Addition Of Organic Substrates Research Articles

Effective remediation of agricultural drainage at three influent strengths by bioaugmented constructed wetlands filled with mixture of iron‑carbon and organic solid substrates: Performance and mechanisms

Agricultural drainage containing a large quantity of nutrients can cause quality deterioration and algal blooming of receiving water bodies, thus needs to be effectively remediated. In this study, iron‑carbon (FeC) composite-filled constructed wetlands (Fe-C-CWs) were employed to treat farmland drainage at three pollution levels, and organic solid substrates (walnut shells) and phosphate-accumulating denitrifying bacteria (Pseudomonas sp. DWP1) were supplemented to enhance the treatment performance. The results showed that the Fe-C-CWs exhibited notably superior removal efficiency for total nitrogen (TN, 52.0–58.2 %), total phosphorus (TP, 67.8–70.2 %) and chemical oxygen demand (COD, 56.7–70.4 %) than the control systems filled solely with gravel (28.5–32.5 % for TN, 33.2–40.5 % for TP and 30.2–55.0 % for COD) at all influent strengths, through driving autotrophic denitrification, Fe-based dephosphorization, and organic degradation processes. The addition of organic substrates and functional bacteria markedly enhanced pollutant removal in the Fe-C-CWs. Furthermore, use of FeC and organic substrates and denitrifier inoculation decreased CO2 and CH4 emissions from the CWs, and reduced global warming potential of the CWs at low influent strength. Pollutant removal efficiencies in the CWs were only marginally impacted by the increasing influent loads except for NO3−-N, and pollutant removal mass was largely increased with the increase of influent strengths. The microbial community in the FeC composite-filled CWs exhibited distinct distribution patterns compared to the gravel-filled CWs regardless of the influent strengths, with obviously higher proportions of dominant genera Trichococcus, Geobacter and Ferritrophicum. Keystone taxa associated with pollutant removal in the Fe-C-filled CWs were identified to be Pseudomonas, Geobacter, Ferritrophicum, Denitratisoma and Sediminibacterium. The developed augmented Fe-C-filled CWs show great promises for remediating agricultural drainage with varied pollutant loads.

Priming is frequently overestimated in studies using 14C-labelled substrates due to underestimation of 14CO2 activity

The priming effect defined as an increased turnover of soil organic matter (SOM) upon organic substrate addition to soils has been investigated for decades, but its underlying mechanisms remain elusive. It has been shown that 14CO2 trapped in NaOH can be rapidly released from the solution when mixing small volume, low molar or highly CO2-saturated NaOH samples with scintillation cocktails. Therefore, liquid scintillation counting can substantially underestimate the 14C-activity of such samples. In this study, we explore the implications of this methodological shortcoming for priming studies.In a literature review, we look at priming studies that use 14C-labelling to differentiate CO2 evolved from substrates and SOM published in 1993–2021. Out of 65 studies in total, 34 use scintillation cocktails that we had previously tested for outgassing of 14CO2. Out of the 21 studies that provide information about the relevant scintillation counting parameters that determine stability of the measurement, 33–43% use scintillation counting parameters that can be expected to underestimate 14C-activity. In an exemplary priming study, we examine a potential magnitude of error resulting from such incorrect measurements for priming determination and a method to correct the results even when the samples are no longer available to be re-measured. A sandy topsoil and subsoil were incubated with and without added nutrients and 500 (μg C) g−114C-labelled sucrose for 33 days, evolving CO2 was trapped in 0.35 M NaOH and scintillation counted with Ultima GoldXR. By repeatedly re-measuring similarly prepared calibration vials of known 14C-activity, we correct the measurements based on the time passed between preparation and measurement of the vial. We find that with these experimental parameters, 14C-activity is underestimated by 10–30% and consequently, priming is overestimated by 53–66 (μg C) g−1 soil. After correction of the data, we find 16–40 (μg C) g−1 primed carbon. Mass balancing reveals that 10.5–12.8% of 14C-activity of the substrate were recovered by the scintillation correction while 7.3–10.2% remain unaccounted for.These findings suggest that if the 14CO2 activity is underestimated during scintillation counting, then priming can be overestimated by a multiple of the true value and priming can even be found where there isn't any. This issue should not be ignored when discussing priming, considering the prevalence of this method in priming studies, the lack of reporting of relevant experimental parameters and the number of reported flawed experimental parameters found in the literature.

