Effect of lime on speciation of heavy metals during composting of water hyacinth

Composting is attractive and inexpensive method for treatment and biomass disposal of water hyacinth. However, the major disadvantage of water hyacinth composting is the high content of heavy metals in the final compost. Addition of lime sludge significantly reduced most bioavailable fractions (exchangeable and carbonate) of heavy metals. Studies were carried on composting of water hyacinth (Eichhornia crassipes) with cattle manure and sawdust (6:3:1 ratio) and effects of addition of lime (1%, 2% and 3%) on heavy metal speciation were evaluated during 30 days of composting period. The Tessier sequential extraction method was employed to investigate the changes in speciation of heavy metals such as Zinc (Zn), Copper (Cu), Manganese (Mn), Iron (Fe), Lead (Pb), Nickel (Ni), Cadmium (Cd) and Chromium (Cr) during water hyacinth composting. Effects of physicochemical parameters such as temperature, pH and organic matter on speciation of heavy metals were also studied during the process. Results showed that, the total metal content was increased during the composting process. The higher reduction in bioavailability factor (BF) of Cu, Fe, Ni, Cd and Cr was observed in lime 2 treatment about 62.1%, 64.4%, 71.9%, 62.1% and 58.9% respectively; however higher reduction in BF of Zn and Pb was observed in lime 1 treatment during the composting process. Reducible and oxidizable fractions of Ni, Pb and Cd were not observed during the process. Addition of lime was very effective for reduction of bioavailability of heavy metals during composting of water hyacinth with cattle manure and sawdust.     

Vacuum promotes metabolic shifts and increases biogenic hydrogen production in dark fermentation systems

The successful operation of any type of hydrogen-producing bioreactor depends on the performance of the microorganisms present in the system. Both substrate and partial gas pressures are crucial factors affecting dark fermentation metabolic pathways. The main objective of this study was to evaluate the impact of both factors on hydrogen production using anaerobic granular sludge as inoculum and, secondly, to study the metabolic shifts of an anaerobic community subjected to low partial gas pressures. With this goal in mind, seven different wastewater (four synthetic media, two industrial wastewater, and one domestic effluent) and the effect of applying vacuum on the systems were analyzed. The application of vacuum promoted an increase in the diversity of hydrogenproducing bacteria, such as Clostridium, and promoted the dominance of acetoclastic- over hydrogenotrophic methanogens. The application of different media promoted a wide variety of metabolic pathways. Nevertheless, reduction of the hydrogen partial pressure by application of vacuum lead to further oxidation of reaction intermediates irrespective of the medium used, which resulted in higher hydrogen and methane production, and improved the COD removal. Interestingly, vacuum greatly promoted biogenic hydrogen production from a real wastewater, which opens possibilities for future application of dark fermentation systems to enhance biohydrogen yields.     

A photolysis coefficient for characterizing the response of aqueous constituents to photolysis

UV photolysis and UV based advanced oxidation processes (AOPs) are gaining more and more attention for drinking water treatment. Quantum yield (ø) and molar absorption coefficient (ε) are the two critical parameters measuring the effectiveness of photolysis of a compound. The product of the two was proposed as a fundamental measure of a constituent’s amenability to transformation by photolysis. It was shown that this product, named the photolysis coefficient, k _p , can be determined using standard bench tests and captures the properties that govern a constituent’s transformation when exposed to light. The development showed the photolysis coefficient to be equally useful for microbiological, inorganic and organic constituents. Values of k _p calculated by the authors based on quantum yield and molar absorption coefficient data from the literature were summarized. Photolysis coefficients among microorganisms ranged from 8500 to more than 600000 and are far higher than for inorganic and organic compounds, which varied over a range of approximately 10 to 1000 and are much less sensitive to UV photolysis than the microorganisms.     

Improving simulations of sulfate aerosols during winter haze over Northern China: the impacts of heterogeneous oxidation by NO2

