex reactions do occur to form PCDD/Fs and PCBs from 800 to 400°C in the presence of oxygen. Oxygen-free atmosphere therefore can prevent formation of dioxin during thermal process thus generating clean solid residues. [Copyright &y& Elsevier]

Activated alumina was studied for removing phosphate from water, and the recovery of adsorbed phosphate on activated aluminum oxide was also tested. Phosphate solution was prepared using distilled water, tap water and Luoshijiang River water, respectively. All the phosphate adsorption tests using activated alumina were proved to be well fitted with Langmuir isotherm and the respective maximum adsorption amount were 20.88, 32.15 and 29.85 mg x g(-1), respectively. The presence of electrolyte in water could be a positive factor for phosphate removal. As the pH value of phosphate solution became lower the Zeta potential of activated alumina increased, which could enhance the phosphate removal efficiency of activated alumina. The recovery tests indicated that NaOH (0.1 mol x L(-1)) solution could almost completely extract the phosphate adsorbed by activated alumina.

Harmful algal bloom (HAB) occurs frequently and causes serious damage. To study the early-warning and prediction technology of HAB is of significance for the early-warning and prediction, ecological control, and disaster prevention and mitigation of HAB. This paper reviewed the research progress in the early-warning and prediction technologies of HAB, including transport prediction, specific factors critical value prediction, data-driven model, and ecological math model, and evaluated the advantages and disadvantages of these four types of technologies. Some new ideas were brought forward about the prediction of cyanobacterial growth rate based on cell characteristics, and the early-warning of cyanobacterial bloom based on algal community characteristics.

The aim of this study was to investigate the effects of current density, gap between electrodes, urine dosage, dilution and hydrolysis on phosphate removal from human urine by electrocoagulation technique using iron as electrodes. It was shown that, although a high current density and a long electrolysis time favored the removal of phosphate, an appropriate value for these two parameters can be obtained by taking into account the consumption of energy and iron in addition to P removal. In this study, current density 40 mA/cm2 and electrolysis time 20 min were shown to be optimal for 1.0 L pure urine to achieve nearly a complete removal (98%) efficiency of phosphate under the conditions of electrode area 160 cm2, the stirring speed 150 rpm, and the gap between electrodes 5 mm. Increase of gap between electrodes had little effect on phosphate removal, although it increased the energy consumption dramatically. The use of a high urine dosage reduced the efficiency of phosphate removal but increased the amount of removed phosphate. When pure urine was diluted with tap water, use of a higher tap water proportion for dilution expedited the electrolysis to achieve a nearly complete removal of phosphate in solution, but dilution caused the increase in energy consumption. It was also revealed that the hydrolysis of urine prior to electrocoagulation treatment impeded phosphate removal.

Nitrification is a key step in the global nitrogen cycle. Classically, nitrifying bacteria are chemoautotroph. Recently, bacteria that have the ability of heterotrophic nitrification have been intensively studied as potential microorganisms that may be used to overcomeproblems inherent in the conventional method. This review gives a broad overview of the current status of heterotrophic nitrification including the heterotrophic species which nitrify actively, optimal condition for nitrification, heterotrophic nitrification pathway, enzymatic system and isolation methods. Also, the promising prospects of heterotrophic nitrification are especially introduced.

Objective: To characterize the heterotrophic nitrifying bacteria., Methods: The bacteria were isolated from membrane bioreactor for treating synthetic wastewater using the method newly introduced in this study. Fluorescence in situ hybridization (FISH) was used to validate the nonexistence of autotrophic ammonia oxidizers and nitrite oxidizers. Batch tests were carried out to investigate the capability of heterotrophic nitrification by the pure culture. Phylogenetic analysis of the pure culture was performed., Results: A heterotrophic nitrifier, named Bacillus sp. LY, was newly isolated from the membrane bioreactor system in which the efficiency of TN removal was up to 80%. After 24-day, incubation, the removal efficiency of COD by Bacillus sp. LY was 71.7%. The ammonium nitrogen removal rate after assimilation nearly ceased by Bacillus sp. LY was 74.7%. The phylogenetic tree of Bacillus sp. LY and the neighbouring nitrifiers were given., Conclusions: The batch test results indicate that Bacillus sp. LY can utilize the organic carbon as the source of assimilation when it grows on glucose and ammonium chloride medium accompanying the formation of oxidized-nitrogen. It also can denitrify nitrate while nitrifying. Bacillus sp. LY may become a new bacterial resource for heterotrophic nitrification and play a bioremediation role in nutrient removal.

In the present study, the chronic toxicity of dietary copper to Moina monogolica Daday was investigated. Microalgal growth inhibition tests were conducted for 96 h with the green algae Chlorella pyrenoidosa exposed to copper. The 96-h median effective concentration (95% confidence interval) was 509.12 (388.68-629.56) microg/L. Then, C. pyrenoidosa was exposed for 96 h to a control and to seven dissolved copper concentrations. Cellular copper concentration accumulated in a dose-dependent manner and was plotted against cell density. These algae were used as food in a 21-d bioassay with M. monogolica in seawater to which no dissolved copper was added. Brood size was not reduced in the first brood, but significant reductions at all algal-exposure copper concentrations (44.78-817.17 microg/L) were observed in all subsequent broods, with increasing magnitude in each brood. Neither longevity nor number of broods per female was significantly affected, even at the highest copper exposure, though both endpoints did show a consistent downward trend with increasing copper exposure. Total reproduction, brood size, and net reproductive rate were decreased significantly in all dietary copper exposures (algae exposed to 44.78-817.17 microg/L). In contrast, the intrinsic rate of natural increase was reduced significantly only with algae exposed to greater than 619.27 microg/L, most likely because of the heavy influence of early reproduction on this metric. Because cell density in algal cultures decreased with increasing copper concentrations, it is possible that changes in the nutritional content of the algal diet could have played a role in causing the observed changes in reproduction of M. monogolica.

