An investigation of mechanisms for the enhanced coagulation removal of Microcystis aeruginosa by low-frequency ultrasound under different ultrasound energy densities.

There is a lack of studies elaborating the differences in mechanisms of low-frequency ultrasound-enhanced coagulation for algae removal among different ultrasound energy densities, which are essential to optimizing the economy of the ultrasound technology for practical application. The performance and mechanisms of low-frequency ultrasound (29.4 kHz, horn type, maximum output amplitude = 10 µm) -coagulation process in removing a typical species of cyanobacteria, Microcystis aeruginosa, at different ultrasound energy densities were studied based on a set of comprehensive characterization approaches. The turbidity removal ratio of coagulation (with polymeric aluminum salt coagulant at a dosage of 4 mg Al/L) was considerably increased from 44.1% to 59.7%, 67.0%, and 74.9% with 30 s of ultrasonic pretreatment at energy densities of 0.6, 1.11, and 2.22 J/mL, respectively, indicating that low-frequency ultrasound-coagulation is a potential alternative to effectively control unexpected blooms of M. aeruginosa. However, the energy density of ultrasound should be deliberately considered because a high energy density (≥18 J/mL) results in a significant release of algal organic matter, which may threaten water quality security. The specific mechanisms for the enhanced coagulation removal by low-frequency ultrasonic pretreatment under different energy densities can be summarized as the reduction of cell activity (energy density ≥ 0.6 J/mL), the slight release of negatively charged algal organic matter from cells (energy density ≥ 1.11 J/mL), and the aggregation of M. aeruginosa cells (energy density ≥ 1.11 J/mL). This study provides new insights for the ongoing study of ultrasonic pretreatment for the removal of algae via coagulation.

A comparative study on the use of palm bark as a supplementary carbon source in partially saturated vertical constructed wetland: Organic matter characterization, release-adsorption kinetics, and pilot-scale performance.

In this study, a comparative investigation of palm bark and corncob (a well-investigated material) for enhancing nitrogen removal efficiency in partially saturated vertical constructed wetland (PSVCW) was performed to evaluate an effective and cost-effective supplementary carbon source. The characteristics of the released organic matter and the release processes were analyzed through optical property characterization and a first-order release-adsorption model, respectively, and the nitrogen removal performance was evaluated in a series of pilot-scale PSVCWs. Results showed that the amount of organic matter released per unit mass of corncob was larger than that released per unit mass of palm bark under the same pretreatment conditions (control, heat, and alkaline pretreatment). The organic matter released from corncob has a higher apparent molecular weight and a higher degree of aromatic condensation than those of the organic matter released from palm bark, whereas the organic matter released from palm bark has higher and more stable bioavailability. Moreover, palm bark showed a more significant improvement of release capacity with the heat and alkaline pretreatment methods. Pilot-scale studies revealed that PSVCW using palm bark as the supplementary carbon source has a longer replacement cycle and higher total nitrogen (TN) removal efficiency than that using corncob, indicating that palm bark can be considered an effective and inexpensive supplementary carbon source. This study provides initial guidance for the ongoing research on supplementary carbon sources for improving nitrogen removal efficiency in constructed wetlands.

[Treatment Effects of Earthworm Constructed Wetlands in Different Working Conditions].

The feasibility of a new sludge treatment technology of earthworm constructed wetlands was tested by adding earthworm into the traditional sludge dying reed beds. The dewatering and stabilization effects of the upper layer sludge were tested under different sludge loading rates of 48, 65, 80 kg·(m2·a)-1, different earthworm stocking densities of 0, 0.43, 0.54, 0.65 kg·m-2 and different sludge loading frequencies. The results indicated that it was feasible to provide a shelter for earthworm during the loading period by setting a damper with a buried depth of 10 mm. The addition of earthworm could effectively improve the dewatering and stabilization effects of earthworm constructed wetlands, by lowering the DHA and decreasing the moisture content and VS of sludge by 15% and 10% respectively. The stabilization effects of earthworm constructed wetlands reached the best under the stocking density of 0.65 kg·m-2. With the increase of sludge loading rate and decrease of loading frequency, the running efficiency of earthworm constructed wetlands would be worse.

Anthropogenic Influences of Paved Runoff and Sanitary Sewage on the Dissolved Organic Matter Quality of Wet Weather Overflows: An Excitation-Emission Matrix Parallel Factor Analysis Assessment.

