Influence of Limnodrilus hoffmeisteri worms population size on cleaning oil polluted bottom sediments

The problem of oil polluted territories and water areas decontamination is one of topical tasks for resolving. The problem is far from being completely solved in spite of a variety of technologies for oil polluted environments cleaning and restoring that exist today. The aim of the current study was to investigate Limnodrilus hoffmeisteri population size influence on oil destruction in contaminated sludge for optimizing the technology for bottom sediments cleaning using Tubificidae worms. The data on oil contained in sediments of the experimental vessels which were obtained in this study indicate the tendency to acceleration of bottom sediments cleaning from oil with the increasing of worm's number. Decreasing of oil concentration in comparison to control conditions was observed in all experimental vessels. Decreasing of oil content in sediments of the control vessels (without worms) was detected both at high temperature (21-22°С) and low temperature (5°C). Oil content in the control vessels decreased in 1.73 times at the temperature of 21-22°С; in 1.37 times at the temperature of 5°C. The decreasing of oil content in sediments is connected with physic and chemical and microbiological aspects of bottom sediments self decontamination. It is necessary to note that cleaning processes were, in average, more intensive at 5°C than at 21-22°С: for 10% at 2500 cohorts/m, for 4% at 5 000 cohorts/m and for 6% at 10 000 cohorts/m. The analysis of initial and final oil content in the experiment revealed its maximum decreasing at the highest oil concentration (11.19 g/kg) and at the temperature of 21-22°С: reduction in 2.8 times at 10 000 cohorts/m and in 2.6 times at 5 000 cohorts/ m. The same characteristics were less at the same oil concentration at 5°С: reduction in 2.4 times at 10 000 cohorts/m and 2.3 times at 5 000 cohorts/m. Reliable (p<0.05) reduction of oil content in sludge was observed with the increasing of worm's number (2 500 cohorts/m - 5 000 cohorts/m - 10 000 cohorts/m) during combining data from different temperatures experiments into common battery with Wilkokson criterion. The possibility of a rather fast cleaning processes in oil contaminated sludge at a low temperature extends the perspectives of the technology application in winter time. For effective realization of cleaning in winter, dissolved oxygen maintenance at the level of 5-6 mg/l is required.

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