Cyanide replaces substrate in obligate-ordered addition of nitric oxide to the non-heme mononuclear iron AvMDO active site.

Thiol dioxygenases are a subset of non-heme mononuclear iron oxygenases that catalyze the O2-dependent oxidation of thiol-bearing substrates to yield sulfinic acid products. Cysteine dioxygenase (CDO) and 3-mercaptopropionic acid (3MPA) dioxygenase (MDO) are the most extensively characterized members of this enzyme family. As with many non-heme mononuclear iron oxidase/oxygenases, CDO and MDO exhibit an obligate-ordered addition of organic substrate before dioxygen. As this substrate-gated O2-reactivity extends to the oxygen-surrogate, nitric oxide (NO), EPR spectroscopy has long been used to interrogate the [substrate:NO:enzyme] ternary complex. In principle, these studies can be extrapolated to provide information about transient iron-oxo intermediates produced during catalytic turnover with dioxygen. In this work, we demonstrate that cyanide mimics the native thiol-substrate in ordered-addition experiments with MDO cloned from Azotobacter vinelandii (AvMDO). Following treatment of the catalytically active Fe(II)-AvMDO with excess cyanide, addition of NO yields a low-spin (S = 1/2) (CN/NO)-Fe-complex. Continuous wave and pulsed X-band EPR characterization of this complex produced in wild-type and H157N variant AvMDO reveal multiple nuclear hyperfine features diagnostic of interactions within the first- and outer-coordination sphere of the enzymatic Fe-site. Spectroscopically validated computational models indicate simultaneous coordination of two cyanide ligands replaces the bidentate (thiol and carboxylate) coordination of 3MPA allowing for NO-binding at the catalytically relevant O2-binding site. This promiscuous substrate-gated reactivity of AvMDO with NO provides an instructive counterpoint to the high substrate-specificity exhibited by mammalian CDO for L-cysteine.

The Clean Water Act and biosolids: A 45‐year chronological review of biosolids land application research in Colorado

The 1972 U.S. Clean Water Act set forth the generation of biosolids. In Colorado, biosolids land application research began in 1976 and continues today. Pastureland research suggested that sewage effluent could effectively be land applied to benefit aboveground plant growth and to polish water prior to reaching receiving waters. Forest wildfire-affected ecosystems can also benefit from biosolids applications; application rates of up to 80 Mg ha-1 can lead to greater plant establishment, soil microbial activity, and nutrient turnover and reduced nutrient and heavy metal concentrations in runoff below livestock and USEPA drinking water standards. Long-term (24-yr) observations in oil shale-mined lands showed that biosolids (up to 224 Mg ha-1 ) can have a positive effect on microbial-mediated nutrient cycling and, in turn, on aboveground plant community structure. Biosolids applications of up to 40 Mg ha-1 in high-elevation shrubland ecosystems, dominated by Mo-containing shale deposits, can aid in reducing imbalances between Mo and Cu in soils and plants; excessive plant Mo, when consumed by ruminants, can lead to molybdenosis. Biosolids and lime applications (both at 224 Mg ha-1 ) have been shown to improve long-term reclamation success on acid-generating, heavy metal-containing fluvial mine tailings. Thirty years of grazing land research, focused on soil and aboveground plant benefits, illustrate that soil health and plant productivity can be improved to the greatest extent at biosolids application rates close to 10 Mg ha-1 . Finally, 40 yr of dryland agroecosystem research (a) have helped identify biosolids N fertilizer equivalency (∼8kg N Mg-1 ) and thus dryland winter wheat application rates (e.g., 4.5-6.7 dry Mg ha-1 ); (b) have identified first-year mineralization rates of 25-32%; (c) dispute the "time bomb" theory by showing that plant metal uptake follows an exponential rise to a maximum; (d) showcase economic return to producers via increased wheat grain protein content; (e) suggest that biosolids-borne proteins and their degradation products are labile C and N sources; (f) have led to long-term tracking of micronutrients and heavy metals in soils and revealed that plants-soil concentrations will not lead to groundwater degradation and that plants are safe for human consumption; and (g) have shown that biosolids provide Zn, helping to overcome soil deficiencies and enhancing Zn biofortification in wheat grain. This latter point is important because ∼2 billion people globally suffer from Zn deficiencies. Forty-five years of research in Colorado have proven that biosolids can enhance environmental quality, improve soil health, and produce healthy food products.

