TECHNOLOGY FOCUS - ENVIRONMENT - Preferred Method: The step (e) comprises: -milling the harvested mature crop; -mixing the milled harvested mature crop with water, thereby forming an aqueous slurry comprising dispersed cellulosic material stemming from the milled harvested mature crop; -converting cellulosic material dispersed in the slurry by acid hydrolysis into levulinic acid and formic acid at an elevated pressure and temperature. The levulinic acid is converted into a biofuel compound of a biofuel containing fuel composition. The acid hydrolysis is carried out at greater than or equal to 180 degrees C and at a pressure above 20 bar. The step (a) further comprises mixing the contaminated water stream with fresh water such that the commingled contaminated and fresh water streams comprise capped fractions of, inter alia, crude oil, salt and metals. The saline tolerant cellulosic crop is used to purify irrigation water passing through the soil of the cascade of soil beds by biodegrading crude oil and by adsorbing metals contained in the irrigation water. The irrigation system of the first of the cascade of soil beds comprises an irrigation water discharge system, in which unused irrigation water that has been passed through the soil of the first soil bed and that is purified during the passage such that its crude oil content is reduced, is collected and is used as irrigation water for growing a second crop on the second of the cascade of soil beds, which second crop is less tolerant to irrigation water that is contaminated with crude oil. The unused irrigation water discharged into the soil of the second of the cascade of soil beds in which the second crop is planted is collected, which unused irrigation water has a crude oil content that has been further reduced through biodegradation in the soil around the roots of the second crop, is used as irrigation water for growing on a third of the cascade of soil beds a third crop, which is less tolerant to irrigation water that is contaminated with crude oil than the cellulosic first and second crops. An impermeable liner is arranged below at least one of the soil beds in which the cellulosic crop is planted to inhibit drainage of contaminated water into adjacent soil layers. The impermeable liner is arranged at an average depth of less than 1 meter below the upper surface at least one of the soil beds. The irrigation water stream discharged by the most downstream soil bed of the cascade of soil beds is fed to a water evaporation pond from which salt is collected. The algae are grown in the water evaporation pond, which algae are collected and converted into a compound of a biofuel and/or other biochemical composition by a chemical conversion process. The first cellulosic crop is reed and the second cellulosic crop comprises eucalyptus trees. EXAMPLE - No suitable example is given.