First-order Removal Rate Research Articles

Electrochemical self-cleaning anodic surfaces for biofouling control during water treatment

Biofilm formation and growth on submerged surfaces causes numerous operational problems, ranging from hindering diffusion of pollutants to electrode surfaces during electrochemical water treatment to harboring pathogens in indoor plumbing. This work evaluates electrochemical biofilm dispersion kinetics from boron-doped diamond (BDD) surfaces in situ using optical coherence tomography microscopy to track the volume of biofilm (biovolume) on the electrode. After starting with a 75 μm thick biofilm, applying 50 mA cm−2 results in near complete biofilm removal after 60 min, with a pseudo first-order biovolume removal rate of 0.023 min−1; higher applied currents had negligible additional benefits. Thus, it appears plausible to attain biofouling mitigation through electrochemical self-cleaning of BDD electrodes, potentially via the following two-step process: 1) hydroxyl radical production on the electrode surface which oxidizes polysaccharides or other cellular materials that attach bacteria to surface, followed by 2) gas evolution on the electrode surface (beneath the biofilm), which pushes and sloughs off the biofilm. This novel approach to biofouling management can find applications in electrochemical water treatment and other important surfaces (e.g., electrodes, membrane spacers, heat exchange surfaces, interior pipe surfaces, etc.) in water treatment systems where biofilms develop and harbor microbial pathogens.

Dynamics of emerging organic contaminant removal in conventional and intensified subsurface flow treatment wetlands

Six pilot-scale treatment wetlands treating municipal wastewater were monitored for classical wastewater parameters and selected Emerging Organic Compounds (EOCs): caffeine (CAF), ibuprofen (IBU), naproxen (NPX), benzotriazole (BTZ), diclofenac (DCL), acesulfame (ACE) and carbamazepine (CBZ) on a weekly basis over the course of one year. Treatment efficacy of the wetland systems was compared to that of a municipal wastewater treatment plant adjacent to the research site (activated sludge technology). The aerated wetlands VAp and HAp, and the two-stage vertical flow system VGp + VSp showed the highest treatment efficacy (>70% removal on a mass basis) and comparable treatment efficacy to the conventional WWTP for removal of CAF, IBU, NPX, BTZ, and DCL. Annual mass removal of ACE in the WWTP was 50% and varied in the wetlands (depending on system design) from zero to 62%. On a mean monthly basis, ACE removal in the treatment wetlands VGp + VSp, VAp, HAp, R was high (> 90%) for six months of the year. Monthly mean mass removal of CBZ was negligible for the WWTP and all treatment wetland systems except H50p, which showed up to 49% mass removal in June. Monthly mean mass removals of classical wastewater parameters and readily biodegradable EOCs (represented by CAF, IBU, NPX) were most stable in the intensified wetland designs VAp, HAp, and R. A statistical analysis confirms that system complexity, aerobic conditions, and temperature have the highest correlation to overall pollutant removal in the treatment wetland systems, including EOCs of high to moderate biodegradability. First-order removal rate coefficents and temperature correction factors for EOCs are reported for the first time in the treatment wetland literature. Limitations on the use of these values in engineering design are discussed.

Evaluating organics removal performance from lagoon-pretreated swine wastewater in pilot-scale three-stage surface flow constructed wetlands

Pilot-scale three-stage surface flow constructed wetlands (SFCWs) planted with Myriophyllum aquaticum were constructed to study the organics removal performance from lagoon-pretreated swine wastewater. The removal performance of organics in the SFCWs was evaluated using deterministic and probabilistic methods and the results were consistent. The SFCWs achieved a relatively high removal efficiency (79.0–82.7%) for a wide influent COD concentration range (456–1010 mg L−1). No significant difference (p > 0.05) of COD removal efficiency and first-order removal rate constant among the various strengths of influent suggested that the present loading rates (2.74–6.06 g m−2 d−1) have not yet reached the maximum removal capacity of the SFCWs. The mean emission fluxes of methane from the SFCW units fed with different strengths of wastewater were 25–1210 mg m−2 d−1. A significantly positive correlation (p < 0.01) between methane emission fluxes and COD loading rates indicated that the anaerobic digestion of organics was an important process for organics removal in the SFCWs. No significant organics accumulation in the sediment over time suggested that plant harvest could be in favor of reducing the organics accumulation in the substrate and should be considered important during management of constructed wetlands.

