Efficiency analysis of reduction and stabilization of biodegradable waste using an aerobic stabilization system

The reduction and stabilization of biodegradable waste were studied using three operational stages in an aerobic stabilization system. The system used for mechanical/biological treatment utilized two-shaft screws in multiple box reactors. In the first operational stage, 50-kg batches of biodegradable waste were charged in each of the three reactors, with peat moss used as a bulking agent. Analysis revealed that peat moss can be used at this initial stage, based on the observed increase in temperature and carbon dioxide levels. The second stage of operation involved adding 100 kg/day of biodegradable waste to the first reactor. It was confirmed that a continuous reaction is possible by the addition of more waste. In the third stage of operation, 20 kg/day of the 100 kg/day of biodegradable waste feed was replaced with material fed back from the third reactor. At this stage, final product was also removed from the third reactor. The temperature was not controlled, and up to 8%–9% carbon dioxide was formed, enabling normal activation of decomposition. This three-stage operational test confirmed the expected decomposition of organic matter and biodegradable materials. The rate of mass reduction calculated for the final product compared with the input amount was 94.3%, which confirmed that this system would be a useful means for the reduction and stabilization of biodegradable waste. This study also measured the water content of the material in the reactors: the water content decreased as the reaction progressed. This indicated that the activation of microorganisms did not occur sufficiently in the second and third reactors. Future studies of methods to control the internal water content of each reactor should improve the decomposition efficiency.     

西海堤垃圾场和西田垃圾场陈垃圾特性研究

结合深圳市宝安区西海堤垃圾场和西田垃圾场现场实验,分析了陈垃圾的物理成分,并将其与新鲜垃圾物理成分作对比,得出易降解有机物含量、塑胶含量和无机物含量与陈垃圾稳定化的关系.     

Evaluation of a chemical stabilization process

Environmental Resources Management (ERM) performed an evaluation of a biosolids chemical stabilization process known as BIO*FIX®, marketed by Bio Gro Systems, Inc., of Annapolis, Maryland. The purpose of the evaluation was (1) to assess major characteristics of the process and its final product, (2) to determine the quantity and final disposition of all components in the incoming biosolids, and (3) to determine if the process conforms to new regulations promulgated and administered by the U.S. Environmental Protection Agency (EPA) titled “Standards for the Use or Disposal of Sewage Sludges” (40 CFR Part 503). The BIO*FIX® chemical stabilization process involves the addition of calcium oxide (CaO) to dewatered biosolids at rates that achieve the pathogen reduction and vector attraction reduction requirements of the 503 program while creating a marketable end product used as an agricultural amendment. ERM's project involved the testing of four process streams in order to create a mass balance on the process. Laboratory analyses were performed on samples of the dewatered biosolids, the chemically-stabilized end product, and the scrubber water effluent. The primary components of concern tested in the above process streams were ammonia, metals, odorous compounds, particulate matter, and organic matter. Through the tests described in the article, ERM drew the following conclusions: (1) The major gaseous pollutant resulting from the BIO*FIX® process is gaseous ammonia. The total gaseous ammonia released from the product depends on the ammonia nitrogen content of the biosolids, and pH and temperature levels reached in the process. Additional ammonia is emitted when the end product is loaded in trucks and stored. Any gaseous ammonia remaining in the end product after processing will slowly dissipate over time. (2) Other potential odor pollutants such as hydrogen sulfide (H₂S) and mercaptans were found to be below detectable levels in the uncontrolled exhaust gas. (3) Metals were not found in the exhaust gas in any detectable quantities. They would not be expected to volatilize during the process. Particulate matter emissions were found to be very low. (4) The pathogen reduction and vector attraction reduction requirements of the 40 CFR 503 regulations were met or exceeded. (5) Finally, through observations and tests, ERM found that the BIO*FIX® chemical stabilization process provides for a simple, viable, and effective conversion of biosolids into a beneficial use product in compliance with all pertinent regulations.     