The quality of dissolved organic matter (DOM) in a wet weather overflow (WWF) can be broadly influenced by anthropogenic factors, such as nonpoint sources of paved runoff and point sources of sanitary sewage within the drainage networks. This study focused on the anthropogenic influences of the paved runoff and sanitary sewage on the DOM quality of WWF using excitation-emission matrix parallel factor analysis (EEM-PARAFAC). Results show that (1) EEM-PARAFAC fitted terrestrial humic-like, anthropogenic humic-like, tryptophan-like, and tyrosine-like components can be regarded as indicators to identify the types of sewage overflows and the illicit connection status of drainage systems. (2) A short emission wavelength (em: 302-313 nm) peak of the tyrosine-like component occurred in the reserved sanitary sewage, while a type of longer emission wavelength (em: 321-325 nm) peak came from the sump deposit. These tyrosine-like components were gradually evacuated in the initial phase of the overflow process with the fading of their EEM signals. Fluorescence signal transformations of all the components confirmed the potential ability of EEM-PARAFAC to monitor the dynamic changes of the primary pollutant sources. (3) The input of the newly increased sanitary sewage had a dominant influence on the quality and yield of the WWF DOM.

[Effect of Intermittent Aeration on Nitrogen Removal Efficiency in Vertical Subsurface Flow Constructed Wetland].

One-stage vertical subsurface flow constructed wetlands (CWs) were used to treat effluent from grit chamber in municipal wastewater treatment plant. The CW was divided into aerobic zone and anoxic zone by means of raising the effluent level and installing a perforated pipe. Two parameters (the ratio of aeration time and nonaeration time, aeration cycle) were optimized in the experiment to enhance nitrogen removal efficiency. The results suggested that the removal rates of COD and NH4⁺-N increased while TN showed a trend of first increasing and then decreasing with the increasing ratio. When the ratio was 3:1, the C/N value in the anoxic zone was 4. 8. And the TN effluent concentration was 15.8 mg · L⁻¹ with the highest removal rate (62.1%), which was increased by 12.7% compared with continuous aeration. As the extension of the aeration cycle, the DO effluent concentration as well as the removal rates of COD and NH: -N declined gradually. The TN removal rate reached the maximum (65.5%) when the aeration cycle was 6h. However, the TN removal rate dropped rapidly when the cycle exceeded the hydraulic retention time in the anoxic zone.

[Characteristics of rainfall and runoff in urban drainage based on the SWMM model.] / 基于SWMM模型的城市排水区域降雨及地表产流特征.

The characteristics of 235 rainfall and surface runoff events, from 2009 to 2011 in a typical urban drainage area in Shanghai were analyzed by using SWMM model. The results showed that the rainfall events in the region with high occurrence frequency were characterized by small rainfall amount and low intensity. The most probably occurred rainfall had total amount less than 10 mm, or mean intensity less than 5 mm·h-1,or peak intensity less than 10 mm·h-1, accounting for 66.4%, 88.8% and 79.6% of the total rainfall events, respectively. The study was of great significance to apply low-impact development to reduce runoff and non-point source pollution under condition of less rainfall amount or low mean rainfall intensity in the area. The runoff generally increased with the increase of rainfall. The threshold of regional occurring runoff was controlled by not only rainfall amount, but also mean rainfall intensity and rainfall duration. In general, there was no surface runoff when the rainfall amount was less than 2 mm. When the rainfall amount was between 2 to 4 mm and the mean rainfall intensity was below 1.6 mm·h-1, the runoff was less than 1 mm. When the rainfall exceeded 4 mm and the mean rainfall intensity was larger than 1.6 mm·h-1, the runoff would occur generally. Based on the results of the SWMM simulation, three regression equations that were applicable to regional runoff amount and rainfall factors were established. The adjustment R2 of the three equations were greater than 0.97. This indicated that the equations could reflect well the relationship between runoff and rainfall variables. The results provided the basis of calculations to plan low impact development and better reduce overflow pollution in local drainage area. It also could serve as a useful reference for runoff study in similar drainage areas.

Combination of powdered activated carbon and powdered zeolite for enhancing ammonium removal in micro-polluted raw water.

