Safe Recycling Research Articles

The transformation sequence of cement–asbestos slates up to 1200 °C and safe recycling of the reaction product in stoneware tile mixtures

Cement–asbestos is the main asbestos containing material still found in most of the European countries such as Italy. Man- and weathering-induced degradation of the cement–asbestos slates makes them a source of dispersion of asbestos fibres and represents a priority cause of concern. This concern is the main prompt for the actual policy of abatement and disposal of asbestos containing materials in controlled wastes. An alternative solution to the disposal in dumping sites is the direct temperature-induced transformation of the cement–asbestos slates into non-hazardous mineral phases. This patented process avoids the stage of mechanical milling of the material before the treatment, which improves the reactivity of the materials but may be critical for the dispersion of asbestos fibres in working and life environment. For the first time, this paper reports the description of the reaction path taking place during the firing of cement–asbestos slates up to the complete transformation temperature, 1200 °C. The reaction sequence was investigated using different experimental techniques such as optical and electron microscopy, in situ and ex situ quali-quantitative X-ray powder diffraction. The understanding of the complex reaction path is of basic importance for the optimization of industrial heating processes leading to a safe recycling of the transformed product. For the recycling of asbestos containing materials, the Italian laws require that the product of the crystal chemical transformation of asbestos containing materials must be entirely asbestos-free, and should not contain more than 0.1 wt% fraction of the carcinogenic substances such as cristobalite. Moreover, if fibrous phases other than asbestos (with length to diameter ratio >3) are found, they must have a geometrical diameter larger than 3 μm. We have demonstrated that using an interplay of different experimental techniques, it is possible to safely verify the complete transformation of asbestos minerals in this temperature-induced process. The product of transformation of cement–asbestos (CATP) has a phase composition similar to that of a natural or a low temperature clinker with the exception of having a larger content of aluminium, iron and magnesium. This product can be safely recycled for the production of stoneware tile mixtures. The addition of 3–5 mass% of CATP does not bear significant variations to the standard parameters of white porcelain tile mixtures.

Safe Recycling of Sewage Sludge on Agricultural Land—Biowaste

More than 50 000 wastewater treatment plants are operating in the European Union, producing more than 7.9 million tons of dry solids per year. The amount of sewage sludge will continue to increase as the Urban Wastewater Treatment Directives continues to be implemented in the different member countries. It is now undeniable that various toxic organic compounds, such as surfactants, hydrocarbons and residues derived from plastics are found in sewage sludge. The BIOWASTE project, under the EU 5th framework programme, offers an integrated study of xenobiotics throughout sludge recycling, using a combination of complementary approaches such as biotechnology, eco-toxicology, plant toxicology, analytical chemistry, microbiology, mathematical modelling, life cycle costing and life cycle analysis. This paper presents an overview of the results as well as their implication on the current EU regulatory work in progress concerning sewage sludge application. Particularly, two major findings are here detailed: the isolation, characterization and use of anaerobic xenobiotic-degrading microorganisms, and the modelling of the fate and impact of xenobiotics on anaerobic digestion.

Chemical and Physical Properties of Dry Flue Gas Desulfurization Products

Beneficial and environmentally safe recycling of flue gas desulfurization (FGD) products requires detailed knowledge of their chemical and physical properties. We analyzed 59 dry FGD samples collected from 13 locations representing four major FGD scrubbing technologies. The chemistry of all samples was dominated by Ca, S, Al, Fe, and Si and strong preferential partitioning into the acid insoluble residue (i.e., coal ash residue) was observed for Al, Ba, Be, Cr, Fe, Li, K, Pb, Si, and V. Sulfur, Ca, and Mg occurred primarily in water- or acid-soluble forms associated with the sorbents or scrubber reaction products. Deionized water leachates (American Society for Testing and Materials [ASTM] method) and dilute acetic acid leachates (toxicity characteristic leaching procedure [TCLP] method) had mean pH values of >11.2 and high mean concentrations of S primarily as SO(2-)4 and Ca. Concentrations of Ag, As, Ba, Cd, Cr, Hg, Pb, and Se (except for ASTM Se in two samples) were below drinking water standards in both ASTM and TCLP leachates. Total toxicity equivalents (TEQ) of dioxins, for two FGD products used for mine reclamation, were 0.48 and 0.53 ng kg(-1). This was similar to the background level of the mine spoil (0.57 ng kg(-1)). The FGD materials were mostly uniform in particle size. Specific surface area (m2 g(-1)) was related to particle size and varied from 1.3 for bed ash to 9.5 for spray dryer material. Many of the chemical and physical properties of these FGD samples were associated with the quality of the coal rather than the combustion and SO2 scrubbing processes used.

