Passive treatment of acid mine drainage with high metal concentrations using dispersed alkaline substrate

Passive treatment systems based on the dissolution of coarse calcite grains are widely used to remediate acid mine drainage (AMD). Unfortunately, they tolerate only low metal concentrations or acidity loads, because they are prone to passivation (loss of reactivity due to coating) and/or clogging (loss of permeability) by precipitates. To overcome these problems, a dispersed alkaline substrate (DAS) composed of a fine-grained alkaline reagent (calcite sand) mixed with a coarse inert matrix (wood chips) was developed. The small grains provide a large reactive surface and dissolve almost completely before the growing layer of precipitates passivates the substrate, whereas the dispersion of nuclei for precipitation on the inert surfaces retards clogging. Chemical and hydraulic performance of DAS was investigated in two laboratory columns fed at different flow rates with natural AMD of pH 2.3 to 3.5 and inflow net acidity 1350 to 2300 mg/L as CaCO(3). The DAS columns removed 900 to 1600 mg/L net acidity, 3 to 4.5 times more than conventional passive treatment systems. Regardless of the flow rate employed, Al, Fe(III), Cu, and Pb were virtually eliminated. Minor Zn, Ni, and Cd were removed at low flow rates. High acidity removal is possible because these metals accumulate intentionally in DAS, and their precipitation promotes further calcite dissolution. During 15 mo, DAS operated without clogging at 120 g acidity/m(2).d, four times the loading rate recommended for conventional passive systems; DAS may therefore be capable of treating AMD at sites where influent chemistry precludes the use of other passive systems.     

分层锰砂滤池去除地下水中铁离子的工程应用

通过工程实例讨论了分层锰砂滤池在地下水去除铁离子中的工艺过程和处理效果。结果表明:滤池对铁离子有较好的去除效果,进水中铁离子浓度由1.57 mg/L降到出水的0.06mg/L,去除率达到96%以上。与传统的锰砂滤池相比,由于采用了适当的预处理以及滤料的分层设计,系统的堵塞情况大为改善,反冲洗频率大幅降低,运行管理更加方便。     

EFFECT OF INFLUENT PHOSPHORUS REDUCTIONS ON GREAT LAKES SEWAGE TREATMENT COSTS1

ABSTRACT: Controlling phosphorus sources, such as laundry detergents, for eutrophication control has been the aim of water resources management in many areas. However, the advisability of limiting phosphorus in raw wastewater continues to be debated. One aspect that has received little attention is the cost savings at sewage treatment plants practing phosphorus removal. It is estimated, based on available data and observations where detergent phosphorus has been reduced, that cost savings could range from about $0.20 to $1.70 per capita per year for an influent reduction of about 1.5 mg/L of phosphorus. These savings result mostly from a decrease in the amount of chemicals needed to remove phosphorus at the plant as well as a decrease in sludge production. For the U.S. Great Lakes basin, total annual savings amounting to several million dollars are projected given a basin-wide ban. Although estimates of cost savings are presented for the Great Lakes basin, the results are applicable to other areas where phosphorus controls are being considered.     

Anaerobic whey treatment by a stirred sequencing batch reactor (ASBR): effects of organic loading and supplemented alkalinity

An assessment was made of cheese whey treatment in a mechanically stirred anaerobic sequencing batch reactor (ASBR) containing granular biomass. The effect of increasing organic load and decreasing influent alkalinity supplementation (as sodium bicarbonate) was analyzed. The reactor operated on 8-h cycles with influent COD concentrations of 500, 1000, 2000 and 4000 mg/L, corresponding to volumetric organic loads of 0.6 to 4.8 mgCOD/L.d. Organic COD removal efficiencies were always above 90% for filtered samples. These results were obtained with an optimized alkalinity supplementation of 50% (ratio between mass of NaHCO3 added and mass of influent mgNaHCO3/mgCOD) in the assays with 500 and 1000 mgCOD/L and of 25% in the assays with 2000 and 4000 mgCOD/L. Initial alkalinity supplementation was equal to the mass of influent COD (100%). The system showed formation of viscous polymer-like substances. These were probably of microbiological origin occurring mainly at influent CODs of 2000 and 4000 mg/L and caused some biomass flotation. This could, however be controlled to enable efficient and stable reactor operation.     

pH,dissolved oxygen,and adsorption effects on metal removal in anaerobic bioreactors

