Advanced Treatment Techniques for Wastewater from Pharmaceutical Industries: A Comprehensive Review

Pharmaceutical compounds are made through batch processes, which produce a wide variety of products. A large amount of water is used in these industries for different purposes, like washing solid cakes, extracting, and cleaning equipment. This leads to the production of a large amount of wastewater.(1)

Pharmaceutical compounds enter water sources mainly from two sources:

1. From the drug production process.
2. From the regular use of medicines by people and animals.

The wastewater produced during different processes contains a mix of harmful pollutants such as active pharmaceutical ingredients (APIs), excipients, and various chemicals. (2) Many developed countries like Japan, France, Germany, the UK, and the United States are leading drug producers and contribute to pharmaceutical pollution. India and China are the top producers of low-cost natural or organic-based medicines globally.(3) Pharmaceutical substances in wastewater show different chemical properties and toxicity. Improper disposal of unused or expired drugs also adds to this problem. These substances can enter water sources such as municipal drinking water, underground water for farming, and rural water supplies without any treatment.(4) Personal care products like toothpaste, lipstick, soap, shampoo, sunscreen, and detergents are also sources of pharmaceutical pollution in the environment. (5)

Because of the presence of pharmaceutical compounds in both urban and rural water sources, it is important to treat wastewater before releasing it into the environment. Even small amounts of pharmaceutical substances in water can be harmful. They may cause serious health issues like hormone problems (endocrine disruption), antibiotic resistance, and long-term health effects due to continuous exposure.(6) Due to water scarcity and environmental pollution, it is necessary to find and develop effective methods for treating pharmaceutical wastewater. Industries, especially pharmaceutical ones, must remove harmful substances from the water and reuse it where possible. (6) Strict rules exist around the world for the discharge of industrial wastewater. Pharmaceutical companies must follow these rules to avoid legal action, penalties, and the risk of losing their licenses. (7)

This review will focus on the current wastewater treatment techniques used in the pharmaceutical industry and look at eco-friendly ways to reduce waste and pollution during drug manufacturing. In recent years, billions of people have suffered from water scarcity due to excessive and careless use of water resources. Pharmaceutical industries require a large amount of potable and fresh water for different purposes, like washing of equipment, formulation, and cleaning of the area, etc.  The used water contains the pollutants (can be organic or inorganic compounds, API, excipients). (1)

It's necessary to treat it. For that purpose, different techniques out there that remove the pollutants from the water. Some of them are as follows.

Types of Pharmaceutical Wastewater Treatment Techniques:

1. Advanced Oxidation Processes (AOPs)

AOPs are special chemical methods that produce powerful substances like hydroxyl radicals. These break down harmful pharmaceutical chemicals in the water. Some common AOPs are ozonation, Fenton reaction, UV with hydrogen peroxide, and photocatalysis. They are useful when regular treatment doesn’t work.(8)

2. Electrochemical Oxidation

In this method, electricity is used to clean the water by producing substances that break down pollutants. It can clean very dirty water, but it uses a lot of energy and may cost more.(9)

3. Photocatalysis

This method uses special materials like titanium dioxide and light (UV or sunlight) to break down harmful chemicals. It’s effective, but sometimes the light can’t reach all parts of the water, and removing the catalyst can be hard. (10)

4. Ozonation

Ozone gas is a strong cleaner that can remove many types of pharmaceutical compounds. It is very effective but can also make unwanted byproducts like bromate, which are harmful.(11)

5. Fenton and Photo-Fenton Processes

These are types of AOPs that use iron salts and hydrogen peroxide (with or without UV light) to make strong oxidants. They work well for many pollutants but create iron waste that must be removed.(12)

6. Wet Air Oxidation

This process uses heat and pressure with air or oxygen to break down tough pollutants in water. It works well but uses a lot of energy, so it's usually used before other treatments. (13)

7. Membrane Bioreactors (MBR)

MBRs combine regular biological treatment with a filter membrane. Bacteria first remove most of the pollution, and then the membranes filter out tiny particles. This method gives spotless water but can be expensive and needs regular cleaning of membranes.(14)

