Nutrient removal in a trapezoidal vegetated drainage ditch used to treat primary domestic sewage in a small catchment of the upper Yangtze River

A trapezoidal constructed ditch (TCD) of 300 m length and 2.2 m width was designed and built in the downstream section of the upper Yangtze River for in situ treatment of primary domestic sewage. The removal efficiencies of TN, NH₄‐N, NO₃‐N, TP and PO₄‐P from the TCD were approximately 61, 63, 48, 58 and 51%, respectively. The concentrations of TN, NH₄‐N, NO₃‐N, TP and PO₄‐P showed a decreasing trend with increasing distance downstream. Plant assimilation and sediment retention were the key mechanisms for N and P removal within the TCD, with subsequent microbial uptake and transformation of the nutrients. The TCD outlet showed significantly higher dissolved oxygen (DO) concentrations and lower values of electrical conductivity and total dissolved solids compared to the influent. Results of this study highlight the potential of TCD to mitigate nutrients from primary domestic sewage transported downstream and could be incorporated into local best management practices.     

Urban Water Journal: Special Issue on Transients

Retention/detention basins are commonly used to remediate runoff from road surfaces in an attempt to remove contaminants before these materials enter adjacent waterways. However, the efficiency of such devices in removing contaminants is not well known, especially for Australian conditions. The efficiency of a retention/detention device adjacent to a major motorway in Sydney (Australia) was assessed for total suspended solids (TSS), a suite of trace metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn), nutrients (TP, TKN, NO_x, TN) and faecal coliforms. The mean removal efficiency of Cu, Pb, Mn and Zn was 23, 41, 43 and 41%, respectively, whereas the mean reduction in Cr, Fe and Ni concentrations was only 0, 3 and 1%, respectively. TSS in stormwater entering the retention/detention basin was highly variable resulting in large variations in removal efficiencies (range: ?12 to 93%; mean: 40%). The mean removal efficiency of Kjeldahl nitrogen (TKN) and total nitrogen (TN) was high (56 and 28%, respectively) in contrast to total NO_x and total phosphorus (TP) (?42 and ?5%, respectively). Faecal coliform was low to very low (<5000 cfu/100 ml) and removal efficiency was 16 to 68%. Possible leaching of fine terrigenous particles from the gravel bed of the retention/detention basin may have contributed to the increase in Cr, Fe and Ni concentrations in effluent stormwater.     

Processes of sorption–desorption in the Cr(Vi)–calcined Zn/Al–hydrotalcite system

Investigated are processes of sorption–desorption of Cr(IV) on model to the efficiency of desorption of Cr(VI) from the sorbent reagents are arrange in the series (NaOH: Na₂CO₃) > NaOH > Na₂CO₃ ≥ H₂CO₃ ≥ H₂SO₄. Calcined Zn/Al–hydrotalcite has been proposed for concentration of Cr(VI) and its spectrophotometric determination in natural waters.     

Efficiency of a continuous deflective separation (CDS) unit in removing contaminants from urban stormwater

The weighted average concentration (WAC) of total suspended solids (TSS) in stormwater effluent from a continuous deflective separation (CDS) unit in Port Jackson (Australia) catchment was reduced by an average 28% during six high-flow events, but some TSS was released during turbulent, high-flow events. The average removal efficiency of metals Cr, Cu, Pb Mn, Ni, Zn and Fe varied considerably (?49% for Pb and +10% for Mn), whereas Ni and Zn were inefficiently removed by the device. Average concentrations of TKN, NO_x and TP were similar at both in- and out-flow points and faecal coliforms counts were slightly reduced.     

