Flow Concentration Research Articles

Elimination of micropollutants in four test-scale constructed wetlands treating combined sewer overflow: Influence of filtration layer height and feeding regime

Municipal wastewater can contain large amounts of organic micropollutants. Some of these substances are harmful to the environment, even at low concentrations, e.g. when being discharged untreated into surface water bodies in case of combined sewer overflows (CSOs) during or after heavy rainfall events. Constructed wetlands can be very effective in treating CSOs. To date, there have only been few investigations about the retention of micropollutants using retention soil filters (RSFs), which basically are vertical flow constructed wetlands with an additional retention area. Thus, focus of this study was set on the interaction between dry periods, loading events, filter operation time, and the resulting removal of micropollutants originating from CSOs. The removal of 1-H-benzotriazole, carbamazepine, diclofenac, metoprolol, sulfamethoxazole and bisphenol A was examined in four test-scale RSFs. Removal efficiencies of approximately 70% were found for metoprolol. 1-H-benzotriazole, diclofenac and bisphenol A were removed moderately between 30 and 40%. For carbamazepine and sulfamethoxazole, negative retention rates were found. No significant correlations were found between removal efficiencies and the length of the antecedent dry period and/or filter operation time. However, the study showed that removal efficiencies depend strongly on respective inflow concentrations. Thickness of the filter layer seems to have an influence as well; does not lead to uniform results, though.

Insights from using in-situ ultraviolet–visible spectroscopy to assess nitrogen treatment and subsurface dynamics in a regenerative stormwater conveyance (RSC) system

Regenerative stormwater conveyance (RSC) is a recently developed stormwater control measure that marries the concepts of bioretention and stream restoration. RSC mitigates stormwater runoff by converting surface flow to subsurface seepage using a series of pools and riffles built over a sand media bed. Subsurface seepage flows through media and exits the RSC beneath the outlet weir. Previous studies on RSC pollutant mitigation have focused on surface flow discharges from the RSC. To date, no known research has been conducted on the potential pollutant contributions of RSC seepage, despite the fact that this water also enters receiving waters. This research used Multi-Point Sampling coupled with in-situ ultraviolet–visual spectroscopy to measure nitrogen in seepage during simulated storm events (n = 9) at a field-scale RSC in Raleigh, North Carolina. Calibrations between light absorbance and concentrations were acceptable (Nash-Sutcliffe coefficient > 0.65) for nitrate and total ammoniacal nitrogen (TAN) and very good (Nash-Sutcliffe coefficient > 0.90) for total Kjehdahl nitrogen (TKN). Early storm simulations revealed some initial nutrient flushing from the substrate, which subsided by the third simulation. Overall, subsurface seepage nitrate, TAN, and TKN concentrations were lower by 29%, 57%, and 4% relative to storm inflow concentrations, respectively. Computed subsurface nitrogen concentrations demonstrated temporal variability, highlighting dynamic transport and biogeochemical transformations in saturated and unsaturated conditions. Nitrogen concentrations were lower in seepage than in surface flow; however, due to the high volume of runoff converted to seepage, nitrogen loads discharged in seepage can be larger than those of surface flow. Further research is needed to examine subsurface pollutant reductions under varying hydrologic and seasonal conditions.

The Efficiency of Constructed Wetlands and Algae Tanks for the Removal of Pharmaceuticals and Personal Care Products (PPCPs): a Systematic Review

Constructed wetlands (CWs) and algae tanks are regarded as promising polishing steps to treat wastewaters for the removal of persistent organic pollutants, such as pharmaceuticals and personal care products (PPCPs). In this systematic review, we provide a synthesis of the relationship between the presence of the most widely studied PPCPs in domestic wastewater and the conformation of the CWs and algae tanks constructed to treat them. The six drugs most commonly found in the reviewed articles were caffeine, carbamazepine, diclofenac, ibuprofen, ketoprofen, and naproxen. Removal efficiency of the PPCPs was evaluated by means of the following selected parameters: hydraulic retention time (HRT), system flow rate, temperature, inflow concentration, and average removal rate. The average removal rate of PPCPs in CWs showed a positive and moderate relationship with the HRT (r = 0.346). A different flow configuration and plant species acted better for different target compounds. The average concentration reduction ranged from 80% for caffeine to zero reduction levels in some conformations for carbamazepine, diclofenac, and ketoprofen. There was a wide variation in the concentration reduction of different plant genera or unplanted tanks, ranging from 81% (caffeine using Phragmites sp.) to no reduction in an unplanted tank for diclofenac. The algae tanks were more efficient in removing most of the six target compounds than the wetlands. Removal rates ranged from 50% for ketoprofen to 16% for naproxen. According to our results, a combination of CW systems and algae tanks might be an effective alternative for the removal of PPCPs from domestic wastewater.

