Effect of amorphous silica and silica sand on removal of chromium(VI) by zero-valent iron

The effect of two surfaces (amorphous silica and silica sand) on the reduction of chromium(VI) by zero-valent iron (Fe(0)) was investigated using batch reactors. The amendment of both surfaces significantly increased the rate and extent of Cr(VI) removal. The rate enhancement by amended surfaces is presumed to result from scavenging of Fe(0)-Cr(VI) reaction products by the provided surfaces, which minimized surface deactivation of Fe(0). The rate enhancing effect was greater for silica compared to sand, and the difference is attributed to silica's higher surface area, greater affinity for reaction products and pH buffering effect. For a given mass of Fe(0), the reactivity and longevity of Fe(0) to treat Cr(VI) increased with increasing dose of silica. Elemental analyses of the reacted iron and silica revealed that chromium removed from the solution was associated with both surfaces, with its mass distribution being approximately 1:1 per mass of iron and silica. The overall result suggests reductive precipitation was a predominant Cr(VI) removal pathway, which involves initial reduction of Cr(VI) to Cr(III), followed by formation of Cr(III)/Fe(III) hydroxides precipitates.     

Nitrate and ammonium ions removal from groundwater by a hybrid system of zero-valent iron combined with adsorbents

Nitrate (NO(3)(-)) is a commonly found contaminant in groundwater and surface water. It has created a major water quality problem worldwide. The laboratory batch experiments were conducted to investigate the feasibility of HCl-treated zero-valent iron (Fe(0)) combined with different adsorbents as hybrid systems for simultaneous removal of nitrate (NO(3)(-)) and ammonium (NH(4)(+)) ions from aqueous solution. The maximum NO(3)(-) removal in combined Fe(0)-granular activated carbon (GAC), Fe(0)-filtralite and Fe(0)-sepiolite systems was 86, 96 and 99%, respectively, at 45 °C for 24 h reaction time. The NO(3)(-) removal rate increased with the increase in initial NO(3)(-) concentration. The NO(3)(-) removal efficiency by hybrid systems was in the order of sepiolite > filtralite > GAC. The NH(4)(+) produced during the denitrification process by Fe(0) was successfully removed by the adsorbents, with the removal efficiency in the order of GAC > sepiolite > filtralite. Results of the present study suggest that the use of a hybrid system could be a promising technology for achieving simultaneous removal of NO(3)(-) and NH(4)(+) ions from aqueous solution.     

Multi-metal resistance and plant growth promotion potential of a wastewater bacterium Pseudomonas aeruginosa and its synergistic benefits

Water and soil pollution by toxic heavy metals (HMs) is increasing globally because of increase in population, industrialization and urbanization. It is a burning problem for the public, scientists, academicians and politicians how to tackle the toxic contaminants which jeopardize the environment. One possible solution for pollution abatement is a bioremediation-effective and innovative technology that uses biological systems for treatment of contaminants. Many bacteria synthesize indole-3-acetic acid (IAA) which is a product of l-tryptophan metabolism and belongs to the auxin class of plant growth-promoting hormone. The present study aimed at assessing the resistance pattern of wastewater bacteria against multiple HMs and plant growth promotion activity associated with IAA. A Gram-negative bacterial strain Pseudomonas aeruginosa KUJM was isolated from Kalyani Sewage Treatment Plant. This strain showed the potential to tolerate multiple contaminations such as As(III) (50 mM), As(V) (800 mM), Cd (8 mM), Co (18 mM), Cu (7 mM), Cr (2.5 mM), Ni (3 mM) and Zn (14 mM). The capability of IAA production at different tryptophan concentration (1, 2, 5 and 10 mg mL⁻¹) was determined, and seed germination-enhancing potential was also estimated on lentil (Lens culinaris). Such type of HM-resistant, IAA-producing and seed germination-enhancing P. aeruginosa KUJM offer great promise as inoculants to promote plant growth in the presence of toxic HMs, as well as plant inoculant systems useful for phytoremediation of polluted soils. Hence, P. aeruginosa KUJM finds significant applications in HM-contaminated poor agricultural field as well as in bioremediation of HM-contaminated wastewater system.

