Acid Neutralizing Capacity Research Articles

Fading positive effect of biochar on crop yield and soil acidity during five growth seasons in an Indonesian Ultisol

Low fertility limits crop production on acidic soils dominating much of the humid tropics.Biochar may be used as a soil enhancer, but little consensus exists on its effect on crop yield. Here we use a controlled, replicated and long-term field study in Sumatra, Indonesia, to investigate the longevity and mechanism of the effects of two contrasting biochars (produced from rice husk and cacao shell, and applied at dosages of 5 and 15tha−1) on maize production in a highly acidic Ultisol (pHKCl3.6).Compared to rice husk biochar, cacao shell biochar exhibited a higher pH (9.8 vs. 8.4), CEC (197 vs. 20cmolckg−1) and acid neutralizing capacity (217 vs. 45cmolckg−1) and thus had a greater liming potential. Crop yield effects of cacao shell biochar (15tha−1) were also much stronger than those of rice husk biochar, and could be related to more favorable Ca/Al ratios in response to cacao shell biochar (1.0 to 1.5) compared to rice husk biochar (0.3 to 0.6) and nonamended plots (0.15 to 0.6).The maize yield obtained with the cacao shell biochar peaked in season 2, continued to have a good effect in seasons 3–4, and faded in season 5. The yield effect of the rice husk biochar was less pronounced and already faded from season 2 onwards.Crop yields were correlated with the pH-related parameters Ca/Al ratio, base saturation and exchangeable K. The positive effects of cocoa shell biochar on crop yield in this Ultisol were at least in part related to alleviation of soil acidity. The fading effectiveness after multiple growth seasons, possibly due to leaching of the biochar-associated alkalinity, indicates that 15tha−1 of cocoa shell biochar needs to be applied approximately every third season in order to maintain positive effects on yield.

Leaching and microstructural properties of lead contaminated kaolin stabilized by GGBS-MgO in semi-dynamic leaching tests

Ground granulated blast furnace slag (GGBS) is widely used to stabilize soils due to its environmental and economic merits. The strength and durability of reactive MgO activated GGBS (GGBS-MgO) stabilized lead (Pb)-contaminated soils have been explored by previous studies. However, the effects of simulated acid rain (SAR) on the leachability and micro-properties of GGBS-MgO stabilized Pb-contaminated soils are hardly investigated. This research studies the leachability and microstructural properties of GGBS-MgO stabilized Pb-contaminated kaolin clay exposed to SAR with initial pH values of 2.0, 4.0 and 7.0. A series of tests are performed including the semi-dynamic leaching tests using SAR as the extraction liquid, acid neutralization capacity (ANC), mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD) tests. The results demonstrate that as the SAR pH decreases from 7.0 to 4.0, the Pb cumulative fraction leached (CFL) and observed diffusion coefficient (Dobs) increases significantly whereas the leachate pH decreases. Meanwhile, increasing the GGBS-MgO content from 12% to 18% results in the decrease of CFL and Dobs. Further decreasing the SAR pH to 2.0 results in the dissolution-controlled leaching mechanism regardless of the binder dosage. The differences in the leaching properties under different pH conditions are interpreted based on the cemented soil acid buffering capacity, hydration products and pore size distributions obtained from the ANC, MIP, and XRD tests, respectively.

Biodeterioration of mortars exposed to sewers in relation to microbial diversity of biofilms formed on the mortars surface

Strong deterioration of concrete in sewer systems is mainly due to microorganisms and especially to sulfur-oxidizing bacteria. Mortars made either with ordinary Portland cement (OPC) or calcium aluminate cement (CAC) were exposed in a waste water collector for five years. Mortar microstructure observed by microscopy reported a larger thickness of the degraded zone for OPC mortar. Taxonomic identification of bacterial communities performed on biofilms collected at the mortar surface reported similar bacterial diversities, but strong differences of relative abundance. A greater neutrophilic sulfur-oxidizing bacterial (NSOB) activity was observed for OPC mortar certainly in conjunction with its larger acid neutralization capacity. Thus, CAC mortar was less biodeteriorated than OPC mortar as less NSOB were able to settle on its surface in relation with its specific microstructure. The results of the reported field experiments have been compared with bioleaching laboratory experiments performed on identical mortars in the presence of Halothiobacillus neapolitanus as NSOB. As the deterioration mechanisms involved were similar, an acceleration factor with respect to the rate of in situ biodeterioration was determined for laboratory experiment.