Characterization and phosphate stabilization of dusts from the vitrification of MSW combustion residues

The use of soluble PO₄³⁻ as a heavy metal chemical stabilization agent was evaluated for a dust generated from melting or vitrification of municipal solid waste combustion residues. Vitrification dusts contain high concentrations of volatile elements such as Cl, Na, K, S, Pb, and Zn. These elements are present in the dusts largely as simple salts (e.g. PbCl₂, ZnSO₄) which are highly leachable. At an experimental dose of 0.4 moles of soluble PO₄³⁻ per kg of residue, the pH-dependent leaching (pH 5,7,9) showed that the treatment was able to reduce equilibrium concentrations by factors of 3 to 100 for many metals; particularly Cd, Cu, Pb and Zn. Bulk and surface spectroscopies showed that the insoluble reaction products are tertiary metal phosphate [e.g. Zn₃(PO₄)₂] and apatite [e.g. Pb₅(PO₄)₃Cl] family minerals. Geochemical thermodynamic equilibrium modeling showed that apatite family and tertiary metal phosphate phases act as controlling solids for the equilibrium concentrations of Ca²⁺, Zn²⁺, Pb²⁺, Cu²⁺, and Cd²⁺ in the leachates during pH-dependent leaching. Both end members and ideal solid solutions were seen to be controlling solids. Soluble phosphate effectively converted soluble metal salts into insoluble metal phosphate phases despite the relatively low doses and dry mixing conditions that were used. Soluble phosphate is an effective stabilization agent for divalent heavy metals in melting dusts where leachable metals are present in high concentrations.     

Overview of waste stabilization with cement

Cement can treat a variety of wastes by improving physical characteristics (solidification) and reducing the toxicity and mobility of contaminants (stabilization). Potentially adverse waste-binder interactions are an important consideration because they can limit solidification. Stabilization occurs when a contaminant is converted from the dissolved (mobile) phase to a solid (immobile) phase by reactions, such as precipitation, sorption, or substitution. These reactions are often strongly affected by pH, so the presence of components of the waste that control pH are critical to stabilization reactions. Evaluating environmental impacts can be accomplished in a tiered strategy in which simplest approach would be to measure the maximum amount of contaminant that could be released. Alternatively, the sequence of release can be determined, either by microcosm tests that attempt to simulate conditions in the disposal zone or by mechanistic models that attempt to predict behavior using fundamental characteristics of the treated waste.     

Toxicological evaluation of the chemical oxidation methods for landfill stabilization

As the stabilization criteria for landfill sites, only chemical criteria for the leachate discharges from the landfill sites have been used in Japan and many other countries. Recently, chemical oxidation has been developed as a method for the early-stabilization of landfills. However, by-products that are difficult to detect by chemical analysis can be produced by this method. Therefore, toxicity tests are useful tools for detecting the changes of leachate quality after application of this method. The heat source in the A landfill was analyzed by organic position inquiry technology, and ozone-treated leachate was sprayed back to the heat source in the landfill. Toxicity changes of the leachate after the spray were monitored using Microtoxtrade mark, ToxScreen-II, and DaphTox tests. The hardly-degradable organic matter was efficiently removed and toxicities of the leachate in the heat source decreased after the application. These toxicity results were significantly related to chemical oxygen demand (COD) changes. Thus, it was concluded that the toxicity tests were effective for monitoring the leachate quality after applying the chemical oxidation method for landfill stabilization, and its incorporation to establish the criteria for early-stabilization of landfill sites needs to be considered.     

Waste stabilization mechanism by a recirculatory semi-aerobic landfill with the aeration system

The main purpose of this research is to clarify and compare the mechanism of waste stabilization by a recirculatory semi-aerobic landfill with the aeration system. Our research is proposing the semi-aerobic landfill system for developing countries because of the simple and low-cost technology for the final disposal. Moreover, this system with leachate recirculation can be a more effective system for waste stabilization because of the improvement of leachate quality as an organic pollutant and, also, nitrogen removal. In this research, five different systems of landfill (Ae: aerobic, An: anaerobic, Se: semi-aerobic, SeR: recirculatory semi-aerobic landfill, and SeRA: recirculatory semi-aerobic landfill with aeration system) are compared with lysimeters which are 1 m high with a diameter of 0.3 m. The results of the leachate quality shows that the leachate treatment effect of the SeRA system can be observed to be as high as the Ae system. To determine the mechanism of this process, all lysimeters are dismantled after 1,100 days in the experimental period and the waste composition, the dissolution test, the mass balance of carbon and nitrogen, the determination of bacterial counts, etc., were analyzed. In this research, it was proven that the SeRA system has an optimal leachate treatment effect that is the same as the Ae system. And, from the results of the mass balance of carbon and nitrogen, the SeR and SeRA systems show higher waste stabilization effectiveness and nitrogen removal than the other systems. Moreover, the number of the aerobic bacteria can be observed to be higher in the SeR and SeRA systems. To determine these results, the waste stabilization mechanism is considered by the results of leachate quality, the mass balance of carbon and nitrogen, and, also, the bacterial numbers.     

