Investigation of the Sustainable Production and Utilization of Biochar and Activated Carbon From Waste

Each year, 1.6 billion tons of food waste is generated, which is predicted to increase to 2.1 billion tons by 2030 resulting in an enormous solid waste management concern. Out of the many food wastes, spent coffee grounds (SCG) comprise almost 15 million tons on a wet basis. Other significant solid wastes generated in Qatar include animal manures, and sewage waste. These wastes can be used for beneficial reuse, such as conversion to carbon rich activated carbons and biochars, which can subsequently be used as a water treatment adsorbent or as an agricultural soil amendment.In Qatar, one of the largest sources of wastewater is the “produced water” from the gas and oil industries containing several pollutants, such as lithium (Li). Out of all the metal pollutants, lithium is of great interest due to its value if recovered in the electronics industry for microelectronics and batteries, and also poses potential health concerns if present in treated wastewater intended for agricultural irrigation applications. Adsorption is a favoured wastewater treatment technology for the removal of metal salts due to its low cost and overall sustainability. Despite this, there is a lack of information on adsorption of lithium from wastewater, particularly using activated carbons from waste materials such as SCG. This thesis therefore contains two areas of work (1) the preparation of activated carbon (AC) from spent coffee ground (SCG) and an experimental study of its ability to remove lithium from wastewater and (2) a suite of simulation studies to investigate the optimum options to utilize biochar, including those produced from SCG, within the context of energy-water-food nexus, considering agriculture and water treatment applications.In the experimental studies, SCG biomass was activated using two reagents, KOH and H₃PO₄, in the presence of two catalysts, bentonite and K₃PO₄, and without catalyst. After activation, the SCG biomass was used to produce biochar by a slow pyrolysis process at three temperatures (300, 500, and 600 °C) for 1-hour residence time and at a heating rate of 5 °C/min. The various physico-chemical properties of activated carbon at three different temperatures were analyzed to select the most suitable one for the batch adsorption study. Out of the activated biochars tested, those produced without catalyst at 600 °C using either 2M KOH or 2% H₃PO₄ at a ratio of 1:1 of SCG were found to be the most efficient adsorbents with a BET surface area greater than 340 m² .g^-1, zeta potential of more than -75 mV and fixed carbon of 65%. Results of this study indicated that the biochar yield can increase with activation but decrease with increasing pyrolysis temperature and with increased concentration of both activating agent and catalyst. A carbon content of more than 75% for these two activated biochar samples was also attained and was congruent with a low impregnation ratio, lowering the concentration of the activating agent, and the absence of a catalyst. The SCG activated biochar at 600 °C showed a high adsorption capacity through the removal of 35 to 80 mg/g of lithium from synthetic wastewater at initial concentrations of 200 to 500 mg/L. Additionally, more than 95% of lithium could be adsorbed within 6 h from a 200 mg/L synthetic wastewater, demonstrating activated biochar produced from SCG is a suitable and cost effective adsorbent.In addition to these experimental investigations, a series of simulation studies were performed to investigate the optimum options for utilizing biochar within the context of energy-water-food nexus for both wastewater treatment and agriculture practice. An optimal blending ratio of various biomass compared to SCG for both single-end use and multi-end use stages was considered to fulfill the objectives within defined scenarios based on maximum savings in energy, water, cost and emissions. The single-end use stage considered using biochar for wastewater treatment and as a soil amendment individually, where 18 optimal solutions were collected. The optimization of the multi-end use stage resulted in 70 optimal solutions where biochar was applied for both wastewater treatment and soil amendment. The solutions that leant towards soil amendment application had BC that consisted of a high (97 – 99%) proportion of date pits. Optimal solutions that leant towards the wastewater treatment pathway suggested consisted of relatively equal proportions of camel manure, sewage sludge and SCG, ranging between 29 – 33% each, with smaller amounts of date pits around 2 to 5%.