Comparisons of four categories of waste recycling in China's paper industry based on physical input-output life-cycle assessment model

Waste recycling for paper production is an important component of waste management. This study constructs a physical input-output life-cycle assessment (PIO-LCA) model. The PIO-LCA model is used to investigate environmental impacts of four categories of waste recycling in China’s paper industry: crop straws, bagasse, textile wastes and scrap paper. Crop straw recycling and wood utilization for paper production have small total intensity of environmental impacts. Moreover, environmental impacts reduction of crop straw recycling and wood utilization benefits the most from technology development. Thus, using crop straws and wood (including wood wastes) for paper production should be promoted. Technology development has small effects on environmental impacts reduction of bagasse recycling, textile waste recycling and scrap paper recycling. In addition, bagasse recycling and textile waste recycling have big total intensity of environmental impacts. Thus, the development of bagasse recycling and textile waste recycling should be properly limited. Other pathways for reusing bagasse and textile wastes should be explored and evaluated. Moreover, imports of scrap paper should be encouraged to reduce large indirect impacts of scrap paper recycling on domestic environment.     

浅谈粉煤灰的资源化利用现状

粉煤灰是电力行业排放的主要固体废弃物,对其的资源化利用已成为环保的首要任务。对粉煤灰进行高附加值的资源化回收利用,是实现可持续发展的必经之路。介绍了大唐国际成功开发研制的从高铝粉煤灰中提取氧化铝技术,开辟了粉煤灰综合利用的新途径。     

国内城市生活垃圾焚烧飞灰研究现状及进展

随着我国经济快速发展及城市化水平提升,城市生活垃圾产量越来越大,焚烧逐渐成为城市生活垃圾处理的主要方式.但焚烧会产生大量的垃圾焚烧飞灰(以下简称飞灰),飞灰属于危险废物.论述了飞灰的来源、成分、特性及危害,介绍了飞灰的处理处置技术:水泥固化技术、化学药剂稳定化技术、熔融固化技术、水热稳定化技术和水泥窑协同处理技术,并分...     

Bio-processing of solid wastes and secondary resources for metal extraction - A review

Metal containing wastes/byproducts of various industries, used consumer goods, and municipal waste are potential pollutants, if not treated properly. They may also be important secondary resources if processed in eco-friendly manner for secured supply of contained metals/materials. Bio-extraction of metals from such resources with microbes such as bacteria, fungi and archaea is being increasingly explored to meet the twin objectives of resource recycling and pollution mitigation. This review focuses on the bio-processing of solid wastes/byproducts of metallurgical and manufacturing industries, chemical/petrochemical plants, electroplating and tanning units, besides sewage sludge and fly ash of municipal incinerators, electronic wastes (e-wastes/PCBs), used batteries, etc. An assessment has been made to quantify the wastes generated and its compositions, microbes used, metal leaching efficiency etc. Processing of certain effluents and wastewaters comprising of metals is also included in brief. Future directions of research are highlighted.     

Neutralization of an extremely acidic sludge and stabilization of heavy metals in flyash aggregates

An extremely acidic, heavy metal-rich sludge (pH=-1.2) was scrubbed with a Class-F fly ash in order to simultaneously neutralize the acidity and stabilize the heavy metals contained in both wastes. This paper outlines the leaching behavior of the aggregate material generated by scrubbing. For proper fly ash/sludge ratios, the fly ash acted as an outstanding neutralizer for the acidic waste. Leaching of heavy metals from the aggregate samples was below the environmental limits within a pH range between 3 and 9. Subsequent washing of the leached aggregate with acidic CALWET solutions did not result in an additional release of heavy metals. It is proposed that coordinative bonding of the metal cations onto neutral surface sites and electrostatic adsorption led to stabilization of the heavy metals within the aggregate structure below hydrolysis pHs.     

