Metal-rich Wastewater Research Articles

Marine materials as innovative metal sorbents suitable for applications in wastewater treatments

The growing interest for urban mining strategies has pushed the research towards innovative strategies for metal recovery from electronic waste. Nevertheless, the treatment of the resulting metal-rich wastewater is still an issue. In this context, the present paper shows a method to use the capacity of Ulva algae to adsorb metals for the treatment of a synthetic solutions which simulates that resulting from a printed circuit board recycling process. The experiments considered a copper‑zinc‑iron system, showing a copper adsorption capacity of biomaterial up to 65 mg/g, at pH 5, favoured by iron presence. The process needs a short time (around 15 min) and it is suitable to be performed in a fixed-bed column able to treat more than 30 L of copper-contaminated wastewater, decreasing the energetic costs for mixing (compared to the typical slurry-reactor configuration) with an almost completed metal removal. The sustainability of the process is further improved by the selection of a macroalga which often accumulates on beaches (becoming a waste to remove) complying with the circular economy pillars.

Biosorptive removal of selected metal ions from simulated wastewater using highly metal-resistant bacteria

Abstract In the current scenario of the need for cost-effective remediation, our study aimed to assess the remedial potential of bacteria obtained from metal-rich wastewater. To simulate the conditions, we prepared wastewater containing five toxic metals (Cu, Cr, Ni, Fe, and Pb). Two types of metal-resistant bacteria were isolated from a prominent wastewater drain in Lahore, Pakistan. These isolated bacteria were thoroughly characterized, both phenotypically and genotypically. Subsequently, the isolated bacteria were exposed to the wastewater solution containing each of the aforementioned metals at a concentration of 250 ppm. The exposed isolates were then incubated for a duration of 15 days. After 5 days, we measured the uptake of metals by the bacterial isolates. Following the 15-day incubation period, we observed that the bacterial isolates demonstrated the maximum efficiency in removing metals, with approximately 47.5% of Fe, 77% of Ni, 75.75% of Cu, 64% of Cr, and 82.5% of Pb being removed. These findings have significant implications for the development of environmentally friendly and cost-effective strategies for metal ion remediation.

A Mathematical Study of Metal Biosorption on Algal–Bacterial Granular Biofilms

A multiscale mathematical model describing the metals biosorption on algal–bacterial photogranules within a sequencing batch reactor (SBR) is presented. The model is based on systems of partial differential equations (PDEs) derived from mass conservation principles on a spherical free boundary domain with radial symmetry. Hyperbolic PDEs account for the dynamics of sessile species and their free sorption sites, where metals are adsorbed. Parabolic PDEs govern the diffusion, conversion and adsorption of nutrients and metals. The dual effect of metals on photogranule ecology is also modelled: metal stimulates the production of EPS by sessile species and negatively affects the metabolic activities of microbial species. Accordingly, a stimulation term for EPS production and an inhibition term for metal are included in all microbial kinetics. The formation and evolution of the granule domain are governed by an ordinary differential equation with a vanishing initial value, accounting for microbial growth, attachment and detachment phenomena. The model is completed with systems of impulsive differential equations describing the evolution of dissolved substrates, metals, and planktonic and detached biomasses within the granular-based SBR. The model is integrated numerically to examine the role of the microbial species and EPS in the adsorption process, and the effect of metal concentration and adsorption properties of biofilm components on the metal removal. Numerical results show an accurate description of the photogranules evolution and ecology and confirm the applicability of algal–bacterial photogranule technology for metal-rich wastewater treatment.

Practice of wastewater irrigation and its impacts on human health and environment: a state of the art