Successful year-round mainstream partial nitritation anammox: Assessment of effluent quality, performance and N2O emissions

For two decades now, partial nitritation anammox (PNA) systems were suggested to more efficiently remove nitrogen (N) from mainstream municipal wastewater. Yet to date, only a few pilot-scale systems and even fewer full-scale implementations of this technology have been described. Process instability continues to restrict the broad application of PNA. Especially problematic are insufficient anammox biomass retention, the growth of undesired aerobic nitrite-oxidizers, and nitrous oxide (N2O) emissions. In this study, a two-stage mainstream pilot-scale PNA system, consisting of three reactors (carbon pre-treatment, nitritation, anammox - 8 m3 each), was operated over a year, treating municipal wastewater. The aim was to test whether both, robust autotrophic N removal and high effluent quality, can be achieved throughout the year. A second aim was to better understand rate limiting processes, potentially affecting the overall performance of PNA systems. In this pilot study, excellent effluent quality, in terms of inorganic nitrogen, was accomplished (average effluent concentrations: 0.4 mgNH4-N/L, 0.1 mgNO2-N/L, 0.9 mgNO3-N/L) even at wastewater temperatures previously considered problematic (as low as 8 °C). N removal was limited by nitritation rates (84 ± 43 mgNH4-N/L/d), while surplus anammox activity was observed at all times (178 ± 43 mgN/L/d). Throughout the study, nitrite-oxidation was maintained at a low level (<2.5% of ammonium consumption rate). Unfortunately, high N2O emissions from the nitritation stage (1.2% of total nitrogen in the influent) were observed, and, based on natural isotope abundance measurements, could be attributed to heterotrophic denitrification. In situ batch experiments were conducted to identify the role of dissolved oxygen (DO) and organic substrate availability in N2O emission-mitigation. The addition of organic substrate, to promote complete denitrification, was not successful in decreasing N2O emission, but increasing the DO from 0.3 to 2.9 mgO2/L decreased N2O emissions by a factor of 3.4.

Bioremediasi air asam tambang batubara dengan pengayaan bakteri pereduksi sulfat dan penambahan substrat organik

Bioremediasi air asam tambang batubara dengan pengayaan bakteri pereduksi sulfat dan penambahan substrat organik

Effectiveness Vetiveria zizanoides plant in ability absorption of heavy metals in coal mining waste

Vetiveria zizanoides plants have considerable potential for phytoremediation, because these plants show relatively high ability to accumulate and translocate heavy metals in wetlands and are able to tolerate acidic water pH. The results of the study showed that the Vetiveria zizanoides plant has a fairly good survival rate in acid mine water conditions and has a fairly high ability to absorb Fe, Mn and sulfur metals. This is evidenced by the treatment of Vetiveria zizanoides plants by planting 20 Vetiveria zizanoides stems into acid mine water media without the addition of organic substrates, seen on day 20 after treatment of 20 Vetiveria zizanoides stems there was only 1 plant that died, the rest still survive in acidic water conditions. In this treatment, the Vetiveria zizanoides plant was able to absorb Fe, Mn and sulfur with an efficiency increase of 93% for Fe metal, 40% for Mn metal and 43% sulfur for 20 days. However, to improve the quality of acid water in this treatment, it was not optimal, so treatment was given with a combination of Vetiveria zizanoides and organic substrates. Treatment 3 was the most effective in improving acid mine water quality, because it had an average effectiveness of 58% for increasing the pH of the air and 97% for decreasing the concentration of Fe and Mn metals. With the efficiency of increasing the metal concentration in plants by 16% for Fe metal, 29% for Mn metal and 35% sulfur for 20 days after being given treatment.

