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.     

Accelerated carbonation of municipal solid waste incineration fly ashes

As a result of the EU Landfill Directive, the disposal of municipal solid waste incineration (MSWI) fly ash is restricted to only a few landfill sites in the UK. Alternative options for the management of fly ash, such as sintering, vitrification or stabilization/solidification, are either costly or not fully developed. In this paper an accelerated carbonation step is investigated for use with fly ash. The carbonation reaction involving fly ash was found to be optimum at a water/solid ratio of 0.3 under ambient temperature conditions. The study of ash mineralogy showed the disappearance of lime/portlandite/calcium chloride hydroxide and the formation of calcite as carbonation proceeded. The leaching properties of carbonated ash were examined. Release of soluble salts, such as SO4, Cl, was reduced after carbonation, but is still higher than the landfill acceptance limits for hazardous waste. It was also found that carbonation had a significant influence on lead leachability. The lead release from carbonated ash, with the exception of one of the fly ashes studied, was reduced by 2-3 orders of magnitude.     

Carbon dioxide utilization with carbonation using industrial waste-desulfurization gypsum and waste concrete

In this study, we propose a process making calcium carbonate and calcium sulfate and recovering absorbent using ammonia absorbent, carbon dioxide, and industrial waste. The main objective of this study is to confirm the possibility of carbon capture and utilization based on waste materials. We assumed desulfurization gypsum and construction waste (ready mixed concrete washing water, waste concrete, etc.) are CaSO₄, Ca(OH)₂, respectively. And concentration of simulated carbon dioxide gas was 15 vol% similar to flue gas. Calcium carbonate was produced by combination reaction between ionic CO₂ in absorbent and metal ion in the solid waste. Experiments were conducted at normal temperature and pressure. Furthermore, the generated products were characterized by X-ray diffraction, and scanning electron microscope.     

Polyethylene conversion by partial oxidation in supercritical water

This paper gives the results of partial oxidation experiments of polyethylene (PE) in supercritical water (SCW). The experiments were carried out at a reaction temperature of 693K and a reaction time of 30 min using 6 cm³ of a batch-type reactor. The loaded sample weight was 0.3 g and there was 2.52 g water (0.42 g/cm³). The ratio of oxygen atoms to carbon atoms was 0.3. The results show a significant CO formation in O₂–SCW, and the 1-alkene/n-alkane ratio in partial oxidation was higher than that in SCW pyrolysis. These results suggest the possibility of the hydrogenation of hydrocarbon through partial oxidation followed by a water–gas shift reaction. Received: July 19, 2000 / Accepted: September 28, 2000     

Fundamental processes and implications during in situ aeration of old landfills

Results of investigations from many old landfills in Germany and Europe indicate that significant emissions occur under conventional landfill operating conditions (i.e., anaerobic conditions). Significant emissions via the gas phase are predicted to last at least three decades after landfill closure, while leachate emissions are predicted to continue for many decades, potentially even lasting for centuries. When considering the specific type and quality, and quite often lack of, protection barriers associated with old landfills, these leachate and gas emissions may result in a significant negative impact on the environment. However, complete sealing of the landfill only temporarily reduces emissions because dry-conservation of the biodegradable waste fraction results, thus not allowing any severe reduction in the emission and hazardous potential of the landfill to occur. If noticeable damage of the surface capping system occurred in these landfills, infiltrating water would restart the interrupted emission formation. In contrast, aerobic in situ stabilization by means of low pressure aeration attempts to stabilize and modify the inventory of organic matter inside the landfill, acting to reduce the emission potential in a more sustainable manner. By enabling faster and more extensive aerobic degradation processes in the landfill (compared with anaerobic processes), the organics (e.g., hydrocarbons) are degraded significantly faster, resulting in an increased carbon discharge via the gas phase, as well as reduced leachate concentrations. Because carbon dioxide (CO(2)) is the main compound in the extracted off-gas (instead of methane (CH(4)), which dominated under anaerobic landfill conditions), the negative impact of diffuse LFG emissions towards an increased global warming effect may be significantly lowered. With respect to leachate quality, a reduction of organic compounds as well as ammonia-nitrogen can be expected. In addition to these positive ecological effects, aerobic in situ stabilization is associated with significant cost savings potential due to both quantitative and qualitative reductions in the aftercare period. This paper describes the fundamental processes and implications of in situ landfill aeration. Additionally, possible criteria for defining an endpoint of the active aeration process are presented and discussed.     