A study of Cr(VI) and NH4+adsorption using greensand (glauconite) as a low‐cost adsorbent from aqueous solutions

This paper investigates the removal of Cr(VI) and NH⁴⁺ from aqueous solutions using greensand (glauconite). The effects of adsorbent dosage, contact time, initial Cr(VI) and NH⁴⁺ concentrations, and pH were investigated in batch experiments. The results show that these parameters influenced Cr(VI) and NH⁴⁺ removal using glauconite considerably. Pseudo‐first‐order, pseudo‐second‐order and intraparticle diffusion kinetic models were applied to explain the kinetic data, and the pseudo‐second‐order model achieved good agreement. The equilibrium isotherm data are coordinated with the Freundlich, Langmuir models, Temkin and Dubinin–Radushkevich; the Freundlich model proved most best suitable. The removal efficiency of Cr(VI) and NH₄⁺ were 12.21 mg/g (54% at pH 3) and 19.24 mg/g (77.08% at pH 7). All in all, the results showed that the adsorption process on glauconite could be used as an effective method for removing Cr(VI) and NH⁴⁺ from aqueous solutions.     

The life cycle impact assessment applied to the Domingo Rubio tidal system by the study of seasonal variations of the aquatic eutrophication potential

The innovative technique of Life Cycle Impact Assessment (LCIA) applied to dynamic environmental systems has been recently developed. In this work we investigate a complex system, the Domingo Rubio tideland (Huelva, Spain), where a tidal marsh and a continental lagoon converge. This wetland, catalogued as Natural Park by the Andalusia government, is subjected to a high eutrophicant pressures related to the strawberry culture and the inputs coming from industrial wastes. NO₂⁻, NO₃⁻ and PO₄³⁻ were analyzed in 41 water samples, obtaining values up to 100 mg L^− 1 Σ(NO₂⁻, NO₃⁻) and 18.5 mg L^− 1 PO₄³⁻. All these values exceed the accepted levels by the European Environment Agency. N/P ratios and the Aquatic Eutrophication Potentials (AEP) for N and P showed a constant imbalance of the system. During one tidal cycle, the tidal channel can have both N and P as limiting nutrient (P is the limiting nutrient during low tide and N is during high tide) and there exists an alternation of AEP domination too between N and P in the continental area, what points to an excess of both nutrients all over the study area, and to the necessity of diminishing the nutrient inputs and a higher control on these pollution sources as well.     

Removal of chromium from aqueous solutions and plating bath rinse by an electrochemical method

In this work, a bipolar packed bed electrolytic cell having steel Raschig rings behaving as electrodes has been used to remove chromium in the form of Cr(VI) from aqueous solutions and a sample of plating bath rinse.

Fe²⁺ ions generated at the anode side of the electrodes have reacted with OH^‐ ions generated at the cathode side forming Fe(OH)₂ in this electrolytic cell.Cr(VI) have coprecipitated as Cr(OH)₃ with Fe(OH)₃ forming after the redox reaction between Fe(OH)₂ and Cr(VI). Meanwhile other impurities have also removed besides Cr(VI) using this process. Removal rate of 100% for Cr(VI) has been achieved in the experiments done with different initial Cr(VI) concentration, duration of electrolysis and applied potential. Fully removal of Cr(VI) has also been achieved from the sample of plating bath rinse.     

Effects of operational parameters on the treatment of nitrate‐rich wastewater by autohydrogenotrophic denitrifying bacteria

The effects of the C/N ratio, as well as hydrogen gas and substrate concentrations, on the treatment of nitrate‐rich wastewater by autohydrogenotrophic denitrifying bacteria in sequencing batch reactors were investigated. Among the various C/N ratios applied in this study, a C/N ratio of 4 was found to be the most suitable ratio that resulted in faster growth and adaptation. The denitrification rate improved with less accumulation of nitrite with increasing H₂ sparging time. Moreover, an increase in nitrate concentration resulted in high nitrite accumulation. The nitrite accumulated to 601 mg/L NO₂‐N when the nitrate concentration was 1000 mg/L NO₃^– ‐ N. The specific degradation rates for nitrate and nitrite were found to be 27.8 mg NO₃^?‐N/g MLVSS/d and 50 mg NO₂^?‐N/g MLVSS/d, respectively, when the C/N ratio was 2, and H₂ as electron donor was sparged for 1 min with 2 h interval.     

