Leachate from Land Disposed Residential Construction Waste

Solid waste from construction and demolition (C&D) activities is often disposed in unlined landfills. Leachate from unlined landfills poses a potential risk to groundwater quality. An understanding of the types of chemical constituents likely to be encountered in C&D waste landfill leachate and the concentrations at which they occur help assess this risk. An experiment was performed to characterize leachate from land-disposed residential construction waste. Four 54 m2 (580 ft2) test cells were excavated, lined, and filled with waste. Leachate samples were collected and analyzed for a number of water quality parameters over a 6 month period. No volatile or semivolatile organic compounds were detected at elevated constituent levels in the leachate. Inorganic ions were found to account for the bulk of the pollutant mass leached. Calcium and sulfate were the predominant ions in the leachate, resulting from the dissolution of gypsum drywall. The concentrations of several leachate constituents were found to exceed water quality standards. These constituents included aluminum, arsenic, copper, manganese, iron, sulfate, and total dissolved solids. Arsenic was the only primary water quality standard exceeded. The arsenic was concluded to result from chromated copper arsenate (CCA)-treated wood. The potential risk of impacting groundwater was examined by comparing the measured constituent concentrations with the water quality standards to assess the amount of dilution and attenuation needed in the groundwater so that a water quality standard would not be exceeded. The water quality standard exceeded by the greatest magnitude was manganese, followed by iron.     

Comparison of Metals Leaching from CCA- and ACQ-Treated Wood in Simulated Construction and Demolition Debris Landfills

Pressure-treated wood is often disposed of in landfills in the United States, very frequently in construction and demolition (C&D) debris landfills. C&D debris landfills in many states are not equipped with liner systems to protect groundwater. With the voluntary withdrawal of chromated copper arsenate (CCA) treated wood for most residential applications in January 2004, copper-based wood preservatives, including alkaline copper quaternary (ACQ), are more widely used. To evaluate the impact of metal losses from ACQ-treated wood disposed in C&D debris landfills and compare to those of CCA-treated wood under similar conditions, leachates from three simulated C&D debris landfills (lysimeters) were collected and analyzed for over a period of one year. The wood component in one lysimeter (the control lysimeter) contained pallet wood; the second lysimeter contained CCA-treated wood, and the third contained ACQ-treated wood. Each lysimeter was buried in an active landfill for temperature control. Several batch leaching tests [including the standardized toxicity characteristic leaching procedure (TCLP) and the synthetic precipitation leaching procedure (SPLP)] were also conducted for comparison purposes. Although the two lysimeters containing treated wood had elevated copper concentrations within the waste matrix, the concentration in the leachate samples from these lysimeters was below detection for Cu (<4?μg/L) throughout the duration of the experiment, likely a result of precipitation as copper sulfide mineral in the reducing conditions of the simulated C&D landfills. As expected, the lysimeter containing CCA-treated wood showed elevated concentrations of arsenic and chromium, with maximum concentrations of 1.16 mg/L and 0.2 mg/L respectively. Greater amounts of boron (B) leached from ACQ-treated wood than CCA-treated wood or pallet wood debris. The results suggest that copper leaching will not be a major concern upon the disposal of ACQ-treated wood in C&D debris landfills. Arsenic leaching from CCA-treated wood remains a concern for unlined C&D debris landfills.     

Stabilization of Arsenic- and Barium-Rich Glass Manufacturing Waste

Effective solidification∕stabilization (S∕S) of arsenic- and barium-containing D004∕D005 waste was accomplished by using a binder of cement with 40% class C fly ash and either ferrous sulfate or ferric sulfate as an additive. Addition of iron salts improves arsenic solidification∕stabilization (S∕S). Barium may be encapsulated within the stabilized matrix as barium sulfate. Recommended mole ratios for iron∕arsenic and barium∕sulfate are at least 6 and 1.2, respectively. A binder∕waste ratio of 0.15 is volume efficient, but the mix design must be carefully controlled to achieve adequate S∕S. In practice, the heterogeneity of waste and large-scale mix operations may preclude close control of reagent dosages, so a binder∕waste ratio of 0.40 is preferable. Ferrous sulfate additive is preferable for arsenic S∕S because it is effective over a wider range of mix designs and over a long-term curing period. Toxicity characteristic leaching procedure results degraded with long curing time for some mix designs with ferric sulfate additive.     

