Geoffrey S. Simate

The heterogeneous coagulation and flocculation of brewery wastewater using carbon nanotubes

Coagulation and flocculation treatment processes play a central role in the way wastewater effluents are managed. Their primary function is particle removal that can impart colour to a water source, create turbidity, and/or retain bacterial and viral organisms. This study was carried out to investigate whether carbon nanotubes (CNTs) can be used as heterogeneous coagulants and/or flocculants in the pretreatment of brewery wastewater. A series of experiments were conducted in which the efficiencies of pristine and functionalised CNTs were compared with the efficiency of traditional ferric chloride in a coagulation/flocculation process. Turbidity and chemical oxygen demand (COD), including the zeta potential were used to monitor the progress of the coagulation/flocculation process. Both pristine and functionalised CNTs demonstrated the ability to successfully coagulate colloidal particles in the brewery wastewater. Overall, ferric chloride was found to be a more effective coagulant than both the pristine and functionalised CNTs.

Human health effects of residual carbon nanotubes and traditional water treatment chemicals in drinking water

The volume of industrial and domestic wastewater is increasing significantly year by year with the change in the lifestyle based on mass consumption and mass disposal brought about by the dramatic development of economies and industries. Therefore, effective advanced wastewater treatment is required because wastewater contains a variety of constituents such as particles, organic materials, and emulsion depending on the resource. However, residual chemicals that remain during the treatment of wastewaters form a variety of known and unknown by-products through reactions between the chemicals and some pollutants. Chronic exposure to these by-products or residual chemicals through the ingestion of drinking water, inhalation and dermal contact during regular indoor activities (e.g., showering, bathing, cooking) may pose cancer and non-cancer risks to human health. For example, residual aluminium salts in treated water may cause Alzheimers disease (AD). As for carbon nanotubes (CNTs), despite their potential impacts on human health and the environment having been receiving more and more attention in the recent past, existing information on the toxicity of CNTs in drinking water is limited with many open questions. Furthermore, though general topics on the human health impacts of traditional water treatment chemicals have been studied, no comparative analysis has been done. Therefore, a qualitative comparison of the human health effects of both residual CNTs and traditional water treatment chemicals is given in this paper. In addition, it is also important to cover and compare the human health effects of CNTs to those of traditional water treatment chemicals together in one review because they are both used for water treatment and purification.

The production of carbon nanotubes from carbon dioxide: challenges and opportunities

Abstract Recent advances in the production of carbon nanotubes (CNTs) are reviewed with an emphasis on the use of carbon dioxide (CO2) as a sole source of carbon. Compared to the most widely used carbon precursors such as graphite, methane, acetylene, ethanol, ethylene, and coal-derived hydrocarbons, CO2 is competitively cheaper with relatively high carbon yield content. However, CNT synthesis from CO2 is a newly emerging technology, and hence it needs to be explored further. A theoretical and analytical comparison of the currently existing CNT-CO2 synthesis techniques is given including a review of some of the process parameters (i.e., temperature, pressure, catalyst, etc.) that affect the CO2 reduction rate. Such analysis indicates that there is still a fundamental need to further explore the following aspects so as to realize the full potential of CO2 based CNT technology: (1) the CNT-CO2 synthesis and formation mechanism, (2) catalytic effects of transitional metals and mechanisms, (3) utilization of metallocenes in the CNT-CO2 reactions, (4) applicability of ferrite-organometallic compounds in the CNT-CO2 synthesis reactions, and (5) the effects of process parameters such as temperature, etc.

Characterisation of Factors in the Bacterial Leaching of Nickel Laterites Using Statistical Design of Experiments

Identifying influential factors in the bacterial leaching of nickel laterites using a mixed culture of chemolithotrophic micro-organisms was explored using the approach of statistical design of experiments. In a series of experiments, pH, particle size, pulp density, type of substrate and inoculum size were statistically combined using a quarter fractional factorial designs 2 5−2 III and tested for their influence on nickel recovery using chemolithotrophic microorganisms. The results indicated that inoculum size was not statistically significant while the rest of the factors were statistically significant. Under the ranges studied the interaction between the variables was found to be weak. The results also showed that recovery was maximized at low pH and low pulp density. In the range studied, particles of less than 38μm had a negative influence on nickel recovery. Sulphur substrate also showed better effects than pyrite.

The Microbial Assisted Leaching of Nickel Laterites Using a Mixed Culture of Chemolithotrophic Microorganisms

Nickel laterite contains metal values but is not capable of participating in the primary chemolithotrophic bacterial oxidation because it contains neither Fe2+ iron nor substantial amount of reduced sulphur. Its metal value can, however, be recovered by allowing the primary oxidation of FeS2, or similar iron/sulphur minerals to provide H2SO4 acid solutions, which solubilise the metal content. This study investigated the possibility of treating nickel laterites using chemolithotrophic microorganisms. Preliminary studies conducted using H2SO4 acid, citric acid and acidified Fe2(SO4)3 gave an insight on the use of chemolithotrophic bacteria in this process,. Results showed that H2SO4 acid performed better, in terms of nickel recovery, than citric acid or acidified Fe2(SO4)3. In the bacterial leaching test works, mixed cultures of Acidithiobacillus ferrooxidans, Acidithiobacillus caldus and Leptospirillum ferrooxidans were used in the presence of elemental sulphur and FeS2 as energy sources. The sulphur substrate exhibited better effects in terms of bacterial growth, acidification and nickel recovery than the FeS2 substrate. Using response surface methodology, the theoretical optimum conditions for maximum nickel recovery (79.8%) within the conditions studied was an initial pH of 2.0, 63μm particle size and 2.6% pulp density.

