Robustness testing of a free-fall triboelectric separation process for plastic waste recovery

Among the separation techniques used in industries, the triboelectric separation of insulating particles using a rotary tube is an effective way employed in the waste recovery of plastic and mineral products. This process, also called free-fall triboelectric separation, is widely used for the sorting of granular mixtures resulting from industrial plastic wastes. Given that the robustness of such a separation process is an important issue, a standard procedure is used for determining the set point and for minimising the process sensitivity of sorting mixed particles of different polymers to changes in the values of some critical factors. The aim of this paper was to analyse the efficiency of the triboelectric separation process of polymers with respect to any slight variation in the values of the most significant factors. Experiments with a sample of high-density polyethylene and polyvinyl chloride plastic granules were carried out on a laboratory experimental bench. Several one-factor-at-a-time experiments, followed by two factorial designs (one composite and the other fractional), were performed based on the following experimental procedure: (1) determination of the variation limits of the input variables; (2) identification of the set point and (3) robustness testing of the process, i.e. testing whether the performance of the system remains high even when the factors vary slightly around the set point.     

Processes for sustainable development using high-intensity electric fields

Intense electric fields up to 10⁷ V/m generate very interesting and useful applications for the environment. Several processes using high electrical voltage for environment preservation were developed in the laboratory. The purpose of this study was to review these applications, highlighting their economic and environmental benefits: (1) electrostatic separators of particles used in industrial wastes recycling; (a) role-type electrostatic separator for granular mixtures of plastic–metal particles; (b) free-fall and rotating belt triboelectric separators for mixtures of plastic–plastic particles; (c) plate-type electrostatic separator for mixtures of metal–metal particles, (2) electrostatic precipitators for gas cleaning and (3) ozone generators for air and water treatment.     

PAH emission from the incineration of three plastic wastes

A batch-type, controlled-air incinerator was used for the treatment of polyvinyl chloride (PVC), high-density polyethylene (HDPE), and polypropylene (PP) plastic wastes. The concentration and composition of 21 individual polycyclic aromatic hydrocarbons (PAHs) in the raw wastes, flue gas (gas and particle phases), and ash were determined. Stack flue-gas samples were collected by a PAH stack-sampling system. Twenty-one individual PAHs were analyzed primarily by a gas chromatograph/mass spectrometer (GC/MS). The CO concentration correlated well with the total PAH (R2 > .89), and thus can be used as a surrogate indicator for PAH emission. Excess amounts of air supply in the incineration of plastic wastes could decrease not only the concentration of the PAHs in the bottom ash but also the emission factor (EF) of the total PAH in the stack flue gas. Of the three plastic wastes, HDPE was found to have the highest mean EF of the total PAHs (462.3 mg/kg waste) from the stack flue gas. Incinerating PVC would result in a higher EF of PAHs (195.4 mg/kg waste) in the bottom ash. When PVC plastic wastes were incinerated, higher-ringed PAHs constituted a larger percentage in the bottom ash as compared to those from PP and HDPE plastics. By judging the output and input (O/I) ratio of the PAHs from the incineration trials of plastic wastes, the PAHs involved in incineration of three plastic wastes were almost entirely destroyed; and a low residual amount between 0.00018 and 0.00032 remained in the emission.     

Analysis of cost–benefit in life-cycle of plastic solid waste: combining waste flow analysis and life cycle cost as a decision support tool to the selection of optimum scenario

Millions of tons of plastic are consumed annually in the world due to its significant characteristics such as durability, flexibility, and low weight. High consumption has made plastic one of the most important municipal solid waste compounds, the quantity of which has increased in recent decades. Plastic solid wastes are known as a threat to the environment, and its efficient management in various aspects such as cost–benefit requires decision-making tools. This study was assessing the cost–benefit of plastic solid waste management by development of an economic model, and definition of different scenarios to change plastic solid waste management status. The results showed that 8971 tons of plastic solid waste were generated annually in the studied city. The plastic solid wastes were finally transferred to either recycling or landfilling site through 5 identified routes. 83 percent of the total recycled plastic solid waste was due to post-separation routes, and only 7.7 percent of the total plastic solid waste was recycled from the source separation route. The economic comparison of scenarios showed that with the aggregation of post-separation routes, the net revenue of plastic solid waste management increases by 334,000 euro per year while increasing the public participation and the ratio of source separation route raises net revenue by 875,000 euro per year, which was the best economic condition among the scenarios. Using life cycle cost method and it’s respected developed economic model truly satisfied the conditions of both, the current plastic solid waste management and the alternative scenarios, and hence can be adopted as a tool for decision-making.

