Efficiency of the activated carbon filtration in the natural organic matter removal

The removal and transformation of natural organic matter were monitored in the different stages of the drinking water treatment train. Several methods to measure the quantity and quality of organic matter were used. The full-scale treatment sequence consisted of coagulation, flocculation, clarification by flotation, disinfection with chlorine dioxide, activated carbon filtration and post-chlorination. High-performance size-exclusion chromatography separation was used to determine the changes in the humic substances content during the purification process; in addition, a UV absorbance at wavelength 254 nm and total organic carbon amount were measured. A special aim was to study the performance and the capacity of the activated carbon filtration in the natural organic matter removal. Four of the activated carbon filters were monitored over the period of 1 year. Depending on the regeneration of the activated carbon filters, filtration was effective to a degree but did not significantly remove the smallest molar mass organic matter fraction. Activated carbon filtration was most effective in the removal of intermediate molar mass compounds (range 1,000-4,000 g/mol). Regeneration of the carbon improved the removal capacity considerably, but efficiency was returned to a normal level after few months.     

Municipal solid waste management in India: From waste disposal to recovery of resources?

Unlike that of western countries, the solid waste of Asian cities is often comprised of 70-80% organic matter, dirt and dust. Composting is considered to be the best option to deal with the waste generated. Composting helps reduce the waste transported to and disposed of in landfills. During the course of the research, the author learned that several developing countries established large-scale composting plants that eventually failed for various reasons. The main flaw that led to the unsuccessful establishment of the plants was the lack of application of simple scientific methods to select the material to be composted. Landfills have also been widely unsuccessful in countries like India because the landfill sites have a very limited time frame of usage. The population of the developing countries is another factor that detrimentally impacts the function of landfill sites. As the population keeps increasing, the garbage quantity also increases, which, in turn, exhausts the landfill sites. Landfills are also becoming increasingly expensive because of the rising costs of construction and operation. Incineration, which can greatly reduce the amount of incoming municipal solid waste, is the second most common method for disposal in developed countries. However, incinerator ash may contain hazardous materials including heavy metals and organic compounds such as dioxins, etc. Recycling plays a large role in solid waste management, especially in cities in developing countries. None of the three methods mentioned here are free from problems. The aim of this study is thus to compare the three methods, keeping in mind the costs that would be incurred by the respective governments, and identify the most economical and best option possible to combat the waste disposal problem.     

Implementing China's circular economy concept at the regional level: a review of progress in Dalian, China

The circular economy (CE) concept was introduced in China to address environmental degradation and resource scarcity associated with rapid economic development. Chosen as a demonstration city, Dalian has implemented the CE strategy as a means of conserving water, materials, energy and land. This paper outlines some of the regional CE initiatives that have been successful to date in Dalian, including those focusing on conserving energy and water resources and others focusing on reduced industrial emissions. The paper details the approach used in implementing the CE concept in Dalian, tracing the foci and goals of the program, and the sectoral approach used to implement a CE. Although Dalian municipality has achieved many successes in implementing a CE, our paper identifies several challenges that, until recently, have held back complete implementation. These include: the lack of incentives for older industries to 'green' their operations, the lack of financial support to expand the CE concept, and a broad-based need for heightened public awareness and participation in CE initiatives. Our paper then identifies several responses by Dalian municipality to overcome these challenges, including pricing and tax reforms that serve as conservation incentives, the provision of financial support for CE promotion through budget reorganization, and the organization of CE training programs. Our paper concludes that, although CE initiatives have been successful in Dalian, more is possible and more is needed before Dalian can be designated a true 'eco-city'. The approach used by Dalian can provide guidance for other Chinese cities, although it is recognized that each city must tailor its own approach for differing contexts and conditions.     

Hydrothermal treatment of MSWI bottom ash forming acid-resistant material

To recycle municipal solid waste incinerator (MSWI) bottom ash, synthesis of hydrothermal minerals from bottom ash was performed to stabilize heavy metals. MSWI bottom ash was mixed with SiO(2), Al(OH)(3), and Mg(OH)(2) so its chemical composition was similar to that of hydrothermal clay minerals. These solid specimens were mixed with water at a liquid/solid ratio of 5. The reaction temperature was 200 degrees C, and reactions were performed for 24-240h. Generation of kaolinite/smectite mixed-layer clay mineral was found in the samples after the reaction of the mixture of bottom ash, SiO(2), and Mg(OH)(2). Calcium silicate hydrate minerals such as tobermorite and xonotlite were also generated. X-ray powder diffraction suggested the presence of amorphous materials. Leaching tests at various pHs revealed that the concentration of heavy metals in the leachates from MSWI bottom ash hydrothermally treated with SiO(2) and Mg(OH)(2) was lower than that in leachates from non-treated bottom ash, especially under acid conditions. Hydrothermal treatment with modification of chemical composition may have potential for the recycling of MSWI bottom ash.     

