Flocculants and their types:

Flocculants are chemical compounds or agents employed in the flocculation technique of water treatment. Their function is to induce the formation of clumps or flocs, which aids in the separation of suspended harmful materials for purification¹². These flocculants come in both organic and inorganic types, each exhibiting a range of characteristics such as charge, molecular weight, charge densities, and morphology. By utilizing flocculants with specific properties, water treatment processes can be tailored to effectively target and remove contaminants, thereby improving the quality of water for various purposes (Figure 2). The efficiency of some of the flocculants is mentioned in (Table 1)¹³.

Fig.2. Removal of suspended material

Organic flocculants:

Organic flocculants encompass a variety of chemical compounds, including polyacrylamides, polydiallyldimethylammonium chloride (polyDADMACs), and polytannates. These agents have demonstrated effectiveness in removing particles and solids from water. Polyacrylamides, for instance, are widely used for their ability to form large flocs, facilitating the removal of suspended materials through sedimentation or filtration processes. PolyDADMACs, on the other hand, are cationic polymers that can adsorb onto negatively charged particles, aiding in their aggregation and subsequent removal. Additionally, polytannates have shown efficacy in the removal of oils and organic contaminants from water. Together, these organic flocculants play a crucial role in water treatment by promoting the formation of larger, easily removable flocs, thereby improving water quality and facilitating the purification process¹⁴.

Advantages of organic flocculants:

The merits are as follows^15,16:

· Produces small floc volume

· The flocculants are rarely affected by the pH of the material

· The organic flocculants are present in liquid form and are non-corrosive therefore, it is easy to use

· The organic flocculants relatively enable the low density to neutralize lower charged suspended particles.

· The primary flocculants have high molecular weight polymers with hydrogen bonding that promotes the separation of particles to clean water.

· They are capable of removing the portion of organic precursors which may combine with the chemicals

Disadvantages of organic flocculants:

The merits are as follows¹⁷:

· It is not easily affordable

· It needs high charge dosage to treat the highly charged particles

· The flocs with lower density do not usually seem to be settled

Inorganic flocculants:

Inorganic flocculants utilize compounds such as aluminium sulfate, silicon, and ferric chloride to treat water through the use of inorganic polymers. They have emerged as effective water treatment reagents, offering a cost-effective alternative to organic flocculants. These polymers are typically prepared via hydrolysis and precipitation processes. The mechanism of actions of inorganic flocculants involves several key steps: first, neutralization of charges occurs, followed by the formation of hydroxide precipitates. Subsequently, adsorption and bridging facilitate the aggregation of suspended materials, leading to floc formation. Finally, the resulting large flocs can be easily settled or filtered out. Inorganic flocculants are renowned for their versatility, as they are effective across a wide range of water treatment applications. Their rapid charge neutralization and ability to promote the formation of large, settleable flocs make them indispensable in the quest for cleaner water¹⁸.

Advantages of inorganic flocculants:

The merits are as follows^{19, 20}:

· Can be used over a broad pH range

· Highly effective in a wide range of water treatment applications

· Inorganic flocculants are usually cost-effective

· These flocculants are easily available

Disadvantages of inorganic flocculants:

The demerits are as follows²¹:

· Some of the aluminum-based flocculants can contribute to increased concentration of aluminium in water during treatment

· The effectiveness of the flocculants can be influenced by factors like temperature, pH, and the nature of suspended particles

Polymeric flocculants:

Through a process known as flocculation, high molecular weight water-soluble polymers known as polymeric flocculants can efficiently remove suspended particles from water and wastewater. Compared to basic coagulants, they can generate large, cohesive flocs that settle and separate from the liquid more quickly. They are easy to use and don't drastically change the medium's pH. To maximize performance, the molecular weight, charge, and structure of synthetic polymeric flocculants can be adjusted. Biodegradable natural polymer-based flocculants, such as starch and chitosan, may need higher dosages and have less shear stability. Based on polyacrylamide and its derivatives, which can have either cationic or anionic charges, synthetic polymeric flocculants are most frequently used²².