A novel approach in red mud neutralization using cow dung.

In this study, cow dung was identified as a neutralizing agent for red mud (RM). Present research estimated a significant reduction in pH value of red mud (10g) from 10.28 to 8.15 and reduction in alkalinity of ~148mg/L from ~488mg/L by adding 80g of cow dung in 40days of anaerobic condition. XRD results exhibit a high intensity of quartz and found new compound, the calcium carbide. The acid neutralizing capacity (ANC) of NRM reduces to ~0.87 from ~1.506mol H+/kg. Based on the resultant research, present study proposes cow dung as an efficient neutralizing agent for reducing the pH and alkalinity in the red mud.

Relationships between indicators of acid-base chemistry and fish assemblages in streams of the Great Smoky Mountains National Park

The acidity of many streams in the Great Smoky Mountains National Park (GRSM) has increased significantly since pre-industrial (∼1850) times due to the effects of highly acidic atmospheric deposition in poorly buffered watersheds. Extensive stream-monitoring programs since 1993 have shown that fish and macroinvertebrate assemblages have been adversely affected in many streams across the GRSM. Matching chemistry and fishery information collected from 389 surveys performed at 52 stream sites over a 22-year period were assessed using logistic regression analysis to help inform the U.S. Environmental Protection Agency’s assessment of the environmental impacts of emissions of oxides of nitrogen (NOx) and sulfur (SOx). Numerous logistic equations and associated curves were derived that defined the relations between acid neutralizing capacity (ANC) or pH and different levels of community richness, density, and biomass; and density and biomass of brook trout, rainbow trout, and small prey (minnow) populations in streams of the GRSM. The equations and curves describe the status of fish assemblages in the GRSM under contemporary emission levels and deposition loads of nitrogen (N) and sulfur (S) and provide a means to estimate how newly proposed (and various alternative) target deposition loads, which strongly influence stream ANC, might affect key ecological indicators. Several examples using ANC, community richness, and brook trout density are presented to illustrate the steps needed to predict how future changes in stream chemistry (resulting from different target deposition loads of N and S) will affect the probabilities of observing specific levels of selected biological indicators in GRSM streams. The implications of this study to the regulation of NOx and SOx emissions, water quality, and fisheries management in streams of the GRSM are discussed, but also qualified by the fact that specific examples provided need to be further explored before recommendations concerning their use as ecological indicators could be proposed.

PH dependent leachings of some trace metals and metalloid species from lead smelter slag and their fate in natural geochemical environment

The influence of pH on the leaching behaviours of As, Cd, Cu, Mo, Ni, Pb, Se and Zn from a lead smelter slag was assessed to understand the ground water pollution potential of slag and the toxicity in geo-environmental conditions. Leaching of slag was investigated by using European EN 12457-2 and prEN 14429 leaching tests. The results obtained from prEN 14429 leaching test were used to determine the acid neutralization capacity (ANC) of slag. The pH dependent leaching results were further assessed by considering existing geo-chemical modeling results of similar types of wastes. Results indicate that the concentrations of some toxic metal and metalloid species in the leachate are higher than their specified limits prescribed for safe landfill disposal as inert or non-reactive hazardous solid waste as well as for safe disposal of effluent in inland surface water. The ANC values obtained for slag at pH values 7, 5 and 4 are 0.75 meqv/g, 3.72 meqv/g and 37.30 meqv/g respectively. The low ANC values as well as the high concentrations of majority of the toxic elements in leachates especially at the pH range of 5–7 indicate hazardous nature of slag for disposal under open atmosphere. The leaching behaviours of iron and calcium under varying pH conditions have profound effect on the pH dependent mobilities of most of the trace elements present in the slag. The sodium, potassium and chloride leaching from slag particularly in the pH range of 4–12 are pH independent and therefore do not have any effect on the mobilities of toxic elements.

