Pollution reduction with processed waste materials

Elaigwu, Sunday Enenche

Abstract

This research aimed at providing an understanding into the waste management options available for developing countries and also to provide insight into the possible application of the processed materials during the waste management processes, thereby helping in converting the waste materials which would have been a nuisance into useful products. Pyrolysis and composting were utilized as the waste management techniques for processing the waste materials for use in pollution reduction.

Carbon materials (biochar and hydrochar) were prepared in the pyrolysis aspect of this research through dry and wet (hydrothermal carbonization) pyrolysis respectively. Under the wet pyrolysis, comparisons were made between the conventional and the microwave-assisted hydrothermal process for carbonisation of waste materials. Three waste materials were investigated Prosopis africana shell (from Nigeria), rapeseed waste (from the UK) and coconut husks (a well-studied material in carbon science). The result shows that the microwave-assisted hydrothermal carbonization process reduced the processing time from 4 hours to 20 minutes for the same level of carbonisation. The biochar and the hydrochar from the pyrolysis and microwave-assisted hydrothermal carbonization of one of the waste materials (Prosopis africana shell) were applied in the adsorption of Pb²⁺ and Cd²⁺ from aqueous solution. In terms of adsorbing the heavy metal ions from aqueous solution, the materials proved to have high adsorption capacities than some previously studied adsorbents. Maximum adsorption capacities for the hydrochar and biochar were 45.3 and 31.3 mg/g for Pb²⁺ and 38.3 and 29.9 mg/g for Cd²⁺ respectively. Interestingly, the hydrochar from microwave-assisted hydrothermal carbonization, which is a green chemistry approach, was capable of adsorbing the metal ions more than the biochar from aqueous solution. The adsorption process was dominated by chemisorptions as it followed the pseudo-second-order kinetics and the adsorption data fitted the Langmuir isotherm model. The thermodynamics study of the adsorption processes showed that it was spontaneous and endothermic.

Microwave-assisted hydrothermal process and evaporation-induced self-assembly (EISA) were also used to synthesize carbon monoliths, using a waste plant material as the carbon precursor. The microwave-assisted hydrothermal process was not successful in the synthesis of the carbon monolith; however novel carbon monolith was produced using the EISA approach. The carbon monolith in comparison to the biochar and hydrochar from the same material is not powdered, has higher surface area and porosity which could enhance its adsorption capacities for heavy metal ions.

In the composting aspect of the research, the Prosopis africana shell showed that it can be composted. The effect of an organic pollutant, in this case anthracene during a starch amended co-composting process was evaluated through total dry matter and extracellular enzyme activities of both starch specific (α-glucosidase) and non-specific (β-glucosidase) substrate. The result showed that the effect of anthracene amendment alone was not highly significant on the process. However, the interaction between the anthracene and starch have consistent effects on the process, which is novel and should be studied further to know the magnitude of sure interaction.

This research showed that the waste material (Prosopis africana shell) from Nigeria can be processed into useful products using pyrolysis and composting. Further work will be required in Nigeria outside the laboratory to see the real applicability of these processed materials.

Citation

Elaigwu, S. E. (2013). Pollution reduction with processed waste materials. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4215585

• Thesis Type: Thesis
• Deposit Date: Apr 15, 2014
• Publicly Available Date: Feb 23, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4215585
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Oct 1, 2013