Effluent Metal Concentrations Research Articles

Effects of plant species and traits on metal treatment and phytoextraction in stormwater bioretention

To study effects of plant species selection on total and dissolved metal treatment performance of bioretention systems (BRS), 12 sets of columns were prepared, each planted with one of 12 species that are either widely used in BRS or have potentially important traits for metal removal (ability to hyperaccumulate metals, C4 photosynthesis, or ability to form mycorrhiza). Artificial stormwater was applied to half of the columns during all of a 31-week test period, while treatment of the others included a 5-week long dry period to test interactive effects of drying and plant traits on BRS metal treatment in more realistic alternating wet and dry conditions. Concentrations of metals (dissolved and total) in the effluent significantly differed between most columns with different plants, and the differences in concentrations of dissolved metals after the dry period were particularly important. Mean dissolved Cd concentrations exceeded Swedish reference values in effluents from BRS with two of the plant species, while mean dissolved Zn concentrations exceeded them in effluents from BRS with three of the species (and non-vegetated controls). Dissolved Cu leaching was observed in effluents from BRS with five of the plant species after the dry period, and mean concentrations exceeded Swedish reference values in effluents from all the BRS (including the constantly watered systems). Some support in terms of metal concentrations in shoots and shoot/soil ratios was obtained for using hyperaccumulators in BRS to remove metals from filter material. For example, Armeria maritima (a hyperaccumulator with the lowest shoot biomass) and Miscanthus sinsenis (a C4 plant with the highest biomass production) took up similar amounts of metals despite large differences in biomass. However, no significant correlations between effluent metal concentrations and plants’ metal uptake were found, possibly because of the short duration of the experiment. The results indicate that root biomass affected effluent metal concentrations more strongly. Root biomass was often positively correlated with total and (particularly) dissolved effluent metal concentrations. Further experiments with different soil metal concentrations, organic matter analyses and stronger focus on root characteristics are recommended, including additional tests of effects of hyperaccumulators and mycorrhiza on metal treatment and phytoextraction.

Characterization of hazards and environmental risks of wastewater effluents from ship hull cleaning by hydroblasting

Hydroblasting is used to remove biofouling and exhausted antifouling paints from ship hulls. Effluents generated from this process contain paint particles, metals, and booster biocides that may have toxic effects on organisms. To understand the potential risks of effluent discharge on marine environments, we analyzed the concentrations of metals in effluents collected during the dry-dock cleaning of ship hulls by hydroblasting. Copper and zinc were the principal metals, with concentrations ranging from 1440 to 9110 μg/L and 1800 to 22,600 μg/L, respectively. These concentrations are sufficiently high to cause harmful effects to most marine organisms. Model predictions suggested that the effluent discharge from hydroblasting posed risks to the wider marine environment of a hull-cleaning site, depending on the scale of the hull-cleaning operations and the size of the receiving environment, as well as various hydrodynamic factors. These effluents are inevitably hazardous, and their environmental release should be managed and regulated on the basis of site-specific risk assessments.

Water pollution and occupational health hazards caused by the marble industries in district Mardan, Pakistan

Abstract The present study was aimed to assess physico-chemical parameters and heavy metals (HM) concentration in marble industrial effluents, and HM bioaccumulation in the workers’ blood employed in the marble industries in Mardan Industrial Estate (MIE) of district Mardan, Khyber Pakhtunkhwa (KP) province, Pakistan. A total of twelve samples were collected from industrial effluents and seven samples of blood were collected from healthy workers of different marble units on volunteer basis. Water samples were collected for analysis of physico-chemical parameters such as electrical conductivity (EC), pH, turbidity, sodium (Na), potassium (K), calcium, hardness, chloride, magnesium (Mg) and heavy metals, that is Copper (Cu), Manganese (Mn), Zinc (Zn) and Arsenic (As), and compared with the National Environmental Quality Standards (NEQS) of World Health Organization ( WHO, 2010 ). Blood samples from the marble industries workers were collected for the analysis of HM i.e. Cu, Mn, Zn and As bioaccumulation. Our results showed that most of the samples showed higher physico-chemical parameters with respect to the permissible limit set by the NEQS of WHO, 2010. Similarly, HM in water as well as in workers blood also revealed higher values than the permissible limit concentrations set by Occupational Health and Safety Act (OSHA), Occupational Health and Safety Division (OHSD) and Agency for Toxic substances and Disease Registry (ATSDR), USA. Therefore, the major findings of the study suggested that higher level of alteration in the physico-chemical parameters and HM in water and workers’ blood will have great impact on freshwater resources and human health in the study area. Therefore, it is highly recommended that wastewater treatment plant should be constructed in the MIE of district Mardan to treat polluted water discharged from the marble manufacturing units prior entering into freshwater courses in the study area. Moreover, an awareness program should be launched to aware the workers of marble manufacturing units, as well as local community, regarding water pollution and heavy metals bioaccumulation caused by marble production units, and its mitigation to protect themselves and aquatic wildlife from the devastating impacts of water pollution occurring in the study area.

