Evaluation of factors for optimisation of biological in situ remediation in petrol-polluted soil

En av de vanligaste föroreningarna i mark och grundvatten är aromatiska kolvä- ten såsom bensen, toluen, etylbensen och xylener. Dessa härstammar från ex. ben- sin och har läckt ut till omgivande miljö från drivmedelsanläggningar. I stället för schaktning och bortforsling av de förorenade jordmassorna som mest förekom- mande ex situ-saneringsmetod behövs mer forskning kring in situ-saneringsmetoder där föroreningen alltså kan angripas på plats. I denna rapport undersöks förhöjd biologisk nedbrytning genom att redogöra för de önskvärda (bio)kemiska reak- tionerna i marken, de parametrar som styr den biologiska nedbrytningen samt huruvida dessa parametrars inverkan har kunnat påvisas i tre stycken fallstu- dier där in situ-sanering utförts vid drivmedelsanläggningar. Studien kommer fram till ett antal primära (ursprungliga) variabler såsom föroreningen i fråga, jordtätheten och klimatet, samt ett antal sekundära (förändringsbara) variabler såsom oxidationsmedlet, mikroorganismerna, näringsämnena och markvattnet. Dessa presenterades sedan i en schematisk skiss som visar hur de växelverkar med parametrarna för optimal biologisk nedbrytning, vilka visade sig ha vissa optimala värden. Dessa konstaterades vara föroreningshalten (<5-10 viktprocent torr jord), pH-värdet (6-9), temperaturen (20-35◦C), vattenmättnaden (40-80%), syrehalten (> 2 500 viktprocent kolväten), C:N:P-kvoten (100:10:1) samt koncent- rationen mikroorganismer (> 103 CFU/ml). När de olika parametrarnas inverkan i fallstudierna undersöktes kunde slutsatsen dras att det skulle behövas ytterliga- re data och mätningar vid varje sanering för att kunna garantera att parametrarna varit inom sina respektive optimala värden. One of the many goals for a sustainable living and a healthy environment is the reduction of toxic substances in soil and groundwater. Within this ambit, one of the most common pollutants is aromatic hydrocarbons such as benzene, tolue- ne, ethylbenzene and xylenes (BTEX) which are spread from e.g. filling stations for fuel as they are constituents of petrol. These are volatile and can constitute a risk for humans and the environment as they percolate through the soil and groundwater resources as well as can exfiltrate from the ground to surrounding buildings and pollute the indoor air. Once these pollutants are present in the soil, the site needs to be remediated, something which is mainly done ex situ by exca- vating the polluted masses to be sent to a treatment facility. An alternative to this is in situ remediation where the pollution can be treated without being excavated and thus having a smaller impact on the environment. In this report, one of these techniques called enhanced biodegradation was studied, which implies the application of oxidisers to faciliate microbial activities. It investigated (1) how this remediation technique works and what (bio)chemical reactions are desired in the soil; (2) what are the principal parameters that enable this remediation process and how do they interact with the surrounding factors, and (3) whether the impact of these parameters can be estimated in three case studies where this technique has been used. The three case studies were filling stations located in Sweden, having similar pollutants and geology, and two diffe- rent oxidisers had been used. The study resulted in the identification of a number of primary (initial) varia- bles such as the pollutant characteristics, the soil density and the climate; as well as a number of secodnary (modifiable) variables such as the oxidiser, microorga- nisms, nutrients and soil moisture. These were then presented in a scheme which shows how their interactions with the parameters for optimal biodegradation. Each parameter was found to have a certain optimum such as the concentration of hydrocarbons (<5-10 mass percent of the dry soil) , pH value (6-9), tempe- rature (20-35◦C), soil water saturation (40-80%), oxygen concentration (> 2,500 mass percent of the hydrocarbons), C:N:P ratio (100:10:1) as well as concentration of microorganisms (> 103 CFU/ml). A negative correlation could be identified between the soil density and the oxygen concentration in the soil, as well as a po- sitive correlation between the soil water saturation in the and the soil moisture, alternatively additional water via irrigation. The impact of each parameter in the case studies of in situ remediation was assessed and the it could be concluded that they would need additional data and measurements for most parameters in order to guarantee that they are within the respective optima.