Ernest K. Yanful

A review of plastic waste biodegradation.

ABSTRACT With more and more plastics being employed in human lives and increasing pressure being placed on capacities available for plastic waste disposal, the need for biodegradable plastics and biodegradation of plastic wastes has assumed increasing importance in the last few years. This review looks at the technological advancement made in the development of more easily biodegradable plastics and the biodegradation of conventional plastics by microorganisms. Additives, such as pro-oxidants and starch, are applied in synthetic materials to modify and make plastics biodegradable. Recent research has shown that thermoplastics derived from polyolefins, traditionally considered resistant to biodegradation in ambient environment, are biodegraded following photo-degradation and chemical degradation. Thermoset plastics, such as aliphatic polyester and polyester polyurethane, are easily attacked by microorganisms directly because of the potential hydrolytic cleavage of ester or urethane bonds in their structures. Some microorganisms have been isolated to utilize polyurethane as a sole source of carbon and nitrogen source. Aliphatic-aromatic copolyesters have active commercial applications because of their good mechanical properties and biodegradability. Reviewing published and ongoing studies on plastic biodegradation, this paper attempts to make conclusions on potentially viable methods to reduce impacts of plastic waste on the environment.

Chemical states in XPS and Raman analysis during removal of Cr(VI) from contaminated water by mixed maghemite-magnetite nanoparticles.

Mixed maghemite-magnetite has been used as adsorbent for Cr(VI) removal in this study. Results show that the adsorption capacity is enhanced with an increase in reaction temperature and decrease in free energy change. Thermodynamic study shows that Cr(VI) adsorption on the mixed maghemite and magnetite is endothermic in nature and is dependent on solution pH between 3 and 6. X-ray photoelectron spectroscopy (XPS) results demonstrate the theoretical multiplet peaks for iron and chromium adsorbed iron at the surface of the γ-Fe(2)O(3) and Fe(3)O(4) mixture. Theoretical multiplet analysis shows that during Cr adsorption, the amount of maghemite increases (from 70 to 89%). In magnetite spectra, the relative content of Fe(II) decreases from 8.2 to 3.6% indicating the reduction of magnetite in the mixture particles. In Raman spectroscopy studies, clear peaks of chromium on iron oxide were generated at 826 cm(-1), which could be attributed to chemical interactions between chromium compound and iron oxide. From the results of Raman and XPS studies, electrostatic attraction and oxidation-reduction between chromium and mixed maghemite-magnetite are postulated as mechanisms for the removal of Cr(VI) from aqueous solutions.

Comparison of municipal solid waste management systems in Canada and Ghana: A case study of the cities of London, Ontario, and Kumasi, Ghana

Integrated waste management has been accepted as a sustainable approach to solid waste management in any region. It can be applied in both developed and developing countries. The difference is the approach taken to develop the integrated waste management system. This review looks at the integrated waste management system operating in the city of London, Ontario-Canada and how lessons can be drawn from the systems development and operation that will help implement a sustainable waste management system in the city of Kumasi, Ghana. The waste management system in London is designed such that all waste generated in the city is handled and disposed of appropriately. The responsibility of each sector handling waste is clearly defined and monitored. All major services are provided and delivered by a combination of public and private sector forces. The sustainability of the waste management in the city of London is attributed to the continuous improvement strategy framework adopted by the city based on the principles of integrated waste management. It is perceived that adopting a strategic framework based on the principles of integrated waste management with a strong political and social will, can transform the current waste management in Kumasi and other cities in developing countries in the bid for finding lasting solutions to the problems that have plagued the waste management system in these cities.

Endocrine disrupting compounds (EDCs) and pharmaceuticals and personal care products (PPCPs) in the aquatic environment: implications for the drinking water industry and global environmental health

Endocrine disrupting compounds (EDCs) and pharmaceuticals and personal care products (PPCPs) are a group of chemical compounds with diverse physical and chemical properties. Recent studies have indicated undesired effects of EDCs and PPCPs at their reported trace concentrations (ng l(-1) to microg l(-1)). This paper reviews the current knowledge on the sources, properties, occurrence and health impacts of EDCs and PPCPs, and their removal from drinking water using ozonation and ozone/hydrogen peroxide-based advanced oxidation. The paper also examines the potential threats posed by these chemicals to drinking water and public health. While these compounds are known to have adverse effects on ecosystem health, notably in the fish population, a similar link is yet to be established between ingestion of these compounds through drinking water and human health. In addition, data on the effectiveness of existing methods for the removal of these compounds are not conclusive. Further studies are required to characterize risks, and also to evaluate and optimize existing removal processes. Also concerted international effort is urgent to cut down the risk of exposure and restrain the production and marketing of toxic chemicals.

