Fly ash and lime-stabilized biosolid mixtures in mine spoil reclamation: simulated weathering

The use of large quantities of neutral coal fly ash (NFA) may be facilitated by co-application with a lime-stabilized biosolid (LSB) for the reclamation of acid mine spoil (AMS). Although NFA may not aid in the mitigation of acid drainage, questions concerning the leachability and mineralogy of native and NFA- and LSB-born metals must be addressed. In this study, the potential long-term influence of LSB and NFA on AMS leachate chemistry and trace element mineralogy was evaluated using laboratory weathering and selective dissolution techniques. The application of LSB at a rate sufficient to neutralize the potential acidity of the AMS increased leachate pH from approximately 3 to 7.5 for the duration of the study. Fly ash rates (1X, 1.5X, and 2X LSB rate) did not affect leachate pH. The dominant electrolytes in all leachates were Ca and SO4, the concentrations of which were mirrored by solution electrical conductivity (EC). Leachate concentrations of Al, Fe, Mn, K, Cu, Ni, and Zn were significantly reduced by LSB application, whereas concentrations of Ca, SO4, Mg, Cl, F, B, and P were increased. Nitrate concentrations were not affected by LSB. With the exception of leachate B, which increased with increasing NFA rate and was regenerated during the weathering study, NFA did not affect leachate composition. Sequential selective dissolution indicated a transformation of Co, Cr, Cu, Ni, Pb, and Zn into less labile mineral pools with weathering. The results of these evaluations suggest that the application of NFA during AMS reclamation would have little effect on leachate chemistry or the mineralogy of trace elements. Thus, the high-volume application of NFA to AMS during reclamation may offer an additional opportunity for the use of this combustion by-product.     

Trace element removal from coal ash leachate by a 10-year-old constructed wetland

This study investigated the ability of a 10-yr-old constructed wetland to treat metal-contaminated leachate emanating from a coal ash pile at the Widows Creek electric utility, Alabama (USA). The two vegetated cells, which were dominated by cattail (Typha latifolia L.) and soft rush (Juncus effusus L.), were very effective at removing Fe and Cd from the wastewater, but less efficient for Zn, S, B, and Mn. The concentrations were decreased by up to 99% for Fe, 91% for Cd, 63% for Zn, 61% for S, 58% for Mn, and 50% for B. Higher pH levels (>6) in standing water substantially improved the removing efficiency of the wetland for Mn only. The belowground tissues of both cattail and soft rush had high concentrations of all elements; only for Mn, however, did the concentration in the shoots exceed those in the belowground tissues. The concentrations of trace elements in fallen litter were higher than in the living shoots, but lower than in the belowground tissues. The trace element accumulation in the plants accounted for less than 2.5% of the annual loading of each trace element into the wetland. The sediments were the primary sinks for the elements removed from the wastewater. Except for Mn, the concentrations of trace elements in the upper layer (0-5 cm) of the sediment profile tended to be higher than the lower layers (5-10 and 10-15 cm). We conclude that constructed wetlands are still able to efficiently remove metals in the long term (i.e.,>10 yr after construction).     

Effect of tomato packinghouse wastewater properties on phosphorus and cation leaching in a spodosol

Land application of wastewater is a common practice. However, coarse-textured soils and shallow groundwater in Florida present favorable conditions for leaching of wastewater-applied constituents. Our objective in this study was to determine phosphorus (P) and associated cations (Ca, Mg, K, Na) leaching in a Spodosol irrigated with tomato packinghouse wastewater. We packed 12 polyvinyl chloride soil columns (30 cm internal diameter × 50 cm length) with two soil horizons (Ap and A/E) and conducted 30 sequential leaching events by irrigating with wastewater at low (0.84 cm d), medium (1.68 cm d), and high (2.51 cm d) rates. The control treatment received deionized water at 1.68 cm d Leachate pH was lower (6.4-6.5) and electrical conductivity (EC) was higher in the wastewater-treated columns (0.85-1.78 dS m) than in the control treatment (pH 6.9; EC, 0.12 dS m) due to the low pH (6.2) and high EC (2.16 dS m) of applied wastewater. Mean leachate P concentrations were greatest in the control treatment (0.70 mg L), followed by the high (0.60 mg L) and low and medium wastewater-treated columns (0.28-0.33 mg L). Leachate concentrations of Na, Ca, Mg, and K were significantly ( < 0.05) greater in wastewater-treated columns than in the control. Concentrations of P, Na, and K in leachate remained lower than the concentrations in the applied wastewater, indicating their retention in the soil profile. In contrast, leachate Ca and Mg concentrations were greater than in applied wastewater during several leaching events, suggesting that additional Ca and Mg were leached from the soil. Our results suggest that tomato packinghouse wastewater can be beneficially land-applied at 1.68 cm d in Florida's Spodosols without significant P and cation leaching.     

