By: Szonja Kiss and Tamás Pásztor, Messer Hungarogáz
Reading time: 3 Minutes
◤ ENVIRONMENT
Millions of times more remediation assistance
Bacteria can help clean up contaminated soil. To do so, they need technical support and a supply of oxygen. That’s why the environmentally friendly and soil remediation firm Geohidroterv is collaborating with Messer.
iStock-1181366400
Roughly the size of four soccer fields, the grounds are situated in an unnamed location in the middle of Hungary. Experts estimate that some 155,000 cubic meters of soil there contain 63,840 kilograms of pollutants – primarily aliphatic and aromatic hydrocarbons such as benzene, toluene, ethylbenzene and xylene. In the past, fuel was stored on this site in half-buried tanks, in accordance with the regulations in place at the time, without precautions that we now take for granted. Today, EU and national regulations are stricter and minimize the occurrence of such pollution, but they can still occur in the event of breakdowns or accidents.
Bioremediation to eliminate soil contamination
The tank farm has since been modernized, but the pollutants in the soil have gradually seeped into the groundwater. They could endanger drinking water wells in the neighborhood and pose other environmental risks. Preventing that from happening to the wells and eliminating the contamination fall under the core expertise of the Budapest-based company Geohidroterv. In this case, it decided to use bioremediation, i.e. the biological decontamination of the soil with the aid of bacteria. Certain species of these microorganisms thrive on the very hydrocarbons that are poisonous to humans.
Geologist Péter Szabó, one of Geohidroterv’s two CEOs, describes how the processes work in the soil: “The
bacteria tear apart the molecular chains of the hydrocarbon pollutants and convert them to harmless compounds. The bacteria suitable for this process are usually naturally present in contaminated soil, but only in relatively low numbers – about 100 to 10,000 bacteria per gram. The goal of our method is to increase this number up to 100 million.”
If the basic stock is just too small, or the biological conversion doesn’t really get going, specially grown bacterial cultures are added to the soil. Above all, however, experts try to create ideal conditions for the reproduction of the bacteria capable of breaking down pollutants.
iStock-522462600
Helping the little helpers breathe
A type of “fertilizer” is needed to create these ideal conditions: nitrogen, phosphorus and potassium facilitate the growth of the bacterial population. Because the helpful microorganisms are aerobic (i.e., air-breathing) bacteria, oxygen is also added to the mix. The gas and the gas distribution system come from Messer. The three solid materials are dissolved in water, which is then injected into the contaminated soil with a pipe system and about a hundred injection wells. The oxygen is also delivered through the wells, using special emitters located below the groundwater level. There the gas flows with 1 bar pressure through porous silicone pipes and is diffused directly into the groundwater.
This method accelerates the natural biodegradation process of hydrocarbons. What would otherwise take decades or centuries can be carried out in a reasonable period of time. For the project described here, a decision will be made in two years as to whether the introduction of the specialized bacterial cultures is necessary, after comprehensive monitoring through chemical and biological laboratory analyses of the soil and groundwater. Continuous monitoring is used to fine-tune the ongoing process. If all goes according to plan, the remediation will be complete after six years.