Here, we report on the ability of two different water treatment residues, a Fe-based (Fe-WTR) and an Al-based (Al-WTR) ones, to accumulate Cd(II) and Zn(II) from aqueous solutions at different pH values (pH 4.5, 5.5, and 7.0). Fe-WTR showed a greater Zn(II) and Cd(II) sorption capacity than Al-WTR at all the pH values investigated, in particular at pH 7.0 (e.g., ∼0.200 and ∼0.100 mmol g⁻¹ of Me(II) sorbed by Fe- and Al-WTR at pH 7.0, respectively). The greater capacity of the Fe-WTR to accumulate Me(II) seems to be linked to its higher content of iron and manganese ions and to its higher CEC value compared to Al-WTR. The role of the inorganic and organic fractions of WTRs in metal sorption was also assessed. A higher affinity of Cd(II) with respect to Zn(II) toward functional groups of the organic matter of both WTRs was observed, while Zn(II) showed a stronger association with the inorganic phases. The sorption of both metal ions appeared mainly governed by the formation of inner-sphere surface complexes with the inorganic and organic phases of WTRs, as suggested by the sequential extraction data.

Poultry litter and bedding materials generated from laying chicken farm often contain high levels of arsenic when roxarsone is included in feed to combat disease and improve egg production. This study was conducted to determine the fate and ecological risk of arsenic species in poultry litter which applied to agricultural field. Three poultry litter application rates (0, 10, 60 % dry weight) were used to amend soil samples under anaerobic and aerobic circumstances, respectively, incubated at 30 % moisture content for 110 days. Experiment indicated that under anaerobic circumstance, As(V) and As(III) decreased in treatments applied 60 and 10 % rates within initial 7 days, subsequently methylated arsenic displayed increasing, suggesting biotic activity transformed inorganoarsenical to methylated arsenic species. In contrast, As(V) dropped in the first 7 days but increased thereafter under aerobic circumstances, with methylated arsenic increasing, implying abiotc and biotic activities enhanced arsenic speciation. Based on different arsenic species, we evaluated their ecological risk in poultry litter respectively. It was found that ecological risks under anaerobic circumstance were higher than under aerobic circumstance of the same poultry litter rates, and higher poultry litter rates applied to soil would bring about higher ecological risk. We suggest that poultry litter should be disposed at low rate (approximately 10 %) and applied to soil surface to create aerobic circumstance for the initial 2 months time, but should be buried into a deeper depth thereafter.

This study compares the efficiency of a synthetic chelate (ethylenediaminetetraacetic acid-EDTA), a natural low-molecular-weight organic acid (citric acid), and their combination for phytoremediation of Cu-pyrene co-contaminated soils. Zea mays was grown in each soil and amended with citric acid and/or EDTA to understand the effect of chelates during phytoremediation of contaminated soils. In Cu or pyrene-contaminated soil, plant growth was negatively affected by EDTA (43 %) and citric acid (44 %), respectively, while EDTA + citric acid promoted (41 %) plant growth in co-contaminated soil. EDTA and EDTA + citric acid increased the phytoextraction of Cu in Cu-contaminated and co-contaminated soils, respectively. In pyrene-contaminated soil, all tested chelates increased the dissipation of pyrene reaching 90.4 % for citric acid, while in co-contaminated soil, only citric acid or EDTA + citric acid enhanced pyrene dissipation. These results show that Z. mays can be effective with the help of chelates in phytoextraction of Cu and dissipation of pyrene in co-contaminated soil.

Surface water bodies can be impaired by turbidity and excessive sediment loading due to urban development, construction activities, and agricultural practices. Turbidity has been considered as a proxy for evaluating water quality, aquatic habitat, and aesthetic impairments in surface waters. The US Environment Protection Agency (USEPA) has listed turbidity and sediment as major pollutants for construction site effluent. Recently proposed USEPA regulations for construction site runoff led to increased interest in methods to predict turbidity in runoff based on parameters that are more commonly predicted in runoff–erosion models. In this study, a turbidity prediction methodology that can be easily incorporated into existing runoff–erosion models has been developed using fractions of sand, silt, and clay plus suspended sediment concentration of eight parent soils from locations in Oklahoma and South Carolina, USA.

Drainage water from acid sulfate soils with sulfuric material has high concentrations of protons and dissolved metals which can have detrimental effects on the surrounding ecosystems. Liming is expensive; therefore, alternative methods are needed. Organic materials such as plant residues, compost or biochars can bind protons and metals but have not been evaluated with respect to remediation of acid drainage water from acid sulfate soils. In this study, eight organic materials (compost, two straws and five biochars differing in feed stock and production temperature) were placed in small PVC cores at 1.5 g C/core and synthetic acid drainage water (pH 3, 28 mg Fe/l and 2 mg Al/l, properties based on long-term averages of drainage water from sulfuric acid sulfate soils) was applied in four leaching events. Mallee biochar produced at 550 °C and wheat biochar produced at 450 °C had high retention capacity for protons, Fe and Al. Retention was low in compost and wheat straw. Retention of protons was positively correlated with organic C concentration of the materials. Retention of Fe and Al was correlated with percentage alkyl, aryl and ketone groups. Other properties such as release of native Fe and Al and amount of material per core could explain differences in ability of organic materials to retain protons, Fe and Al. We conclude that some organic materials such as mallee biochar produced at 550 °C and wheat biochar produced at 450 °C could be used to remediate acidic drainage water.

To treat PCP-contaminated soil, abiotic methods for PCP degradation have been developed, where heme or powder hemoglobin acts as a catalyst and hydrogen peroxide as an oxidant. Degradation of PCP had the first-order kinetics, and rate coefficients, k, were 0.073 and 0.104/day for heme and hemoglobin, respectively, indicating that the hemoglobin was a more efficient catalyst than heme. Approximately 96 % of the initial PCP was degraded at day 35. Thus, hemoglobin might be recommended as the catalyst of choice, since it is much less expensive than heme.