Incorporating the missing heterogeneous oxidation of S(IV) by NO₂ into the WRF-Chem model. Sulfate production is not sensitive to increase in SO₂ emission. The newly added reaction reproduces sulfate concentrations well during winter haze. We implemented the online coupled WRF-Chem model to reproduce the 2013 January haze event in North China, and evaluated simulated meteorological and chemical fields using multiple observations. The comparisons suggest that temperature and relative humidity (RH) were simulated well (mean biases are -0.2K and 2.7%, respectively), but wind speeds were overestimated (mean bias is 0.5 m?s⁻¹). At the Beijing station, sulfur dioxide (SO₂) concentrations were overpredicted and sulfate concentrations were largely underpredicted, which may result from uncertainties in SO₂ emissions and missing heterogeneous oxidation in current model. We conducted three parallel experiments to examine the impacts of doubling SO₂ emissions and incorporating heterogeneous oxidation of dissolved SO₂ by nitrogen dioxide (NO₂) on sulfate formation during winter haze. The results suggest that doubling SO₂ emissions do not significantly affect sulfate concentrations, but adding heterogeneous oxidation of dissolved SO₂ by NO₂ substantially improve simulations of sulfate and other inorganic aerosols. Although the enhanced SO₂ to sulfate conversion in the HetS (heterogeneous oxidation by NO₂) case reduces SO₂ concentrations, it is still largely overestimated by the model, indicating the overestimations of SO₂ concentrations in the North China Plain (NCP) are mostly due to errors in SO₂ emission inventory.     

Chemical poison and regeneration of SCR catalysts for NOx removal from stationary sources

Selective catalytic reduction (SCR) of NO_x with NH₃ is an effective technique to remove NO_x from stationary sources, such as coal-fired power plant and industrial boilers. Some of elements in the fly ash deactivate the catalyst due to strong chemisorptions on the active sites. The poisons may act by simply blocking active sites or alter the adsorption behaviors of reactants and products by an electronic interaction. This review is mainly focused on the chemical poisoning on V₂O₅-based catalysts, environmental-benign catalysts and low temperature catalysts. Several common poisons including alkali/alkaline earth metals, SO₂ and heavy metals etc. are referred and their poisoning mechanisms on catalysts are discussed. The regeneration methods of poisoned catalysts and the development of poison-resistance catalysts are also compared and analyzed. Finally, future research directions in developing poisoning resistance catalysts and facile efficient regeneration methods for SCR catalysts are proposed.     

Disinfection byproducts in drinking water and regulatory compliance: A critical review

Disinfection by-products (DBPs) are regulated in drinking water in a number of countries. This critical review focuses on the issues associated with DBP regulatory compliance, including methods for DBP analysis, occurrence levels, the regulation comparison among various countries, DBP compliance strategies, and emerging DBPs. The regulation comparison between China and the United States (US) indicated that the DBP regulations in China are more stringent based on the number of regulated compounds and maximum levels. The comparison assessment using the Information Collection Rule (ICR) database indicated that the compliance rate of 500 large US water plants under the China regulations is much lower than that under the US regulations (e.g. 62.2% versus 89.6% for total trihalomethanes). Precursor removal and alternative disinfectants are common practices for DBP regulatory compliance. DBP removal after formation, including air stripping for trihalomethane removal and biodegradation for haloacetic acid removal, have gained more acceptance in DBP control. Formation of emerging DBPs, including iodinated DBPs and nitrogenous DBPs, is one of unintended consequences of precursor removal and alternative disinfection. At much lower levels than carbonaceous DBPs, however, emerging DBPs have posed higher health risks.     

Nexus between polymer support and metal oxide nanoparticles in hybrid nanosorbent materials (HNMs) for sorption/desorption of target ligands

Metal oxide nanoparticles like hydrated ferric oxide (HFO) or hydrated zirconium oxide (HZrO) are excellent sorbents for environmentally significant ligands like phosphate, arsenic, or fluoride, present at trace concentrations. Since the sorption capacity is surface dependent for HFO and HZrO, nanoscale sizes offer significant enhancement in performance. However, due to their miniscule sizes, low attrition resistance, and poor durability they are unable to be used in typical plug-flow column setups. Meanwhile ion exchange resins, which have no specific affinity toward anionic ligands, are durable and chemically stable. By impregnating metal oxide nanoparticles inside a polymer support, with or without functional groups, a hybrid nanosorbent material (HNM) can be prepared. A HNM is durable, mechanically strong, and chemically stable. The functional groups of the polymeric support will affect the overall removal efficiency of the ligands exerted by the Donnan Membrane Effect. For example, the removal of arsenic by HFO or the removal of fluoride by HZrO is enhanced by using anion exchange resins. The HNM can be precisely tuned to remove one type of contaminant over another type. Also, the physical morphology of the support material, spherical bead versus ion exchange fiber, has a significant effect on kinetics of sorption and desorption. HNMs also possess dual sorption sites and are capable of removing multiple contaminants, namely, arsenate and perchlorate, concurrently.     