A heterotrophic nitrifier, named Bacillus sp. LY, was newly isolated from a membrane bioreactor (MBR). Bacillus sp. LY could utilize the organic carbon as the source of assimilation when it grew on glucose and ammonium chloride medium companying the formation of oxidized-nitrogen. It also could denitrify nitrate while nitrification. After 24 days incubation, the removal efficiencies of the COD and TN by Bacillus sp. LY were 71.7% and 61.2%, respectively. The phylogenetic analysis of Bacillus sp. LY was performed and the phylogenetic tree of Bacillus sp. LY and the neighbouring nitrifiers was given. Bacillus sp. LY could become a new bacterial resource for heterotrophic nitrification and might play a bioremediation role for nutrient removal.

Characteristics of simultaneous removal of ammonium and phosphate from wastewater by zeolite synthesized from fly ash was investigated. The amount of ammonium and phosphate removed by zeolitized fly ash changed with time, and approached to a constant value after adsorption time of 24h was reached. The amount of ammonium and phosphate removed also increased with the rise in the amount of zeolite added, but slackened above the solid/liquid ratio of 8 g x L(-1). The removal rate of ammonium by zeolitized fly ash could rise to the maximum value of 60% when pH was between 7 and 9, and declined out of the pH range. For phosphate, minimum removal rate of about 85% was obtained within pH 7-9, and the removal rate increased to about 100% out of the pH range. The adsorption of ammonium on zeolitized fly ash was an exothermic reaction; the removal rate of ammonium could decrease with the rise in temperature. On the contrary, the adsorption of phosphate was an endothermic reaction, and the rise in temperature favored the removal of phosphate by zeolitized fly ash. The adsorptive ability of ammonium on zeolitized fly ash was: Al-Z > Mg-Z > Ca-Z > Na-Z > Fe-Z. The order for phosphate was: Al-Z > Fe-Z > Ca-Z > Mg-Z > Na-Z. It was proposed that the mechanism for the removal of ammonium from wastewater by zeolitized fly ash was cation exchange process, while the mechanism for phosphate was not only the precipitation reaction of phosphate with cation in solution, but also adsorption mechanism.

Method of isolating the heterotrophic nitrifiers and the characterization of the heterotrophic nitrification were studied. Two heterotrophic nitrifiers were newly isolated from a membrane bioreactor (MBR) in which the TN removal efficiency was 80.1%. The batch test results indicate that Bacillus sp. LY and Brevibacillus sp. LY could utilize the organic carbon as the source of assimilation when they grew on glucose and ammonium chloride medium companying the formation of oxidized-nitrogen. After 24 days incubation, the removal efficiencies of the COD by Bacillus sp. LY and Brevibacillus sp. LY were 71.7% and 52.6%, respectively. The removal efficiencies of ammonium nitrogen by the two isolates were 78.2% and 51.2% and the TN removal efficiencies by the two isolates were 61.2% and 35.6%, respectively.

The study presented the method for isolating the heterotrophic nitrifiers and the characterization of heterotrophic nitrification. Continuous tests via a membrane bioreactor (MBR) were operated under the controlled conditions to proliferate the nitrifiers. Heterotrophic nitrifying bacteria were isolated from the system in which the efficiency of total nitrogen (TN) removal was up to 80%. Since no autotrophic ammonium and nitrite oxidizers could be detected by fluorescence in situ hybridization (FISH), oxidized-N production was unlikely to be catalyzed by autotrophic nitrifiers during the heterotrophic nitrifiers' isolation in this study. The batch test results indicate that the isolated heterotrophic bacteria were able to nitrify. After 3 weeks incubation, the efficiencies of the COD removal by the three isolated bacterial strains B1, B2, and B3 were 52.6%, 71.7%, and 77.7%, respectively. The efficiencies of the TN removal by B1, B2, and B3 were 35.6%, 61.2% and 68.7%, respectively.

In recent years, worldwide concern over global warming has been expressed. It has been reported that domestic wastewater and its treatment processes are sources of CH4 and N2O, designated as greenhouse gases, the reduction of which was noted to be extremely important at the Third Conference of the Framework Convention on Climate Change (Conference Of the Parties; COP3). Here we report a study of a field that has been unexplored until now: analytical evaluation of the properties of the emission of CH4 and N2O and methods of restricting their emission in soil-trench wastewater treatment processes, the use of which is spreading, mainly in developing nations. The results have provided the following information. A field fact-finding survey has confirmed that soil trenches emit 9.3-13.9 g CH4 m(-3) and 8.2-12.2 gN2O m(-3) in Japan, and 3.0-4.5 g CH4 m(-3) and 3.3-5.0 g N2O m(-3) in China. The emission properties widely vary according to the structure of the treatment system. The conversion ratio for nitrogen in the wastewater influent to N2O by a soil trench is between 2 and a maximum of 8%, and ranges from a few- to several 10-fold as much as that with the activated sludge method, suggesting that this can be a large source of N2O emission. It has also clearly been shown that the aerobic-anaerobic state inside the treatment system is closely related to its CH4 and N2O emission characteristics. By performing ventilation to maintain the oxidation-reduction potential (ORP) near the trench at an aerobic condition of +200 mV or more, the quantities of CH4 and N2O emitted can be reduced by as much as 50% from the levels without this ventilation, and that this can make a large contribution.