Effect of flue gas desulfurization residue on plant establishment and soil and leachate quality

Effects on soil quality and crop establishment after incorporation of flue gas desulfurization by-product (FGD) into soil as an amendment was assessed in a mesocosm study. Mesocosm units received applications equivalent to 0, 2.5, 5.0, 7.5, and 10% FGD residue [0, 25, 50, 75, and 100 tons acre(-1)]. Germination, biomass production, and elemental composition of corn (Zea mays L. var. Dekalb DK-683), soybean [Glycine max (L.) Merr. var. Haskell Pupa 94], radish (Raphanus sativus L. var. Sparkler), and cotton (Gossypius hirsutus L. var. Deltapine 51) were determined. The quality of leachates and soil were also determined periodically. Flue gas desulfurization residue did not affect germination and all application rates stimulated aboveground biomass. Plants grown in FGD-amended soil contained significantly elevated tissue concentrations of As, B, Se, and Mo. The FGD residue elevated surface soil pH from 5.5 (Control) to 8.1 (at 10% FGD). Leachate pH was unaffected by FGD, but salinity rose sharply with increasing application rates of FGD. Leachates contained higher concentrations of B, with small increases in Se and As. Flue gas desulfurization residue application caused an increase in total B, As, Mo, Se, and extractable Ca in the soil, but decreased Mn and Zn. Using FGD residues could have beneficial effects on crop establishment without detrimental effects on soil or leachate quality, at an optimum rate of approximately 2.5%. This material could alleviate surface acidity, and B and Mo deficiencies in plants.     

Soil biogeochemical characteristics influenced by alum application in a municipal wastewater treatment wetland

Constructed treatment wetlands are a relatively low-cost alternative used for tertiary treatment of wastewater. Phosphorus (P) removal capacity of these wetlands may decline, however, as P is released from the accrued organic soils. Little research has been done on methods to restore the treatment capacity of aging constructed wetlands. One possibility is the seasonal addition of alum during periods of low productivity and nutrient removal. Our 3-mo mesocosm study investigated the effectiveness of alum in immobilizing P during periods of reduced treatment efficiency, as well as the effects on soil biogeochemistry. Eighteen mesocosms were established, triplicate experimental and control units for Typha sp., Schoenoplectus californicus, and submerged aquatic vegetation (SAV) (Najas guadalupensis dominated). Alum was slowly dripped to the water column of the experimental units at a rate of 0.91 g Al m(-2) d(-1) and water quality parameters were monitored. Soil cores were collected at experiment initiation and completion and sectioned into 0- to 5- and 5- to 10-cm intervals for characterization. The alum floc remained in the 0- to 5-cm surface soil, however, soil pH and microbial parameters were impacted throughout the upper 10 cm with the lowest pH found in the Typha treatment. Plant type did not impact most biogeochemical parameters; however, data were more variable in the SAV mesocosms. Amorphous Al was greater in the surface soil of alum-treated mesocosms, inversely correlated with soil pH and microbial biomass P in both soil layers. Microbial activity was also suppressed in the surface soil of alum-treated mesocosms. This research suggests alum may significantly affect the biogeochemistry of treatment wetlands and needs further investigation.     

