The mobility and distribution of metals in the environment is related not only to their concentration but also to their availability in the environment. Most chromium (Cr) exists in oxidation states ...ranging from 0 to VI in soils but the most stable and common forms are Cr(0), Cr(III), and Cr(VI) species. Chromium can have positive and negative effects on health, according to the dose, exposure time, and its oxidation state. The last is highly soluble; mobile; and toxic to humans, animals, and plants. On the contrary, Cr(III) has relatively low toxicity and mobility and it is one of the micronutrients needed by humans. In addition, Cr(III) can be absorbed on the surface of clay minerals in precipitates or complexes. Thus, the approaches converting Cr(VI) to Cr(III) in soils and waters have received considerable attention. The Cr(III) compounds are sparingly soluble in water and may be found in water bodies as soluble Cr(III) complexes, while the Cr(VI) compounds are readily soluble in water. Chromium is absorbed by plants through carriers of essential ions such as sulfate. Chromium uptake, accumulation, and translocation, depend on its speciation. Chromium shortage can cause cardiac problems, metabolic dysfunctions, and diabetes. Symptoms of Cr toxicity in plants comprise decrease of germination, reduction of growth, inhibition of enzymatic activities, impairment of photosynthesis and oxidative imbalances. This review provides an overview of the chemical characteristics of Cr, its behavior in the environment, the relationships with plants and aspects of the use of fertilizers.
The performance of a vertical and a horizontal subsurface flow wetland (v-SSF and h-SSF), designed for treating domestic wastewater from a single family, was investigated by monitoring total nitrogen ...(TN), nitrate nitrogen (NO₃-N), ammonium nitrogen (NH₄-N), total phosphorus (TP), chemical oxygen demand (COD) and the dissolved oxygen (DO) content of the influent and the effluent wastewater of each system during the first two years of operation. The growth of Phragmites australis in each system was recorded by measuring the height and observing their general conditions. The treated domestic wastewater presented similar chemical–physical characteristics in the two systems which operated in analogous environmental conditions. The median influent characteristics were: TN 81.9 mg L⁻¹, NO₃-N 0.19 mg L⁻¹, NH₄-N 33.5 mg L⁻¹, TP 11.9 mg L⁻¹ and COD 354.5 mg L⁻¹. During the whole monitoring period median reductions in the v-SSF were TN 71%, NH₄-N 94%, TP 27% and COD 92% whereas in the h-SSF they were TN 59%, NH₄-N 21%, TP 52% and COD 70%. Internal production of NO₃-N was observed, mainly in the v-SSF probably due to the difference in oxygen availability in the medium and the design of the system. DO concentration increased in the effluents in both years, with higher values measured in v-SSF than in h-SSF. The reduction performance increased in the second year, particularly in v-SSF, whereas no statistical differences were observed between spring–summer and autumn–winter periods. P. australis reached maximum development at the end of summer in both systems and maintained a stable height during autumn–winter. In h-SSF the vegetation located close to the influent showed lower growth than in the rest of the bed.
•We studied the efficiency of a full-scale hybrid constructed wetland system (HCW).•We investigated the seasonal influence in the removal performance of the system.•We observed the presence of a ...temperature breakpoint that caused variation in nutrient removal.•We observed higher TN and NO3-N percentage abatement at temperatures above 14.2°C.
The objective of this research was to investigate the efficiency and seasonal performance of a full-scale hybrid constructed wetland system (HCW) in reducing total nitrogen (TN), ammonia nitrogen (NH4-N) and nitrate nitrogen (NO3-N). HCW with a total area of about 130m2 and hydraulic load of 2m3/day was composed of three subsurface flow vertical systems (VF), working in parallel and one horizontal (HF) connected in series. The system was loaded daily with synthetic wastewater having an average concentration of TN of 250mg/L (about 125mg/L of NH4-N and 125mg/L of NO3-N). Water samples were collected and analyzed from May to July 2011 and from January 2012 to July 2012. Variations were observed in nutrient removal performance related to temperature.
During the whole monitoring period median reduction efficiency (RE) in the HCW was TN 95%, NH4-N 95% and NO3-N 93%, although three sub-periods characterized by different performances have been observed. During the first period (from May to July 2011) the RE was positive for the three nitrogen forms considered, whereas from January to the end of March 2012 the RE was lower, particularly for TN and NO3-N. From April 2012, when the temperature rose above 14.8°C, there was an increase in the performance that reached the 2011 values.