The fate of polar trace organic compounds in the hyporheic zone

The hyporheic zone (HZ) is often considered to efficiently remove polar trace organic compounds (TrOCs) from lotic systems, mitigating potential adverse effects of TrOCs on ecosystem functioning and drinking water production. Predicting the fate of TrOCs in the hyporheic zone (HZ) is difficult as the in-situ removal rate constants are not known and the biogeochemical factors as well as hydrological conditions controlling the removal efficiency are not fully understood. To determine the in-situ removal efficiency of the HZ for a variety of TrOCs as a function of the biogeochemical milieu, we conducted a field study in an urban river near Berlin, Germany. Subsurface flow was studied by time series of temperature depth profiles and the biogeochemical milieu of the HZ by concentration depth profiles. These results, in conjunction with a 1D advection-dispersion transport model, were used to calculate first-order removal rate constants of several polar TrOCs in the HZ. For the majority of TrOCs investigated, removal rate constants were strongly dependent on redox conditions, with significantly higher removal rates observed under predominantly suboxic (i.e. denitrifying) compared to anoxic (i.e. Fe and Mn reducing) conditions. Compared to previous studies on the fate of TrOCs in saturated sediments, half-lives within oxic/suboxic sections of the HZ were relatively low, attributable to the site-specific characteristics of the HZ in a stream dominated by wastewater treatment plant effluent. For nine out of thirteen investigated TrOCs, concentrations decreased significantly in the HZ with relative removal percentages ranging from 32% for primidone to 77% for gabapentin. For many TrOCs, removal efficiency decreased drastically as redox conditions became anoxic. For the majority of compounds investigated here, the HZ indeed acts as an efficient bioreactor that is capable of removing TrOCs along relatively short flow paths. Depending on the TrOC, removal capacity may be enhanced by either increasing the magnitude of groundwater-surface exchange fluxes, by increasing the total residence time in the HZ or the exposure time to suboxic zones, respectively.

Evaluation of sulfamethazine removal kinetics using fixed structured bed bioreactor

ABSTRACTThe use of anaerobic biomass attached to a support has been recently presented as a good prospect in the treatment of wastewater containing recalcitrant compounds, such as sulfamethazine (SMZ). SMZ has been found in swine wastewater and sewage treatment plants, which motivates assessing their degradation by new wastewater treatment technologies. Thus, this paper describes the use of a continuous fixed structured bed bioreactor for the purpose of evaluating SMZ removal kinetics present in lab-made wastewater. The analysis of SMZ used online solid-phase extraction coupled to liquid chromatography/tandem mass spectrometry (SPE online-LC-MS/MS). Chemical oxygen demand (COD) was also monitored to evaluate the organic matter removal. The bioreactor was operated under mesophilic conditions (30C), with a hydraulic retention time of 24 h. In order to evaluate SMZ removal, four different concentration levels were studied: 200, 400, 600, and 800 ng L−1. COD removal efficiency obtained for filtered effluent kept at 91.01% and there was no interference due to the increase of SMZ concentration. For SMZ, the removal efficiencies were of for 200 ng L−1 concentration level; for 400 ng L−1; for 600 ng L−1, and for 800 ng L−1. COD removal kinetics presented a first-order apparent removal rate constant () of h−1. SMZ also showed a first-order apparent removal rate constant of h−1 for the following concentrations levels: 200, 400, 600, and 800 ng L−1.