Removal of organic matter in stormwater ponds: a plug-flow model generalisation from waste stabilisation ponds to shallow rivers

ABSTRACT

This study investigates the effect of flow conditions on the organic matter concentration, removal efficiency, and reaction kinetics in a stormwater pond in Fortaleza, Brazil. As a result of unauthorized sewage discharges, BOD and COD concentrations were similar to those of combined sewer systems. The concentrations remained roughly the same during the rainy season, which was attributed to sewage network overflow. Removal efficiencies ranged from 70–90%, similar to primary facultative ponds. Fitting different hydraulic models to the field data, it was possible to obtain BOD and COD removal rates that could be described as functions of the Reynolds number. The best fit was achieved considering the plug-flow assumption, and a general BOD model including data reported in the literature for waste stabilisation ponds, stormwater ponds and shallow rivers was derived. Lastly, simulations with this general model were performed to assess the impact of remediation measures on the studied pond.     

Analysis for chromium traces in the aquatic ecosystem II. A study of Cr(III) and Cr(VI) in the susquehanna river basin of New York and Pennsylvania

A new procedure for the differential analysis of ppb concentrations of Cr(III) and Cr(VI) in natural waters has been developed. In this method, three-liter samples are filtered, acidified to pH 6.0, and divided into three parts. One liter is passed through an anion-exchange resin bed (AG-1X4, 100–200 mesh, Cl^? form), one liter is passed through a cation-exchange resin bed (50 WX4, 100–200 mesh, Na⁺ form), and one liter remains untreated. 10 ml of 1.0 M HNO₃ are then added to each of the three aliquots and they are individually reduced in volume by evaporation to 10 ml. Analysis by A.A. employing the method of standard addition follows. By difference, cationic, anionic, and non-ionic Cr concentrations in the sample become available. Cr(III) concentration is probably closely related to (cationic + non-ionic), and Cr(VI) concentration in the original sample corresponds to the anionic portion. Precision is ±20 % or better for total, cationic, and anionic Cr at the 1 ppb level. Precision of the non-ionic analyses is closely linked to these other precisions as the concentration of non-ionic Cr species in the original sample is obtained by the mass balance requirement set up by the other three analyses.Application of this technique to the analysis of natural water samples revealed the predominance of trivalent Cr in uncontaminated waters of the Upper Susquehanna River Basin (1–2 ppb). River water samples taken downstream of Binghamton, N.Y. area sewage outfalls revealed an increase in the mean Cr(VI) content of the river from ～0.5 ppb to ～1.6 ppb. The persistence of the Cr(VI) at least as far as 60 km downstream of the outfall area leads to the conclusion that at these levels, little dissolved Cr(VI) is removed from the river as it flows away from a point of contamination. Concentrations of Cr in samples of river sediments also revealed Cr contamination below the outfall area, and Cr contamination extended at least as far as 60 km downstream of the outfall area.     

Integrative quantification and balancing of contaminant fluxes in urban groundwater, case study Darmstadt

The qualitative and quantitative impact of a city on groundwater is presented in the case study of Darmstadt. The impact of land use on groundwater quality in Darmstadt is higher than the impact of background geological processes. The occurrence of Cl, B and Fe is only influenced by land use, while EC, HCO₃ and PO₄ are controlled by geology and land use. An integrative, spatially differentiating quantification of mass fluxes shows that e. g. Cl and B are introduced from urban sources such as leaking sewers and road salting. Input is highest under industrial areas (Cl 317 mg/d?·?m², B 0,6 mg/d?·?m²). For N_tot agricultural input (114 mg/d?·?m²) is more important than urban input with a maximum of 14 mg/d?·?m². Comparing overall urban input with estimated urban input, it can be concluded that there are additional sources for HCO₃, Ca, Mg, SO₄, Na, Cl, B and NO₃, which are not included in the estimated input (e. g. geogenic sources, fill material, industrial sources & degradation processes). PO₄ and N_tot on the other hand are being degraded and COD is consumed. A decrease of concentrations downstream from the city can be ascribed to diving plumes.     

