The rapid increase of anthropogenic activities has led to the ubiquitous presence of organic contaminants. There is an urgent need for understanding the fate and behavior of organic contaminants in the environment. In this dissertation research, the physiochemical and biological behaviors of organic contaminants in multi-phase media have been investigated. Considerable research efforts have been made in characterizing the transport of polycyclic aromatic hydrocarbons (PAHs) at solid-liquid interface, as well as exploring the remediation of pollutants through solvent extraction and composting. The effects of short-chain organic acids (SCOAs) on the behaviors of PAHs in soil-water system have been systemically investigated. The amendment of SCOAs could influence the adsorption and desorption behaviors of pyrene in soil-water system. The mobility of phenanthrene in soil could be also enhanced by introducing organic acids. The biosurfactant-enhanced remediation of PAH-contaminated soil in the presence of SCOAs has been studied. The results supported the combined use of biosurfactant and SCOAs could further enhance the desorption of phenanthrene from soil into aqueous phase. The quantity and species of organic acids could affect the tendency of phenanthrene distribution in the presence of biosurfactant. The adsorption of phenanthrene on fly ash in solid-liquid system was investigated. The adsorption of phenanthrene onto fly ash showed significant stepwise pattern. The developed stepwise multisite Langmuir model can help well simulate the adsorption process. The solution chemistry played an important role in the distribution of phenanthrene in fly ash-water system. The performance of food waste composting in the presence of fly ash and uric acid has been investigated. Different trends of degradation intensity, O2 uptake amount, microbial population and C/N ratio were observed in the series with additional fly ash and uric acid. The results can be used to understand the environmental patterns and mechanisms of organic contaminant behaviors in a complex system. They have important implications for environmental risk assessment and pollution control at contaminated sites.