GB2353792A

GB2353792A - Bioremediation process

Info

Publication number: GB2353792A
Application number: GB9923031A
Authority: GB
Inventors: Richard Geoffrey Mattison
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-09-06
Filing date: 1999-09-30
Publication date: 2001-03-07
Also published as: GB9920937D0; GB9923031D0

Abstract

According to the present invention there is provided the use of bacterivorous protozoa (particularly flagellates) to increase the efficiency of bioremediation processes involving the biodegrading organic pollutants such as petroleum-derived hydrocarbons and sewage compounds. The bacterivorous protozoa can be added alone or in combination with appropriate bacteria to contaminated sites in order to facilitate and enhance <U>in situ</U> bioremediation. A ratio of one flagellate to between 10<SP>1</SP> to 10<SP>5</SP> bacteria can be added to provide a dynamic control of bacterial growth. This method prevents bacterial clogging preventing further bioremediation.

Description

2353792 1 1 "Process" 2 3 The present invention relates to a method for

improving 4 the efficiency of a bioremediation process and in particular to the breakdown of petroleum derived 6 hydrocarbons (oils) by bacteria.

7 8 This field has considerable commercial potential and

9 numerous companies have already been set up to exploit the ability of bacteria to 'clean up' oil spills in 11 natural environments such as soils.

12 13 Contamination with organic pollutants including 14 pet roleumderived hydrocarbons and sewage is of widespread importance in the terrestrial (soils, 16 subsurface and groundwater aquifers), aquatic (rivers 17 and lakes) and marine environments. The toxicity 18 associated with many comparatively soluble petroleum 19 derived hydrocarbons poses a risk not only to the environment but also to human health. This results 21 from the fact that groundwater aquifers, rivers and 22 lakes supply the bulk of our drinking water. The most 23 toxic and frequently encountered petroleum- derived 24 hydrocarbons are benzene, toluene, ethylbenzene and xylenes (BTEX). These pet rol eum- derived hydrocarbons 2 1 are often lighter than water and so when a spill occurs 2 they percolate from the surface through the 3 soil/sediment matrix and often settle in a film at the 4 groundwater table. This water table is variable in 5. depth, say 3-7 metres.

6 7 Bioremediation processes designed to treat contaminated 8 sites typically employ bacteria to utilize the organic 9 pollutant as their main carbon and energy source.

These process may be divided into two classes, namely 11 (1) in situ and (2) ex situ. In situ bioremediation 12 involves the direct delivery of bacteria and/or 13 oxygen/oxidants to the affected site. Ex situ 14 bioremediation involves physical excavation or removal is of the affected material with it's subsequent treatment 16 in reactor vessels. In situ bioremediation is widely 17 considered to be an environmentally friendly and cost 18 effective approach to the treatment of contamination in 19 groundwater aquifers. This approach relies on the collective ability of bacteria present and/or added to 21 degrade pollutants under optimal conditions which 22 include sufficient hydraulic conductivity to permit 23 adequate flow of soluble pollutants and oxygen/oxidants 24 through the affected area. Numerous naturally occurring bacteria are capable of degrading and 26 detoxifying pet roleum- derived hydrocarbons. Of 27 particular importance are members of the genus 28 Pseudomonas members of the beta subdivision of 29 Proteobacteria most notably the genus Azoarcus and members of the delta subdivision of Proteobacteria 31 which include many sulphate reducing bacteria. These 32 bacteria degrade pet rol eumderived hdyrocarbons under 33 various redox conditions ranging through aerobic to 34 nitrate reducing and sulphate reducing.

36 The efficiency of in situ bioremediation can be limited 3 1 in two ways namely, (1) if unrestricted growth of 2 bacteria leads to rapid exhaustion of oxidants and 3 other growth factors and/or (2) if unrestricted growth 4 of bacteria leads to bioclogging with a reduction in bydraulic conductivity. [In other words a bioclog 6 resulting from bacterial biomass and/or exopolymeric 7 slime, produced by many growing bacteria reduces the 8 permeability of a matrix (e.g. soil/sediment) to 9 water]. Both phenomena have been noted in the field.

They have also been demonstrated in model systems under 11 laboratory conditions in the absence of bacteria 12 feeding (bacterivorous) protozoa.