Leaching behavior of aluminum, copper, iron and zinc from cement activated fly ash and slag stabilized soils

The use of industrial by-products such as fly ash and slag have become very prevalent in soil stabilization owing to its suitable physical and mechanical properties, and economical advantages. However, fly ash and slag have been identified as the potential source of toxic substances, and may pose environmental risk by leaching heavy and trace metals into soil, surface and groundwater. Toxicity characteristic leaching procedure (TCLP) tests were conducted to investigate the environmental hazards associated with the leaching of aluminum (Al), copper (Cu), iron (Fe) and zinc (Zn) from fly ashes, slag, type I/II cement and cement activated fly ash and slag stabilized soils. Sulfate (SO4), dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) concentrations were also quantified to evaluate their influence on metal leaching. To understand the effect of pH on the leaching behavior, pH-dependent leach tests were conducted at the pH ranges of 2–14. Results indicated that an increase in fly ash or slag content may not necessarily increase the effluent metal concentrations. Al, Cu, Zn and DOC followed an amphoteric leaching pattern where concentrations increased in both acidic and basic conditions. In contrast, maximum DIC concentrations occurred at neutral or near neutral pH values. Fe and SO4 showed cationic leaching behavior where concentrations decreased with an increase in effluent pH. Additionally, the leaching controlling mechanisms of the metals were identified by implementing geochemical modeling program Visual MINTEQ. The geochemical analyses indicated that the solubility of Al3+ and Fe3+ were controlled by precipitation/dissolution reactions of oxide/hydroxide minerals at all pH values. Leaching of Cu2+ was only solubility controlled at pH higher than 7, whereas Zn2+ leaching was solubility controlled in the pH range of 8–12.

An experimental study of cotransport of heavy metals with kaolinite colloids.

Cotransport of heavy metals, Pb, Cu and Zn (multi-metal system), and transport of those metals (single-metal system) were investigated by performing laboratory soil column experiment under the presence of kaolinite colloids. Preequilibrated kaolinite colloids with heavy metal solution was injected to the column until 10 pore volumes under two different flow rates and three different concentration of kaolinite colloids. Heavy metal concentration in effluent showed that the mobility of Pb was facilitated as kaolinite colloids concentration (Cc0) increases under high flow rate while the mobility of Pb and Cu were retarded as Cc0 increases under low flow rate. In addition, optimized first order rate coefficient related to sand-heavy metal interaction and estimated bed efficiency of experimental breakthrough curves demonstrated that the presence of mobile kaolinite colloids delayed the adsorption of heavy metals to the sand and facilitated the transport. Colloid associated contaminant transport model used in this study was found to be well fitted to the experimental breakthrough curves with the parameters associated with observed heavy metal transport without kaolinite colloids and adsorption/desorption between the heavy metals and the mobile kaolinite colloids.

Occurrence of Selected Metals in Wastewater Effluent and Surface Water in Ireland

ABSTRACTMetals occur naturally in the environment and as constituents of the Earth’s crust. They have many uses, and metals such as iron, copper, and zinc are widely used in industries. Elevated levels of metals in the environment also occur as a result of human activities (municipal, residential, and traffic–related activities). A list of 15 metals chosen for this study included priority substances and those listed in the European Union Water Framework Directive 2000/60/EC. The concentrations of heavy metals in the environment are affected by several factors that must be taken into account when monitoring heavy metals released into the environment through wastewater treatment plants (WWPTs). This work examines the concentrations of metals found in WWPTs and the effects of treatment type on dissolved metal concentrations. Effluent samples were collected from the outflow of nine WWPTs in Dublin and Cork, Ireland from July 2009 to June 2011. All samples were found to contain priority metals that exceeded environmental quality standards in several cases. We present the frequency of occurrence and concentrations of metals in effluents of studied WWPTs and discuss relationships between the occurrence of heavy metals, the influence of factors such as industrial inputs, levels of treatment at WWPTs, and percentage urban area in an agglomeration. The results of this study are an indication that WWPTs may be contributing to the high levels of heavy metals found at discharge points back into river systems.

