Turbidity: size particle in to a larger one by

Turbidity:

In simple words turbidity is basically the cloudiness or
muddiness of water. Turbidity occur due to suspended particles, bacteria,
dissolved organic substances and suspended clay particles. In case of textile effluent,
the presence of suspended solids either in dissolved or in undissolved state
can caused turbidity. Untreated water remains turbid for a longer period as
fine particle takes days or weeks to settle down.

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Coagulation:

Coagulation is a technique of converting smaller size
particle in to a larger one by sticking them together chemically. Water
characteristics is concerned as the coagulants used either work efficiently or
not depending upon the effluent water, mainly used coagulants are alum, ferric
chloride, poly aluminium chloride, the process is carried out through jar test
along with correct dosage through feed pump calibration. The effluent water is
added after the coagulant mixed for some time with static mixer, proper mixing
is required for coagulation as the process kicks start as soon as the chemicals
are added. The effluent can either mixed through motorised paddle or it may
splash in to the jar.

Flocculation:

Flocculation is a three-stage process and activates when
particulates start sticking together more clearly. First stage is fastest as
compare to the second and third stage. The process uses motorised paddle for
mixing sometimes in opposite direction to resist the breakdown of heavy
particulates during stirring. During sedimentation heavy particulates are
settle down at the bottom. The process is proceeding through filtration. At the
end of flocculation daily turbidity reading is taken.

Dye characteristics:

Capacity to absorb light in
visible region is a common property for all dyes. The reductive cleavage of azo
linkages can result in the creation of toxic amines in the effluent.
Anthraquinone-based dyes consist of bonded aromatic structures and are more
resilient to degradation. Basic dyes are applied widely in small-scale
industries such as textiles and carpets 3,4. The most challenging are anionic
dyes because they are intensely coloured, water-soluble, and show acidic
properties.

dyes

Ionic character

chromophore

In aqueous solution

 

acid

anionic

azo groups or anthraquinones.

Net negative charge (sulphonate and/or carboxylic group)

 

reactive

anionic

azo groups or anthraquinones.

Net negative charge (sulphonate and/or carboxylic group)

 

direct

anionic

azo groups or anthraquinones.

Net negative charge (sulphonate and/or carboxylic group)

 

basic

cationic

 

Net positive charge

 

dispersed

non-ionic

azo groups or anthraquinones.

 

 

 

Water soluble reactive dyes:

Reactive dyes are widely used in textile industries because
od wide range of wet fastness, colour range. Straightforward application and minimum
energy consumption. The structure of reactive dye molecule consists of four
characteristics:

·        
Chromophoric group

·        
The reactive group

·        
Bridging group

·        
Solubilising group

 

They all contribute towards the substantivity for cellulose
fibre. Reactive group can react through nucleophilic substitution or
nucleophilic addition reaction. During high alkaline condition in reactive dyes
a hydrolysed reaction take place which result in non-fibre reactive form, which
cannot covalently bond with the substrate and end up in dyebath effluent.

Adsorption:

Adsorption is a separation process and a technique for water
refinement application such as decolourisation from dye waste water.
Decolourisation is done by ion exchange and adsorption and is affected by many
physio-chemical factors that includes particle size, pH, Temperature, contact
time, sorbent surface area and sorbent interaction. The low-cost absorbent is
typically   as peat, bentonite, steel
plant slag, fly
ash, china clay, maize cob, wood shavings and silica for colour removal. These
absorbents are used in large amount because of their low absorption capacities.

Mechanism:

The term adsorption expresses a
procedure where in a material is concentrated at a solid surface from its
liquid or gaseous environments. Two types of adsorption techniques are there: Phys
sorption “If the attraction between the solid surface and the adsorbed
molecules is physical in nature, the adsorption is referred to as physical
adsorption wherein the attractive forces are weak van der Waals forces,
resulting in reversible adsorption”. Chemisorption “has higher strength of
chemical bonding between adsorbed molecules and the solid surface, making it
difficult to
remove the chemisorbed species from the solid surface.”

Adsorption technique is used to
remove such pollutants that are not easily biodegradable. the process
completion take place in three steps:

1)     
diffusion of dye molecules through the solution
on to the surface of the adsorbent. (affected by dye concentration and
agitation)

2)     
adsorption of dye molecules on the surface of
the material through molecular interactions (dependent on the nature of dye
molecule)

3)     
diffusion of dye molecules from the surface to
the interior of the adsorbent material.