Heavy metal migration at a landfill site, Sarnia, Ontario, Canada—2: metal partitioning and geotechnical implications

Abstract Heavy metal profiles below a 15-year old sanitary landfill overlying a 30 m thick natural clay deposit are presented. Results indicate that unlike soluble species such as Cl − and Na + which have migrated distances up to 130 cm, Cu, Zn and Pb have migrated only up to 10 cm. The extent of Fe migration is estimated to be 20 cm. Highly reducing conditions at the interface ( E h = −130mV), coupled with the alkaline nature of the clay pore waters, have resulted in the precipitation of migrated heavy metals as carbonates. At the clay/waste interface, 88, 84 and 80% of the excess Fe, Zn and Pb, respectively, are present as secondary carbonates. This is confirmed by selective chemical dissolution analyses which also show that Fe, Zn, Pb and, to a greater extent, Cu are present in solid organic forms at the interface. Batch equilibrium studies clearly show that Cu and Pb removal from leachate is significantly increased by the presence of carbonates in the soil. For example, 75% more Pb is removed by the carbonate-rich bulk soil than the carbonate-free soil. The batch studies also show that when the pH > 5.2, removal of metal increases significantly due to precipitation as carbonates. From the results it is concluded that the presence of metal sludges in landfills lined naturally or artifically by a carbonate-rich clayey barrier reduces the rate of migration of numerous toxic transition metals and may also decrease the barrier porosity by precipitation. The decreases in porosity will be beneficial to the performance of the barrier due to reductions in both advection and diffusion.

Modeling and measurement of evaporation in moisture-retaining soil covers

Abstract Soil covers are widely used in mine waste and landfill applications to protect the environment. For an effective soil cover, the infiltration and oxygen barrier must have a low hydraulic conductivity and also maintain a high degree of saturation. Soil water evaporation significantly affects water content, and as a result the degree of saturation of the soil. Therefore, knowledge of the rate of evaporation at the soil–atmosphere interface is required to estimate the water content of candidate cover soils. Clayey soil is commonly used, either separately as a single cover or in various combinations with other soils as a layered cover system. In this study, water flow through a single clayey till cover and a layered soil cover were modeled using a coupled liquid flow, vapor diffusion and heat transfer finite-element model (SoilCover). The layered soil cover studied was a typical mine-waste soil cover intended to control oxygen diffusion and infiltration in a temperate climate and consisted of three layers: coarse sand and fine sand as upper and lower capillary barriers, respectively, and clayey till as an infiltration and oxygen barrier. The water level was located at the bottom of the cover. Evaporation and drainage predicted by the model reasonably agreed with experimental results and showed that the clayey till would be an effective oxygen barrier in sulfide-bearing mine waste covers, for which a very low oxygen flux is desired in order to achieve environmental protection. The results emphasize the need to have evaporation and drainage barriers above and below clay barriers designed to retain moisture. Further analysis using SoilCover showed that coarse sand would perform better than either fine sand or silt as a protective top layer over a clayey till barrier.

Soil Covers for Controlling Acid Generation in Mine Tailings: a Laboratory Evaluation of the Physics and Geochemistry

To evaluate the effectiveness of soil covers, column experiments were conducted on tailings protected by a three-layer soil cover and tailings directly exposed in the open laboratory for a period of 760 days. Periodic rain application was performed to simulate field conditions, and at four times during the experiments the pore water was completely flushed out of each column for analysis. Profiles of oxygen, temperature, and volumetric water content were measured throughout the experiment, and the post-testing pore water quality was also characterized. A one-dimensional semi-analytic diffusion model was used to simulate oxygen profiles in the uncovered tailings. Modelling performed using the geochemical code MINTEQ showed that in the laboratory, aluminium concentrations in the tailings pore water were controlled by Al(OH)SO4, sulphate by gypsum and Al(OH)SO4and iron by lepidocrocite in the upper half and by ferrihydrite in the lower half. In the field, however, the iron oxyhydroxide minerals formed in the oxidized zone appear to be dissolving. It was found that the cover was effective in preventing significant desaturation of the clay, even over a 150-day drying period. The covered tailings did not oxidize much during the experiments. In the uncovered tailings, oxygen modelling and examination of the geochemistry show that the rate of gross oxidation and the advancement of the oxidation front decreases with time. However, pore water quality is controlled by geochemical processes other than oxidation, as reported in the field.

