The effluent water was collected from 43 processing units and treated by the following stages.
Objective screens are provided to remove relatively large solids to avoid abrasion of mechanical equipments and clogging of hydraulic system.
The collection tank collected the effluent water from the screening chamber and stored it and then pumped it to the equalization tank. The effluents are not having similar concentrations at all the time; the pH vary time to time. Standard pH is greater than 10. The effluents are stored from 8 to 12 hours in the equalization tank. This results in a homogenous mixing of effluents by air circulation and helps in neutralization. In addition, it eliminates shock loading on the subsequent treatment system. Continuous mixing also eliminates settling of solids within the equalization tank.
Coagulants are added to the effluents. They are
Lime (800-1000 ppm) – To raise the pH 8-9
Ferrous sulphate (200-300 ppm) – To remove colour
Polyelectrolyte (0.2 ppm) – To settle the suspended matters
Ferrous Sulphate and Lime react with dyes & chemicals to separate them from water to coagulate them. Polyelectrolyte helps to coagulate quickly by enlarging the molecules. Coagulated sludge is removed in 1 hour interval. There are FRB sheet (plastic fiber) which keeps the coagulated sludge in uniform distribution.
Water is pumped to Ph control tank to maintain neutral pH. Normally pH range is 6.5-9.0.HCl or NaOH is mixed when required.
In the clarriflocculator, the water is circulated continuously through fibre sheet contains bacteria. Overflowed water is taken out to the aeration tank. The solid particles are settled down and collected separately and dried. Flocculation provides slow mixing that leads to the formation of macro flocs, which then settles out in the clarifier zone. The settled solids i.e. primary sludge is pumped into sludge drying beds.
The water was passed like a thin film over the staircase arrangement. Here the water got direct contact with the air to dissolve the oxygen into water. The main function of this tank is to control BOD(Biological Oxygen Demand), COD(Chemical Oxygen Demand) and DO(Dissolved Oxygen) values. The required amounts are
BOD→less than 50mg/l
COD→less than 200mg/l
DO →4.5-8.0 mg/l
Bacteria consume the effluents and control BOD, COD and DO. Bacteria is feed with urea and DAP
( diammonium phosphate).
The clarifier collects the biological sludge. The overflowed water is called as treated effluent and it is disposed out. The outlet water quality is well within the tolerance limit.
The treated water may contain some infestations. To remove the water is treated with Sodium oxychloride.
The inlet water consists of 60% water and 40% solids. The effluents are passed through the centrifuge. Due to centrifugal action, the solids and liquids are been separated. The sludge thickener reduces the water content in the effluent to 40% water and 60% solids. The effluent is then reprocessed and the sludge is collected at the bottom.
Primary and secondary sludge was dried on the drying beds. Here the sludge was subjected to solar evaporation.
Sludge management is the final stage in textile effluent treatment process. Huge amount of sludge is generated after textile effluent treatment. The sludge is collected and packed in polythylene bags and finally covered in the water proof sheets. Sludge is disposed off in an offsite designated landfill area. The sludge are sometimes used as fertilizers and mostly fuel.