Environmental management and potential use of heavy oil fly ash

Heavy oil fly ash (HOFA) is a by-product generated in power plants by the burning of heavy fuel oil. The main constituent of HOFA is unburned carbon; it also contains other elements such as arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), mercury (Hg), nickel (Ni), lead (Pb), copper (Cu), zinc (Zn), selenium (Se), calcium (Ca), magnesium (Mg), sodium (Na), silicon (Si), aluminium (Al), iron (Fe), and vanadium (V) in different forms of oxides or sulfates. Due to insufficient knowledge of the physical and chemical properties and related applications of this by-product, it is usually disposed off into landfills. In order to explore the beneficial utilization of HOFA, this research study analyzes the physical, chemical, and morphological characteristics of HOFA. It also includes an in-depth investigation on its reuse as (i) a natural absorbent such as activated carbon (AC), (ii) fill material for construction use, and (iii) a colour ingredient in ornamental concrete. Chemical and physical activation techniques were used to produce fly ash activated carbon (FAC). Before activation, the minerals and other metals present in the HOFA were removed by standard leaching procedures. The performances of the produced FAC were tested for the removal of selected pollutants such as dyes, naphthalene, and metals from aqueous solutions. The results from the laboratory batch experiments indicated that the developed FAC has the potential to remove organic and inorganic (e.g., 85% to 90%) pollutants from wastewater. Soil stabilizer or fill material for construction use was prepared by mixing HOFA with Portland cement at different ratios. The leaching behaviour of the trace elements and compounds within HOFA and fill materials was studied by standard laboratory batch and column leaching tests. The results of the study showed that the toxic elements in HOFA are easily leachable and can be toxic to the environment. However, the addition of 40% Portland cement with HOFA significantly decreased the leaching concentration of most elements below the permissible level. To explore the possible use of HOFA as a black pigment or admixture in ornamental concrete, it was mixed with cement mortar at different percentages. The standard compressive strength test with 50 mm cement mortar cubes showed that the addition of 2% to 5% HOFA in cement mortar does not affect its compressive strength. The leaching behaviour of trace elements within HOFA mixed concrete material was also investigated through laboratory batch leaching experiments. The findings confirmed that HOFA can be used as a black pigment in ornamental concrete, which is environmentally safe, and provides a good balance between colour and concrete quality. In the final phase of this research, a human health risk assessment methodology was developed in order to assess the potential health risk to people living in the area surrounding the HOFA dumping site. This study also explores environmental concerns and the importance of HOFA management practices

Decision making tool for produced water management : an application of multicriteria decision making approach

Produced water (PW) is the most significant source of waste discharge from the oil and gas operations. As such, development of an effective PW management system is important to minimize/mitigate the environmental impacts. However, there are challenges with respect to the selection of the best option due to competing and conflicting criteria. Selection of the best alternative often involves multiple criteria, which requires sophisticated multiple-criteria decision making (MCDM) methods. The Analytical Hierarchy Process (AHP) has widespread application in MCDM problems. It can effectively handle both qualitative and quantitative data. In this study AHP is integrated with an additive value model to enhance the decision making process. Linguistic terms are used to capture the subjective judgment of decision makers in the absence of quantitative data. -- However, the traditional AHP involves human subjectivity which leads to decision uncertainty. The vagueness type uncertainty associated in the decision making process is considered using the fuzzy based technique. The traditional AHP is modified to fuzzy AHP using extent analysis and integrated with the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) algorithm to solve the decision matrix. A hypothetical case study for PW management is demonstrated to illustrate and compare both traditional AHP and fuzzy based AHP methodology. -- The ecological risk assessment (ERA) of PW is conducted for this study and the ERA results for different PW management options are used in the integrated MCDM model under ecological risk criteria. -- This study has provided a framework for a decision support system which will be helpful for oil and gas industry persons to select the best PW management options with minimum efforts