Treatment of Polluted Soils and Bioremediation

Treatment of Polluted Soils and Bioremediation

• Industrial and motor vehicle development in the last two centuries has disrupted environmental balances, leading to the release of xenobiotic pollutants into the air, water, and soil
• Modern agricultural practices contribute fertilizers and pesticides to the environment that can cause eutrophication in water and harm to plants
• There is an increased ecological awareness paired with effective control activities to identify contaminated sites and attempt biological recovery

Contaminated Sites and Bioremediation

• A contaminated site poses significant short, medium, and long-term risks to residents due to hazardous xenobiotic substances
• Contaminated sites can threaten all forms of life and disrupt ecological balance
• Distinctions can be made between an unsaturated or vadose zone, a saturated zone, and the groundwater affected by the contamination
• Remediation treatments can be in situ or ex situ, where they are divided into on-site and off-site, and can be physical, chemical, or biological

Techniques and Sustainability

• Bioremediation is a recommended treatment due to its sustainability
• Bioremediation utilizes naturally occurring or artificially introduced microorganisms for pollutant degradation
• Plants can be more effective than microorganisms at removing heavy metals
• Continuous monitoring is required for bioremediation techniques to control factors like nutrient availability, temperature, pH, and oxygen levels
• These techniques are less aggressive toward the environment because they integrate into natural biogeochemical cycles

Italian Legislative Decree 152/2006

• Italian Legislative Decree 152/2006 distinguishes between contaminated sites exceeding risk thresholds for human health, and potentially contaminated sites exceeding pollutant concentrations that warrant monitoring
• Site-specific characterization plans are prepared based on hydrogeological and environmental assessments to determine risk levels following figure 7.2 on page 73

Analyzing Matrices

• Matrices that are analyzed include soil, sediments, drilling materials, groundwater, surface water, and gases
• Samples are analyzed to identify pollutants, types, and quantities present
• A risk level is fixed to calculate the maximum contaminant concentration at the source that is compatible with acceptable risk values
• Mathematical models are used to achieve reliable assessments

Feasibility of Biological Remediation

• Assessing the feasibility of biological remediation involves analyzing the environment's microbial community to find microorganisms capable of degrading existing pollutants in the site

Objective of This Phase

• The research goal is to identify indigenous microorganisms with enzymatic-metabolic capabilities to degrade pollutants, leading to mineralization
• Multiple water and soil sample from different depths are taken
• Microbial charge by culture techniques or molecular methods are analyzed
• The metabolic activity of microorganisms against pollutants is evaluated by selecting pure cultures, identifying them, and assessing their growth on substrates containing specific pollutants
• Qualitative and quantitative research on denitrifying, methane-producing, and sulfate-reducing bacteria is useful for overall microbial characterization
• These bacteria can biodegrade various organic substances in the absence of oxygen
• It is useful to provide substances like nitrates as electron acceptors
• Limited availability of organic nutrients can restrain microorganisms
• Providing nutrients such as molasses or lactate is beneficial

Microorganisms and Pollutant Degradation

• Pollutants can be both nutrient sources and electron donors for degrading microorganisms (mostly bacteria and fungi)
• Aerobic microorganisms transfer electrons from pollutants to oxygen, while anaerobic microorganisms transfer them to oxidized inorganic substances or metals.

Soil Composition and Biodegradation

• Surface soils have higher microbial loads than deeper layers, leading to increased biodiversity, metabolic versatility, and efficient degradation
• Biodegradation is rapid and aerobic in surface layers, but slower and anaerobic in deeper soil

Microbial Communities

• Organic pollutants are degraded by microbial communities via synergistic reactions for partial or complete breakdown of xenobiotics
• Co-metabolism involves the casual degradation of a xenobiotic by reactions that serve different metabolic purposes
• Degradation can be incomplete if reaction products are more stable than the starting substance

Biodegradability Factors

• Chemical structure, properties, and concentration influences a substance's biodegradability
• Steric structure is crucial, especially with complex groups or chains that hinder contact between microbial enzymes and the substrate

Increasing Molecular Substituents

• Biodegradability decreases with increasing molecular substituents due to reduced oxidizable carbon atoms and increased hydrophobicity
• Surfactants are controversial as they can aid transfer but harm microorganisms
• Low water solubility affects distribution
• Hydrophobic compounds either float on water or deposit on the bottom