Evaluation of environmental impacts of food waste management by material flow analysis (MFA) and life cycle assessment (LCA)

This paper focuses on the evaluation of potential environmental impacts of food waste management practices by material flow analysis (MFA) and life cycle assessment (LCA) during different life cycle stages toward the environmentally sustainable options for Daejeon Metropolitan City (DMC) in Korea. The MFA and LCA studies were conducted to examine different recycling facilities of food waste. The results of the LCA study indicate that, among the different recycling methodologies currently in practice in DMC, Scenario 4 (wet and dry feed site) conduced to higher global warming potential (GWP) and higher acidification potential (AP), whereas Scenarios 2 (wet feed site 1) and 3 (wet feed site 2) resulted in the lowest impact. This is mainly due to the emission caused during the treatment stage. For eutrophication potential (EP), Scenario 1 (composting site) contributed to higher environmental impacts due to the emission of ammonia generated during the treatment process, while in case of photochemical ozone creation potential (POCP), the collection stage for all recycling facilities led to higher impacts to the environment due to the combustion of fossil fuels. This study indicates that the proper disposal of the final residues, such as solid sludge and screened materials, could aid in reducing environmental burdens.     

Estimation of residual MSW heating value as a function of waste component recycling

Recycling of packaging wastes may be compatible with incineration within integrated waste management systems. To study this, a mathematical model is presented to calculate the fraction composition of residual municipal solid waste (MSW) only as a function of the MSW fraction composition at source and recycling fractions of the different waste materials. The application of the model to the Lisbon region yielded results showing that the residual waste fraction composition depends both on the packaging wastes fraction at source and on the ratio between that fraction and the fraction of the same material, packaging and non-packaging, at source. This behaviour determines the variation of the residual waste LHV. For 100% of paper packaging recycling, LHV reduces 4.2% whereas this reduction is of 14.4% for 100% of packaging plastics recycling. For 100% of food waste recovery, LHV increases 36.8% due to the moisture fraction reduction of the residual waste. Additionally the results evidence that the negative impact of recycling paper and plastic packaging on the LHV may be compensated by recycling food waste and glass and metal packaging. This makes packaging materials recycling and food waste recovery compatible strategies with incineration within integrated waste management systems.     

A goal-oriented characterization of urban waste

More stringent requirements for the protection of the environment coupled with new incentives for materials recovery, lead modern waste management practice on the line of a more differentiated approach. Separation, or more precisely, non-mixing at the source, is one of the most promising strategies. However, before deciding which categories of urban waste should be collected separately, it is useful to have more detailed knowledge regarding the characteristics of waste. A 5-year investigation has produced enough information to answer such questions as “if one decides to convert food and garden waste to compost instead of burning them, how much less cadmium would be released into the atmosphere?” or, “if the quantities of mercury released into the environment should be drastically reduced, which categories of waste should be collected and treated separately?” This paper discusses sampling and analytical techniques and defines what is a representative sample. It presents the methods applied to determine the annual flow of various chemical elements from 52 waste categories from a European urban area. The results determined through this approach are compared to the total outputs in the gas, wastewater, cinders and fly ashes of the incinerator which currently burns these wastes.     

Hydrological performance of MSW incineration residues and MSW co-disposed with sludge in full-scale cells

Water flows were analysed for the filling phase and the first 4 years after closure of two types of full-scale landfill cells: 'special cells' containing mostly fly ash from municipal solid waste (MSW) incineration disposed with other special/hazardous waste, and 'biocells' (biological cells) containing co-disposed MSW and food industry sludge. The landfill cells were constructed about -1.5 m above sea level (masl) at Lomma Bay, southern Sweden. The hydrological effects of water intrusion into the special cells from surroundings and sludge moisture within the biocells were studied. HELP modelling of hydrological processes predicted delay in peaks of leachate generation from uncovered special cells following rain, which was not confirmed. Faster leachate production as a response to rainfall from special cells than from biocells was observed. It was inferred that special waste has more intensive channelling, lower water absorption and higher hydraulic conductivity than mixtures of sludge/MSW. To avoid convergence problems in modelling uncovered special cells, the use of a 5 cm deep top layer with saturated hydraulic conductivity 1.7 x 10(-3) cm s(-1), porosity 0.437, and field capacity 0.105, is suggested.     