Anaerobic bioreactors were used to test the effect of the pH of influent on the removal efficiency of heavy metals from acid-rock drainage. Two studies used a near-neutral-pH, metal-laden influent to examine the heavy metal removal efficiency and hydraulic residence time requirements of the reactors. Another study used the more typical low-pH mine drainage influent. Experiments also were done to (i) test the effects of oxygen content of feed water on metal removal and (ii) the adsorptive capacity of the reactor organic substrate. Analysis of the results indicates that bacterial sulfate reduction may be a zero-order kinetic reaction relative to sulfate concentrations used in the experiments, and may be the factor that controls the metal mass removal efficiency in the anaerobic treatment systems. The sorptive capacities of the organic substrate used in the experiments had not been exhausted during the experiments as indicated by the loading rates of removal of metals exceeding the mass production rates of sulfide. Microbial sulfate reduction was less in the reactors receiving low-pH influent during experiments with short residence times. Sulfate-reducing bacteria may have been inhibited by high flows of low-pH water. Dissolved oxygen content of the feed waters had little effect on sulfate reduction and metal removal capacity.     

Microcosm wetlands for wastewater treatment with different hydraulic loading rates and macrophytes

Constructed wetlands (CW) usually require large land areas for treating wastewater. This study evaluated the feasibility of applying CW with less land requirement by operating a group of microcosm wetlands at a hydraulic retention time (HRT) of less than 4 d in southern Taiwan. An artificial wastewater, simulating municipal wastewater containing 200 mg L(-1) of chemical oxygen demand (COD), 20 mg L(-1) of NH4+-N (AN), and 20 mg L(-1) of PO4(3-)-P (OP), was the inflow source. Three emergent plants [reed, Phragmites australis (Cav.) Trin. ex Steud.; water primrose, Ludwigia octovalvis (Jacq.) P.H. Raven; and dayflower, Commelina communis L.] and two floating plants [water spinach, Ipomoea aquatica Forssk.; and water lettuce, Pistia stratiotes L.] plants were tested. The planted systems showed more nutrient removal than unplanted systems; however, the type of macrophytes in CW did not make a major difference in treatment. At the HRTs of 2 to 4 d, the planted system maintained greater than 72,80, and 46% removal for COD, AN, and OP, respectively. For AN and OP removal, the highest efficiencies occurred at the HRT of 3 d, whereas maximum removal rates for AN and OP occurred at the HRT of 2 d. Both removal rates and efficiencies were reduced drastically at the HRT of 1 d. Removals of COD, OP, and AN followed first-order reactions within the HRTs of 1 to 4 d. The efficient removals of these constituents obtained with HRT between 2 and 4 d indicated the possibility of using a CW system for wastewater treatment with less land requirement.     

MANGANESE OXIDATION RELATED TO THE RELEASES FROM RESERVOIRS1

ABSTRACT: Stratified reservoir waters frequently contain objectionable quantities of dissolved manganese. The oxidation and removal of dissolved manganese during transport below Normandy Dam, Tennessee, was shown to be much more rapid than expected from chemical oxidation. Oxidation took place in only a day of travel time rather than months or years. Laboratory studies showed that removal was associated with a slime found on rock surfaces below the dam and led to the development of column technology as a possible method of treating natural waters containing manganese. Hydraulic loadings on the columns in the range of 390–780 m³/hr.ha accomplished a 90 percent removal rate of soluble manganese over an influent concentration range of 2 to 15 mg/l.     

Nitrogen removal in laboratory model leachfields with organic-rich layers

Septic system leachfields can release dissolved nitrogen in the form of nitrate into ground water, presenting a significant source of pollution. Low cost, passive modifications, which increase N removal in traditional leachfields, could substantially reduce the overall impact on ground water resources. Bench-scale laboratory models were constructed to evaluate the effect of placing an organic layer below the leachfield on total N removal. The organic layer provides a carbon source for denitrification. Column units representing septic leachfields were constructed with sawdust-native soil organic layers placed 0.45 m below the influent line and with thicknesses of 0.0, 0.3, 0.6, and 0.9 m. Using a synthetic septic tank effluent, NO(3)-N concentrations at 3.8 m below the influent line were consistently below 1 mg L(-1) during 10 months of operation compared with a NO(3)-N concentration of nearly 12 mg L(-1) in the control column. The average total N removal increased from 31% without the organic layer to 67% with the organic layer. Total N removal appeared limited by the extent of organic N oxidation and nitrification in the 0.45-m aerobic zone. Design modifications targeted at improving nitrification above the organic layer may further increase total N removal. Increased organic layer thicknesses from 0.3 m to 0.9 m did not significantly improve average total N removal, but caused a shift in residual nitrogen from organic N to ammonia N. Results indicate that addition of a layer of carbon source material at least 0.3 m thick below a standard leachfield substantially improves total N removal.     

