Abstract

Introduction: The performance of in-vessel composting process, as one of the most effective methods of oily sludge treatment, depends on factors such as nutrients, temperature and pH.

Objective: The aim of the present study was to investigate the trend of changes of temperature, pH, organic carbon, nitrogen, and phosphorus in the in-vessel composting of bottom sludge of crude oil storage tanks pre-treated with hydrogen peroxide and Fenton.

Materials and Methods: In the first step of this descriptive study, the sludge was pre-treated with mixed hydrogen peroxide and Fenton. Then, the immature compost was mixed with the sludge at the ratios of 1:8, and 1:10 with the initial C/N/P of 100/5/1 and composted for a period of 10 weeks. The process of mixing and moisture adjustment of the mixtures was done 3 times a day during the composting period. Sampling and analysis were performed every week for organic carbon, nitrogen, and phosphorus, every other day for pH, and every day for temperature.

Results: The results showed that the concentrations of organic carbon, nitrogen, and phosphorus decreased sharply during the first weeks of the process period and then, they decreased gently. In addition, the increase of C/N and C/P indicated that the consumption rate of organic carbon was higher than that of the nitrogen and phosphorus. The changes of temperature and pH were not significant during the composting period.

Conclusions: The similar trend of decrease of organic carbon, nitrogen, and phosphorus in the composting reactors is an indication of decrease in the activity of the microorganisms involved in petroleum hydrocarbons degradation.