BIOREMEDIATION

Environmental Engineering - Bioremediation

What is Bioremediation?

• According to the EPA, bioremediation is a treatment that uses naturally occurring organisms to break down hazardous substances into less toxic or nontoxic substances.

Classifications of Bioremediation

A. Based on remediation aiding organisms

1. Bacterioremediation

2. Mycoremediation

3. Phytoremediation

4. Compost bioremediation

B. Based on location for removal technique

1. In situ bioremediation

2. Ex situ bioremediation

Microbial Remediation

Types of Microbial Remediation

• Enzymatic Cellular Bioremediation:

  • Enzymes produced by the microbial cells are extracted and applied on the contaminant site.

• Extracellular Enzymatic Bioremediation:

  • Enzymes produced by the microbes are secreted directly into the medium facilitating degradation of the pollutant.

Essential Factors for Microbial Bioremediation

Bacterioremediation

• Bacteria are the most crucial microbes in this process as they break down the waste into nutrients and organic matter.

• Bacteria can easily digest contaminants like chlorinated pesticides or clean oil spills, but microorganisms fail to destroy heavy metals like lead and cadmium.

Examples of bacteria involved in bioremediation:

Mycoremediation

• Uses fungi's digestive enzymes to break down contaminants such as pesticides, hydrocarbons, and heavy metals.

• Participates in the cycling of elements through decomposition and transformation of organic and inorganic materials.

• Have a higher advantage over bacterial not just in metabolic versatility but also their environmental resilience.

White-rot fungi

• White-rot fungi - are considered the most efficient lignin degrader in nature - degraded all structural constituents of plant cell wall.

• It can degrade both cellulose and lignin.

• Common species: Phanerochaete chrysosporium, Pleurotus ostreatus, and Trametes versicolor

• Phanerochaete chrysosporium - was the first fungi linked to degradation of organic pollutants. Extensive research has shown this it has strong potential for bioremediation in pesticides, PAHs, dioxins, carbon tetrachloride, and many other pollutants.

Classification of Bioremediation

A. Natural Attenuation

• Occurs without human intervention other than monitoring. The process relies on natural conditions and behavior of soil microorganisms that are indigenous to soil.

B. Biostimulation

• Also utilizes indigenous microbial populations to remediate contaminated soils. The process consists of adding nutrients and other substances to soil to catalyze natural attenuation processes.

C. Bioaugmentation

• Involves introduction of exogenic microorganisms capable of detoxifying a particular contaminant.

Bioremediation Methods/Techniques

In Situ bioremediation

• Treating the contaminated material at the site

a. Bioventing

• In bioventing, the activity of the indigenous bacteria is enhanced by inducing air (or oxygen) flow into the unsaturated zone (using extraction or injection wells) and, if necessary, by adding nutrients.

• All aerobically biodegradable constituents can be treated by bioventing. In particular, bioventing has proven to be very effective in remediating releases of petroleum products including gasoline, jet fuels, kerosene, and diesel fuel.

• Targets the Unsaturated Zone.

b. Biosparging

• In biosparging, air (or oxygen) and nutrients (if needed) are injected into the saturated zone to increase the biological activity of the indigenous microorganisms.

• Biosparging is effective in reducing petroleum products at underground storage tank (UST) sites.

• Biosparging is most often used at sites with mid-weight petroleum products (e.g., diesel fuel, jet fuel); lighter petroleum products (e.g., gasoline) tend to volatilize readily and to be removed more rapidly using air sparging.

• Targets the Saturated Zone

c. Phytoremediation

• Treatment of environmental problems (bioremediation) through the use of plants that mitigate the environmental problem without the need to excavate the contaminant material and dispose of it elsewhere.

• Plants can extract, volatilize, degrade, and immobilize contaminants.

• Used for:

  • Landfill leachates

  • Hydrocarbons

  • Explosives

  • Chlorinated Solvents

  • Heavy Metals

• SUBPROCESSES

  1. Rhizodegradation/Phytostimulation

  • Is the breakdown of contaminants in the rhizosphere through microbial activity that is enhanced by the presence of plant roots.

  • PROCESS: The process of breaking down an organic contaminant in soils through active microbial behavior enhanced by the rhizosphere.

  • CONTAMINANTS: BTEX, Petroleum Hydrocarbons, PAHS, PCP, Perchlorate, pesticides, PCBs and other organic compounds

  2. Phytodegradation/Phytotransformation

  • Instead of using microorganisms (Rhizodegradation), Phytodegradation utilizes enzymes. These enzymes are capable of breaking down PCPS, PCBs, Chlorinated Solvents, Herbicides and Pesticides

  • As the plants uptake the toxins, the enzymes convert them into a non-toxic compound

  • PROCESS: Exuded enzymes (by the plants) are capable of detoxifying organic compounds without microbial assistance. It is the process of breaking down the contaminants by plant metabolic activity

  • CONTAMINANTS: Chlorinated solvents, bromide, atrazine, methyl, DDT, tetrabromoethene, tetrachloroethane, dichloroethene, CI and P-based pesticides, PCBs, Phenols, anilines, nitrites, nutrients

  3. Phytoextraction/Phytoaccumulation

  • The uptake of contaminants by plant roots and movement of the contaminants from the roots to aboveground parts of the plants

  • Metals such as nickel, zinc, and copper are the best candidates for removal by phytoextraction

  • PROCESS: The uptake of contaminants by plant roots and movement of the contaminants from the roots to aboveground parts of the plants

  • CONTAMINANTS: Metals, metalloids, radionuclides, perchlorate, BTEX, PCP, organic chemicals not tightly bound to soil particles

  4. Rhizofiltration

  • Similar to Phytoextraction, but the plants are used to clean up contaminated groundwater rather than soil.