Effect of unburned carbon on lead, zinc, and copper recovery from molten fly ash by chloride-induced volatilization

The present work focuses on investigation of the effective recovery of heavy metals from molten fly ash by applying chloride-induced volatilization. In particular, the effect of unburned carbon on the chloride-induced volatilization of lead, zinc, and copper from model and real molten fly ashes was investigated in the temperature range 873–1173 K under a N₂ atmosphere. As a result, almost 100% of lead and a significant proportion of zinc were volatilized from the real molten fly ash samples at 1173 K. In contrast, for the model fly ash, volatilization ratios of lead and zinc at 1173 K were only 85% and 25%, respectively. Further, the results of X-ray diffraction analysis suggested that PbO in molten fly ash was converted either to Pb₂OCl₂ or Pb by respective chlorination and reduction reactions. Meanwhile ZnO and CuO in the molten fly ash were reduced to Zn and Cu by reaction with unburned carbon. Subsequently, Pb, Zn, and Pb₂OCl₂ were volatilized, but Cu remained in the solid residue. Finally, the volatilization ratio of zinc increased with the addition of carbon, and more than 98% of zinc was volatilized at 1173 K from a fly ash with a carbon content of 20%.     

钙基固定剂对制氢和污染性气体减排的影响

在未来相当长的一段时间内,煤气化仍是大规模制取氢气的主要途径。目前,常规煤气化过程得到的是H2、CO和CO2为主的混合气,需要通过净化、变换和分离工艺才能得到洁净的氢气,工艺过程复杂。采用连续式超临界水反应装置,以质量分数为20%的水煤浆为反应原料,考察了Ca/C摩尔比和温度对褐煤制氢系统的影响。试验结果表明：Ca（OH）2不仅可以很好地固定气相中的CO2和硫化物,而且对煤气化过程也表现出较好的催化作用。反应温度600℃,压力为25MPa的条件下,与未加Ca（OH）2相比,Ca/C摩尔比为0.45时,气体中CO2的体积分数由50.7%降至1.0%,趋于完全固定;硫化物浓度由10 878mg/m3降至807mg/m3;H2的体积分数由32.4%增至73.3%。Ca（OH）2对煤气化的催化作用在高温下更加明显。     

超临界二氧化碳萃取再生吸苯活性炭的研究

以工业废水中的典型污染物苯作为单一吸附质,进行了超临界二氧化碳萃取再生活性炭研究,探讨了操作温度、操作压力、CO2流速、活性炭粒度、循环再生次数等因素对再生效率及再生速率的影响。试验结果表明,超临界CO2对活性炭中的苯具有良好的再生效果。     

Reducing volatilization of heavy metals in phosphate-pretreated municipal solid waste incineration fly ash by forming pyromorphite-like minerals

This research investigated the feasibility of reducing volatilization of heavy metals (lead, zinc and cadmium) in municipal solid waste incineration (MSWI) fly ash by forming pyromorphite-like minerals via phosphate pre-treatment. To evaluate the evaporation characteristics of three heavy metals from phosphate-pretreated MSWI fly ash, volatilization tests have been performed by means of a dedicated apparatus in the 100-1000 °C range. The toxicity characteristic leaching procedure (TCLP) test and BCR sequential extraction procedure were applied to assess phosphate stabilization process. The results showed that the volatilization behavior in phosphate-pretreated MSWI fly ash could be reduced effectively. Pyromorphite-like minerals formed in phosphate-pretreated MSWI fly ash were mainly responsible for the volatilization reduction of heavy metals in MSWI fly ash at higher temperature, due to their chemical fixation and thermal stabilization for heavy metals. The stabilization effects were encouraging for the potential reuse of MSWI fly ash.     

光催化还原CO2的研究进展

介绍了多种将CO2转化为化工产品的光催化还原体系,包括TiO2体系、金属修饰的TiO2体系、有机光敏化剂修饰的TiO2体系和其他光敏半导体材料体系.评述了不同光催化体系的特点及其催化性能.讨论了光源波长、反应温度、CO2压力和浓度、H2O和CO2摩尔比等实验条件对反应产物种类及其产量的影响,指出催化剂的活性、光源波长和...     

A kinetic analysis of solid waste composting at optimal conditions

Six municipal solid waste (MSW) and yard waste components (food waste, mixed paper, yard waste, leaves, branches, grass clippings) were aerobically decomposed to measure the extent of decomposition under near optimal conditions. Decomposition was characterized by at least two principal stages, for most components, as was indicated by the carbon dioxide production rates. An aerobic biodegradation conceptual model is presented here based on the principle that solids hydrolysis is the rate-limiting step during solid waste composting. The mineralizable solid carbon of each solid waste component was assumed to comprise the readily, the moderately and the slowly (or refractory) hydrolysable carbons, each hydrolyzing at different rates to aqueous (water soluble) carbon. Aqueous carbon mineralizes to CO2 at rapid rates that are not rate-limiting to the process. Solids hydrolysis rate constants were calculated after fitting the experimentally determined carbon dioxide production rate data to model results. Hydrolysis rates for the readily hydrolysable carbon in all components ranged from approximately 0.06 to 0.1 d(-1); hydrolysis rates for the moderately hydrolysable carbon ranged from 0.005 to 0.06 d(-1). Leaves, branches and grass clippings did not have a readily hydrolysable carbon fraction, whilst the leaves and branches had the largest slowly hydrolysable carbon fractions (70%, 82%, respectively, of the total solid organic carbon). Grass and yard waste did not contain slowly hydrolysable carbon fractions. Food waste had the largest readily hydrolysable carbon fraction and produced the highest amount of CO2 among all substrates. Moderately hydrolysable solid carbon fractions ranged from 16% to 90% of the total solid organic carbon for all substrates used.     