某铀矿床淡化少试剂地浸关键技术及工艺参数研究

某铀矿床地下水矿化度高,在地浸时容易产生化学堵塞。在室内研究基础上,进行淡化少试剂现场浸出试验,得出该工艺的关键技术和最佳参数。结果表明,淡化技术、氧化技术、酸化技术、加助溶剂技术是本工艺的关键技术。最佳技术参数为:地下水矿化度小于4g/L、溶解氧浓度250³50mg/L、溶液pH小于6.9、HCO3-浓度600350mg/L、溶液pH小于6.9、HCO3-浓度600⁸00mg/L。     

Pilot-Scale Simulation of Landfill Bioreactor and Controlled Dumping of Fresh and Partially Stabilized Municipal Solid Waste in a Tropical Developing Country

Four pilot-scale lysimeters were used to study the benefits of landfill operation with and without leachate recirculation in tropical weather conditions. Young and old landfills were simulated by filling lysimeters with a segregated fraction of fresh municipal solid waste (MSW) and MSW mined from an open dump site, respectively, and periodically monitoring leachate quantity and quality and biogas quality. For each substrate, one lysimeter was operated as a bioreactor with leachate recirculation and another lysimeter was operated as a controlled dump, for a period of 10 months. Densities between 652 and 825??kg/m3 could be achieved with fresh and mined MSW. Despite such compaction during waste placement, bioreactor technology helps in leachate management, especially in the case of the young landfill lysimeter operated in tropical weather. The benefits of leachate recirculation in the young landfill lysimeter were evident from the significant decrease in chemical oxygen demand (COD) (86%), biochemical oxygen demand (BOD) (82%), dissolved organic carbon (DOC) (85%), and volatile solids (75%) in leachates. However, ammonia nitrogen (amm-N) and chlorides in the leachates accumulated in bioreactor landfills. Operating an old landfill lysimeter as a bioreactor seemed to have no exceptional advantage in the context of leachate management, although leachate recirculation enhanced the methane potential of both fresh and mined MSW.     

Methanogenic Characteristics of Formate-Utilizing Sludge

The formate-utilizing sludge was first enriched in a chemostat reactor for over 90 days; at steady state, the sludge yield averaged 0.066 mg volatile suspended solids (VSS)∕mg chemical oxygen demand (COD). The methanogenic characteristics of this sludge were then investigated in three series of batch experiments at 37°C using formate, acetate, and H2∕CO2, individually, as substrates. At pH 6.4–8.0, the formate-degrading rate averaged 0.76 mg∕mg VSS∕h (6.35 mg COD∕mg VSS∕d). At pH 3.0, the sludge completely lost its bioactivity, and required a lengthy recovery period to regain a fraction of its bioactivity after the pH was adjusted to pH 7.1. The sludge was also able to utilize H2∕CO2 as substrate at an average rate of 0.0167 mg H2∕mg VSS∕h (3.21 mg COD∕mg VSS∕d). At pH ≤ 8.0, the sludge degraded acetate at a very low rate of 3.0 μg∕mg VSS∕h (0.077 mg COD∕mg VSS∕d). The sludge exhibited a slight homoacetogenic activity at pH > 8.0 using formate as substrate; the homoacetogenic reaction using H2∕CO2 as substrate was thermodynamically infeasible, according to chemical free energy analysis.     