13 14 According to the present invention there is provided the use of bacterivorous protozoa (particularly 16 flagellates) to increase the efficiency of in situ 17 bioremediation processes involved in biodegrading 18 organic pollutants such as petroleum-derived 19 hydrocarbons and sewage compounds.

21 The invention also provides a bioremediation process 22 including a step wherein bacterivorous protozoa are 23 added to the bacteria in the process.

24 Bacterivorous protozoa appear to reduce the phenomenon 26 of bacterial bioclogging and in so doing improve 27 hydraulic conductivity in aquifers.

28 29 Bacterivorous protozoa accelerate biodegradation and mineralization of such organic pollutants.

31 32 Bacterivorous protozoa increase the bioavailability of 33 mineralized organic pollutants by contributing carbon, 34 nitrogen and phosphorus to the ecosystem.

36 Comparatively large populations of these bacteria along 4 1 with bacterivorous protozoa occur at organically 2 contaminated groundwater aquifers and other sites.

3 [Large populations of bacteria cir 108/gram of 4 soil/sediment and protozoa 105/gram of soil/sediment occur in the surface and normally decrease with depth.

6 In the presence of the organic pollutants mentioned the 7 numbers of bacteria and protozoa at the water table is 8 comparable with that found at the surface.] These 9 protozoa are comprised of ciliates, flagellates and amoebae with flagellates being the most numerous group 11 in groundwater aquifers. Most ciliates are absent 12 below a depth of about 1 metre. The role of 13 bacterivorous protozoa (especially flagellates) in in 14 situ bioremediation is considered to be an indirect result of their ability to selectively graze on and 16 control the biomass of the bacterial community. A 17 controlled bacterial biomass would lead to a reduction 18 in bioclogging with subsequent improvement in hydraulic 19 conductivity. Protozoa may also enhance bioremediation by increasing the metabolic rate of pollutant degrading 21 bacteria. They may also facilitate this by 22 remineralising growth limiting nutrients such as 23 ammonium and phosphorus.

24 This method would add bacterivorous protozoa 26 (especially flagellates) either alone or in combination 27 with appropriate bacteria to contaminated sites in 28 order to facilitate and enhance In situ bioremediation.

29 Appropriate bacteria would be those capable of degrading the pollutant in question and would also be 31 an acceptable food source for the flagellates., Organic 32 pollutants would include petrol eum- derived hydrocarbons 33 and sewage. A ratio of one flagellate to between 101 34 and 101 bacteria would be added to provide a dynamic control of bacterial growth. This would improve the 36 efficiency of in situ bioremediation process by (1) 1 leading to a reduction in bioclogging with subsequent 2 improvement in hydraulic conductivity in the aquifer, 3 and/or (2) increasing the metabolic rate of individual 4 pollutant degrading bacteria.

6 Natural environments also contain protozoa which live 7 by feeding on bacteria. In laboratory cultures 8 containing bacteria, protozoa and hydrocarbons it was 9 noticed that the presence of protozoa actually speeds up (rather than reducing) the breakdown rate of 11 hydrocarbons by bacteria. The invention therefore 12 relates to the effects of protozoa on increasing the 13 breakdown rate of hydrocarbons by bacteria. It is 14 therefore proposed that commercial companies could is utilize protozoa to improve and accelerate their 16 existing bioremediation processes. Since hydrocarbon 17 spills are of global importance, any additional 18 improvement to bioremediation processes could be very 19 significant.

21 Example

22 23 Assume that a pristine groundwater aquifer has the 24 following characteristics. It is comprised of a sandy soil with a gravel/clay lens and an underlying base 26 of impervious clay/rock. The groundwater flow rate is 27 2 metres /day. An indigenous population of bacteria 28 (approx. 107 /gram sediment) and protozoa 29 (approx. 104 /gram sediment) occurs at the water table.

The protozoan community is comprised mostly of 31 bacterivorous flagellates.

32 33 Assume that this aquifer is contaminated by a spill of 34 petroleum derived hydrocarbons comprised mainly of toluene (Figure 1A). Assume that 103 litres 36 of toluene forms a film or non aqueous phase liquid 6 1 (NAPL) in the saturated aquifer below the water table.