8. Constructed Wetlands

These are man-made areas that work like natural wetlands. They use plants, soil, and microbes to clean the wastewater. This method is eco-friendly and low-cost, but it's not good for very polluted water unless used with other treatments.(15)

9. Biological Treatment (Activated Sludge Process)

This is a common method where bacteria eat the organic waste in water. It’s simple and low-cost, but many pharmaceutical chemicals do not break down easily this way.(16)

10. Activated Carbon Adsorption

Activated carbon is a type of charcoal that has lots of tiny holes. It can trap leftover pharmaceutical chemicals from water. It’s often used as a final step to make water cleaner. But the carbon gets full over time and needs to be replaced or cleaned.(17)

11. Enzymatic Degradation

This uses enzymes (natural proteins) to break down pharmaceutical pollutants. It’s a selective and eco-friendly method, but still needs more research before it can be used widely in industries. (18)

12. Anaerobic Digestion

This is a biological method done without oxygen. Microorganisms break down the pollutants and produce biogas. It's useful for very dirty wastewater but may not remove all pharmaceutical compounds.(19)

MATERIALS AND METHODS:

1. Advanced Oxidation Processes:

Advanced Oxidation Processes are unique water treatments. They use strong chemical reactions to break down tough pollutants. These processes create hydroxyl radicals (OH-). These radicals are very active. They attack and destroy contaminants. They break apart the chemical bonds. AOPs generate these reactive OH- radicals. This happens by mixing oxidants with energy sources. Sources include UV light, ultrasound, or certain metals. These radicals quickly react with organic waste. They change the waste into smaller, safer bits. These smaller bits are easier to break down. Different AOP methods use different oxidants.(20)

Different methods of AOPs also depend upon the oxidising agent used in the respective AOP.

Different methods of AOPs are:

1. Electrochemical oxidation
2. Photo-catalysis
3. Ozonation
4. Fenton reaction
5. Wet air oxidation

Requirements:

To make AOPs work, you need a few things.

1. You need oxidising agents. Good examples are hydrogen peroxide, ozone, or persulfates.
2. You also need energy. This can be UV light, sunlight, or ultrasound.
3. Catalysts like titanium dioxide or iron are also used. These speed up the reaction.
4. A special container is needed. This is where oxidants, waste, and catalysts meet.
5. The pH must be controlled. Some methods need an acidic environment. Others work best in a neutral one.
6. Lastly, good mixing is important. This ensures radicals reach the waste. It gives them enough time to break it down.(21)

Result:

When AOPs are used correctly, they really work. They remove tough organic pollutants. This includes medicines, pesticides, and dyes. The chemical structure of pollutants is broken. They turn into simple things like water and carbon dioxide. The treated water is less harmful. This also makes the wastewater easier to clean later.(20)

1. Electrochemical Oxidation:

Figure 1: Schematic of an Electrochemical Reactor for Wastewater Treatment

Electrochemical oxidation treats water using electricity. Special electrodes help break down waste. Wastewater moves through a cell with two electrodes. A current creates reactive agents near the anode. These agents attack and change harmful organic compounds. They ideally become carbon dioxide, water, and simple salts. Direct oxidation occurs on the anode. Pollutant molecules touch the anode. They lose electrons and get oxidised. (22)

Requirements:

An electrochemical cell. It must resist corrosion.

1. Electrodes. The anode is key. Examples are boron-doped diamond (BDD) or mixed metal oxides/dimensionally stable anode (MMO/DSA). Graphite also works. BDD is effective but costly. MMO/DSA are cheaper and stronger. They make active chlorine in salty water. The cathode can be graphite or steel. Advanced cathodes can make hydrogen peroxide.
2. A DC power supply. It needs adjustable current and voltage.
3. An electrolyte salt. This helps current flow. Sodium sulphate is inert.
4. Sodium chloride makes active chlorine. Use it carefully to avoid unwanted salts.
5. A mixing system. A stirrer or pump ensures even contact.
6. Temperature control is optional. Room temperature is common.
7. Safety gear is needed. Use ventilation for chlorine. Wear gloves and goggles.(9)(22)

Procedure:

1. Test the wastewater. Check COD, TOC, pH, and salt content.
2. pH control. Buffers or acids/bases are used. Most systems work near neutral. Electro-Fenton prefers acidic conditions.
3. Prepare the cell. Clean the electrodes. Rinse them well.
4. Add wastewater and electrolyte. Use about 0.01–0.1 M sodium sulphate.
5. Set electrode spacing. Ensure good flow across the anode.
6. Adjust the pH. Aim for neutral, around 6–8. Avoid extremes unless needed.
7. Choose an operating mode. Apply current. Start with low to medium current density.
8. Mix and monitor. Stir or pump the mix. Check current, voltage, and temperature.
9. Take samples often. Analyse them for COD, TOC, colour, and pH. Check for chlorine if salt was used.
10. Stop when targets are met. Neutralise if needed.
11. Post-treatment may be required. Aeration can remove chlorine. Carbon filters can polish the water. Biological steps can handle partial breakdown.
12. Handle waste and electrodes safely. Rinse electrodes. Dispose of samples correctly.(23)

Result: 

COD and TOC levels drop significantly. This is especially true with BDD or active chlorine. Colours and odours disappear quickly. Pathogens can be killed by the strong oxidants. Little sludge is produced, unlike other methods. Be cautious of by-products in salt water. High currents or long times can create unwanted salts or chlorinated compounds. Monitor and control these. Energy use varies. It depends on current, water conductivity, and waste load. Better cell design lowers energy needs. Pre-treating with this method helps the biological steps. It breaks down tough molecules for easier breakdown later.(23)(9)

2. Photo-catalysis:

Figure 2 : Photocatalytic Reactor for Wastewater Treatment

Photocatalysis is the use of light energy (like sunlight) with a catalyst (e.g., TiO?) to degrade toxic organic and inorganic pollutants in water. The catalyst absorbs light and generates active species. These species then react with the water and oxygen. They create reactive species that attack and degrade pollutants. These substances then convert to harmless by-products, such as CO? and H?O.(24)

Requirements:

1. Photocatalyst: Usually TiO?, ZnO or something similar.
2. Light Source: A UV lamp or natural sunlight. 
3. Polluted Water: Should contain pharmaceuticals or organic waste. 
4. Oxygen: Dissolved oxygen or air bubbles help this process. 
5. Reactor: A vessel to safely perform this process.(25)

Procedure:

1. Mix the catalyst and water. Add the catalyst, like TiO? powder, to the dirty water.
2. Shine light on it. Put the mix under UV light or sunlight for a set time.
3. Stir or add air. Keep the mix moving or bubble air/oxygen into it.
4. Check pollutant levels. Take small samples. Test for less pollution using a UV reader or COD/BOD tests.
5. Remove the catalyst. After treatment, filter out the catalyst bits. This lets you reuse the catalyst. It also leaves clean water.(24)(25)

Results:

Photocatalysis can significantly reduce or eliminate harmful drugs, dyes, and organic waste. The final products are often safe, e.g., CO?, H?O, and mineral acids.(26) This is an eco-friendly method. It mainly needs only light and a catalyst. No additional toxic chemicals are used. (24) (25)

3. Ozonation:

Figure 3 : Ozonation Process for Wastewater Treatment

Ozonation is a method for treating wastewater. It uses ozone gas. Ozone is a strong oxidiser. It breaks down pollutants. Pollutants are broken down and become smaller, safer pieces. Or they can be broken down by nature. This method removes harmful and toxic chemicals. It also removes bad colour and smells. Even medicine traces can be removed. (26)

Requirements:

1. Ozone maker: This creates ozone from oxygen.
2. Oxygen or air source: Needed to make ozone.
3. Contact tank: A closed tank. Ozone mixes with dirty water here.
4. Sprayer/feeder: Helps spread ozone evenly in the water.
5. Safety gear: Stops ozone leaks. High amounts are bad for health. (27)(28)

Procedure:

1. Put oxygen or air into the ozone maker. Oxygen is the main ingredient.
2. Make ozone. Use electric sparks or UV light. This produces ozone gas.
3. Mix ozone gas into the dirty water. Use the sprayer/feeder. This mixes it well.
4. Let the ozone and water mix in the tank. More time means better cleaning.
5. Control the ozone amount and time. This saves resources and ensures safety.
6. Remove extra ozone. Use a vent or carbon filter; this stops ozone release. (28)(29)

Results:

Organic waste, medicines, and dyes break apart. They become smaller or less harmful. Harmful or toxic colours, bad smells, and tastes disappear. Wastewater breaks down more easily. This helps with later cleaning steps. It creates little waste. It is good for the environment.(28) (29)

4. Fenton Process:

Figure 4 : Fenton Process Flow Diagram

The Fenton process is an advanced oxidation method. It uses hydrogen peroxide and iron. Ferrous iron acts as a catalyst. This creates very active hydroxyl radicals. These radicals powerfully oxidise organic matter. They break down tough, toxic pollutants. The breakdown yields simple forms like carbon dioxide and water.(30)

Requirements:

1. Hydrogen peroxide (H?O?) is the oxidiser.
2. Ferrous salts (Fe²?) start the reaction.
3. An acidic pH of 2-4 is best.
4. A vessel holds the mixture.
5. Mixing ensures good contact. (31)

Procedure:

1. Make the wastewater acidic (pH 2-4). The reaction needs this.
2. Add iron (Fe²?). It helps make radicals.
3. Slowly add hydrogen peroxide (H?O?) while stirring. This controls radical release.
4. Let the mix react for 30-60 minutes. This gives time for oxidation.
5. Neutralise the liquid. Remove any solid sludge. Sludge contains iron solids.(32)

Result:

Breakdown of complex pharmaceutical and industrial pollutants. Removal of colour, odour, and reduction in Chemical oxygen demand (COD). Improved biodegradability of wastewater, making it easier for further biological treatment. (30)

5. Wet Air Oxidation:

Figure 5 : Schematic of Wet Air Oxidation Process

Wet air oxidation is a modern method for treating industrial wastewater. It is effective for waste containing harmful, non-biodegradable organic matter. Pharmaceutical wastewater often falls into this category. This process uses oxygen or air. It oxidises organic and inorganic pollutants in water. This occurs at high temperatures, from 125 to 320°C. High pressure, around 220 bars, is also needed. Many industries now use this technique. (33)

Requirements:

A reactor built for extreme heat and pressure. Air or pure oxygen serves as the oxidant. A system to heat and pressurise the setup is required. A wastewater sample with pollutants is essential. (34)

Procedure:

1. The process begins by gathering a wastewater sample. This confirms the effluent type. 
2. The sample is loaded into a high-pressure reactor. This ensures safe operation.
3. Pressurised air or oxygen is then added. This keeps oxygen dissolved for better oxidation.
4. The mixture is heated between 150 and 320°C. This speeds up reactions and breaks down tough pollutants.
5. The reaction is held for 30 to 120 minutes. This allows pollutants to oxidise fully.
6. Finally, the system is cooled and depressurised safely. This avoids sudden pressure release risks.
7. The treated water is then checked. This confirms reductions in COD and BOD.(33)(35)

Results:

It shows significant COD reduction, often 80–90%. Harmful organics transform into biodegradable forms. The final products are safer. These include CO?, H?O, and simple acids.(35)

2. Membrane Bioreactors:

Figure 6 : Schematic of Membrane Bioreactor System

Membrane bioreactors (MBRs) are now preferred over activated sludge processes (ASPs). MBRs are a major advance in treating wastewater. They fix problems with older ASPs. These problems include large space needs for clarifiers. They also fix issues with separating liquids and solids. MBRs also create less sludge. An MBR combines biological treatment with membrane filtration. This filtration physically separates solids from liquids. (36)

Requirements:

An MBR needs key parts. These are a pretreatment screen and biological tanks. It needs anoxic, aerobic, and anaerobic zones. An air blower is also required. Sludge needs to be recycled. Chemical dosing and a cleaning tank are also part of it. Its function relies on pressure known as TMP. Permeability and water flow matter too. Design should focus on the food-to-microorganism ratio. High levels of mixed liquor suspended solids (MLSS) are good. Choosing the right membrane is vital. This helps with cleaning and upkeep. Pretreatment protects membranes from clogging. Ultrasound or ozone can be used. Most membranes are made of polymers. PVDF is a common choice. Composite membranes with special coatings are better. They reduce clogging. The membrane pore size must be right. Smaller pores clog less easily. They are simpler to clean than large pores.(37)