Bacterial Leaching of Metals from Tannery Sludge by Indigenous Sulphur-Oxidizing Bacteria—Effect of Sludge Solids Concentration

An investigation on the effect of sludge solids concentration on bioleaching of Cr(III) and other metals from tannery sludge by indigenous sulphur-oxidizing bacteria was carried out. The sludge solids concentrations ranged from 13 to 60 g/L. The concentration of elemental sulphur was fixed at 30 g/L. The results showed that the lowest pH reached after 25 days of bioleaching at all studied sludge solids concentration was about 1.3. The optimum sludge solids concentration for maximum metal leaching from tannery sludge was 40 g/L and about 87% of Cr(III), 73% of Al, 72% of Fe, 62% of Mg, and 73% of Zn could be leached in this case. During bioleaching, the concentrations of total and volatile suspended solids of the tannery sludge significantly decreased. The sulphur-oxidizing bacteria could tolerate a Cr(III) concentration as high as 5,930 mg/L at pH 1.3. The leaching efficiencies of Cr(III), Al, and Fe for both chemical leaching and bioleaching of tannery sludge were similar at pH 1.3. The leaching efficiency of Ca, Mg, and Zn in both leaching processes were identical for pH values in the range of 1.3 to 3.0.     

Understanding Environmental Leachability of Electric Arc Furnace Dust

Dust from production of steel in an electric arc furnace (EAF) contains a mixture of elements that pose a challenge for both recovery and disposal. This paper relates the leachability of six Canadian EAF dusts in four leaching tests [distilled water, Ontario Regulation 347 Leachate Extraction Procedure, Amount Available for Leaching (AALT), and pH 5 Stat] to their mineralogy. Chromium and nickel contaminants in EAF dust are largely unleachable (<5% available in AALT and pH 5 Stat), as they are found with the predominant spinel ferrite phase in EAF dust. However, even a small proportion of oxidized chromium can result in significant leachate concentrations of highly toxic chromate. The leachability of zinc (7–50% available), lead (2–17% available), and cadmium (9–55% available) can be significant, as large fractions of these contaminants are found as chlorides and oxides. The leaching of these metals is largely controlled by pH. The acid neutralization capacity of the EAF dusts appeared to be controlled by dissolution of lime and zincite, and results from regulatory leaching tests can be misleading because the variable acid neutralization capacity of EAF dusts can lead to very different final leachate pHs (5–12.4). A more informative approach would be to evaluate the total amounts of contaminants available in the long term, and the acid neutralization capacity.     

Performance of North American Bioreactor Landfills. I: Leachate Hydrology and Waste Settlement

An assessment of state-of-the-practice at five full-scale North American landfills operating as bioreactors is presented in this two-paper set. This paper focuses on effectiveness of liners and leachate collection systems, leachate generation rates, leachate recirculation practices and rates, effectiveness in moistening the waste, and settlement of the waste over time. Except in one case, the liner and leachate collection systems at the bioreactor landfills were similar to those used for landfills operated conventionally. Leachate generation rates increased approximately linearly with recirculation rate, but in all cases, the leachate generation rate was <300?L/m2?year. Leachate depths generally were maintained within regulatory requirements, even with the highest recirculation rates. Leakage rates from liners at bioreactor landfills, including alternative liner designs employing geosynthetic clay liners, are comparable to leakage rates from conventional landfills. Thus, based on the information gathered in this study, additional requirements or features for liners or leachate collection systems are not warranted for bioreactor landfills. Diminishing capacity of horizontal recirculation trenches is common. Experience at one landfill suggests that small doses at high frequency under substantial injection pressure can deter loss of trench capacity. Only those landfills that were aggressive in recirculation had achieved water contents near the field capacity. Increasing the amount of liquid that is added may be required to achieve field capacity at some landfills, particularly if a final cover is placed soon after waste grades are reached. The rate of time-dependent waste settlement attributed to biodegradation is about 1.6 times larger in bioreactor landfills than in conventional landfills, and increases as the recirculation dosage increases.     