城市污水Al盐化学除磷的试验研究

针对新疆地区污水厂总磷去除效率有限,出水总磷存在超标排放风险的问题。试验中采用自配不同总磷含量的生活污水,通过小试试验,投加AlCl3进行试验室模拟化学除磷试验。研究结果表明:进水总磷浓度为2～4mg/L时,投加AlCl3/TP质量比为8.6;进水总磷浓度为6mg/L时,投加AlCl3/TP质量比上升到13.1,出水总磷浓度均<0.5mg/L,AlCl3投加不会改变污水的pH值,化学沉淀最佳时间为30min。建议设计除磷沉淀池的停留时间为25min～30min。     

Field application of farmstead runoff to vegetated filter strips: surface and subsurface water quality assessment

Farmstead runoff poses significant environmental impacts to ground and surface waters. Three vegetated filter strips were assessed for the treatment of dairy farmstead runoff at the soil surface and subsurface at 0.3- or 0. 46-m and 0. 76-m depths for numerous storm events. A medium-sized Michigan dairy was retrofitted with two filter strips on sandy loam soil and a third filter strip was implemented on a small Michigan dairy with sandy soil to collect and treat runoff from feed storage, manure storage, and other impervious farmstead areas. All filter strips were able to eliminate surface runoff via infiltration for all storm events over the duration of the study, eliminating pollutant contributions to surface water. Subsurface effluent was monitored to determine the contributing groundwater concentrations of numerous pollutants including chemical oxygen demand (COD), metals, and nitrates. Subsurface samples have an average reduction of COD concentrations of 20, 11, and 85% for the medium dairy Filter Strip 1 (FS1), medium dairy Filter Strip 2 (FS2), and the small Michigan dairy respectively, resulting in average subsurface concentrations of 355, 3960, and 718 mg L COD. Similar reductions were noted for ammonia and total Kjeldahl nitrogen (TKN) in the subsurface effluent. The small Michigan dairy was able to reduce the pollutant leachate concentrations of COD, TKN, and ammonia over a range of influent concentrations. Increased influent concentrations in the medium Michigan dairy filter strips resulted in an increase in COD, TKN, and ammonia concentrations in the leachate. Manganese was leached from the native soils at all filter strips as evidenced by the increase in manganese concentrations in the leachate. Nitrate concentrations were above standard drinking water limits (10 mg L), averaging subsurface concentrations of 11, 45, and 25 mg L NO-N for FS1, FS2, and the small Michigan dairy, respectively.     

Decolorization of triphenylmethane dye-bath effluent in an integrated two-stage anaerobic reactor

In the present study, decolorization of a simulated dye waste containing three different triphenylmethane (TPM) dyes--Magenta, Malachite Green and Crystal Violet, was investigated in a laboratory scale, two-stage anaerobic high-rate reactor. The effect of various parameters (influent dye concentration, hydraulic and co-substrate loading rates) on color and COD removal efficiency of the reactor has been studied. It has been shown that the influent dye concentration had little effect on overall COD and color removal efficiency. More than 99% color removal and 96% COD removal efficiency were maintained even at a dye concentration of 500 mg/l and a dye loading rate of 1000 mg/l day. However, a minimum level of glucose as supplementary carbon source is required to maintain the maximum color removal efficiency and it drops appreciably when no glucose is added to the influent. The study also showed that the acidogenic phase of the reaction plays an important role in decolorization of the TPM dyes. In addition, the two-stage anaerobic reactor was observed to have distinct advantages over the single-stage system, as the drop in color and COD removal efficiency of stage 1 are adequately compensated by stage 2 of the reactor especially under high dye loading rates accompanied by low co-substrate loading and under reduced HRTs.     

Adsorption of cadmium, copper, nickel, and zinc to a poly(tetrafluorethene) porous soil solution sampler

