• Pattern shows a shift toward integrated anaerobic/aerobic waste treatment with emphasis on reactor design, start-up acclimatization and temperature-driven optimization of decomposition and methane yield [1], [4], [10], [13].

• Heavy metal management emerges as a core concern across waste streams, focusing on uptake/removal in activated sludge, incineration metal emissions, and leachate/landfill metal dynamics [5], [6], [12], [14], [16], [20].

• Microbial ecology and community dynamics underpin both solid waste composting and activated sludge processes, governing degradation rates, bulking control and metal interactions [14], [15], [17], [18].

• Incineration research centers on characterization of emitted particles and metal contaminants, linking particle size distributions to environmental dispersion and metal fate [6], [11], [20].

• Methodological foundations emphasize standardized measurement, leachate treatment, and process monitoring for water/wastewater and waste streams [7], [9], [12], [19].