Study on the Permeability and TSS Removal Efficiency of Permeable Pavement Using Constant Head Particle Loading Test

Kim, J.Y.; Choi, Y.S.; Kim, T.Y.; Lee, S.H., and Kwon, S., 2019. Study on the permeability and TSS removal efficiency of permeable pavement using constant head particle loading test. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 236-240. Coconut Creek (Florida), ISSN 0749-0208.Climate changes cause extreme disasters frequently such as storms, floods and tsunmai in lowlands and coastal areas. A new paradigm for the prevention of disaster damages has been required. To date, LID technologies using porous materials has been paid attention to control direct runoff, floods and NPSs. Permeable pavement among LID technologies which prevent floods and reduce NPSs can be actively applied to sidewalks, parking lots and driveways in lowlands and coastal areas. However, the loss of permeability in the material matrix has been considered as a critical issue when pore is clogged by particles for maintaining the constructed facility in the field. Herein, we conducted particle loading test at constant head to obtain the permeability coefficient and TSS removal efficiency to evaluate the cyclic performance of the permeable pavement system, and further determine their correlation. We found that the change of permeability coefficient was 273 ∼ 72 mm/s when the ∼ 4.2 kg/m2 particles were loaded for 60 minutes. Trend of permeability coefficient depends on amount of particle per time. This means that loading particles in a short time make more clogging than a long time. The TSS removal efficiency was >80% at different hydraulic gradient and inflow concentration. Trend of TSS removal efficiency increased as particles were loaded. The correlation between the permeability coefficient and TSS removal efficiency is inversely proportional. Although the results will vary depending on the specification of the pavement system, this method can be used to estimate the effective replacement period with further researches.

Analysis of Flow Dynamics and Outcomes of Cerebral Aneurysms Treated with Intrasaccular Flow-Diverting Devices.

Intrasaccular flow diversion offers a promising treatment option for complex bifurcation aneurysms. The purpose of this study was to compare the flow conditions between successfully occluded and incompletely occluded aneurysms treated with intrasaccular devices. The hemodynamics in 18 completely occluded aneurysms after treatment with intrasaccular devices was compared against 18 that were incompletely occluded at follow-up. Hemodynamic and geometric parameters were obtained from computational fluid dynamics models constructed from 3D angiographies. Models of the intrasaccular devices were created and interactively deployed within the vascular models using posttreatment angiography images for guidance. Hemodynamic and geometric variables were compared using the Mann-Whitney test and univariate logistic regression analysis. Incomplete occlusion was associated with large posttreatment mean aneurysm inflows (P = .02) and small reductions in the mean inflow rate (P = .01) and inflow concentration index (P = .03). Incompletely occluded aneurysms were larger (P = .002) and had wider necks (P = .004) than completely occluded aneurysms and tended to have more complex flow patterns, though this trend was not significant after adjusting for multiple testing. The outcome of cerebral aneurysm treatment with intrasaccular flow diverters is associated with flow conditions created immediately after device implantation. Flow conditions unfavorable for immediate and complete occlusion seem to be created by improper positioning or orientation of the device. Complete occlusion is more difficult to achieve in larger aneurysms, aneurysms with wider necks, and aneurysms with stronger and more complex flows.

Flow-splitting-based computation of outlet boundary conditions for improved cerebrovascular simulation in multiple intracranial aneurysms.