Overcoming establishment thresholds for peat mosses in human-made bog pools.

Globally, peatlands have been affected by drainage and peat extraction, with adverse effects on their functioning and services. To restore peat‐forming vegetation, drained bogs are being rewetted on a large scale. Although this practice results in higher groundwater levels, unfortunately it often creates deep lakes in parts where peat was extracted to greater depths than the surroundings. Revegetation of these deeper waters by peat mosses appears to be challenging due to strong abiotic feedbacks that keep these systems in an undesired bare state. In this study, we theoretically explore if a floating peat mat and an open human‐made bog lake can be considered two alternative stable states using a simple model, and experimentally test in the field whether stable states are present, and whether a state shift can be accomplished using floating biodegradable structures that mimic buoyant peat. We transplanted two peat moss species into these structures (pioneer sp. Sphagnum cuspidatum and later‐successional sp. S. palustre) with and without additional organic substrate. Our model suggests that these open human‐made bog lakes and floating peat mats can indeed be regarded as alternative stable states. Natural recovery by spontaneous peat moss growth, i.e., a state shift from open water to floating mats, is only possible when the water table is sufficiently shallow to avoid light limitation (<0.29 m at our site). Our experiment revealed that alternative stable states are present and that the floating structures facilitated the growth of pioneer S. cuspidatum and vascular plants. Organic substrate addition particularly facilitated vascular plant growth, which correlated to higher moss height. The structures remained too wet for the late‐successional species S. palustre. We conclude that open water and floating peat mats in human‐made bog lakes can be considered two alternative stable states, and that temporary floating establishment structures can induce a state shift from the open water state to peat‐forming vegetation state. These findings imply that for successful restoration, there is a clear water depth threshold to enable peat moss growth and there is no need for addition of large amounts of donor‐peat substrate. Correct species selection for restoration is crucial for success.

Straw Mulching and Nitrogen Fertilization Affect Diazotroph Communities in Wheat Rhizosphere

Diazotrophs that carry out the biological fixation of atmospheric dinitrogen (N2) replenish biologically available nitrogen (N) in soil and are influenced by the input of inorganic and organic substrates. To date, little is known about the effects of combined organic substrate addition and N fertilization on the diazotroph community composition and structure in purple soils. We investigated the effects of N fertilization and straw mulching on diazotroph communities by quantifying and sequencing the nifH gene in wheat rhizosphere. The abundance and richness of diazotrophs were greater the higher the fertilization level in the mulched treatments, whereas in the nonmulched treatments (NSMs), richness was lowest with the highest N fertilization level. The abundance and α-diversity of diazotrophs correlated with most of the soil properties but not with pH. At the genus level, the relative abundances of Azospirillum, Bacillus, and Geobacter were higher in the NSMs and those of Pseudacidovorax, Skermanella, Azospira, Paraburkholderia, Azotobacter, Desulfovibrio, Klebsiella, and Pelomonas in the mulched treatments. The differences in community composition between the mulched and the NSMs were associated with differences in soil temperature and soil organic carbon and available potassium contents and C:N ratio. Overall, straw mulching and N fertilization were associated with changes in diazotroph community composition and higher abundance of nifH gene in alkaline purple soils.

Manganese and cobalt redox cycling in laterites; Biogeochemical and bioprocessing implications