English

The listing of the Monongahela River as an impaired waterway prompted the Pennsylvania Department of Environmental Protection (PADEP) to adjust aqueous discharge limits to the river to no more than 250 mg/L of sulfate. In response to this, an analysis of water treatment options for a coal mining company was conducted at several non-operating mines in western Pennsylvania that discharge directly or indirectly to the Monongahela River. Given the extremely high capital and operations costs for typical sulfate reduction methods such as reverse osmosis and ion exchange, novel passive and semi-passive treatment options were explored. An ethanol-fed bioreactor system was selected, designed, and constructed in 2014 to test whether sulfate reducing bacteria could be utilized to remove sulfate in alkaline mine water to meet discharge limits. The unique design elements consist of metals removal circuit, ethanol feed circuit, and twin bioreactors bedded with large cobbles and seeded with sulfate reducing bacteria, but containing no additional carbon source. Biochemical performance has shown that sulfate reduction approaches 1500 mmol SO4 m -3/ day during warmer weather, one of the highest rates recorded in the literature. Effluent sulfate ranged from 58 to 400 mg/L at 16oC and about 1400 mg/L at 2oC compared to influent sulfate concentrations that averaged 2800 mg/L. In addition, the bioreactor produced 500-1500 mg/L of total alkalinity due to microbial metabolism supported by the ethanol, typically corresponding with sulfate decreases. Effluent metal concentrations were decreased to 1 mg/L Fe and 0.2 mg/L Mn. The recirculation loop was found to remove 90% of iron in the original settling pond prior to entering the reactors to minimize sludge accumulation. Additional

Heavy Metals Removal Using Natural Jordanian Volcanic Tuff

AbstractThe removal performance and the selectivity sequence of separate metal ions (Fe2+, Cr3+, Cu2+, Zn2+ and Ni2+) in aqueous solution were studied by adsorption process on untreated and natural volcanic tuff. A series of experiments were conducted in batch-wise and fixed-bed columns to investigate the removal efficiency of natural Jordanian volcanic tuff as low cost and an effective adsorbent for heavy metal ions and to examine its economical application in water purification and treatment practices.Water and wastewater samples containing metal ions with concentrations ranging from 1 to 15 mg/L were used. The plexi glas columns were filled with natural occurring volcanic tuff particles ranging between (0.350 – 3.000) mm. Photometric methods were used for laboratory analysis of samples.The experiments were carried out under changing conditions as a function of different pH-values (2,4,6 and 7), initial solute concentrations (1, 5, 10, 15) mg/L, and different room temperatures (20, 25 and 30 Cº ), and varying tuff particle sizes (0.35 -3.0) mm. The breakthrough curves were derived by plotting the normalized effluent metal concentrations (C/C0) versus bed volume.Obtained results showed that natural Jordanian volcanic tuff has an adsorption capacity of 0.417 mg/g for Fe 2+ and 0.151mg/g for C 2+. Factors in the reaction medium such as pH and ionic strength influenced the adsorption process. The quantity of particular ionic species (Cu2+, Pb2+, Cr2+ ,Fe2+, Zn2+) bound in dependence on the initial concentrations, indicates that the removal efficiency from the liquid phase follows the sequence Fe2+>Cu2+>Pb2+> Cr2+>Zn2+ when keeping the pH at 4 and follows the sequence Cu2+>Zi2+>Fe2+>Cr2+>Pb2+ when keeping the pH at 6. Equilibrium modeling of the removal showed that the adsorption of the metal cations Cr2+, Pb2+, Zn2+ , Cu2+ and Fe2+ were fitted to one of the adsorption isotherms.

Heavy Metals Concentration in Effluents of Textile Industry, Tikur Wuha River and Milk of Cows Watering on this Water Source, Hawassa, Southern Ethiopia

Heavy Metals Concentration in Effluents of Textile Industry, Tikur Wuha River and Milk of Cows Watering on this Water Source, Hawassa, Southern Ethiopia

Copper, Cadmium and Ferrous Removal by Membrane Bioreactor

One of the important concerns in Tehran municipal landfill is the production of leachate and its potential for water resources pollution. This paper investigates the removal of heavy metals from landfill leachate by using a membrane Bioreactor (MBR). The leachate was collected from a landfill in the vicinity of Tehran nearly 1 year old, The results of this study indicated that the system provided high removals of Fe, Cu and Cd equal to 96%, 23% and 84% respectively and heavy metal concentration in MBR effluent is a function of aeration ratio and bioaccumulation. Among the metals investigated in the present study it can be concluded that the extracellular adsorption, is the principal removal process of the metals, compared to other removal mechanisms such as bioaccumulation or intracellular accumulation.