Types of polymeric flocculants:

The types are as follows:

Synthetic polymeric flocculant:

Through a process known as flocculation, synthetic polymeric flocculants—high molecular weight water-soluble polymers—can efficiently remove suspended particles from water and wastewater. Because they may generate big, cohesive flocs that settle and separate from the liquid more quickly than basic coagulants, they are frequently utilized in water treatment applications. A variety of molecular weights and charge densities are obtainable for synthetic polymeric flocculants. Their nature might be nonionic, cationic, or anionic. Anionic polymers are usually employed as flocculants, whereas cationic polymers are frequently used as coagulants or flocculants. The correct preparation of the flocculant solution is crucial to ensure the optimum solution is prepared every time and that expensive polymers are used to their maximum efficiency²³.

Advantages of synthetic polymeric flocculants:

The merits are as follows:

· High Efficiency: Synthetic polymers are a cost-effective option for water treatment procedures because of their great effectiveness at low dosages.

· Tailorability: By adjusting chemical structure, molecular weight, and molecular weight distribution, synthetic polymers can be made to work as best they can.

· High Molecular Weight: Higher molecular weight polymers produce less sludge and have improved water clarity due to their increased ability to flocculate and sedimentate.

· Non-Toxicity: Synthetic polymers can be used in water treatment procedures since they are non-toxic and do not change the pH of the medium.

· Convenience: Synthetic polymers are easily handled and utilized since they are available in a variety of forms, such as dry powders, liquid dispersions, and emulsions.

Disadvantages of synthetic polymeric flocculants

The demerits are as follows²⁴:

· Poor Shear Stability: The lack of shear resistance in synthetic polymers can have an impact on how well they function in high-shear situations.

· Environmental Challenges: Because synthetic polymers are not biodegradable, handling and disposal of them may need to be done with great care.

· Higher Cost: The cost of synthetic polymers is typically higher than that of natural polymers, which raises the total cost of water treatment procedures.

· Restricted Availability: The usage of synthetic polymers may be restricted in some areas due to their limited availability in some places or the need for specialized suppliers.

Natural polymeric flocculants:

Natural polymeric flocculants are shear stable, biodegradable, and effective at high dosages. They are utilised to support solid-liquid separation processes in water treatment and are obtained from plants and marine life. Organic polymers decompose organically, mitigating their negative environmental effects. They are economical since they are frequently sourced from renewable resources. The resistance of natural polymers to shear forces can have an impact on their performance²⁵.

Some natural polymers that are employed as flocculants are as follows:

· Lignin: A naturally occurring polymer that comes from wood, lignin is very effective in situations requiring intense cleaning.

· Tannins: Tannins, which are present in plants and are used to make wine, are also important for the filtration of water.

· Polysaccharides: These sugar chains are a common option for water treatment because of their exceptional ability to clump particles together.

Advantages of natural polymeric flocculants:

The merits are as follows²⁶:

· Biodegradability: Natural polymers break down naturally, reducing environmental impact and making them a more sustainable choice compared to synthetic polymers.

· Affordability: Derived from renewable sources, natural polymers are often cost-effective and can be sourced at a lower cost than synthetic polymers.

· Non-toxicity: Natural polymers are non-toxic, which is particularly important in applications where water is used for human consumption or other sensitive processes.

· Shear Stability: Natural polymers tend to be more shear stable, which means they can withstand the mechanical forces involved in water treatment processes without breaking down.

· Customizability: Natural polymers can be modified to enhance their flocculation efficacy, making them more effective in specific applications

Disadvantages of natural polymeric flocculants:

The demerits are as follows:

· Dosage Requirements: Compared to synthetic polymers, natural polymers usually require higher doses, which can raise costs and reduce process efficiency.

· Shelf Life: Natural polymers' biodegradability might shorten their shelf life, necessitating careful handling and storage.

· Restricted Availability: Several natural polymers might be more difficult to find or manufacture in big amounts, which could prevent them from being widely used.

· Performance Variability: Compared to synthetic polymers, natural polymers may be less dependable due to their varying performance, which can be attributed to various factors like processing, ambient conditions, and polymer sources.

Chemical Coagulants and Flocculants:

Chemical coagulants and flocculants are crucial components in water treatment processes. They are used to purge water of impurities and suspended particles, improving efficiency and water quality. The particular use, water quality, and environmental factors all influence the choice of coagulant or flocculant²⁷.