Results of the California Healthy Homes Indoor Air Quality Study of 2011–2013: impact of natural gas appliances on air pollutant concentrations

This study was conducted to assess the current impact of natural gas appliances on air quality in California homes. Data were collected via telephone interviews and measurements inside and outside of 352 homes. Passive samplers measured time‐resolved CO and time‐integrated NO_X, NO₂, formaldehyde, and acetaldehyde over ~6‐day periods in November 2011 – April 2012 and October 2012 – March 2013. The fraction of indoor NO_X and NO₂ attributable to indoor sources was estimated. NO_X, NO₂, and highest 1‐h CO were higher in homes that cooked with gas and increased with amount of gas cooking. NO_X and NO₂ were higher in homes with cooktop pilot burners, relative to gas cooking without pilots. Homes with a pilot burner on a floor or wall furnace had higher kitchen and bedroom NO_X and NO₂ compared to homes without a furnace pilot. When scaled to account for varying home size and mixing volume, indoor‐attributed bedroom and kitchen NO_X and kitchen NO₂ were not higher in homes with wall or floor furnace pilot burners, although bedroom NO₂ was higher. In homes that cooked 4 h or more with gas, self‐reported use of kitchen exhaust was associated with lower NO_X, NO₂, and highest 1‐h CO. Gas appliances were not associated with higher concentrations of formaldehyde or acetaldehyde.     

Inter-relationships between nitrogen balance, pH and dissolved oxygen in an oxidation ditch treating farm animal waste

The pathways of N in aerobic farm waste treatment systems are discussed in relation to the dissolved oxygen (DO) and pH of the mixed liquor. The change in pH, DO, oxygen uptake rate and nitrogen balance were monitored under steady, and non-steady, state conditions in an oxidation ditch treating undiluted pig waste. A kinetic analysis of the mass balance for nitrogen allowed an interpretation of the fate of nitrogen under different prevailing conditions. Undesirable accumulations of nitrite were noted in the presence of high levels of free NH₃ and HNO₂. The process was self-promoting and was encouraged by the influx of raw waste. Concentrations of 500 mg 1⁻¹ NO₂-N and 1200 mg 1⁻¹ NO₃-N were the maximum values observed and were considered to be the concentrations at which product inhibition arrested nitrifying activity. Attainment of these levels prevented complete nitrification despite an adequate retention time. pH and DO were inversely related probably through nitrification, but pH appeared to be lowered by accumulation of nitrite and nitrate anions, and thus by the balance between nitrification and denitrification. Considerable N loss through denitrification was found to occur despite apparently aerobic mixed liquors. At low DO simultaneous nitrification-denitrification could eliminate 90 per cent of the soluble-N. NH₃ desorption in laboratory cultures was found to be first order in free NH₃ but was not a significant mode of N loss under field conditions.     

Effect of Organic Carbon on Tertiary Denitrification of the Secondary Effluent in Biofilters Packed with Suspended Carriers

Denitrifying biokinetics in biofilters packed with suspended carriers were evaluated under different empty bed residence times (EBRT) with ethanol or acetate as the electron donor. The two denitrifying biofilters removed nitrate (NO₃^––N) effectively after only 3–4 days operation. At EBRT of 30; 15 and 7.5 min, the NO₃^––N removal percentage was 84; 72 and 59% in the ethanol biofilter, and was 89; 70 and 62% in the acetate biofilter, respectively. With the influent NO₃^––N loading rate ranged from 0.4 to 1.8 g/(m²·d), the NO₃^––N removal loading rate increased with increasing influent NO₃^––N loading rates, and the system was substrate limited. While when the influent nitrate loading rate was above 3 g/(m²·d), the system was biomass limited. The half-order coefficients were 0.162; 0.175 and 0.274 (mg/L)^1/2/min for the ethanol biofilter with the influent NO₃^––N concentration of 7.3–7.7 mg/L, and were 0.107; 0.165 and 0.303 (mg/L)^1/2/min for the acetate biofilter with the influent NO₃^––N concentration of 6.8–8.0 mg/L. Denitrification efficiency varied slightly during the backwashing cycle, and the effect of backwashing on the effluent turbidity was relatively large, especially for the biofilter with ethanol as the organic carbon.     

