Abstract. 1 Introduction

Transcription

1 Solvent enhanced boremedaton of weathered ol contamnaton G. Gray, K. Chappell & V. K. Broscomb-Smth School of Envronmental and Appled Scences, Unversty of Abstract Ths paper descrbes a novel boremedaton process for the treatment of ol splls on land. The method was developed specfcally to deal wth long term ol contamnaton where the volatle fractons have evaporated leavng the more recalctrant fractons. A model system of sand and Kuwat crude ol was used to test the system. A combned treatment whch ntroduced an addtonal solvent component was found to enhance moblty and avalablty of ol, enhancng boremedaton. 1 Introducton The Gulf War n Kuwat has resulted n one of the largest man made envronmental dsasters, and almost certanly the greatest acute contamnaton of land and water wth ol, n hstory. A total of 788 wells were sabotaged by the Iraq army on ther retreat, of whch 613 were set alght and 76 left to pour ol onto the land L In addton to the wells, ol dstrbuton centres, ol loadng termnals, storage tanks and refneres were also severely damaged. For 300 days n 1991, between 2 and 4 mllon barrels of ol per day were splled nto the Kuwat desert. The Gulf was also heavly contamnated wth estmates beng between 160 and 340 mllon gallons of crude ol enterng the sea. A legacy of ths contamnaton has been the Kuwat lakes of ol whch formed from a mxture of crude ol and large quanttes of sea water used to extngush the well fres. Ol densty n these lakes^ s approxmately 1 g ml"l wth ol penetraton varyng from surface contamnaton to a depth of 1 m, average penetraton s calculated to be m. These heavly contamnated stes along wth sols contamnated by oly msts and soot pose a serous envronmental problem n the regon.

2 316 Ol & Hydrocarbon Splls, Modellng, Analyss & Control Penetraton of ols nto the sol provdes a sgnfcant threat to valuable groundwater supples. The man rsk s from the monoaromatc fractons, especally benzene, toluene, ethylbenzene and xylene. Rsks are also posed to wldlfe wth large klls of brds, mammals and nsects beng reported. In the seven years snce the wthdrawal of Iraq troops there has been a massve clean-up operaton utlsng a wde range of physcal, chemcal and bologcal technques. However, the ol lakes and large areas of contamnated sands stll pose a sgnfcant problem. Economc consderatons mean that, potentally, the most favourable approach for decontamnaton of the area s boremedaton. There are several problems wth the use of boremedaton n Kuwat, these are as a result of envronmental condtons and the current condton of the ol n the lakes and sand. Envronmental condtons whch can prove problematc are hgh desert temperatures and low precptaton. Temperatures whch can exceed 40 C n July and August, and low precptaton rates, annual average of 115 mm, place water at a premum^. Sols n Kuwat are manly sandy calcareous ardsol sol wth an organc matter content of under 0.02%, nutrents are lackng and hgh calcum and magnesum content further decrease the avalablty of nutrents. Typcally, sols contan 10^ - 10& bactera, and 10-10^ fung 6. Due to the use of sea water n the fre fghtng operatons, and subsequent evaporaton, salnty levels are hgh n the lakes and surroundng sols'. Attempts at the applcaton of boremedaton n Kuwat, ncludng landfarmng, wndrow compostng and statc sol ples, have met wth varyng degrees of success 7. Up to 74.1% of alkanes were degraded wthn sx months usng a landfarmng technque whlst the use of statc ples acheved 53.8% degradaton over the same tme perod. Statc sol ples, however, provde a relatvely cheap opton wth lower labour requrements. Work at the Boremedaton Unt at the Unversty of Derby has prevously dentfed enhanced boremedaton n such systems wth the addton of solvents to water/nutrent mxes. Low concentratons of solvents appear to ncrease ol moblsaton and avalablty to bactera. A recrculatng system avods rsks posed to groundwater by ncreased moblty of the ol. The followng paper descrbes a laboratory scale applcaton of a solvent enhanced system to sand contamnated wth weathered Kuwat crude ol.

3 Ol & Hydrocarbon Splls, Modellng, Analyss & Control Expermental Method Schematc Dagram of Model System \ ' v \ Recrculatec Contamnated soluton sand Perforated metal sheet ^ Fgure Preparaton of weathered crude on substrate Washed sharp sand was coated wth crude ol at a rato of 47:1 sand and ol by weght. The resultng substrate was mxed and then spread thnly n enamelled trays. The trays where heated at a constant 60 *C n a fume cupboard for 7 days. The resultng weathered crude was extracted from the sand (see 2.3) and subsequent analyss by GC/MS confrmed that n excess of 80% of the orgnal mass of the crude ol had been lost. Whlst evaporaton greatly reduced the mass of all major consttuents, concentratons of all alphatcs smaller than Cjg were reduced to trace levels. 2.2 Trals Sx smultaneous systems where constructed for the treatment of 320g of weather crude ol on sand (Fg. 1). Each system was actvated by the addton of 80 ml of aqueous soluton to the system. The composton of the soluton for each soluton s detaled n Table 1. Ths soluton was collected from the base of apparatus after passng through the sand. The volume of the soluton was adjusted to 80 ml by the addton of water