     

Some physical and chemical features of the variability of kd distribution coefficients for radionuclides

k_d distribution coefficients are widely used as a first approach to the understanding and determination of the eventual fate of metals and radionuclides released into the aquatic environment. For some radionuclides, k_d varies within a range of more than two orders of magnitude. Based on some physical and chemical aspects of the interactions between the dissolved and the particulate phases, some mathematical equations have been developed to explain some features of the observed k_d variability quantitatively. Thus, we have studied the decrease in particle size of k_d in the case of man-made radionuclides interacting with natural particles, and its increase in the case of naturally occurring radionuclides. For the latter, the dependence of k_d on the instantaneous water state has also been investigated. The study also shows the competition effects, particularly the dependence of k_d on pH and salinity. Finally, the effects produced by the size distribution of a given population of particles or the mixture of different populations, are also included. The present work provides for each situation, experimental support from literature data and/or modelling exercises.     

Energy consumption analysis of ABS plastic parts injected in a hybrid injection moulding machine

The energy analysis of injection moulding processes is influenced by complex interactions amongst the moulded part, its material, the injection machine, the process parameters and the environmental conditions. The availability of energy usage analyses that comprehend information on specific materials and machine kind is limited. This paper reports a study that estimates and analyses the power usage profile (PUP), the specific energy consumption (SEC), and the energy distribution at an operation level of two different injected parts made of acrylonitrile-butadiene-styrene and produced in a hybrid injection moulding machine. The methodology followed by the authors incorporates an experiment carried out in an industrial facility. A large sample size, and data-acquisition and data post-processing processes to obtain an accurate PUP and SEC are used. A breakdown of the energy consumed by the injection moulding process of the parts studied at an operation level using Sankey diagrams is discussed. The study results are used to identify strategies to reduce the energy consumed by the processes. The methodology employed, and the strategies reported could be used with other plastic parts regardless of the material and machine used. The results reported are new experimental data useful input for theoretical models.     

Comparative toxicity of solid waste leachates to Daphnia magna

The comparative acute and chronic toxicities of municipal, industrial, coal-fired power plant, and synthetic fuel solid waste leachates to the aquatic invertebrate Daphnia magna were determined. Seventeen leachates were laboratory-derived by extraction with 0.5 N acetic acid, and one, an arsenic-contaminated groundwater, was naturally derived. The acute toxicity 48-h LC₅₀ estimates (concentrations of the test materials that killed 50% of the test organisms in 48 h) ranged from 0.0005% for a dye waste leachate to > 100% (i.e., undiluted) for a coal gasification waste leachate. The most toxic leachates were derived from a dye waste, a plater's waste, and the arsenic-contaminated groundwater, and the least toxic were from a soybean process cake waste and a coal gasification waste. Of the 16 leachates used in the 28 day chronic toxicity tests, only the arsenic-contaminated groundwater and a municipal sewage sludge significantly affected D. magna reproduction. The former material at 1.0% concentration and the sludge at 0.1% caused about an 88% reduction in the numbers of young produced by exposed females compared with controls. Generally, the industrial waste leachates were more toxic than those from the power plant and synthetic fuel wastes. Because its presence in the test materials interfered with interpretation of the results, acetic acid may not be an appropriate extraction medium for preparation of leachates.     

Afforestation for reduction of NOX concentration in Lanzhou China

Lanzhou is one of the major industrial cities in northwest China, the capital of Gansu Province, and located at a northwest-to-southeast oriented valley basin with elevation about 1500–1600-m. Due to topographic and meteorological characteristics, Lanzhou is one of the most polluted cities in China. Meteorological conditions (low winds, stable stratification especially inversion), pollutant sources and sinks affect the air quality. Lanzhou government carried out afforestation and pollutant-source reduction (closing several heavy industrial factories) to improve the air quality for the past two decades. In this study, effect of afforestation on reducing the NO_X concentration is investigated numerically using RAMS-HYPACT model.     

