BACKGROUND: Many studies have reported that most Fenton pre-oxidation steps either do more damage to the indigenous hydrocarbon degraders (IHD) or produce lower concentrations of ammonium-nitrogen (NH4+-N) during Fenton oxidation combined with bioremediation for oil-contaminated soils, which causes the subsequent bioremediation to be unsustainable and poor. The aim of the present study was to find an instant Fenton pre-oxidation for the efficient sustainable biodegradation of long-chain alkanes, and to determine the ratio (K) of residual concentration of NH4+-N to residual population of IHD that can reach a balance after this instant Fenton pre-oxidation. RESULTS: Five Fenton oxidation experiments were carried out with iron bound to soil organic matter (SOM). On this basis, a 75-day field experiment of instant Fenton pre-oxidation with K = 46 combined with bioremediation was performed. Experimental results showed that a similar efficient biodegradation (approximate to 261 mg kg(-1)) of long-chain alkanes C-30-C-25 at each stage was obtained after instant Fenton pre-oxidation with K = 46. So up to 75% of the biodegradation of long-chain alkanes occurred after instant Fenton pre-oxidation with K = 46, which was 2.3- and 2.0-fold greater than the corresponding biodegradation of long-chain alkanes after noninstant Fenton pre-oxidation with K not equal 46. CONCLUSION: The study indicated that efficient sustainable bioremediation of long-chain alkanes can be achieved after instant Fenton pre-oxidation with K = 46. Analyses of microbial diversity revealed that a possible explanation for the efficient sustainable bioremediation of long-chain alkanes in soils was that sensitive, slow growth of the IHDs Nocardiode and Noviherbaspirillum was not damaged after instant Fenton pre-oxidation with K = 46. (C) 2019 Society of Chemical Industry