Evaluation of leachate recirculation on nitrous oxide production in the Likang Landfill,China

Landfill leachate recirculation is efficient in reducing the leachate quantity handled by a leachate treatment plant. However, after land application of leachate, nitrification and denitrification of the ammoniacal N becomes possible and the greenhouse gas nitrous oxide (N2O) is produced. Lack of information on the effects of leachate recirculation on N2O production led to a field study being conducted in the Likang Landfill (Guangzhou, China) where leachate recirculation had been practiced for 8 yr. Monthly productions and fluxes of N2O from leachate and soil were studied from June to November 2000. Environmental and chemical factors regulating N2O production were also accessed. An impermeable top liner was not used at this site; municipal solid waste was simply covered by inert soil and compacted by bulldozers. A high N2O emission rate (113 mg m-2 h-1) was detected from a leachate pond purposely formed on topsoil within the landfill boundary after leachate irrigation. A high N2O level (1.09 micrograms L-1) was detected in a gas sample emitted from topsoil 1 m from the leachate pond. Nitrous oxide production from denitrification in leachate-contaminated soil was at least 20 times higher than that from nitrification based on laboratory incubation studies. The N2O levels emitted from leachate ponds were compared with figures reported for different ecosystems and showed that the results of the present study were 68.7 to 88.6 times higher. Leachate recirculation can be a cost-effective operation in reducing the volume of leachate to be treated in landfill. However, to reduce N2O flux, leachate should be applied to underground soil rather than being irrigated and allowed to flow on topsoil.     

Switchgrass biochar affects two aridisols

The use of biochar has received growing attention because of its ability to improve the physicochemical properties of highly weathered Ultisols and Oxisols, yet very little research has focused on its effects in Aridisols. We investigated the effect of low or high temperature (250 or 500°C) pyrolyzed switchgrass () biochar on two Aridisols. In a pot study, biochar was added at 2% w/w to a Declo loam (Xeric Haplocalcids) or to a Warden very fine sandy loam (Xeric Haplocambids) and incubated at 15% moisture content (by weight) for 127 d; a control (no biochar) was also included. Soils were leached with 1.2 to 1.3 pore volumes of deionized HO on Days 34, 62, 92, and 127, and cumulative leachate Ca, K, Mg, Na, P, Cu, Fe, Mn, Ni, Zn, NO-N, NO-N, and NH-N concentrations were quantified. On termination of the incubation, soils were destructively sampled for extractable Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Zn, NO-N, and NH-N, total C, inorganic C, organic C, and pH. Compared with 250°C, the 500°C pyrolysis temperature resulted in greater biochar surface area, elevated pH, higher ash content, and minimal total surface charge. For both soils, leachate Ca and Mg decreased with the 250°C switchgrass biochar, likely due to binding by biochar's functional group sites. Both biochars caused an increase in leachate K, whereas the 500°C biochar increased leachate P. Both biochars reduced leachate NO-N concentrations compared with the control; however, the 250°C biochar reduced NO-N concentrations to the greatest extent. Easily degradable C, associated with the 250°C biochar's structural make-up, likely stimulated microbial growth, which caused NO-N immobilization. Soil-extractable K, P, and NO-N followed a pattern similar to the leachate observations. Total soil C content increases were linked to an increase in organic C from the biochars. Cumulative results suggest that the use of switchgrass biochar prepared at 250°C could improve environmental quality in calcareous soil systems by reducing nutrient leaching potential.     

Substrate organic matter to improve nitrate removal in surface-flow constructed wetlands

A wetland mesocosm experiment was conducted in eastern North Carolina to determine if organic matter (OM) addition to soils used for in-stream constructed wetlands would increase NO3--N treatment. Not all soils are suitable for wetland substrate, so OM addition can provide a carbon and nutrient source to the wetland early in its development to enhance denitrification and biomass growth. Four batch studies, with initial NO3--N concentrations ranging from 30 to 120 mg L-1, were conducted in 2002 in 21 surface-flow wetland mesocosms. The results indicated that increasing the OM content of a Cape Fear loam soil from 50 g kg-1 (5% dry wt.) to 110 g kg-1 (11% dry wt.) enhanced NO3--N wetland treatment efficiency in spring and summer batch studies, but increases to 160 g kg-1 (16% dry wt.) OM did not. Wetlands constructed with dredged material from the USACE Eagle Island Confined Disposal Facility in Wilmington, NC, with initial OM of 120 g kg-1 (12% dry wt.), showed no improvement in NO3--N treatment efficiency when increased to 180 g kg-1 (18% dry wt.), but did show increased NO3--N treatment efficiency in all batch studies when increased to 220 g kg-1 (22% dry wt.). Increased OM addition and biosolids to the Cape Fear loam and dredged material blends significantly increased biomass growth in the second growing season when compared to no OM addition. Results of this research indicate that increased OM in the substrate will reduce the area required for in-stream constructed wetlands to treat drainage water in humid regions. It also serves as a demonstration of how dredged material can be used successfully in constructed wetlands, as an alternative to costly storage by the USACE.     