Analyses and assessment of the spatial and temporal distribution of nitrogen compounds in surface waters

The temporal concentration variations and spatial distribution of nitrogen compounds (nitrate, nitrite, ammonium) in the natural surface waters of Stara Zagora Region, Bulgaria, over a period of 1 year were assessed in the present study. Nitrate‐nitrogen concentrations in all surface water samples, except for the December value – 21.8 mg/L in Zetyovo Reservoir, were within the permissible national quality standards. NO₂ ^–‐N could be classified as a priority pollutant of Chirpan and Zetyovo Reservoirs waters. The greatest extent of NH ₄ ⁺‐N pollution was registered in Chirpan Reservoir surface waters. The correlation study revealed appreciable mutual relationship only between NH₄ ⁺‐N and NO ₂ ^–‐N in the surface waters. The hierarchical cluster analysis (HCA) exhibited divergent apportionment of nitrogen compounds in the surface water bodies.     

Chromate reduction by zero-valent Al metal as catalyzed by polyoxometalate

In spite of a high reduction potential of zero-valent Al (ZVAl), its ability to reduce Cr(VI), a widespread pollutant, to less toxic Cr(III) remains to be uncovered. In the present study, Cr(VI) reduction by ZVAl was conducted to evaluate the potential application of Al as a reductant for Cr(VI). Polyoxometalate (POM, HNa₂PW₁₂O₄₀), a catalyst, was used to accelerate Cr(VI) reduction by Al. The reaction of 0.192 mM Cr(VI) on ZVAl was investigated in the presence of N₂ or O₂ at pH 1. A slight decrease in Cr(VI) concentration was observed on as-received (uncleaned) ZVAl due to the presence of oxide layer with a low surface area (ca. 3.4 × 10⁻³ m²/g) of ZVAl. On addition of 0.1 mM POM, Cr(VI) reduction on uncleaned ZVAl increased significantly. This is attributed to the unique properties of POM, which has a Brφnsted acidity higher than usual inorganic acids such as H₂SO₄ and HCl. Thus, POM could remove rapidly the oxidize layer on ZVAl, followed by acting as a shuttle for electron transfer from ZVAl to Cr(VI). Under a N₂ atmosphere, one- or two-electron reduction of POM by ZVAl was responsible for Cr(VI) reduction in the early stage of the reaction. However, during reaction with ZVAl over 120 min, three-electron reduction of POM predominated over Cr(VI) reduction. On interaction of O₂ with reduced POM, the formation of H₂O₂ was responsible for subsequent Cr(VI) reduction. The results suggest that POM is an efficient catalyst for Cr(VI) reduction by Al due to the extremely rapid consumption of reduced POM or H₂O₂ by Cr(VI).     

Root uptake and reduction of hexavalent chromium by aquatic macrophytes as assessed by high-resolution X-ray emission

Aquatic macrophytes Salvinia auriculata, Pistia stratiotes and Eichhornia crassipes were chosen to investigate the Cr(VI) reduced by root-based biosorption in a chromium uptake experiment, using a high-resolution XRF technique. These plants were grown in hydroponics medium supplied with non-toxic Cr concentrations during a 27-day metal uptake experiment. The high-resolution Cr-Kβ fluorescence spectra for dried root tissues and Cr reference material (100% Cr, Cr₂O₃, and CrO₃) were measured using an XRF spectrometer. For all species of aquatic plant treated with Cr(VI), the energy of the Cr-Kβ_2,5 line was shifted around 8 eV below the same spectral line identified for the Cr(VI) reference, but it was also near to the line identified for the Cr(III) reference. Moreover, there was a lack of the strong Cr-Kβ″ line assigned to the Cr(VI) reference material within the Cr(VI)-treated plant spectra, suggesting the reduction of Cr(VI) for other less toxic oxidation states of Cr. As all Cr-Kβ spectra of root tissue species were compared, the peak energies and lineshape patterns of the Cr-Kβ_2,5 line are coincident for the same aquatic plant species, when they were treated with Cr(III) and Cr(VI). Based on the experimental evidence, the Cr(VI) reduction process has happened during metal biosorption by these plants.     

