Environment: All process water is treated via a biological plant. From a central drain in the processing shed the process water goes to a balance tank where the biological treatment takes place. The waste water then moves on through a time specific process of aeration, clariﬁcation, ﬂocculation and settling which takes place in various tanks on the treatment plant. The final clean water is discharged to the river.
The produced sludge are then taken into filter press machine to drain out the water in it and form as cake.
The plant can process 64 cubic meters of water per hour at capacity.
Apart from complying with number of leading global customer’s Code Of Conduct (COC) audit; we are also audited and awarded certificates like BRC (British Retail Consortium), SEDEX & BSCI for ensuring working & social environment up to the expected level.
What causes pollution?
a) settle on stream bed, smothering plant and animal life
b) settle in stagnant areas forming beds of sludge which decay and cause smells
c) damage gills of fish etc
d) visually offensive especially if coloured
Organic matter: (in suspension or solution)
Oxidised by bacteria absorbing oxygen from the water killing animals and fish by suffocation
Reduce the amount of light available for plant growth, also very visible
Bleach, disinfectants, metals etc
Cause foam in fast flowing rivers
Purpose of treatment
a) to remove suspended solids
b) to oxidise organic matter
c) to remove dyes and detergents
d) to remove toxic compounds
The treatment process includes a biological stage which is susceptible to toxic compounds. If these are present in very small quantities the bacteria can oxidise or absorb them, but if there is a spillage the shock dose will kill the bacteria and destroy the treatment process.
Suspended solids – these are usually settled or sometimes floated out of the water. In our case the effluent contains so little solid matter that we do not remove it but allow it to accumulate in the biological sludge.
All bleach and dye wastes are discharged to a sump and then pumped to a balancing tank for three reasons:-
a) To smooth out sudden changes in composition as tanks are emptied in the mill
b) To eliminate peak flows;- to allow pumping at a constant rate to the treatment plant
c) To store some liquors during the week for treatment at weekend when little is discharged from the mill.
Organic matter is removed by bacteria in the activated sludge process. Some of the organics are oxidised to carbon dioxide whilst some is converted to new bacteria which is then removed as sludge.
Biological treatment is basically the conversion of organic matter in solution into something which can be easily separated from water:- carbon dioxide, a gas, bacterial cells, solids.
To work correctly the bacteria need enough oxygen and nutrients:- nitrogen and phosphorus:- for them to grow.
The biological treatment system is called the Activated Sludge Process and its operation is as follows.
The effluent is pumped at a set rate to two aeration tanks where it is mixed and aerated with activated sludge and nutrient solution. The aerators can operate at two speeds depending on oxygen demand. Control is by dissolved oxygen probe which monitor the oxygen in the tank. If this is too low the aerators switch to high speed; if to high they switch to low speed.
The mixed liquors (ML) flow from the aerators via a weir box which is adjustable in height to set the required tank level.
The liquors then pass to the settling tank where solids settle out. This sludge is scraped to the centre hopper and is then pumped back to the aeration tank. (Return Activated Sludge RAS)
The clarified water flows over the peripheral weir.
All the treatment processes produce sludge’s which must be disposed of. They are produced at a low concentration e.g. 2% solids 98% water and therefore surplus activated sludge (SAS) is thickened and then dewatered in the sludge thickening tank.
Dyes, detergents and toxics – most of these compounds, especially toxics are either absorbed or degraded by the sludge. If the toxic concentration is too high the sludge will be killed. Detergents (soaps, wetting agents, emulsifiers etc) interfere with flocculation and settlement of sludge’s. This plant includes chemical and physical processes to remove as much colour and brightener as possible. These are described later.
This treatment plant was designed to produce an effluent to meet the NRA conditions of consent to discharge to the river Blackbrook in Chinley United Kingdom.