Simon J. T. Pollard

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.

Biodrying for mechanical-biological treatment of wastes : A review of process science and engineering

Biodrying is a variation of aerobic decomposition, used within mechanical-biological treatment (MBT) plants to dry and partially stabilise residual municipal waste. Biodrying MBT plants can produce a high quality solid recovered fuel (SRF), high in biomass content. Here, process objectives, operating principles, reactor designs, parameters for process monitoring and control, and their effect on biodried output quality are critically examined. Within the biodrying reactors, waste is dried by air convection, the necessary heat provided by exothermic decomposition of the readily decomposable waste fraction. Biodrying is distinct from composting in attempting to dry and preserve most of biomass content of the waste matrix, rather than fully stabilise it. Commercial process cycles are completed within 7-15 days, with mostly H(2)O((g)) and CO(2) loses of ca. 25-30% w/w, leading to moisture contents of <20% w/w. High airflow rate and dehumidifying of re-circulated process air provides for effective drying. We anticipate this review will be of value to MBT process operators, regulators and end-users of SRF.

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.

Characterisation and applications of activated carbon produced from Moringa oleifera seed husks by single-step steam pyrolysis

Abstract The seed husks of the multipurpose tree Moringa oleifera are potentially a waste product that may be available in large quantities, and previous work has demonstrated that a microporous activated carbon can be produced from them by carbonisation under nitrogen followed by activation in steam. This research examines the efficacy of a simpler and cheaper activation process, single-step steam pyrolysis activation, with a view to promoting the production of low-cost activated carbon in the developing world. Husks were heated in a steam atmosphere to 750°C for 30 or 120 min, or 800°C for 30 min, then the resulting carbons were tested to determine their iodine numbers and adsorption isotherms for phenol, 4-nitrophenol and methylene blue. Phenol and 4-nitrophenol were adsorbed rapidly by all three carbons, with 80–90% w/w adsorbed in the first 30 min, whereas methylene blue adsorption was slower. Pyrolysis at 800°C for 30 min produced a carbon (yield 12.2% w/w) with an iodine number of 703 mg g −1 , a phenol specific surface area (SSA) of 629 m 2 g −1 , a 4-nitrophenol SSA of 664 m 2 g −1 and a methylene blue SSA of 211 m 2 g −1 . The carbon produced at 750°C for 120 min (yield 11.9% w/w) had similar properties, but the one produced at 750°C for 30 min (yield 16.6% w/w) had a less developed porosity. The adsorbance characteristics of the two best carbons were superior to those produced previously by the conventional two-stage carbonisation-activation, and were competitive with commercial carbons. These results demonstrate that steam pyrolysis activation of M. oleifera husks could provide a low-cost, local source of high quality activated carbon in the developing world.

Microporous carbons from Moringa oleifera husks for water purification in less developed countries

High quality activated carbon can be prepared from the waste husks of Moringa oleifera, an indigenous tropical plant material. Steam activated husks exhibited a well-developed micropore volume of 0.57 cm3 g−1 and a corresponding apparent surface area 734 m2 g−1, as determined by BET N2 adsorption hysteresis. In an assessment of aqueous phase adsorptive performance, activated Moringa carbon was found to be comparable to commerical powdered activated water treatment carbons (PACs) and exhibited a Langmuir monolayer coverage constant (Q0) of 1.89 mmol g−1 for phenol adsorption from the aqueous phase. Cultivation of Moringa oleifera in developing countries for the coagulant properties of its seed extract provides a well founded economic incentive for the utilisation of treated waste husks as activated carbon during in situ water purification.

Weathered Hydrocarbon Wastes: A Risk Management Primer

We provide a primer and critical review of the characterization, risk assessment, and bioremediation of weathered hydrocarbons. Historically the remediation of soil contaminated with petroleum hydrocarbons has been expressed in terms of reductions in total petroleum hydrocarbon (TPH) load rather than reductions in risk. There are several techniques by which petroleum hydrocarbons in soils can be characterized. Method development is often driven by the objectives of published risk assessment frameworks. Some frameworks stipulate analysis of a wide range of petroleum hydrocarbons; for example, the United Kingdom (UK) approach suggests compounds from EC5 to EC70 be examined. Methods for the extraction of petroleum hydrocarbons from soil samples have been reviewed extensively in the open literature. Although various extraction and analytical methods are available for petroleum hydrocarbons, their results suffer from inter-method variation, with gas chromatography methods being used widely. Currently, the implications for risk assessment are uncertain. Bioremediation works well for remediating soils contaminated with petroleum hydrocarbons. As a result, the optimization of environmental conditions is imperative. For petroleum hydrocarbons in soil, international regulatory guidance on the management of risks from contaminated sites is now emerging. There is also growing support for the move toward compound-specific risk-based approaches for the assessment of hydrocarbon-contaminated land.