Aerosol filtration by a cocurrent moving granular bed: Penetration mechanisms

An experimental apparatus has been constructed to investigate aerosol filtration by a cocurrent moving granular bed filter (CMGBF). In a CMGBF, aerosol passes downward through a descending bed of dirty granules while clean granules are added continously at the bed top. The effect of an intergranular dust deposit on penetration in a CMGBF was investigated in a 2⁴ factorial experiment in which the control variables were superficial gas velocity (100 and 250 mm/s), bed depth (130 and 230 mm), granule size (2.1 and 2.7 mm), and the intergranular dust deposit expressed as percent by weight of collected dust in the bed (1% and 5%). All tests were conducted at ambient temperature and pressure using resuspended utility boiler fly ash as the test aerosol.Mass penetration data identified two major penetration mechanisms: (1) straight through penetration and (2) reentrainment due to granular motion. A static, intergranular dust deposit produced high filtration efficiency (>99%) at the low superficial velocity. When the bed was moving, reentrainment of collected dust was significant and accounted for about three-quarters of the penetrating dust. Particle size analyses reveal that the two penetration mechanisms are size dependent. Most particles larger than about one micrometer in diameter that penetrate the CMGBF do so by reentrainment after being collected initially. Virtually no particles smaller than about 0.3 μm in diameter penetrate by reentrainment; when these small particles penetrate, they pass straight through without being collected.     

Experimental investigation of diesel engine using EGR and fuelled with Karanja oil methyl ester

Karanja oil methyl ester (KOME), a biodiesel prepared from Karanja oil, a potential source of non-edible oil in India and a prospective alternative to the diesel fuel, shows comparable performance and considerable reduction in emissions except NO_x. Exhaust gas recirculation (EGR) is a popular method of reducing the NO_x emission. The aim of this experimental work was to study the potential of the cooled EGR in a direct injection compression ignition engine operating with the KOME and its blend. The study was conducted with the different EGR rates. Performance and emission parameters were compared by using diesel, KOME and its blend employing EGR and with the same fuels without EGR. The study also differentiates the effect of EGR on KOME and its blend with the neat diesel. The effect of EGR was found to be slightly higher for KOME biodiesel and its blend than for neat diesel. Increased NO_x emission using KOME biodiesel was also found to be reduced by using EGR.     

The Frequency of Micronuclei among Newborns from Kragujevac, Central Serbia, after NATO Bombing in the Spring of 1999

Kragujevac, as an important industrial and economic center of the region, is now placed on the top of the list of environmentally endangered cities in our country. The aim of this biomonitoring study was to evaluate cytogenetic damage in a sample of newborns from Kragujevac after contamination of the environment entailed by the intensive bombing of the industrial zone of this city in the spring of 1999. The frequency of micronuclei (MN) in peripheral blood lymphocytes in a total of 61 phenotypically healthy newborns was analyzed before and after the NATO bombing. Analysis of micronuclei has been performed using the cytokinesis-block technique (CB MN test). Average MN frequency in lymphocytes of newborns before the bombing (N = 25) was 5.77 ± 0.85/1000 analyzed cells. After the bombing (N = 36), the average frequency of MN increased by a factor of 1.4 (8.11 ± 0.85), compared to the control frequency before the bombing. Statistical difference (p < 0.05) was established by Student's t-test. Our data suggest that such changes in genetic material were a direct consequence of contamination of the living environment.     

Drying wastes from urban forestry as an option for their recovery and use in furniture and small wooden objects

The management of urban trees generates wood wastes that are commonly destined for use as firewood or compost. However, they can be used for more noble purposes such as making furniture or small wooden objects. This study aimed to investigate the drying and the shrinkage of the wood of seven typical urban afforestation species to determine the possibility of high-valued alternative use(s). Samples of these species (Cenostigma pluviosum (DC.) E. Gagnon & G.P. Lewis.; Delonix regia (Bojer ex Hook.) Raf.; Ficus benjamina L.; Licania tomentosa (Benth.) Fritsch; Nectandra megapotamica (Spreng.) Mez; Terminalia catappa L.; and Tipuana tipu (Benth.) Kuntze) underwent a drastic drying test in a laboratory oven at 103?±?2 °C, followed by weighing on an analytical balance to monitor the weight over a 24-h period, separated into four intervals of 4 h and one of 8 h. The drying rate, shrinkage and anisotropy coefficient of the species were evaluated. Wood wastes of the species C. pluviosum and L. tomentosa showed greater shrinkage during drying, with the lowest drying rates being found among the other species. F. benjamina, D. regia, N. megapotamica, T. catappa and T. tipu showed lower values of shrinkage and regular anisotropy coefficients close to ideal for application to make small wooden objects according to the characteristics of the species already present in the industrial market. The seven species thus have potential for application in the production of small wooden objects and furniture. This use is a potential alternative for environmental and social betterment.