Image-based hemodynamic simulations have great potential for precise blood flow predictions in intracranial aneurysms. Due to model assumptions and simplifications with respect to boundary conditions, clinical acceptance remains limited. Within this study, we analyzed the influence of outflow-splitting approaches on multiple aneurysm studies and present a new outflow-splitting approach that takes the precise morphological vessel cross sections into account. We provide a detailed comparison of five outflow strategies considering eight intracranial aneurysms: zero-pressure configuration (1), a flow splitting inspired by Murray's law with a square (2) and a cubic (3) vessel diameter, a flow splitting incorporating vessel bifurcations based on circular vessel cross sections (4) and our novel flow splitting including vessel bifurcations and anatomical vessel cross sections (5). Other boundary conditions remain constant. For each simulation and each aneurysm, we conducted an evaluation based on common hemodynamic parameters, e.g., normalized wall shear stress and inflow concentration index. The comparison of five outflow strategies for image-based simulations shows a large variability regarding the parameters of interest. Qualitatively, our strategy based on anatomical cross sections yields a more uniform flow rate distribution with increased aneurysm inflow rates. The commonly used zero-pressure approach shows the largest variations, especially for more distal aneurysms. A rank ordering of multiple aneurysms in one patient might still be possible, since the ordering appeared to be independent of the outflow strategy. The results reveal that outlet boundary conditions have a crucial impact on image-based blood flow simulations, especially for multiple aneurysm studies. We could confirm the advantages of the more complex outflow-splitting model (4) including an incremental improvement (5) compared to strategies (1), (2) and (3) for this application scenario. Furthermore, we discourage from using zero-pressure configurations that lack a physiological basis.

Highly heterogeneous interior structure of biofilm wastewater for enhanced pollutant removals

Biofilm processes are widely used in wastewater treatment. The biofilm has highly heterogeneous interior structure, which can significantly affect the transport processes and the biological reactions over the biofilm. This study for the first time detailed the complicated velocity and concentration fields of substrate in a real biofilm structure. With a real biofilm interior being profiled and meshed to numerical solutions, the flow-through mode has significant distortion of inflow velocity fields and concentration distributions, which lead to enhanced biological reactions at regimes nearby major pores. Conversely, the crossflow mode depends weakly on the biofilm interior structure. The uniform biofilm model fails to describe the real biofilm processes. Future research needs based on real biofilm structures were discussed.

Machine Perfusion of Liver Grafts With Implantable Oxygen Biosensors: Proof of Concept Study in a Rodent Model.

Background.Normothermic machine perfusion (NMP) is emerging as a novel preservation strategy in liver transplantation, but the optimal methods for assessing liver grafts during this period have not been determined. The aim of this study was to investigate whether implantable oxygen biosensors can be used to monitor tissue oxygen tension in liver grafts undergoing NMP.Methods.Implantable phosphorescence-based oxygen sensors were tested in 3 different experimental groups: (1) in vivo during laparotomy, (2) during NMP of liver grafts with an acellular perfusate (NMP-acellular), and (3) during NMP with perfusate containing red blood cells (NMP-RBC). During in vivo experiments, intrahepatic oxygen tension was measured before and after occlusion of the portal vein (PV). In NMP experiments, intrahepatic oxygen tension was measured as a function of different PV pressure settings (3 vs 5 vs 8 mm Hg) and inflow oxygen concentration (95% O2 vs 6% O2).Results.In vivo, intrahepatic oxygen tension decreased significantly within 2 minutes of clamping the PV (P < 0.05). In NMP experiments, intrahepatic oxygen tension correlated directly with PV pressure when high inflow oxygen concentration (95%) was used. Intrahepatic oxygen tension was significantly higher in the NMP-RBC group compared with the NMP-acellular group for all conditions tested (P < 0.05).Conclusions.Implantable oxygen biosensors have potential utility as a tool for real-time monitoring of intrahepatic oxygen tension during NMP of liver grafts. Further investigation is required to determine how intrahepatic oxygen tension during NMP correlates with posttransplant graft function.

Seasonal Efficacy of Vegetated Filter Strips for Phosphorus Reduction in Surface Runoff

A vegetated filter strip (VFS) is a measure commonly implemented in agricultural landscapes for the purpose of improving water quality. However, much of the evidence to support their effectiveness comes from warm regions dominated by rainfall driven runoff. This study assessed the performance of VFS plots and compared them with annual crop strips to reduce phosphorus (P) levels in runoff in the cold climate of the Canadian Prairies. Analysis of water samples from 22 events during the study indicated no significant difference in the inflow and outflow concentrations of total dissolved P (TDP) or total P (TP) for either the VFS or the annual crop strips. Although the VFS plots had little effect on TDP or TP during the spring, they performed better during the growing season, reducing mean TP concentrations in five out of seven, or 71%, of these events. The VFS plots did not perform as well during the fall events, with the overall mean TP concentration in runoff increasing after flowing through the filters during this time period.