Constituents of organic alkalinity in pore water of marine sediments

Abstract In this study we investigated the components of organic alkalinity (AO) in pore water from marine sediments. We used absorbance and fluorescence of pore water to characterize dissolved organic matter (DOM), the source of AO. Research material was collected during growing season (September 2016) from two sites located in the eutrophic Gulf of Gdansk (southern Baltic). Concentration of AO ranged from 104 to 1505 μmol l−1 and increased with sediment depth. Our results demonstrate a clear link between AO and composition of DOM in pore water. Measurements of pore water fluorescence showed that the main source of AO is humic substances. The protein-like fluorescence, pointing to presence of freshly produced organic substances, was clearly visible in the upper layers and diminished with depth. There are changes in absorbance spectra with depth indicating decrease of molecular weight of DOM. In anoxic sediments the concentration of AO was close to the alkalinity from non‑carbonate inorganic bases (N-CIBs) and did not exceed 8% of total alkalinity (AT). In the sediments where organic matter was mineralized with the use of substances preceding sulfate in the sequence of oxidants (i.e. oxygen, nitrate, Mn, Fe), DOM was the source of up to 17% of AT. The results from this study indicate that DOM has a large effect on acid neutralizing capacity of pore water of marine sediments. We suggest the production of AO in sediment and its benthic efflux should be taken into account in modeling acid-base system in shelf seas.

Long-term changes (1990–2015) in the atmospheric deposition and runoff water chemistry of sulphate, inorganic nitrogen and acidity for forested catchments in Europe in relation to changes in emissions and hydrometeorological conditions

The international Long-Term Ecological Research Network (ILTER) encompasses hundreds of long-term research/monitoring sites located in a wide array of ecosystems that can help us understand environmental change across the globe. We evaluated long-term trends (1990–2015) for bulk deposition, throughfall and runoff water chemistry and fluxes, and climatic variables in 25 forested catchments in Europe belonging to the UNECE International Cooperative Programme on Integrated Monitoring of Air Pollution Effects on Ecosystems (ICP IM). Many of the IM sites form part of the monitoring infrastructures of this larger ILTER network. Trends were evaluated for monthly concentrations of non-marine (anthropogenic fraction, denoted as x) sulphate (xSO4) and base cations x(Ca+Mg), hydrogen ion (H+), inorganic N (NO3 and NH4) and ANC (Acid Neutralising Capacity) and their respective fluxes into and out of the catchments and for monthly precipitation, runoff and air temperature. A significant decrease of xSO4 deposition resulted in decreases in concentrations and fluxes of xSO4 in runoff, being significant at 90% and 60% of the sites, respectively. Bulk deposition of NO3 and NH4 decreased significantly at 60–80% (concentrations) and 40–60% (fluxes) of the sites. Concentrations and fluxes of NO3 in runoff decreased at 73% and 63% of the sites, respectively, and NO3 concentrations decreased significantly at 50% of the sites. Thus, the LTER/ICP IM network confirms the positive effects of the emission reductions in Europe. Air temperature increased significantly at 61% of the sites, while trends for precipitation and runoff were rarely significant. The site-specific variation of xSO4 concentrations in runoff was most strongly explained by deposition. Climatic variables and deposition explained the variation of inorganic N concentrations in runoff at single sites poorly, and as yet there are no clear signs of a consistent deposition-driven or climate-driven increase in inorganic N exports in the catchments.