The practice of wastewater irrigation lessens the pressure on the aquatic environment by minimizing the use of freshwater resources. However, this may lead to significant damage to the human health and environments. Recycled wastewater possesses a substantial amount of nutrients that act as fertilizers for crops and facilitate the metabolic action of microorganisms. The major advantages of wastewater irrigation are increased agricultural production, nutrient recycling, reduced stress on freshwater, economical support and provision of livelihoods for farmers. However, several harmful impacts of wastewater irrigation are also prominent due to inappropriate wastewater management and irrigation practices. These include severe hazards to farmer’s health, contamination of agricultural land and crops with toxic metals, chemical compounds, salts and microbial pathogens. In addition, long-term irrigation using wastewater can significantly affect the groundwater through leakage of salty and toxic metal-rich wastewater making it unfit for human consumption. Wastewater irrigation may also alter the physicochemical properties and microbiota of soil, which in turn can disturb land fertility and crop productivity. Several factors need to be considered while using treated or partially treated wastewater for irrigation such as diversity and type of pollutants, available nutrients, pathogenic microorganisms and soil salinity. In this review paper, we assess the impact of wastewater irrigation on humans as well as on the environment based on available case studies globally, outline current use of wastewater for irrigation of agricultural crops such as cereals, vegetables, fodder crops, including agroforestry and discuss suitable management practices of wastewater reuse for irrigation.

Bioproduct Potential of Outdoor Cultures of Tolypothrix sp.: Effect of Carbon Dioxide and Metal-Rich Wastewater.

Rising CO2 levels, associated climatic instability, freshwater scarcity and diminishing arable land exacerbate the challenge to maintain food security for the fast growing human population. Although coal-fired power plants generate large amounts of CO2 emissions and wastewater, containing environmentally unsafe concentrations of metals, they ensure energy security. Nitrogen (N2)-fixation by cyanobacteria eliminate nitrogen fertilization costs, making them promising candidates for remediation of waste CO2 and metals from macronutrient-poor ash dam water and the biomass is suitable for phycocyanin and biofertilizer product development. Here, the effects of CO2 and metal mixtures on growth, bioproduct and metal removal potential were investigated for the self-flocculating, N2-fixing freshwater cyanobacterium Tolypothrix sp. Tolypothrix sp. was grown outdoors in simulated ash dam wastewater (SADW) in 500 L vertical bag suspension cultures and as biofilms in modified algal-turf scrubbers. The cultivation systems were aerated with air containing either 15% CO2 (v/v) or not. CO2-fertilization resulted in ∼1.25- and 1.45-fold higher biomass productivities and ∼40 and 27% increased phycocyanin and phycoerythrin contents for biofilm and suspension cultures, respectively. CO2 had no effect on removal of Al, As, Cu, Fe, Sr, and Zn, while Mo removal increased by 37% in both systems. In contrast, Ni removal was reduced in biofilm systems, while Se removal increased by 73% in suspension cultures. Based on biomass yields and biochemical data obtained, net present value (NPV) and sensitivities analyses used four bioproduct scenarios: (1) phycocyanin sole product, (2) biofertilizer sole product, (3) 50% phycocyanin and 50% biofertilizer, and (4) 100% phycocyanin and 100% biofertilizer (residual biomass) for power station co-located and not co-located 10 ha facilities over a 20-year period. Economic feasibility for the production of food-grade phycocyanin either as a sole product or with co-production of biofertilizer was demonstrated for CO2-enriched vertical and raceway suspension cultures raised without nitrogen-fertilization and co-location with power stations significantly increased profit margins.

Effect of CO2 and metal-rich waste water on bioproduct potential of the diazotrophic freshwater cyanobacterium, Tolypothrix sp.

Continued economic growth is reliant on stable, affordable energy, requiring at present fossil fuel-derived energy production. Coal-fired power stations produce metal-rich but macro-nutrient-poor waste waters and emit flue gas, containing ∼10% CO2. Algae and cyanobacteria remediate metals and CO2, but use of N2-fixing (diazotrophic) cyanobacteria can reduce nitrogen-fertilization costs. The resulting biomass represents a promising source for biofuel and bio-product development. This study investigated the effect of CO2- and trace metals on growth performance, biochemical profiles and metal content of the freshwater diazotrophic cyanobacterium Tolypothrix sp. to assess bioproduct potential. Aerated 2 L batch cultures were grown in simulated ash-dam water (SADW) and BG11 without nitrogen (BG11(-N) controls). Supplied air was supplemented with either 15% CO2 or not (non-CO2 controls). CO2 supplementation resulted in 2.4 and 3.3-fold higher biomass productivities and 1.3 and 1.2-fold higher phycocyanin and phycoerythrin contents, whilst metals (media) had no effect. Al, Cu, Ni and V were more efficiently removed (50–90%) with CO2-addition, while As, Mo, Se and Sr removal was higher (30–87%) for non-CO2 controls. No significant effect on Zn and Fe removal was evident. Calculated biomass metal concentrations, at quantities required to meet N-requirements of wheat, suggests no metal toxicity when applied as a mineral-nitrogen biofertilizer. With a carbohydrate content of 50%, the biomass is also suitable for bioethanol production. In summary, Tolypothrix sp. raised in ash dam waste water supplemented with flue gas CO2 could yield high-value phycobiliproteins, bioethanol or biogas, and mineral-rich nitrogen fertilizer which would offset remediation costs and improve agricultural productivity.

