Biochar in water treatment

Biochar is a carbon-rich material produced from biomass through pyrolysis. It offers a promising and sustainable approach for wastewater treatment and environmental remediation of polluted water bodies. Its effectiveness stems from a combination of unique physicochemical properties.

The video below shows an example of a pilot project in Colorado, US, testing the use of biochar for improving water quality.

How can biochar be used for water treatment?

As an adsorbent material: Biochar can be directly added to contaminated water bodies or used in filtration systems. It can be applied in batch reactors or continuous flow systems. After saturation, the biochar can potentially be regenerated or used as a soil amendment, providing a circular economy approach.  

In constructed wetlands: Incorporating biochar into constructed wetlands can enhance the removal of various pollutants through adsorption and by supporting microbial processes.  

As a component in filtration systems: Biochar can be used in combination with other filter materials like sand and gravel to create multi-barrier water treatment systems.  

As a catalyst support: Engineered biochar supporting catalytic nanoparticles can be integrated into reactors for the degradation of specific pollutants.  

For sediment remediation: Biochar can be applied to polluted sediments to immobilize contaminants, reducing their bioavailability and release into the water column.

How does biochar remove pollutants from water?

Adsorption: Biochar's high surface area and porous structure provide numerous binding sites for pollutants. It can effectively adsorb a wide range of contaminants, including:  

• Organic pollutants: These include pesticides, pharmaceuticals, dyes, polycyclic aromatic hydrocarbons (PAHs), and other emerging organic contaminants. Adsorption occurs through mechanisms like hydrophobic interactions, π-π interactions, hydrogen bonding, and pore filling. Biochar produced at higher temperatures is generally more effective for non-polar organic compounds due to its increased surface area and micropore volume.

• Inorganic pollutants: Biochar can remove heavy metals (e.g., lead, cadmium, arsenic) and some nutrients (e.g., ammonium, phosphate). Removal mechanisms include electrostatic attraction, surface complexation with functional groups (especially oxygen-containing groups), and ion exchange. Biochar produced at lower temperatures often has more oxygen-containing functional groups, making it suitable for adsorbing inorganic contaminants.

• Nutrients: Biochar can adsorb nitrogen and phosphorus compounds, helping to mitigate eutrophication in water bodies. The effectiveness depends on the biochar's properties and the specific nutrient.  

• Pathogens: Biochar's adsorptive properties can also contribute to the removal of some bacteria and other microorganisms.  

Catalysis: Modified biochar can act as a catalyst or a support for catalysts in advanced oxidation processes (AOPs).These processes generate reactive oxygen species that can degrade organic pollutants. Biochar can enhance catalytic activity by:

• Dispersing and supporting active nanoparticles (e.g., metal oxides).  

• Facilitating electron transfer.  

• Activating oxidants like hydrogen peroxide, persulfate, and ozone.  

• Acting as a photocatalyst itself or supporting photocatalytic materials like titanium dioxide.  

Filtration: Biochar can be used as a filter medium to remove suspended solids and turbidity from water due to its porous structure.  

Support for microbial activity: Biochar can enhance biological wastewater treatment processes by:

• Providing a surface for microbial attachment and biofilm formation.  

• Increasing the buffering capacity of the system.

• Adsorbing inhibitory compounds, thus protecting the microorganisms.

• Providing a carbon source for denitrifying bacteria in some cases.

Why use biochar for water treatment?

Cost-effective: Biochar is often produced from waste biomass, making it a potentially low-cost alternative to conventional adsorbents like activated carbon.  

Environmentally friendly: It is derived from renewable resources and can contribute to waste management.  

Effective for a wide range of pollutants: Its versatile properties allow for the removal of diverse contaminants.  

Can be produced locally: The production process is relatively simple and can be implemented in decentralized systems.  

Potential for resource recovery: Spent biochar can sometimes be used as a soil amendment, closing the loop.