PHYSIO CHEMICAL TREATMENT

Particles of various sizes can be found in waste water. As a result, various treatment procedures are required to make recycled water safe for consumption, disposal, and compliance with severe regulatory requirements. The treatment efficiency can also be determined by particle size.

For removing bigger and visible contaminated particles, separation by flotation, filtering, or gravitational influence is usually highly useful. Physicochemical treatment procedures, on the other hand, are more effective for colloidal particles that can easily filter through and have similar electrostatic surface charges that prevent coagulation. Chemicals are used in physicochemical treatment to change the physical state of colloidal particles, making them more stable and coagulable for further treatment or filtering. These therapy procedures have been utilised in conjunction with biological treatment methods for over a century. With increased efficiency and lower prices, these approaches have been effectively used for industrial water treatment and conditioning of waste water sludge as part of pre-treatment. The biodegradation capacity of organic material in waste water can be significantly influenced by physicochemical treatment.

A physicochemical treatment consists of a series of processes that can be carried out in a single unit or in separate units. Coagulation, flocculation, and sedimentation are the three processes involved. The overall performance of a physicochemical treatment procedure can be influenced by a variety of factors and waste water physicochemical qualities. As a result, laboratory tests are commonly performed to discover properties that can be used to modify the whole treatment procedure in terms of timeframes, chemical kinds, and dosage, among other things.

The coagulation procedure involves adding coagulant to the waste water and rapidly mixing it to neutralise the charges (typically negative) on the colloid surfaces. Some of the most often used coagulants include ferric chloride, aluminium polychloride, ferric sulphate, aluminium sulphate, iron polychloride, and sodium aluminate, which are used in varied amounts depending on the quality of waste water, such as home, agricultural, or industrial. Coagulation and quick mixing with brief contact times aid in the destabilization of colloid surfaces, allowing them to clump together and prepare for the next step of flocculation.

During the slow mixing phase, floculation involves gathering of previously created flocs or clumps. This aids flocs in developing more volume and density, which will assist them prepare for sedimentation. Flocculants are chemicals that aid in the process of flocs coming together and increasing in density and volume. Organic flocculants are made from algins (a seaweed derivative), starch, or cellulose (a plant derivative) and are usually less effective. Synthetic flocculants, such as polyelectrolytes, on the other hand, are extremely effective. They are synthetic macromolecules that are water soluble and may have charges on them. Lower doses are more effective due to their high efficiency, however excessive dosage can be damaging to the entire process while also increasing costs. A gradient is applied during the flocculation stage so that the next stage of sedimentation can begin. Slow mixing can occur spontaneously owing to Brownian movement in water (perikinetic flocculation) or through artificial agitation of waste water to allow for extended contact durations (orthokinetic flocculation).

The final stage of sedimentation is crucial for separating liquid from solids that form as a result of previous coagulation and flocculation processes. Depending on the state of the waste water at this point, settlers with varied rates (low, medium, or high) are utilised.

Chlorine, hydrogen peroxide, and ozone can also be used for waste water treatment to remove hazardous biological agents and poisonous compounds, depending on the type of contaminants. Chlorine is particularly effective at oxidising harmful cyanide compounds (such as those produced in the mining and metal industries) and converting them to carbon dioxide and nitrogen. Ozone and hydrogen peroxide, on the other hand, can be utilised to effectively degrade organic compounds in waste water.

Physicochemical treatment can eventually remove total suspended solids, biological oxygen demand (BOD), chemical oxygen demand (COD), nutrients like nitrogen and phosphorus, heavy metals, and even biological agents like helminthis eggs, virus, and protozoa from waste water in variable percentages.