The pulp and paper industry use pulp as raw material, which also produced from various kind of cellulosic materials..
The pulp and paper mill waste contains high COD and color. COD/BOD ratio of wastewater is very high because of presence of lignin in wastewater.
In this industry manufacturing in two phase one is pulp making and second is paper making from pulp.
1st Phase Pulp making
In pulp making cellulosic material digested at high pressure and temperature with digestive chemicals in closed vessel.
spent liquor produce from digestion is call "Black liquor"
Black liquor high in lignin and COD generate by other chemicals.
Black liquor treated separately for recovery of material.
The cellulosic fiber seperated from liquor is washed aand dewatered.
The washed cellulosic fibres bleach with chlorine, causitc and hypochlorite.
2nd Phase of Manufacturing Process
Bleached pulp is sent for paper manufacturing., where it mix with various filler material like alum. talc etc.
After mixing it beaten in separate tank.
After beating pulp is refined.
Refined pulp is diluted for paper making pass through various screen to remove lumps and knotes. After that pass through numbers of rollers where final product generate.
Wastewater Treatment
(A)Recovery from Black liquor
black liquor concentrated by evaporation and than incinerated with addition of sodium sulphate. The organic like lignin, resin burnt out and smelt dissolved in water resulting liquid known as "Green Liquor". Lime is added added to liquor to form "White Liquor". mud generated in this process is calcium carbonate. calcium carbonate is calcined by burning which forms calcium oxide.which reuse to convert green liquor to white liquor . generated White liquor sent to digester.
(B) Wastewater Treatment
Where recovery of black liquor not possible sen for water treatment.
first wastewater equalize in equalizing tank or collection tank from there taken for first physical treatment
Physical Treatment
that is clarification/ settling where 70 to 80 percent of .suspended solids removed. BOD removal is is around 30 to 40 percent. and COD removal around 50 percent. Here Surface loading rate 25 Cum/Sq.M/Day and retention time is around half hour. maintain.
Biological Treatment
For wastewater of pulp and paper mill is aerated lagoon where nearly 80 to 90 percent BOD reduction can be achieve.It is very essential to maintain BOD:N:P ratio 100 :5:1.
Activated Sludge Process also found effective.
Tertiary Treatment
It is use for color removal Activated Carbon treatment is most effective treatment for color removal Activated Carbon remove 90 percent of color at 3 pH it is essential maintain pH, if activated carbon use for color removal in that case it provide in before primary treatment and wastewater is neutralize for further treatment you can use same treatment in last but you require to neutralize before final disposal
Treat wastewater of pulp and paper mill can be use for irrigation purpose.
https://www.youtube.com/watch?v=UOn0j1p7kf4