Estimation of Reservoir Sediment Flux through Bottom Outlet with Combination of Numerical and Empirical Methods

Sediment deposition issues for reservoirs are important in Taiwan because the severe deposition could excessively decrease the reservoir lifecycle. Extreme storm events usually can carry a massive amount of sediment into reservoirs, and deposition will happen unless the incoming material can pass through sluice gates. When it comes with high concentration, the density current flow is prone to be generated, and the bottom outlets are the most effective sluice gate to release the sediment. In order to improve the sediment release efficiency, an accurate estimation of arriving concentration and time of the density current can be useful for the reservoir management. This study develops a two-stage approach which combines a numerical model (SRH2D) and the modified Rouse equation to predict the sediment flux of the reservoir. The numerical model was verified and applied to establish the relation between inflow and dam face concentration. The modified Rouse equation then adopted this relation to estimate the proper exponential parameter. As a result, the sediment flux amount at each bottom outlet can be accurately predicted by this equation. With this means, an early warning system can be established for reservoir operation, which can improve release efficiency during typhoons.

Efficient phosphate removal from contaminated water using functional raw dolomite powder

Phosphate, when present in water, forms one of the basic nutrients that lead to eutrophication and its associated negative impacts. The use of raw dolomite powder as an adsorbent was found to be very effective in the removal of phosphates from various waters and wastewater matrices. Ayoub and Kalinian (Water Environ Fed 78:353–361, 2006) reported phosphate removals, amounting to 100%, over more than 300 bed volumes at inflow concentrations between 0.30 and 0.40 mg/L. This marked achievement led to the present study with the objective of defining the effects of the various parameters involved in the process and determining the optimal operating condition to achieve effective and sustainable removal efficiencies. Experimental work was conducted by passing three types of influent water and two types of wastewater jacked with a phosphate salt (KH2PO4) through a fluidized column bed of dolomite powder, where the effect of various parameters, including system operation mode, adsorbent particle size, rate of flow through the bed (contact time), initial phosphate concentration, influent pH, and the presence of competing anionic solutes on the adsorption of phosphate was evaluated. The results asserted that the most effective mode of operation for the system was the fluidized bed configuration. Results further showed that the smaller-sized dolomite powder (< 0.074 mm) sustains better adsorption. Also, higher contact time and lower feed phosphate concentration result in increased adsorption. Adsorption capacity was found to decrease with increased influent pH values. Competitive adsorption with existing anions was noted to occur, leading to reduced efficiency in phosphate removal. The Thomas and Yoon–Nelson models were deemed to agree best with the experimental data, while the Thomas model was determined to be the most descriptive of the column runs and to produce the most accurate predictive results. The use of dolomite as an adsorbent in the removal of phosphates, considering its wide availability, ease of application and regeneration capability, if operated under optimal conditions as determined by the present study, will present a highly sustainable process with added advantages over the more complex and costly adsorbents.

Stent-induced vessel deformation after intracranial aneurysm treatment – A hemodynamic pilot study

BackgroundStent-assisted coiling has become an important treatment option for intracranial aneurysms. However, studies have shown that this procedure can lead to the deformation of the local vasculature. Its effect on intra-aneurysmal hemodynamics still remains unclear. MethodsPre- and post-interventional image data of three representative middle cerebral artery aneurysms are considered in this study. This includes virtually deployed stents and coils. To evaluate the proportional effect of a) vessel deformation, b) stent deployment, and c) coil placement, 24 unsteady blood flow simulations were carried out focusing on the separated effects related to intra-aneurysmal hemodynamics. Four flow parameters (velocity within the aneurysm sac, aneurysm neck inflow rate, inflow concentration index, and ostium inflow area) and four shear parameters (wall shear stress, normalized wall shear stress, shear concentration index, and high shear area) were quantified. ResultsAll of the considered flow and shear parameters, except for the shear concentration index, were clearly reduced due to treatment. Coiling and stenting caused a distinct and smaller neck inflow rate, respectively, while the impact of deformation was inconsistent among the aneurysms. Overall, coiling appears to have the strongest impact on local hemodynamics. ConclusionStent-induced vessel deformation has a clear impact on intra-aneurysmal hemodynamics. This effect is neglected by the majority of previous studies, which consider the pre-interventional state for investigating the relation of stents and hemodynamics. The findings of this pilot study suggest that while stent-assisted coiling can lead to an improved hemodynamic situation, undesired flow conditions may occur in response to treatment.