Removal and distribution of iron, manganese, cobalt, and nickel within a Pennsylvania constructed wetland treating coal combustion by-product leachate

A flow-through wetland treatment system was constructed to treat coal combustion by-product leachate from an electrical power station at Springdale, Pennsylvania. In a nine-compartment treatment system, four cattail (Typha latifolia L.) wetland cells (designated Cells 1 through 4) successfully removed iron (Fe) and manganese (Mn) from the inlet water; Fe and Mn concentrations were decreased by an average of 91% in the first year (May 1996-May 1997), and by 94 and 98% in the second year (July 1997-June 1998), respectively. Cobalt (Co) and nickel (Ni) were decreased by an average of 39 and 47% in the first year, and 98 and 63% in the second year, respectively. Most of the metal removed by the wetland cells was accumulated in sediments, which constituted the largest sink. Except for Fe, metal concentrations in the sediments tended to be greater in the top 5 cm of sediment than in the 5- to 10- or 10- to 15-cm layers, and in Cell 1 than in Cells 2, 3, and 4. Plants constituted a much smaller sink for metals; only 0.91, 4.18, 0.19, and 0.38% of the Fe, Mn, Co, and Ni were accumulated annually in the aboveground tissues of cattail, respectively. A greater proportion of each metal (except Mn) was accumulated in cattail fallen litter and submerged Chara (a macroalga) tissues, that is, 2.81, 2.75, and 1.05% for Fe, Co, and Ni, respectively. Considerably higher concentrations of metals were associated with cattail roots than shoots, although Mn was a notable exception.     

Soil profile distribution of phosphorus and other nutrients following wetland conversion to beef cattle pasture

Largely influenced by the passage of the Swamp Land Act of 1849, many wetlands were lost in the coastal plain region of the southeastern United States, primarily as a result of drainage for agricultural activities. To better understand the chemical response of soils during wetland conversion, soil core samples were collected from the converted beef cattle pastures and from the natural wetland at Plant City, FL in the summers of 2002 and 2003. Data collected from the natural wetland sites were used as reference data to detect potential changes in soil properties associated with the conversion of wetlands to improved beef cattle (Bos taurus) pastures from 1940 to 2003. The average concentration of total phosphorus (TP) in pasture soils (284 mg kg(-1)) was significantly (p 相似文献   

Chemical residence time and hydrological conditions influence treatment of fipronil in vegetated aquatic mesocosms

Fipronil, a phenyl-pyrazole insecticide, is often used in rice (Oryza sativa L.) production agriculture, with elevated runoff concentrations and loads having potential toxicological effects on downstream aquatic environments. This study evaluated two species of aquatic plants-broadleaf cattail (Typha latifolia L.) and powdery alligator-flag (Thalia dealbata Fraser ex Roscoe)-placed in series against a nonvegetated mesocosm in reducing concentrations and loads of fipronil, and associated metabolites. Vegetation type and hydrological condition (inundated vs. dry) were treatment effects used for comparison. The vegetated mesocosms significantly reduced higher loads and concentrations of fipronil, fipronil sulfone, and sulfide in both inundated and dry hydrological conditions over nonvegetated nesocosms. Under inundation conditions, vegetated mesocosms reduced >50% of influent fipronil concentrations and betweeen 60 and 70% of fipronil loads, which was significantly higher than the dry conditions (10-32% concentration and load). These results show that agricultural management strategies usingephemeral aquatic zones, such as drainage ditches, can be optimized to couple chemical applications with vegetation presence and hydrology to facilitate the reduction in chemical waste loads entering downstream aquatic ecosystems. Such reduction is critical for use with fipronil, where negative impacts have been demonstrated with several nontarget species.     

