C.J. Sollars

Low-cost adsorbents for waste and wastewater treatment: a review

The recent research interest in low-cost alternatives to activated carbon for waste and wastewater treatment is reviewed. An examination of the selection criteria and activation methods for the preparation of active carbon is followed by a critical assessment of low-cost adsorbents prepared from carbonaceous industrial wastes, agricultural by-products and mineral-derived sources. Emphasis is given to in situ reuse applications where stated in the literature and rudimentary economic analyses provided, where available, for comparative operations with commercial activated carbon.

Ambient air levels of volatile organic compounds in Latin American and Asian cities

Levels of volatile organic compounds (VOCs) have been measured during short monitoring campaigns in four cities in Latin America; Caracas (Venezuela), Quito (Ecuador), Santiago (Chile), Sao Paulo (Brazil), and two cities in Asia; Bangkok (Thailand) and Manila (Philippines). The aim of the study was to identify typical levels of VOCs in these cities where monitoring of this unregulated but important group of pollutants has rarely been conducted. Levels monitored were relatively high in comparison to typical European and US levels. Mean benzene levels ranged from 5–18μg/m3 and toluene from 15–186μg/m3. VOC levels in the Latin American cities were similar and considerably lower than those measured in the two Asian cities. Levels in Quito were the lowest of all the cities studied and this may reflect its high altitude which allows the use of fuels with a low aromatic content. The relative abundances of the different VOCs monitored and the ratios between different VOCs are largely consistent with vehicles being the predominant source of VOCs in these cities. The levels of VOCs measured during this study were generally higher than proposed UK standards and as such represent a direct health risk to the inhabitants of the cities. High levels of VOCs will also affect the incidence and severity of photochemical episodes with further consequences for human health and the environment.

EVALUATION OF INORGANIC ADSORBENTS FOR THE REMOVAL OF PROBLEMATIC TEXTILE DYES AND PESTICIDES

This paper evaluates three inorganic adsorbents (activated bauxite, fullers earth and a synthetic clay), relative to activated carbon, for the removal of several representative contaminants of major concern and frequent occurrence in UK textile industry efflupnts; reactive dyes; penlachlorophenol and Propetamphos. The results indicate that, for the removal of reactive dyes, the synthetic clay was the most effective adsorbent over the pH range from pH 5.5 to pH 8.5 and temperature range from 20 to 4Q?C,~although comparable dye removals were exhibited by activated carbon under neutral and alkaline conditions. Under acidic conditions activated bauxite was as effective as activated carbon. Pullers Earth was largely ineffective. With regard to the removal of pesticides activated «arbon was highly, effective^whereas *he three inorganic adsorbents showed negligible removals. ©1997 IAWQ. Published by Elsevipr Science Ud. .. : . : f i

Organic compounds in the cement-based stabilisation/ solidification of hazardous mixed wastes—Mechanistic and process considerations

Abstract The pretreatment of hazardous wastes by cement-based stabilisation/solidification is of increasing importance as an alternative to the direct landfill of toxic materials. Inorganic and organic compounds are known to have a range of beneficial or harmful effects on cement hydration and their presence within construction materials has been strictly controlled. This paper reviews cement and pozzolanic hydration and the use of organic admixtures as a prerequisite to a discussion of the effects of organic wastes in cement. The pre-adsorption of organic contaminants is reviewed and presented as a potential extension of existing solidification processes for the successful treatment of mixed organic/inorganic wastes.

Ceramic processing of incinerator bottom ash.

The <8 mm fraction of aged incinerator bottom ash from a commercial incinerator (energy from waste) plant has been collected at regular intervals, characterised and processed to form ceramic materials. Ashes were sieved, wet ball milled, dried, compacted and sintered at temperatures between 1080 and 1115 degrees C. Variations in the chemical composition and mineralogy of the milled ash, and the mineralogy, physical properties and leaching of sintered products have been assessed. Milling produces a raw material with consistent chemical and mineralogical composition with quartz (SiO(2)), calcite (CaCO(3)), gehlenite (Ca(2)Al(AlSi)O(7)) and hematite (Fe(2)O(3)) being the major crystalline phases present. Different batches also milled to give consistent particle size distributions. Sintering milled incinerator bottom ash at 1110 degrees C produced ceramics with densities between 2.43 and 2.64 g/cm(-3) and major crystalline phases of wollastonite (CaSiO(3)) and diopside (CaMgSi(2)O(6)). The sintered ceramics had reduced acid neutralisation capacity compared to the as-received ash and exhibited reduced leaching of Ca, Mg, Na and K under all pH conditions. The leaching of heavy metals was also significantly reduced due to encapsulation and incorporation into glassy and crystalline phases, with Cu and Al showing greatly reduced leaching under alkali conditions.