Chemical Coagulants:

Coagulants are substances that neutralize an object's negative electrical charge, causing the particles to group and separate from the water.

Typical coagulants that are employed are:

· Metal Coagulants: The most often used metal coagulants are ferric chloride, aluminium sulphate, and ferric sulphate. They work well to rid water of organic materials and suspended particles.

· Coagulants of organic matter: Natural sources like fungi and plants are the source of organic coagulants. Compared to inorganic coagulants, they are thought to be safer and generate less sludge.

· Synthetic Coagulants: Synthetic coagulants have high charge densities and are composed of polymers. Depending on their makeup, they may act as flocculants.

Chemical Flocculants:

Flocculants are chemicals that promote the growth of small particles into larger particles, making them easier to separate from the water.

Commonly used flocculants include:

· Polymeric Flocculants: These are high molecular weight polymers that enhance van der Waal's forces and hydrogen bonding between particles, causing them to clump together.

· Biopolymer Flocculants: Biopolymer flocculants are derived from natural sources and are considered safer and more environmentally friendly compared to synthetic polymers.

Advantages of chemical coagulants:

The merits are as follows:

· Effectiveness: Chemical coagulants are very good at causing charged particles to become less stable and larger flocs to form that are easier to separate from the water.

· Customizability: The molecular weight, charge, and structure of synthetic polymeric coagulants can be adjusted to maximize their effectiveness in particular applications.

· Convenience: Chemical coagulants are simple to use and handle since they come in a variety of forms, such as dry powders, liquid dispersions, and emulsions.

· Non-Toxicity: A lot of chemical coagulants don't substantially change the pH of the treated water and are safe to use, such as derivatives of polyacrylamide.

Disadvantages of chemical coagulants

The demerits are as follows:

· Sludge Generation: When chemical coagulants are used, a lot of sludge may be produced. This sludge needs to be handled and disposed of properly, which can be expensive and bad for the environment.

· Sludge Toxicity: Because of the additional chemicals, the sludge produced by chemical coagulation may be toxic and need special handling and disposal techniques.

· Environmental Concerns: Because synthetic polymeric coagulants are not biodegradable, handling and disposal of them may require extra care to avoid negative effects on the environment.

· Shear Sensitivity: The efficacy of synthetic polymeric coagulants in high-shear conditions may be impacted by the fact that they are often not shear-resistant.

· Cost: Using chemical coagulants can be more costly than using natural coagulants, particularly when you take into account the extra expenses related to processing and disposing of sludge.

Natural bio-flocculants:

Natural bio-flocculants offer several advantages, including biodegradability, non-toxicity, shear stability, customizability, availability, cost-effectiveness, and health and environmental benefits. However, they also have some limitations, such as complex extraction processes, limited availability, higher dosage requirements, and performance variability. The choice between natural bio-flocculants and synthetic polymers ultimately depends on the specific application and the trade-offs between performance, cost, and environmental impact.

Advantages of natural bio-flocculants:

The merits are as follows:

· Biodegradability: Because natural bio-flocculants decompose naturally, there is less need for special handling and disposal, which helps to protect the environment.

· Non-Toxicity: The pH of the treated water is not considerably impacted by natural bio-flocculants, which are non-toxic.

· Shear Stability: Shear stability refers to the ability of natural bio-flocculants to endure the mechanical pressures inherent in water treatment procedures without degrading.

· Customizability: By modifying their flocculation efficacy, natural bio-flocculants can be made more effective in particular applications.

· Availability: Local resources can provide natural bio-flocculants, negating the requirement for storage and shipping.

· Cost-Effectiveness: Natural bio-flocculants are frequently environmentally friendly, low-cost commodities that are used in industrial settings.

· Health and Environmental Benefits: Compared to synthetic polymers, natural bio-flocculants have less of an adverse effect on the environment and human health.

Disadvantages of natural bio-flocculants:

The demerits are as follows:

· Complex Extraction Process: The availability of these ready-to-use compounds is restricted due to the complexity and lack of development of extraction methods for natural bio-flocculants.

· Limited Availability: The more intricate and poorly maintained nature of natural bio-flocculants manufacture may prevent their widespread use.

· Higher Dosage Requirements: Compared to synthetic polymers, natural bio-flocculants usually require higher doses, which can raise costs and reduce process efficiency.

· Performance Variability: Compared to synthetic polymers, natural bio-flocculants may be less dependable due to their variable performance, which can be influenced by various factors including source, processing, and environmental conditions.

Primary process variables used to measure flocculation efficiency:

Numerous factors affect the flocculation process' effectiveness, such as the kind and quantity of coagulant used, the length and intensity of the mixing process, and the properties of the particles being treated. To assess flocculation performance and optimize these parameters, jar testing is frequently employed.

The primary process variables commonly measured to justify flocculation efficiency include:

Settling rate of the flocs

One important measure of flocculation efficiency is the settling of flocs. Some key points regarding floc settling during the flocculation process²⁸:

· As floc size grows as a result of aggregation, floc settling velocity increases. Denser, larger flocs settle more quickly.

· One important factor influencing the settling velocity of ballasted flocs is floc density. Based on density, an empirical model has been created to forecast floc settling velocity.

· Higher flocculant dosages cause flocs to settle more quickly, which raises thickening underflow concentrations. Stronger particle interactions, however, cause floc density to drop and may result in lower underflow concentrations.

· During electrocoagulation, complex and fragile flocs assemble with coagulants, pollution particles, and fine bubbles (10-50 μm). These flocs' pace of settling is a crucial parameter to measure.

· Sediment finer than 20–50 μm flocculates in rivers and wetlands with settling velocities of 0.1–1 mm/s, median floc widths of 30-90 μm, and bulk solid ratios of 0.05–0.3. These results are in line with semi-empirical models, which suggest that floc settling velocity variation is limited by turbulence.

Sediment volume:

The sludge volume index (SVI) is a measure of the settling characteristics of activated sludge in wastewater treatment. It is defined as the volume in milliliters occupied by one gram of a suspension after 30 minutes of settling. A lower SVI indicates better settling and compaction of the sludge. Typical values for municipal sewage are in the range of 80-150mL/g.

A few important things to know about SVI are that it's utilized to determine whether poor settling in secondary clarification processes stems from the growth of troublesome filamentous organisms. Before analyzing the SVI, the sludge must be diluted with clarified secondary effluent if it is very thick. We refer to this as diluted SVI (DSVI). Factors such as influent wastewater parameters, operations, and plant design have an impact on SVI. Activated sludge that has settled effectively usually has an SVI of less than 150 mL/g.

Percentage solid settled:

The percentage of solids settled is a key metric for measuring the efficiency of the flocculation process. It directly quantifies the amount of solids that have been removed from the liquid through flocculation and settling. Some key points about the percent solids settled:

· A higher percentage of settled solids indicates improved flocculation efficiency. It suggests that a greater proportion of the suspended particles have settled out as dense flocs.

· One important element affecting the percentage of solids settled is the floc settling rate. Higher solids removal is the result of faster-settling flocs.

· Jar testing is frequently used to maximize the percentage of solids settled by optimizing the kind and amount of flocculant. Particle charge, pH, and temperature are just examples of the variables that affect ideal conditions.

· In one study, a small amount of substance A23, a supplementary flocculant, was added to the primary flocculant B90 to increase the percent of solids settled. As a result, turbidity decreased and the rate of sedimentation rose.

· Depending on the application, different percentages of solids settle at different rates. For instance, efficient flocculation can remove 90–95% of the particles during the processing of iron ore.

Turbidity or supernatant clarity

Turbidity or supernatant clarity are important parameters for measuring the efficiency of the flocculation process. They provide information on the state of aggregation and removal of suspended particles from the water. Some key points about turbidity and supernatant clarity²⁹:

· The cloudiness or haziness of water due to suspended particles is measured as turbidity. It is a crucial water quality metric that needs to be decreased with efficient flocculation.

· The clarity of the liquid layer above the settled flocs following the flocculation and settling process is referred to as supernatant clarity. Improved particle removal is indicated by increased clarity.

· Measurements of turbidity and supernatant clarity are frequently used to evaluate flocculation effectiveness. Higher clarity and lower turbidity indicate more efficient particle settling and aggregation.

· The quality of the resulting floc and the transparency of the liquid supernatant after settling are the parameters obtained in jar testing to maximize flocculation. The turbidity of the supernatant provides insight into the suspension's aggregation status.

