FlocTalk AB
Coagulation and Flocculation
Some of the chemistry behind flocculation and coagulation, and the most common processes used on farms and ranches.
On-site surface water management
On-site surface water management is important for operators as it protects natural water sources, and it can allow them to reuse both the water, and the nutrients contained in manure if done properly. Water treatment can then mitigate risks associated with water scarcity, and the costs associated with soil nutrient amendments.
Coagulation and flocculation are physical-chemical processes used in wastewater treatment to promote the settling and aggregation of suspended waste, allowing them to be filtered off easily. Following this treatment, the slurry can be separated into two components: the liquid, which contains dissolved nitrogen and low amounts of phosphorus, and the solid, rich in phosphorus, and low in moisture. Separation efficiency is dependent on the type and amount of chemical additive used, and the separation technique that is combined with the process.
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The most accessible option for operators is to mix a coagulant or flocculant into wastewater being held in a dugout, after which the clarified water can be pumped out using a screened intake. The solids can be collected from the bottom of the dugout, or left to accumulate there until the dugout becomes too shallow for reuse.
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More costly systems, used to process the slurry produced on larger confined feeding operations, involve vertical flow filtration technologies. These help process big volumes of wastewater, mixing in flocculants and separating the products in a efficient way, producing a liquid fraction that can be used for irrigation or further processed into clean water, and a solid fraction that can be used for composting, anaerobic digestion, or directly as fertilizer on fields.
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What Happens at the Molecular Level?
Livestock runoff wastewater contains all kinds of solids that are suspended in the slurry, such as sediment, organic matter and certain pathogens. Many of these particles carry a negative electric charge, which causes them to repel each other, preventing them from naturally clumping together and settling out of the water. The type of chemical additive used to induce aggregation of these particles can influence the size and density of the formed masses, affecting the amount of time required for their settling, and/or what type of filtration can be used to isolate them from the liquid fraction.
Coagulants are positively charged chemicals, typically metal salts like aluminum sulfate (alum) or ferric chloride that are added to wastewater to neutralize the negative charges on suspended particles. This neutralization reduces the repulsive forces between particles, allowing them to aggregate into larger clusters known as flocs, which accelerates the settling rate of the solids contained in wastewater. In chemical terms, this mechanism is referred to as neutralization, and it is the cheapest and most abundantly used to clear dugouts and ponds, although it requires the largest amount of additives.​​
For flocs that can be handled, dewatered and transported more easily, the chemical additives typically used are long molecular strands with multiple positive charges along their backbones: these bridge the negatively charged particles together into more cohesive solid masses that are usually filtered out of the cleared liquid through mechanical means.
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The most abundantly used chemical additives for these more efficient patching and bridging flocculation mechanisms are synthetic polymer molecules like cationic polyacrilamides (CPAM). These materials are derived from the oil and gas industry, and although they have been assessed as non-toxic to the environment, they are non-natural chemicals that persist in the soil and water for a long time, just like microplastics.
Natural polymers do exist as molecules called polysaccharides that are sourced from abundant biomass like crustacean shells, wood, plants and starchy vegetables. They require some chemical modifications to work effectively as flocculants, and have been shown to perform as effectively as metal salts and CPAMs, in some cases. Biomass-derived polymers are a sustainable and potentially cost-effective alternative to existing market flocculants - they are currently being explored by researchers and agricultural operators world-wide. Our team of chemists at UCalgary is working on developing these types of more eco-friendly and sustainable flocculants, with a goal to help keep Alberta’s natural resources, including soils and waterways, intact.
More Reading
Nutrient Recycling with Flocculation
