Fact sheet: Bioreactor

From: Public Services and Procurement Canada

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Description

The principle of the bioreactor is, under controlled conditions, to increase the contact surface between the contaminants present in the target matrix and the microorganisms responsible for their biodegradation present in the system.

Two biological reactor processes are primarily used for the treatment of contaminated water, the suspended or fixed film systems. In both cases, the water extracted from the site is brought into contact with microorganisms adapted for the biodegradation of the targeted contaminants, circulating in an aeration pond or on a biofilm. Microorganisms may be native to the site or from an inoculum.

Water is the main matrix to be treated, but slurry phase bioreactors can also be used for the treatment of contaminated soil, sediment, sludge or other solids. In these cases, the contaminated soils or other solids are first excavated and sieved to retain only the fine fractions. These are mixed with water and other substrates to keep them in suspension during the treatment and in contact with microorganisms to promote biodegradation.

Other types of reactors are also under development, depending on the type of contaminant to be treated.

Sources:

Implementation of the technology

In a suspended film system, the contaminated water or that containing the fine fraction, circulates in a pond or aeration tank containing suspended microorganisms. The microorganisms are kept in suspension by means of pneumatic aeration or mechanical agitation. Biodegradation of contaminants usually occurs during aerobic processes, although anaerobic processes are also possible. The biomass resulting from the process can be clarified and returned to the system or accumulated as sludge for disposal.

These systems can take different configurations:

The activated sludge reactor includes a sludge of organic material and a population of microorganisms that can treat contaminated water under aerobic conditions.

The fluidized bed reactor uses granular or solid materials (sand, activated carbon or pearls) on which microorganisms are present which are suspended in the water to be treated in order to ensure contact between the latter and the contaminants. Effluents from this system are continuously recycled into the system.

In a sequential biological reactor, treatment is based on time rather than flow in terms of contact between microorganisms and contaminants. In this system, all contaminated water is included from the beginning (batch), treated for the removal of contaminants and rejected. Microorganisms are included in the system during the process. The sludge created is then aerated until the reaction is completed.

Membrane bioreactors make it possible to combine the clarification, aeration and filtration steps within the same process. This technology is considered very powerful, leaving a minimal footprint and having a simplified operation.

Fixed film bioreactors are available in several configurations such as rotary filter bioreactors, where microorganisms are attached to a circular disk that rotates in the contaminated affluent to initiate treatment. Bacterial bed reactors include a permeable matrix (rock, plastic or wood), a water distribution system and a drainage system. Contaminated water flows at a constant rate to promote contact with the matrix and promote the development of a biofilm. Fixed film bioreactors are characterized by large areas that promote microbial colonization. This support is generally adsorbent, which retains the contaminants while releasing them slowly so that the microorganisms can degrade them.

The size of the bioreactors can vary by several orders of magnitude depending on the volume of water or solids to be treated. In all cases, the environmental conditions within the bioreactor must be controlled to optimize the biochemical activity levels of the microorganisms.

The implementation of a bioreactor may include:

  • Mobilization, access to the site and setting up temporary facilities.
  • Establishment of a system for pumping contaminated groundwater, including wells, collection trenches and/or permeable drainage as well as pumping equipment.
  • Excavation of contaminated soils or sediments and the installation of equipment necessary to separate coarse and fine fractions.
  • Establishment of the necessary equipment for the mixing of fine particles with water.
  • The installation of bioreactor equipment (may require the construction of a building or container).
  • The establishment of tanks for the recovery of sludge resulting from treatment or treated soils.
  • Vapour treatment equipment resulting from the treatment process as required.
  • Discharge equipment for treated water (for reinjection into the ground using wells or trenches for the connection to a sewer system or into surface water).

This type of system should generally be piloted tested prior to full-scale implementation.

Materials and Storage

  • The development of wells, collection trenches and/or permeable drains is performed using traditional/readily available methods and equipment readily available for installation of wells, drainage systems, water supply or public utility.
  • The bioreactor can be built on-site or pre-assembled and delivered to the site inside a container, trailer or truck.
  • The operation of the bioreactor requires energy and products such as substrates, water, nutrients, inoculum, etc.
  • Installation activities for this type of system generally have little impact but may require on-site storage, notably for residues produced (treated soil, biomass, sludge, etc.).

