Monitoring of biopile composting of oily sludge

Abstract

This paper describes a bioreactor set-up used to simulate degradation of petroleum hydrocarbons in a static biopile. The large-scale test was performed in a 28 m3 custom-designed reactor. Oily sludge (40% by weight, having 7% dry matter [DM], and hydrocarbons C10—C40 160,000 mg kg—1 DM) was mixed with organic-rich amendments — mature oil-compost (40%) and garden waste compost (20%). Within the reactor, the temperature and soil gases were monitored continuously during 370 days via 24 measurement points. Also, moisture content was continuously recorded and airflow through compost mix occasionally measured. Three-dimensional ordinary kriging spatial models were created to describe the dynamic variations of temperature, air distribution, and hydrocarbon concentration. There were large temperature differences in horizontal and vertical sections during initial months of composting only. Water content of the mixture was uneven by layers, referring on relocation of moisture due to aeration and condensation. The air distribution through the whole reactor varied largely despite of continuous aeration, while the concentration of O2 was never reduced less than 1—2% on average. The results showed that composting of sludge using force-aerated static biopile technology was justified during the first 3—4 months, after which the masses could be re-mixed and heaped for further maturation in low-tech compost windrows. After 370 days of treatment, the content of hydrocarbons (C 10—C40) in the compost mixture was reduced by 68.7%.