Influence of Air Pollution Control (APC) Systems and Furnace Type on the Characteristics of APC Residues from Municipal Solid Waste Incinerators

The characteristics of air pollution control (APC) residues are influenced by the furnace type, APC system, and waste composition. In this study, the characteristics of APC residues from nine municipal solid waste incineration plants (the compositions of incinerated solid waste are similar) with different furnace types and APC systems were compared.APC residues contain a great amount of Ca and Cl, and the contents of Al, Si, and Fe in the APC residues from fluidized bed incinerators are higher. The mineral compositions of APC residues are not influenced by the flue gas treatment process, but their contents vary. The contents of Cd, Pb, and Zn in the APC residues from fluidized bed incinerators are lower, while those of Cr, Ba, Cu, and Ni are greatly influenced by the APC systems, with the "grate+dry scrubber" APC residues having the lowest values. The differences in the heavy metal contents in the APC residues from two incinerators before and after the upgrading of the APC systems are not significant. The leaching toxicity of Pb in the APC residues from grate incinerators is higher than that from fluidized bed incinerators, while some elements with low contents in fluidized bed APC residues can be leached more in acetic acid buffer solution. The acid neutralization capacity of the APC residues is related to Ca content. The leaching concentrations of most heavy metals are significantly increased under strong acidity (Cd, Ni, and Zn:leachate pH < 8; Pb, Cu, and Cr:leachate pH < 4). The maximum leaching concentrations of As, Ba, Cu, Ni, and Pb in the APC residues from grate incinerators are mainly controlled by their total content. The leaching concentrations of As, Ba, Cu, Ni, and Pb in the APC residues from fluidized bed incinerators are lower than those from grate incinerators with similar metal contents, which may be due to their different chemical speciation influenced by furnace types and the complexation with Al and Fe compounds.

Impacts and Effects Indicators of Atmospheric Deposition of Major Pollutants to Various Ecosystems - A Review

In this paper, we review the current understanding on ecosystem and human health impacts from the atmospheric deposition of acidifying pollutants, eutrophying nitrogen (N), polycyclic aromatic hydrocarbons (PAHs), mercury (Hg), trace metals, and ozone (O3), as well as the biological indicators that have been used to assess the health of ecosystems following exposure to these pollutants. We provide overviews of the impacts of deposition for these pollutants and discuss the currently known biomonitors for each pollutant. The deposition of acidifying pollutants impacts terrestrial ecosystems by altering plant physiology and growth and by increasing plant susceptibility to stresses that can be indirectly damaging to the health of fish and birds. Indicators of the deposition of acidifying pollutants include soil base cation content and acid neutralizing capacity, among others. Eutrophying N deposition has been studied extensively; N enrichment directly impacts vegetative plant species cover, richness, growth rates, and susceptibility to other stressors. It indirectly impacts wildlife through changes in their habitats and food sources. Indicators for N deposition include changes in plant species and in tissue and litter N content. The deposition of PAHs has been found to cause significant damage to plant organisms and to be carcinogenic and mutagenic to humans and animals. Useful biomonitors of PAH deposition include lichens, mosses, and pine needles. Deposited Hg can undergo methylation (in the presence of sulphur reducing bacteria); bioaccumulation of methylmercury is highly toxic to animals. Effective biomonitors of Hg contamination of aquatic ecosystems are fish and marine birds. The impacts of O3 are well understood, with well-established “flux” models being vast improvements on the previous AOT40 approaches. This review highlights the impacts that the above-mentioned pollutants have on terrestrial and aquatic organisms and the biomonitors that are currently being used to assess the deposition levels and effects of these pollutants.