Residues and Rejects

In general, bioreactors destroy contaminants. Some residues such as sludge may be produced during this treatment.

Installing systems for pumping water or excavating contaminated soil to be treated can lead to the handling of contaminated soils that may need to be disposed of off-site.

Soils resulting from the treatment and sludge from the reactor must be recovered, returned to the site or disposed of off-site. The nature of these rejects will have to be determined in order to make an adequate disposition.

Treated groundwater must meet the applicable criteria for its discharge. However, releases may contain by-products or an unacceptable pH that may be hazardous to the receptors and require a polishing step.

Potential vapours from the treatment may also constitute an effluent from the bioreactor.

Recommended analyses for detailed characterization

Biological analysis

  • Total heterotrophic and specific bacterial counts (according to the contaminants of interest)
  • Biological Oxygen Demand

Chemical analysis

  • pH
  • Alkalinity
  • Organic carbon content
  • Organic matter content
  • Chemical oxygen demand
  • Metals concentrations
  • Contaminant concentrations present in the following phases:
    • adsorbed
    • dissolved
  • Nutrient concentrations including:
    • ammonia nitrogen
    • total Kjeldahl nitrogen
    • nitrates
    • nitrites
    • total phosphorus
  • Electron acceptor concentrations/reaction by-products including:
    • dissolved oxygen
    • nitrate
    • sulfate
    • ferric and ferrous iron
    • methane
    • dissolved manganese
  • Total suspended solids

Physical analysis

  • Temperature
  • Soil water content
  • Soil granulometry

Recommended trials for detailed characterization

Biological trials

  • Microcosm mineralization and transformation
  • Biological evaluation and ecological factors

Physical trials

  • Evaluation of optimal mixing rates

Other information recommended for detailed characterization

Phase II

  • Regional climatic conditions (precipitation, temperature, etc.)

Phase III

  • Volume of contaminated material to treat
  • Circulating water flow to be treated

Notes:

On-site pilot scale treatment is recommended to determine the operating parameters of the bioreactor as well as its effectiveness (retention time, dissolved oxygen, etc.).

Applications

  • Ex situ groundwater and soil treatment.
  • Municipal and industrial wastewater treatment.
  • Addition of co-metabolites may be useful for the treatment of recalcitrant organic contaminants.

Applications to sites in northern regions

The use of a bioreactor in a northern region may be limited since one of the main limitations for groundwater treatment is its temperature. Low temperature limits degradation and biomass creation. Heating the water would not be economically viable.

Treatment type

Treatment typeApplies or Does not apply
In situ
Does not apply
Ex situ
Applies
Biological
Applies
Chemical
Does not exist
Control
Does not exist
Dissolved contamination
Applies
Free Phase
Does not exist
Physical
Does not exist
Residual contamination
Applies
Resorption
Applies
Thermal
Does not exist

State of technology

State of technologyExist or Does not exist
Testing
Does not exist
Commercialization
Exist

Target contaminants

Target contaminantsApplies, Does not apply or With restrictions
Aliphatic chlorinated hydrocarbons
With restrictions
Chlorobenzenes
Applies
Explosives
With restrictions
Metals
With restrictions
Monocyclic aromatic hydrocarbons
Applies
Non metalic inorganic compounds
Does not apply
Pesticides
With restrictions
Petroleum hydrocarbons
Applies
Phenolic compounds
Applies
Policyclic aromatic hydrocarbons
Applies
Polychlorinated biphenyls
With restrictions

Treatment time

Treatment timeApplies or Does not apply
Less than 1 year
Applies
1 to 3 years
Applies
3 to 5 years
Applies
More than 5 years
Does not apply

Long-term considerations (following remediation work)

None.

Secondary by-products and/or metabolites

Partial decomposition of chlorinated compounds, explosives and pesticides can generate toxic secondary compounds.