  • Example: Sunflowers remove radioactive contaminants

  • PROCESS: Refers to the approach of using hydroponically cultivated plant roots to remediate contaminated water through absorption, concentration, and precipitation of pollutants. It also filters through water and dirt.

  • CONTAMINANTS: Metals, radionuclides, organic chemicals, nitrate, ammonium, phosphate and pathogens

  5. Phytovolatilization

  • The process where plants take up contaminants which are water soluble and release them into the atmosphere as they transpire the water

  • Then, the contaminants evaporate or volatilize into the air surrounding the plant

  • PROCESS: The process where plants take up contaminants which are water soluble and release them into the atmosphere as they transpire the water

  • CONTAMINANTS: Se, Tritium, As, Hg, Xylene, Tetrachloromethane, trichloromethane, trichloroethane, and other chlorinated solvents

  6. Phytostabilization

  • The immobilization of contaminants in soil through absorption and accumulation by roots, adsorption onto roots or precipitation within the root zone

  • PROCESS: The immobilization of contaminants in soil through absorption and accumulation by roots, adsorption onto roots or precipitation within the root zone

  • CONTAMINANTS: Metals, phenols, tetrachloromethane, trichloromethane, and other chlorinated solvents

B. Ex Situ - removal of the contaminated material to be treated elsewhere

a. Composting

• Mixing organics with contaminated soil

• Most effective when removing Polycyclic aromatic hydrocarbon (PAH), trinitrotoluene (TNT), and Research department explosive (RDX).

Types of Composting

• Windrow Composting - Consists of placing the mixture of raw materials in a long narrow pile which are agitated or turned on a regular basis

• Aerated Static Pile - A Blower is used to supply air to the composting materials and no turning or agitation of the materials occurs once the pile is formed

• In-Vessel Composting - Confined within a building, container or vessel. This method requires a variety of forced aeration and mechanical turning techniques to speed up the process

b. Landfarming

• Soil is excavated and mechanically separated via sieving. The polluted soil is then placed in layers no more than 0.4 meters thick.

• A synthetic, concrete, or clay membrane is then used to cover the contaminated soil layer.

• Oxygen is added and mixing occurs via plowing, harrowing, or milling. Nutrients and moisture may also be added to aid the remediation process.

• The pH of the soil is also regulated (keeping it near 7.0) using crushed limestone or agricultural lime.

• Most effective for PAH and PCP removal.

c. Biopiling

• This technology involves heaping contaminated soils into piles (or "cells") and stimulating aerobic microbial activity within the soils through the aeration and/or addition of minerals, nutrients, and moisture.

• Biopiles are similar to landfarms in that they are both above-ground, engineered systems that use oxygen, generally from air, to stimulate the growth and reproduction of aerobic bacteria which, in turn, degrade the petroleum constituents adsorbed to soil.

• Biopiles are aerated most often by forcing air to move by injection or extraction through slotted or perforated piping placed throughout the pile

• Most effective in treating pollutants such as BTEX, phenols, PAHs with up to 4 aromatic rings, and explosives such as TNT and RDX.

• Most successful in removing PAH and PCP

d. Bioreactor

• Treat contaminated soils in both solid and liquid (slurry) phases

• The solid phase treatment process - mechanically decomposes the soil by attrition and mixing in a closed container. The objective of the mixing is to guarantee that the pollutants, water, air, nutrients, and microorganisms are in permanent contact.

  • In fixed bed reactors, composts are added and significantly increases the degradation rate.

  • In rotating drum reactors, the drum has a screw like mechanism in the middle of it that rotates to mix and transport the soil.

• The liquid phase treatment process - uses suspension bioreactors and treats soils as slurry.

  • The slurry feed enters the system and is rinsed through a vibrating screen to remove debris. Sand is then removed using a sieve or hydrocyclone. If a hydrocyclone is used to remove the sand, the sand falls to the bottom of the cyclone and the fines remain on top. The fines are then treated in a bioreactor. After the treatment, the slurry must be dewatered and the water is then treated with standard wastewater techniques.

Additional Mediums used for Bioremediation

Biomimetics

• Biomimetics represents the studies and imitation of nature's methods, mechanisms, and processes (Bar-Cohen, 2006).

• It implies the understanding of biological structures and processes and their comparable technological applications, methods, or procedures (Pohl & Nachtigall, 2000).

• The concept of biomimetics stems from the realization that microbes, plants, and animals have been continuously evolving to cope with environmental and other challenges.

• An approach to innovation that seeks sustainable solutions to human challenges by emulating nature's time-tested patterns and strategies.

Examples of Biomimetics:

• The nose shape of the Shinkansen in Japan was inspired by the beak of a species of bird, the Kingfisher.

• The design of wind turbines, specifically the Tubercle Blade, is designed based on the flippers of the Humpback whale.

• The cooling principle of some structures, such as the Eastgate Centre, is inspired by the cooling of termite mounds.

Summary of Ex Situ Bioremediation Techniques

Summary of In Situ Bioremediation Techniques