· Depending on the application, typical values for supernatant turbidity following flocculation vary. For instance, to achieve water quality criteria in drinking water treatment, the supernatant turbidity should be very low (e.g., < 1 NTU).

Percentage of pollutant removal or water recovery:

One of the most important metrics for assessing the flocculation process' effectiveness is the proportion of contaminants eliminated or water recovered. A few important points are³⁰:

· Applications such as iron ore processing can achieve 90–95% elimination of suspended particles through effective flocculation.

· According to several recent research conducted worldwide, wetlands technology may eliminate up to 99% of pollutants.

· TSS, BOD5, and COD reductions were 86–95%, 65–83%, and 57–84%, respectively, at various hydraulic loading rates in a tropical-built wetland research.

· With its metal recovery technique, Clean TeQ Water can extract over 98% of the metal that is present in the feed solution.

· Early studies on an electrochemical method of treating water showed that organic dye could be reduced by 97% and TOC and COD could be reduced by 78% in effluent.

Table 1. Efficiency of the flocculants to remove the suspended material

Flocculent	Concentration	Flocculation efficiency (%)
Aluminum sulphate	82.5 ppm	>95
Ferric chloride	82.5 ppm	>95
Tanfloc	10 ppm	98
AFlok-BP1	160 PPM	92
Mung bean protein concentrate	20 ml/L	>90
γ-poly glutamic acid	22 ppm	96

How to choose flocculants:

In the process of wastewater treatment, it needs to go through a series of operation steps, and after being tested to meet the discharge standard, it is discharged. In this series of processes, the flocculant plays a vital role. The Flocculant can flocculate the suspended matter of small molecules in the water. Settling, making it easy to filter. The types of flocculants are also very rich. How to choose the flocculant that suits you is also relevant and important. The peculiarities of the wastewater in a particular industry should be taken into consideration when selecting a flocculant for wastewater treatment. However, it also relies on the purpose and location of the flocculant addition. A suitable inorganic flocculant (iron salt, aluminium salt, iron-aluminum salt, silicon-aluminum salt, silicon-ferric salt, etc.) should generally be chosen after taking the wastewater's composition into account. Examples of inorganic polymer flocculants are polyaluminium chloride (PAC), polyaluminium sulphate (PAS), polyaluminium sulfochloride (PACS), and polyferric sulphate (PFS), among others. The more typical PAC and PAS among them have the following qualities: good coagulation and purification effects, low cost of treatment, and good adaptability to variations in water quality treated by raw water treatment chemicals.

It primarily relies on whether anionic, cationic, or nonionic polyacrylamide is being utilized when selecting an organic flocculant (such as polyacrylamide PAM). The degree of hydrolysis determines the anionic polyacrylamides. In sludge dewatering, the choice of cations is typically employed. The choice of cationic polyacrylamide is crucial. The most common cationic polyacrylamide used in urban sewage treatment facilities is medium-strong. Papermaking, printing, and dyeing facilities typically employ weak cations for sludge dehydration and pharmaceutical effluent is typically utilized. Select powerful cations, etc. Every kind of wastewater has unique properties of its own. The majority of applications for non-ionic polyacrylamide (PAM) are in printing and dyeing facilities, and it is primarily utilized in weakly acidic environments.

Selecting the appropriate flocculant is crucial to ensure the success of water treatment processes and to guarantee the safety and quality of the treated water. By carefully considering factors such as water composition, treatment objectives, and environmental considerations, you can make an informed decision and choose the most suitable flocculant for your specific needs³¹.

Mechanism of flocculation:

Flocculation is a process where colloidal particles in a suspension come together to form larger aggregates called flocs. This process is driven by the addition of flocculants, which are chemicals that promote the aggregation of particles. The mechanism by which the flocculants operate depends upon their types and properties but generally involves as per Figure 3. The flocculation mechanism can be described as follows:

Charge Neutralization:

Charge neutralization is a key mechanism involved in the flocculation process. It refers to the process by which the surface charges on the particles are neutralized, allowing them to come closer together and form aggregates. This is achieved by the addition of coagulants like metal salts, which neutralize the negative charges on the particles. A key mechanism in the flocculation process that enables particles to assemble and form aggregates is charge neutralization. To obtain more effective and efficient water treatment, we can better design and optimize flocculation methods by understanding the function that charge neutralization plays in the process.