Cement Stabilization/Solidification of Heavy Metal-Contaminated Sediments Aided by Coal Fly Ash

Discharge of various wastewater containing heavy metals from metallurgical, chemical engineering industries, etc. into water body results in the accumulation of heavy metals in sediments of rivers and lakes, and further severe sediment contamination. When the severely contaminated sediments are dredged, they must be handled before disposal. In this paper, the dredged sediments were stabilized/solidified with cement aided by coal fly ash. The compressive strength of stabilization/solidification specimens decreased with the increase of sediment/binder ratio. All specimens showed a satisfactory compressive strength except that the compressive strength of the specimen with the high sediment/binder ration of 3.33 was lower than 0.35 MPa, the requirement of US EPA. Coal fly ash effectively acted as the binder, but the excessive addition of coal fly ash resulted in the reduction of specimen compressive strength. The pH of TCLP leachates for the specimens, which met the requirement of the compressive strength, was distributed between 11.07 and 12.50, and the heavy metal concentration of the TCLP leachates was lower than 0.029 mg/L. A similar trend of acid neutralization capacity of the stabilization/solidification specimens was observed as that of the compressive strength. Curing in a hermetically sealed plastic bag at ambient temperature and a longer curing period improved the stabilization/solidification effect. Humidity and temperature played an important role during curing period. Under an aggressive condition with a fixed leachate pH of 4, the stabilization/solidification technology increased the heavy metals fixed to 88.47%, 93.30% and 87.71% for zinc, lead and cadmium, respectively, and the concentration of zinc, lead and cadmium in the leachates was lower than the limits of the identification standards for hazardous wastes-identification for extraction toxicity (GB 5085.3-2007). So cement stabilization/solidification aided by coal fly ash can be an alternative disposal technology for dredged sediments contaminated by heavy metals.

Critical biomass harvesting – Applying a new concept for Swedish forest soils

Abstract The contribution of forest harvesting to base cation losses and soil acidification has increased in recent years in Sweden, as the demand for bioenergy has increased and the sulphur deposition has decreased. Thus, new policy tools are required to evaluate the progress of the recovery from acidification, and as a basis for forest management recommendations. In this study we introduce and test a concept, “Critical biomass harvesting”. The concept builds on the concept “Critical loads”, which has been used world-wide for several decades as a bridge between science and policies related to transboundary air pollution and acidification. The basis for the concept is an acidity mass balance, with sources and sinks of acidity. A critical limit defines the highest acceptable acidification status of the water leaving the root zone. Based on the critical limit, the highest allowed biomass harvesting can be calculated, keeping the other parameters constant. In this study the critical limit was set to ANC (Acid Neutralizing Capacity) = 0. Nitrogen was assumed to be affecting acidity only if it leaches from the root zone. The critical biomass harvesting was calculated for almost 12 000 National Forest Inventory sites with spruce and pine forest, using the best available data on deposition, weathering and nitrogen leaching. The exceedance of critical biomass harvesting was calculated as the difference between the estimated harvest losses and the critical biomass harvesting. The results were presented as median values in merged catchments in a catchment database, with totally 2079 merged catchments in Sweden. According to the calculations, critical biomass harvesting was exceeded in the southern half of Sweden already at stem harvesting in spruce forests. Whole-tree harvesting expanded the exceedance area, and increased the exceedance levels in southern Sweden. The exceedance in pine forest was lower and affected smaller areas. It was concluded that the concept of critical biomass harvesting can be successfully applied on the same database that has been used for critical load calculations in Sweden, using basically the same approach as has been extensively applied, evaluated and discussed in a critical load context. The results from the calculations in Sweden indicate that whole-tree harvesting, without wood ash recycling, can be expected to further slow down recovery, especially in the most acidified parts of the country, in the southwest.