Limitations and Undesirable Effects of the Technology

  • High concentrations of contaminants can be toxic to microorganisms.
  • The rate of treatment is directly dependent on the rate of degradation of the bacteria.
  • The addition of nutrients may be required if the water to be treated does not have sufficient nutrients to support the growth of the microbial population.
  • Control of air emissions may be necessary if volatile compounds are present or if volatilization is caused by the degradation process.
  • Low temperatures may decrease the biodegradation efficiency and increase the operating costs of the system.
  • Undesirable microorganisms may colonize bioreactors and inhibit the growth of those involved in contaminant biodegradation.
  • For soil treatment, the presence of infrastructure on or near the site may limit excavation opportunities.
  • For soil treatment, dust control during soil handling may be required.
  • If the process generates sludge, the management of sludge including dewatering and disposal can be an expensive.

Complementary technologies that improve treatment effectiveness

  • Heavily charged water or very high soil concentrations may require pretreatment steps (e.g. physical separation of free phases and total suspended solids).
  • Removal of metals from the water may be required before treatment.
  • Discharge of treated effluent (containing bacteria and high levels of dissolved oxygen) into groundwater can be used to promote in situ biodegradation.
  • The treatment of excavated soil requires the removal of stones and rubble. The sand and gravel fractions can be separated and mechanically washed before the treatment of the finest fraction of the bioreactor soils.
  • The use of activated sludge (e.g. from the municipal water treatment pond) as an inoculum to improve the performance of bioreactors.

Required secondary treatments

  • Prior to discharge of water from the bioreactor, subsequent treatment may be required.
  • If the process generates sludge, management of sludge including treatment, dewatering and disposal may be required.

Application examples

Bioreactors have been widely used for a variety of compounds including petroleum hydrocarbons, gasoline additives such as methyl tert-butyl ether (MTBE) and tertiary butyl alcohol (TBA), semi-volatile compounds and some halogenated compounds.

The following site provides an application example for the technology:

Performance

  • To be assessed on a case to case basis.
  • This technology destroys contaminants and only small volumes of wastes are generated.
  • If good operating conditions are present, the processing performance can be high.
  • Microbial biomass within the bioreactor is relatively resistant, adapts well to changes in contaminant concentrations and to certain temperature variations.

Measures to improve sustainability or promote ecological remediation

  • Optimization of equipment selection based on-site conditions to reduce equipment size and energy consumption.
  • Optimization of the time of year when the bioreactor is in operation.
  • Optimization of the calendar to promote the sharing of resources and reduce the number of days of mobilization.
  • Use of renewable energy and low-energy equipment.
  • Use of telemetry for remote monitoring of site conditions and limit the number of visits.

Potential impacts of the application of the technology on human health

Main Exposure Mechanisms

Applies or Does Not Apply

Monitoring and Mitigation

Dust

Applies only for soil treatment

Monitoring conditions favourable to dispersion during the excavation of the soil to be treated.

Atmospheric/Steam Emissions—Point Sources or Chimneys

Applies

Emissions monitoring (choice of parameters, types of samples and type of intervention [source, risk or local requirements]).

Atmospheric/Steam Emissions—Non-point Sources

Does not apply

N/A

Air/steam—by products

Applies

Emissions monitoring (choice of parameters, types of samples and type of intervention [source, risk or local requirements]).

Runoff

Does not apply

N/A

Groundwater—displacement

Applies

Modelling the effects of required pumping and monitoring using pressure sensors.

Groundwater—chemical/geochemical mobilization

Applies

Pilot testing, monitoring of groundwater quality.

Groundwater—by-product

Applies

Monitoring the water quality

Accident/Failure—damage to public services

Applies

File checks and licensing prior to excavation, development of excavation and emergency procedures.

Accident/Failure—leak or spill

Applies

Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions.

Accident/Failure—fire/explosion

Applies

Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions.

Other—Direct contact with the bioreactor matrix that may contain pathogenic bacteria (if inoculum comes from a treatment plant)

Applies

Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions.

Other—Handling contaminated soils or other Solids

Applies

Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions.

References

Author and update

Composed by : Claudie Bonnet, M. Sc. , National Research Council

Updated by : Jennifer Holdner, M.Sc., Public Works Government Services Canada

Updated Date : April 12, 2016

Latest update provided by : Nathalie Arel, P.Eng., M.Sc., Christian Gosselin, P.Eng., M.Eng. and Sylvain Hains, P.Eng., M.Sc., Golder Associés Ltée

Updated Date : March 22, 2019

Date Modified: