History of engineering & technology Technology: general issues aerobic denitrification ammonium anaerobic co-digestion anaerobic digestion (AD) anaerobic digestion acceptance biogas dewaterability energy policy food wastes heterotrophic nitrification iron oxide nano particles life cycle assessment (LCA) livestock wastewater mesophilic methane nano magnetite nano particles nano zero valent iron organic wastes rural development sewage sludge sludge quality sludge valorisation structural equation model sustainable energy technology synthetic microbial community temperature-phased anaerobic digestion (TPAD) thermophilic