     

Industrial complexes and their relevance for pulp and paper mills

Advantages and disadvantages of the concept of an industrial complex are discussed. From an environmental standpoint an ideal industrial complex is one containing a group of compatible industrial plants utilizing completely each other's wastes and products as raw materials and manufacturing products with no adverse environmental impact and at a minimum of cost. A typical complex centering about a pulp and papermill is pictured in this paper. This complex produces six products for external sale and four products for internal use. In addition, all major wastes of suspended solids, cooking liquor, fillers, heat and bark are reused within the complex in the manufacture of these products. A literature review evolved typical concentrations of recoverable suspended solids in various process effluents. A mass balance was prepared assuming that the total production of fine paper is 907.2 kg × 10³ (1000 tons) per day. Little or no air or water pollution results from this complex. In addition, it is anticipated that no expensive waste-water treatment plant would be required for this complex. Ten additional practices are described which, when used, will reduce operating costs even further. A continuing study with more precise data on the production requirements for the service plants in the complex will yield a more balanced and realistic system.     

Determination of phthalate ester plasticizers in the aquatic environment of Southwestern Nigeria

Water from the Lagos, Oyo, Osun, Ondo, and Delta states of Nigeria and the cities' water treatment plants had been analized for the presence of ubiquitous phthalate esters using liquid chromatography. Extraction with CH₂Cl₂ and liquid chromatography was used for compound separation. Several phthalate esters, dimethyl- (DMP), diethyl- (DEP), and di-n-butyl- (DBP) were found present at levels of 10 mg L⁻¹ to 1472 mg L⁻¹ in river water and 91 mg L⁻¹ to 1219 mg L⁻¹ in tap water from the cities' water treatment plants. A study of uncontaminated water was done to establish blank levels.     

Bioavailability of sediment-associated and low-molecular-mass species of radionuclides/trace metals to the mussel Mytilus edulis

Sediments can act as a sink for contaminants in effluents from industrial and nuclear installations or when released from dumped waste. However, contaminated sediments may also act as a potential source of radionuclides and trace metals to the water phase due to remobilisation of metals as dissolved species and resuspension of particles. The marine mussel Mytilus edulis is a filter-feeding organism that via the gills is subjected to contaminants in dissolved form and from contaminants associated to suspended particles via the digestive system. In this paper the bioavailability of sediment-associated and seawater diluted Cs, Co, Cd and Zn radioactive tracers to the filtering bivalve M. edulis has been examined. The mussels were exposed to tracers diluted in ultrafiltered (<10 kDa) seawater (Low Molecular Mass form) or to tracers associated with sediment particles from the Stepovogo Fjord at Novaya Zemlya in short-term uptake experiments, followed by 1-month depuration experiments in flow-through tanks. A toxicokinetic model was fitted to the uptake and depuration data, and the obtained parameters were used to simulate the significance of the two uptake pathways at different suspended sediment loads and sediment-seawater distribution coefficients. The results of the model simulations, assuming steady state conditions, suggest that resuspended particles from contaminated sediments can be a highly significant pathway for mussels in the order ¹⁰⁹Cd ≌ ⁶⁵Zn < ¹³⁴Cs < ⁶⁰Co. The significance increases with higher suspended sediment load and with higher K_d. Furthermore, the experimental depuration data suggest that Cs is retained longer and Co, Cd and Zn shorter by the mussels when associated with ingested sediments, than if the metals are taken up from the low molecular mass (LMM) phase.     

Environmental and economic viability of Alkali Activated Material (AAM) comprising slag,fly ash and spent coffee ground

ABSTRACT

This paper presents a concept of reusing spent coffee ground (CG) as a construction material. Through creating a CG-filled Alkali Activated Material (AAM) with industrial wastes such as fly ash (FA) and slag (S), a strong recycled material was synthesised and found suitable to be used as a road subgrade fill material. Potential groundwater contamination tests were done in accordance to the Australian Standard Leaching Procedure (ASLP). The environmental analysis done on this green material shows that albeit being composed of various industrial wastes and chemicals, CG-filled AAMs in the ground will not cause adverse environmental impacts to surrounding soils and groundwater. Heavy metals and cyanide leached from the AAMs were well below hazardous thresholds. Comparing the carbon footprint of CG, it is found that recycling CG into a construction material would reduce the nett global carbon emission by reducing dependency on quarried material. Cost analyses done on CG-filled AAMs show that these AAMs are expensive to produce relative to traditional construction materials. However, as recycling technology is progressively advancing, in the future the economic value of CG-filled AAM may increase to match those of contemporary construction materials.     