Pyrite Oxidation Model for Assessing Ground-Water Management Strategies in Acid Sulfate Soils

A theoretical approach for calculating pyrite oxidation in acid sulfate soil with a macropore∕matrix structure is described. This approach accounts for vertical oxygen transport through soil macropores and the subsequent lateral diffusion of oxygen into the soil matrix. As oxygen is supplied into the matrix, it is consumed by pyrite and other oxygen-consuming processes. A numerical solution to the theoretical model was developed and used in the computer simulation model ACID3D. The numerical approach is based on a linear relationship between oxygen consumption and dissolved oxygen concentration. The numerical scheme is shown to be in good agreement with the analytical solutions. ACID3D was used in conjunction with a commercially available saturated∕unsaturated water flow model to assess the effectiveness of a ground-water management strategy to minimize acid generation caused by pyrite oxidation currently being carried out on a trial site on the south coast of New South Wales, Australia.     

Removal of Heavy Metals and COD by SRB in UAFF Reactor

Sulfate-reducing bacteria, under anaerobic conditions, reduce sulfate, SO4?2, to sulfide, S?2, which in turn can effectively precipitate heavy metals. In this research project, sulfate-reducing bacteria were grown in an upflow anaerobic fixed-film (UAFF) reactor using optimum growth conditions obtained in previous studies. These reactors were then fed with different heavy metals at increasing loading rates until complete failure occurred as metal removal reached zero and residual sulfide dropped to zero. The metal concentrations were measured as total, dissolved, and free ions both in the influent and in the effluent streams. The results of this research showed that 100% removal efficiencies could be obtained with individual concentrations up to 200 mg∕L for Cu, 150 mg∕L for Ni and Zn, 75 mg∕L for Cr, 50 mg∕L for Cd, and 40 mg∕L for Pb. Also, the corresponding organic matter removal as total organic carbon was found to be about 50% of the influent total organic carbon. A set of mathematical equations were derived to express the mass balance inside the UAFF reactor, with respect to metal influent concentrations and sulfide production. These equations were corrected by incorporating a correction product, α?β, to represent the toxicity effect of the increasing metal concentrations.     

Effectiveness of Covers and Liners Made of Red Mud Bauxite and/or Cement Kiln Dust for Limiting Acid Mine Drainage

This paper presents a laboratory investigation to evaluate the capacity of alkaline residues to inhibit acid mine drainage. Column tests were used to evaluate the geochemical behavior of cement kiln dust (CKD) and red mud bauxite (RMB) used as covers, liners, or mixed with acid producing tailings and waste rocks. The most important indicators of neutralization are pH and the concentrations of metals in solution. Initial leachate pH of samples with an alkaline cover composed of 10% CKD or 10% of a mixture of CKD and RMB was low, but rapidly increased to near 7.0 and stabilized for the duration of this study. The use of alkaline materials as a liner had a positive effect on the reduction of Fe, SO4 and other metals such as Cu and Zn concentrations and the number of viable bacteria. In the cases where the alkaline layer was used as a liner or mixed with the waste rocks, near neutral pH values were rapidly reached in the leachate. However, in these columns the leachate pH values decreased over time.     

乙酸根配位浸出硫酸铅的热力学分析

采用热力学平衡计算和验证性实验的方法, 研究乙酸根配位浸出硫酸铅的热力学问题。首先, 通过Pb(OH)₂-H₂O体系的热力学计算评价了Pb(OH)₆4-形成常数的合理性。结果表明, 考虑Pb(OH)₆4-存在时所得计算结果明显不符合Pb(OH)₂两性化合物的性质, 因而不建议采用。然后, 计算并绘制了乙酸根配位浸出硫酸铅的热力学平衡图。结果表明, 在不同总乙酸根浓度下, pH值在6~9的范围对乙酸根浸出硫酸铅更有利, Pb(Ac)₄2-是该pH值区域中铅的主要物种; 并且, 总乙酸根浓度越高, 浸出液中, Pb(Ac)₄2-与游离Ac-的浓度比越高, 表明浸出硫酸铅的乙酸根利用率随之增大。此外, 根据电中性原则、质量守恒原则和同时平衡原理, 计算并绘制了不同HAc和NaAc比例的初始液浸出硫酸铅平衡后各溶解物种的lgc-[Na]/[Ac]_T图, 表明总乙酸根一定时浸出液铅浓度随着初始液乙酸钠比例增加而增加, 验证性实验结果与热力学计算结果趋势上一致。      