Remediation and accumulation characteristics of dissolved pollutants for stormwater in improved bioretention basins

Dissolved pollutants in stormwater are more mobile/bioavailable, and are captured via different mechanisms than particles. Column-scale bioretention basins are constructed by filling different media, which is used to study the remediation and accumulation characteristics of dissolved pollutants by improved bioretention basins (increased infiltration and adsorption capacity of the media). The media factor (ratio of specific surface area to cubic of porosity) is used to characterize the basic properties of different media, while considering the key factors: infiltration capacity, inflow concentration, recurrence interval, discharge ratio, antecedent dry period, and rainfall duration. The results showed that stormwater pollutants load reduction rate decreased with the increase of recurrence interval and discharge ratio, and increased with the increase of inflow concentration. Based on response surface methodology (RSM), a quantitative relationship model between major pollutants and influencing factors were established (R2 > 0.715), which can be used to estimate the design and operation of the media. By detecting changes in media carbon, nitrogen and phosphorus contents, the results showed that partial pollutants leaching were greater than their accumulation in the initial stage of system operation, and their contents in the media reduced during simulated rainfall. After the pollution contents tend to stabilize, the accumulated pollutants were greater than the leaching, and media pollution contents showed the trend of upper > middle > lower (corresponding to the 10, 35, and 60 cm sections of the media from top to bottom). Six enzymes closely related to the accumulation and migration of nitrogen, phosphorus and organic matter in the media were selected. Pearson correlation analysis found that: the significant correlations between the selected enzyme activity and pollutants were not consistent in bioretention system. For example, catalase was significantly correlated with all the pollutants (P < 0.01), whereas acid phosphatase was not significantly correlated with all the pollutants.

Retention Efficiency of Vegetative Filter Strips for Nitrogen in Danjiangkou Reservoir Area, Central China

Abstract To investigate the retention efficiency and mechanism of nitrogen of Vegetative filter strips (VFSs) in the Danjiangkou Reservoir area, simulated runoff discharging experiments were carried out in a new-established Bermuda VFS. The results showed that the Bermuda VFS reduced 73.1-86.1 % of surface runoff through infiltration. The outflow rate of runoff increased first and then became stable with time. The concentration reduction rates (CRRs) and load reduction rates (LRRs) of NH3-N increased initially and then decreased with the increase of inflow concentration. The average CRRs and LRRs of NH3-N in three treatments ranged 66.1-90.3 % and 90.0-96.7 %, respectively. The concentration reduction of NH3-N was primarily achieved by soil adsorption. The optimal inflow concentration of NH3-N for the optimum CRR was between 0.65 and 3.52 mg/dm3. The CRRs and LRRs of NO3-N fluctuated between 6.8-14.0 % and 72.0-77.9 % in three treatments. The concentration reduction of NO3-N was primarily achieved by plant uptake and soil microbe assimilation. The optimal inflow concentration of NO3-N for optimum CRR exceeded 6.78 mg/dm3. The CRRs and LRRs of TN increased with the increase of inflow concentrations. The average CRRs in the low, moderate and high treatments reached 9.7, 14.8 and 27.4 %, respectively, and the average LRRs reached 72.1, 74.3 and 81.2 %, respectively. The optimal inflow concentration of TN for optimum CRR exceeded 10.21 mg/dm3. The study showed that Bermuda grass can retain nitrogen in runoff efficiently and should be promoted around the Danjiangkou reservoir.