Solidification and stabilization of hazardous wastes using geopolymers as sustainable binders

Journal of Material Cycles and Waste Management - Solidification/stabilization (S/S) of hazardous waste using cement for immobilization of contaminants has been recognized as Best Demonstrated...     

Sulfur polymer solidification/stabilization of elemental mercury waste

Elemental mercury, contaminated with radionuclides, presents a waste disposal problem throughout the Department of Energy complex. In this paper we describe a new process to immobilize elemental mercury wastes, including those contaminated with radionuclides, in a form that is non-dispersible, will meet EPA leaching criteria, and has low mercury vapor pressure. In this stabilization and solidification process, elemental mercury is combined with an excess of powdered sulfur polymer cement (SPC) and sulfide additives in a mixing vessel and heated to approximately 40 degrees C for several hours, until all of the mercury is converted into mercuric sulfide (HgS). Additional SPC is then added and the temperature of the mixture raised to 135 degrees C, resulting in a molten liquid which is poured into a mold where it cools and solidifies. The final treated waste was characterized by powder X-ray diffraction and found to be a mixture of the hexagonal and orthorhombic forms of mercuric sulfide. The Toxicity Characteristic Leaching Procedure was used to assess mercury releases, which for the optimized process averaged 25.8 microg/l, with some samples being well below the new EPA Universal Treatment Standard of 25 microg/l. Longer term leach tests were also conducted, indicating that the leaching process was dominated by diffusion. Values for the effective diffusion coefficient averaged 7.6x10(-18) cm2/s. Concentrations of mercury vapor from treated waste in equilibrium static headspace tests averaged 0.6 mg/m3.     

Cement based solidification/stabilization of arsenic-contaminated mine tailings

Cement was used to solidify/stabilize the abandoned mine tailings contaminated primarily with arsenic (up to 88 mg/kg) and lead (up to 35 mg/kg). Solidified/stabilized (s/s) forms with a range of cement contents, 5–30 wt%, were evaluated to determine the optimal binder content. Unconfined compression strength test (UCS), Korean standard leaching tests, toxicity characteristic leaching procedures (TCLP), and synthetic precipitation leaching procedure (SPLP) were used for physical and chemical characterization of the s/s forms. Addition of 5% cement was enough for the s/s forms to satisfy the UCS requirements (0.35 MPa). The addition of 7.5% cement remarkably reduced the leachability of arsenic in tailings. However, that of lead tends to increase slightly with increase of cement content due to its amphoteric nature. The discussions were made for determination of optimal binder content and for results from different evaluation procedures.     

Cement-clay pastes for stabilization/solidification of 2-chloroaniline

Immobilization of a model liquid organic pollutant, i.e. the 2-chloroaniline (2-CA), into a cement matrix using organoclays as pre-sorbent agents was investigated. Five cement-clay pastes were prepared with different nominal water-to-cement ratios (w/c=0.40, 0.25 and 0.15 wt/wt) and various amounts of waste (waste-to-cement o/c=0.20, 0.60 and 1.00 wt/wt); for comparison, a neat cement paste was also prepared. Dynamic leach tests were performed on solidified monoliths in order to assess the successful immobilization of the 2-CA. In monoliths at constant w/c ratio (0.40) the total amount of pollutant released increases with its initial content, and ranges from 15 to 35% with respect to it. By lowering w/c from 0.40 to 0.15 at constant o/c, the performances improved (<25% released). The microstructure of the hardened cement-clay pastes was characterized by quantitative X-ray diffraction (QXRD) and electronic microscopy (SEM-EDS) techniques; hydration degree was estimated by means of thermogravimetric analysis (TGA) in addition to QXRD. No evidence of any chemical reaction between 2-CA and cement phases was found. Moreover, it was shown that the most important factors affecting the cement hydration process were the total water content, i.e. the one taking also into account the water contained in the wet polluted clay, and the amount of 2-CA not firmly sorbed by the organoclay, and then freely dispersed in the paste.     