Possibility of using waste tire rubber and fly ash with Portland cement as construction materials

The growing amount of waste rubber produced from used tires has resulted in an environmental problem. Recycling waste tires has been widely studied for the last 20 years in applications such as asphalt pavement, waterproofing systems and membrane liners. The aim of this study is to evaluate the feasibility of utilizing fly ash and rubber waste with Portland cement as a composite material for masonry applications. Class C fly ash and waste automobile tires in three different sizes were used with Portland cement. Compressive and flexural strength, dry unit weight and water absorption tests were performed on the composite specimens containing waste tire rubber. The compressive strength decreased by increasing the rubber content while increased by increasing the fly ash content for all curing periods. This trend is slightly influenced by particle size. For flexural strength, the specimens with waste tire rubber showed higher values than the control mix probably due to the effect of rubber fibers. The dry unit weight of all specimens decreased with increasing rubber content, which can be explained by the low specific gravity of rubber particles. Water absorption decreased slightly with the increase in rubber particles size. These composite materials containing 10% Portland cement, 70% and 60% fly ash and 20% and 30% tire rubber particles have sufficient strength for masonry applications.     

Quantitative mineralogical composition of complex mineral wastes – Contribution of the Rietveld method

The objective of the work presented in this paper is the quantitative determination of the mineral composition of two complex mineral wastes: a sewage sludge ash (SSA) and a municipal solid waste incineration fly ash (MSWIFA). The mineral compositions were determined by two different methods: the first based on calculation using the qualitative mineralogical composition of the waste combined with physicochemical analyses; the second the Rietveld method, which uses only X-ray diffraction patterns. The results obtained are coherent, showing that it is possible to quantify the mineral compositions of complex mineral waste with such methods.The apparent simplicity of the Rietveld method (due principally to the availability of software packages implementing the method) facilitates its use. However, care should be taken since the crystal structure analysis based on powder diffraction data needs experience and a thorough understanding of crystallography. So the use of another, complementary, method such as the first one used in this study, may sometimes be needed to confirm the results.     

Assessment of mobility and bioavailability of contaminants in MSW incineration ash with aquatic and terrestrial bioassays

Incineration of municipal solid waste (MSW) is a waste treatment method which can be sustainable in terms of waste volume reduction as well as a source of renewable energy. In the process fly and bottom ash is generated as a waste material. The ash residue may vary greatly in composition depending on the type of waste incinerated and it can contain elevated levels of harmful contaminants such as heavy metals. In this study, the ecotoxicity of a weathered, untreated incineration bottom ash was characterized as defined by the H14 criterion of the EU Waste Framework Directive by means of an elemental analysis, leaching tests followed by a chemical analysis and a combination of aquatic and solid-phase bioassays. The experiments were conducted to assess the mobility and bioavailability of ash contaminants. A combination of aquatic and terrestrial bioassays was used to determine potentially adverse acute effects of exposure to the solid ash and aqueous ash leachates. The results from the study showed that the bottom ash from a municipal waste incineration plant in mid-Sweden contained levels of metals such as Cu, Pb and Zn, which exceeded the Swedish EPA limit values for inert wastes. The chemical analysis of the ash leachates showed high concentrations of particularly Cr. The leachate concentration of Cr exceeded the limit value for L/S 10 leaching for inert wastes. Filtration of leachates prior to analysis may have underestimated the leachability of complex-forming metals such as Cu and Pb. The germination test of solid ash and ash leachates using T. repens showed a higher inhibition of seedling emergence of seeds exposed to the solid ash than the seeds exposed to ash leachates. This indicated a relatively low mobility of toxicants from the solid ash into the leachates, although some metals exceeded the L/S 10 leaching limit values for inert wastes. The Microtox® toxicity test showed only a very low toxic response to the ash leachate exposure, while the D. magna immobility test showed a moderately high toxic effect of the ash leachates. Overall, the results from this study showed an ecotoxic effect of the solid MSW bottom ash and the corresponding ash leachates. The material may therefore pose an environmental risk if used in construction applications. However, as the testing of the solid ash was rather limited and the ash leachate showed an unusually high leaching of Cr, further assessments are required in order to conclusively characterize the bottom ash studied herein as hazardous according to the H14 criterion.     

