Natural Attenuation

En la presente investigación se ha aplicado y comparado el método de bioestimulación con el de atenuación natural sobre suelos contaminados con hidrocarburos en la zona norte del país. La atenuación natural es la degradación generada por los microorganismos del suelo sin adición de nutrientes, mientras que en la bioestimulación se le da las condiciones de aireación, humedad y nutrientes para que los microorganismos puedan tener mayor eficiencia de remoción por su
mayor actividad, así como una mayor división de los mismos.

Otro parámetro de comparación es la relación de nutrientes C:N:P que afecta también a la remoción de hidrocarburos. El principal factor de medida de remoción ha sido establecido en función al análisis de TPH (hidrocarburos totales de petróleo).

Autores: Huguez Ames, Tecsup (Perú)/ Lizardo Visitación, Rosa Altuna y Lena Téllez, UNALM (Perú)

Large-scale contaminated megasites like Bitterfeld in eastern Germany are characterized by a regional contamination of soil, surface water and groundwater as a result of a long and varied history of chemical production. While the contaminants in soils and sediments mostly represent a localized problem, pollutants in groundwater may spread to uncontaminated areas and endanger receptors like surface water and drinking water wells according to the site-specific hydrologic regime. From the toxicological point of view, the contaminants at the Bitterfeld megasite represent a dangerous cocktail of various harmful substances coming from a multitude of sources. Appropriate remediation techniques must be able to remedy the specific problems arising from hot spot areas within the megasite in addition to preventing a further extension of the contaminated zone towards uncontaminated compartments. Therefore, a combination of specifically designed remediation technologies based on the pump and treat-principle with in situ technologies, such as reactive walls and monitored/enhanced natural attenuation, is necessary to efficiently address the miscellaneous challenges at this megasite. In this paper, the currently known contaminant distribution, the associated problems for human health and the environment and possible remediation strategies are presented for the Bitterfeld megasite.

Biogeochemical processes controlling nitrate attenuation in aquifers are critically reviewed. An understanding of the fate of nitrate in groundwater is vital for managing risks associated with nitrate pollution, and to safeguard groundwater supplies and groundwater-dependent surface waters. Denitrification is focused upon as the dominant nitrate attenuation process in groundwater. As denitrifying bacteria are essentially ubiquitous in the subsurface, the critical limiting factors are oxygen and electron donor concentration and availability. Variability in other environmental conditions such as nitrate concentration, nutrient availability, pH, temperature, presence of toxins and microbial acclimation appears to be less important, exerting only secondary influences on denitrification rates. Other nitrate depletion mechanisms such as dissimilatory nitrate reduction to ammonium and assimilation of nitrate into microbial biomass are unlikely to be important in most subsurface settings relative to denitrification. Further research is recommended to improve current understanding on the influence of organic carbon, sulphur and iron electron donors, physical restrictions on microbial activity in dual porosity aquifers, influences of environmental condition (e.g. pH in poorly buffered environments and salinity in coastal or salinized soil settings), co-contaminant influences (particularly the contrasting inhibitory and electron donor influences of pesticides) and improved quantification of denitrification rates in the laboratory and field.

The understanding of groundwater flow and contaminant migration is based on our ability to characterize aquifers and represent these processes with numerical simulators. This understanding is required to efficiently remediate contaminated sites since the failure of remediation actions are often related to an insufficient understanding of aquifer heterogeneity. During the last decades, continuous development of numerical simulators allowed models to

Nitrate-contaminated groundwater from an aquifer in the Osona region (NE Spain) was chemically and isotopically (δ15NNO3,δ18ONO3,δ34SSO4,δ18OSO4δ15NNO3,δ18ONO3,δ34SSO4,δ18OSO4, δ  D, δ18OH2Oδ18OH2O and δ13CDICδ13CDIC) characterized. Diffuse- NO3- contamination reached values of 366 mg/L. Nearly 75% of the 37 sampled sites had higher concentrations than the 50 mg/L in NO3- limit for drinking water. To identify the source of pollution δ15NNO3δ15NNO3 and δ18ONO3δ18ONO3 were used with results, for most samples, in the range of pig manure NO3-. Nitrification processes were evaluated by means of the δ18O of NO3- and water. Isotopic data suggested that natural attenuation of NO3- was taking place. This process was confirmed using the δ18ONO3δ18ONO3 coupled with the NO3-/Cl- ratio, avoiding the influence of continuous NO3- inputs. A further insight on denitrification processes was obtained by analyzing the ions involved in denitrification reactions. Although the role of organic matter oxidation could neither be confirmed nor discarded, this approach showed a link between denitrification and pyrite oxidation. Therefore, in areas with no adequate infrastructure (e.g. multipiezometers), such as the one studied, this approach could be useful for implementing better water management.

The Niger Delta region of Nigeria, famous for its rich oil deposits, is one of the most productive ecosystems in the world. Paradoxically, since the discovery of oil in Nigeria in 1956, the country has suffered environmental degradation from oil spillage. Ecological restoration of oil spill sites involves passive restoration (natural attenuation and secondary succession) or interventionist restoration (clean up/removal of oil, bioremediation of the site, introduction of desired species, and ecosystem management). The paper reviews relevant literature and examines the process of ecological restoration in the Niger Delta. Although oil companies and regulatory officials suggest that some form of restoration, which usually involves planting seeds, is carried out in the mangroves, there are little documented materials of restoration activities on oil spill sites in the Niger Delta. The paper concludes that the legislations on the practice of restoration are shallow and need to be revised...