Temporary stabilization of air pollution control residues using carbonation

Carbonation presents a good prospect for stabilizing alkaline waste materials. The risk of metal leaching from carbonated waste was investigated in the present study; in particular, the effect of the carbonation process and leachate pH on the leaching toxicity of the alkaline air pollution control (APC) residues from municipal solid waste incinerator was evaluated. The pH varying test was conducted to characterize the leaching characteristics of the raw and carbonated residue over a broad range of pH. Partial least square modeling and thermodynamic modeling using Visual MINTEQ were applied to highlight the significant process parameters that controlled metal leaching from the carbonated residue. By lowering the pH to 8-11, the carbonation process reduced markedly the leaching toxicity of the alkaline APC residue; however, the treated APC residue showed similar potential risk of heavy metal release as the raw ash when subjected to an acid shock. The carbonated waste could, thereby, not be disposed of safely. Nonetheless, carbonation could be applied as a temporary stabilization process for heavy metals in APC residues in order to reduce the leaching risk during its transportation and storage before final disposal.     

锑污染土壤固化-稳定化的影响因素

通过比较不同稳定剂、固化剂、土壤pH条件下土壤中重金属锑的修复效果,研究了锑的固化-稳定化影响因素并探讨了相关稳定化机理.实验结果表明:铁基稳定剂的效果明显优于磷酸二氢钾和腐殖酸钠,而零价铁的稳定化效果更优于硫酸铁和硫酸亚铁,较适宜的稳定剂投加量为5％(w);水泥做固化剂对锑的稳定化效果优于氧化钙,最佳投加量为5％(w...     

Monitoring the stabilization of municipal solid waste incineration fly ash by phosphation: mineralogical and balance approach

The application of a micro-characterization protocol coupled with a balance approach has allowed the relevant monitoring of a phosphation process for fly ash produced by municipal solid waste incineration. The three main steps of this process consist in removing the salts (chlorides, sulfates) by dissolution at basic pH, phosphation of the residue to trap metals, and its calcination to destroy dioxin-like compounds. The chemical and mineralogical balances compiled on the samples after each step of the process validate these main objectives and highlight the wide phosphorus distribution throughout the sample during the phosphation process, as well as the formation of apatite-type crystallized phosphates. During calcination, the increase in the proportion of crystallized phosphates apatite and whitlockite is largely attributable to the presence of an available calcium source, corresponding to the calcite formed during washing. The metals Pb and Zn, initially distributed in the silicate and carbonate phases, are broadly redistributed in the phosphate neoformations after carbonate dissolution, thus guaranteeing a more permanent stabilization.     

Calcium phosphate stabilization of fly ash with chloride extraction

Municipal solid waste incinerator by products include fly ash and air pollution control residues. In order to transform these incinerator wastes into reusable mineral species, soluble alkali chlorides must be separated and toxic trace elements must be stabilized in insoluble form. We show that alkali chlorides can be extracted efficiently in an aqueous extraction step combining a calcium phosphate gel precipitation. In such a process, sodium and potassium chlorides are obtained free from calcium salts, and the trace metal ions are immobilized in the calcium phosphate matrix. Moderate calcination of the chemically treated fly ash leads to the formation of cristalline hydroxylapatite. Fly ash spiked with copper ions and treated by this process shows improved stability of metal ions. Leaching tests with water or EDTA reveal a significant drop in metal ion dissolution. Hydroxylapatite may trap toxic metals and also prevent their evaporation during thermal treatments. Incinerator fly ash together with air pollution control residues, treated by the combined chloride extraction and hydroxylapatite formation process may be considered safe to use as a mineral filler in value added products such as road base or cement blocks.     

