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Physicochemical Methods of Wastewater Management

by | Mar 26, 2022 | Wastewater Management

Introduction

Physicochemical methods of wastewater management are used for pre-treatment, final treatment, and specific treatment for wastewater reuse as process water. Wastewater contains particles of varying sizes. As a result, multiple treatment techniques are needed to make recycled water safe for consumption, disposal, and compliance with stringent regulatory standards. The particle size has an impact on treatment efficiency.

Chemicals are used in physicochemical methods of wastewater management to change the physical state of colloidal particles, making particles more stable and coagulable for further processing or filtering. These treatment procedures have been utilized in combination with biological treatment methods for over a century. With increased efficiency and lower prices, these approaches have effectively employed industrial water treatment and conditioning of wastewater sludge as part of pre-treatment. The biodegradation capacity of organic material in wastewater can be significantly influenced by physicochemical treatment.

A physicochemical treatment consists of a series of procedures that can be carried out in a single unit or separate units. Coagulation, flocculation, and sedimentation are the three processes involved. Various factors and wastewater physicochemical qualities can influence the overall efficacy of a physicochemical method of wastewater management.

Types of Physicochemical Process

Flocculation, coagulation, flotation, neutralization, electro flotation, membrane technology or membrane filtration, NH3 stripper-absorbers, and sludge treatment are all common physicochemical methods of wastewater management.

Coagulation/Flocculation process

Introduction 

Coagulation-flocculation is a chemical water treatment procedure used before sedimentation and filtration (e.g., quicksand filtration) to improve a treatment process’ capacity to remove particles. Coagulation is a method of neutralizing charges and generating a gelatinous material that traps (or bridges) particles and allows them to settle or be caught in the filter. Flocculation is the gentle stirring or agitation of particles generated in this way to encourage them to agglomerate into masses big enough to settle or be filtered out of the solution.

Types of Coagulants

While Aluminium sulphate is the most often used chemical for coagulation. Coagulants such as ferric sulphate, ferric chloride, and sodium aluminate are also common.

Aluminium Sulphate: Aluminium sulphate forms an aluminium hydroxide floc when added to naturally alkaline water (which generally contains calcium bicarbonate).

Ferric Chloride: Ferric chloride is a less preferred alternative to ferric sulphate because chloride can make water more corrosive.

Ferric Sulphate: When combined with chlorine, this chemical combination can produce a denser floc than aluminium sulphate.

Sodium Sulphate: This chemical’s solid forms typically comprise 70-80 percent sodium aluminate, whereas liquid forms have approximately 30% sodium aluminate

Physicochemical methods of wastewater management

Pros and Cons of Reactors

Pros:

  • The reactors are easy to use and cost-effective 
  • Removes a variety of particulates from water.
  • Improves the filtering process.
  • Chemicals are plentiful and inexpensive

 Cons:

  • Chemical input is necessary.
  • Design (e.g., chamber construction and chemical dose) and system maintenance require qualified staff.
  • Toxic substances are transferred to the solid phase, resulting in the production of sludge that must be handled later.
  • The process takes a long time.

Electro Coagulation

Introduction

Electrocoagulation (EC) is a Physicochemical method of wastewater management technology that is employed in many different sectors. Using an electrical charge to keep contaminating particles, colloids in solution, and ions such as heavy metals, the method destabilizes and aggregates them. The technique generally uses an anode and a cathode to destabilize the charges, both of which are stimulated by a DC power source. This procedure separates flocculated particulates from water, enabling them to be removed and replaced with pure water.

Types of reactors available to treat the wastewater

Horizontal flow reactors and vertical flow reactors are two types of filter press reactors. However, there is no standard design because reactors are customized for each process and contaminant.

Filter Press Reactors: The coagulants are created through metal plates that serve as electrodes and are supported by frames in this sort of reactor, which uses a filter press mechanism.

Rectangular Horizontal Flow Reactors: This design is a variation of the batch reactor in which the water to be treated is delivered by a pump, resulting in a continuous flow

Vertical Flow Reactors: This kind of reactor has also been researched in a variety of configurations and has been demonstrated to be effective at removing a variety of contaminants. The tainted water travels through a porous tube with this configuration.

Pros and Cons of Reactors

Pros:

  • Does not need chemicals for the treatment. 
  • Eliminates the risk of leftover chemicals which cause toxicity and odour.
  • Lowers the initial cost of the procedure.
  • It can reduce the total quantity of suspended particles in a solution by up to 95%.
  • Metals can be recovered from the solution.

Cons:

  • The electrodes must be cleaned and maintained on a regular basis.
  • The electrodes have a short life period and must be changed often.
  • This can take a long time and cost a lot of money.

Membrane Process

Introduction

Membrane processes are the physical dispersion of particles via aqueous membranes. They work because some membranes enable particles with certain properties to flow through while inhibiting particles with different characteristics from passing through. 

With the invention of high-performance synthetic membranes in the 1960s, membranes became a practical water filtration method. Membranes for water treatment have improved, with more modern membranes created from novel materials and used in a variety of designs.

Membranes are increasingly being used to produce potable drinking water from the ground, surface, and ocean sources and improve chemical improved methods of wastewater management and desalination. Over the previous two decades, these technologies have been one of the most widely employed for water treatment. It’s a system with a lot of power

Types of Membranes

Membranes are used for the water treatment process to separate impurities from water depending on size or charge. Microfiltration, ultrafiltration, and nanofiltration are all common membranes used in the process.

Microfiltration: Microfiltration membranes have pore sizes ranging from 0.1 to 10 micrometers, which are large enough to contain bacteria, turbidity, macromolecules, colloidal, and other contaminants. These are employed in the cold sterilization of liquid food and pharmaceutical items, reducing water microorganisms, preparing water for nanofiltration and reverse osmosis, and other applications.

Ultrafiltration: Particles of a size of 0.001-0.1 m are removed using ultra-filtration. Viruses, macro proteins, antibiotics, and other substances are held in check by these membranes. These can be used to remove hazardous organic compounds from the food and beverage sectors.

Nanofiltration: Particles having a size of 0.1 nm-0.001 m are restricted by nanofiltration, allowing the water filtration from most molecules. However, low molecular weight particles are only partially restrained in the membrane.

Pros and Cons of Reactors

Pros: 

  • Exceptional performance.
  • Compact units require less room than traditional treatment methods.
  • The operation is simple.
  • Membranes can be used to separate a wide variety of pollutants.
  • Disinfection can be done without the use of chemicals.

 Cons: 

  • Fouling of the membrane,
  • Pollution of the water supply (from backwashing)
  • Membranes must be changed on a consistent basis.

          

 

Author

  • The author has done a master's in Environmental science and is currently working as chief Environmental Advisor with New Delhi State Government.

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