Numerical modeling study to compare the nutrient removal potential of different floating treatment island configurations in a stormwater pond

Constructed wetlands, which are commonly used in wastewater treatment, are difficult to use for stormwater treatment, because the water level variation in a stormwater pond makes it difficult for rooted vegetation to survive. As an alternative, vegetation can be grown on floating mats, called floating treatment islands (FTI), with roots extending downward into the water. Nutrient removal is achieved through uptake and trapping by the matrix of roots and bio-film. The overall treatment provided by a pond with FTIs depends on the fraction of flow exposed to the root zone. This study used numerical modeling to study the flow through the root zone, with the goal of determining which configuration of FTI achieved the greatest overall treatment. Six different configurations were considered, all with root zone volume equal to 11% of the pond volume. The permeability of the root zone was estimated using velocity measurements within real floating vegetation. A first-order removal rate within the root zone (kr) was estimated from removal rates reported in the literature. Preliminary studies considered the similarity in flow and removal between systems of different physical scale. Geometric similarity of the root zone guaranteed flow similarity within the root zone. To achieve performance similarity (same mass reduction), systems need to have the same non-dimensional removal rate (krtn, with tn the nominal residence time of the pond). The consideration of different FTI configurations showed that wakes generated by upstream FTIs lowered the mass removal of downstream FTIs, so that segmenting a single large FTI into multiple smaller FTIs in series did not improve overall nutrient removal. However, segmenting a single FTI into a pair of parallel FTIs did improve the nutrient removal, and this configuration provided the best pond-scale removal.

Removal of nutrients, trace organic contaminants, and bacterial indicator organisms in a demonstration-scale unit process open-water treatment wetland

A demonstration-scale unit process open-water wetland system was built to treat water from an effluent-dominated river (i.e., a river in which the flow consisted almost entirely of municipal wastewater effluent from May to October). Monitoring of the system over a two-year period indicated effective removal of nitrate, with concentrations decreasing by over 90% during summer. The temperature-independent areal first-order nitrate removal rate constant, k20, ranged from 61.7 to 68.1myr−1 after the microbial community was established, which is significantly higher than values typically observed in full-scale surface flow wetlands. The beta-adrenergic blockers, atenolol and propranolol, as well as the antiviral drug, acyclovir, were removed by photolysis and biotransformation in the wetland biomat, whereas the antiepileptic drug, carbamazepine, exhibited little removal. The bacterial indicators E. coli and enterococci decreased substantially during summer, mainly through sunlight exposure. Models of contaminant removal based upon measured flow rates and performance data collected at a similar pilot-scale system agreed well with measured data for nitrate and the trace organic contaminants. The model accurately predicted removal of enterococci but systematically over-predicted the removal of E. coli. During the two-year study period, routine maintenance was necessary to prevent colonization of the water surface with duckweed (Lemna spp.). Unit process open-water (UPOW) wetlands may offer a low-cost means of improving water quality in natural treatment systems that can be integrated with conventional surface-flow wetlands and other managed natural systems. The quantitative models of contaminant removal described in this study can be used to design natural treatment systems that balance the needs for local water quality requirements, available land and site-specific requirements.

SUSTAINABLE NITROGEN REMOVAL USING APPROPRIATE TECHNOLOGIES

Nitrogen and phosphorus are two major pollutants that lead to eutrophication, adversely impact ecosystems, and lead to degradation of water quality, which impacts human health and sustainability. Pollution from point sources like wastewater and industry discharge is easier to control than non-point source pollution due to agricultural runoff and related activities. The USEPA is considering more strict standards for nitrogen and phosphorus discharge from point sources. The objective of this study was to use an appropriate low-cost wastewater technology to demonstrate removal of nitrogen from wastewater discharge using rotating biological contactors (RBCs) using different C:N ratios. The first-order nitrogen removal rate constant was found to be about 3.88 day-1 in experimental reactor systems, using RBC media from a local wastewater treatment plant (Greater Peoria Sanitary District). Phase I experiments, at C:N ratio of 2:1, with nitrogen removal rates of 60% in a single flow-through system. Phase II experiments for the limited carbon availability condition showed that the removal rate constant reduced by 30% and N-removal efficiency dropped to around 48%. Modeling showed that even under these conditions, multiple bioreactors operated in series could help achieve design treatment goals. The system achieved stability within a week of operation. Economics and sustainability issues are analyzed to determine if the process developed in this research is scalable to pilot-and full-scale conditions.