Cobalt is essential for the modern technology that underpins the decarbonisation of our economies, but its supply is limited leading to its designation as a critical metal. Cobalt biogeochemistry is poorly understood, yet knowledge of how biogeochemical cycling impacts cobalt behaviour could assist the development of new techniques to recover cobalt from ores, and so improve the security of supply. Laterites are an important source of cobalt, they are primarily processed for nickel using energy or chemical intensive processes, with cobalt recovered as a by-product. Metal-reducing conditions were stimulated in laterite sediment microcosms by the addition of simple and cheaply available organic substrates (acetate or glucose). At the end of the experiment the amount of easily recoverable cobalt (aqueous or extractable with acetic acid) increased from < 1% to up to 64%, which closely mirrored the behaviour of manganese, while only a small proportion of iron was transformed into an easily recoverable phase. Sequencing of the microbial community showed that the addition of organic substrates stimulated the growth of indigenous prokaryotes closely related to known manganese(IV)/iron(III)-reducers, particularly from the Clostridiales, and that fungi assigned to Penicillium, known to produce organic acids beneficial for leaching cobalt and nickel from laterites, were identified. Overall, the results indicate that the environmental behaviour of cobalt in laterites is likely to be controlled by manganese biogeochemical cycling by microorganisms. These results are compelling given that similar behaviour was observed in four laterites (Acoje, Çaldağ, Piauí and Shevchenko) from different continents. A new bioprocessing strategy is proposed whereby laterites are treated with an organic substrate to generate metal-reducing conditions, then rinsed with acetic acid to remove the cobalt. Not only are organic substrates environmentally-friendly and potentially sourced from waste carbon substrates, a minimal amount of iron oxides was mobilised and consequently less waste generated.

Removal of radioactive cesium from an aqueous solution via bioaccumulation by microalgae and magnetic separation

We evaluated the potential sequestration of cesium (Cs+) by microalgae under heterotrophic growth conditions in an attempt to ultimately develop a system for treatment of radioactive wastewater. Thus, we examined the effects of initial Cs+ concentration (100–500 μM), pH (5–9), K+ and Na+ concentrations (0–20 mg/L), and different organic carbon sources (acetate, glycerol, glucose) on Cs+ removal. Our initial comparison of nine microalgae indicated that Desmodesmus armatus SCK had removed the most Cs+ under various environmental conditions. Addition of organic substrates significantly enhanced Cs+ uptake by D. armatus, even in the presence of a competitive cation (K+). We also applied magnetic nanoparticles coated with a cationic polymer (polyethylenimine) to separate 137Cs-containing microalgal biomass under a magnetic field. Our technique of combining bioaccumulation and magnetic separation successfully removed more than 90% of the radioactive 137Cs from an aqueous medium. These results clearly demonstrate that the method described here is a promising bioremediation technique for treatment of radioactive liquid waste.

Priming effects of soil organic matter decomposition with addition of different carbon substrates

The addition of organic substrates can change the decomposition rate of soil organic matter (SOM), which is termed as “priming effect.” The objective of this study was to explore the priming effects of SOM decomposition with the addition of different organic carbon substrates, including glucose, oxalic acid, and tannin. We hypothesized that with additions from labile to recalcitrant carbon substrates, the soil priming effects changed from positive to negative. Representing from labile to recalcitrant carbon substrates, glucose, oxalic acid, and tannin were added to soil, respectively. Physicochemical properties of soil, carbon dioxide emission rate, soil organic carbon in the labile and recalcitrant carbon pools, microbial biomass carbon (MBC), and microbial community diversity and structure were measured in different treatments. Results showed that the addition of glucose and tannin produced positive priming effects, while the addition of oxalic acid led to a negative priming effect. The addition of glucose and tannin significantly increased the MBC. The addition of glucose significantly promoted the carbon decomposition in both the labile and recalcitrant soil carbon pools. The addition of tannin greatly promoted carbon decomposition in the labile carbon pool and slightly decreased carbon decomposition in the recalcitrant carbon pool of the soil. However, the addition of oxalic acid reduced the MBC and resulted in insignificant changes of the different soil carbon pools. The addition of organic carbon substrates reduced the soil microbial community diversity, especially the addition of glucose. The different priming effects of the treatments with glucose and tannin were attributable to the different phases in the succession of SOM decomposition processes. The treatment with oxalic acid reduced the soil pH, resulting in inactive microbial growth and reproduction. The addition of both glucose (labile carbon) and tannin (recalcitrant carbon) produced positive priming effects. In contrast, the addition of oxalic acid produced a negative priming effect. Except the treatment with tannin, the hypothesis was successfully tested. The results from this study should be useful to better understand the turnover processes of soil carbon pools with exogenous carbon inputs.