Heavy metal rich stone-processing wastewater inhibits the growth and development of plants

Large amounts of wastewater are generated from stone processing, which are toxic and cause serious environmental and health risks. To quantify the content of stone processing wastewater and estimate its effects on plant growth, we collected water samples from sewage outfall of four stone processing factories and nearby water bodies. The concentration of potential toxic metals were much higher in the wastewater than background controls. Wastewater inhibited plant primary root elongation, lateral root formation, and growth of aerial part. Seedlings treated with the effluents were unhealthy with deep purple leaves and usually died before flowering. Chlorophyll a/b contents and chloroplast number were reduced in those abnormal mesophyll cells. Transcriptional levels were decreased for chloroplast formation genes, but increased for those participated in chloroplast degradation and catabolism. Six out of nine tested senescence-associated genes were up-regulated. Furthermore, our results show that endogenous toxic metal levels indeed increased after wastewater treatment. Altogether, these results indicated that the potential toxic metals rich wastewater had significant inhibition on plant growth and led to senescence-associated program cell death, which could be helpful for the government and enterprises to understand the environmental risks and formulate reasonable wastewater emission standards for the stone processing industry.

Implication of highly metal-resistant microalgal-bacterial co-cultures for the treatment of simulated metal-loaded wastewaters.

Microalgal-bacterial co-cultures were employed for the treatment of artificially prepared metal-rich wastewaters in this study. For the purpose, highly metal-resistant microalgal and bacterial species were isolated from a leading wastewater channel flowing through Lahore, Pakistan, and characterized at the molecular level. The microbial identities were proved after BLAST analysis. The microalgal (Chlorella vulgaris-BH1) and bacterial (Exiguobacterium profundum-BH2) species were then co-cultured in five different proportions. Five different proportions of potentially mutualistic microbial co-cultures (comprising of microalgal to bacterial cells in ratios of 1:3, 2:3, 3:3, 3:1, and 3:2) prepared thus were employed to remediate artificially prepared metal-loaded wastewaters. Three randomly selected toxic metals (Cu, Cr, and Ni) were used in this study to prepare metal-rich wastewaters. The microalgal-bacterial co-cultures were then exposed independently to the wastewaters containing 100ppm of each of the above mentioned metals. The inoculated wastewaters were incubated maximally for a period of 15days. The metal uptake was noted periodically after every 5days. The results of the present study depicted that maximally about 78.7, 56.4, and 80% of Cu, Cr, and Ni were removed, respectively after an incubation period of 15days. The microbial co-culture consisting of microalgal to bacterial cells in a ratio of 3:1 showed the highest remedial potential. The findings of the present study will be helpful in developing effective microalgal-bacterial consortia for economical, efficient, and environment-friendly rehabilitation of the polluted sites.

Acid Rock Drainage Treatment Using Membrane Distillation: Impacts of Chemical-Free Pretreatment on Scale Formation, Pore Wetting, and Product Water Quality.