Soil and water characteristics of a young surface mine wetland

Coal companies are reluctant to include wetland development in reclamation plans partly due to a lack of information on the resulting characteristics of such sites. It is easier for coal companies to recreate terrestrial habitats than to attempt experimental methods and possibly face significant regulatory disapproval. Therefore, we studied a young (10 years) wetland on a reclaimed surface coal mine in southern Illinois so as to ascertain soil and water characteristics such that the site might serve as a model for wetland development on surface mines. Water pH was not measured because of equipment problems, but evidence (plant life, fish, herpetofauna) suggests suitable pH levels. Other water parameters (conductivity, salinity, alkalinity, chloride, copper, total hardness, iron, manganese, nitrate, nitrite, phosphate, and sulfate) were measured, and only copper was seen in potentially high concentrations (but with no obvious toxic effects). Soil variables measured included pH, nitrate, nitrite, ammonia, potassium, calcium, magnesium, manganese, aluminum, iron, sulfate, chloride, and percent organic matter. Soils were slightly alkaline and most parameters fell within levels reported for other studies on both natural and manmade wetlands. Aluminum was high, but this might be indicative more of large amounts complexed with soils and therefore unavailable, than amounts actually accessible to plants. Organic matter was moderate, somewhat surprising given the age of the system.     

Papermill biosolids effect on soil physical and chemical properties

Papermill biosolids (PB) can provide multiple benefits to the soil system. The purpose of this study was to quantify the effects of a high C/N ratio (C/N = 100) de-inked PB on soil physical and chemical properties, including soil bulk density, infiltration rates, wet aggregate stability, total soil carbon, and heavy metal concentrations. Four rates of PB (0, 50, 100, and 150 Mg ha(-1)) were applied annually, for up to 3 yr, on four agricultural soils in Ontario, Canada. Decreases in soil bulk density between 0.27 and 0.35 g cm(-3), relative to the nonamended treatment, were observed in soils receiving PB treatments over 3 yr. Total soil carbon increased within 1 yr on PB-amended soils planted to soybeans but not on soils planted to corn. Hydraulic conductivities (K fs) were greater in all soils receiving PB amendments relative to the nonamended treatment throughout the study. Other properties measured, such as pH and electrical conductivity, were relatively unchanged after 2 yr of PB applications. While some increases in heavy metal accumulation occurred, there were no clear trends observed at any of the sites related to PB rates. The results of this study provide support to the idea that annual applications of PB can add significantly to the stability of soil structure.     

NITROGEN ACCUMULATION IN A CONSTRUCTED WETLAND FOR DAIRY WASTEWATER TREATMENT1

ABSTRACT: A free water surface (FWS) constructed wetland was installed at a dairy in Glendale, Arizona, to study the potential of such a wetland to remove nitrogen (N) from wastewater. The study objectives were: (1) to determine N removal from the wastewater, and (2) to evaluate N accumulation in soil and plant tissues. The system consisted of eight cells (70 × 9 × 1.5 m) planted with Typha domingensis, Scirpus validus, and Phragmites australis. The four cells in series were lined with plastic, and the four cells in a parallel series were lined with clay. Cells received approximately 180 m³/d of partially treated dairy effluent. Plant tissues and soil samples were collected above and below ground from 24 locations during one year. Total N removal from wastewater was about 17 percent. Clay‐lined cells accumulated more N in the soil and less N in plant biomass compared with plastic lined cells. Plant biomass accounted for approximately 60 percent of total N accumulated in cells with dense plant communities. Ninety percent of accumulated soil N was organic. Total N accumulated in soil reached a maximum (1,100 mg/kg) eight months after the introduction of wastewater.     

Lability of drinking water treatment residuals (WTR) immobilized phosphorus: aging and pH effects