Changes in metal mobility associated with bark beetle-induced tree mortality

Recent large-scale beetle infestations have caused extensive mortality to conifer forests resulting in alterations to dissolved organic carbon (DOC) cycling, which in turn can impact metal mobility through complexation. This study analyzed soil-water samples beneath impacted trees in concert with laboratory flow-through soil column experiments to explore possible impacts of the bark beetle infestation on metal release and transport. The columns mimicked field conditions by introducing pine needle leachate and artificial rainwater through duplicate homogenized soil columns and measuring effluent metal (focusing on Al, Cu, and Zn) and DOC concentrations. All three metals were consistently found in higher concentrations in the effluent of columns receiving pine needle leachate. In both the field and laboratory, aluminum mobility was largely correlated with the hydrophobic fraction of the DOC, while copper had the largest correlation with total DOC concentrations. Geochemical speciation modeling supported the presence of DOC-metal complexes in column experiments. Copper soil water concentrations in field samples supported laboratory column results, as they were almost twice as high under grey phase trees than under red phase trees further signifying the importance of needle drop. Pine needle leachate contained high concentrations of Zn (0.1 mg l(-1)), which led to high effluent zinc concentrations and sorption of zinc to the soil matrix representing a future potential source for release. In support, field soil-water samples underneath beetle-impacted trees where the needles had recently fallen contained approximately 50% more zinc as samples from under beetle-impacted trees that still held their needles. The high concentrations of carbon in the pine needle leachate also led to increased sorption in the soil matrix creating the potential for subsequent carbon release. While unclear if manifested in adjacent surface waters, these results demonstrate an increased potential for Zn, Cu, and Al mobility, along with increased deposition of metals and carbon beneath beetle-impacted trees.

Removal of Contaminating Metals from Soil by Sulfur-Based Bioleaching and Biogenic Sulfide-Based Precipitation

The potential of a hybrid process incorporating sulfur-based bioleaching and sulfide-based precipitation for treatment of metal-contaminated soil was examined in batch-type experiments. The sulfur-based soil bioleaching process with Acidithiobacillus sp. could be initiated at a wide range of initial pH from 4.0 to 6.3. After 15 days, 98% of Zn, 89% of Cu and 79% of Cd was bioleached. The gaseous sulfides recycling from Desulfovibrio sp.-mediated sulfate-reducing reactor via N2 sparging efficiently treated metal-loaded soil leachate. With a sulfide/metal ratio of 3.0, 88% of Zn, 100% of Cu and 95% of Cd were precipitated, resulting in effluent metal concentrations of 3.5 mg Zn2+/L, 0.2 mg Cu2+/L and 0.03 mg Cd2+/L. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.

Evaluating Removal Efficiency of Heavy Metals in Constructed Wetlands

AbstractIn recent decades, there has been a growing interest in using constructed wetlands (CWs) for the treatment of contaminated waters. There has been an increase in the use of wetland technology because of its low greenhouse effects, low maintenance and operational costs, and energy efficiency. However, there exists a level of uncertainty in regards to the performance of CWs and in some cases, CWs act as sources of contaminants. To address the issue, this paper presents the removal efficiencies for different heavy metal elements and identifies the factors affecting the removal processes. Using the San Joaquin Marsh constructed wetlands, removal efficiencies for four heavy metal elements—Cd, Cu, Pb and Zn—were evaluated. It was found that the effluent metal concentrations were not substantially lower than the influent. The removal efficiencies of 23.9%, 10.6%, and 17.6% were found for Cd, Cu, and Zn, respectively. No significant reduction was observed for concentrations of Pb. Different aspects of the ...