Suction cups made of poly(tetrafluorethene) (PTFE) are widely used for sampling of soil solution. A brand (Prenart) of PTFE cups was tested for adsorption of Cd, Cu, Ni, and Zn at low concentrations under different conditions. In a laboratory experiment adsorption from a 10 microg L(-1) heavy metal solution with a 0.01 M NaCl background electrolyte was investigated at pH 3.6, 4.5, and 5.8 by pumping the solutions through the cups. The effect of three different ionic compositions was also investigated using 0.01 M CaCl2, 0.01 M NaCl, and no background electrolyte at pH 4.5. In 0.01 M NaCl electrolyte at pH 5.8 the cups acted as effective filters. At pH 3.6 after 300 mL of solution had passed through the cup, equivalence between the Cd and Ni concentrations in influent and effluent was found. No equivalence between effluent and influent concentrations was found for Zn and Cu at pH 4.5 and 5.8. With Ca as the electrolyte, no adsorption of Cd, Ni, or Zn was found. In Na electrolyte, equivalence between influent and effluent concentrations for Cd, Ni, and Zn was reached. The difference between effluent and influent concentrations of Zn, Ni, and Cd remained significant in the absence of electrolyte. For all pH values and electrolytes the difference between effluent and influent concentrations of Cu was significant. It is concluded that PTFE cups affect the concentrations of heavy metals sampled at low soil solution concentrations. Cadmium, Cu, Ni, and Zn adsorb to the cup at pH > 4.5 and low ionic strength.     

重金属废水生化处理技术的研究进展

处理重金属废水的传统方法在投资和运行费用上都较高，加之沉淀去除效果不太理想，近年来国内外进行了大量的生化法去除重金属的研究。本文介绍了生物吸附法、生物絮凝法、微生物代谢法和植物吸收法。生化法处理重金属废水，成本低，效益高，易管理，可回收重金属，有利于生态环境的改善，具有十分广阔的应用前号。     

Use of cattails in treating wastewater from a Pb/Zn mine

This article describes the use of a combined treatment system, which includes an aquatic treatment pond withTypha latifolia Linn. (Typhaceae) as the dominant species and a stabilization pond, to treat the wastewater from a Pn/Zn mine at Shaoguan, Guangdong Province, China. In 1983, it was noted thatT. latifolia bloomed in areas affected by the wastewater emitted from the mine, hence a combined purification system was subsequently built. The influent contained high levels of total suspended solids (4635 mg/liter), chemical oxygen demand (14.5 mg/liter) as well as Pb (1.6 mg/liter) and Zn (1.9 mg/liter). The results of the effluent after treatment showed that the total suspended solids, chemical oxygen demand, Pb, and Zn had been reduced by 99%, 55%, 95%, and 80% respectively. The results of plant tissue analysis indicled thatT. latifolia assimilated significant amounts of Pb and Zn, especially in the root portion. During 1986 several species of algae and fish were present in the pond, usually with a higher density in areas containing lower metal concentrations in the water. Paper was presented in part at the conference “The Use of Constructed Wetlands in Water Pollution Control” held 24–28 September 1990, Cambridge, UK.     

Bioleaching of heavy metals from sewage sludge: A review

During the treatment of sewage, a huge volume of sludge is generated, which is disposed of on land as soil fertilizer/conditioner due to the presence of nitrogen, phosphorus, potassium and other nutrients. However, the presence of toxic heavy metals and other toxic compounds in the sludge restricts its use as a fertilizer. Over the years, bioleaching has been developed as an environmentally friendly and cost-effective technology for the removal of heavy metals from the sludge. The present paper gives an overview of the various bioleaching studies carried out in different modes of operation. The various important aspects such as pathogen destruction, odor reduction and metal recovery from acidic leachate also have been discussed. Further, a detailed discussion was made on the various technical problems associated with the bioleaching process, which need to be addressed while developing the process on a larger scale.     

Land management impacts on dairy-derived dissolved organic carbon in ground water

Dairy operations have the potential to elevate dissolved organic carbon (DOC) levels in ground water, where it may interact with organic and inorganic contaminants, fuel denitrification, and may present problems for drinking water treatment. Total and percent bioavailable DOC and total and carbon-specific trihalomethane (THM) formation potential (TTHMFP and STHMFP, respectively) were determined for shallow ground water samples from beneath a dairy farm in the San Joaquin Valley, California. Sixteen wells influenced by specific land management areas were sampled over 3 yr. Measured DOC concentrations were significantly elevated over the background as measured at an upgradient monitoring well, ranging from 13 to 55 mg L(-1) in wells downgradient from wastewater ponds, 8 to 30 mg L(-1) in corral wells, 5 to 12 mg L(-1) in tile drains, and 4 to 15 mg L(-1) in wells associated with manured fields. These DOC concentrations were at the upper range or greatly exceeded concentrations in most surface water bodies used as drinking water sources in California. DOC concentrations in individual wells varied by up to a factor of two over the duration of this study, indicating a dynamic system of sources and degradation. DOC bioavailability over 21 d ranged from 3 to 10%, comparable to surface water systems and demonstrating the potential for dairy-derived DOC to influence dissolved oxygen concentrations (nearly all wells were hypoxic to anoxic) and denitrification. TTHMFP measurements across all management units ranged from 141 to 1731 microg L(-1), well in excess of the maximum contaminant level of 80 microg L(-1) established by the Environmental Protection Agency. STHMFP measurements demonstrated over twofold variation ( approximately 4 to approximately 8 mmol total THM/mol DOC) across the management areas, indicating the dependence of reactivity on DOC composition. The results indicate that land management strongly controls the quantity and quality of DOC to reach shallow ground water and hence should be considered when managing ground water resources and in any efforts to mitigate contamination of ground water with carbon-based contaminants, such as pesticides and pharmaceuticals.     