Time constraints associated with conducting long-term (>20 yr) field experiments to test the stability of drinking water treatment residuals (WTR) sorbed phosphorus (P) inhibit improved understanding of the fate of sorbed P in soils when important soil properties (e.g., pH) change. We used artificially aged samples to evaluate aging and pH effects on lability of WTR-immobilized P. Artificial aging was achieved through incubation at elevated temperatures (46 or 70 degrees C) for 4.5 yr, and through repeated wetting and drying for 2 yr. Using a modified isotopic ((32)P) dilution technique, coupled with a stepwise acidification procedure, we monitored changes in labile P concentrations over time. This technique enabled evaluation of the effect of pH on the lability of WTR-immobilized P. Within the pH range of 4 to 7, WTR amendment, coupled with artificial aging, ultimately reduced labile P concentrations by > or = 75% relative to the control (no-WTR) samples. Soil samples with different physicochemical properties from two 7.5-yr-old, one-time WTR-amended field sites were utilized to validate the trends observed with the artificially aged samples. Despite the differences in physicochemical properties among the three (two field-aged and one artificially aged) soil samples, similar trends of aging and pH effects on lability of WTR-immobilized P were observed. Labile P concentrations of the WTR-amended field-aged samples of the two sites decreased 6 mo after WTR amendment and the reduction persisted for 7.5 yr, ultimately resulting in > or = 70% reduction, compared to the control plots. We conclude that WTR application is capable of reducing labile P concentration in P-impacted soils, doing so for a long time, and that within the commonly encountered range of pH values for agricultural soils WTR-immobilized P should be stable.     

Effects of glyphosate and two herbicide mixtures on microbial communities in prairie wetland ecosystems: a mesocosm approach

A multitrophic outdoor mesocosm system was used to mimic a wetland ecosystem and to investigate the effects of glyphosate and two herbicide mixtures on wetland microbial communities. The glyphosate concentration used was 1000 times the environmentally relevant concentration (ERC). One herbicide mixture consisted of six auxin-type herbicides (2,4-D, MCPA, clopyralid, dicamba, dichlorprop, mecoprop), each at 1000 times the ERC. The second mixture was comprised of eight herbicides, including the six auxin-type herbicides as well as bromoxynil and glyphosate. For this mixture, a dose-response approach was used to treat mesocosms with the ERCs of each herbicide as the base concentration. Algal biomass and production and bacterial production and numbers for pelagic and attached communities were measured at different times over a 22-d period. The experimental results indicate that the eight-herbicide mixture, even at low concentrations, produced negative effects on microbial communities. Glyphosate on its own suppressed algal biomass and production for the duration of the study in pelagic and biofilm communities. Algal biomass and production, although initially depressed in the auxin-type herbicide treatment, were stimulated from Day 9 until experiment end. Due to their similar modes of action, the effects of this herbicide mixture appear to be a result of concentration addition. Such negative effects, however, were brief, and microbial communities recovered from herbicide exposure. Based on evidence presented in this study, it appears that glyphosate has a higher potential to inhibit primary production and chlorophyll content in pelagic and attached wetland algal communities than the auxin-type herbicide mixture.     

Leaching from organic matter-rich soils by rain of different qualities: I. Concentrations

Soil monoliths from an area exposed to acid precipitation and from an unpolluted area were used in a lysimeter experiment to study effects of different rain qualities on the chemical composition of the leachate from shallow soils rich in organic matter. The vegetation was either dominated by moorgrass [Molinia caerulea (L.) Moench] or heather [Calluna vulgaris (L.) Hull]. The lysimeters received either "acid rain" (pH 4.3) or "normal rain" (pH 5.3). High concentrations of dissolved organic carbon (DOC) were characteristic of the leachate. The different "rain" qualities had no significant influence on the DOC concentration. More DOC was, however, leached from lysimeters with heather vegetation. Roughly 50% of the aluminum (Al) was in complex with organic material and the Al charge was calculated to be between +1.4 and +2.0. Sulfate (SO4(2-)) was the only component that was significantly influenced by the treatment, as more was leached from lysimeters receiving "acid rain." Sulfate was poorly correlated with pH, suggesting that reduced SO4(2-) input would not necessarily lead to reduced acidity. Differences in the pH of the leachate due to the treatments were less than 0.15 pH units. Nitrate (NO3-) was only leached in very low concentrations and of little consequence for the leachate acidity. Some observations do, however, suggest that NO3- may contribute to acidification in episodes with high precipitation. High concentrations of Cl- in the leachate and a significant positive correlation between Cl-, H+, and base cations indicate that sea salt episodes may be important for soil acidification and acidity of the leachate.     

