G.D. Fowler

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.

Sewage sludge-based adsorbents: A review of their production, properties and use in water treatment applications

The imposition of more stringent legislation governing the disposal and utilisation of sewage sludge, coupled with the growth in its generation and the loss of traditionally accepted disposal routes, has prompted a drive for alternative uses for sewage sludge. One option that exhibits special promise, due to its potential to valorise the sludge, is the conversion of the sludge into adsorbents. This paper seeks to review the published research in this field: it covers the means of production, the characteristics and the potential applications of sewage sludge-based adsorbents (SBAs). The literature has indicated that chemical activation utilising alkali metal hydroxides is the most effective technique for producing high surface area SBAs. In addition, acid washing is highly effective at raising the BET surface area of SBAs, especially when coupled with physical activation. Due to their relatively low microporosity, the phenol uptake of SBAs produced by physical activation is low, but through a combination of their favourable surface chemistry and relatively high mesoporosity, the best of these adsorbents can attain high uptakes of organic dyes. The SBAs produced by carbonisation, through their high cation exchange capacity, generally exhibit a high metal cation capacity. For further research, the following investigations are recommended: the utilisation of alternative chemical activation reagents; the optimisation of the most effective chemical activation techniques; the combined utilisation of different activation and surface chemistry modification techniques to produce application-specific adsorbents.

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

Pore structure and adsorption characteristics of steam pyrolysis carbons from Moringa oleifera

Abstract A series of activated carbons has been prepared from the waste seed husks of the tropical multi-purpose tree Moringa oleifera, using a single-stage steam pyrolysis activation. Carbons were characterised by N2 adsorption, CHN analysis and scanning electron microscopy. Nitrogen adsorption isotherms were analysed by the BET, t-plot and Horvath and Kawazoe methods. All the carbons were microporous, with those activated at 750 °C for 120 minutes ( 750 120 ) and 800 °C for 30 or 60 minutes having the highest BET surface areas, of 730, 713 and 774 m2 g−1, respectively. A simple acid rinse of the 800 °C/30 minutes carbon increased the surface area to 932m2g−1. The 800/60 carbon had the highest mesopore and macropore surface area, 135.7 m2g−1, compared to 92.7m2g−1 for the 800 30 carbon. Scanning electron micrographs of the 800 30 carbon showed a lignocellulosic macropore structure, cleaned by the steam pyrolysis. These results show that it is possible to produce a high quality microporous activated carbon from M. oleifera husks using a simple single-stage steam pyrolysis activation.

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.

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.

Application of sludge-based carbonaceous materials in a hybrid water treatment process based on adsorption and catalytic wet air oxidation

This paper describes a preliminary evaluation of the performance of carbonaceous materials prepared from sewage sludges (SBCMs) in a hybrid water treatment process based on adsorption and catalytic wet air oxidation; phenol was used as the model pollutant. Three different sewage sludges were treated by either carbonisation or steam activation, and the physico-chemical properties of the resultant carbonaceous materials (e.g. hardness, BET surface area, ash and elemental content, surface chemistry) were evaluated and compared with a commercial reference activated carbon (PICA F22). The adsorption capacity for phenol of the SBCMs was greater than suggested by their BET surface area, but less than F22; a steam activated, dewatered raw sludge (SA_DRAW) had the greatest adsorption capacity of the SBCMs in the investigated range of concentrations (<0.05 mol L(-1)). In batch oxidation tests, the SBCMs demonstrated catalytic behaviour arising from their substrate adsorptivity and metal content. Recycling of SA_DRAW in successive oxidations led to significant structural attrition and a hardened SA_DRAW was evaluated, but found to be unsatisfactory during the oxidation step. In a combined adsorption-oxidation sequence, both the PICA carbon and a selected SBCM showed deterioration in phenol adsorption after oxidative regeneration, but a steady state performance was reached after 2 or 3 cycles.

Metal leaching from monolithic stabilised/solidified air pollution control residues

Portland cement (CEM I) and ground granulated blast furnace slag (ggbs) have been used to treat air pollution control (APC) residues from an energy-from-waste plant burning municipal solid waste. Stabilised/solidified (s/s) products were prepared with binder additions ranging from 10 to 50 wt.% of total dry mass and water/solids ratios between 0.40 and 0.80. Monolithic leach tests (EA NEN 7375:2004) indicated that 50% binder additions were necessary to meet the UK monolithic Waste Acceptance Criteria (monWAC) for Pb and Zn, and previous work indicated that chloride leaching exceeded WAC even at this binder addition. Lower binder additions (20 and 10%) did not sufficiently reduce leaching of Pb. Although the monWAC are based on an assumption that leaching is diffusion-controlled, evaluation of leaching mechanisms indicates that more complex processes than diffusion occur for s/s APC residues.

THERMAL-CONVERSION OF GASWORKS CONTAMINATED SOIL INTO CARBONACEOUS ADSORBENTS

Contaminated soil from a gas works site has been successfully converted into a carbonaceous adsorbent utilising ZnCl2 as an activating agent. The organic contamination, consisting of coal tars, phenols and associated compounds, was converted into a carbonaceous material. Extensive reduction (95%) in the cyanide content of the soil after treatment was observed and entrapment of metallic contamination within the carbonaceous matrix has been observed through XRF analysis. Surface area and porosity analysis by gas adsorption indicates surface areas ranging from 110 to 570 m2/g, and development of microporosity within the carbons. The

Use of a liquid chemical waste to produce a clay–carbon adsorbent

The feasibility of producing an adsorbent from an alkaline aqueous tarry industrial waste has been investigated in this study. The inherent disadvan- tages of producing a solid carbonaceous material from a waste with its organic content in a dissolved state were overcome by neutralising the waste liquor to pH \ 2 in the presence of fullerIs earth, -ltering and producing a solid cake more suitable for thermal treatment. Optimisation of this procedure, followed by activation, produced clayEcarbon adsorbents with surface areas of up to ZnCl 2 225 m2 g~1 capable of adsorbing 28% of phenol and 35% of 4-nitrophenol from 10 mM aqueous solution. The potential of this procedure in a bene-cial waste reduction and re-use context are highlighted. 1998 SCI (