Optimizing synthesis conditions of nanoscale zero-valent iron (nZVI) through aqueous reactivity assessment

Nanoscale iron particles (nZVI) is one of the most important engineered nanomaterials applied to environmental pollution control and abatement. Although a multitude of synthesis approaches have been proposed, a facile method to screen the reactivity of candidate nZVI materials produced using different methods or under varying synthesis conditions has yet been established. In this study, four reaction parameters were adjusted in the preparation of borohydride-reduced nZVI. The reductive properties of the resultant nanoparticles were assayed independently using two model aqueous contaminants, Cu(II) and nitrate. The results confirm that the reductive reactivity of nZVI is most sensitive to the initial concentration of iron precursor, borohydride feed rate, and the loading ratio of borohydride to ferric ion during particle synthesis. Solution mixing speed, in contrast, carries a relative small weight on the reactivity of nZVI. The two probing reactions (i.e., Cu(II) and nitrate reduction) are able to generate consistent and quantitative inference about the mass-normalized surface activity of nZVI. However, the nitrate assay is valid in dilute aqueous solutions only (50 mg·L⁻¹ or lower) due to accelerated deactivation of iron surface at elevated nitrate concentrations. Additional insights including the structural and chemical makeup of nZVI can be garnered from Cu(II) reduction assessments. The reactivity assays investigated in this study can facilitate screening of candidate materials or optimization of nZVI production parameters, which complement some of the more sophisticated but less chemically specific material characterization methods used in the nZVI research.     

Microbial communities biostimulated by ethanol during uranium (VI) bioremediation in contaminated sediment as shown by stable isotope probing

Stable isotope probing (SIP) was used to identify microbes stimulated by ethanol addition in microcosms containing two sediments collected from the bioremediation test zone at the US Department of Energy Oak Ridge site, TN, USA. One sample was highly bioreduced with ethanol while another was less reduced. Microcosms with the respective sediments were amended with ¹³C labeled ethanol and incubated for 7 days for SIP. Ethanol was rapidly converted to acetate within 24 h accompanied with the reduction of nitrate and sulfate. The accumulation of acetate persisted beyond the 7 d period. Aqueous U did not decline in the microcosm with the reduced sediment due to desorption of U but continuously declined in the less reduced sample. Microbial growth and concomitant ¹³C-DNA production was detected when ethanol was exhausted and abundant acetate had accumulated in both microcosms. This coincided with U(VI) reduction in the less reduced sample. ¹³C originating from ethanol was ultimately utilized for growth, either directly or indirectly, by the dominant microbial community members within 7 days of incubation. The microbial community was comprised predominantly of known denitrifiers, sulfate-reducing bacteria and iron (III) reducing bacteria including Desulfovibrio, Sphingomonas, Ferribacterium, Rhodanobacter, Geothrix, Thiobacillus and others, including the known U(VI)-reducing bacteria Acidovorax, Anaeromyxobacter, Desulfovibrio, Geobacter and Desulfosporosinus. The findings suggest that ethanol biostimulates the U(VI)-reducing microbial community by first serving as an electron donor for nitrate, sulfate, iron (III) and U(VI) reduction, and acetate which then functions as electron donor for U(VI) reduction and carbon source for microbial growth.     

Assessment of oxidative and UV-C treatments for inactivating bacterial biofilms from groundwater wells

Microorganisms are ubiquitous in natural environments and in water supply infrastructure including groundwater wells. Sessile-state microorganisms may build up on well surfaces as biofilms and, if excessive, cause biofouling that reduces well productivity and water quality. Conditions can be improved using biocides and other traditional well rehabilitation measures; however, biofilm regrowth is inevitable given the continuous introduction of microorganisms from the surrounding environment. Alternative and less invasive well maintenance approaches are desirable for reducing biofilm densities while also minimizing harmful disinfection-by-products. The primary objective of this research was to evaluate effectiveness of alternative treatments for inactivating microorganisms comprising biofilms. A novel approach was designed for in situ growth of biofilms on steel coupons suspended from ‘chandeliers’. After more than 100 days of in situ growth, biofilms were harvested, sampled, and baseline biofilm densities quantified through cultivation. Ultraviolet-C (UV-C) and oxidative treatments including hydrogen peroxide (H₂O₂), ozone (O₃) and mixed oxidants were then applied to the biofilms in laboratory-scale treatments. Microbial inactivation was assessed by comparing treated versus baseline biofilm densities. H₂O₂ was the most effective treatment, and decreased density below baseline by as much as 3.1 orders of magnitude. Mixed oxidants were effective for the well having a lower density biofilm, decreasing density below baseline by as much as 1.4 orders of magnitude. Disparity in the response to treatment was apparent in the wells despite their spatial proximity and common aquifer source, which suggests that microbiological communities are more heterogeneous than the natural media from which they originate.