Acid rock drainage (ARD) is a metal-rich wastewater that forms upon oxidation of sulfidic minerals. Although ARD impacts >12,000 miles of rivers in the U.S. and has an estimated cleanup cost of $32-$72 billion, the low pH and high metal concentrations in ARD make rapid, high volume treatment without chemical addition difficult. This research focuses on a novel method of ARD treatment, membrane distillation (MD). In MD, heated ARD is separated from a cooled distillate by a hydrophobic, water-excluding membrane. Because water only passes through the membrane in the vapor phase, nonvolatile sulfate and heavy metals are retained in the concentrate stream. A preliminary in silico analysis using an electrolyte thermodynamic model indicated that MD of 10 different mine wastes yields product water containing no contaminants at concentrations >0.2 ppm. MD tests of synthetic ARD used a ∼34 °C temperature difference, operated at 80% recovery, and produced an initial flux of 38.4 ± 1.1 L·m-2·h-1. This flux decreased slightly after scaling by iron oxyhydroxide; however, membranes maintained >99% dissolved solids rejection. Both flux decline and membrane scale formation decreased after a chemical-free, thermal precipitation pretreatment. These results indicate that MD can purify contaminated, acidic wastewater using low-grade heat sources, such as geothermal energy, without chemical addition.

Coordination of arsenic and nickel to aluminum and magnesium phases in uranium mill raffinate precipitates

The Key Lake U mill uses a stepwise neutralization process (pH 4.0, 6.5, 9.5, and 10.5) to treat raffinate (acidic, metal-rich wastewater) prior to safely releasing effluent to the environment. This process generates a complex mixture of precipitates that are deposited to a tailings facility. In this study, the coordination environments of As and Ni with respect to Al-Mg phases precipitated in the presence and absence of Fe in mill-generated and synthetic precipitates were defined using bulk X-ray absorption spectroscopy complemented with bulk X-ray diffraction. In low pH (pH 4.0–4.6) samples, As(V) precipitates as ferric arsenate and adsorbs to AlOHSO4 (an amorphous hydrobasaluminite-like phase) and ferrihydrite via bidentate-binuclear complexes. Nickel(II) predominantly adsorbs to amorphous Al(OH)3 via edge-sharing bidentate-mononuclear complexes. In high pH (pH 9.5–9.9) samples, As(V) adsorbs to amorphous Al(OH)3, ferrihydrite, and MgAlFe-hydrotalcite (bidentate complex). Nickel(II) octahedra adsorb to amorphous Al(OH)3 and likely form a Ni-Al layered double hydroxide (LDH) surface precipitate on MgAlFe-hydrotalcite via Al dissolution-precipitation. In the final solids (blended low and high pH precipitates) discharged at ∼ pH 10.5, As(V) adsorbs to amorphous Al(OH)3, ferrihydrite, and MgAlFe-hydrotalcite. Nickel(II) adsorbs to amorphous Al(OH)3 and forms Ni-Al LDH surface precipitates on hydrotalcite. This study demonstrates that neutralization of chemically complex wastewater precipitates multiple phases capable of controlling dissolved As and Ni concentrations. Knowledge gained from this study will aid investigations in understanding the long-term fate of these potential contaminants in the environment and can be applied to other industries and environmental systems with similar conditions.

The effects of temperature and pH on the kinetics of an acidophilic sulfidogenic bioreactor and indigenous microbial communities

Biosulfidogenesis (the microbial generation of H2S by reduction of more oxidized sulfur species) is a very useful technology for remediating acidic, metal-rich waste-waters, such as acid mine drainage. Many transition metals form highly insoluble sulfide phases when contacted with H2S, and bacterial reduction of sulfate to sulfide is, in acidic liquors, a proton-consuming reaction. Commercial-scale sulfidogenic bioreactors use neutrophilic species of sulfate- (or sulfur-) reducing bacteria that need to be shielded from direct contact with acidic waste waters, which is not the case with acidophilic and acid-tolerant species (aSRB). Here we report the kinetics and microbial dynamics of a low pH, laboratory-scale sulfidogenic bioreactor, operated as a continuous flow system for 462days, at pH values between 4.0 and 5.0, and temperatures between 30 and 45°C. While changing an operating parameter caused minor perturbations in the performance of the bioreactor, these were transient, and the system performed consistently well throughout the entire test period, with pH4.0 and 35°C being marginally the optimum operating conditions. Two species of aSRB mediated sulfide formation: Desulfosporosinus acididurans, preferentially at higher pH and lower temperatures, and Peptococcaceae CEB3, at lower pH and higher temperatures. The relative abundances of these two bacteria changed in response to an operational (pH, temperature) change. The results highlighted the robustness and adaptability of the low pH microbial consortium used to generate sulfide, and to precipitate transition metals both in situ and ex situ.