Comparative analysis of physicochemical, nutrient, and spectral properties of agricultural residue biochars as influenced by pyrolysis temperatures

The objectives of this study were to assess the physicochemical, nutrient, and spectral properties of biochar prepared from four major agricultural residues of India [rice straw (RSB), wheat straw (WSB), maize stover (MSB), and pearl millet stover (PSB)] at three (400, 500, and 600 °C) pyrolysis temperatures. Pyrolysis temperatures and residue types profoundly influenced biochar properties, for instance, PSB biochar had the greatest pH (10.75 ± 0.01), calcium carbonate equivalent (CCE) (47.8 ± 0.5), and carbonate (CO 3 = ) content (432 ± 17 meq kg−1). Irrespective of residue, greater pyrolysis temperature improves the biochars’ acid-neutralizing capacity by increasing pH in water (pHw), CCE, and CO 3 = content. The CCE of biochar showed a significant positive correlation with pHw (R 2 = 0.51, p < 0.001) and ash content of biochar (R 2 = 0.54, p < 0.001). A great amount of water-soluble potassium (20.6–29.5 g kg−1) in all the biochars made them suitable for supplying potassium to plants. Infrared spectroscopy explained the functional group formation, while XRD revealed mineral formation in the biochar. Thus, depending on the requirement, diverse properties of biochar can be prepared by designing residue type and pyrolysis temperature suitable for application in a specific soil to alleviate nutrient deficiency and improve soil productivity.

Trace metal(loid) mobility in waste deposits and soils around Chadak mining area, Uzbekistan

The assessment of potential trace metal(loid) contamination in tailing dumps and soils was characterized in the Chadak mining area (Uzbekistan). Concentrations of trace elements (V, Cr, Co, Ni, Cu, Zn, As, Cd, Sb, Pb) were determined by X-ray fluorescence analysis and compared with background and intervention values (IV). The concentrations of As, Zn, Sb, and Pb were higher in the abandoned than in the active tailing dump, ranging from 42–1689mg/kg for As, 73–332mg/kg for Zn, 14–1507mg/kg for Sb, and 27–386mg/kg for Pb. Selective extractions were applied in order to assess the mobility and availability of trace metal(loid)s in samples. Oxyanion-forming elements such as As and Sb were immobilized by Fe oxides, although to some extent also extractable with acetic acid and soluble-in-water forms were detected, indicating potential bioavailability that can impose a potential toxicity risk for the environment. Selective extractions data also showed that Zn and Pb were relatively immobile, although in higher contamination sites significant amounts of these elements were also extractable with acetic acid. In tailing materials Zn and Pb mobility were negatively correlated by the cation-exchange capacity (CEC) and clay content, indicating the importance of these factors in the reduction of the potential toxicity for these elements. Total concentration of As, Sb, and Pb were also negatively correlated with soil pH, indicating that the oxidation process of sulphide tailings and thus the generation of acidic conditions may lead to release of contaminants over time. However, due to the calcium carbonate content, the acid neutralization capacity of the tailings is not yet exhausted and contaminant concentrations in soil-pore water are still relatively low. The results of our investigation suggest that environmental risk associated with these wastes in semi-arid climate is therefore not a short-term problem but rather requires constant monitoring and additional ecotoxicological studies.

Effect of an alkaline environment on the engineering behavior of cement-stabilized/solidified Zn-contaminated soils.

Although the stabilization/solidification method has been widely used for remediation of heavy metal-contaminated soils in recent decades, the engineering behavior and mobility of heavy metal ions under alkaline groundwater conditions are still unclear. Therefore, the unconfined compressive strength test (UCS) combined with toxicity characteristic leaching procedure (TCLP) and general acid neutralization capacity (GANC) was used to investigate the effects of alkalinity (using NaOH to simulate alkalinity in the environment) on the mechanical and leaching characteristics of cement-solidified/stabilized (S/S) Zn-contaminated soils. Moreover, the microstructure was analyzed using the scanning electron microscope (SEM) technology. The results indicated that alkaline environment could accelerate the UCS development compared with specimens without soaking in NaOH solution,, regardless of whether the specimens contained Zn2+ or not. And the UCS varied obviously attributed to the variations of both NaOH concentration and soaking time. Except for the specimens soaked for 90days, the leached Zn2+ concentrations were higher than that of without soaking. However, the leachability of Zn2+ in all the stabilized specimens is in the regulatory level. ANC results indicated that the Zn2+ leaching behavior can be divided into three stages related to the initial leachate pH. Moreover, SEM results proved that the alkaline environment could actually facilitate the cement hydration process. The results proved in the present paper could be useful in treating the heavy metal-contaminated soils involved in the solidification/stabilization technology under alkaline environment.

