The object of the invention is a method of bioremediation of soil and/or soil-based masses polluted with petroleum-derived compounds

There have been many physical, chemical and biological methods, known so far, of removing petroleum derivatives from the ground (soil) in which various technical systems are used. Soils contaminated with petroleum derivatives are most often treated in their contamination site by means of biological methods which employ the use of micro-organisms able to use hydrocarbons as the source of coal and energy.

A method of reclamation of post-industrial or municipal wastelands is known from the Polish patent description no. PL 175432 which consists in mixing the sediment from an industrial sewage treatment plant in the ratio of 1 : 2 to 1 : 10 with organic substances or hydrated sediments from a municipal treatment plant. Moreover, artificial fertilisers, biological vaccine, bark, straw or sawdust are added. The pulp produced in this way is transported to a waste storage site where it is formed into prisms. In the prisms, the biological transformation process is performed through aeration and moisture control, as a result of which artificial soil is produced, which is sown with plants after levelling.

A method of microbiological treatment of soils polluted with paraffin compounds by means of the in situ method is known from the Polish patent description PL 180141. For remediation, preferably 5 to 10 different species of bacteria revealing the highest hydrocarbon biodegradation activity are selected. Multiplied bacteria are introduced into the soil by sprinkling it with a suspension of bacteria or in a layered mode, on a solid mineral carrier, especially in the form of light expanded clay aggregate.

In the method known from the Polish patent description no. PL 184203, a prism of polluted soil is formed with a deaerating-aerating bio-ventilation system connected to it, its size being adapted to the oxygen demand, with the possibility to control the intensity of air flow depending on the actual demand. To a batch of soil prepared in such a way, a culture medium of mineral fertilisers and bacterial microflora is added, which has been isolated beforehand from the batch of polluted soil and properly multiplied.

Searching for new solutions, especially for the removed large quantities of soil and/or soil-based masses polluted with petroleum derivatives, results from the need to increase the pollution reduction speed considering economical circumstances and elimination of the seasonal nature of the process. As it is known, hydrocarbons contained in soil are reduced thanks to the natural occurrence of specific species of aerobic micro-organisms, for which the major source of nutritional medium are hydrocarbons. Therefore, the biodegradation of hydrocarbons is a natural phenomenon, the speed of which depends among others on the concentration of hydrocarbons and the characteristics of their hydrocarbon chain as well as other nutritional components, especially C : N : P and from moisture, temperature and oxidation.

The subject matter of the invention consists in the fact, that during the first phase of the process, the biological waste undergoing biodegradation is arranged into at least one prism along the axis of the aerating ducts and, when the that prism is heated up to the temperature of at least 45 °C, it is overlaid with a layer of soil and/or soil-based mass containing petroleum pollutions in the weight ratio from 6:4 to 8:2, preferably 7:3 and, at a temperature of 37 - 45 °C achieved in such a way, it is left for the period of at least 2 days. Then, every few days, preferably four, the prism is in the known method mixed, scarified and moisturised to the level of 39 - 41 % and aerated under pressure in the amount of 10-20 m ³ , preferably 15 m ³ of air counted per 000 kg s. m. of the prism, preferably with the frequency of 0.5 hour of aeration per 0.5 hour break. Depending on the size of the prism, conducting this process takes from several days up to three weeks till the moment, when the microbiological transformation is completed. In the second phase of the first stage of the process, according to the invention, the active initiating compost produced in such a way is mixed with soil and/or soil masses containing petroleum-derived pollutions, in the weight ration from 6:4 to 8:2, preferably 7:3, and, similarly to the first phase of the first stage of the process, it is arranged into at least one prism, which is then aerated under pressure and scarified, this process being conducted in the prism heating temperature not lower than 32 °C, until the moment when compost soil containing trace quantities of petroleum-derived pollutions is produced. Afterwards the compost soil produced in such a way can alternatively be subject to humification in the last stage.

According to the invention, it is preferable to place the prism with the initiating compost and the prism with the fresh compost soil produced under shields.

In the invention, both in the first and the second stage, the prisms are placed on an separated platform arranged in accordance with the environmental protection requirements for the known plant or animal (biological) waste undergoing biodegradation and arranged in prisms along the axis of aerating ducts and covered with sliding chamber shields. Each chamber shield covers two prisms and is adapted to receive post-process air in the under-pressure system which is then directed to a biofilter. Biofiltration consists in passing of used air from the first stage, containing odorants and volatile hydrocarbons, though layers of biological material colonised by micro-organisms and through a layer of activated coal. Effluents produced by the biofilter are directed into the common effluent reservoir into which effluents from prisms from the first stage also flow. The effluents are directed to re-moisturising of the prisms. In case there are no effluents coming from the reservoir, preferably containing rich microflora which speeds up the biodegradation of petroleum derivatives as well as biological transformation of organic matter contained in the prisms, rainwater sewage coming from the surface drainage of the platform is additionally collected for moisturising and accumulated in a separate reservoir. The flow of effluents and rainwater sewage is a closed loop circulation system. In the first stage, the biomass decomposition process combined with the biodegradation of petroleum derivatives takes up to 14 weeks. As a result, fresh compost soil is produced, free from odour compounds and with hydrocarbons reduced by at least 65%. In the second stage, the process of bioremediation and biological transformation of fresh compost soil is performed on a separate spot of the platform. Prisms are transported and arranged in the known method by means of loaders and dump trailers. The scarification of the prisms, combined with aeration, is carried out every 4 - 7 days. The temperature of the compost soil can reach 27 °C with a decreasing trend. In the second stage, the microbiological activity of microorganisms degrading petroleum derivatives makes them decompose into harmless forms. In that phase, compost soil which is free from or contains trace quantities of petroleum derivatives is produced. The compost soil matures within 3 - 4 months, depending on the season of the year and the weather conditions. In the last stage, the microbiological transformations of the compost soil are dominated by humification processes, which are similar to those occurring in normal soil. Therefore, it is important that the prisms are laid on a platform with a mesh surface which makes it possible for the soil micro- and macro- organisms to enter the prisms directly, which speeds up the humification process. The prisms are aerated and scarified by means of a mobile compost turner with a caterpillar track drive system. The turner usage frequency: every 5 - 8 days. The temperature of the prisms should not be lower than 18 °C. The duration of the last stage is 3 - 5 months. The end product is humus soil free from petroleum-derived compounds, with the humus content not lower than 5,5% in dry matter, in which humic acids prevail over fulvic acids. The final moisture of the humus soil does not exceed 23%.

Presently, the new challenge is, besides removing anthropogenic pollutions, restraining further drop of the humus compounds in the widely understood soil. The invention allows in a simple method or proceeding to combine the total biodegradation of petroleum-derivative compounds contained in the removed and delivered soil and/or soil- based masses with humification processes leading to the creation of a new biological body - the humus soil to be used for cultivation purposes.

The invention has been explained in the embodiment.

Embodiment.

A batch of soil polluted with petroleum products with weight of approx. 1010 Mg is isolated on a platform provided for the production of compost with the annual capacity in fresh compost soil amounting to over 16,000 Mg/yr. The initial content of pollutions in the soil was between 1 84 mg/kg of dry matter up to 9 5 mg/kg of dry matter. The soil moisture fluctuated from 18.42% to 20.63% and the pH factor was within the range of 6.8 - 7.1. In order to carry out efficient bioremediation combined with the biomass biological transformation and humification, slightly more than 1050 Mg of waste undergoing biodegradation was prepared with the composition and unit weight values presented in the table.