Stress response of heavy metal mixture present in wastewater and leachate on heat-shock protein 47-transfected cells

Heavy metals present in water environment and hazardous sites as single compounds or mixture may drastically affect human health. In the present work, we investigated the risk assessment of wastewater effluents and leachate with a focus on three heavy metals-nickel (Ni), cadmium (Cd), and lead (Pb)-and their combined effect on mammalian cells, using Chinese hamster ovary cells transfected with the heat-shock protein (HSP) 47 promoter. The heavy metal mixture model was designed based on the concentrations of metals in wastewater effluents and leachate sampled in Tunisia. Using a ternary diagram, we investigated the stress response of the interaction model. This research indicated that the single heavy metals induced the stress response on HSP(+) cells even at concentrations lower than the local and international guidelines. Differences in water quality likely influenced the metal responses such that the organic composition of the leachate increased the stress response induced by the heavy metals exclusively, whereas the effluents included organic compounds that were able to mask the heavy metal effect. The mixture characterization discovered the key role played by the high levels of Ni or combination of Cd and Pb to induce the highest stress response following 3-h incubation. Heat-shock protein 47 has proven its effectiveness for assessing the heavy metal mixture effect even at low concentrations. Furthermore, the combination of a bioassay system with a statistical model proved extremely useful for better understanding the major contributors to the stress response of the mixture.

Influence of organic acids on the transport of heavy metals in soil

Vegetation historically has been an important part of reclamation of sites contaminated with metals, whether the objective was to stabilize the metals or remove them through phytoremediation. Understanding the impact of organic acids typically found in the rhizosphere would contribute to our knowledge of the impact of plants in contaminated environments. Heavy metal transport in soils in the presence of simple organic acids was assessed in two laboratory studies. In the first study, thin layer chromatography (TLC) was used to investigate Zn, Cd, and Pb movement in a sandy loam soil as affected by soluble organic acids in the rhizosphere. Many of these organic acids enhanced heavy metal movement. For organic acid concentrations of 10mM, citric acid had the highest R(f) values (frontal distance moved by metal divided by frontal distance moved by the solution) for Zn, followed by malic, tartaric, fumaric, and glutaric acids. Citric acid also has the highest R(f) value for Cd movement followed by fumaric acid. Citric acid and tartaric acid enhanced Pb transport to the greatest degree. For most organic acids studied, R(f) values followed the trend Zn>Cd>Pb. Citric acid (10mM) increased R(f) values of Zn and Cd by approximately three times relative to water. In the second study, small soil columns were used to test the impact of simple organic acids on Zn, Cd, and Pb leaching in soils. Citric acid greatly enhanced Zn and Cd movement in soils but had little influence on Pb movement. The Zn and Cd in the effluents from columns treated with 10mM citric acid attained influent metal concentrations by the end of the experiment, but effluent metal concentrations were much less than influent concentrations for citrate <10mM. Exchangeable Zn in the soil columns was about 40% of total Zn, and approximately 80% total Cd was in exchangeable form. Nearly all of the Pb retained by the soil columns was exchangeable.

A rapid Chelex column method for the determination of metal speciation in natural waters

A simple, rapid Chelex resin column method has been developed for the determination of metal speciation in natural water samples. A water sample (pH 6–8.2) was pumped through a small plug of the Ca-form of Chelex 100 at a flow rate of 48 ± 4 mL/min. The flow regime was optimised to give the shortest possible contact time (0.25 s) but at the same time ensured quantitative uptake of inorganic metal standards onto the resin. Labile metal was calculated as the difference between influent and effluent metal concentrations, measured by some form of atomic spectrometry. In tests with six metal-spiked natural freshwater samples (10 μg/L added metal, pH 7.0–8.2), the labile fraction measured ranged from 87 to 98%, 32 to 64%, 12 to 78%, 38 to 91% and 63 to 89% for cadmium, copper, lead, nickel and zinc, respectively. Application of the method to copper-contaminated waters showed that the results provided a conservative estimate of the fraction inhibiting growth of a copper-sensitive bacterium, thus proving to be a useful measure of bioavailability. Tests on a range of model metal complexes showed that the measured labile metal fraction was inversely proportional to log K, and controlled by the kinetics of metal complex dissociation. Iron-containing colloids, present in natural freshwaters were not retained by the column. The method therefore discriminates trace metal species on the basis of both size and kinetics.

Effects of hydraulic retention time and sulfide toxicity on ethanol and acetate oxidation in sulfate-reducing metal-precipitating fluidized-bed reactor.