A comparative study on the raft chemical properties of various alginate antacid raft-forming products

Objective: Research to measure the chemical characterization of alginate rafts for good raft performance and ascertain how formulation can affect chemical parameters.Significance: A selection of alginate formulations was investigated all claiming to be proficient raft formers with significance between products established and ranked.Methods: Procedures were selected which demonstrated the chemical characterization allowing rafts to effectively impede the reflux into the esophagus or in severe cases to be refluxed preferentially into the esophagus and exert a demulcent effect, with focus of current research on methods which complement previous studies centered on physical properties. The alginate content was analyzed by a newly developed HPLC method. Methods were used to determine the neutralization profile and the acid neutralization within the raft determined along with how raft structure affects neutralization.Results: Alginate content of Gaviscon Double Action (GDA) within the raft was significantly superior (p < .0001) to all competitor products. The two products with the highest raft acid neutralization capacity were GDA and Rennie Duo, the latter product not being a raft former. Raft structure was key and GDA had the right level of porosity to allow for longer duration of neutralization.Conclusion: Alginate formulations require three chemical reactions to take place simultaneously: transformation to alginic acid, sodium carbonate reacting to form carbon dioxide, calcium releasing free calcium ions to bind with alginic acid providing strength to raft formation. GDA was significantly superior (p <.0001) to all other comparators.

The response of soil and stream chemistry to decreases in acid deposition in the Catskill Mountains, New York, USA

The Catskill Mountains have been adversely impacted by decades of acid deposition, however, since the early 1990s, levels have decreased sharply as a result of decreases in emissions of sulfur dioxide and nitrogen oxides. This study examines trends in acid deposition, stream-water chemistry, and soil chemistry in the southeastern Catskill Mountains. We measured significant reductions in acid deposition and improvement in stream-water quality in 5 streams included in this study from 1992 to 2014. The largest, most significant trends were for sulfate (SO42−) concentrations (mean trend of −2.5 μeq L−1 yr−1); hydrogen ion (H+) and inorganic monomeric aluminum (Alim) also decreased significantly (mean trends of −0.3 μeq L−1 yr−1 for H+ and −0.1 μeq L−1 yr−1 for Alim for the 3 most acidic sites). Acid neutralizing capacity (ANC) increased by a mean of 0.65 μeq L−1 yr−1 for all 5 sites, which was 4 fold less than the decrease in SO42− concentrations. These upward trends in ANC were limited by coincident decreases in base cations (−1.3 μeq L−1 yr−1 for calcium + magnesium). No significant trends were detected in stream-water nitrate (NO3−) concentrations despite significant decreasing trends in NO3− wet deposition. We measured no recovery in soil chemistry which we attributed to an initially low soil buffering capacity that has been further depleted by decades of acid deposition. Tightly coupled decreasing trends in stream-water silicon (Si) (−0.2 μeq L−1 yr−1) and base cations suggest a decrease in the soil mineral weathering rate. We hypothesize that a decrease in the ionic strength of soil water and shallow groundwater may be the principal driver of this apparent decrease in the weathering rate. A decreasing weathering rate would help to explain the slow recovery of stream pH and ANC as well as that of soil base cations.