Application of a full-scale newly developed stacked constructed wetland and an assembled bio-filter for reducing phenolic endocrine disrupting chemicals from secondary effluent

To mitigate the detrimental risk of residual phenolic endocrine disrupting chemicals (PEDCs) from the discharge of sewage treatment plants (STPs) and to increase the utilization of constructed wetlands (CWs), both a stacked CW (SCW), comprising vertical and horizontal flow CWs, and an assembled bio-filter (ABF) were developed and their capability to remove PEDCs from STP discharge at high hydraulic loading rates (HLRs) of 0.5–2.0 m/d evaluated. The SCW and ABF showed different performance on PEDCs removal because of process structural difference. The removal percentages of PEDCs were associated with their octanol-water partition coefficients (LogKow), except 4-nonlyphenol (4-NP) whose apparent removal rate was affected by its precursors, and declined in the order of triclosan (TCS) at 80% and 69%, 4-t-octylphenol (4-t-OP) at 58% and 51%, estrone (E1) at 48% and 44%, and bisphenol-A (BPA) at 45% and 32% in the SCW and ABF systems on average, respectively. The efficiencies of SCW and ABF were superior to the single type of CWs, such as surface flow CW, vertical flow CW, and horizontal flow CW, in terms of removal rates or first-order removal rate constants. Recommended value of HLR for optimal utilization of SCW and ABF to ensure essential removal of PEDCs from STP discharge was between 1.5 and 2.0m/d.

Effects of wetland restoration on nitrate removal in an irrigated agricultural area: The role of in-stream and off-stream wetlands

Eleven in-stream and five off-stream wetlands were restored in the southern portion of the Flumen River basin, an intensively irrigated agricultural area located in NE Spain, to evaluate their efficiency for nitrate removal and to assess the factors affecting their performance. Samples were taken during different periods of the year during 2011–2014 to evaluate the influence of agricultural activities during the two years following their completion. Nitrate concentration was significantly higher in the in-stream wetlands, showing a clear dilution effect caused by the inputs of the irrigation return flows. The patterns followed by the first-order nitrate removal rate constant were different for in-stream and off-stream wetlands and during irrigation and non-irrigation seasons. During non-irrigation seasons, the nitrate outflowing concentration was found to be negatively correlated (p<0.01) to the first-order nitrate removal rate constant for in-stream wetlands, indicating that high nitrate inputs may restrict the effectiveness of the wetlands. Temperature and dissolved oxygen were also found to significantly influence the performance of off-stream wetlands during non-irrigation seasons, but only dissolved oxygen promoted the nitrate removal during the irrigation period, indicating the influence of the seasonal factor on nitrate and wetlands dynamics. The results of this study showed that although a longer time is required to achieve optimal wetland development, wetlands can be used as buffer zones that effectively remove nitrates. This study emphasizes the influence of the agricultural seasonality of the factors affecting nitrate removal in wetlands, expanding the information provided by similar studies and validating a model that is applicable to a wide range of agricultural, hydrological and seasonal conditions.

Anodic TiO2 nanotube layer directly formed on the inner surface of Ti pipe for a tubular photocatalytic reactor