Procedure:

The reactor ran at 30 L/m²/h. Effluent was pumped out. The hydraulic retention time was 19 hours. The organic loading rate was 0.62 kg COD m?³ d?¹. Membranes were backwashed for one minute. This happened every nine minutes of filtering. This occurred throughout the study. The system ran for seven days first. No dyes were added then. Dyes were added for the next thirty days. Influent COD stayed at about 1000 mg/L. Mixed liquor solids were around 8384 mg/L. Volatile solids were about 4916 mg/L. Wastewater pH was between 8.0 and 8.5. The reactor temperature was kept at 20 °C.

Samples were taken every 48 hours. These came from influent, mixed liquor, and permeate. We checked the flow rate and effluent clarity. Transmembrane pressure (TMP) was monitored. Dissolved oxygen (DO) and pH were checked. Conductivity and temperature were also measured. COD and NH?-N were analysed. Sulphates, nitrites, nitrates, and phosphates were measured. ML-TSS and ML-VSS were also measured. Turbidity was checked with a meter. DOC was measured using a TOC analyser. EPS and SMP were extracted. Their protein and carbohydrate content was found. Dye levels were measured using a spectrophotometer. (38)(39)

Result:

The MBR system worked very well. It removed most pollutants. The MBR removed 91% of COD. It removed 97% of dyes. Ammonia removal was 95%. These rates were higher than the control. It also removed more nitrogen and phosphate. The MBR system kept TMP stable. Its effluent was clearer. It clogs less. This was due to lower EPS and SMP levels.(37)

3. Constructed Wetlands:

Figure 7 : Diagram of Constructed Wetland System

The engineered systems are called constructed wetlands, which use natural wetland processes to clean wastewater. Vegetation, soil, and microbes are key. These systems often treat water from cities, farms, and industries. They clean pollutants using settling, filtering, absorbing, plant taking, and microbes breaking down waste.(40)

Requirements:

Constructed wetlands need a sealed basin that stops water from leaking out. A good base material, like gravel or sand, is needed to help plants grow. Proper pipes for water entering and leaving are also important cause they ensure water flows evenly. Plants such as reeds or cattails are important as they absorb nutrients and move oxygen. For good work, wetlands need a specific water flow time. They also need areas with and without oxygen. Sometimes, trash needs pre-filtering. Plant health, soil, and water quality need regular checks. Climate also impacts how well they work. (41)

Procedure:

Wastewater flows into a shallow, sealed pool. This pool holds layers of gravel, sand, and soil. Wetland plants are grown here. They help microbes clean the water. Water spreads evenly at a controlled pace. It moves through the system. Filtering, plant absorption, and microbial action remove waste. Plants are trimmed. Sludge is removed. Water is then collected and tested. This confirms pollutants are reduced.(42)

Result:

These wetlands effectively remove waste. They clean organic matter, solids, and nutrients. Heavy metals and germs are also removed. They can lower COD, BOD, and TSS. This meets water discharge rules. Wetlands also help nature. They offer homes for wildlife. They make places look nicer. They can also store carbon from the air.(41)

4. Activated Sludge Process:

Figure 8 : Flow Diagram of Activated Sludge Process

The activated sludge method is a common biological way to clean wastewater. It uses a mix of tiny life forms. These include bacteria, tiny animal-like cells, fungi, and other small organisms. They form clumps called flocs. These microbes eat up waste. They turn organic matter and pollution (BOD5) into new cell material. This happens with oxygen. This cleans the water. The types and amounts of microbes show how well the system works. Key players are bacteria, tiny cells called ciliates and flagellates, and rotifers. They help remove waste and shape the sludge.(43)

Requirements:

The process needs enough oxygen. It also requires the right balance of food. This includes carbon, nitrogen, and phosphorus. These feed the microbes. For clean water with oxygen, the food mix should be about 100 parts carbon, 5 parts nitrogen, and 1 part phosphorus. Factors such as pH, temperature, and oxygen levels influence how microbes function. This is true for bacteria that change nitrogen. The effectiveness of nitrogen removal depends on the type of food and environmental conditions. (44)

Procedure:

Wastewater first has solids removed. Then, it goes to a cleaning stage. Here, dirty water mixes with trained microbes. This mix is put into tanks with air. Air is added all the time. This oxygen helps microbes eat. The microbe clumps break down waste. They turn it into more microbe cells. The mixed solids, including the active microbes, are then separated. Some of this sludge is sent back to the start. This keeps the right amount of microbes working. The system runs all the time. The amount of sludge and the amount of waste it produces are controlled. Checking the microbes under a microscope helps monitor the system.(45)

Result:

The process greatly reduces waste. This is seen in BOD5 and COD levels. A healthy microbe mix, with many tiny cells and rotifers, means good cleaning. Water quality is stable. pH is around 7.5. COD, BOD5, and total suspended solids are controlled. Changes from COVID-19 affected the microbes and water. But the process stayed effective. The mix of microbes relates to how steady the cleaning is. Adding special bacteria can help break down sludge. This can reduce total and volatile solids by about 21% and 14%. This works by using enzymes to break down sludge proteins and starches. Best results are at pH 10 and 50 °C for 48 hours.(44)

5. Activated Carbon Adsorption:

Figure 9 : Activated Carbon Filtration System for Wastewater

Activated carbon (AC) is a great adsorbent. It has a large surface area. Its pore structure helps it capture many pollutants. These include CO?, heavy metals, and organic compounds. AC works on gases and liquids. Adsorption depends on surface chemistry. Pore size distribution matters. Operating conditions like temperature and pressure also play a role. Adsorption speed is often explained by models. The Langmuir model and pseudo-second-order model are common. These suggest single-layer chemisorption. They also indicate diffusion-controlled steps.(46)

Requirements:

Materials: Granular activated carbon is needed. It usually has a 20–60 mesh particle size. Chemicals for changing the AC are also required. Ammonium persulfate is an example. The target pollutant, like Cr (VI) or CO?, is also a material.

Reagents: Solutions to control pH are necessary. Nitric acid and sodium hydroxide work. Standard solutions of the pollutant are also needed.

Equipment: A Brunauer-Emmett-Teller (BET) surface area Analyzer is useful. Fourier-transform infrared (FTIR) spectroscopy can analyze functional groups. A pH meter is essential. A mechanical shaker is used for mixing. Filtration equipment is needed. Analytical devices, like ICP-AES for metals, are also required.(47)

Procedure:

1. Preparing Activated Carbon: Mix the base material, such as brown coal. Add an activating agent, such as K?CO?. Let them sit for 24 hours at room temperature.
2. Dry the mix at 110 °C. Heat it in a nitrogen environment. Then raise the temperature to the activation point, often 700 °C.
3. After heating, wash the sample. Use hot HCl and boiling water. Dry it until its weight is constant.
4. Modifying the Carbon (if needed): Change the AC surface. This can improve its adsorption. Using ammonium persulfate is one way.
5. Adsorption Test: Use a batch method for testing. Put a known amount of AC in a flask. Add a solution with the target pollutant. Shake it at a set temperature and pH.
6. When adsorption stops, filter the mixture. Measure the pollutant left in the liquid.
7. Repeat tests with different amounts. Change initial concentrations, pH, temperature, and time. This helps study adsorption patterns and speed.(48)

Result:

 Adsorption capacity increases with higher pressure. It also goes up with higher temperatures. In batch tests, modified AC captured 108.69 mg/g of Cr(VI). Adsorption typically fits the Langmuir model. It also matched the pseudo-second-order speed model. This suggests single-layer chemisorption. The process was endothermic and spontaneous. Efficiency depended on pH, temperature, and initial concentration. Changing the surface and pores greatly improved adsorption.(47)(48)