Buffer capacity of seawater at high pCO2

Measurements of the variation of the carbon dioxide partial pressure in water were performed up to pCO₂ and CO₂ using 6.000 ppm. The consistent data so far obtained were compared with calculated pCO₂ using the Lynan constants. A plot of the experimental and calculated data evidences that comparisons are only possible by using varying carbonate alkalinity.     

Radon, helium and CO2 measurements in soils overlying a former exploited oilfield, Pechelbronn district, Bas-Rhin, France

The Pechelbronn oilfield (Rhine Graben, France), where mining activity ended in the 1960s, has been used for waste disposal for twenty years. Since the wastes are varied, work is underway to identify the discharged materials and their derivatives, as well as to locate and quantify potential discharge sites. Two major goals were assigned to the present work. The first was to identify or refine the location of hidden structures that could facilitate gas emanation up to the surface, by studying soil gas concentrations (mainly ²²²Rn, CO₂, CH₄ and helium) and carbon isotope ratios in the CO₂ phase. The second was devoted to examining, from a health and safety viewpoint, if the use of the oilfield as a waste disposal site might have led to enhanced or modified gas emanation throughout the area.It appeared that CO₂ and ²²²Rn evolution in the whole area were similar, except near some of the faults and fractures that are known through surface mapping and underground observations. These ²²²Rn and CO₂ anomalies made it possible to highlight more emissive zones that are either related to main faults or to secondary fractures acting as migration pathways. In that sense, the CO₂ phase can be used to evaluate ²²²Rn activities distant from tectonic structures but can lead to erroneous evaluations near to gas migration pathways. Dumping of wastes, as well as oil residues, did not appear to have a strong influence on soil gaseous species and emanation. Similarly, enhanced gas migration due to underground galleries and exploitation wells has not been established. Carbon isotope ratios suggested a balance of biological phenomena, despite the high CO₂ contents reached. Other monitored gaseous species (N₂, Ar, H₂ and alkanes), when detected, always showed amounts close to those found subsurface and/or in atmospheric gases.     

Study of fluxing in Al refining process by rotary and crucible furnaces

The process used to obtain recycled Al alloys depends on the scrap quality. Rotary furnaces are normally used in Europe as they allow a great productivity and they can process low quality scrap using a salt flux to protect the molten metal from oxidation. In this article, the effect of the quantity of salt on the metal recovery has been experimentally investigated by melting several types of scrap under a mixture of NaCl–KCl–Na₃AlF₆ salts. The quantity of salt has been related to the salt factor (SF), which is the ratio between the non-metallic content in the scrap and the quantity of salt required. The same levels of salt factor have been tested by melting the scrap in rotary and crucible furnaces. The metal recovery increases with the salt content for both furnaces. The results obtained with the different melting processes are comparable because the yield difference is similar considering different salt factors. Crucible furnace gives greater metal recovery but it cannot replace rotary furnace in Al refining industry due to lower melting capacity. However, the results highlight that the optimisation of the Al refining process can be supported by preliminary tests through crucible furnaces reducing the time and material consumptions.     

Human impacts on methane emission from mangrove ecosystems in India

This study deals with the emission of methane in relation to changing environmental conditions and human impact, in three mangrove ecosystems of south India. Time-varying fluxes of methane adopting the close chamber technique were used to estimate CH₄ emission from an unpolluted site (Pichavaram mangroves) and two polluted sites viz. (1) Ennore Creek mangroves (affected by fertilizer effluents and crude oil discharges) and (2) Adyar estuary mangroves (affected by the discharges of organic and industrial wastes), covering monthly and seasonal variations. The results indicate annual average CH₄ emissions of 7.4, 5.02 and 15.4 mg m⁻² h⁻¹ from the sediment–water interface of the Pichavaram, Ennore Creek and Adyar estuary respectively. Emission characteristics obtained at Pichavaram mangroves represent a natural variability with changing physico-chemical factors, whereas the emission characteristics at Ennore Creek and Adyar estuary mangroves show anthropogenic influence. Several environmental factors such as oxygen availability, organic matter, soil physical and chemical properties, in addition to human-mediated interventions have been identified as influencing emission rates in the mangrove ecosystems. Preliminary CH₄ emission estimates for the mangrove ecosystems along the Indian sub- continent and the tropical and subtropical coastline of the world by linear extrapolation based on surface area range from 0.05 to 0.37 and 2.8 to 19.25 Tg CH₄ year⁻¹ respectively. Our results also highlight the impact of human activities on future emission of methane from the mangrove ecosystems. Received: 3 March 1999 / Accepted: 14 September 1999