Inorganic and organic coagulants: Making an informed decision

Pre-treatment processes in water treatment systems can be crucial to maintain efficiency and the longevity of equipment, such as membrane filters. Many systems incorporate a coagulation step that will encourage small suspended solids to clump together, thereby making them easier to remove. Coagulants can be used to remove a wide variety of hazardous materials from water, ranging from organic matter and pathogens, to inorganics and toxic materials, like arsenic, chemical phosphorus and fluoride. By eliminating the larger particles in the solution, filtration membranes won’t foul, tear or clog as quickly.

There are two types of chemical coagulants for water treatment: organic and inorganic. Each type has its own advantages that can influence sludge production, pH levels and operational costs, so it is important to be well informed about what each chemical has to offer before making a decision. 

Inorganic Coagulants

These are often considered to be more cost-effective than their organic counterparts, and they can be applied to a wide variety of water treatment operations including food and drink manufacturing and oil purification. As the coagulant is largely aluminium or iron based, it is particularly effective at treating raw water with low turbidity.  

Once added to water, inorganic coagulants form aluminium or iron precipitates, which will absorb impurities and serve to clean the water. The aluminium sulphate in the coagulant is the most commonly used chemical to treat wastewater globally and remains one of the most cost-effective coagulants because the price per unit is cheaper when compared to organic coagulants.

Often, inorganic coagulants are chosen simply because this has been the traditional wastewater treatment method for many years. There are many different scenarios such as water quality and budget that can favour the selection of inorganic coagulants. However, it is always good to look at organic alternatives as a wastewater solution. 

Organic Coagulants

These are typically used for solid-liquid separation when a reduction in sludge generation is required. Organic coagulants can be based on two types of chemistries: 

  • Polyamines and polyDADMAC, are considered to be the most widely used organic coagulants due to their cationic nature, which largely function by charge neutralisation. Cationic coagulants neutralise the negative charge of colloids and create a spongy mass called microflocs.  
  • Melamine formaldehydes and tannins are used to coagulate colloidal material in water. This coagulant is especially well-suited to treating hazardous sludge, as it absorbs organic materials like oil and grease very effectively.

Organic coagulants are also cost effective as they can be applied at a far lower dosage while still remaining effective across a wide range of applications. This solution also naturally produces far lower quantities of sludge to dispose of, again reducing costs. 

Furthermore, unlike inorganic coagulants, organic coagulants do not consume any alkalinity from the liquid they are added to, this helps to minimise any pH or conductivity changes. Also, due to the composition of the coagulant, there is also no increase in salt within the liquid, and as such, any concerns about pollution are greatly reduced. 

Combined, the properties of organic coagulants help to eliminate many of the challenges of wastewater treatment and allow organisations to operate a safer, more sustainable processes.

At VWT UK, we offer our Hydrex 6861, an organic vegetable-based coagulant made from a renewable source. The coagulant works at a much lower pH (4.5 to 7) than metal-based coagulants. This means sodium hydroxide or other caustic chemicals are not required to correct the pH level before treatment. In addition, the amount of sludge produced can be minimised by up to 50% therefore reducing transportation costs. Furthermore, by decreasing sludge formation, facilities with systems that use dissolved air flotation (DAF) to remove the sludge, will find the process becomes far more efficient due to a reduced load.

Coagulants play an increasingly important role in the effluent water treatment process. A combination of rising running costs and stringent administrative concerns means that there is now a pressing need to optimise operational performance. 

Getting the right water treatment chemical program can be complex and requires the help of an expert. At VWT UK, when it comes to recommending coagulants to our customers, it’s important for us to go to site and evaluate the situation as each plant is different. We take samples of the water in order to make a recommendation that is right for the individual site’s needs


For more information about Hydrex 6861, please contact one of our experts. 


Brian Jones

About the Author

Brian Jones

Brian has over 30 years experience in the chemical and water purification industry. The first 18 years were spent working for Hays Chemical Distribution in senior roles, working in quality, safety and process management. His problem solving approach and chemical background made going into wastewater treatment a good fit. He has spent the last 14 years working in sales in this industry having bought a wealth of knowledge to the role, proving to be a valuable asset.