4 318 Ol & Hydrocarbon Splls, Modellng, Analyss & Control (Deonsed or salne as approprate), pror to beng feed back onto the sand. Ths process was repeated for all sx trals for 14 days under ambent condtons. Chemcal composton and bacteral abundance were assessed for each system at day 0, day 2 and day 14. System Soluton Composton System F FN FSN S SN SSN Water Fresh Fresh Fresh Salne Salne Salne Table 1. Nutrent Lmonene 2.3 Extracton and Analyss of Ol Components 1 g samples were transferred to paper thmbles (Whatman) and under went an 8 hr soxhlet extracton nto Dchloromentane (HPLC grade). Sample volumes were adjusted by rotary evaporaton at 20 *C and the volume samples were then made up to ml samples. Determnaton of alphatc consttuents was performed GC FID/MS usng a Hewlett Packard 5890 Seres II GC wth 50 m C]g capllary column and 5971 Seres Mass Selectve Detector. 2.4 Bacteral Counts Water samples (2 ml) were removed from each system on days 2 and 12 for total bacteral counts. Samples were preserved wth 2% fnal concentraton neutral fltered formaldehyde and refrgerated for up to 48 hours pror to countng. Two replcate subsamples were staned wth acrdne orange, concentrated on black, 0.2jm pore sze polycarbonate membranefltersand counted by epfluorescence mcroscopy 3 4 usng a Leca DMLB mcroscope. More than 600 cells were counted per preparaton; 95% confdence ntervals were < ±8% of the count 5.

5 Ol & Hydrocarbon Splls, Modellng, Analyss & Control Expermental Results Extract Composton : Dav 14 0) c 0>C25,C21-C25 o (/),C16-C20 QC11-C15 F SSN FSN SS Fgure 2. The use of deonsed water wthout addtonal nutrent resulted n no detectable change n the composton of the weathered crude ol. The addton of a nutrent mx (System FN) resulted n a marked reducton n the mass of total hydrocarbon. Concentratons of larger alphatcs ( > C20) were found to be greatly reduced and a correspondng ncrease n the relatve abundance of alphatc fracton ( C16-20 ) was observed. The major speces remanng n the ol remaned alkanes and ther branched homologues. The addton of lmonene solvent (system FSN) resulted n enhanced breakdown of all fractons from C]g and above compared to the non solvent systems. Despte the presence of a substantal carbon source, growth wthn system F, wth the addton of just deonsed water, was lmted. Ths s possbly due to the absence of macro and /or mcro nutrents. Nutrents for other systems were provded n the form of sea weed nutrent mx, however system S (sea water alone) gave smlar results to those of system FN (deonsed water wth added nutrent) ndcatng that perhaps the use of could reduce the need for addtonal nutrent addton. Further support for ths s provded by the absence of any enhancement of breakdown on the addton of nutrent to the sea water and solvent system. Most systems exhbted sgnfcant bacteral growth between days 2 and 14, ndcatng the development of establshed mcrobal populatons.

6 320 Ol & Hydrocarbon Splls, Modellng, Analyss & Control Bacteral numbers on both days 2 and 14 ndcate that the FSN system was the most favourable for mcrobal growth. Wthn the sea water systems the addton of solvent dd not promote ncreased mcrobal growth but dd promote breakdown. It s possble that moblsaton of ol wthn the solvent ncreased the avalable surface area for breakdown, ths would also ndcate that mcrobal growth rates were lmted by factors other than avalablty of the carbon source. It s lkely that dfferent rates of breakdown between populatons of smlar szes are due to dfferences n populaton composton, ths s clearly an area requrng further work. Bacteral Numbers 3.0E+8 2.5E+8 2.0E+8 O CO 1.5E+8 1.0E+8 5.0E+7 O.OE+0 _.nf Jl QDay2 QDay14 Fgure 3. 4 Conclusons The results of ths prelmnary tral ndcate marked enhancement of boremedaton processes wth the addton of a solvent component. It appears that ths s due to ncreased moblsaton of ols, thus provdng addtonal surface area for bacteral acton. Use of ether sea water or freshwater had lttle effect on the rate of ol degradaton. Ths may have sgnfcant mplcatons for the use of seawater n boremedaton n Kuwat, provded problems wth sol salnaton can be overcome. Ths

7 Ol & Hydrocarbon Splls, Modellng, Analyss & Control 321 tral presents only prelmnary work and t s clear that more work s requred n order to develop a workng system for large scale treatment of weathered ol. 5 References 1. Bader, M.S.H. and Clarkson, W.W, An Overvew of the Ol Lakes n Kwat: The Problem and Remedal Methods, Journal of Envronmental Scence and Health, A30 (5). 2. Al-Houty, W., Abdal, M. and Zaman, S Prelmnary Assessment of the Gulf War on the Kuwat Desert Ecosystem, Journal of Envronmental Scence and Health, A28 (8). 3. Carr O.J. and Goulder R., Drectly counted bactera n a trout farm and ts effluent, Aquacult. Fsh. Managem., 24, Daley R.J., Drect epsluorescence enumeraton of natve aquatc bactera: uses, lmttatons, and comparatve accuracy, n Costerton, J.W. and Colwell, R.R. (Eds), Natve Aquatc Bactera: Enummeraton, Actvty, and Ecology. Am. Soc. c. 7ec/z. f %6/. Wo. 691 pp Jones J.G., A Gude to Methods for Estmatng Mcrobal Numbers and Bomass n Fresh Water. Freshwater BoL Asssoc. &%. 7W,/. M,JP. 112pp. 6. Al-Awadh N.; Al-Daher R.; El-Nawawny A.; Balba M.T., 1996, Boremedaton of ol contamnated sol n Kuwat: Land farmng to remedate ol contamnated sol, Journal of Sol Contamnaton, Vol. 5, (3). 7. Balba M.T.; Al-Awadh N.; Al-Daher R., 1995, Boremedaton: An overvew based on nternatonal project experence, Journal of Ard Land Studes.