Evaluation of Leaching Tests for Cement Based Immobilization of Hazardous Compounds

A range or arsenic containing compounds, including arsenic trioxide, pentoxide and a lead arsenate insecticide have been stabilized using formulations of cement alone, cement+lime and cement+ferrous sulfate and subsequently exposed to a range of leaching regimes in order to compare their effectiveness for metal stabilization. Leaching tests used were two regulatory tests, the Toxicity Characteristic Leaching Procedure (TCLP) and the Australian Bottle Leaching Procedure (ABLP), as well as column leaching. Arsenic leachate concentrations from cement-stabilized lead arsenate insecticide were similar when subjected to either the TCLP or ABLP using the same leachant. Lead, known to be immobilized by means different to that of arsenic, yielded varying leachate concentrations when using either of the regulatory tests, even though the leachant was of the same type. The leaching of calcium influences the filtered arsenic leachate, whereas the leaching of lead is greatly affected by leachate pH. As expected, both regulatory tests generally proved to be very severe in terms of the masses of the hazardous constituents leached when compared to conceptually more realistic column leaching scenarios. Sodium arsenate-containing formulations behaved anomalously, with column leaching tests resulting in larger arsenic masses being leached than the regulatory tests. Sodium arsenate, known to inhibit cementation reactions, serves as a reminder of the perils that can be faced when generalizing the results obtained from leaching tests.     

Effects of Solid Levels and Chemical Additives on Removal of Solids and Phosphorus in Swine Manure

Experiments were conducted to determine the effect of solid levels on natural sedimentation of swine manure. Total solids (TS) levels of 0.5, 1.0, 2.0, 4.0, and 6.0% were evaluated. Natural sedimentation was impeded at higher than 2.0% and also at lower than 1.0% TS concentrations. Two flocculants (ferric chloride and aluminum sulfate) commonly used in the municipal wastewater treatment industry were then evaluated for their enhancement of natural sedimentation and concomitant removal of phosphorus from swine manure. Each flocculant was evaluated at five levels—0 (control), 500, 1,000, 1,500, and 2,000 mg∕L—on swine manure with an adjusted TS level of 1.0%. At dosage levels of 1,500 mg∕L (5.4 mM Fe+3), ferric chloride removed 76% suspended solids (SS) and 86% phosphorus, while aluminum sulfate at the same dosage level removed 96% SS and 78% phosphorus. Unaided natural sedimentation at this TS concentration removed 66% and 42% of the SS and phosphorus, respectively. Chemical flocculation can, therefore, be an effective method of removing solids and phosphorus in swine manure.     

Removal of Dissolved Organic Carbon in Sanitary Gravity Sewer

Utilization of dissolved organic matter in a 1.5 km section of a sanitary gravity concrete sewer with an inner diameter of 450 mm constructed on a slope of 0.0075 was studied. Continuous measurements of dissolved organic carbon (DOC), suspended solids, dissolved oxygen, and flow rate were performed along the sewer. About 14% of the DOC was removed in an 18-min retention time. A slower flow rate in the sewer would favor higher DOC removal efficiency because it offers a longer retention time. Oxygen was not a limiting factor as the dissolved oxygen level was at least 1 mg∕L. Batch tests using raw sewage and either suspended solids or settled sediments yielded specific DOC rates of 1.3 mg and 2.6 mg DOC∕mg dry wt/day for the sewage phase and sediment phase, respectively. Adenosine triphosphate content analysis of the suspended solids and sediment samples confirmed that both contained substantial amounts of active biomass. In the 1.5-km sewer system, it is estimated that 39.13 kg of DOC can be stabilized∕day; the sewage phase contributes 40% while the sediment phase contributes 60%.     