Even zeolite is promising in ammonia pollution disposing, its removal efficiency is frequently interfered by organics. As activated carbon has good removal efficiency on organic contaminants, combination of two adsorbents may allow their respective adsorption characteristics into full play. This paper provides a performance assessment of the combination for enhancing ammonium removal in micro-polluted raw water. Gel-filtration chromatography (GFC) was carried out to quantify the molecular weight (MW) range of organic contaminants that powdered activated carbon (PAC) and powdered zeolite (PZ) can remove. The polydispersity difference which also calculated from GFC may indicate the wider organic contaminants removal range of PAC and the relatively centralized removal range of PZ. The jar tests of combination dosing confirm a synergistic effect which promotes ammonium removing. Nevertheless, it also shows an antagonism hindering the due removal performance of the two adsorbents on CODMn, while it is not much evident on UV254. Furthermore, a comparison study with simulated coagulation-sedimentation process was conducted to evaluate the optimum dosing points (spatial and temporal) of PAC and PZ among follows: suction well, pipeline mixer, early and middle phase of flocculation. We suggest to dose both two adsorbents into the early phase of flocculation to maximize the versatile removal efficiency on turbidity, ammonium and organic contaminants.

[Agricultural Non-Point Source Pollutants Removal by Enhanced Riverbank Interception Facilities Under Different Operating Conditions].

Treatment of agricultural non-point source pollution in a pilot scale by enhanced riverbank interception facilities with different temperatures, rainfall intensities and rainfall interval conditions was investigated. The results showed that if water temperature decreased from 20 degrees to 4. 3 degrees, the removal efficiencies of COD, TN, NH4+ -N, TP decreased by 15. 58%, 48. 93%, 42. 26%, 57. 75% respectively, and no significant effect on the removal of SS was found. If rainfall intensity increased doubled from 0.65 mm.min-1 to 1. 30 mm.min-1, it made the average removal rate of COD decrease 15. 19%, TN, NH4+ -N did not change and removal efficiency of TP increased 11.21%. But the total removed quantity per unit area of COD, TN, NH4+ -N, TP increased by 26. 27%, 68. 3%, 32. 6%, and 104. 2%. If rainfall interval increased from 2 to 4 days, it would make NH4+ -N, TN removal efficiencies increase by 19. 31%, 13. 95% respectively, and the removed quantity per unit area of TP increased 71. 43%, but the total removal quantity of TP was limited.

[Research of controlling condition for aeration stabilization pond dealing with sanitary waste of countryside].

According to research of some problems, such as the hydraulic detention time that aeration stabilization pond deals with sanitary waste of countryside, dissolved oxygen in pond during the process of aeration, the concentration distribution of sludge and different aeration periods affecting on the treatment efficiency, we can acquire good treatment efficiency and energy consumption of economy. The results indicate that under the aeration stabilization pond of this experiment, 4 d is the best hydraulic detention time with this aeration stabilization pond. Time of the discontinuous running aeration should be greater than 15 min. The concentration distribution of sludge can reach equilibrium at each point of aeration stabilization pond between 2 min and 10 min. The best aeration period of dislodging the pollutant is 0.5 h aeration/1.0 h cut-off.

[Dynamic rule of organic matter removal in vertical-flow constructed wetland].

Based upon the analysis of the removal rate and form change of the organic pollutants with the different height of the vertical-flow constructed wetland, it comes to the conclusion of the average longitudinal removal rate of variant forms organics and presents the influent concentration and the hydraulic load curve. The results indicated that: Under this experimental condition, the reduction of the organics in the vertical subsurface flow constructed wetland mainly occurred within the 0-10 cm substrate below the pipe distributor. In the meantime, the smaller the hydraulic load of influent, the higher the removal ratio of the organic pollutants in the substrate section. Under the condition that the vertical subsurface flow constructed wetland used the coarse sands as the substrate and kept the influent hydraulic load less than or equal to 0.5 m3/(m2 x d), the effective height of the organics removal was 60 cm. It also showed that the average degradation rate of different kinds of the organic pollutants has a maximum value in the 0-10 cm substrate section below the pipeline. Moreover, the degradation ratio of different kinds of the organics is in significant decreasing tendency with increasing the depth of the longitudinal direction along the pipe. Using sands as the substrate in the vertical subsurface flow constructed wetland, the relationship of the influent concentration and influent hydraulic load can be expressed by formula:(c(in) - c(out)) x q = 1107.02-2.96 c(in) x q.