Biowaste weight in Mg

In the Outside the

Item Biodegradable waste type agricultural agricultural engineering engineering season season

1. Stabilised municipal sewage

sediments 820 690

2. Rye straw 90 -

3. Sawdust - 145

4. Chicken broilers' manure 60 64

5. Green waste matter 35 -

6. Biodegradable kitchen waste 51 72

7. Raw materials and products not

suitable for eating and processing - 83

T O T A L 1056 1054 In the first part of the first stage, the biowaste was mixed and arranged mechanically in 12 prisms, each with the dimensions of 35 m (length) x 5.0 m (width) x 1.2 m (height). The prisms were arranged along the axis of the aerating ducts. 6 chamber shields were polled over the prisms and then the pressurised 15 m ³ aeration was automatically turned on with the frequency of 1 hour of aeration per 0.5 hour break. After 4 - 7 days (depending on the season of the year) had passed, when the prism heating temperature was reaching 49 °C, soil polluted with petroleum derivatives was added to the prisms with heating biomass by pouring it mechanically so that the target height of the prisms of approx. 1.6 m was achieved. The 0.4 m thick layer of polluted soil was left on the heating prism for 2 days. Then, after pulling away the chamber shields, each prism was mixed, scarified and moisturised with the use of a turner with a caterpillar track drive system. Following that operation, the average biomass moisture was reaching 39.1 %. Further intensive pressurised aeration required delivering 15 m ³ of air as converted per 1000 kg of dry matter of the prism with the frequency of 1 hour of aeration per 0.5 hour break. After microbiological transformation, which lasted 15 days, approx. 1410 Mg of the initiating compost were produced.

In the second part of the first stage, approx. 618 Mg of soil polluted with petroleum derivatives were added to the initiating compost, mechanically mixed and arranged in 12 prisms. The prisms were covered with 6 chamber shields and then the pressurised aeration was started. Every 4 days, the biomass accumulated in the prisms was scarified and watered with effluents of up approx. 34% moisture level with the use of a turner with a caterpillar track drive system. Used post- process air containing odorous substances and volatile hydrocarbons for biofiltration were transported by a vacuum system. The decomposition of biomass combined with the biodegradation of petroleum derivatives was carried out during 48 days (the agricultural engineering season).

After completing the first stage, approx. 1990 Mg of fresh compost soil was produced, in which the average content of petroleum products was reduced by 79.4 % to the level of 319 mg/kg of dry matter.

In the second stage, the fresh compost soil was transported to the isolated area of the platform and then it was mechanically arranged in prisms with the following dimensions: 80 m (length) x 5.0 m (width) x 1.6 m (height). The prisms were scarified and aerated at the same time every 5 - 7 days with the use of a turner with a caterpillar track drive system. The temperature of the compost soil heat was 25.3 °C with a decreasing trend. The biological transformation combined with the bioremediation lasted for 3 months. As a result, mature compost soil with a trace quantity of petroleum derivatives amounting to 0.11 mg/kg of dry matter was produced.

In the last stage, the compost soil was transported and laid mechanically on a separated platform with mesh surface. The dimensions of prisms did not vary from the dimensions given for the second stage. The prisms were scarified gravitationally and aerated at the same time with the use of a turner with a caterpillar track drive system with a frequency of every 5 - 7 days. The average temperature of the prisms was 22.5 °C. The humification transformations were carried out for 3.5 months. Humus soil was produced in which no presence of petroleum-derived compounds was found. The average conversion content of humus in the humus soil was 17,63 % at the ration of C : N equal to 9.83. The analysis humus compounds showed that that content of humic acids (CKH) was 12.33 g/kg of dry matter whereas that of fulvic acids (CKF) was 7.91 g/kg of dry matter.

Similar results were obtained outside the agricultural engineering season in the processes of bioremediation and the microbiological transformation of soil polluted with petroleum-derived compounds with the initial weight of approx. 980 Mg, which was mixed in an adequate way with biodegradable biological waste with the weight of approx. 1050 Mg (see the table). Considering the worse environmental conditions, among others lower temperature, the duration of each stage was extended by 24 - 31 %.