Mechanism of Charge Neutralization:

· Electrostatic Repulsion: The negative surface charge that most particles in a suspension have helps to keep them stable and dispersed throughout the suspension. The particles are kept apart from forming aggregates by this electrostatic repulsion.

· Coagulant Addition: The negative charges on the particles are neutralized by the addition of a coagulant, like a metal salt. By encasing the particles and neutralizing their surface charges, a metal hydroxide precipitate is formed, achieving this goal.

· Particle Aggregation: Once the surface charges have been balanced, the particles can now assemble into aggregates, or flocs, as they are no longer repulsed by one another. The presence of flocculants, which can adsorb onto particle surfaces and improve the aggregation process, facilitates this process.

Sweep Coagulation:

Sweep coagulation is a type of coagulation mechanism that involves the use of metallic salts, such as aluminum sulfate or ferric chloride, to remove suspended solids and impurities from water. This mechanism is particularly effective for raw water with high turbidity and high alkalinity. A popular and efficient technique for filtering contaminants and suspended particles out of water is sweep coagulation. To create a precipitate that encapsulates and eliminates contaminants from the water, metallic salts are used. The method is widely used for water treatment applications since it is inexpensive, easy to use, and very successful³².

Mechanism of sweep coagulation:

· Addition of Metallic Salt: The metallic salt is mixed with raw water and reacts to produce a metal hydroxide precipitate.

· Formation of the Precipitate: The metal hydroxide precipitate encases and extracts suspended materials and contaminants from the water by forming a large, insoluble solid.

· Floc Formation: A floc is a big group of particles that are easily separated from the water by the precipitation.

· Floc Strength: The pH and ionic strength of the water regulate the electrostatic forces that act between the particles to determine how strong the floc is.

· Effective quick mixing is essential for sweep coagulation because it guarantees that the precipitate and the metallic salt are dispersed equally throughout the water.

Bridging:

The bridging mechanism is a critical process in flocculation, allowing polymer molecules to act as bridges between particles, forming larger flocs. Understanding the factors that affect this mechanism is essential for optimizing flocculation processes and achieving effective water treatment.

Mechanism of bridging:

· Polymer Adsorption: The molecules of the polymer attach themselves to the surface of the particles, creating a thin coating that can radiate outward from the surface of the particle.

· Bridge Formation: A network of polymer bridges that link the particles is created when the polymer chains stretch and bridge between different particles.

· Floc Formation: The particles start to group as the polymer bridges take shape, creating bigger flocs. The quantity and quality of the polymer bridges determine the flocs' strength.

· Floc Growth: When more polymer bridges form, the flocs can expand farther, getting bigger and more stable.

Patch Flocculation:

Patch flocculation is a flocculation mechanism in which polymer molecules attach themselves to the surface of suspended particles to form a "patch" that attracts other particles' bare surface areas electrostatically. The particles group and create bigger flocs as a result of this attraction. Patch flocculation is a flocculation mechanism in which polymer molecules attach themselves to the surface of suspended particles to form a "patch" that attracts other particles' bare surface areas electrostatically. The particles group and create bigger flocs as a result of this attraction. To achieve effective water treatment and optimize flocculation procedures, it is imperative to comprehend the components that influence patch flocculation³³.

Mechanism of patch flocculation

· Adsorption of polymers onto suspended particles results in the formation of a thin layer that can spread outward from the surface of the particle.

· Patch Formation: On the surface of the particles, the polymer molecules create a "patch" that is drawn to areas of bare surface on other particles by electrostatic forces.

· Particle Interaction: The interaction between the patches on the particles leads to the aggregation of the particles into larger flocs.

· Floc Growth: As more polymer molecules adsorb onto the particle surface, the flocs can expand even more, producing new patches and becoming stronger.

Fig. 3: Mechanism of flocculation

Future perspective:

Significant developments and applications are anticipated in flocculation in the upcoming years. Flocculation is the act of aggregating tiny particles in fluids to generate larger flocs for easier removal. The importance of flocculation technology grows as the world's problems with industrial effluent, pollution, and water scarcity continue to rise. With anticipated developments in materials science, integration with cutting-edge technologies, sustainability strategies, and wider industrial uses, flocculation technology has a bright future. The global adoption of effective and sustainable water management strategies depends on these advancements.