The leaching of inorganic species from activated carbons produced from waste tyre rubber

Waste tyre rubber can be used as a precursor for the production of high quality activated carbons. However, there is concern that inorganic impurities present in the rubber feed may restrict their use in liquid phase applications with high purity requirements. This paper presents an investigation of the presence and the leaching of inorganic species from activated carbons derived from waste tyre rubber. For the purpose of this work, a number of carbons were produced, characterised for their BET surface area and analysed for their inorganic composition. Subsequently, a number of tests were performed to evaluate the leaching of different inorganic species into solution at various pH values and carbon doses. Results showed that rubber-derived carbons contained elevated concentrations of sulphur and zinc, as well as traces of other metals such as lead, cadmium, chromium and molybdenum. Inorganic levels were significantly affected by production conditions, particularly degree of carbon activation and the nature of the gasification agent. However, leaching tests showed that the availability of these species in neutral pH conditions was very limited. Results demonstrated that, when using carbons doses comparable to those employed in water treatment works, only sulphur levels exceeded, in some occasions, health based quality standards proposed for drinking water.

Treatment of Organic-Contaminated Industrial Wastes Using Cement-Based Stabilization/Solidification— I. Microstructural Analysis of Cement-Organic Interactions

The major deficiencies in cement-based stabilization/solidification (S/S) processes are their inability to treat inorganic wastes contaminated with organic material or organic wastes. In general, organic compounds are poorly retained in a cement matrix and frequently have a detrimental, poorly understood, effect upon cement hydration and strength development. These interactions need to be understood as fully as possible, however, if S/S processes are to be developed in ways which will assure the long-term integrity of the resultant products.The work presented in this paper investigates some fundamental aspects of the interactions of two organic compounds, 3-chlorophenol and chloronaphthalene, with a cement matrix. Phenolic compounds have previously been shown to have a detrimental effect upon the macrostructural properties of ordinary Portland cement (OPC), for example, the strength, setting rate and leachability (Montgomery et al. 1988). Microstructural studies in this work have shown that 3-chlorophenol...

Adsorption of organic compounds from solution by activated carbons produced from waste tyre rubber

Activated carbons produced from waste tyre rubber have shown exceptional characteristics for the adsorption of organic species from solution. Adsorption capacities were found to be dependent primarily on the degree of activation and the molecular size of the adsorbate compound. For the purpose of this work, a series of activated carbons were produced by steam activation of waste tyre rubber at 925°C over a period of 80–640 min. The resulting carbons were investigated for their porosity, using nitrogen gas adsorption, and for their aqueous adsorption characteristics, using phenol, methylene blue, and textile dyes Turquoise H-A and Red H-E2B. Two widely used commercial adsorbents were also tested for comparative purposes. Aqueous adsorption data were modeled to the Langmuir equation in order to determine the adsorption capacities (X m) and affinity parameters (b) associated with each sample. Rubber-derived carbons proved superior to the commercial adsorbents for the removal of medium and large molecular weight compounds from solution, which was attributed to their extensive total micropore volume and external surface area.

Effect of Sintering Temperature on the Properties and Leaching of Incinerator Bottom Ash

The fine particle size fraction of municipal solid waste incinerator bottom ash is often problematic because reuse applications for this material are limited. In these experiments incinerator bottom ash with a particle size of less than 8 mm was processed using conventional ceramic production techniques involving wet milling, drying, compacting and sintering. The effect of sintering temperature on the sintered density, microstructure, acid neutralization capacity (ANC) and the release of metal ions as a function of leachate pH are reported. Sintering at 1080 °C produced samples with maximum density. This material contained diopside (CaMgSi2O6), clinoenstatite (Mg2Si2O6) and wollastonite (CaSiO3) as the major crystalline phases. The acid neutralization capacity of sintered samples is significantly lower than milled bottom ash, and further reduces as the sintering temperature increases. This is associated with reduced leaching of Ca from sintered ash samples under all leachate pH conditions. Heavy metals present in the incinerator bottom ash included Cr, Cu, Ni, Zn, Cd and Pb. Sintering under optimum conditions reduced the leachable fraction of these metals under aggressive acid conditions (leachate pH 3) by factors ranging from 90% for Ni to greater than 99% for Cr, Cd, Zn and Pb.

Organophilic clays for the successful stabilisation/solidification of problematic industrial wastes

Abstract Cement‐based stabilisation/solidification has been used for treatment of inorganic industrial waste for a number of years. An urgent need now exists to expand the use of this technique to inorganic wastes containing a significant level (up to ‐15%) of organic contaminants. Application of organophilic clays to this problem is reported and the successful retention of the organic component of some problematic industrial wastes is demonstrated.