Improvement of biological sulfate reduction by supplementation of nitrogen rich extract prepared from organic marine wastes

Organic marine waste was treated by both chemical and biological method to supplement it as nitrogen source in the growth media of sulfate reducing bacteria (SRB), and the resulting extracts were termed as marine waste extract (MWE) and Lactobacillus fermented MWE, respectively. Because of higher nitrogen content and other micro-nutrients, MWE could support higher sulfate reduction (83%) as compared to Lactobacillus fermented MWE (71%). The study further demonstrated that when compared to each optimized single process parameters (pH, MWE and sulfate concentration), optimization of multiple parameters based on Box-Behnken design and response surface methodology improved SRB growth and sulfate reduction by 5–6% and 10–11%, respectively. The experimentally optimized process parameters (1500 mg/L sulfate, pH 7.5 and 20% v/v MWE) resulted in 98% sulfate reduction which was close to the values derived from the theoretical model. This study highlights the use of MWE to improve the treatment of sulfate and metal rich wastewater.

Poster #S132 COPY NUMBER VARIANT ANALYSIS ON 401 CASES OF SCHIZOPHRENIA: A SEARCH FOR CAUSAL GENES FINDS DISRUPTION IN THE NEUROGENESIS REGULATOR JAGGED 2

Biosulfidogenesis (the microbial generation of H2S by reduction of more oxidized sulfur species) is a very useful technology for remediating acidic, metal-rich waste-waters, such as acid mine drainage. Many transition metals form highly insoluble sulfide phases when contacted with H2S, and bacterial reduction of sulfate to sulfide is, in acidic liquors, a proton-consuming reaction. Commercial-scale sulfidogenic bioreactors use neutrophilic species of sulfate- (or sulfur-) reducing bacteria that need to be shielded from direct contact with acidic waste waters, which is not the case with acidophilic and acid-tolerant species (aSRB). Here we report the kinetics and microbial dynamics of a low pH, laboratory-scale sulfidogenic bioreactor, operated as a continuous flow system for 462 days, at pH values between 4.0 and 5.0, and temperatures between 30 and 45 °C. While changing an operating parameter caused minor perturbations in the performance of the bioreactor, these were transient, and the system performed consistently well throughout the entire test period, with pH 4.0 and 35 °C being marginally the optimum operating conditions. Two species of aSRB mediated sulfide formation: Desulfosporosinus acididurans, preferentially at higher pH and lower temperatures, and Peptococcaceae CEB3, at lower pH and higher temperatures. The relative abundances of these two bacteria changed in response to an operational (pH, temperature) change. The results highlighted the robustness and adaptability of the low pH microbial consortium used to generate sulfide, and to precipitate transition metals both in situ and ex situ.

A modular continuous flow reactor system for the selective bio-oxidation of iron and precipitation of schwertmannite from mine-impacted waters

A novel modular bioremediation system which facilitates the selective removal of soluble iron from extremely acidic (pH ∼2) metal-rich wastewaters by ferrous iron oxidation and selective precipitation of the ferric iron produced is described. In the first of the three modules, rapid ferrous iron oxidation was mediated by the recently-characterized iron-oxidizing autotrophic acidophile, “ Ferrovum myxofaciens”, which grew as long “streamers” within the reactor. Over 90% of the iron present in influent test liquors containing 280 mg/L iron was oxidized at a dilution rate of 0.41 h −1, in a proton-consuming reaction. The ferric iron-rich solutions produced were pumped into a second reactor where controlled addition of sodium hydroxide caused the water pH to increase to 3.5 and ferric iron to precipitate as the mineral schwertmannite. Addition of a flocculating agent promoted rapid aggregation and settling of the fine-grain schwertmannite particles. A third passive module (a packed-bed bioreactor, also inoculated with “ Fv. myxofaciens”) acted as a polishing reactor, lowering soluble iron concentrations in the processed water to <1 mg/L. The system was highly effective in selectively removing iron from a synthetic acidic (pH 2.1) mine water that contained soluble aluminum, copper, manganese and zinc in addition to iron. Schwertmannite was again produced, with little or no co-precipitation of other metals.