6. Enzymatic Degradation:

Figure 10 : Diagram of an Enzymatic Degradation System

Enzymes break down large molecules into smaller ones. This process uses enzymes like cellulases and lipases. It is important for recyc

Requirements:

Enzymatic breakdown needs specific things. You need the right enzymes in the right amounts. Porcine pancreatin or Rhizopus oryzae lipase are examples. The conditions must also be right. This includes temperature, usually 30–40°C. Buffer solutions, like phosphate buffers, are used. Degradation time is also controlled, perhaps 28 days. Enzymes and buffers should be changed weekly. This keeps the enzymes working well. Lab incubators keep the temperature steady. They also move air around. (50)

Procedure:

A typical process involves several steps. Polymer samples are mixed with enzymes. This happens in a buffer solution at a set temperature. For pig pancreas enzymes, 37°C is common. The buffer and enzyme are changed often. This keeps the enzymes active. Changes are usually made weekly for four weeks. Samples are checked at set times. This might be every 7 days. Appearance and structure changes are noted. Control tests are run too. These tests use no enzyme or just water. This shows the baseline for breakdown.(49)(51)

Result:

Recent studies show clear results. Material samples broke down well. Epoxy-polyurethane lost up to 5% of its weight. This happened with pig pancreas enzymes. The amount of breakdown depends on several factors. These include the enzyme used, its amount, and the conditions. Substrate type also plays a role. Further tests show smaller fragments of material. This happened when enzymes were present and under certain conditions. DNA breakdown tests show similar findings. (50)(51)

7. Anaerobic Digestion:

Figure 11 : Anaerobic Digestion System Diagram

Anaerobic digestion is a natural process. Microbes break down organic matter in the absence of oxygen. This process creates biogas, primarily consisting of methane and carbon dioxide. It also produces digestate. This process helps manage waste. It also recovers energy. It protects the environment too. Four stages make up this process. They are hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Each stage uses specific microbes. They break down complex matter into its simpler components. Finally, methane and CO? are made.(52)

Requirements:

Anaerobic digestion requires several things to function effectively. The organic matter needs to be right. It should be rich in carbs, proteins, or fats. Chemical and physical conditions are also key. The pH should be about 6.5 to 7.5. Temperatures can be mesophilic (30–40°C) or thermophilic (50–60°C). The carbon-to-nitrogen ratio matters. Good buffering is also needed. Harmful things like ammonia and excess acids must be controlled. Mixing the contents is important. The time the material stays in the digester is also critical.(53)

Procedure:

The process follows specific steps.

First, the organic matter is readied. Then it is put into the digester. Next, the four biological stages begin. Hydrolysis breaks down large molecules. These are carbs, fats, and proteins. They become smaller units. Acidogenesis changes these units. It makes volatile fatty acids, alcohols, ammonia, and hydrogen. Acetogenesis converts these intermediates. Acetic acid, CO?, and hydrogen are produced. Methanogenesis uses methanogenic archaea. They create methane and CO?. The process variables are watched. This includes pH, temperature, and concentration. Biogas is then collected and used. The leftover digestate is managed.(54)(55)

Result:

Anaerobic Digestion Outcomes Enhanced anaerobic digestion, like in a three-stage reactor, gives better results. Methane output increases by 11–23%. Organic matter reduction is higher. It can be up to 71%. Each reactor stage develops special microbial groups. Both easy and hard-to-break-down wastes are processed better. Overall performance improves. This means higher processing rates. It also means smaller digester sizes are needed. (53) (54)

Applications:

1. Electrochemical Oxidation:

• It is widely used in municipal or industrial effluent to remove the pollutants, including dyes, ammonia, pesticides, and organic matter, which are persistent.
• Pharmaceutical and antibiotic removal: Effective for breaking pharmaceuticals like sulfamethoxazole, paracetamol, and amoxicillin, which are emerging contaminants.
• Pesticide degradation: Used to mineralize and to break down pesticides. (malathion, glyphosate, 2,4-D)
• Dye removal: Effective in decolorization and dye removal from wastewater.
• Aquaculture wastewater treatment: Uses the Flow-through EO process to efficiently treat marine aquaculture wastewater. (56)