An overview of metals recovery from thermal power plant solid wastes

Thermal power plants (TPPs) that burn fossil fuels emit several pollutants linked to the environmental problems of acid rain, urban ozone, and the possibility of global climate change. As coal is burned in a power plant, its noncombustible mineral content is partitioned into bottom ash, which remains in the furnace, and fly ash, which rises with flue gases. Two other by-products of coal combustion air-pollution control technologies are flue gas desulfurization (FGD) wastes and fluidized-bed combustion (FBC) wastes. This paper analyzed and summarized the generation, characteristics and application of TPP solid wastes and discussed the potential effects of such solid wastes on the environment. On this basis, a review of a number of methods for recovery of metals from TPP solid wastes was made. They usually contain a quantity of valuable metals and they are actually a secondary resource of metals. By applying mineral processing technologies and hydrometallurgical and biohydrometallurgical processes, it is possible to recover metals such as Al, Ga, Ge, Ca, Cd, Fe, Hg, Mg, Na, Ni, Pb, Ra, Th, V, Zn, etc., from TPP solid wastes. Recovery of metals from such wastes and its utilization are important not only for saving metal resources, but also for protecting the environment.     

Optimal design for sustainable development of a material recovery facility in a fast-growing urban setting

Installing material recovery facilities (MRFs) in a solid waste management system could be a feasible alternative to achieve sustainable development goals in urban areas if current household and curbside recycling cannot prove successful in the long run. This paper addresses the optimal site selection and capacity planning for a MRF in conjunction with an optimal shipping strategy of solid waste streams in a multi-district urban region. Screening of material recovery and disposal capacity alternatives can be achieved in terms of economic feasibility, technology limitation, recycling potential, and site availability. The optimization objectives include economic impacts characterized by recycling income and cost components for waste management, while the constraint set consists of mass balance, capacity limitation, recycling limitation, scale economy, conditionality, and relevant screening constraints. A case study for the City of San Antonio, Texas (USA) presents a vivid example where scenario planning demonstrates the robustness and flexibility of this modeling analysis. It proves especially useful when determining MRF ownership structure. Each scenario experiences two case settings: (1) two MRF sites are proposed for selection and (2) a single MRF site is sought. Cost analysis confirms processing fees are not the driving force in the City's operation, but rather shipping cost. Sensitivity analysis solidifies the notion that significant public participation plays the most important role in minimizing solid waste management expenses.     

粉煤灰综合利用研究进展

介绍了粉煤灰的物理化学性质。综述了粉煤灰在建材制造、建筑工程、道路工程、农业、废水处理和催化反应中的应用现状以厦未来的应用前景。     

Assessment and analysis of industrial liquid waste and sludge disposal at unlined landfill sites in arid climate

Municipal solid waste disposal sites in arid countries such as Kuwait receive various types of waste materials like sewage sludge, chemical waste and other debris. Large amounts of leachate are expected to be generated due to the improper disposal of industrial wastewater, sewage sludge and chemical wastes with municipal solid waste at landfill sites even though the rainwater is scarce. Almost 95% of all solid waste generated in Kuwait during the last 10 years was dumped in five unlined landfills. The sites accepting liquid waste consist of old sand quarries that do not follow any specific engineering guidelines. With the current practice, contamination of the ground water table is possible due to the close location of the water table beneath the bottom of the waste disposal sites. This study determined the percentage of industrial liquid waste and sludge of the total waste dumped at the landfill sites, analyzed the chemical characteristics of liquid waste stream and contaminated water at disposal sites, and finally evaluated the possible risk posed by the continuous dumping of such wastes at the unlined landfills. Statistical analysis has been performed on the disposal and characterization of industrial wastewater and sludge at five active landfill sites. The chemical analysis shows that all the industrial wastes and sludge have high concentrations of COD, suspended solids, and heavy metals. Results show that from 1993 to 2000, 5.14+/-1.13 million t of total wastes were disposed per year in all active landfill sites in Kuwait. The share of industrial liquid and sludge waste was 1.85+/-0.19 million t representing 37.22+/-6.85% of total waste disposed in all landfill sites. Such wastes contribute to landfill leachate which pollutes groundwater and may enter the food chain causing adverse health effects. Lined evaporation ponds are suggested as an economical and safe solution for industrial wastewater and sludge disposal in the arid climate of Kuwait.     