Potential use of lateritic and marine clay soils as landfill liners to retain heavy metals

The potential of a lateritic soil and a marine clay, typical of those found in hot and humid climatic regions, was assessed for use as a landfill liner material. A series of tests were conducted - physical and chemical, batch adsorption, column, hydraulic conductivity, etc., - to evaluate the heavy metal sorption capacity, chemical compatibility of hydraulic conductivity, and transport parameters of the soils. Experimental results showed that the marine clay had better adsorption capacity than that of the lateritic soil and that its hydraulic conductivity was an order of magnitude lower. In addition, the hydraulic conductivities of both soils when permeated with low concentration heavy metal solutions were below 1x10(-7)cm/s. When permeated with Cr, Pb, Cd, Zn, and Ni solutions, the retardation factors of the lateritic soil and the marine clay ranged from 10 to 98 and 37 to 165, respectively, while the diffusion coefficients ranged from 1.0x10(-5) to 7.5x10(-6) and 3.0 to 9.14x10(-7)cm2/s, respectively. For both soils, Cr and Pb were retained relatively well, while Cd, Zn, and Ni were more mobile. The marine clay had higher retardation factors and lower diffusion coefficients, and its hydraulic conductivity was more compatible with Cr solution, than that of the lateritic soil. In general, the properties of the marine clay indicate that it has significant advantages over the lateritic soil as landfill liner material.     

Leaching from MSWI bottom ash: evaluation of non-equilibrium in column percolation experiments

Impacts of non-equilibrium on results of percolation experiments on municipal solid waste incineration (MSWI) bottom ash were investigated. Three parallel column experiments were performed: two columns with undisturbed percolation and one column with two sets of 1-month-long flow interruptions applied at liquid-to-solid (L/S) ratios of L/S 2L/kg and 12L/kg, respectively. Concentrations of Na, K, Cl(-), Ca, Si, SO(4)(2-), Al, Cu, Ni, Mo, Ba, Pb, Zn, and dissolved organic carbon (DOC) were monitored throughout the entire leaching period; geochemical modeling was used to identify non-equilibrium-induced changes in the solubility control. Despite both physical and chemical non-equilibrium, the columns were found to provide adequate information for readily soluble compounds (i.e., Na, Cl(-), and K) and solubility-controlled elements (i.e., Ca, SO(4)(2-), Ba, Si, Al, Zn, and Pb). The leaching of Cu and Ni was shown to depend strongly on DOC leaching, which was likely affected by physical non-equilibrium during flow interruptions. Consequently, the leaching of Cu and Ni in the undisturbed columns was shown to be by about one order of magnitude lower compared with the interrupted column. The results indicate that the leaching of DOC-related metals in laboratory column experiments may be considerably underestimated compared with full-scale scenarios in which the impacts from non-equilibrium may be significantly lower. The leaching of Mo (or MoO(4)(2-)) may be controlled solely by its availability in the mobile zone, which in turn appeared to be controlled by diffusion from the stagnant zone; no Mo controlling minerals were predicted by the geochemical modeling.     

Residences with anomalous soil concentrations of dioxin-like compounds in two communities in Michigan, USA: a case study

Most contamination of residential property soil with dioxin-like compounds occurs as a result of proximity to industrial activity that produces such compounds and, outside the industrially impacted zone, the soil concentrations are at background levels. However, as part of the University of Michigan Dioxin Exposure Study, residential properties in the lower peninsula of Michigan, USA, were identified that were located far enough from known sources of these compounds that the soil concentrations should have been at background levels and yet the toxic equivalent (TEQ) of some properties' soil was greater than 2.5 standard deviations above the mean background level. In the three cases presented here from Midland/Saginaw Counties, the anomalously high-TEQ values were primarily due to the presence of polychlorinated dibenzofurans. Based on interviews with the residents and a comparison of soil congener profiles, it was deduced that these values resulted from anthropogenic soil movement from historically contaminated areas. In the cases from Jackson/Calhoun Counties, the unusually high-TEQ values were primarily due to polychlorinated biphenyls. In the case profiled here, it appears that the soil became contaminated through sandblasting to remove paint from the swimming pool. This study identified two mechanisms for soil contamination outside zones of industrial impact; thus, an assumption of background levels of soil contamination outside industrial zones may not be valid.     