We demonstrated the successful water treatment performance of a continuous-flow tubular TiO2 nanotube reactor made of Ti pipe where a TiO2 nanotube (TNT) layer was directly formed on the inner wall by an electrochemical anodization process. A cylindrical UV lamp was inserted into the pipe to irradiate the inner TNT surface as a light source. To optimize the thickness of TNT layer on Ti pipe, TNT layers with 1, 5 and 10μm thickness were prepared and their photocatalytic activities were tested for the degradation of various organic substrates (acid orange 7 (AO7), dichloroacetate (DCA), and 4-chlorophenol (4-CP)) under UV illumination. The TNT layer with 10μm thickness showed the highest photocatalytic activity, with first-order removal rate constants (k:min−1) of 0.019, 0.039, and 0.025 for AO7, 4-CP, and DCA, respectively. The directly formed TNTs (10μm thickness) on Ti pipes in the continuous-flow tubular TNT reactor, having a strong adhesiveness and a high surface area, enabled the successful degradation of organic compounds and to have kept the activity without decrease during the repeated cycles and long-term experiments. The photocatalytic performance of the tubular TNT reactor was tested with a higher concentration, smaller volume ([4-CP]0=100μM, solution vol.=15mL) and a lower concentration, larger volume ([4-CP]0=20μM, solution vol.=100mL) in the circulation-flow mode (20mLmin−1). A good performance was achieved under the low intensity UV illumination (≈2mWcm−2) with a half-life of ca. 50min and ca. 11h with 80% and 79% removal of TOC for the above two test conditions, respectively. The proposed tubular TNT reactor can be an effective option in the design of continuous flow-type photocatalytic reactors for practical water purification.

Removal of the pharmaceuticals ibuprofen and iohexol by four wetland plant species in hydroponic culture: plant uptake and microbial degradation.

We aimed at assessing the effects of four wetland plant species commonly used in constructed wetland systems: Typha, Phragmites, Iris and Juncus for removing ibuprofen (IBU) and iohexol (IOH) from spiked culture solution and exploring the mechanisms responsible for the removal. IBU was nearly completely removed by all plant species during the 24-day experiment, whereas the IOH removal varied between 13 and 80 %. Typha and Phragmites were the most efficient in removing IBU and IOH, respectively, with first-order removal rate constants of 0.38 and 0.06 day(-1), respectively. The pharmaceuticals were taken up by the roots and translocated to the aerial tissues. However, at the end of the experiment, plant accumulation constituted only up to 1.1 and 5.7 % of the amount of IBU and IOH spiked initially. The data suggest that the plants mainly function by facilitating pharmaceutical degradation in the rhizosphere through release of root exudates.

Active removal of ibuprofen by Money plant enhanced by ferrous ions

In this study, the removal of ibuprofen (IBP), a pharmaceutical compound, from aqueous media by Money plant (Epipremnum aureum) was investigated. The effect of ferrous iron (Fe2+) on enhancing the IBP removal rate was also analyzed. The first-order removal rate constants showed higher values for lower IBP initial concentrations in the range of 0.20–0.28 d−1 for an initial concentration of 125 μg L−1 to 0.03–0.13 d−1 for an initial concentration of 1000 μg L−1. Introducing ferrous iron to the aqueous media enhanced the first-order removal rate constant up to 6.5 times in a 3 d time period. Along with the removal of IBP from the media, the endogenous concentration of H2O2 also decreased presumably by the production of hydroxyl radical (OH). Reduction in the endogenous H2O2 concentration was recorded to be 38% and 98% in the absence and presence of Fe2+ respectively in the first day and the H2O2 level remained considerably low until day 7 which then gradually increased slightly. Simultaneous reduction of IBP and endogenous H2O2 concentration could be due to the reaction of IBP with OH and presumably OH production itself accelerated via Fenton reaction. In addition, presence of sodium bicarbonate (NaHCO3) as OH scavenger in the system showed reduction of first-order removal rate constant from 1.30 d−1 to 0.07 d−1 which could be a possible evidence of biological advanced oxidation process which is believed to play an important role in phytoremediation.

Green Technology for the Removal of Chloro-Organics from Pulp and Paper Mill Wastewater

This study evaluates the treatment efficiency of a horizontal subsurface-flow constructed wetland (HSSF-CW) for the removal of chloro-organic compounds from pulp and paper mill wastewater. The surface area of the HSSF-CW unit was 5.25 m² and was planted with Colocasia esculenta. The wastewater was characterized for different chloro-organic compounds, that is, adsorbable organic halides (AOX), chlorophenolics, and chlorinated resin and fatty acids (cRFAs). Under a hydraulic retention time of 5.9 days, the average AOX, chlorophenolics, and cRFA removal from wastewater was 87, 87, and 93%, respectively. Some of the chlorophenolics were found to accumulate in the plant biomass and soil material. The mass balance studies show that a significant fraction of chlorophenolics and cRFA was degraded in the constructed wetland system. Modeling studies were carried out to estimate the first-order area-based removal rate constants (k) for chemical oxygen demand removal. The HSSF-CW was found to be an effective treatment technology for the remediation of pulp and paper mill wastewater.