     

Microbial transformation of dissolved organic matter from different sources and its influence on disinfection byproduct formation potentials

Biodegradation-induced changes in the characteristics of dissolved organic matter (DOM) and the subsequent effects on disinfection byproduct formation potentials (DBPFPs) were investigated using six different sources of DOM (algae, leaf litter, reed, compost, paddy water, and treated municipal sewage effluent). Microbial incubation of the DOM samples increased the specific ultraviolet absorbance and humic-like fluorescence but decreased the protein/tannin-like fluorescence and relative distribution of smaller-sized DOM components. Comparison of the original versus biodegraded DOM samples using resin fractionation and pyrolysis–gas chromatography/mass spectrometry revealed that the biodegradation-induced changes were highly dependent on DOM sources and exhibited no consistent trends among the different sources. Changes in DBPFPs also differed with DOM source. Vascular plant-derived DOM (leaf litter and reed) demonstrated an enhancement in specific DBPFP after biodegradation, whereas little change or even a slight decrease was observed for the other DOM sources. Correlations that were significant between specific DBPFPs and the aromatic content or humic-like fluorescence for the original DOM samples were no longer significant after microbial degradation. The relative abundance of hydrophobic to hydrophilic structures in DOM is suggested to be a general indicator for the formation potential of trihalomethanes irrespective of DOM source and the state of biodegradation.     

Isolation and fractionation of natural organic matter: evaluation of reverse osmosis performance and impact of fractionation parameters

Dissolved organic matter (DOM) from three surface waters was isolated using reverse osmosis (RO) and subsequently fractionated using resin adsorption chromatography (RAC). Efficacy of RO was evaluated by closing mass balances for dissolved organic carbon (DOC). RAC was evaluated by investigating the effect of column operational parameters (column capacity factor, k', and solute initial concentration, C0) on DOM fractionation and subsequent disinfection by-product formation. Efficacy of RO was dependent on both isolation conditions and source water characteristics. In general, RO more effectively isolated DOM in high specific ultraviolet absorbance (SUVA254) water than low SUVA254 water, and showed higher DOM recovery at ambient pH (approximately 7) than at low pH (approximately 4). The fractionation of the isolated DOM indicated that the relative amount of the hydrophobic fraction decreased with increasing k', thus affecting the overall distribution of DOM. However, the distribution of DOM fractions was not influenced by varying C0 up to 150 mg l(-1) at k' of 15. The effect of k' on the formation and speciation of trihalomethanes (THM) and haloacetic acids (HAA) was not significant up to k' of 30.     

Influence of drought and municipal sewage effluents on the baseflow water chemistry of an upper piedmont river

The Reedy River in South Carolina is affected by the urban area of Greenville, the third most populous city in the state, and by the effluents from two large-scale municipal wastewater treatment plants (WWTPs) located on the river. Riverine water chemistry was characterized using grab samples collected annually under spring season baseflow conditions. During the 4-year time period associated with this study, climatic variations included two severe drought spring seasons (2001 and 2002), one above-normal precipitation spring season (2003), and one below-normal precipitation spring season (2004). The influence of drought and human activities on the baseflow chemistry of the river was evaluated by comparing concentrations of dissolved anions, total metals, and other important water chemistry parameters for these different years. Concentrations of copper and zinc, common non-point source contaminants related to urban activities, were not substantially elevated in the river within the urban area under baseflow conditions when compared with headwater and tributary samples. In contrast, nitrate concentrations increased from 1.2–1.6 mg/l up to 2.6–2.9 mg/l through the urban stream reach. Concentrations of other major anions (e.g., sulfate, nitrate) also increased along the reach, suggesting that the river receives continuous inputs of these species from within the urban area. The highest concentrations of major cations and anions typically were observed immediately downstream from the two WWTP effluent discharge locations. Attenuation of nitrate downstream from the WWTPs did not always track chloride changes, suggesting that nitrate concentrations were being controlled by biochemical processes in addition to physical processes. The relative trends in decreasing nitrate concentrations with downstream distance appeared to depend on drought versus non-drought conditions, with biological processes presumably serving as a more important control during non-drought spring seasons.     