Internal production of NO3-N was observed, mainly in the VF systems between January and March 2012. The median removals of mass pollutants per m2 of HCW per day were TN 3.1g/m2/d, NH4-N 1.5g/m2/d, NO3-N 1.5g/m2/d. Segmented regression analysis identified a breakpoint at 14.2°C for wastewater temperature that caused variations in TN and NO3-N concentration reduction performances. According to this approach the abatement was always positively correlated with temperature, but different regression slopes were obtained below and above the breakpoint. In particular, with lower temperature the abatement of NO3-N and TN increased by 1.7 and 2.0% per °C of temperature increase; with temperature higher than 14.2°C the increase in abatement due to increased temperature was sharper, especially for NO3-N.
•Hybrid constructed wetland can represent a valid solution to treat digestate liquid fraction.•Floating wetland treatment showed a good performance under high pollutants load.•The system areal load ...reduction was 169.0gm−2d−1 for COD and 18.1gm−2d−1 for TN.•P. australis showed higher COD, TN and NO3-N abatement than A. donax.•Subsurface beds emitted as CO2 and CH4 less than 100% of C removed from digestate acting as C sink.
A pilot hybrid constructed wetland (subsurface flow line (SSL, 15m2)+floating treatment wetland line (FTWL, 90m2)) treating digestate liquid fraction (DLF) in northeast Italy was monitored to determine its depuration efficiency in treating COD, total nitrogen (TN), ammonia nitrogen (NH4-N), nitrate nitrogen (NO3-N), total phosphorus (TP) and orthophosphate (PO4-P). CO2, CH4, and N2O emissions were also measured in SSL beds. The system was fed with diluted DLF (0.7m3day−1) containing high COD (4580–6000mgL−1) and TN (378.0–657.5mgL−1). Removal efficiency was 57.9% for COD, 64.6% for TN, 65.1% for NH4-N, 35.6% for NO3-N, 49.2% for TP, 45.1% for PO4-P in SSL and of 89.2% for COD, 90.0% for TN, 89.0% for NH4-N, 93.8% for NO3-N, 50.3% for TP, 49.9% for PO4-P in FTWL. SSL showed a higher areal load reduction than FTWL. The carbon emitted (CO2-C+CH4-C) was always below 100% of C removed from digestate as COD, showing that during monitored periods SSL acted as C sink. The results indicate that the set-up composed by a sequence of vertical subsurface, horizontal subsurface and floating wetland represent a valid solution as secondary treatment for DLF.
Although selenium (Se) is a known anticarcinogen, little is known regarding how Se affects other nutritional qualities in crops. Tomato (Solanum lycopersicon) was supplied with 0–50 μM selenate and ...analyzed for elemental composition and antioxidant compounds. When supplied at low doses (5 and 10 μM) via the roots, Se stimulated the synthesis of phenolic compounds in leaves and reduced the levels of Mo, Fe, Mn, and Cu in roots. At higher doses (25 and 50 μM Se) leaf glutathione levels were 3–5-fold enhanced. Supply of selenate via foliar spray (0, 2, or 20 mg Se plant–1) resulted in Se-biofortified tomato fruits, with Se levels low enough not to pose a health risk. The Se-biofortified fruits showed enhanced levels of the antioxidant flavonoids naringenin chalcone and kaempferol and a concomitant decrease of cinnamic acid derivatives. Thus, tomato fruits can be safely enriched with Se, and Se biofortification may enhance levels of other neutraceutical compounds.
The performance of three integrated wetland treatment plants (horizontal sub-surface flow (h-SSF) and floating treatment wetland (FTW) with differentiated primary treatments) designed for treating ...domestic wastewater was investigated, monitoring total (TN), nitrate (NO3-N), nitrite (NO2-N) and ammonia nitrogen (NH4-N), total (TP) and phosphate phosphorus (PO4-P), chemical (COD) and biological oxygen demand (BOD5), and dissolved oxygen (DO) at the inlet and outlet of each wetland section from February 2011 to June 2012. Sediments settled in the FTW were collected and analyzed. The growth of plants in each system was also monitored, observing their general conditions. The chemical-physical characteristics of the pretreated domestic wastewater depended on the primary treatment installed. During the monitoring period we observed different reduction performance of the wetland sector in the three sites. In general, the wetland systems demonstrated the capacity to reduce TN, COD, BOD5 and Escherichia coli, whereas NO3-N and NH4-N removal was strictly influenced by the chemical conditions, in particular DO concentration, in the h-SSF and FTW. Vegetation (Phragmites australis, Alnus glutinosa and Salix eleagnos) was well established in the h-SSF as well as in the floating elements (Iris pseudacorus), although there were some signs of predation. FTW is a relatively novel wetland system, so the results obtained from this study can pave the way for the application of this technology.