Nitrogen removal in an ecological ditch receiving agricultural drainage in subtropical central China

Nitrogen (N) loss from agricultural field can cause eutrophication in downstream freshwater systems. Ecological ditches (eco-ditches) which are engineered to mitigate N loss from agricultural runoff. This study presents an analysis of water quality data for a 200m long eco-ditch treating agricultural drainage in subtropical central China. Inflow concentrations of total N (TN) ranged from 2.3 to 3.1mgl−1 and typically contained 1.1–1.7mgl−1 nitrate (NO3−-N) and <0.4mgl−1 ammonium (NH4+-N). Mean concentration removal efficiencies (η) in the eco-ditch for TN, NO3−-N, and NH4+-N were 75.8, 63.7, and 77.9%, respectively. Mean area-based first-order removal rate constant (J) and removal rate constant (k) of TN were 942.1mg-Nm−2d−1 and 1.11md−1, respectively. Outflow from the eco-ditch typically contained <0.85mgl−1 TN and <0.70mgl−1 NO3−-N. Rate of N loss in the eco-ditch was highly seasonal, generally peaking in the summer months (May–August). Results show that the eco-ditch can be effective at reducing transport of non-point source of N in-situ, particularly in warm environments. Its use should be expanded to similar areas, although managing the eco-ditch to maximize N removal in the long-term will require dynamic management.

Multiple linear modeling of outflow nitrogen dynamics in vertical-flow constructed wetlands under two different operating states

This paper proposed an assumption that the area-based first-order removal rate constant (k) of constructed wetland (CW) could be linearly determined by multiple influencing factors based on the classic k-C* model. The assumption was further validated by STELLA® using datasets from nine-batch pilot-scale vertical-flow CWs treating aquaculture wastewater under two different operating conditions: i.e., submersed state (SS) and non-submersed state (NS). A before-and-after comparison indicated that wetland state shift impacted N removal. Under SS, TN was mainly removed by sedimentation coupled with nitrification/denitrification, while under NS, it was mainly through sedimentation. Factor loadings showed that temperature presented heavier impact on k compared to the other factors. The simulations reflected the variation trend of observations well but the model precision was poor. Sensitivity analysis revealed that the dynamic model was more sensitive to the influencing factors under NS than it was under SS with temperature, pH and concentration having relatively higher SI compared to the other factors. Overall, this work might provide a new approach to simulate outflow and could be used for system design, prediction or optimization.

Phosphorus removal performance of a large-scale constructed treatment wetland receiving eutrophic lake water

Eutrophication continues to impact watersheds and their receiving water bodies. One approach to mitigate this problem is to use constructed treatment wetlands. Our objectives were to determine long-term phosphorus (P) removal by a large-scale constructed treatment wetland (the marsh flow-way at Lake Apopka, Florida, USA) that treats lake water and to quantify the monetary costs for performance. The marsh flow-way treated substantial amounts of lake water (30myr−1, which is about 30% of the lake’s volume on an annual basis). Associated with this, P was removed at an average rate of 0.85gm−2yr−1 (2.6 metric tons yr−1). The marsh flow-way removed mostly particulate P, while it released dissolved P fractions (mostly during the first few years of operation; thereafter, release was negligible). The long-term first-order removal rate constant (k) for P averaged 27myr−1. Phosphorus removal performance varied seasonally, with greater removal during cool periods (September–May) and poor removal during warm periods (June–August). Incurred annual operation and maintenance (O&M) costs averaged $455,000 (2012$), which was equivalent to $1,648hayr−1 or $177 per kilogram of P removed. We also calculated costs for a 25-year project life cycle, and compared the incurred and the 25-year costs to other systems that illustrated the marsh flow-way was cost competitive. Both P removal and costs were useful metrics in helping us determine operational and management changes. This resulted in a seasonal management strategy that contributed to increased P removal and a reduction in O&M, thereby increasing cost effectiveness. In addition to costs, treatment wetlands provide benefits that include a range of ecosystem services. We challenge ourselves and other treatment wetland managers to adopt both a cost and benefit approach to assessing system performance.