The dried powder of the alligator weed root (AWR) was employed as a biosorbent to remove As(III) from aqueous solution, using acid pre-treated AWR (HAWR) and As(V) as the contrasts. The results of batch adsorption experiment suggested that there is no substantial difference between As(III) and As(V) adsorption. Both of them are affected by the solution pH significantly, but insensitive to the ionic strength. The speciation analysis indicated that more than 95 % of the total As(III) in aqueous solution is oxidized into As(V) in the presence of AWR, while barely oxidized in the presence of HAWR. It proves that without pre-oxidation, AWR can oxidize and adsorb As(III), simultaneously. The properties of the biosorbent were characterized by various techniques including scanning electronic microscopy-energy dispersive spectrometer, Fourier transform infrared spectra analysis, inductive coupled plasma emission spectrometer and Zeta potential detection. The results suggested that typical metals including Mn, Fe and Al enrich in the morphology of metal (hydro) oxide over the surface of AWR, originally. Based on the nature of the biosorbent and arsenic besides the adsorption and oxidation performances, the metal (hydro) oxides are proved as the essential role to drive the adsorption and oxidation. The proof is that with the metal (hydro) oxides denuded, as the contrast of AWR, HAWR loses its capability of adsorption and oxidation for As(III), totally.

This study investigated drivers of denitrification and overall NO₃ ⁻ removal in an agricultural riparian area in central New York. Denitrification was measured using an in situ “push-pull” method with ¹⁵N–NO₃ ⁻ as a tracer during summer and fall 2011 at a pair of riparian sites characterized by different hydrologic regimes. Median denitrification rates were 1347 and 703 μg N kg soil⁻¹ day⁻¹ for the two study sites. These rates are higher than those reported for other riparian areas, emphasizing the role of some riparian areas as hotspots of NO₃ ⁻ removal. N₂O production was significantly higher at one site, demonstrating that riparian areas can be a greenhouse gas source under certain conditions. Denitrification was negatively correlated with groundwater flux, suggesting that slower flushing of water, and thus longer residence time, promotes denitrification. A mass balance of NO₃ ⁻ loss revealed that denitrification only accounted for 5–12 % of total NO₃ ⁻ loss, and production of NH₄ ⁺ indicated that dissimilatory NO₃ ⁻ reduction to NH₄ ⁺ (DNRA) may be occurring at both sites. While both sites were characterized by high NO₃ ⁻ removal, differences in denitrification rates and NO₃ ⁻ removal processes demonstrate the need to improve our ability to capture spatial and process heterogeneity in landscape biogeochemical models.

Arsenic (As) is a ubiquitous metalloid known for its adverse effects to human health. Microorganisms are also impacted by As toxicity, including methanogenic archaea, which can affect the performance of a process in which biological activity is required (i.e., stabilization of activated sludge in wastewater treatment plants). The novel ability of a mixed methanogenic granular sludge consortium to adapt to the inhibitory effect of arsenic As was investigated by exposing the culture to approximately 0.92 mM of arsenite (Asᴵᴵᴵ) for 160 days in an arsenate (Asⱽ)-reducing bioreactor using ethanol as the electron donor. The results of shaken batch bioassays indicated that the original, unexposed sludge was severely inhibited by Asᴵᴵᴵ as evidenced by the low 50 % inhibition concentrations (IC₅₀) determined, i.e., 19 and 90 μM Asᴵᴵᴵ for acetoclastic and hydrogenotrophic methanogenesis, respectively. The tolerance of the acetoclastic and hydrogenotrophic methanogens in the sludge to Asᴵᴵᴵ increased 47-fold (IC₅₀ = 910 μM) and 12-fold (IC₅₀ = 1100 μM), respectively, upon long-term exposure to As. In conclusion, the methanogenic community in the granular sludge demonstrated a considerable ability to adapt to the severe inhibitory effects of As after a prolonged exposure period.

Deterioration of natural water resources due to runoff from agricultural land is a major problem in the US Great Plains. Changes in earth climate can create heavy storms and alter precipitation patterns which would affect the element concentrations in runoff. A 2-year study (dry and wet years) was conducted to assess the impact of annual precipitation on element concentrations in runoff from soils and element loadings to Salt Creek in the Roca watershed, NE. Both dissolved and sediment-associated forms of five elements (Al, Fe, Mn, Cu, and Zn) were determined in runoff. The amount of dissolved element in runoff during the wet year was greater than the dry year. Except for Zn, the total amount of element associated with sediment was greater than that found in dissolved form. The Mehlich3 extraction was applied to determine the reactive fraction of element in sediment. A small fraction of element associated with sediment was in reactive form, ranging from 1 to 33 % of the total element content. The sum of both the reactive fraction of element in sediment and amount of element dissolved in water were used to calculate the total bioactive element concentration (BEC) in runoff. During the dry year, the total BEC in runoff was 424, 349, 387, 5.2, and 26.8 μg/L for Al, Fe, Mn, Cu, and Zn, respectively. The corresponding total BEC during the wet year was 622, 479, 114, 3.7, and 19.8 μg/L for Al, Fe, Mn, Cu, and Zn, respectively. Further, the bioactive element loading (BEL) into Salt Creek was greater during the wet year than the dry year. Aluminum, Fe, and Mn contributed to the greatest BEL into the surface water body while Zn and Cu had the least contribution. We concluded that greater precipitation during the wet year would increase the negative impact of runoff from soils and BEL to surface water systems in the US Great Plains.