Fixed-bed column study for the removal of cadmium (II) and nickel (II) ions from aqueous solutions using peat and mollusk shells

The study was conducted to examine the effectiveness of 4.0–4.75 mm crushed shells and Sphagnum peat moss as low-cost natural adsorbent filter materials for the removal of cadmium and nickel ions from binary aqueous solutions. The effects of column depth and flow rate on effluent metal breakthrough, metal removal and pH were investigated as a function of throughput volume (TPV). Metal removal efficiencies and adsorption capacities for each of the columns were estimated to identify the better filter material and operational conditions for the treatment of cadmium and nickel. During the column testing, a flow rate of 1.5 mL/min (surface loading of 27.5 cm 3/cm 2 day) and bed depth of 15 cm were found to represent the better operational conditions, where 47.9% and 42.7% cadmium and nickel cumulative removals were obtained under these operational conditions, respectively. The results will be valuable in the development of a mixed-media adsorption system for the treatment of metal-rich wastewaters such as municipal landfill leachate.

Biodiversity and interactions of acidophiles: Key to understanding and optimizing microbial processing of ores and concentrates

Mining companies have become increasingly aware of the potential of microbiological approaches for recovering base and precious metals from low-grade ores, and for remediating acidic, metal-rich wastewaters that drain from both operating and abandoned mine sites. Biological systems offer a number of environmental and (sometimes) economical advantages over conventional approaches, such as pyrometallurgy, though their application is not appropriate in every situation. Mineral processing using micro-organisms has been exploited for extracting gold, copper, uranium and cobalt, and current developments are targeting other base metals. Recently, there has been a great increase in our knowledge and understanding of both the diversity of the microbiology of biomining environments, and of how the microorganisms interact with each other. The results from laboratory experiments which have simulated both stirred tank and heap bioreactor systems have shown that microbial consortia are more robust than pure cultures of mineral-oxidizing acidophiles, and also tend to be more effective at bioleaching and bio-oxidizing ores and concentrates. The paper presented a concise review of the nature and interactions of microbial consortia that are involved in the oxidation of sulfide minerals, and how these might be adapted to meet future challenges in biomining operations.

Studies on an economically viable remediation of chromium rich waters and wastewaters by PTPS fly ash

Abstract Application of fly ash, a waste material of thermal power plants for the removal of chromium from aqueous solutions and wastewaters has been investigated. The adsorption follows a first order rate kinetics and the value of Kad, rate constant for removal was found to be 3.0 × 10−2 s−1 at 298 K, 100 rpm, 2.5 pH and at other optimum conditions. Intraparticle diffusion was found to control the removal of Cr(VI) and the value of coefficient of intraparticle diffusion was found to be 2.25 × 10−11 cm2 s−1 at 298 K. The value of the coefficient of mass transfer, βl, 2.15 × 10−2 cm s−1 at 298 K, suggested the transfer of Cr(VI) onto the adsorbent surface to be rapid enough. The process of removal is highly dependent on pH of the solutions with maximum removal (89.12%) at pH 2.5. Values of Langmuir's constants were also calculated. Various thermodynamic parameters namely free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) were calculated and found to be −0.68, 5.26 and 1.77 K cal mol−1at 298 K. Comparison of the adsorbent used with other non-conventional adsorbents shows that fly ash is a good adsorbent and can be recommended for treatment of metal rich wastewater in general and that of Cr(VI) in particular.

