Surface modification of toner-based recyclable iron oxide self-doped graphite nanocomposite to enhance methylene blue and tetracycline adsorption.

An innovative task was undertaken to convert ubiquitous and toxic electronic waste, waste toner powder (WTP), into novel adsorbents. Alkaline modification with KOH, NaOH, and NH4OH was employed for the first time to synthesize a series of surface-modified WTP with enhanced dispersibility and adsorption capacity. XRD, XRF, FTIR, and BET analyses confirmed that the prepared KOH-WTP, NaOH-WTP, and NH4OH-WTP were oxygen-functionalized self-doped iron oxide-graphite nanocomposites. The prepared adsorbents were used to remove methylene blue and tetracycline from aqueous solutions. KOH-WTP (0.1 g/100 mL) adsorbed 80% of 10 mg/L methylene blue within 1 h, while 0.1 g/100 mL NH4OH-WTP removed 72% of 10 mg/L tetracycline in 3 h. Exploring surface chemistry by altering solution pH and temperature suggested that hydrogen bonding, electrostatic interactions, π-π electron stacking, and pore filling were plausible adsorption mechanisms. Scanning electron microscopy revealed a diminishing adsorbents porosity after adsorption proving the filling of pores by the adsorbates. KOH-WTP and NH4OH-WTP removed 77% and 61% of methylene blue and tetracycline respectively in the fourth reuse. The adsorption data of methylene blue and tetracycline fitted the Freundlich isotherm model. The maximum adsorption capacities of KOH-WTP and NH4OH-WTP for methylene blue and tetracycline were 59 mg/g and 43 mg/g respectively. The prepared adsorbents were also compared with other adsorbents to assess their performance. The transformation of waste toner powder into magnetically separable oxygen-functionalized WTP with outstanding recyclability and adsorption capacity showcases a significant advancement in sustainable wastewater treatment. This further aligns with the principles of the circular economy through the utilization of toxic e-waste in value-added applications. Additionally, magnetic separation of surface-modified WTP post-treatment can curtail filtration and centrifugation expenses and adsorbent loss during wastewater treatment.

Integrated AHP-TOPSIS under a Fuzzy Environment for the Selection of Waste-To-Energy Technologies in Ghana: A Performance Analysis and Socio-Enviro-Economic Feasibility Study.

Energy recovery from waste presents a promising alternative for several countries, including Ghana, which has struggled with unsustainable waste treatment methods and an inadequate power supply for several decades. The current study adopts a comprehensive multi-criteria decision-making approach for the selection of an optimal waste-to-energy (WtE) technology for implementation in Ghana. Four WtE technologies are evaluated against twelve selection criteria. An integrated AHP-fuzzy TOPSIS method is applied to estimate the criteria's weights and rank the WtE alternatives. From the AHP results, technical criteria obtained the highest priority weight, while social criteria emerged as the least important in the selection process. The overall ranking order of WtE technologies obtained by fuzzy TOPSIS is as follows: anaerobic digestion > gasification > pyrolysis > plasma gasification. The sensitivity analysis indicates highly consistent and sturdy results regarding the optimal selection. This study recommends adopting a hybrid system of anaerobic digestion and gasification technologies, as this offers a well-balanced system under all of the evaluation criteria compared to the standalone systems. The results of the current study may help the government of Ghana and other prospective investors select a suitable WtE technology, and could serve as an index system for future WtE research in Ghana.