Flocculation is expected to continue playing a key role in water and wastewater treatment, with several promising future developments:

Increasing use of microbial flocculants:

Polysaccharides, proteins made by microbes during fermentation, and nucleic acids released mostly during cell lysis make up the majority of microbial flocculants. Microbial flocculants have the advantages of biodegradation, non-toxicity, and no secondary contamination over inorganic and organic polymeric flocculants. Microbial flocculants so demonstrate good safety benefits in post-treatment fermentation and food processing procedures. For instance, when microalgae cells are used to produce biodiesel, 30–50% of the total cost of manufacturing goes towards the concentration of the cells. One useful technique for lowering the price of microalgae harvesting is flocculation. Still, flocculants' safety is a crucial factor to take into account because, besides generating biodiesel, microalgae cells can also be utilized for the extraction of microalgae polysaccharides or the production of animal feed. As microbial flocculants are effective and environmentally friendly, they are being employed more and more to treat wastewater instead of synthetic polymers. These flocculants, which are active at low concentrations, are made by fungi, bacteria, and microalgae (Figure 4). They possess various structures. Microbial flocculants have the following main benefits:

· They can efficiently eliminate organic contaminants, suspended particles, and turbidity from a variety of wastewater sources, such as wastewater from paper mills, biological factories, waste incinerators, and aquaculture facilities. For instance, a flocculant derived from Paenibacillus mucilaginous removed 81.5-88% of the SS and 70-75.2% of the COD from wastewater from paper mills.

· Compared to synthetic polymers like PAM, they are more successful at improving sludge dewaterability, lowering capillary suction time, and reducing specific resistance to filtration. Compared to FeCl₃ and Al₂(SO₄)₃, the acidithiobacillus ferrooxidans bio flocculant decreased the sludge moisture content to 70% at a lower optimal dosage.

· The health and environmental risks linked to synthetic polymers—which are recognized to be neurotoxic, carcinogenic, and non-biodegradable that can be avoided by using microbial flocculants.

Fig.4. Microbial flocculant produced by one-step integrated biotechnology

Combining microbial flocculants with other agents:

Compatibility, dosage, and particular application needs must all be taken into account when combining microbial flocculants with other agents. Certain combinations might function better under specific circumstances or with specific kinds of sludge or wastewater. Pilot testing and optimization are frequently required to find the best combination for a given application.

Microbial flocculants can work better and require less expenditure on application when combined with other agents, such as conventional inorganic flocculants or organic polymeric flocculants:

· A dual-coagulant containing both aluminium sulfate and microbial flocculants greatly increased the flocculating efficiency of a Kaolin-humic acid solution as compared to utilizing either substance alone.

· When poly-aluminum chloride and a polysaccharide microbial flocculant are combined, the removal of dissolved organic carbon from low-temperature drinking water is improved and the rate of floc development is accelerated.

· When applied to synthetic dye wastewater, a composite flocculant consisting of microbial flocculant and aluminium salt demonstrated positive results, enhancing floc size in acidic conditions and accelerating floc formation speed in neutral or alkaline situations.

· A microbial flocculant derived from Bacillus pumilus JX860616 was enhanced in its flocculating ability for household wastewater by grafting acrylamide chains onto it, resulting in removals of 98% COD, 54% BOD, 53% TN, and 57% TP.

· Poly (acrylamide [2-(methacryloyloxy)ethyl]-trimethylammonium chloride] in combination with a microbial flocculant improved activated sludge dewatering, raising dry solids to 29.9% from 21.7% when the microbial flocculant was used alone.

· Chlorella regularis harvesting efficiency was 96.77% when a microbial flocculant was combined with AlCl3 and CaCl₂, which is significantly higher than when the flocculants were used alone.

· To achieve >90% removal of COD, TN, NH₃, and Mn(PO₄)₃ from black, odorous water, the ideal conditions for a composite microbial flocculant with CaCl2 were neutral Ph, 2 Ml/L 1% CaCl2, and 3 g/L microbial flocculant.

