# Sustainable Environmental Technologies: Recent Development, Opportunities, and Key Challenges
## 3 Waste-To-Energy Conversion  
Waste management technology is currently undergoing a significant transformation, revolutionizing how we manage different types of waste [17]. Recent innovations in this field are enabling the conversion of waste into energy, producing sustainable resources, and replacing traditional, non-renewable materials with energy derived from plant and animal sources [17; 18; 19]. As a result, biomass waste is increasingly being converted into valuable products such as ethanol, biofuels, bioenergy, and biogas, all of which are key contributors to a more sustainable future. For example, [PERSON] et al. [20] conducted a detailed analysis of biogas production, specifically methane (CH4), from textile waste. Their study found that using biological pretreatments, instead of chemical methods, could boost methane production by up to 360%, while being more environmentally friendly and cost-effective. This method not only generates clean energy but also reduces environmental impact by facilitating the reuse of textile wastewater. In another study, [PERSON] et al. [19] investigated the potential of lignocellulosic biomass like rice straw and other agricultural residues as potential raw material for high-value-added products like bioethanol and biodiesel. The result indicated that the use of these biomasses can replace petrochemical products, positioning them as essential components of sustainable and renewable energy production. For instance, rice straw can be gasified using fermentation techniques to produce biogas or methane. Furthermore, rice straw could be used for renewable biohydrogen production, where it undergoes fast pyrolysis to produce bio-oil, which is then reformed with steam to produce hydrogen [18]. Additionally, [PERSON] et al. [21] experimented with the potential of converting human and animal waste into biofuels, sustainable materials, and value-added chemicals. These technologies could significantly reduce waste deposition as well as greenhouse gas emissions into the atmosphere. The study demonstrates considerable advancements in converting human and animal waste into biofuels and value-added materials through thermochemical and biological conversion pathways. It also noted that the USA, China, and England are the leading nations in research on resource recovery from human or animal waste4. Remediation of Emerging/Toxic Contaminants  
With the increasing presence of emerging/chemical contaminants in the environment, the use of sustainable, low-cost materials plays a major role for the cleanup of contaminated sites and the treatment of wastewater or contaminated water bodies [6; 22; 23; 24]. Several studies are currently underway to address this formidable pollution crisis. [PERSON] et al. [23] studied the role of carbon nanotubes as a nano-remediation approach for water decontamination. Their results indicated that carbon nanotubes are regarded as effective adsorbents for the removal of both organic and inorganic pollutants such as heavy metals, harmful organic contaminants including Dichlorodiphenyltrichloroethane (DDT), pesticides, chlorinated solvents, and perfluoroalkyl and polyfluoroalkyl substances (PFAS). The high adsorption capacity of carbon nanotubes is due to their large surface area and hollow layered structure, making them a promising alternative to conventional methods. In contrast to many conventional techniques, nano-remediation techniques offer long-term sustainable solutions by reducing the cost of cleaning up polluted areas and producing less waste. In addition, biochar, a low-cost sustainable material, has shown enormous potential as an engineered material in environmental remediation. [PERSON] et al. [24] reviewed the diverse applications of biochar in remediating contaminated soil, water, and air. The review highlighted biochar's sustainability and eco-friendly characteristics from lab-scale to field-scale experiments, demonstrating its effectiveness to in mitigate contaminants, improving soil quality and restoring ecosystems. Similarly, [PERSON] et al.