Coagulation for Water and Wastewater Treatment Processes – coagulation is an essential part of potable drinking water treatment as well as wastewater treatment. In modern water treatment, coagulation and flocculation are the essential components of the treatment processes. Coagulation is essential in wastewater treatment operations to chemically reduce suspended solids before primary clarifiers.
What types of coagulants are there?
Metal coagulants fall into two categories: those based on aluminium and those based on iron. The aluminium coagulants include aluminium sulphate and aluminium chloride and iron coagulants ferric sulphate, ferrous sulphate, and ferric chloride. Along with these, other chemicals also used as coagulants include hydrated lime.
Inorganic coagulants include alum, polyaluminum chloride and polyaluminum chloride. They have the advantages of being able to function efficiently over wide ranges of pH and raw water temperatures. These inorganic coagulants are prepared with varying basicity ratios. Nearly all water treatment requirements are unique and need to be determined by jar testing.
Polymers are a large range of natural or synthetic, water-soluble compounds that can destabilize or enhance flocculation in a body of water.
Coagulation for Removal of Natural Organic Matter
Natural organic material is usually humid substances arising from the aqueous extraction of living woody substances. This includes the degradation of products in decaying wood and the solution of soil organic matter. They tend to colour water, act as a vehicle for transporting toxic substances and micro-pollutants such as heavy metals and organic pollutants.
Coagulation for Removal of Inorganics & Arsenic
Coagulation can be used for the removal of inorganics such as and mercury reductions from wastewater plant effluents. There are various ways of removing arsenic from wastewater, however, the removal of arsenic by coagulation can be more economical than other treatments.
Coagulation for Wastewater Treatment
Adding coagulant chemicals to primary clarifiers and physical separation processes is an effective way of reducing the load to downstream biological processes.
Flash / Rapid Mixing
The initial flash or rapid mixing stage is the most important component of coagulation processes in creating destabilisation reactions. The correct mixer for the tank volume and retention time is critical with a short window to primary mixing.
Coagulation Treatment Mixers
Coagulation Treatment Mixer systems are designed for several applications, including:
- Wastewater flocculation prior to Dissolved Air Flotation (DAF)
- Sludge flocculation prior to dewatering
- Polymer solution preparation
- Wastewater pH control
These Coagulation Treatment Mixers are designed to match specific application requirements and feature heavy-duty Mixers. For DAF systems that have more complicated chemistries, flash mix and coagulation tank systems are available. These are used for the introduction of coagulating and flocculating chemicals into a waste stream.
Continuous Flow 3 Stage Tanks
These tanks are split into 3 stages, one for each process distinctive processes – coagulation, flash mixing, flocculation, and clarification. These tanks are sized to give sufficient time and velocity are necessary to maximise the effectiveness of the flocculent.
Step 1. Adding the Flocculent
- During the coagulation process, chemical coagulants or flocculants are added in the 3-stage flash mixer. This is to destabilise the smaller individual particles and cause them to begin aggregating.
Step 2. Flash Mixing
- After the flocculent is introduced, the water is mixed vigorously by the flash mixer to disperse the chemcails throughout the water. This step plays a large role in the effectiveness of water treatment. Flash mixers are used for about 30-60 seconds to ensure chemicals are evenly distributed. Coagulation begins during the flash mixing process as the coagulants neutralise the electrical charge of the fine particles. This stops the repulsion of the individual particles and allows them to begin sticking together to form bigger ‘flocs through positive and negatively charged particles.
Step 3. Flocculation
- After the initial aggressive mixing, flocculation begins by slowing down the mixing. Here the smaller particles produced during the coagulation start adhering together. The flocculation stage usually goes continues for around 30-45 minutes in a flocculation tank that may have several compartments. Each compartment has a different mixing speed, and the speed decreases as the water flows from the top of the basin to its bottom. This approach allows the growing flocs to form without being shattered by the mixing blades.
After the flocculation process, most of the particles should have bonded together, which is called the Floc. Floc consists of larger masses of particulates bonded together in clusters of about 0.1 to 3 mm in size. It is critical that the floc is not too small as it will not settle. However, if it is too big it will likely break apart in the flocculation tank.
Step 4. Clarification
- Clarification is the last of the steps in the flocculation process. Clarifiers include polyethene cone tanks which hold the water long enough to allow the floc and other particulates to move to the bottom of the tank. The clarification process makes the water clear by removing all kinds of particles, sediments, oil, natural organic matter, and colour.
More details of these tanks are available here
Polymer Mixing Tanks
Polymer Mixing Tanks are manual preparation systems for powder polymers. These provide an economical and effective solution for effluent treatment in process and industrial applications. Part of an essential part water treatment are a complement to any chemical dosing system. Polymer mixers for these polymer mixing vessels are designed as a low-speed mixer for low sheer to minimise the risk of damaging the product.
The Enduramaxx Coagulation Mixer Tank Advantage
Enduramaxx has many years’ experience in coagulation tanks and the supply of flash mixers for these tanks. Tanks and vessels for clean water and treated wastewater for wastewater treatment plant are available pre-fitted to connect to process pipework. For more details on mixer tanks for coagulation and water and wastewater treatment processes, please contact us on 01778 562810 to discuss your needs.