Solid wastes management in sulphide mines: from waste characterisation to safe closure of disposal sites

Environmentally compatible Waste Management schemes employed by the European extractive industry for the development of new projects, and applied in operating sulphide mines, are presented in this study. Standard methodologies used to assess the geotechnical and geochemical properties of the solid wastes stemming from mining and processing of sulphidic metal ores are firstly given. Based on waste properties, the measures applied to ensure the environmentally safe recycling and disposal of sulphidic wastes are summarised. Emphasis is given on the novel techniques developed to effectively prevent and mitigate the acid drainage phenomenon from sulphidic mine wastes and tailings. Remediation measures taken to minimise the impact from waste disposal sites in the post‐closure period are described.

Recovery of aluminium, nickel–copper alloys and salts from spent fluorescent lamps

This study explores a combined pyro-hydrometallurgical method to recover pure aluminium, nickel–copper alloy(s), and some valuable salts from spent fluorescent lamps (SFLs). It also examines the safe recycling of clean glass tubes for the fluorescent lamp industry. Spent lamps were decapped under water containing 35% acetone to achieve safe capture of mercury vapour. Cleaned glass tubes, if broken, were cut using a rotating diamond disc to a standard shorter length. Aluminium and copper–nickel alloys in the separated metallic parts were recovered using suitable flux to decrease metal losses going to slag. Operation variables affecting the quality of the products and the extent of recovery with the suggested method were investigated. Results revealed that total loss in the glass tube recycling operation was 2% of the SFLs. Pure aluminium meeting standard specification DIN 1712 was recovered by melting at 800 °C under sodium chloride/carbon flux for 20 min. Standard nickel–copper alloys with less than 0.1% tin were prepared by melting at 1250 °C using a sodium borate/carbon flux. De-tinning of the molten nickel–copper alloy was carried out using oxygen gas. Tin in the slag as oxide was recovered by reduction using carbon or hydrogen gas at 650–700 °C. Different valuable chloride salts were also obtained in good quality. Further research is recommended on the thermodynamics of nickel–copper recovery, yttrium and europium recovery, and process economics.

The potential for disinfection of separated faecal matter by urea and by peracetic acid for hygienic nutrient recycling

No efficient, reliable, and scale independent disinfection methods for toilet waste are available today for safe recycling of plant nutrients. Therefore, two chemical treatment methods, addition of urea or of PAA (a quaternary mixture of 15% peracetic acid, 15% hydrogen peroxide and 30% acetic acid), were evaluated for disinfection of faecal matter. Degradation of the added urea resulted in 30 g of ammonia nitrogen per kilogram of treated matter and a pH increase to approximately 9.3. This produced an efficient disinfection of E. coli, Enterococcus spp., and Salmonella spp. within 3 weeks (>6log 10 reduction) and a reduction of the chemical resistant Salmonella typhimurium 28b phage, corresponding to a decimal reduction within 7.5 days. No viable Ascaris suum eggs were found after 50 days of treatment. No reduction of spore forming Clostridia spp. was observed. Urea treatment proved to be efficient for disinfection of source separated faecal matter in a scale independent method used for safe recycling of nutrients found in the faecal matter. PAA reduced all of the above indicator organisms within 12 h after application. For this faecal material, with a dry matter content of approximately 10%, an addition of 0.5–1% of PAA (active substance, corresponding to 3.3–6.7% of the Proxitane ® 15 used) was required before no viable organisms were found in the material. However, this was not tested for the A. suum. No viable spore-forming bacteria or phages were detected. A high rate of bacteria regrowth occurred at 0.15% dosage and 5 days of treatment. PAA is an efficient alternative for disinfection of separated faeces if a rapid treatment is needed.

Glass sand processing by oxalic acid leaching and photocatalytic effluent treatment

As part of an EC programme oxalic acid leaching technology has been studied on the pilot scale to reduce the iron content of the silica sand for use in the production of clear flat glass. Heated sulphuric acid is usually employed for this purpose causing environmental problems with neutralisation and discharge of leachate effluents. The primary advantage of using oxalic acids is in formation during leaching of soluble complexes (e.g., trisoxalatoiron(III) anions) which are both photochemically and microbiologically degradable. The paper outlines pilot scale operations which have been developed to prepare and leach sand in heaps or stirred tanks and to detoxify and utilise the effluents. These operations are unusual in applying a relatively expensive leach reagent at high solid—liquid ratio to remove surface deposits from a bulk industrial mineral, and to make use of sunlight and/or microbial activity to facilitate safe recycle or discharge of process water. Emphasis is placed on the photocatalytic processes employed, particularly the precipitation of crystalline iron(II) oxalate. Calcination of this oxalate is outlined as a possible route to added-value iron products.

Effect of radiation processing as an integral part of the safe recycling animal waste

Recycling animal waste as a feedstuff could have a considerable effect on reducing costs and solving some disposal problems. Although the technology of animal waste handling, treatment and disposal is available in many cases it is not adequate to guarantee a pathogen-free end product. However, radiation processing can make an important contribution to solve these problems. Effects of radiation processing, on crude and true protein, amino acid profile, minerals and thiamine content of dried broiler and cow manure, at dose levels of 5, 10 and 25 kGy have been studied. Short-term feeding tests were carried out to determine the effect of radiation pasteurization of such animal waste on growth performance of young chicks. The results suggested that radiation pasteurization of dried manure has a beneficial effect on recycling of such waste and it permits waste to be included in animal diet without nutritional problems.

RECYCLING PROPELLANTS AND EXPLOSIVES INTO THE COMMERCIAL EXPLOSIVE INDUSTRY

As part of environmentally safe recycling of unwanted ordnance, the commercial blasting industry is a significant potential user of recovered energetic materials. This industry utilizes significant quantities of explosive materials on an annual basis and can easily become an even larger consumer of military energetics if their requirements are properly addressed. Significant quantities of solid rocket motor propellant are about to emerge in the world market as a product requiring recycling. The commercial explosive market is a willing consumer of these materials, albeit at a very low price. The majority of the world's supply of solid propellants contain high value explosives, fuels and oxidizers. A challenge for the technical community is to develop products or processes that can return higher values because of the constituent propellant ingredients.

RECYCLING PROPELLANTS AND EXPLOSIVES INTO THE COMMERCIAL EXPLOSIVE INDUSTRY

Abstract : As part of environmentally safe recycling of unwanted ordnance, the commercial blasting industry is a significant potential user of recovered energetic materials. Their industry utilizes significant quantities of explosive materials on an annual basis and can easily become an even larger consumer of military energetics if their requirements are properly addressed. This paper identifies their concerns and offers methods for satisfying them.

Potential of recycling gamma-irradiated sewage sludge for use as a fertilizer: A study on chickpea ( Cicer arietinum)

The effects of gamma-irradiated sludge on the growth and yield of chickpea ( Cicer arietinum) in pot cultures have been studied. Compared to plants grown only in soil, root length, fresh weight and dry weight of plants grown in soil supplemented with unirradiated skudge were found to be significantly reduced. This inhibition in growth was found to be nullified when plants were grown in soil supplemented with gamma-irradiated sludge, suggesting that gamma radiation induced inactivation of toxic substance(s) in sludge. The protein content of plants grown in soil supplemented with irradiated sludge was also found to be significantly increased compared to those grown with unirradiated or no sludge, after 45 days. There was no significant effect of gamma irradiated sludge on shoot length, total soluble sugars, starch content and yield of chickpea plants. The results obtained suggest that the sludge tested, and obtained from the digester of a conventional domestic sewage treatment plant, is inhibitory to several growth parameters. Gamma irradiation of sewage resulted in removal of this inhibition. This suggests a possibility of beneficial and safe recycling of gamma-irradiated sludge for agricultural uses.

Survival of Eggs and Larvae of Swine Nematode Parasites in Aerobic and Anaerobic Waste Treatment Systems

AbstractExperiments were conducted at 12 and 22°C to compare the effects of aerobic and anaerobic treatment systems on the development and survival of eggs and larvae of swine nematode parasites. Swine feces containing eggs of Ascaris suum, Metastrongylus spp., Oesophagostomum dentatum, Hyostrongylus rubidus, and Strongyloides ransomi were used in both experiments. Treatment system fluids were sampled and examined periodically for the presence of parasite eggs and larvae. Cultures of fluids were prepared and examined for the presence of larvae after 7 days of incubation at 25°C. Ascaris eggs embryonated in 28 days in the 22°C aerobic system. Unembryonated Ascaris eggs in the other three treatment systems completed their development when transferred to 2% formalin at 25°C. Metastrongylus eggs survived in all treatment systems, but some larvae hatched and died in both aerobic systems. Oesophagostomum and Hyostrongylus larvae survived well under 12°C aerobic conditions, but were destroyed within 11 days at 22°C. Eggs of Strongyloides hatched rapidly under aerobic conditions, but survived at least 7 days under anaerobic conditions in both experiments. The development of free‐living adults of Strongyloides and the survival of third‐stage larvae were favored in 22°C aerobic conditions. Knowledge of the parasite genera present in a swine herd and of the responses of the eggs and larvae to different temperatures and treatment systems is important for effective management and safe recycling of wastes.