Effects of inlet design and vegetation type on tracer dynamics and hydraulic performance were investigated using lithium chloride in 18 experimental free water surface wetlands. The wetlands received ...similar water flow but had different vegetation types: 6 emergent vegetation wetlands (EVWs), 6 submerged vegetation wetlands (SVWs) and 6 free development wetlands (FDWs). Two types of inlet designs were applied: half of each wetland vegetation type had a barrier near the inlet to help distribute incoming tracer solution, while the rest had no barrier. Residence time distribution (RTD) functions were calculated from tracer data using two techniques: method of moments and a novel Gauss modelling approach. RTD functions were used to quantify hydraulic parameters: active wetland volume (e-value), water dispersion (N-value) and hydraulic efficiency (λ-value).
For wetlands without barrier, significantly lower tracer mass recoveries were found from EVWs compared to FDWs and SVWs, signifying a risk of tracer methodological problems in small densely vegetated wetlands. These problems were minimized in wetlands with an inflow construction promoting distribution of incoming tracer solution.
Compared to the method of moments, Gauss modelling seemed to produce more reliable λ-values but less reliable N-values. Data for precise hydraulic quantification were lost by Gauss modelling, as indicated by overall lower variance in these data sets and lower mass recoveries. However, Gauss modelling may minimize uncertainties associated with lithium immobilization/mobilization. Parameters were significantly affected by the RTD data analysis method, showing that the choice of method could affect evaluation of wetland hydraulics.
The experimental wetlands in this study exhibited relatively high e-values and low N-values. This was probably caused by the small size of the wetlands and low water flow velocities, emphasizing that hydraulic parameter values obtained in small experimental wetlands may not be applicable to hydraulics in larger wetlands.
The method of moments revealed lower e-values from EVWs compared to SVWs and FDWs. It was indicated that lower e-values were mainly caused by vegetation volumes. This highlighted a need for regular maintenance to secure efficient treatment volume in wetlands with dense vegetation.
Effects of inlet design and vegetation type on tracer dynamics and hydraulic performance were investigated using lithium chloride in 18 experimental free water surface wetlands. The wetlands received ...similar water flow but had different vegetation types: 6 emergent vegetation wetlands (EVWs), 6 submerged vegetation wetlands (SVWs) and 6 free development wetlands (FDWs). Two types of inlet designs were applied: half of each wetland vegetation type had a barrier near the inlet to help distribute incoming tracer solution, while the rest had no barrier. Residence time distribution (RTD) functions were calculated from tracer data using two techniques: method of moments and a novel Gauss modelling approach. RTD functions were used to quantify hydraulic parameters: active wetland volume ( e -value), water dispersion ( N -value) and hydraulic efficiency ( λ -value).
For wetlands without barrier, significantly lower tracer mass recoveries were found from EVWs compared to FDWs and SVWs, signifying a risk of tracer methodological problems in small densely vegetated wetlands. These problems were minimized in wetlands with an inflow construction promoting distribution of incoming tracer solution.
Compared to the method of moments, Gauss modelling seemed to produce more reliable λ -values but less reliable N -values. Data for precise hydraulic quantification were lost by Gauss modelling, as indicated by overall lower variance in these data sets and lower mass recoveries. However, Gauss modelling may minimize uncertainties associated with lithium immobilization/mobilization. Parameters were significantly affected by the RTD data analysis method, showing that the choice of method could affect evaluation of wetland hydraulics.
The experimental wetlands in this study exhibited relatively high e -values and low N -values. This was probably caused by the small size of the wetlands and low water flow velocities, emphasizing that hydraulic parameter values obtained in small experimental wetlands may not be applicable to hydraulics in larger wetlands.
The method of moments revealed lower e -values from EVWs compared to SVWs and FDWs. It was indicated that lower e -values were mainly caused by vegetation volumes. This highlighted a need for regular maintenance to secure efficient treatment volume in wetlands with dense vegetation.
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