The removal of chromium(VI) from dilute aqueous solution by activated carbon

The removal of chromium(VI) by activated carbon, filtrasorb 400, is brought by two major interfacial reactions: adsorption and reduction. Chemical factors such as pH and total Cr(VI) that affect the magnitude of Cr(VI) adsorption were investigated. The adsorption of Cr(VI) exhibits a peak value at pH 5–6. The particle size of carbon and the presence of cyanide species do not change the magnitude of chromium removal. The reduced Cr(VI), e.g. Cr(III) is less adsorbable than Cr(VI).The free energy of specific chemical interaction, ΔG^chem was computed by the Gouy-Chapman-Stern-Grahame model. The average values of ΔG^chem are −5.57 RT and −5.81RT, respectively, for Cr(VI) and CN. These values are significant enough to influence the overall magnitude of Cr(VI) and CN adsorption. Results also indicate that HCrO⁻₄ and Cr₂O²⁻₇ are the major Cr(VI) species involved in surface association.     

The impact of wastewater irrigation on the chemical quality of groundwater

The purpose of this investigation was to assess the groundwater impact of irrigation with industrial wastewater (baker's yeast wastewater, BYW) and to determine if agricultural reuse can be considered as an efficient wastewater treatment method. The impact of the irrigation and the status of the groundwater quality were determined using chemical parameters that are typical contaminants of BYW and characterise the content of total suspended solids (TSSs), organic matter (biochemical and chemical oxygen demands), nutrients (N_org, N‐NH₄, N‐NO₃, N_total, P_total and K), salts (Cl, SO₄ and Na) and pH. The study revealed that BYW irrigation did not cause a significant increase in the content of these parameters in groundwater at a low water table region (WTR). However, at a high WTR, the irrigation had an extremely significant (P < 0.001) impact on the chemical status of groundwater that has been demonstrated by substantially high values of COD, N‐NH₄, Cl, SO₄ and Na.     

Influences of humic acid, bicarbonate and calcium on Cr(VI) reductive removal by zero-valent iron

The influences of various geochemical constituents, such as humic acid, HCO₃⁻, and Ca²⁺, on Cr(VI) removal by zero-valent iron (Fe⁰) were investigated in a batch setting. The collective impacts of humic acid, HCO₃⁻, and Ca²⁺ on the Cr(VI) reduction process by Fe⁰ appeared to significantly differ from their individual impacts. Humic acid introduced a marginal influence on Fe⁰ reactivity toward Cr(VI) reduction, whereas HCO₃⁻ greatly enhanced Cr(VI) removal by maintaining the solution pH near neutral. The Cr(VI) reduction rate constants (k_obs) were increased by 37.8% and 78.3%, respectively, with 2 mM and 6 mM HCO₃⁻ in solutions where humic acid and Ca²⁺ were absent. Singly present Ca²⁺ did not show a significant impact to Cr(VI) reduction. However, probably due to the formation of passivating CaCO₃, further addition of Ca²⁺ to HCO₃⁻ containing solutions resulted in a decrease of k_obs compared to solutions containing HCO₃⁻ alone. Ca²⁺ enhanced humic acid adsorption led to a minor decrease of Cr(VI) reduction rates. In Ca²⁺-free solutions, humic acid increased the amount of total dissolved iron to 25 mg/l due to the formation of soluble Fe-humate complexes and stably dispersed fine Fe (oxy)hydroxide colloids, which appeared to suppress iron precipitation. In contrast, the coexistence of humic acid and Ca²⁺ significantly promoted the aggregation of Fe (oxy)hydroxides, with which humic acid co-aggregated and co-precipitated. These aggregates would progressively be deposited on Fe⁰ surfaces and impose long-term impacts on the permeability of PRBs.