Iranian Journal of

Background & Objectives: Remaining crude oil in storage tanks lead to accumulation of oily sludge at the bottom of the tank, which should be treated and disposed of in a suitable manner. The aim of the present study was to investigate the efficiency of chemical oxidation using H₂O₂ and Fenton’s reagent in removal of Total Petroleum Hydrocarbons (TPH) from bottom sludge of crude oil storage tanks. Materials & methods: In this experimental study, hydrogen peroxide and Fenton’s reagent were added to the sludge in six concentrations including 2, 5, 10, 15, 20, and 30% (w w^-1) and TPH was measured for a period of 24 and 48 h of reaction time. The oxidants were added in a single and stepwise addition way, both to the pristine and saturated sludge. The elemental analysis of sludge and TPH measurement were carried out using ICP and TNRCC methods respectively. Results: The mean TPH removal of 2, 5, 10, 15, 20, and 30% oxidant concentrations were 1.55, 9.03, 23.85, 33.97, 41.23, and 53.03%, respectively. The highest removal efficiency was achieved in stepwise addition to the saturated sludge. Increasing oxidation time from 24 to 48 h had a little effect on increase in TPH removal. Moreover, the removal efficiency of H₂O₂ and Fenton was nearly similar. Conclusions: Mere application of chemical oxidation is not capable of complete treatment of the sludge but it is an effective process as a pre-treatment step for decreasing toxicity and increasing its biodegradability.

Background and Objectives: Remaining of crude oil in storage tanks usually results in accumulating oily sludge at the bottom of the tank, which should be treated and disposed of in a suitable manner. The efficiency of in-vessel composting process in removing total petroleum hydrocarbons (TPH) from bottom sludge of crude oil storage tanks was investigated in the present study.

Material and methods: The sludge was mixed with immature compost at the ratios of 1:0 (as control), 1:2, 1:4, 1:6, 1:8, and 1:10 (as dry basis) with the initial C:N:P and moisture content of 100:5:1 and 55% respectively for a period of 10 weeks. The moisture adjustment and mixing process were done 3 times a day during the composting period. Sampling and analysis of TPH and pH were done every week and every two days, respectively.

Results: TPH removal in the 1:2, 1:4, 1:6, 1:8, and 1:10 composting reactors was 66.59, 73.19, 74.81, 80.20, and 79.91%, respectively. Thus, initial adjustment of sludge to immature compost ratios plays a great role in reduction of TPH. The results of the control reactors indicated that the main mechanism of TPH removal in the composting reactors was biological process.

Conclusions: In-vessel composting by addition of immature compost as amendment is a viable choice for bioremediation of the bottom sludge of crude oil storage tanks.

Background and Objective: The performance of in-vessel composting process, as one of the most effective methods of oily sludge treatment, depends on factors such as nutrients and temperature. Therefore, it is crucial to investigate the trend of changes of these factors. The aim of the present study was to investigate the trend of changes of organic carbon, nitrogen, phosphorus, and temperature during the composting of bottom sludge of crude oil storage tanks.

Materials and Methods: The sludge was mixed with the immature compost at the various ratios of sludge to compost including 1:2, 1:4, 1:6, 1:8, and 1:10 with the initial C/N/P of 100/5/1 and then was 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 and every day for temperature.

Results: The research indicated that the concentrations of organic carbon, nitrogen, and phosphorus were decreased sharply during the first weeks of the process and then they were decreased gently. At the final stage of the composting, the ratios of C/N and C/P increased from 20:1 and 100:1 to 26:1 and 166:1, respectively. In addition, the temperature of the reactors was kept in the mesophilic range during the process period.

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