[Clogging mechanism in vertical-flow constructed wetland: clogging cause and accumulation distribution characteristics].

In order to solve the problem of clogging in the vertical-flow constructed wetland, the reason of clogging and the distribution rule of clogging substance in the vertical-flow constructed wetland was investigated first. Based on the correlativity of accumulation quantity and banked-up water area or lacuna rate in constructed wetland systems, the results show that the accumulation of non-filter materials is the main reason of clogging. The banked-up phenomenon will occur when the accumulation of non-filter materials is more than 18.23 mg in the per milliliter substrate. Under the condition of this experiment, the clogging phenomenon is easy to take place around current outlet, and accumulation materials mainly distribute in the 10-20 cm upper layer under water pipe. In the substrate, the accumulation degree of that of non-filter inorganic is more obvious than non-filter organic, with the trend of migrating along the water direction. The accumulation of organic and the depth of substrate is negatively correlated, i.e. deeper substrate,less organic content. The organic content in the surface layer of substrate is higher than that in other layers after banking up.

[Difference between subsurface wetlands for different water treatment].

By analysis of oxygen balance and material balance as well as empirical study, contribution of root oxygenation, water-carried oxygen and plant absorbance of nutrient in subsurface wetlands (SW) was examined, and free drainage in substrate was also adopted to check its effect on air transfer. The results showed that plant play important role when SW treating surface water with low concentration of contaminants. In such case, root oxygenation and water-carried oxygen sustains the substrate aerobic and so effluent DO > 0; N and P removal is stable for plant absorbance and media adsorption. However, in the case of higher load, namely domestic wastewater, role of root oxygenation becomes < or = 20% and effluent DO approximately 0. It is also found that amount of nitrate and nitrite bacteria are only 1/1 000 - 1/100 of amonifying bacteria in saturated substrate, which has strong negative effect on anti-clogging and nitrogen removal. Nitrogen removal percentage is often < or = 20%. Phosphorous initial removal percentage is 54%, but decreases to 5% after a year operation for the consumption of absorption capacity. Because pollutants load is too high for root oxygenation and plant absorbance and media absorption, limitations do exist in SW for domestic wastewater treatment. It is necessary to take use of air-reoxygenation in SW. The results showed that COD, NH4(+) -N, TN and TP removal percentage of SW with high water lever was 79%, 34%, 36% and 34% and those of SW with free drainage was 79%, 88%, 14%, 69%, which suggest that only air transfer is used properly, total nitrogen removal could be achieved in single-stage wetland.

[Enhancement strategies in vertical flow constructed wetlands for domestic wastewater treatment].

Because pollutants load is too high for root oxygenation, plant absorbance of nutrient and media absorption in vertical down flow wetland to remove pollutants from domestic wastewater, some deficiency do exist, which were confronted by pre-treatment enhancement, media optimization and technological revolution in this study. The strategies include chemically enhanced settlement, pre-aeration, addition of N-adsorption media and P"adsorption media, high, middle and low water level and dynamic saturation line within the soil profile. Chemically enhanced settlement can not only remove P but reduce 63% of the surface area of the connected wetland, but can not remove N effectively. Pre-aeration just increase 1% of the removal percentage of NH4+-N. The wetland with addition of N-adsorption media has the initial removal percentage of 84 % , which decreases to 64 % for consumption of adsorption capacity in 5 months. The saturation time of P-adsorption media is longer for the lower load of P on wetland. So, nitrogen removal only can be achieved by microorganism. Under stable saturation line, removal percentage of COD, NH+ -N, TN, TP in wetland with high water level is 50% , 21% , 32% , - 26% , and those in wetland with middle water level is 53% , 48% , 48% , - 14%, and those in wetland with low water level is 74 % , 96% , 35 % , 22 % . Dynamic saturation line was proposed and Cyclic Batch Subsurface Wetland (CBSW) was invented in this paper, which achieves removal percentage of 67% , 62%, 53%, 33% individually for COD, NH4+ -N, TN, TP. The result suggest that CBSW enhances N removal ability in single-stage wetland and perform better in anti-clogging, and so is the best enhancement strategy in subsurface wetland for domestic wastewater treatment.