Impact of different DOM size fractions on the desorption of organic micropollutants from activated carbon

Whereas the adsorption of organic micropollutants (OMP) onto activated carbon (AC) is relatively well studied, little is known about potential OMP desorption effects, especially in real waters. In this study, the impact of different fractions of drinking water DOM on OMP desorption from AC was examined. By different pre-treatments of a raw drinking water, a high molecular weight (hmw) and a low molecular weight (lmw) DOM solution were prepared. These solutions were used as background matrix in AC adsorption/desorption batch tests, simulating a drop of the OMP inflow concentration to a fixed-bed adsorber. The tests were conducted in parallel with three AC of different pore structures (microporous, mesoporous/balanced, macroporous). The tests were evaluated with respect to the extent of OMP adsorption and its reversibility, which represents the potential extent of OMP desorption. In terms of OMP adsorption, the lmw-DOM fraction induced a higher competitive effect on OMP adsorption in comparison to the hmw-DOM fraction. In terms of their impact on OMP desorption extent, both fractions led to very similar results. In case of the macroporous AC, both DOM fractions induce an enhanced OMP desorption that can be attributed to displacement effects in both cases. For the microporous AC, an increased irreversibility of OMP adsorption was found in both cases, which shows that DOM adsorption prevents OMP desorption, independently of the size of the adsorbed DOM compounds. Whereas results from this study as well as from former studies indicate that this effect might be induced by permanent pore blockages by adsorbed DOM, further results show that there could be more complex DOM interactions that lead to the decreased desorption in case of microporous AC. Nonetheless, the very similar impact of the different DOM fractions on the reversibility of OMP adsorption indicates that the potential extent of desorption is similar in different waters (with different DOM composition) and primarily depending on the pore structure of the used AC.

The relationship between suspended solids and nutrients with variable hydrologic flow regimes

The hypothesis that “freshwater inflow variability over space and time can drive suspended solids and nutrient concentrations” was tested by comparing three micro-tidal estuaries (Guadalupe, Lavaca-Colorado, and Nueces) in Texas with different hydrologic flow regimes over three years with wet and dry conditions. In all three estuaries, Total suspended solids (TSS) was less than 50 mg/L most of the time. In the Nueces Estuary, TSS of higher than 100 mg/L occurred during frontal events. Dissolved inorganic nitrogen (ammonia+nitrite+nitrate) concentrations were most of the time lowest in the Nueces Estuary (i.e. ≤0.5μmol/L), with low inflow rates and high average salinity of 37.6. Salinity was highest in the river-estuary mouth (average salinity 38.3) of the Nueces Estuary relative to the other oceanic-side stations (average salinity 37), indicating that the system was a “reverse estuary” where evaporation exceeds freshwater inflow, resulting in net inflow of marine water into the estuary. The inverse correlation between ammonium and salinity in all three estuaries and the corresponding negative correlation between nitrite+nitrate concentrations and salinity in the Guadalupe Estuary indicate that the quantity of inflow controls nitrogen concentrations and transformations in the three estuaries. Drought conditions limited riverine transport of nitrogen and sediment to the three estuaries, demonstrating the importance of freshwater inflow to maintaining these constituents. Average silica and orthophosphate concentrations correlated positively with chlorophyll-a in combined data from all three estuaries. Silica and orthophosphate concentrations remained constant over the study period, but correlated with chlorophyll-a when suspended solid was low. Therefore, inflow dynamics drive changes in the salinity regime, suspended solids, and act to maintain nutrient concentrations.

A field investigation on ephemeral gully erosion processes under different upslope inflow and sediment conditions

Ephemeral gullies (EGs) are important erosion features that could account for as much as 70% of total erosion on the Loess Plateau of China. However, few quantitative studies have been conducted in the field on the impact and mechanism of upslope sediment runoff in EG erosion processes. A series of field rainfall simulation experiments were conducted on an artificial EG to investigate the impacts of upslope inflow with two flow rates (15 and 30 L min−1) and five sediment concentrations (20, 40, 80, 120, and 160 g L−1) on runoff and erosion processes within the EG. The results showed that the lower flow rate of 15 L min−1 increased soil loss by 26% compared with the higher inflow rate (30 L min−1). The lower inflow rate triggered greater sheet or rill erosion, whereas the higher rate mainly strengthened the incision of the main EG channel and led to increasing gully erosion. The channel shoulders expanded laterally very little, especially under the higher flow rate. Inflow sediment concentration had a major influence on EG erosion processes. With increasing sediment concentration, EG erosion and total slope erosion first increased, and then decreased. When sediment concentration exceeded 120 g L−1, the inflow sediment began to be deposited, and 120 g L−1 can be regarded as a critical value of EG erosion. These results are beneficial to establish a soil erosion model and to control ephemeral gully erosion in loess areas.