Kinetic model of carbon nanotube production from carbon dioxide in a floating catalytic chemical vapour deposition reactor

The production of carbon nanostructures, including carbon nanotubes (CNTs), by chemical vapour deposition (CVD) occurs by thermally induced decomposition of carbon-containing precursors. The decomposition of the feedstock leading to intermediate reaction products is an important step, but rarely incorporated in rate equations, since it is generally assumed that carbon diffusion through or over the catalyst nanoparticles is the rate-limiting step in the production of CNTs. Furthermore, there is no kinetic model to date for the production of CNTs from carbon dioxide. These aspects are addressed in this study with the aid of a series of experiments conducted in a floating catalytic CVD reactor in which the effects of reactor temperature, concentration and flow rate of CO2 were investigated. A simple rate equation for the reductive adsorption of CO2 onto the catalyst surface followed by carbon diffusion leading to the production of CNTs is proposed as follows: d[CNT]/dt = K[CO2], where K is proportional to the diffusion coefficient of carbon. The derived kinetic model is used to calculate the amount of CNTs for a given concentration of CO2, and the experimentally measured data fits the simple rate equation very well at low carbon dioxide concentration.

Synthesis of Carbon Nanomaterials in a Swirled Floating Catalytic Chemical Vapour Deposition Reactor for Continuous and Large Scale Production

Carbon nanotubes (CNTs), ‘rediscovered’ (Monthioux & Kuznetsov, 2006) by Iijima as a byproduct of fullerene synthesis (Iijima, 1991), have attracted enormous scientific and technological interest. Their myriad applications in various fields since their rediscovery are no longer debatable. However, their commercial applications still depend on large scale synthesis (several thousands of tons per year) and associated cost of production. Various methods have been developed for the production of CNTs (Dresselhaus et al., 2001; Agboola et al., 2007). However, the three very useful and widespread methodologies include arc discharge, laser ablation and chemical vapour deposition (CVD) (Robertson, 2004; Agboola et al., 2007). Two key requirements revealed in these methods are as follows, (i) a carbon source, and (ii) a heat source to achieve the desired operating temperature (See & Harris, 2007). In the arc discharge, CNTs are produced from carbon vapour generated by an electric arc discharge between two graphite electrodes (with or without catalysts), under an inert gas atmosphere (Journet et al., 1997; Lee et al., 2002; Agboola et al., 2007). In the laser ablation, a piece of graphite target is vapourised by laser irradiation under an inert atmosphere (Journet & Bernier, 1998; Paradise & Goswami, 2007). As for the technique of CVD , it involves the use of an energy source such as plasma, a resistive or inductive heater, or furnace to transfer energy to a gas phase carbon source in order to produce fullerenes, CNTs and other sp2-like nanostructures (Meyyappan, 2004). As would be expected, some of these methods are more effective than others. The arc-discharge, though it produces CNTs of high quality with fewer structural defects, uses high temperature of up to 1500°C, which makes it difficult to be scaled up for commercial purposes. On the other hand, laser vaporisation method is an expensive technique because it involves high purity graphite rods and high power lasers. At the moment, the CVD methodology (or variations thereof) is the only promising process for the production of CNTs on a reasonably large-scale compared to arc-discharge and laser vaporization methods (Coleman, 2008). In addition, the process tends to produce nanotubes with fewer impurities (catalyst particles, amorphous carbon and non-tubular fullerenes) compared to other techniques (Esawi & Farag, 2007). The variants of the CVD are as a result of the means by which chemical reactions are initiated, the type of

Water treatment and reuse in breweries

Abstract The perpetual necessity for high-quality but ever insufficient water in the brewery industry has continued to drive the need to find other sources of water. Therefore, water treatment and reuse in breweries are now being considered as a very appealing alternative source of water. This chapter explores the prospective opportunities that may be available for treating brewery wastewater for reuse. Firstly, it discusses the production and composition of brewery wastewater. It then analyses the current pretreatment processes. This is followed by a discussion of advanced treatment methods. Finally, challenges and future prospects are discussed.

The use of Carbon Nanotubes in Medical Applications - Is It a Success Story?

Since their rediscovery [1] by Iijima [2] carbon nanotubes (CNTs) have attracted a lot of interesting research due to their outstanding properties that have potential impact on broad areas of science and technology [3]. The name CNT originates from their nanometer-scale size. An ideal nanotube can be described as a network of carbon atoms assembled into a cylinder, which is covered at the end by half a fullerene molecule [4,5].

The availability of second generation feedstocks for the treatment of acid mine drainage and to improve South Africa's bio-based economy

South Africa has a wide range of mining activities making mineral resources important economic commodities. However, the industry is responsible for several environmental impacts; one of which is acid mine drainage (AMD). Despite several years of research, attempts to prevent AMD generation have proven to be difficult. Therefore, treatment of the resulting drainage has been common practice over the years. One of the recommended treatment methods is the use of second generation feedstocks (lignocellulosic biomass). This biomass is also acknowledged to be an important feedstock for bio-refineries as it is abundant, has a high carbon content and is available at minimal cost. It can also potentially be converted to fermentable sugars (e.g. glucose) through different treatment steps, which could further yield other valuable commodities (cellulase, poly-β-hydroxybutyric acid (PHB) and penicillin V). It is estimated by a generic flowsheet model that 7 tons of grass biomass can produce 1400 kg of glucose which can subsequently produce 205 kg, 438 kg and 270 kg of cellulase, PHB and Penicillin V, respectively. In this paper we investigate the feasibility of grass as feedstock for AMD treatment and the subsequent conversion of this acid pre-treated grass into valuable bio-products.