利用盐泥制取轻质氧化镁

采用二氧化碳法提取盐泥中的镁，研究了使之转化为轻质氧化镁的影响因素以及主要反应的动力学性质。实验确定的最佳条件为固液比1∶15、二氧化碳通入时间90min、水解温度90℃、水解时间25min，在此条件下，盐泥中镁的总提取率为75%;采用微分法求得氢氧化镁与二氧化碳反应的反应级数和活化能分别为1.7和68.1kJ/mol。     

加压酸浸法提取粉煤灰中的Al2O3和Fe2O3

采用加压酸浸法提取粉煤灰中的A12O3和Fe2O3.实验研究了粉煤灰粒径、硫酸质量分数、反应时间、反应温度对粉煤灰中Al2O3和Fe2O3浸取率的影响,并通过SEM对粉煤灰酸浸前后的形貌进行了分析.实验结果表明,当粉煤灰粒径为75μm、硫酸质量分数为50％、反应温度为180℃、反应时间为4h时,粉煤灰中的Al2O3浸取率可达82.4％,Fe2O3浸取率为76.1％,经酸浸后粉煤灰的剩余率为72.4％.     

Gasification and its emission characteristics for dried sewage sludge utilizing a fluidized bed gasifier

Various research has attempted to determine the proper treatment of sewage sludge, including thermal technologies. Efficient thermal technologies have been focused on because of their energy saving/energy recovery. Gasification technology can be considered one of these approaches. In this study, the characteristics of gasification reactions were investigated with the aim of finding fundamental data for utilizing sewage sludge as an energy source. For the experiments on sewage sludge gasification reaction characteristics, a laboratory-scale experimental apparatus was set up with a fluidizing bed reactor of 70-mm inner diameter and 600-mm total height using an electric muffle furnace. The experimental materials were prepared from a sewage treatment plant located in Seoul. The reaction temperature was varied from 630 to 860°C, and the equivalence ratio from 0.1 to 0.3. The gas yields, compositions of product gas, and cold gas efficiencies of product gas were analyzed by GC/TCD and GC/FID installed with a carboxen-1000 column. The experimental results indicated that 800°C, ER 0.2 was an optimum condition for sewage sludge gasification. The maximum yield of product gas was about 44%. Producer gas from experiments was mainly composed of hydrogen, carbon monoxide, carbon dioxide, and methane. The cold gas efficiency of sewage sludge gasification was about 68%. The H₂/CO ratio and CO/CO₂ ratio were about 1.1 and 1.4, respectively, in optimum reaction conditions. Gaseous pollutants such as SO₂, HCl, NH₃, H₂S, and NO₂ were also analyzed at various gasification/combustion conditions, and their gaseous products were compared, showing significantly different oxidized product distributions.     

二氧化碳资源化技术研究进展

过量的二氧化碳(CO2)排放可导致温室效应的不断加剧,因此CO2减排受到越来越多的关注,其中将CO2转化为附加值较高的化工产品,即CO2资源化利用技术不仅可实现CO2减排,同时具有一定的经济效益。CO2资源化利用技术主要包括光化学还原法、电化学还原法和催化转移氢化法等。重点介绍并总结了以上3种方法的特点、优势和不足,指出未来需研究解决的关键问题和研究方向,为实现高效的CO2资源化利用提供借鉴和参考。     