Removal of TDS from Cooling Tower Water by Using EDTA-Modified Bagasse Fibers

Modified by ethylenediaminetetraacetic acid (EDTA) salts and unmodified bagasse fibers were tested for the removal of total dissolved solids (TDSs) from cooling tower water. Parameters such as hydrogen ion concentration (pH), particle size of bagasse fibers, and the concentrations of adsorbent and adsorbate were studied to optimize the conditions to be applied on a commercial scale for the decontamination of effluents of cooling tower water. The optimum pH for TDS removal was between 6 and 6.5. The efficiency of TDS removal increased when the size of fiber particles decreased (100?μm) and when the concentration of EDTA salt increased to reach 78 mg/g of modified bagasse fibers. The adsorption parameters were determined using both Langmuir and Freundlich isotherms. The preferential mechanisms for the retention of TDSs are a complexation process between the TDSs and chemical functions present on the surface of fibers, and the chelation process with the EDTA attached to the fibers. The results obtained could be valuable for application to cooling tower water treatment and for the softening of hard drinking water.     

Empirical Partitioning Leach Model for Solidified∕Stabilized Wastes

A model has been developed to describe dynamic leaching of metal contaminants from solidified wastes using data for calibration that are taken only from batch tests. The model describes the three major factors affecting leaching: (1) acid∕base reactions that determine the pH within the waste; (2) pH-dependent reactions that determine whether the contaminants are in mobile or immobile forms; and (3) diffusion that transports mobile contaminants from the waste. Acid∕base reactions and mobilization∕immobilization reactions of contaminants are described by empirical equations calibrated from batch equilibrium tests. Precipitation or sorption reactions are used to describe partitioning of contaminants among mobile and immobile forms. Fickian diffusion is used to describe transport of soluble compounds. Model predictions for observed diffusivities of copper, chromium, lead, and zinc agreed well with the experimental data obtained from dynamic leaching tests. Little difference was observed in model predictions when contaminant immobilization was assumed to be caused by precipitation or by sorption. Model simulations indicate that the assumption of an infinite bath may not apply to dynamic leach tests when contaminants are strongly immobilized.     

Effect of pH and VFA on Hydrolysis of Organic Solid Waste

The anaerobic hydrolysis rate of organic solid waste was studied at fixed volatile fatty acid (VFA) concentrations ranging from 3 to 30 g COD∕L and fixed pH values between 5 and 7. For separate control of both VFA and pH, a special completely mixed reactor was designed. In this way, it was possible to distinguish between the inhibitory effects of pH, total VFA, and undissociated VFA on anaerobic hydrolysis. It was shown that hydrolysis of the organic solid waste followed first-order kinetics. Using a statistical analysis, it was found that the hydrolysis rate constant was pH dependent but was not related to the total VFA and undissociated VFA concentrations.     

Hydrogen-Based Nitrate and Selenate Bioreductions in Flue-Gas Desulfurization Brine

The H2-based membrane biofilm reactor (MBfR) was shown to simultaneously reduce nitrate and selenate in flue-gas desulfurization (FGD) brines (15–33 g/L TDS). The MBfR also used polyester fibers, which differ from the composite gas-transfer fibers used in previous MBfR studies. Selenate reduction was nearly 100% in all media tested and was immediate, which suggests that selenate was coreduced with nitrate, possibly by the same microorganisms. A step increase in the nitrate removal flux was observed at a H2 pressure greater than 20 psig (138 kPa) using polyester fibers. High concentrations of nitrate and sulfate had no inhibitory effect on selenate reduction as long as H2 was available. In comparison with previous MBfR experiments treating ion-exchange brine, total electron equivalent fluxes were 29% lower and in contrast to earlier work on selenate reduction in fresh water, sulfate reduction was inhibited, likely due to the high total dissolved solids in the FGD brine or insufficient H2 availability due to CaCO3 or Se° precipitation onto the tighter polyester fibers.