Concentration Level

• Pollutant concentration is important; low concentrations may not trigger enzyme synthesis required for degradation, while high concentrations can be toxic to microorganisms
• Key characteristics of a contaminated site include interactions between the environment, pollutants, and microorganisms

In Situ Bioremediation

• In situ techniques address soil contamination without excavation, using the unsaturated or saturated zones

Common Techniques

• Passive remediation
• Bioventing and biosparging
• Bioaugmentation
• Biostimulation
• Active or microbiological barriers
• Phytoremediation
• In-situ bioremediation of groundwater

Passive or Intrinsic Bioremediation

• Passive bioremediation uses natural biodegradation by indigenous microorganisms
• Microorganisms use contaminants through metabolic degradation and/or co-metabolism
• Xenobiotic compounds act as selective factors, favouring specific microbial populations

Bioventilation and Biosparging

• Supplying air or oxygen (and sometimes minerals) to microorganisms accelerates biodegradation
• These techniques are used for both unsaturated and saturated soils
• Bioventilation is for unsaturated soils, while biosparging is for saturated soils
• Air (or oxygen) is injected via pipes or injection wells as it is employed to treat soils contaminated by hydrocarbons

Bioaugmentation Technique

• This involves introducing selected microorganisms with enzyme systems for pollutant degradation
• Given the complexity of the issues and variety of xenobiotics, microorganisms that are specific for each are rare
• Choice of microbial species is based on degradation capacity and efficiency
• For proliferation and activity, microorganisms must have available ecological niche
• To promote development, environmental parameters can be influenced

Biostimulation Techniques

• To increase the rate of metabolism in microorganisms by altering factors like nutrients is a technique often used in situ, to increase the rate of natural bioremediation
• Nutrients such as nitrogen and phosphorus are used

Bioactive Barriers

• Used for in-situ groundwater decontamination
• These barriers involve installing aeration wells and permeable supports colonized by microorganisms
• Installed in the aquifer perpendicularly to the water flow to intercept the contaminant plume
• The pollutant is not removed but controlled to block further migration
• Bioaugmentation is inoculated microbes into the permeable barrier

Phytoremediation Uses

• Used to detoxify or extract contaminants
• Consists of absorbing water and contaminants by plants to detoxify or extract contaminents
• Roles of plants include absorbing pollutants accumulating in roots, modifying soil structure, releasing root exudates, and promoting water drainage
• Fitoextraction of metals absorbed and accumulated in plant structures
• Soil/root microbiota degrades the soil (rizosfera)
• In order to slow absorption, plants stall bio availability of water-soluble pollutants accumulated in plant structures

Ex Situ Bioremediation Techniques

• Utilizes excavated and accumulated on-site or transported off-site from contaminated soils
• Consists of landfarming, composting and/or bioreactors

Landfarming Practices

• Matrix is integrated granulated with silicone materials
• A network of tubes is installed to decontaminate the soil
• Systems must be monitored and controlled with the used of irrigation systems

Composting Method

• The addition of ammendments, nutrition and microbes (selected ex-situ) to remediating terrain

Composting Parameters

• Lignosus residual materials (cortex segments)
• pH correctors (calcium carbonate, etc)
• Surfactants
• Organic, simplistic and easily degradable elements

Inoculating Materials

• Can speed up degradation activities

Bio-piles

• Referred to as cumuli rivoltati
• Involves using machineries that allow for aeration
• Soil-windrow composting

Cumuli Statici

• Are aerated by way of insufflating air within the solid form
• Piles can be strato-singolo or strati sovrapposti utilizing inert granulated tubes

Bioreactors

• The utilization of engineered microorganisms that operate using water contents of 40 to 90 percent
• Used post-removal of course materials from terrain, and then the blend runs through continual stimulation and oxygenation methods, running to a separator for removal or liquid

Risk Analysis

• Includes procedures and methodologies that allows one to extrapolate a humane conclusion to a damaged event with probabilistic reasoning.
• Must consider contamination source, mode of transport and populace at risk of contamination
• The analyst takes the future, function of the site into account and those individuals most at risk

Determination Is Function of 3 Primary Parameters

• The contamination source, the methods of which the contaminant(s) traverse (by air, land water etc) and any potential populace at risk.
• The analyst must take the future, function of the site, into account and those individuals most at risk