Impact of Simulated Land Treatment with Oily Sludges on Ryegrass Emergence and Yield1

Abstract

AbstractThe proper design and management of facilities for the land treatment of hazardous industrial wastes require information on the effects of the oily wastes on the soil and on the growth of vegetation. Measurements were made on the impact of two oil‐water separator sludges (a refinery sludge which originated from a petroleum refinery, and a petrochemical sludge which originated from a petrochemical plant) on the emergence and dry matter yield of ryegrass (Lolium multiflorum Lem.) grown on four diverse soils in the greenhouse. Each sludge was applied at 0, 5, 10, and 20% v/v to each of four soils to determine the influence of application rates. After growth periods of approximately 6 weeks, the grass was harvested and the soil‐sludge mixture was air‐dried, remixed, and reseeded. A total of eight sequential harvests were made. Measurements of soil wettability were made twice to evaluate physical problems.Concentrations of refinery sludge at 5% v/v and above depressed ryegrass emergence and yield through two mechanisms. Phytotoxic constituents initially acted to retard plant growth. Several months were required for the sludge to degrade sufficiently to allow normal plant growth. Subsequent yield reductions resulted from impaired water relations associated with residual hydrophobic hydrocarbons.The petrochemical sludge had higher concentrations of both organic carbon and aromatics and suppressed emergence and yield proportional to the amount of sludge applied. The suppression lasted longer than that caused by the refinery sludge. Seedling emergence from soils treated with 20% refinery sludge did not differ from those in the unamended control by the second planting, while the corresponding treatments using petrochemical sludge were less than those in the control for the first five replantings. Grass yield from the 20% refinery sludge treatment required 13 months to reach control levels. The corresponding petrochemical treatment yield increased to only 47 % of the control, 17 months after application.Thus, while oily sludge may initially be phytotoxic and may reduce the yield of vegetation that managed to emerge, the toxicity diminishes with time, so that soils used for land treatment of oily sludges can eventually be revegetated.