Optimizing scale-up and application process:

Several crucial elements must be taken into account to maximize the microbial flocculant application and scale-up process:

· Sorting and refining effective strains: Reducing manufacturing costs requires screening high-yield strains and maximizing their fermentation conditions. It is also possible to create strains with increased flocculant production through genetic engineering.

· Investigating low-cost culture medium and fermentation techniques: The cost of producing microbial flocculants can be greatly reduced by using inexpensive alternative media, such as industrial and agricultural wastes. It’s also critical to optimize fermentation factors including agitation, temperature, aeration, and Ph.

· Creating extraction and storage techniques that are affordable: More than 30% of the entire manufacturing expenses are related to the extraction process. This expense can be avoided by looking into less expensive extraction techniques like employing liquid fermentation broth directly. Enhancing the durability of liquid microbial flocculants during storage is also crucial, which can be achieved by deleting genes that degrade enzymes in strains that have been modified.

· When used with conventional flocculants: Microbial flocculants can work in concert with organic or inorganic polymeric flocculants to reduce the need for the more costly microbial flocculants by reducing their dosage. For instance, wastewater containing synthetic dye responded favorably to a composite flocculant made of aluminium salt and microbiological flocculant.

· Optimizing application conditions: For every unique wastewater treatment application, parameters like Ph, dose, and the addition of agents like CaCl₂ must be optimized. A composite flocculant removed >90% of the COD, TN, NH₃, and Mn(PO₄)₃ from dark, foul-smelling water when Ph 7, 2 Ml/L 1% CaCl₂, and 3 g/L microbial flocculant were added.

Improving monitoring and control:

To improve the monitoring and control of microbial flocculant performance, several key aspects can be optimized³⁴:

· Monitoring flocculation efficiency: Monitoring flocculation efficiency is essential to optimizing application circumstances. Performance can be assessed using parameters such as sludge dewaterability, COD reduction, turbidity removal, and flocculating rate. For instance, a recently developed method is the first of its kind to effectively remove contaminants by producing large enough floc clumps utilizing a flocculation monitoring system.

· Optimizing application conditions: For every unique wastewater treatment application, parameters like pH, dose, and the addition of agents like CaCl₂ must be optimized. When pH 7, 2 mL/L 1% CaCl₂, and 3 g/L microbial flocculant were added, a composite flocculant was able to remove >90% of the COD, TN, NH₃, and Mn(PO₄)₃ from the dark, foul-smelling water.

· Combining with traditional flocculants: Microbial flocculants can work in concert with organic or inorganic polymeric flocculants to reduce the need for the more costly microbial flocculants by reducing their dosage. For instance, compared to employing them alone, a dual-coagulant comprising microbial flocculants and aluminium sulphate greatly increased the flocculating efficiency for a Kaolin-humic acid solution.

· Exploring new monitoring techniques: Sophisticated methods such as zeta potential analysis can shed light on the various microbial flocculants' aggregation mechanisms, which differ according to electrostatic interactions, neutralization, and bridging. This can enhance the choice and use of flocculants.

CONCLUSION:

Flocculation stands as a cornerstone in wastewater treatment, efficiently removing suspended solids by promoting the aggregation of particles into larger flocs. This process, facilitated by both organic and inorganic flocculants, is highly cost-effective and adaptable, finding utility across diverse industries such as paper, pharmaceuticals, and cosmetics. By aiding in the aggregation of hazardous materials, flocculation plays a vital role in environmental protection, ensuring compliance with regulatory standards and mitigating the discharge of pollutants into water bodies. Its integration into comprehensive treatment processes, alongside coagulation, sedimentation, filtration, and disinfection, underscores its importance in achieving desired water quality standards. Overall, flocculation emerges as an indispensable component of wastewater treatment, offering an effective, economical, and versatile solution for addressing water pollution challenges and supporting sustainable environmental practices.

CONFLICT OF INTEREST:

The authors declare no conflict of interest.

ACKNOWLEDGMENTS:

The authors are thankful to the college management for the support and encouragement.

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Received on 25.09.2024 Revised on 30.11.2024

Accepted on 14.01.2025 Published on 03.03.2025

Available online from March 10, 2025

Res. J. Pharma. Dosage Forms and Tech.2025; 17(1):41-52.

DOI: 10.52711/0975-4377.2025.00007

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