The effects of pH, bromide and nitrite on halonitromethane and trihalomethane formation from amino acids and amino sugars

In this study, the effects of pH, bromide and nitrite on the formation of halonitromethanes (HNMs) and trihalomethanes (THMs) from eight amino acids (glycine, alanine, serine, cysteine, aspartic acid, glutamic acid, lysine and histidine) and four amino sugars (glucosamine, galactosamine, N-acetylglucosamine and N-acetylneuraminic acid) were examined for chlorination and ozonation followed by chlorination. During ozonation-chlorination, two amino acids, glycine and lysine, exhibited distinctly higher HNM formation than the other compounds. The formation of HNMs was higher at pH 8 than 6. Glycine and lysine also produced higher levels of THMs than the other compounds at pH 8. The presence of nitrite resulted in an increase in HNM formation. The presence of bromide increased the HNM formation, especially brominated HNM species. Bromine incorporation factors of trihalogenated HNMs were higher than those of THMs. For chlorination alone, HNM levels were about the detection limit (4 nM or 0.7 μg L⁻¹) at pH 6 and 8, and in the presence of bromide or nitrite. Amino acids and amino sugars tested, except glycine and lysine, showed relatively low levels of THM (∼15 μg L⁻¹) formation.     

Amendment of hydroxyapatite in reduction of tetrachloroethylene by zero-valent zinc: its rate enhancing effect and removal of Zn(II)

The effects of hydroxyapatite (HAP) on dechlorination of tetrachloroethylene (PCE) by zero-valent zinc (ZVZ) were examined in batch systems. PCE was primarily transformed to trichloroethylene by ZVZ, with 1,2-trans-dichloroethylene representing a minor product. Dechlorination of PCE was accelerated by the presence of HAP, and the pseudo-first order rate constants increased with increasing amount of HAP. Zn(II), mostly generated from oxidative dissolution of ZVZ by PCE, was effectively removed from the solution by HAP. Ion substitution, coprecipitation, and adsorption are proposed as the possible mechanisms for Zn(II) removal. These reactions appeared to occur simultaneously and the contribution of each reaction to overall removal of Zn(II) was primarily dependent on HAP loading at constant ZVZ loading. The results indicate that the use of HAP in combination with conventional zero-valent metals is promising in that it can achieve both degradation of organic contaminants and stabilization of inorganic contaminants.     

Comparative effectiveness of mixed organic substrates to mushroom compost for treatment of mine drainage in passive bioreactors

Bioreactors are one possible best sustainable technology to address the mine-impacted water problems. Several prospective substrates (mushroom compost, cow manure, sawdust, wood chips, and cut rice straw) were characterized for their ability to serve as a source of food and energy for sulfate-reducing bacteria. Twenty bench-scale batch bioreactors were then designed and set up to investigate relative effectiveness of various mixtures of substrates to that of mushroom compost, the most commonly used substrate in field bioreactors, for treating mine drainage with acidic (pH 3) and moderate pH (pH 6). Overall, reactive mixtures showed satisfactory performances in generating alkalinity, reducing sulfate and removing metals (Al>Fe>Mn) (up to 100%) at both pH conditions, for all substrates. The mixture of sawdust and cow manure was found as the most effective whereas the mixture containing 40% cut rice straw gave limited efficiency, suggesting organic carbon released from this substrate is not readily available for biodegradation under anaerobic conditions. The mushroom compost-based bioreactors released significant amount of sulfate, which may raise a more concern upon the start-up of field-scale bioreactors. The correlation between the extent of sulfate reduction and dissolved organic carbon/SO(4)(2-) ratio was weak and this indicates that the type of dissolved organic carbon plays a more important role in sulfate reduction than the absolute concentration and that the ratio is not sensitive enough to properly describe the relative effectiveness of substrate mixtures.