Novel passive co-treatment of acid mine drainage and municipal wastewater

A laboratory-scale, four-stage continuous-flow reactor system was constructed to test the viability of high-strength acid mine drainage (AMD) and municipal wastewater (MWW) passive co-treatment. Synthetic AMD of pH 2.6 and acidity of 1870 mg L(-1) as CaCO3 equivalent containing a mean 46, 0.25, 2.0, 290, 55, 1.2, and 390 mg L(-1) of Al, As, Cd, Fe, Mn, Pb, and Zn, respectively, was added at a 1:2 ratio with raw MWW from the City of Norman, OK, to the system which had a total residence time of 6.6 d. During the 135-d experiment, dissolved Al, As, Cd, Fe, Mn, Pb, and Zn concentrations were consistently decreased by 99.8, 87.8, 97.7, 99.8, 13.9, 87.9, and 73.4%, respectively, pH increased to 6.79, and net acidic influent was converted to net alkaline effluent. At a wasting rate of 0.69% of total influent flow, the system produced sludge with total Al, As, Cd, Cr, Cu, Fe, Pb, and Zn concentrations at least an order of magnitude greater than the influent mix, which presents a metal reclamation opportunity. Results indicate that AMD and MWW passive co-treatment is a viable approach to use wastes as resources to improve water quality with minimal use of fossil fuels and refined materials.     

某公司印染废水处理工程实例

某公司采用“一级混凝沉淀一水解酸化-A／O法-二级混凝沉淀”工艺处理印染废水,工程日常运行结果表明,在废水主要指标CODQ为660～690mg／L、色度为1200倍时,处理后出水COD0为70-90mg／L,色度为28-35倍,CODo的去除率为86％-89％,色度的去除率约为97％。废水处理系统综合电耗0．8kW·h／t污水,废水处理总运行费用2．2元／t污水,具有较好的技术经济指标。     

Wastewater treatment with multilayer media of waste and natural indigenous materials

Wastewater treatment using waste materials (refuse concrete, waste paper and charcoal) and natural indigenous rocks (andesite, limestone, granite and nitrolite) in the form of multilayer media was investigated. The removal of suspended solids (SS), phosphate ion, nitrate ion, ammonium ion, toxic metals and chemical oxygen demand (COD) were evaluated for the multilayer wastewater treatment system. Effective removal of heavy metals such as cadmium, chromium, mercury and lead was demonstrated. SS and phosphate ion were removed with relatively high efficiency and the COD after treatment was lessened using certain combinations of media. The present wastewater treatment system is simple, convenient and low cost. Therefore, this method can be applied in small scale plants for wastewater treatment in local and nonexclusive areas.     

The possibility of in situ heavy metal decontamination of polluted soils using crops of metal-accumulating plants

The decontamination of soils and wastes polluted with heavy metals presents one of the most intractable problems for soil clean-up. Present technology relies upon metal extraction or immobilization processes, both of which are expensive and which remove all biological activity in the soil during decontamination. They may only be appropriate for small areas of valuable redevelopment land. In this paper the use of metal-accumulating plants is explored for the removal of metals from superficially-contaminated soils such as those resulting from the long-term application to land of metal-contaminated sewage sludges. Green remediation employs plants native to metalliferous soils with a capacity to bioaccumulate metals such as zinc and nickel to concentrations greater than 2% in the aerial plant dry matter (hyperaccumulators). Growing such plants under intensive crop conditions and harvesting the dry matter is proposed as a possible method of metal removal and for ‘polishing’ contaminated agricultural soils down to metal concentrations below statutory limits. Not only are the biological activity and physical structure of soils maintained but the technique is potentially cheap, visually unobtrusive and offers the possibility of biorecovery of metals. The limitations of the process are reviewed and the future requirements for the development of efficient phytoremediators are outlined.