Designing green walls for greywater treatment: The role of plants and operational factors on nutrient removal

Green walls, installed on the side of the buildings, mainly for their aesthetics and micro climate benefits, could become effective on-site greywater treatment solutions. However, far more research is needed to convert these nature-based systems into low-cost water purification technologies. This process study presents the first step in development of greywater-treating green walls by examining how variation in plant spaces and operational conditions (hydraulic loading rate, inflow concentrations and intermittent drying) influence nutrient removal from light greywater. The experiment was conducted over 12 months on a large-scale pilot green wall located in a laboratory in Melbourne, Australia. The results showed that ornamental plant species can successfully adapt to greywater only irrigation regime and play an important role in nitrogen and phosphorus uptake from greywater. Higher performing plants, C. appressa, N. obliterate, M. parvifolium and L. muscari, had on average 7–10% higher TN removal than unvegetated configuration (over 88% removal overall), which is attributed to consistently high NOx uptake. On the other hand, poorer performing plants O. japonicus, P. occidentalis and N. officinale tended to leach NOx, likely due to their shallow or slow developing root systems. While low retention times hindered high TP removal from all tested configurations, high dependency on plant species and operational conditions was still observed, with C. appressa and N. obliterata being the two highest performing plants (34–53% removal during standard operation). The overall phosphorus uptake was found to improve over time, suggesting that plant growth is a significant TP removal mechanism in green walls. While drying caused a performance drop for all designs, higher performing plant species were less affected by changes in operational conditions. The tested configurations showed good resilience to sudden inflow concentration increases, suggesting green walls could be used as a robust and aesthetically attractive on-site greywater treatment system.

The role of water and mass balances in treatment assessment of a flooded natural wetland receiving wastewater effluent (Frank Lake, Alberta, Canada)

Constructed, and to a lesser extent, natural wetlands are increasingly used to treat treated wastewater effluent from small municipalities and industries. Wetland treatment efficiency evaluation typically involves comparison of solute inflow and outflow concentrations, or estimation of the export of nutrients per unit wetland area. A more holistic approach, which evaluated water and solute mass balances, in addition to seasonal changes in water quality, yielded an improved understanding of where nutrient storage occurred, long-term wetland treatment capabilities, and downstream water quality impacts of a flooded natural wetland receiving wastewater. The lowest solute concentrations in the flooded wetland were observed soon after ephemeral creek flow in the spring, increasing concentrations over the summer attributed to evaporation, and the highest concentrations under winter ice. Chloride accumulation in shoreline sediments was attributed to transpiration pumping, and high salt and phosphorus accumulation in lake and shoreline sediments were a long-term concern at Frank Lake. Limited historic data suggested water quality impacts on the receiving watershed, the Little Bow River, were significant, with about 80, 230, and 20 times increased mass fluxes for chloride, total phosphorus, and total nitrogen, respectively. The flooded wetland, Frank Lake, is not a sustainable approach to wastewater effluent treatment in its current form.

Reduction of Escherichia coli, Enterococcus faecalis and Pseudomonas aeruginosa in stormwater bioretention: Effect of drying, temperature and submerged zone

The impact of drying and temperature on the reduction of Escherichia coli, Enterococcus faecalis and Pseudomonas aeruginosa in stormwater bioretention systems with and without a submerged zone was assessed using 16 pilot-scale bioretention columns under controlled laboratory conditions. The experimental design enabled analysis of possible interactions between the factors. First outflow and event-based samples were collected. Outflow concentrations were independent of inflow concentrations and hence controlled by internal processes. Overall TSS removal was high but sensitive to bacterial synthesis. Event-based samples had significantly higher bacteria concentrations than first outflow samples, suggesting that remaining/surviving bacteria in the bioretention cells have little effect on initial peak outflow concentrations. The effect of temperature varied between bacterial species and sample types. Long dry periods seemed beneficial for bacteria reduction, but outflow bacteria concentrations peaked during the second watering after long dry periods. Submerged zones significantly reduced bacteria outflow concentrations. However, sudden temperature increases caused bioretention cells with a submerged zone to produce significantly higher bacteria outflow concentrations than before the temperature increase, which was not the case for standard cells. Bioretention cells with submerged zones may thus be poor choices for reducing bacterial concentrations in stormwater runoff in areas experiencing winter conditions. Finally, our results suggest that adsorption (e.g. further enhanced by biofilm formation) is the major mechanism governing bacteria reduction in bioretention systems.