A battery of toxicity tests as indicators of decontamination in compostingoily waste

Heterogenous oily waste from an old dumping site was composted in three win drows constructed from different proportions of waste, sewage sludge, and b ark. The objectives of this pilot study were to examine the usefulness of c omposting as a treatment method for this particular waste and to study deco ntamination in the composting process by using a battery of toxicity tests. Five samples from the windrow having intermediate oil concentrations were tested with toxicity tests based on microbes (Pseudomonas putida growth inh ibition test, ToxiChromotest, MetPLATE, and three different modifications o f a luminescent bacterial test), enzyme inhibition (reverse electron transp ort), plants (duckweed growth inhibition and red clover seed germination), and soil animals (Folsomia candida, Enchytraeus albidus, and Enchytraeus sp .). The luminescent bacterial tests were used as prescreening tests. Chemic al analyses of samples were carried out simultaneously. Both toxicity and o il concentration, including those of polyaromatic hydrocarbons (PAHs), were reduced during composting and soil qualify improved significantly. The tot al oil hydrocarbon concentration decreased from 90,000 to 19,000 mg/kg, mea sured with the IR method, in 4 months, and from 86,000 to 1400 mg/kg, measu red with GC method. The concentration of PAHs decreased from 135 to 23.5 mg /kg. During the fourth month of composting (stabilization stage), the propo rtion of the heaviest oil fractions (asphaltenes) became dominant. Toxicity varied between different samples and between different bioassays; however, the first sample was significantly more toxic than the others, and most of the tests revealed a decrease in toxicity during the composting process. ( C) 2000 Academic Press.