Phosphorus Removal in a Surface-Flow Constructed Wetland Treating Agricultural Runoff

Agricultural runoff is a leading source of phosphorus (P) pollution to lakes and streams. The objective of this study was to evaluate P removal dynamics in a constructed treatment wetland (CTW) treating agricultural irrigation return flows. The CTW included a sedimentation basin (SB) followed by two surface-flow wetlands in parallel. Typical retention times and total P (TP) loading were 1.4 d and 50 to 110 g m yr P, respectively, for the SB and 5 to 6 d and 4 to 10 g m yr P, respectively, for wetlands. On the basis of this multiyear study, concentration removal efficiency in the SB averaged 21% for TP and 32% for reactive phosphorus (RP). Concentration removal efficiency in wetlands averaged 37 and 43% for TP and 22 and 33% for RP. Areal first-order removal rates for TP averaged 22 and 31 m yr in wetlands. Total P removal in wetlands exhibited a strong seasonal pattern, with minimum removal in the summer when high temperatures likely enhanced P release from decaying plant biomass. The performance of the CTW was stochastic, with removal unpredictably poorer in some years in part as a result of muskrat bioturbation and plant harvesting. In years before muskrat impacts, concentration removal efficiencies in wetlands were 50% for TP and 65% for RP.

Modeling seasonal variation in bacteriophage removal in constructed wetlands using convection–dispersion equation

When livestock manure is applied to drained cropland, viruses in the manure can quickly move through preferential flow paths to tile drains. Contaminated tile drain effluent can then contaminate surface waters. Experiments were conducted to explore the applicability of constructed wetlands in treating tile-drainage. Tub-scale, two-stage, constructed wetlands were spiked with the bacteriophage P22 and the effluent was monitored to quantify removal. The convection–dispersion equation (CDE) was used to estimate convective, dispersive, first-order removal, and retardation parameters. Results showed a mean removal coefficient of 0.065 and 0.285 per day for surface flow (SF) wetlands and 2.67 and 5.36 per day for subsurface flow (SSF) wetlands in winter and summer months, respectively. SSF wetlands were 41 times more effective in winter and 19 times more effective in summer in removing bacteriophage than were SF wetlands. There was greater removal in warm than in cold weather. The P22 bacteriophage was not suitable as a biological tracer for evaluation of the hydraulic properties of the wetlands based on the minimum first-order removal rates of 0.04 per day.

Carbofuran degradation by the application of MW-assisted H2O2 process

Carbofuran removal performance of a microwave (MW)-assisted H2O2 system under different MW-power levels (300-900 W) was investigated. Batch experiments were conducted at 100 mg/L carbofuran concentration using a modified-MW reactor with 2450 MHz of fixed frequency. As a precursor, control experiments were carried out with H2O2 alone, MW alone and conventional heating (CH). A maximum carbofuran removal of 14 % was observed in both H2O2 alone and CH systems. On the other hand, only 2 % removal was observed in the MW alone system irrespective of the operation-mode, i.e. continuous or pulsed. The combination of MW and H2O2 produced 100 % carbofuran removal in all the MW-assisted experiments. The MW-assisted system operated under continuous-mode and at 750 W has showed rapid carbofuran degradation, i.e. 30 sec, with the highest first-order removal rate constant of 25.82/min. However, 97 % carbon oxygen demand (COD) removal was observed in the same system only after 30 min. On the other hand, 100 % carbofuran removal and 49 % COD removal were observed in the pulsed-mode MW-assisted H2O2 system after 10 and 30 min, respectively. Carbofuran mineralization in the system was evidenced by the formation of ammonium and nitrate, and carbofuran intermediates.