Vacuum pyrolysis of waste tires with basic additives

Granules of waste tires were pyrolyzed under vacuum (3.5-10kPa) conditions, and the effects of temperature and basic additives (Na(2)CO(3), NaOH) on the properties of pyrolysis were thoroughly investigated. It was obvious that with or without basic additives, pyrolysis oil yield increased gradually to a maximum and subsequently decreased with a temperature increase from 450 degrees C to 600 degrees C, irrespective of the addition of basic additives to the reactor. The addition of NaOH facilitated pyrolysis dramatically, as a maximal pyrolysis oil yield of about 48wt% was achieved at 550 degrees C without the addition of basic additives, while a maximal pyrolysis oil yield of about 50wt% was achieved at 480 degrees C by adding 3wt% (w/w, powder/waste tire granules) of NaOH powder. The composition analysis of pyrolytic naphtha (i.b.p. (initial boiling point) approximately 205 degrees C) distilled from pyrolysis oil showed that more dl-limonene was obtained with basic additives and the maximal content of dl-limonene in pyrolysis oil was 12.39wt%, which is a valuable and widely-used fine chemical. However, no improvement in pyrolysis was observed with Na(2)CO(3) addition. Pyrolysis gas was mainly composed of H(2), CO, CH(4), CO(2), C(2)H(4) and C(2)H(6). Pyrolytic char had a surface area comparable to commercial carbon black, but its proportion of ash (above 11.5wt%) was much higher.     

Production of hydrogen by steam gasification of dehydrochlorinated poly(vinyl chloride) or activated carbon in the presence of various alkali compounds

Steam gasification of dehydrochlorinated poly(vinyl chloride) (PVC) or activated carbon was carried out in the presence of various alkali compounds at 3.0 MPa and 560°C–660°C in a batch reactor or in a semi-batch reactor with a flow of nitrogen and steam. Hydrogen and sodium carbonate were the main products, and methane and carbon dioxide were the minor products. Yields of hydrogen were high in the presence of sodium hydroxide and potassium hydroxide. The acceleration effect of the alkali compounds on the gasification reaction was as follows: KOH > NaOH > Ca(OH)₂ > Na₂CO₃. The rate of gasification increased with increasing partial steam pressure and NaOH/C molar ratio. However, the rate became saturated at a molar ratio of NaOH/C greater than 2.0.     

Catalytic detoxification of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in fly ash

An efficient catalytic detoxification method for polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in fly ash produced by municipal waste incinerator has been studied using palladium on carbon (Pd/C) catalyst. As one of the trace components in fly ash, the detoxification of PCDD/Fs is very difficult because of the interferences of other persistent components with higher concentrations. However, the detoxification reaction of PCDD/Fs shows higher activity in water/isopropanol solution using commercial Pd/C catalyst at 40 degrees C under normal pressure. The results indicated that the catalytic degradation of PCDFs has been found to be easier than that of PCDDs. Moreover, the dechlorination ratios were higher for octa- and hepta-chlorinated congeners than those for tetra- and penta-chlorinated ones. The detoxification process worked well in water. The dechlorination efficiencies of almost all of the PCDD/Fs congeners can reach over 99% within a shorter reaction time.     

Feasibility of a monitoring system for detecting changes in dioxin concentrations of both in flue gas and fly ash in incineration plants

Surrogate measurements should be low in cost and quick to perform. To examine its feasibility, continuous surrogate monitoring was performed using an organic halogen compound (OHC) analyzer. Surrogates for dioxins (DXNs) from waste incinerators were examined by changing the operating conditions such as the atomized volume of activated carbon added and the temperature at the inlet of the dust collector. OHCs were measured along with DXNs in flue gas at the inlet and the outlet of the dust collector of two waste incinerators over five runs; the fly ash was sampled at the same time. Although the final flue gas concentration of DXNs at the incineration plants was below the regulation criteria, this does not mean complete reduction of DXNs. In addition, the de novo synthesis of DXNs inside the dust collectors was studied by analyzing the mass balance for DXNs concentrations in flue gas and fly ash. Semivolatile chlorinated organic compound concentrations at the outlet of the bag filter were basically well correlated with DXNs levels at the inlet of the bag filter in the test runs. When advanced flue gas treatment is applied by using a bag filter and lime/activated carbon adsorbent, DXNs that may be generated during flue gas cooling processes move to the fly ash, and this amount determines the mass balance of the entire system. It may be useful to monitor surrogate organic halogens for detecting changes in DXN concentrations of both flue gas and fly ash in incineration plants.     

Bioremediation of contaminated soil and sediment by composting

There are many well‐established bioremediation technologies applied commercially at contaminated sites. One such technology is the use of compost material. Composting matrices and composts are rich sources of microorganisms, which can degrade contaminants to innocuous compounds such as carbon dioxide and water. In this article, composting of contaminated soil and sediment was performed on a laboratory bench‐scale pile. Fertilizer was added to increase the nutrient content, and the addition of commercial compost provided a rich source of microorganisms. After maintaining proper composting conditions, the feasibility of composting was assessed by monitoring pH, total volatile solids, total microbial count, temperature, and organic contaminant concentration. The entire composting process occurred over a period of five weeks and resulted in the degradation of contaminants and production of compost with a high nutritional content that could be further used as inocula for the treatment of hazardous waste sites. © 2006 Wiley Periodicals, Inc.