Occurrence of methanogenesis during start-up of a full-scale synthesis gas-fed reactor treating sulfate and metal-rich wastewater

The start-up of a full-scale synthesis gas-fed gas-lift reactor treating metal and sulfate-rich wastewater was investigated. Sludge from a pilot-scale reactor was used to seed the full-scale reactor. The main difference in design between the pilot- and full-scale reactor was that metal precipitation and sulfate reduction occurred in the same reactor. After 7 weeks the full-scale reactor achieved the sulfate conversion design rate of 15 kg/m 3 day. Zinc sulfide precipitation inside the reactor did not interfere with obtaining a high rate of sulfate reduction. 16S rRNA gene analysis demonstrated that the bacterial communities in both reactors were dominated by the sulfate-reducing genus Desulfomicrobium. Archaeal communities of both reactors were dominated by the methanogenic genus Methanobacterium. Most Probable Number (MPN) counts confirmed that heterotrophic Sulfate-Reducing Bacteria (SRB) were dominant (10 11–10 12 cells/g VSS) compared to homoacetogens (10 5–10 6 cells/g VSS) and methanogens (10 8–10 9 cells/g VSS). Methanogenesis was not suppressed during start-up of the full scale-reactor, despite the predominance of SRB, which have a lower hydrogen threshold. Due to the short sludge retention time (4–7 days) competition for hydrogen is determined by Monod kinetics, not hydrogen thresholds. As the kinetic parameters for SRB and methanogens are similar, methanogenesis may persist which results in a loss of hydrogen.

Sediment-Based Study of the Effects of Decreasing Mine Water Pollutionon a Heavily Modified, Nutrient Enriched Lake

Ni and Cu mining and ore processing in Hitura, Western Finland, have resulted in emissions of metal-rich wastewaters into the nearby Kalajoki River since 1970. The wastewaters are discharged into the river 3 km upstream from the eutrophic Lake Pidisjarvi, which is a widening of the river by the town of Nivala. The water level of the lake was elevated by 1.5 m and the extensive macrophyte stands were cut in 1979, profoundly changing the environmental conditions. The effects of the decreasing metal emissions and nutrient concentrations since 1979 on the now open 3.9 km2 lake were studied with paleolimnological techniques. A 2-m sediment core was taken from the lake in February 2004 and analysed for sediment chemistry and diatom assemblages. At the coring site, 13 cm of sediment had been deposited since 1979, on top of a bed of undecomposed macrophyte remains. When the sediment chemistry was compared with records of decreasing metal loading since 1979, no correlation was found because post-depositional mobility and changes in sediment characteristics affect the sediment metal profiles. Thus, the reduced emissions from the mine and the lower lake water phosphorus levels have not caused a corresponding decrease in sediment metal and P concentrations. However, both of these environmental variables accounted for a statistically significant percentage of variation in the sedimentary diatom assemblages in a redundancy analysis constrained to a single variable. This relationship persisted for Ni loading even in a partial analysis, while the importance of nutrients was confirmed by the good correlation between diatom-inferred and measured P concentrations. The results suggest that reductions in metal and nutrient loading have had an effect on the algal assemblages even though the sediment concentrations of Ni, Cu or P have not decreased.

Removal of heavy metals by cement kiln dust.

Heavy metals and other toxic pollutants are considered extremely pernicious because they are toxic, nondegradable, and environmentally persistent (Weng C.H., 1994). Electroplating, metal finishing and or leather tanning are producing wastewater streams contaminated with heavy metals such as chromium, zinc, cadmium, lead, nickel, and mercury. In Egypt, the dust emitted was estimated to be about two million tons (Authorities of Cement Companies) which are accumulating annually at domestic cement plants. This finely divided dust emitted from cement kilns must be disposed at waste disposal sites. The cost for storage, transportation, and disposal are high. To minimize the undesirable environmental impacts and to conserve materials, many researches have been conducted for recycling or reuse the cement kiln dust (CKD) as raw materials, fertilizer, constructing material and improving the sand soil properties (Thorbjorn, 1969). Recently, the use of CKD as adsorbent in wastewater treatment has a great attention as no cost material and clay structure (El-Awady, 1996). For many years, most metal-rich wastewaters are treated by conventional alkaline neutralization precipitation (ANP) process, as well as coagulation, pH adjustment, reduction, polymer coagulant, electrokinetic process (Kaichum, 1994; Masaki, 1994; Mcintosph et al, 1995, Weng et al, 1994; Yuasa et al, 1994; Zhang, 1994). The aim of this study is to evaluate the capability of CKD, as heavy metal scavenger, for removing some heavy metals such as chromium, iron, cobalt, and copper from aqueous solutions. Moreover, the treatment of tannery industrial wastewater was taken as a case study.