The effects of hydraulic retention time (HRT) and sulfide toxicity on ethanol and acetate utilization were studied in a sulfate-reducing fluidized-bed reactor (FBR) treating acidic metal-containing wastewater. The effects of HRT were determined with continuous flow FBR experiments. The percentage of ethanol oxidation was 99.9% even at a HRT of 6.5 h (loading of 2.6 g ethanol L(-1) d(-1)), while acetate accumulated in the FBR with HRTs below 12 h (loading of 1.4 g ethanol L(-1) d(-1)). Partial acetate utilization was accompanied by decreased concentrations of dissolved sulfide (DS) and alkalinity in the effluent, and eventually resulted in process failure when HRT was decreased to 6.1 h (loading of 2.7 g ethanol L(-1) d(-1)). Zinc and iron precipitation rates increased to over 600 mg L(-1) d(-1) and 300 mg L(-1) d(-1), respectively, with decreasing HRT. At HRT of 6.5 h, percent metal precipitation was over 99.9%, and effluent metal concentrations remained below 0.08 mg L(-1). Under these conditions, the alkalinity produced by substrate utilization increased the wastewater pH from 3 to 7.9-8.0. The percentage of electron flow from ethanol to sulfate reduction averaged 76 +/- 10% and was not affected by the HRT. The lowest HRT did not result in significant biomass washout from the FBR. The effect of sulfide toxicity on the sulfate-reducing culture was studied with batch kinetic experiments in the FBR. Noncompetitive inhibition model described well the sulfide inhibition of the sulfate-reducing culture. (DS) inhibition constants (K(i)) for ethanol and acetate oxidation were 248 mg S L(-1) and 356 mg S L(-1), respectively, and the corresponding K(i) values for H(2)S were 84 mg S L(-1) and 124 mg S L(-1). In conclusion, ethanol oxidation was more inhibited by sulfide toxicity than the acetate oxidation.

The effect of natrojarosite addition to mine tailings.

An increasingly common practice for metallurgical plants is to discard their wastes by combining them with mine tailings prior to disposing the blended material to a containment facility. This practice has occurred since 1985 at the Kidd Creek tailings impoundment where natrojarosite, a waste produced from the adjacent Zn refinery, is combined with mine tailings and is deposited in a single impoundment. To assess the environmental impact of the co-disposal, a laboratory column experiment was conducted. The column material was flotation tailings from the Kidd Creek site containing 3 wt % natrojarosite residue. Dilute sulfuric acid was passed through the column to simulate the acid generated in the unsaturated zone of the tailings impoundment. The results of this experiment were compared to the results of a previous experiment conducted on unamended flotation tailings. The results showed that the effluent from the column containing the natrojarosite-bearing mixture had a faster decrease in pH, earlier increases in the concentrations of dissolved metals such as Pb and Cd, and a greater persistence in effluent metal concentrations such as Pb, Zn and Ni. To prevent the observed enhanced release of dissolved metals from mine waste disposal areas, natrojarosite should not be co-disposed with tailings.

Development of a Sulfate‐Reducing Biological Process To Remove Heavy Metals from Acid Mine Drainage

The feasibility of using sulfate‐reducing bacteria to remove heavy metals from aqueous streams such as acid mine drainage was evaluated using three anaerobic reactors: an upflow anaerobic sludge blanket (UASB) reactor, a packed filter reactor, and a filter reactor that was partially packed with floating plastic pall rings. The packed filter reactors removed more than 99% of the influent metals. The performance of the partially packed reactor was superior based on effluent metal and sludge concentrations. Although the UASB reactor reduced the concentration of dissolved iron, the effluent concentration of total suspended solids remained greater than 18 g/L. This elevated solids concentration indicated that the UASB reactor was not operating as an effective clarifier, and, as a result, UASB reactor operation was discontinued after 4 months. The packed filter reactors were operated in parallel and received influent containing a combination of heavy metals. By withdrawing sludge from the bottom of these reactors, the accumulation of solids such as metal precipitates and biomass was controlled. The effluent concentrations of most metals were low, often less than drinking water standards, with the exception of manganese.

Compatibility of slurry wall backfill soils with acid mine drainage

The use of slurry walls to contain oxidized tailings and provide cutoff below tailings dams is generally a cost-effective way of preventing environmental degradation due to seepage of acid water from tailings areas. Long-term environmental protection dictates that the slurry wall materials be compatible with the acid water. Six percent Avonseal bentonite by weight was added separately to two natural soils to represent slurry wall backfill materials, which were then permeated with several pore volumes of acid mine drainage (AMD) in the laboratory. Results using both flexible wall and fixed wall permeameters were similar. The carbonate-rich backfill gave an average hydraulic conductivity ( K) of 1×10 −9 cm/s, buffered the AMD at circumneutral pH, and kept effluent metal concentrations to very low values (for example, less than 0.05 mg/l zinc). Although the carbonate-free backfill also maintained low K (average 3×10 −8 cm/s) during AMD permeation, it could not neutralize the AMD as effluent pH decreased to approximately 3.5, and metal concentrations reached those of the influent or permeant after approximately 17 pore volumes.