When Lead Acid Batteries are replaced, they contain
spent acid with some lead dissolved in it. These used batteries are soldin
the open market to lead recyclers where they are drained before being put
into the process of recycling. Further in manyunits, plastic containers of
the batteries, after cutting and opening, are washed to remove any lead in
them. The drained acid alongwith any washing effluent of the plastic scrap
comprises of the effluent that needs treatment at the Effluent
TreatmentPlant (ETP). This ETP is also commonly called Acid Neutralisation
System.If unchecked, these untreated effluent will seep in to land and would
lead to soil contamination, pollution in ground watertable and their runoff
may also lead to pollution of nearby water sources. Hence, their proper
treatment before disposal isnecessary.
Effluent from such used batteries mainly consists
of sulphates and sulphides of lead, small quantity of lead and
dilutedsulphuric acid. Further effluent from container washing which mainly
contains small quantity of lead is also fed to the ETP.This effluent has low
pH values. pH balancing agent (caustic or lime in this case) is added to
adjust the pH and also for coagulation. The effluent is then mixed for
Flocculation. The floccs so formed are settled and dewatered on a Sludge Bed
(orthrough Filter Press). Treated effluent after this is further polished
using filters. While treated water may be disposed or usedas permitted by
law, sludge is recharged into furnaces for recycling and reclamation of
lead*.
An Effluent Treatment Plant for lead recycling
units can be designed as a Batch Type unit or as a Continuous Unit. This
mainlydepends on the quantity of effluent to be handled. While smaller
quantities can be treated in batches, quantities above 10kl/day are to be
treated in Continuous
Operating Units
- Batch Type Unit
- Continuous Treatment Unit
Effluent from used batteries and from container
washing is stored in a receiving tank. It is then lifted with the help of an
acidproof pump and fed to a Clari-flocculator. Required dosing of alkaline
additive is mixed in fresh water in a separate dosing tankand also fed to
this Clari-flocculator. The Clari-flocculator is a PVC lined cylindrical
tank in mild steel construction. It has anelectro-mechanized stirrer for
mixing of the effluent with dosing chemical. It has conical bottom with
drain valve. Effluent isfed from the top and after requisite dosing, is
agitated and mixed. This leads to neutralization, coagulation and
thereafterflocculation. Once mixing is stopped and floccs are formed they
are allowed to settle at the bottom of the conical tank.
After Characteristics of Effluent before and after Treatment (*However,
where only spent acid is fed into the ETP, sludge generated is in the form
of sodium sulphate or calcium sulphatewith lesser quantities of lead will be
dewatered and stored as hazardous waste instead)
- pH 3.0 - 4.0 6.5 - 8.5
- Suspended Solids 600 - 800 mg/l < 50 mg/l
- Lead 30 - 40 mg/l < 0.1 mg/l
some time, treated effluent is drained from the side of the tank.
Sludge is disposed through the bottom of the tank fordewatering to either
Sludge Beds or to Filter Press. Treated effluent is passed through a series
of Polishing Filters (a set of Pressure Sand Filter & Activated Carbon
Filter) beforedisposal. This improves upon the characteristics of the
treated effluent.This is called a Batch type unit as the Clari-flocculator
is designed to process effluent of a particular capacity in one
operationcycle and no more. After it is completely treated and drained, a
second batch of effluent can be treated.
In a Continuous type unit, effluent is consistently fed into the system and
is treated continually. Hence, it is suggested fortreatment where higher
capacities of effluent is involved. Effluent from used batteries and from
container washing is stored in a receiving tank. It is then lifted with the
help of an acidproof pump and fed to a Flocculator. Required dosing of
alkaline additive is mixed in fresh water in a separate dosing tank andalso
fed to this Flocculator. The Flocculator is a PVC lined tank in mild steel
construction. It has an electro-mechanized stirrerfor mixing of the effluent
with dosing chemical. It has conical bottom with drain valve. Effluent is
fed from the top and afterrequisite dosing, is agitated and mixed. This
leads to neutralization, coagulation and thereafter flocculation.Effluent
with floccs is passed to a Tube Settler. It is a PVC lined tank in mild
steel construction. Hexagonal PVC settling mediais fitted in this tank.
Effluent is allowed to settle here and as a result, the floccs settle on the
PVC media provided and arepassed to the conical bottom of the settler.
Sludge is disposed through the bottom of the tank for dewatering to either
Sludge
Beds or to Filter Press.
Treated effluent is passed through a series of
Polishing Filters (a set of Pressure Sand Filter & Activated Carbon
Filter) beforedisposal. This improves upon the characteristics of the
treated effluent.
Note: Due to continuous up-gradation in technology,
specified & projected values may differ in actual products