2. Photocatalysis:

• Wastewater treatment: Wastewater is cleaned by removing drugs and pesticides.
• Antibiotic degradation: Antibiotics break down, like oxytetracycline.
• Ion reduction:  Ions, such as nitrates and metals, are removed.
• H?O? generation: For the production of H?O? for the advanced oxidation process as a precursor.
• Eco-friendly remediation: Mineralization of pollutants into simple byproducts like CO? and water. (57)

3. Ozonation:

• Disinfection: Effective against bacteria, viruses, and pathogens in water.
• Decolouration: Removal of colour from contaminated water and wastewater.
• Micropollutant removal: Elimination of Pharmaceutical pesticides and other trace organics, which are fine in size.
• Antibiotics wastewater treatment: Breakdown resistant antibiotics like sulphonamide, quinolones, β-lactam.
• Sewage and medical wastewater treatment: Use in hospital effluents and treatment of sewage. (58)

4. Fenton Process:

• Antibiotic elimination from water breaks them fully.
• Photo-Fenton is used to break down tough antibiotics.
• Electro-Fenton, which uses power, is used to make hydrogen peroxide for treatment.
• Solar photoelectron-Fenton is used for fast antibiotic breakdown.
• Heterogeneous Fenton uses solid bits as a catalyst to clean water.(59)

5. Wet air oxidation:

• Organic pollutants are degraded effectively. This traces non-biodegradable compounds in oil refinery waste.
• Catalysts are employed, which are derived from Oily sludge and Petroleum coke, which yield carbon materials for catalyst use. This enables circular wastewater treatment.
• Uses Fe basic site catalyst to form OH radical for efficient COD reduction. (60)

6. Membrane Bioreactors:

• Removes 95-99% pollutants like Acetaminophen, Ibuprofen, Phenolics, and other solvents.
• Achieves 80-92% of COD removal and greater than 90% of nitrogen removal from petroleum refinery wastewater.
• Removes 85% COD and 90% ammonium from manure-based effluents from livestock wastewater.
• Achieves 99% of ammonium removal and 63% COD reduction from steel pickling water. (61)

7. Constructed wetlands:

• Constructed wetlands are used to remove biochemical oxygen demand and chemical oxygen demand.
• The system is used to degrade organic pollutants and pharmaceutical active compounds, also making them suitable for hospital effluent, which is difficult to treat.
• Reduces volume and pathogens to treat the sewage sludge.
• Effectively reduces pharmaceuticals, personal care products, and chemicals that pose the threat of endocrine disruption.(62)

8. Activated sludge process:

• Activated sludge is used to remove pharmaceutical compounds like carbamazepine and diclofenac, which are common contaminants.
• This process is applied for the biological degradation of pharmaceuticals and their byproducts to decrease the risk to health and the environment.
• In semi-arid regions like Spain, the treated effluents of ASP are used for the irrigation of crops and plants.
• It is used to treat the effluents and reduce the contaminants that can affect the drinking water sources.(63)

9. Activated carbon adsorption:

• Used to remove drugs such as carbamazepine, sulfamethoxazole, ibuprofen, etc, from municipal effluents and wastewater by adsorption.
• Magnetic activated carbons are used to increase the recovery of carbon and enhance efficiency.
• Activated carbons are modified and turned into carbon paste, which can modify the sensing and adsorption of electrodes. (64)

10. Enzymatic degradation:

• Similar to all methods, it plays a key role in the biotransformation of pharmaceuticals and drugs, and reduces their potential contaminants and risk.
• Can be used in hospitals or industrial effluents for bioremediation to remove pollutants from them.
• Can be used for enzyme-assisted degradation of emerging contaminants that disrupt the endocrine system. (65)

11. Anaerobic Digestion:

• Used to generate Biogas, which mainly consists of Methane and CO₂ that can be used for electricity generation and household purposes.
• It decreases toxic pollutants and increases microbial activity and its effectiveness when it is combined with the Bio-electrochemical system.
• Treatment of solid waste like sewage sludge, food waste, and organic substances. (66)

Advantages and Disadvantages:

Table 1: Comparative analysis of  Wastewater Treatment Technologies