Unique Fe³⁺/Fe²⁺/Al₂SiO₅/Ti⁴⁺ nano-photocatalyst (FA_NPC*) was successfully prepared employing fly ash (FA)-based unique nano-Al₂SiO₅ and nano-Fe³⁺/Fe²⁺ in an innovative assimilated energy-system comprising tungsten-halogen radiation and ultrasound (THUS). The energy-efficient THUS activated optimal FA_NPC* (FA_NPC*^O) possessed favourably higher specific surface area (142.11 m²_/g), finer nanoparticles (47.50 nm) and lower band gap energy (2.78 eV) compared (89.72 m²_/g, 62.43 nm, 2.97 eV respectively) to its conventionally prepared analog (FA_NPC^CO). The FA_NPC*^O rendered a significantly higher HMF yield (38.37 mol %) from a kitchen waste viz., cooked rice water (CRW) under THUS at 70 °C in only 60 min compared to 21.67 mol % HMF yield provided by FA_NPC^CO. The DFT based study revealed that the CRW conversion process to HMF occurred through water adsorption on FA_NPC* surface for H₃O⁺ formation, followed by H₃O⁺ induced CRW hydrolysis, subsequent glucose isomerization on -Ti active sites and finally fructose dehydration by H₃O⁺. The LCA of the overall process confirmed that the FA_NPC*^O catalysed CRW conversion process could appreciably alleviate harmful environmental parameters, viz. global warming, fossil depletion, human toxicity and metal depletion by 7.65%, 4.15%, 8.56% and 13.57% respectively in comparison with FA_NPC^CO. Thus, the THUS stimulated system could favourably demonstrate the efficient and eco-friendly utilisations of two abundant waste resources, viz. fly ash and cooked rice water for a sustainable production of HMF.