2 The indigenous population of bacteria and protozoa at 3 the water table increases to approx. 108 /gram sediment 4 and 105 /gram sediment, respectively. only 1% of the indigenous population of bacteria can degrade toluene.

6 7 Assume that immediately downstream of the NAPL some 8 four wells are installed in an arrangement shown in 9 Figure 1B & C. These wells are located at the corners of a 1 metre square and extend into the 11 saturated aquifer below the water table. Each well is 12 screened except for the bottom 1 metre in the 13 saturated aquifer which is left unscreened. The 14 unscreened sections of the four wells delimit a volume is of 1 cubic metre sediment in the saturated aquifer.

16 This cube (approx. 500 kilograms sediment) will be 17 referred to as the flow cell. Wells A'and B are the 18 injection wells while C and D are the extraction wells.

19 Assume that toluene achieves maximum saturation in the 21 groundwater (5.6 mM) and is transported horizontally in 22 a plume downstream of the NAPL at 2 metres /day through 23 the flow cell. Thus approx. 1 litre /day toluene 24 passes through the flow cell.

26 (1) Estimation of the consumption of toluene by the 27 indigenous bacterial population in the untreated 28 aquifer 29 Assume that toluene is consumed at a rate of approx. 2 31 micromoles /gram sediment/day. The amount of toluene 32 consumed in the flow cell is approx. 1 mole /day which 33 corresponds with approx. 100 millilitres /day.

34 'Therefore in the untreated aquifer approx. 10% of toluene transiting the flow cell is consumed.

36 7 1 (2) Estimation of the consumption of toluene during in 2 situ bioremediation without accounting for bioclogging 3 4 Assume that sufficient oxidants, nutrients and toluene degrading bacteria are added to injection wells A and B 6 to support the population of introduced bacteria at 7 approx. 109 cells/ gram sediment. The introduced 8 population is initially ten fold higher than the 9 indigenous population and would be expected to increase. Assume this results in a minimum ten fold 11 increase in toluene degrading ability. Therefore in 12 the in situ bioremediated aquifer approx. 100% 13 of toluene transiting the flow cell is consumed.

14 (3) Estimation of the consumption of toluene during in 16 situ bioremediation accounting for bioclogging 17 18 Assume that progressive bioclogging occurs from the 19 injection wells and results in approx. one hundred fold reduction in hydraulic conductivity across the flow 21 cell after approx. 30 days. Groundwater flow is 22 reduced and the introduced and indigenous population of 23 bacteria in the flow cell become progressively depleted 24 in oxidants, nutrients and toluene. Therefore bioclogging will result in an approx. 99% reduction in 26 toluene transiting the flow cell after one month.

27 Furthermore, in the short term, bioclogging will 28 be a largely irreversible phenomenon.

29 (4) Estimation of the consumption of toluene during in 31 situ bioremediation with the addition of bacterivorous 32 protozoa 33 34 Assume that sufficient bacterivorous protozoa are added to injection wells to support the population of 36 introduced protozoa at approx. 106 cells/ gram 8 1 sediment. The introduced population is ten fold higher 2 than the indigenous population and maintains an 3 equilibrium ratio of approx. 1:1000 with introduced 4 bacteria. Protozoan control on the bacterial 5 population would significantly reduce the development 6 of bioclogging in the flow cell as described in (3) 7 Therefore in the in situ bioremediated aquifer, the 8 addition of bacterivorous protozoa should facilitate 9 those conditions favourable to the degradation of 10 toluene as described in (2) 11 12 9

Claims

1 CLAIMS

2 3 1. A bioremediation process including a step wherein 4 bacterivorous protozoa are added to the bacteria in the process.

6 7

2. A process as claimed in claim 1 wherein the 8 bacterivorous protozoa are flagellates.

9

3. A bioremediation process as claimed in any of the 11 preceding claims wherein the bacterivorous 12 protozoa are added alone.

13 14

4. A bioremediation process as claimed in any of the preceding claims wherein the bacterivorous 16 protozoa are added in combination with a bacteria.

17 18

5. A bioremediation process wherein the ratio of one 19 flagellate to between 101 to 105 bacteria is added.

21

6. Use of bacterivorous protozoa to increase the 22 efficiency of in situ bioremediation processes.

23 24 julmurlspecS/p24569.2 0