Bioclogging or biological clogging is clogging of pore space in soil by microbial biomass; their body and their byproducts such as

extracellular polymeric substance Extracellular polymeric substances (EPSs) are natural polymers of high molecular weight secreted by microorganisms into their environment. EPSs establish the functional and structural integrity of biofilms, and are considered the fundamental comp ...

(EPS). The microbial biomass blocks the pathway of water in the pore space, forming a certain thickness of impermeable layer in soil, and it reduces the rate of infiltration of water remarkably. Bioclogging is observed under continuous ponded infiltration at various field conditions such as artificial recharge ponds, percolation trench,

irrigation Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow crops, landscape plants, and lawns. Irrigation has been a key aspect of agriculture for over 5,000 years and has been dev ...

channel,

sewage treatment Sewage treatment (or domestic wastewater treatment, municipal wastewater treatment) is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable for discharge to the surrounding e ...

system and

landfill liner A landfill liner, or composite liner, is intended to be a low permeable barrier, which is laid down under engineered landfill sites. Until it deteriorates, the liner retards migration of leachate, and its toxic constituents, into underlying aqui ...

. It also affects groundwater flow in

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characteri ...

, such as permeable reactive barrier and microbial enhanced oil recovery. In the situation where infiltration of water at appropriate rate is needed, bioclogging can be problematic and countermeasures such as regular drying of the system are taken. In some cases bioclogging can be utilized to make impermeable layer to minimize the rate of infiltration.

General description

Change in permeability with time

Bioclogging is observed as the decrease of the infiltration rate. Decrease in the infiltration rate under ponded infiltration was observed in 1940s for studying the infiltration of artificial recharge pond and the water-spreading on agricultural soils. When soils are continuously submerged, permeability or saturated

hydraulic conductivity Hydraulic conductivity, symbolically represented as (unit: m/s), is a property of porous materials, soils and rocks, that describes the ease with which a fluid (usually water) can move through the pore space, or fractures network. It depends on ...

changes in 3 stages which was explained as follows. # Permeability decreases for 10 to 20 days possibly due to physical changes of the structure of the soil. # Permeability increases due to dissolving the entrapped air in soil into the percolating water. # Permeability decreases for 2 to 4 weeks due to disintegration of aggregates and biological clogging of soil pores with microbial cells and their synthesized products, slimes or polysaccharides. The 3 stages are not necessarily distinct in every field condition of bioclogging; when the second stage is not clear, permeability just continues to decrease.

Various types of clogging

The change in permeability with time is observed in various field situations. Depending on the field condition, there are various causes for the change in the

, summarized as follows. # Physical causes: Physical clogging by

suspended solids Suspended solids refers to small solid particles which remain in suspension in water as a colloid or due to motion of the water. Suspended solids can be removed by sedimentation if their size or density is comparatively large, or by filtration. It ...

or physical changes of soils such as disintegration of aggregate structure. Dissolving of the entrapped air in soil into the percolating water is physical cause for the increase of the hydraulic conductivity. # Chemical causes: Change in the electrolyte concentration or the

sodium adsorption ratio The Sodium adsorption ratio (SAR) is an irrigation water quality parameter used in the management of sodium-affected soils. It is an indicator of the suitability of water for use in agricultural irrigation, as determined from the concentrations of t ...

in the aqueous phase, which causes dispersion and swelling of clay particles. # Biological causes: Usually bioclogging means the first of the following, while bioclogging in broader sense means all of the following. ## Bioclogging by microbial cell bodies (such as

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

algae Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from ...

and

fungus A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...

) and their synthesized byproducts such as

(EPS) (also referred to as slime), which form

biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...

or microcolony aggregation on soil particles are direct biological causes of the decrease in hydraulic conductivity. ## Entrapment of gas bubbles such as

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ear ...

produced by methane producing microorganisms clog the soil pore and contributes in decreasing hydraulic conductivity. As gas is also microbial byproducts, it can also be considered to be bioclogging. ## Iron bacteria stimulates ferric oxyhydroxides deposition which may cause clogging of soil pores. This is an indirect biological cause of decrease in hydraulic conductivity.