Acid sulfate soil evolution models and pedogenic pathways during drought and reflooding cycles in irrigated areas and adjacent natural wetlands

The severe Millennium Drought (2007–2010) left an area of over 5000ha in the Lower Murray River (South Australia) dried, cracked and acidified as river and groundwater levels fell nearly 2m. In this study, we examined irrigated agricultural areas and an adjacent natural wetland for comparison, which were both affected by the drought. Approximately 3m deep soil cores were collected along transects in three sections of the Lower Murray Reclaimed Irrigation Area (LMRIA) on multiple occasions between 2011 and 2015 and an adjacent natural wetland in 2007. Soil properties measured included pH, reduced inorganic sulfur (RIS, pyrite), titratable actual acidity (TAA), retained acidity, acid neutralising capacity (ANC), X-ray diffraction analyses and scanning electron microscopy. A series of explanatory soil-regolith hydro-toposequence models were developed during the pre-drought period, drying period, and subsequent wetting/reflooding post-drought period. These models indicate that prior to draining of the natural wetlands for irrigated agriculture the region cycled between wetting and flushing, and partial drying conditions in response to seasonal and climatic cycles causing the build-up of hypersulfidic material to be kept in check by oxidation of pyrite during dry periods/droughts and removal during scouring floods. As the region became managed for navigation and irrigation by installing barrages and locks, pyrite began to build-up. The extreme lowering of the water table during the Millennium Drought resulted in deep oxidation of sulfides in anaerobic hypersulfidic material to depths >3.5m in the previously saturated irrigated pastures and within 50cm of the soil surface in the natural wetlands. Oxidation and acidification between 0.5 and 3.5m of Hypersulfidic clayey soils was enhanced by the formation of large cracks up to 3.5m deep. Rewetting and flooding after the drought caused mobilization of sulfuric acid, soluble sulfates, ferrous iron, nutrients and metals with transport into the River Murray. Our findings highlight that irrigated areas formed deeper sulfuric materials (>3.5m) than in adjacent natural wetlands (<1m) due to the difficulties in the management of water tables in irrigation areas because of the installation of high levee banks and deep drains. Maintaining water tables on agricultural soils via irrigation and subsequent drainage will promote the rapid formation of deep (>3.5m) acid sulfate soils with sulfuric material containing extensive retained acidity (jarosite), which can persist for decades or longer.

Impact of co-landfill proportion of bottom ash and municipal solid waste composition on the leachate characteristics during the acidogenesis phase

Incineration has become an important municipal solid waste (MSW) treatment strategy, and generates a large amount of bottom ash (BA). Although some BA is reused, much BA and pretreatment residues from BA recycling are disposed in landfill. When BA and MSW are co-landfilled together, acid neutralization capacity and alkaline earth metal dissolution of BA, as well as different components of MSW may change environmental conditions within the landfill, so the degradation of organic matter and the physical and chemical properties of leachate would be affected. In this study, the effect of co-landfilled BA and MSW on the leachate characteristics during the hydrolysis and acidogenesis phase was studied using different BA/MSW ratios and MSW compositions. The results showed that the co-landfill system increased leachate pH, electric conductivity and alkalinity. For MSW with a high content of degradable components, the release and degradation of total organic carbon (TOC) and volatile fatty acids (VFA) from MSW were promoted when the BA ratio by wet weight was less than 50%, and the biodegradability of leachate was improved. When the BA ratio exceeded 50%, the degradation of organic matters was inhibited. For MSW with low content of degradable components, when the proportion of BA was less than 20%, the release and degradation of TOC and VFA from MSW were promoted and alkalinity increased. When the BA ratio exceeded 20%, the degradation of organic matters was inhibited. The 50% BA ratio could improve the bio-treatability of leachate indicated by the leachate pH and C/N ratio. However, BA inhibited the release of nitrogen (TN and NH4+-N) at all BA ratios and MSW compositions. At the same time, the addition of BA increased the risk of leachate collection system clogging due to the dissolution and re-precipitation of alkaline earth metals contained in BA.

In-vitro characterization of the acid-neutralizing capacity of ENO® Regular and other commercially-available antacids

In-vitro characterization of the acid-neutralizing capacity of ENO® Regular and other commercially-available antacids