Production and Quality Assurance of Solid Recovered Fuels Using Mechanical—Biological Treatment (MBT) of Waste: A Comprehensive Assessment

The move from disposal-led waste management to resource management demands an ability to map flows of the properties of waste. Here, we provide a comprehensive review of how mechanical–biological treatment (MBT) plants, and the unit processes that comprise them, perform in relation to management of material flows, while transforming inputs into output fractions. Focus is placed on the properties relating to the quality of MBT-derived fuels. Quality management initiatives for refuse-derived fuels (RDF) or solid recovered fuels (SRF) are reviewed and SRF quality from MBT plants is assessed through a statistical analysis of published data. This can provide a basis for a targeted reduction in pollution load from solid MBT outputs and subsequent end-user emissions. Our analysis, among else, (1) verifies the difficulty of chemical separation solely by mechanical means; (2) illustrates the trade-off between achieving a high quality of recoverable outputs and the quantity/properties of reject material; and (3) indicates that SRF quality could respond to legislative requirements and market needs, if specific improvements (reduction of Cl, Cu, and Pb content) are achieved. Further research could enhance the confidence in the ability of MBT plants to produce a quality-assured SRF suitable for specific end-users, without contradicting the wider requirement for an overall sustainable management of resources.

The influence of interference effects on the mechanical, microstructural and fixation characteristics of cement-solidified hazardous waste forms

Abstract The hydration behaviour of ordinary Portland cement (OPC) and other hydraulic binder systems in the presence of industrial wastes considered “suitable” for cement-based solidification is not always consistent. Waste-binder interference effects can significantly alter the short and long term mechanical, microstructural and binding characteristics of solidified waste forms containing materials from a wide variety of waste streams. In general, the mechanisms of interference can be explained and this lends support to the need for a critical evaluation of current waste form quality control procedures and the development of additional pre-treatment/alternative treatment methods. Future research studies including the in-situ examination of waste forms together with an in-depth quantitative analysis of the effects of waste species on the short- and long-term properties of solidified products is warranted.

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.

An integrated appraisal of energy recovery options in the United Kingdom using solid recovered fuel derived from municipal solid waste

This paper reports an integrated appraisal of options for utilising solid recovered fuels (SRF) (derived from municipal solid waste, MSW) in energy intensive industries within the United Kingdom (UK). Four potential co-combustion scenarios have been identified following discussions with industry stakeholders. These scenarios have been evaluated using (a) an existing energy and mass flow framework model, (b) a semi-quantitative risk analysis, (c) an environmental assessment and (d) a financial assessment. A summary of results from these evaluations for the four different scenarios is presented. For the given ranges of assumptions; SRF co-combustion with coal in cement kilns was found to be the optimal scenario followed by co-combustion of SRF in coal-fired power plants. The biogenic fraction in SRF (ca. 70%) reduces greenhouse gas (GHG) emissions significantly ( approximately 2500 g CO(2) eqvt./kg DS SRF in co-fired cement kilns and approximately 1500 g CO(2) eqvt./kg DS SRF in co-fired power plants). Potential reductions in electricity or heat production occurred through using a lower calorific value (CV) fuel. This could be compensated for by savings in fuel costs (from SRF having a gate fee) and grants aimed at reducing GHG emission to encourage the use of fuels with high biomass fractions. Total revenues generated from coal-fired power plants appear to be the highest ( 95 pounds/t SRF) from the four scenarios. However overall, cement kilns appear to be the best option due to the low technological risks, environmental emissions and fuel cost. Additionally, cement kiln operators have good experience of handling waste derived fuels. The scenarios involving co-combustion of SRF with MSW and biomass were less favourable due to higher environmental risks and technical issues.