The mobility of radium-226 and trace metals in pre-oxidized subaqueous uranium mill tailings

The exchange of 226Ra and trace metals across the tailings-water interface and the mechanisms governing their mobility were assessed via sub-centimetre resolution profiling of dissolved constituents across the tailings–water interface in Cell 14 of the Quirke Waste Management Area at Rio Algoms Quirke Mine, near Elliot Lake, Ontario, Canada. Shallow zones ( 2 m water depth) fosters stagnant bottom waters and permits the development of anoxia above the benthic boundary. These anoxic tailings are characterized by substantial remobilization of 226Ra, resulting in a relatively large flux of 226Ra from the tailings to the water column. The strong correlation between the porewater profiles of 226Ra and Ba (r2=0.99), as well as solubility calculations, indicate that the mobility of Ra is controlled by saturation with respect to a poorly ordered and/or impure barite phase [(Ra,Ba)SO4]. In the anoxic zones, severe undersaturation with respect to barite is sustained by microbial SO4 reduction. Flux calculations suggest that the increase in 226Ra activity in the water cover since 1995 (from <0.5 to 2.5 Bq l−1) can be attributed to an increase in the spatial distribution of anoxic bottom waters caused by increased density of benthic flora. The anoxic, vegetated areas also exhibit minor remobilization with respect to dissolved As, Ni and Zn. The removal of trace metals in the anoxic bottom waters appears to be limited by the availability of free sulphide. Collectively, the data demonstrate that while the water cover over the U mill tailings minimizes sulphide oxidation and metal mobility, anoxic conditions which have developed in deeper areas have led to increased mobility of 226Ra.

A review of binders used in cemented paste tailings for underground and surface disposal practices

Increased public awareness of environmental issues coupled with increasingly stringent environmental regulations pertaining to the disposal of sulphidic mine waste necessitates the mining industry to adopt more competent and efficient approaches to manage acid rock drainage. Cemented paste tailings (CPT) is an innovative form of amalgamated material currently available to the mining industry in developed countries. It is made usually from mill tailings mingled with a small amount of binder (customarily Portland cement) and water. The high cost associated with production and haulage of ordinary Portland cement and its alleged average performance as a sole binder in the long term (due to vulnerability to internal sulphate attack) have prompted users to appraise less expensive and technically efficient substitutes for mine tailings paste formulations. Generally, these binders include but are not limited to sulphate resistant cements, and/or as a partial replacement for Portland cement by artificial pozzolans, natural pozzolans, calcium sulphate substances and sodium silicates. The approach to designing environmentally efficient CPT is to ensure long-term stability and effective control over environmental contaminants through the use of composite binder systems with enhanced engineering properties to cater for inherit deficiencies in the individual constituents. The alkaline pore solution created by high free calcium rich cement kiln dust (CKD) (byproduct of cement manufacturing) is capable of disintegrating the solid glassy network of artificial pozzolans to produce reactive silicate and aluminate species when attacked by (OH(-)) ions. The augmented pozzolanic reactivity of CKD-slag and CKD-fly ash systems may produce resilient CPT. Since cemented paste comprising mine tailings and binders is a relatively new technology, a review of the binding materials used in such formulations and their performance evaluation in mechanical fill behaviour was considered pertinent in the study.

Water balance during evaporation and drainage in cover soils under different water table conditions

Abstract Experimental measurement and analytical methods were performed to study water flow through four different cover soils: clayey till, silt, coarse sand and fine sand. The upward and downward water fluxes (i.e. evaporation and drainage) were measured in the laboratory under different water table conditions. Both experimental and analytical results indicated that downward water flow (drainage) significantly affected upward water flow (evaporation) during changes in the water table elevation. Deepening water table elevation decreased evaporation in the sands and to a lesser extent in the silt, by promoting gravity-driven drainage and hence limiting water supply to the soil surface. Evaporation and drainage in the fine-textured clayey till did not change significantly as the water table dropped from the soil surface to 1 m below the soil column. The results suggest that the clayey till would be an effective oxygen barrier in sulfide-bearing mine waste covers, while the sands would be effective evaporation and drainage barriers for the till. The experimental results showed that the air entry value and hydraulic conductivity of the soil are critical parameters controlling drainage and evaporation in soils under different water table conditions. The study emphasizes the need to have evaporation and drainage barriers above and below a soil layer intended to maintain high water saturation under adverse environmental conditions, such as high evaporation and a fluctuating water table.