Prediction of unconfined compressive strength of cement paste containing industrial wastes

Neural network analysis was used to construct models of unconfined compressive strength (UCS) as a function of mix composition using existing data from literature studies of Portland cement containing real industrial wastes. The models were able to represent the known non-linear dependency of UCS on curing time and water content, and generalised from the literature data to find relationships between UCS and quantities of five waste types. Substantial decreases in UCS were caused by all wastes; except for EAF dust, the effect was nonlinear with the greatest decrease caused initially by approx. 12% plating sludge, 40% foundry dust, 58% other ash, and 72% MSWI fly ash by mass of dry product. It appears that the maximum waste additions used in modelling may approximate the practical limits of waste additions used in modelling may approximate the practical limits of waste addition to Portland cement, i.e., 50% plating sludge or EAF dust, 64% foundry dust, 92% other ash, and 85% MSWI fly ash by mass of dry product. The laboratory was found to be a key predictive variable and acted as a surrogate for laboratory-specific variables related to cement composition, strength and hardening class, product mixing and preparation details, laboratory conditions, and testing details. While the neural network modelling approach has been shown to be feasible, development of better models would require larger data sets with more complete information regarding laboratory-specific variables and waste composition.     

Recycling MSWI bottom and fly ash as raw materials for Portland cement

Municipal solid waste incineration (MSWI) ash is rich in heavy metals and salts. The disposal of MSWI ash without proper treatment may cause serious environmental problems. Recently, the local cement industry in Taiwan has played an important role in the management of solid wastes because it can utilize various kinds of wastes as either fuels or raw materials. The objective of this study is to assess the possibility of MSWI ash reuse as a raw material for cement production. The ash was first washed with water and acid to remove the chlorides, which could cause serious corrosion in the cement kiln. Various amounts of pre-washed ash were added to replace the clay component of the raw materials for cement production. The allowable limits of chloride in the fly ash and bottom ash were found to be 1.75% and 3.50% respectively. The results indicate that cement production can be a feasible alternative for MSWI ash management. It is also evident that the addition of either fly ash or bottom ash did not have any effect on the compressive strength of the clinker. Cement products conformed to the Chinese National Standard (CNS) of Type II Portland cement with one exception, the setting time of the clinker was much longer.     

Fly ash reinforced thermoplastic vulcanizates obtained from waste tire powder

Novel thermoplastic composites made from two major industrial and consumer wastes, fly ash and waste tire powder, have been developed. The effect of increasing fly ash loadings on performance characteristics such as tensile strength, thermal, dynamic mechanical and magnetic properties has been investigated. The morphology of the blends shows that fly ash particles have more affinity and adhesion towards the rubbery phase when compared to the plastic phase. The fracture surface of the composites shows extensive debonding of fly ash particles. Thermal analysis of the composites shows a progressive increase in activation energy with increase in fly ash loadings. Additionally, morphological studies of the ash residue after 90% thermal degradation shows extensive changes occurring in both the polymer and filler phases. The processing ability of the thermoplastics has been carried out in a Monsanto processability testing machine as a function of shear rate and temperature. Shear thinning behavior, typical of particulate polymer systems, has been observed irrespective of the testing temperatures. Magnetic properties and percolation behavior of the composites have also been evaluated.     

Investigation of hydrogen generation from municipal solid waste incineration fly ash

Hydrogen generation from municipal solid waste incineration fly ash was investigated to understand the influences of contacting method, kinds of contact solution, liquid to solid ratio, and particle size distribution of materials. Redox properties of materials and hydrogen generation were also studied. The largest quantity of gas generated in contact with water was 29.1 ml/g-ash, most of which was hydrogen. Fluidized bed fly ash generated more gas than stoker fly ash. In order to calculate the hydrogen generation potential (the maximum quantity of gas generated in contact with water), a novel system using a Y-shaped test tube and NaOH was utilized. This method gives values which are related to the quantity of generated gas in contact with water. A relationship between the aluminum content and hydrogen generation potential was observed, especially for fluidized bed fly ash. The reducing potential of fluidized bed fly ash was higher than that of stoker fly ash. Only fluidized bed fly ash showed a positive correlation between aluminum content and reducing potential, and between reducing potential and hydrogen generation potential. These results suggest that fluidized bed fly ash contains more Al⁰ than stoker fly ash. Received: September 11, 1998 / Accepted: March 19, 1999