Laboratory Column Evaluation of High Explosives Attenuation in Grenade Range Soils.

High explosives (HEs) deposited on military ranges can leach through the soil and contaminate groundwater. We examined the transport and fate of HEs in laboratory columns containing soils from two hand grenade bays (Bays C and T) and the impact of organic amendments on biodegradation. Soil characteristics were similar; however, Bay C had somewhat higher clay and organic C. Experimental treatments included addition of crude glycerin and lignosulfonate, and parallel control columns. Experimental results showed extensive 2,4,6-trinitrotoluene (TNT) degradation with minimal leaching, consistent with prior batch microcosm results. Amendment addition enhanced TNT degradation in both Bays C and T compared with controls. Although hexahydro-1,3,5-trinitro-1,3,5-triazine (Royal Demolition Explosive, or RDX) did not biodegrade in prior aerobic batch microcosms, 64 to 77% of RDX biodegraded in untreated soil columns with O present in the mobile soil gas. The RDX biodegradation was likely associated with short-term anoxic conditions or anoxic micro-niches. In nearly saturated Bay C columns, RDX removal increased to >92%. Amendment addition to unsaturated Bay T columns increased RDX removal to >86%. In one column, the soil remained anoxic (O < 5% by volume) for about a year after amendment addition, significantly reducing RDX leaching. Nitroso degradation products were produced equivalent to 9 to 39% of the RDX degraded, with most retained in the soil (9-37%) and 0 to 3% in the effluent. These results demonstrate that RDX biodegradation can occur in soils with measurable O, and that amendment addition can reduce RDX leaching by stimulating anaerobic biodegradation.

Effect of oyster shell medium and organic substrate on the performance of a particulate pyrite autotrophic denitrification (PPAD) process

The use of pyrite as an electron donor for biological denitrification has the potential to reduce alkalinity consumption and sulfate by-product production compared with sulfur oxidizing denitrification. This research investigated the effects of oyster shell and organic substrate addition on the performance of a particulate pyrite autotrophic denitrification (PPAD) process. Side-by-side bench-scale studies were carried out in upflow packed bed bioreactors with pyrite and sand, with and without oyster shells as an alkalinity source. Organic carbon addition (10% by volume wastewater) was found to improve PPAD denitrification performance, possibly by promoting mixotrophic metabolism. After organic carbon addition and operation at a six-hour empty bed contact time, total inorganic nitrogen (TIN) removal reached 90% in the column with oyster shells compared with 70% without. SEM images and biofilm protein measurements indicated that oyster shells enhanced biofilm growth. The results indicate that PPAD is a promising technology for treatment of nitrified wastewater.

Temporal responses of microorganisms and native organic carbon mineralization to 13C-glucose addition in a sandy loam soil with long-term fertilization

The altered mineralization rate of soil organic carbon (SOC) in the presence of exogenous organic substrates occurs by stimulating microbial activity. In this study, 13C-glucose was applied at a rate of 1000 μg 13C g−1 soil to arable soils following a 20-year application of compost (CM), inorganic NPK fertilizer (NPK) and a no-fertilizer Control. It was incubated for 30 days to evaluate how the labile substrate affected the microbial abundance and native SOC decomposition. Phospholipid fatty acids (PLFAs) were used as biomarkers for bacteria (Gram-positive bacteria, Gram-negative bacteria and actinobacteria) and fungi. 13C-glucose application resulted in a significant increase in microbial abundance and positive priming effect for all treatments. The primed CO2 flux derived from native SOC peaked on day 11, then increased gradually again from day 15 onwards in all treatments. The increase of abundance peaked on days 7 and 15 for Gram-negative (G−) bacteria and Gram-positive (G+) bacteria, however, fungal and actinobacterial PLFAs increased steadily from day 3 onwards under all three fertilization regimes. The results suggest that G+ and G− bacteria make a greater contribution to priming effects during the first 15 days of incubation, while fungi and actinobacteria are more important at the latter stages. The difference between glucose-derived 13C remaining in soils and primed CO2 from native SOC was 480, 381 and 263 mg C kg−1 in CM, NPK and Control treatments, respectively. Our study demonstrates that the exogenous labile organic substrate addition can more effectively promote C sequestration in organic C-rich soil (CM) than in organic C-poor soil (NPK or Control).