Metal immobilization in soils using synthetic zeolites

In situ immobilization of heavy metals in contaminated soils is a technique to improve soil quality. Synthetic zeolites are potentially useful additives to bind heavy metals. This study selected the most effective zeolite in cadmium and zinc binding out of six synthetic zeolites (mordenite-type, faujasite-type, zeolite X, zeolite P, and two zeolites A) and one natural zeolite (clinoptilolite). Zeolite A appeared to have the highest binding capacity between pH 5 and 6.5 and was stable above pH 5.5. The second objective of this study was to investigate the effects of zeolite addition on the dissolved organic matter (DOM) concentration. Since zeolites increase soil pH and bind Ca, their application might lead to dispersion of organic matter. In a batch experiment, the DOM concentration increased by a factor of 5 when the pH increased from 6 to 8 as a result of zeolite A addition. A strong increase in DOM was also found in the leachate of soil columns, particularly in the beginning of the experiment. This resulted in higher metal leaching caused by metal-DOM complexes. In contrast, the free ionic concentration of Cd and Zn strongly decreased after the addition of zeolites, which might explain the reduction in metal uptake observed in plant growth experiments. Pretreatment of zeolites with acid (to prevent a pH increase) or Ca (to coagulate organic matter) suppressed the dispersion of organic matter, but also decreased the metal binding capacity of the zeolites due to competition of protons or Ca.     

我国煤炭开采和燃烧过程中的硫污染对土壤环境的影响

我国煤炭在开采和燃烧过程中形成的硫污染物主要是酸性矿井水和二氧化硫,由煤炭燃烧造成的硫的干湿沉降以及煤炭开采过程中形成的酸性矿井水使土壤的物理化学性质发生变化,从而对土壤造成严重的破坏。主要表现在造成土壤中可溶性硫酸盐的大幅度升高;引起土壤的pH值下降;植物营养元素特别是K、Na、Ca、Mg等产生淋失;活性铝溶出量增加;有毒重金属活化;抑制土壤酶的活性等方面。可以通过脱硫除尘、加强绿化、建立合理的工业布局、加入土壤改良剂等措施来减少硫污染物的排放量和改善其对土壤环境的影响,但总量控制是关键,是最根本的途径。     

Evaluation of groundwater and soil pollution in a landfill area using electrical resistivity imaging survey

Landfills are sources of groundwater and soil pollution due to the production of leachate and its migration through refuse. This study was conducted in order to determine the extent of groundwater and soil pollution within and around the landfill of Seri Petaling located in the State of Selangor, Malaysia. The condition of nearby surface water was also determined. An electrical resistivity imaging survey was used to investigate the leachate production within the landfill. Groundwater geochemistry was carried out and chemical analysis of water samples was conducted upstream and downstream of the landfill. Surface water was also analyzed in order to determine its quality. Soil chemical analysis was performed on soil samples taken from different locations within and around the landfill in the vadose zone (unsaturated zone) and below the water table (in the soil saturated zone). The resistivity image along line L–L₁ indicated the presence of large zones of decomposed waste bodies saturated with highly conducting leachate. Analysis of trace elements indicated their presence in very low concentrations and did not reflect any sign of heavy metal pollution of ground and surface water or of soil. Major ions represented by Na, K, and Cl were found in anomalous concentrations in the groundwater of the downstream bore hole, where they are 99.1%, 99.2%, and 99.4%, respectively, higher compared to the upstream bore hole. Electrical conductivity (EC) was also found in anomalous concentration downstream. Ca and Mg ions represent the water hardness (which is comparatively high downstream). There is a general trend of pollution towards the downstream area. Sulfates (SO₄) and nitrates (NO₃) are found in the area in low concentrations, even below the WHO standards for drinking water, but are significantly higher in the surface water compared to the groundwater. Phosphate (PO₄) and nitrite (NO₂), although present in low levels, are significantly higher at the downstream. There is no significant difference in the amount of fluoride (F) in the different locations. In the soil vadose zone, heavy metals were found to be in their typical normal ranges and within the background concentrations. Soil exchangeable bases were significantly higher in the soil saturated zone compared to the vadose zone, and no significant difference was obtained in the levels of inorganic pollutants. With the exception of Cd, the concentration ranges of all trace elements (Cu, Zn, Cr, Pb, and Ni) of Seri Petaling landfill soils were below the upper limits of baseline concentrations published from different sources.