Genotoxicity evaluation of water soil leachates by Ames test, comet assay, and preliminary Tradescantia micronucleus assay

Combining genotoxicity/mutagenicity tests and physico-chemical methodologies can be useful for determining the potential genotoxic contaminants in soil samples. The aim of our study was to evaluate the genotoxicity of soil by applying an integrated physico-chemical-biological approach. Soil samples were collected at six sampling points in a Slovenian industrial and agricultural region where contamination by heavy metals and sulphur dioxide (SO₂) are primarily caused by a nearby power plant. The in vitro alkaline version of the comet assay on water soil leachates was performed with Caco-2 and HepG2 cells. A parallel genotoxicity evaluation of the samples was performed by Ames test using Salmonella typhimurium and the Tradescantia micronucleus test. Pedological analyses, heavy metal content determination, and different physico-chemical analyses, were also performed utilizing standard methodology. Water leachates of soil samples were prepared according to standard methods. Since only a battery of biotests with prokaryotic and eukaryotic organisms or cells can accurately estimate the effects of (geno)toxicants in soil samples and water soil leachates, a combination of three bioassays, with cells or organisms belonging to different trophic levels, was used. Genotoxicity of all six water soil leachates was proven by the comet assay on both human cell lines, however no positive results were detected by bacterial assay, Ames test. The Tradescantia micronucleus assay showed increase in micronuclei formation for three samples. According to these results we can assume that the comet assay was the most sensitive assay, followed by the micronucleus test. The Ames test does not appear to be sensitive enough for water soil leachates genotoxicity evaluations where heavy metal contamination is anticipated.     

Monitoring pollution in River Mureş, Romania, part II: metal accumulation and histopathology in fish

As a part of an exposure and effect monitoring conducted along the river Mureş, Western Romania in 2004, the health status of two indigenous fish species, sneep (Chondrostoma nasus) and European chub (Leuciscus cephalus) was investigated upstream and downstream the city of Arad. In fish, histopathology was assessed in liver and gills, and heavy metals (cadmium, copper, lead and zinc) were analyzed in liver samples. In both fish species, histopathological reactions in the gills (epithelial lifting, focal proliferation of epithelial cells of primary and secondary lamellae and resulting fusion of secondary lamellae, hyperplasia and hypertrophy of mucous cells, focal inflammation and necrosis of epithelial cells) were most severe at the two sampling sites upstream Arad city, which were shown to be polluted by copper, cadmium, faecal coliforms and streptococci in a parallel study. At these two sites, also histopathology in the liver of L. cephalus was more prominent than at the two downstream sites. In C. nasus, symptoms in the liver (focal inflammation with lymphocytic infiltrations, macrophage aggregates and single cell necrosis) were also highly pronounced at the sampling site located directly downstream the municipal sewage treatment plant of Arad. With the exception of copper accumulation in L. cephalus caught at the most upstream sampling site, in both fish species cadmium and copper accumulation were exceptionally high and did not differ significantly between the four sampling sites.     

Photocatalytic degradation of NOx in a pilot street canyon configuration using TiO2-mortar panels

Titanium dioxide is the most important photocatalysts used for purifying applications. If a TiO₂- containing material is left outdoors as a form of flat panels, it is activated by sunlight to remove harmful NOx gases during the day. The photocatalytic efficiency of a TiO₂-treated mortar for removal of NOx was investigated in the frame of this work. For this purpose a fully equipped monitoring system was designed at a pilot site. This system allows the in situ evaluation of the de-polluting properties of a photocatalytic material by taking into account the climatologic phenomena in street canyons, accurate measurements of pollution level and full registration of meteorological data The pilot site involved three artificial canyon streets, a pollution source, continuous NOx measurements inside the canyons and the source as well as background and meteorological measurements. Significant differences on the NOx concentration level were observed between the TiO₂ treated and the reference canyon. NOx values in TiO₂ canyon were 36.7 to 82.0% lower than the ones observed in the reference one. Data arising from this study could be used to assess the impact of the photocatalytic material on the purification of the urban environment.