Influence of organic matters on AsIII oxidation by the microflora of polluted soils.

The global AsIII-oxidizing activity of microorganisms in eight surface soils from polluted sites was quantified with and without addition of organic substrates. The organic substances provided differed by their nature: either yeast extract, commonly used in microbiological culture media, or a synthetic mixture of defined organic matters (SMOM) presenting some common features with natural soil organic matter. Correlations were sought between soil characteristics and both the AsIII-oxidizing rate constants and their evolution in accordance with inputs of organic substrates. In the absence of added substrate, the global AsIII oxidation rate constant correlated positively with the concentration of intrinsic organic matter in the soil, suggesting that AsIII-oxidizing activity was limited by organic substrate availability in nutrient-poor soils. This limitation was, however, removed by 0.08g/L of added organic carbon. In most conditions, the AsIII oxidation rate constant decreased as organic carbon input increased from 0.08 to 0.4g/L. Incubations of polluted soils in aerobic conditions, amended or not with SMOM, resulted in short-term As mobilization in the presence of SMOM and active microorganisms. In contrast, microbial AsIII oxidation seemed to stabilize As when no organic substrate was added. Results suggest that microbial speciation of arsenic driven by nature and concentration of organic matter exerts a major influence on the fate of this toxic element in surface soils.

Effect of Organic Inputs on Strength and Stability of Soil Aggregates Under Rice-Wheat Rotation

Abstract The study aims to elucidate the impact of organic inputs on strength and structural stability of aggregates in a sandy loam soil. Tensile strength, friability and water stability of aggregates, and the carbon contents in bulk soil and in large macro (&gt;2 mm), small macro (0.25-2 mm), micro (0.053-0.25 mm) and silt+clay size (&lt;0.053) aggregates were evaluated in soils from a long-term experiment with rice-wheat rotation at Modipuram, India, with different sources and amounts of organic C inputs as partial substitution of N fertilizer. Addition of organic substrates significantly improved soil organic C contents, but the type and source of inputs had different impacts. Tensile strength of aggregates decreased and friability increased through organic inputs, with a maximum effect under green gram residue (rice)-farmyard manure (wheat) substitution. Higher macroaggregates in the crop residue- and farmyard manure-treated soils resulted in a higher aggregate mean weight diameter, which also had higher soil organic C contents. The bulk soil organic C had a strong relation with the mean weight diameter of aggregates, but the soil organic C content in all aggregate fractions was not necessarily effective for aggregate stability. The soil organic C content in large macroaggregates (2-8 mm) had a significant positive effect on aggregate stability, although a reverse effect was observed for aggregates &lt;0.25 mm. Partial substitution of nitrogen by organic substrates improved aggregate properties and the soil organic C content in bulk soil and aggregate fractions, although the relative effect varied with the source and amount of the organic inputs.

Effects of sterile storage, cation saturation and substrate additions on the degradability and extractability of nonylphenol and phenanthrene in soil

The main objective of this study was to determine the effects of long-term abiotic processes during aging of organic pollutants in soil on their microbial degradability and formation of non-extractable residues. The specific aims of our study were to investigate how the fate of p353-nonylphenol (NP) and phenanthrene (Phe) in soils might be affected by: (i) saturation of soil by cations with different valency (Na+, Ca2+ or Al3+), (ii) addition of organic substrate (wood flour) during incubation period and (iii) different soil moisture levels.This study showed positive effect of long-term aging of sterilized samples on respiration of re-inoculated samples. However, the lack of aging effects on the mineralization of NP and Phe indicates that slow sorption processes by diffusion into less bioaccessible domains were not relevant in studied soils. Similarly, the lower respiration and xenobiotic mineralization rates in the Na+ and Al3+ treated soils indicate that this is due to toxic effects on microbial activity and not due to xenobiotic accessibility. Instead, the formation of non-extractable residues was strongly promoted by biological activity, most likely through formation of more reactive metabolites. The addition of wood flour greatly stimulated microbial respiration and enhanced NP mineralization while inhibiting that of Phe. Along with negligible effect of water addition after 4weeks of incubation on kinetics of soil respiration, the soil moisture effect on xenobiotics mineralization indicates that most probably the bioavailability of NP and Phe increased due to bridging role of water films in soil.