Laboratory stabilization/solidification of surrogate and actual mixed-waste sludge in glass and grout

Grout and glass formulations were developed for the stabilization of highly radioactive tank sludges. These formulations were tested in the laboratory with a surrogate and with a sample of an actual mixed waste tank sludge. The grout formulation was tested at wet-sludge loadings of 50–60 wt%, giving a volume increase of about 40–50 vol%. Dried sludge was vitrified into glass at waste oxide loadings of 40–50 wt%, giving a volume decrease of about 50–60 vol%. The Resource Conservation and Recovery Act (RCRA) metals included in surrogate testing were Ag, Ba, Cd, Cr, Ni, Pb, Se, Tl and Hg. Since vitrification would volatilize, not stabilize mercury, it was not included in the surrogates vitrified. The actual sludge sample was only characteristically hazardous for mercury by the toxic characteristic leaching procedure (TCLP) but exceeded the Universal Treatment Standard (UTS) limit for chromium. The grout and glass formulations stabilized these RCRA metals within UTS limits. In addition, a grout leachability index of about 9–10 was measured for both ⁸⁵Sr and ¹³⁷Cs, meeting the recommended requirement of >6. The glass leachability index was estimated to be >18 for cold cesium and strontium.     

Decomposition of hazardous organic materials in the solidification/stabilization process using catalytic-activated carbon

The application of a catalytic-activated carbon to the solidification/stabilization (S/S) process for immobilization of phenol and 2-chlorophenol and catalytic decomposition was investigated. The effect of the catalytic-activated carbon, in amounts of 0.25-1% (by dry sand wt.), on the leaching of phenol and 2-chlorophenol was studied. H2O2 was added as a source of oxygen in the amounts of 1 or 5%, with respect to liquid solution weight. Toxicity characteristic leaching procedure (TCLP) leaching tests showed that adding the catalytic-activated carbon to the S/S matrix significantly reduced the leachability of both phenol and 2-chlorophenol. Only trace amounts of phenol were found in the leaching solution, while the concentration of 2-chlorophenol was below the detection limit of the gas chromatography (GC). Without addition of the catalytic-activated carbon, 87% of the phenol and 92% of the 2-chlorophenol leached. Additional tests on TCLP leachate solutions using GC-mass spectrometry indicated the existence of simple, less hazardous, hydrocarbons, including alcohol. Catalytic-activated carbons treated with phenol in the presence of H2O2 were also analyzed using time of flight-secondary ion mass spectroscopy (TOF-SIMS). Results indicate that the phenol aromatic ring was broken by the catalytic reaction.     

Matrix stability and leaching behaviour in ettringite-based stabilization systems doped with heavy metals

A stabilizing matrix able to generate ettringite from calcium sulphoaluminate in the presence of CaSO₄·2H₂O and Ca(OH)₂ has been studied. Ten series of stabilized samples have been produced, each containing 10% of one of the following heavy metal salts: Cd(NO₃)₂, Cr(NO₃)₃ Cu(NO₃)₂, Fe(NO₃)₃, Mn(NO₃)₃, Ni(NO₃)₂, Pb(NO₃)₂, Zn(NO₃)₂, K₂CrO₄ and K₂MoO₄. The study has been directed towards the matrix stability and metal release behaviour in three different dynamic leaching tests carried out with the following media: distilled water, pH 4 HNO₃ solution and pH 4.74 acetic acid/sodium acetate buffer solution. It has been found that the matrix stability and leaching behaviour strongly depend on the nature of the dopant salt, as well as on the nature of the leaching medium. In many cases the leaching medium attack causes disaggregation of the matrix but this does not imply complete dissolution of the dopant metal. When the leaching medium is the acetate buffer the chemical resistance to dissolution increases as the physico-mechanical resistance to disgregation decreases. This apparently contradictory result has been explained in terms of microstructure of the stabilized samples.     

稳定化技术在铅砷复合污染土壤修复中的应用

以铅砷复合污染土壤为研究对象,采用硫酸亚铁和氧化钙作为稳定剂,通过正交实验得出各因素对土壤中铅的稳定率影响程度的大小顺序为:氧化钙添加量>硫酸亚铁添加量=养护周期>两种稳定剂的交互作用.最佳实验条件为硫酸亚铁添加量2 g/kg,氧化钙添加量10 g/kg,养护时间2 d.添加硫酸亚铁后,土壤pH对砷的稳定化效果影响不大...