17 research outputs found
Modelling of ionic interactions with organic components in wastewater.
M. Sc. Eng. University of KwaZulu-Natal, Durban 2014.In current biological wastewater treatment models, physico-chemical processes (ionic speciation reactions, gas-liquid exchange, and liquid-solid interactions such as precipitation and adsorption) either are not explicitly considered, or are incorporated as simplified descriptions. This may result in an inaccurate prediction of digester behaviour. Specifically, the ionic behaviour of biomass is not explicitly included in standard models. The objectives of this study were to develop a model component that describes ionic behaviour of biomass, use this to predict the overall solution pH buffering capacity and determine its impact in an anaerobic digester’s operating range (pH 6-8). The study hypothesises that the ionic behaviour of biomass can be described in terms of glycine equivalence; alternatively, it can be described by a model component consisting of functional groups characterised by concentration per unit mass of sludge and pKₐ value for each group, either at equilibrium conditions, or considering kinetic effects.
The methodology involved constructing a mass balance / ionic speciation model capable of simulating alkaline and acidimetric experimental titrations with modifications for each hypothesis. Varying concentrations of glycine or suspensions of biomass (particulate organic matter) in background salt solutions were titrated and the model was fitted to the data by changing the parameters associated with the biomass description and, (where appropriate) associated kinetic terms, with associated estimation of parameter uncertainty.
A model component, UKZiNe was developed consisting of 4 functional groups; 2 carboxyl groups, 1 phosphate group and 1 amine group. Kinetic effects including carbon dioxide exchange and pH probe lag were explored.
The hypothesis that glycine could represent the ionic behavior of biomass was not supported. The alternate hypothesis, considering UKZiNe at equilibrium conditions, required further testing to evaluate the effects of kinetic reactions; the second alternate hypothesis that non-equilibrium effects significantly influence the measured experimental pH value, was supported.
All model formulations predicted that the biomass contribution to the overall buffer capacity in the operating region of an anaerobic digester was insignificant. The study implies that the inclusion of an ionic description of biomass does not considerably improve the pH prediction in digester simulations and can be excluded in future model development
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Innovative concept for creating an air purification pavement surface coating by atmospheric pressure cold plasma
Air pollution from automobiles, in the form of nitrogen oxides (NOx) and volatile organic compounds (VOCs) are increasing continuously due to the rapid development of transportation activities, which can cause a number of environmental and social issues and impact public health. Nano titanium dioxide (TiO2) has been found to have photocatalytic properties, which, under UV light can oxidize and remove VOCs and NOx from the atmosphere. Although TiO2 treated paving materials have great potential to improve air quality, current techniques to adhere TiO2 to substrate materials are either not durable or reduce direct contact of TiO2 with UV light, reducing the photocatalytic effect. To solve this technical difficulty, this study innovatively introduces atmospheric pressure cold plasma (APCP) techniques to transportation engineering to coat TiO2 to pavement. The objective of this study is to test the concept of using APCP techniques to create a durable TiO2 coating on the surface of paving materials to reduce NOx and VOCs at the street level. An APCP generator was developed to produce activated radicals from precursor molecules using high voltage streamers as the plasma source, and to immobilize nano TiO2 powder to substrate pavement materials. Preliminary results are promising, showing that TiO2 can be incorporated successfully into an APCP environment. Evidence of TiO2 has been identified based on field emission scanning electron microscope (FE SEM) images. The TiO2 coated material with APCP shows some ability to reduce nitrogen oxides when exposed to UV light in an environmental chamber. However, such effect is limited which is hypothesized due to either limited deposition rate of the plasma polymerized film or the plasma polymerized film blocking the direct contact of TiO2 with the UV light. Further research is therefore recommended to optimize the APCP generator for improved efficiency. Also a more in depth study should be conducted on the plasma polymerized film and its interaction with the TiO2