Field observation

Under ponded infiltration

Field problem and countermeasure

Bioclogging is observed under continuous ponded infiltration in such places as artificial recharge ponds and percolation trench. Reduction of infiltration rate due to bioclogging at the infiltrating surface reduces the efficiency of such systems. To minimize the bioclogging effects, pretreatment of the water to reduce

, nutrients, and organic carbon might be necessary. Regular drying of the system and physical removal of the clogging layer can also be effective countermeasures. Even operated cautiously in this way, bioclogging is still likely to occur because of microbiological growth at the infiltrating surface.

Septic drain field Septic drain fields, also called leach fields or leach drains, are subsurface wastewater disposal facilities used to remove contaminants and impurities from the liquid that emerges after anaerobic digestion in a septic tank. Organic materials in ...

s are also susceptible to bioclogging because nutrient rich

wastewater Wastewater is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of domestic, industri ...

flows continuously. The bioclogging material in the

septic tank A septic tank is an underground chamber made of concrete, fiberglass, or plastic through which domestic wastewater ( sewage) flows for basic sewage treatment. Settling and anaerobic digestion processes reduce solids and organics, but the trea ...

is sometimes called biomat. Pretreatment of water by

filtration Filtration is a physical separation process that separates solid matter and fluid from a mixture using a ''filter medium'' that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filte ...

or reducing the load of the system could delay the failure of the system by bioclogging.

Slow sand filter Slow sand filters are used in water purification for treating raw water to produce a potable product. They are typically deep, can be rectangular or cylindrical in cross section and are used primarily to treat surface water. The length and brea ...

system also suffers from bioclogging. Besides the countermeasures mentioned above, cleaning or backwashing sand may be operated to remove biofilm and recover the permeability of sand. Bioclogging in

river A river is a natural flowing watercourse, usually freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the ...

s can impact aquifer recharge especially in dry regions where losing rivers are common.

Benefit

Bioclogging can have a positive effect in certain cases. For example, in the dairy waste stabilization ponds used for the treatment of dairy farm wastewater, bioclogging effectively seals up the bottom of the pond. Algae and bacteria may be inoculated to promote bioclogging in

channel for seepage control. Bioclogging is also beneficial in

such as compacted clay liners. Clay liners are usually applied in landfill to minimize the pollution by landfill leachate to the surrounding soil environment. Hydraulic conductivity of clay liners become lower than the original value because of bioclogging caused by microorganism in the leachate and pore spaces in clay. Bioclogging is now being studied to be applied for

geotechnical engineering Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics for the solution of its respective engineering problems. It a ...

In aquifer

Water withdrawal from well

Bioclogging can be observed when water is withdrawn from

(below groundwater table) through a

water well A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. T ...

. Over months and years of continued operation of water wells, they may show a gradual reduction in performance due to bioclogging or other clogging mechanisms.

Bioremediation

Biofilm formation is useful in

bioremediation Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi, and plants), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluent ...

of biologically degradable

groundwater pollution Groundwater pollution (also called groundwater contamination) occurs when pollutants are released to the ground and make their way into groundwater. This type of water pollution can also occur naturally due to the presence of a minor and unwan ...

. Permeable reactive barrier is formed to contain the groundwater flow by bioclogging and also to degrade pollution by microbes. Contaminant flow should be carefully analyzed because preferential flow path in the barrier may reduce the efficiency of the remediation.

Oil recovery

extraction of petroleum Petroleum is a fossil fuel that can be drawn from beneath the earth's surface. Reservoirs of petroleum was formed through the mixture of plants, algae, and sediments in shallow seas under high pressure. Petroleum is mostly recovered from oil dr ...

, a technique of

enhanced oil recovery Enhanced oil recovery (abbreviated EOR), also called tertiary recovery, is the extraction of crude oil from an oil field that cannot be extracted otherwise. EOR can extract 30% to 60% or more of a reservoir's oil, compared to 20% to 40% using ...

is implemented to increase the amount of oil to be extracted from an oil field. The injected water displaces the oil in the reservoir which is transported to recovery wells. As the reservoir is not uniform in permeability, injected water tends to go through high permeable zone, and does not go through the zone where oil remains. In this situation, bacterial profile modification technique, which injects bacteria into the high permeable zone to promote bioclogging can be employed. It is a type of microbial enhanced oil recovery.

References

{{reflist, 2 Soil Environmental soil science Soil physics Microbiology