Fe(II)- and sulfide-facilitated reduction of 99Tc(VII)O4− in microbially reduced hyporheic zone sediments

Redox-reactive, biogeochemical phases generated by reductive microbial activity in hyporheic zone sediments from a dynamic groundwater–river interaction zone were evaluated for their ability to reduce soluble pertechnetate [99Tc(VII)O4−] to less soluble Tc(IV). The sediments were bioreduced by indigenous microorganisms that were stimulated by organic substrate addition in synthetic groundwater with or without sulfate. In most treatments, 20μmolL−1 initial aqueous Tc(VII) was reduced to near or below detection (3.82×10−9molL−1) over periods of days to months in suspensions of variable solids concentrations. Native sediments containing significant lithogenic Fe(II) in various phases were, in contrast, unreactive with Tc(VII). The reduction rates in the bioreduced sediments increased with increases in sediment mass, in proportion to weak acid-extractable Fe(II) and sediment-associated sulfide (AVS). The rate of Tc(VII) reduction was first order with respect to both aqueous Tc(VII) concentration and sediment mass, but correlations between specific reductant concentrations and reaction rate were not found. X-ray microprobe measurements revealed a strong correlation between Tc hot spots and Fe-containing mineral particles in the sediment. However, only a portion of Fe-containing particles were Tc-hosts. The Tc-hot spots displayed a chemical signature (by EDXRF) similar to pyroxene. The application of autoradiography and electron microprobe allowed further isolation of Tc-containing particles that were invariably found to be ca 100μm aggregates of primary mineral material embedded within a fine-grained phyllosilicate matrix. EXAFS spectroscopy revealed that the Tc(IV) within these were a combination of a Tc(IV)O2-like phase and Tc(IV)–Fe surface clusters, with a significant fraction of a TcSx-like phase in sediments incubated with SO42−. AVS was implicated as a more selective reductant at low solids concentration even though its concentration was below that required for stoichiometric reduction of Tc(VII). These results demonstrate that composite mineral aggregates may be redox reaction centers in coarse-textured hyporheic zone sediments regardless of the dominant anoxic biogeochemical processes.

In-situ zinc bioprecipitation by organic substrate injection in a high-flow, poorly reduced aquifer

We investigated if in-situ metal bioprecipitation (ISMP) is applicable to remediate a highly permeable zinc-contaminated aquifer at a metal-processing factory in Maasmechelen, Belgium. A large (more than 200m long and 70m wide) groundwater contamination plume has developed, with zinc concentrations in the range of 1-100mg/L, whereas the legal Flemish clean-up standard is 0.5mg/L. The estimated groundwater flow velocity is in the range 0.2-1m/d. The groundwater is relatively oxidized, naturally low in DOC (<1mg/L) and relatively low in sulfate (40-50mg/L). We conducted both laboratory feasibility tests as well as a long-term field pilot test in two sections of the plume. In the laboratory microcosm tests, zinc bioprecipitation (following addition of organic substrate and sulfate) removed more than 99% of the zinc from the water phase. Lactate, glycerol and vegetable oil were equally effective as substrates. 28-day anaerobic leaching tests indicated that the metal precipitates that were formed are stable, but they also suggested that substrate addition increases the solubility (leachability) of arsenic and manganese. In the field test, Zn concentrations were reduced by 2 to 3 orders of magnitude within the 232 day testing period and stayed low for the following 6 months in both pilot zones. In the field, no mobilization of arsenic occurred but manganese groundwater concentrations increased from 0.01-0.6mg/L to 0.4-6.5mg/L. Dissolved iron concentrations also increased markedly from below detection limits to concentrations as high as 67mg/L. Zinc concentrations in groundwater were closely correlated to pH and redox potential (Eh): plotting y=[Zn] against x=pH/log(Eh), an exponential relationship was found: