Page 439 - Industrial Power Engineering and Applications Handbook

Switchgear and controlgear assemblies 13/41 3
effluents, it is essential to determine the physio-chemical Table A1 3.6 Recommended tolerance levels
characteristics of the effluents. For this:
SI: Parameter Recommended tolerance
Composite samples can be collected over an 8- or 24- no. level (for the disposal of
hour period at half-hour or one-hour intervals from treated effluent into inland
the regular effluent discharges such as from the pre- sur$ace waters)
treatment tanks. The volume of each sample will depend 1 Level of BOD 30 mg/l
upon the variation in the discharge flow rate. (biochemical oxygen
Grab samples can be collected from periodic discharges demand)
such as from the spray booth where the fresh water is 2 Level of COD (chemical 250 mg/l
replenished only periodically. oxygen demand)
Direct samples can be obtained from the pre-treatment 3 Presence of alkali traces Maximum up to 9.0, as
tanks, when a new bath is made and the old one is measured by pH value
drained at an interval of two or three days or so, 4 Presence of acid traces Not less than 5.5 as
measured by pH value
depending upon the amount of work. The samples so Notes:
collected should be analysed in a recognized test (a) Clean water has a pH
laboratory to ascertain the constituents of the effluents. value of I to 7.5
A typical analysis report of the samples collected (b) 1 mg/l = parts per
from a medium-sized paint shop handling about 5 MT/ million (ppm)
day of sheet-metal work, is provided in Table A13.5. (c) pH: the logarithm of
These results are only of a final discharge, and may the reciprocal of the
hydronium ion
vary from plant to plant, depending upon the amount concentration.
of work and the process of pre-treatment employed. (Hydronium ion
Although the values obtained are not alarming, they concentration of a
do require effluent treatment, as the untreated effluent solution varies on the
does not conform to the limits prescribed as standard degrees of alkalinity
tolerance level, to comply with the environmental and acidity)
legislation. Using environmental engineering practices 5 Total suspended solids 100 mgll
10 mg/l
one can obtain the desired standard levels in all 6 Oil and grease 5 mgll
I
Dissolved phosphates
parameters as in Table A1 3.6 or as may be prescribed (as P)
by the local civic authorities of a particular area. 8 Chlorides (as CI) 600 mg/l
(drinking water contains
TableA13.5 also indicates the test results of the samples around 400-500 mg/l)
of the final discharge when the effluents are treated along 9 Sulphates (as SO4) 1000 mg/l
similar lines as discussed later. The test results are well 10 Cyanides (as CN) 0.2 mgll
11
within the tolerable limits. The recommended tolerance 12 Total chromium (as Cr) 2 mg/l
Hexavalent chromium
0.1 mg/l
levels are provided in Table A13.6. Any constituent (Cr)
exceeding the prescribed limits must be properly treated 13 Zinc (as Zn) 5 mg/l
before final discharge. 14 Iron (as Fe) 3 mg/l
The recommended tolerance levels, as noted in Table 15 Total heavy metals 7 mgn
A13.6, are applicable to an industrial area where the 16 Phenolic compounds
final discharge of the treated effluent is let through a (as C6H50H) 1 mg/l
public sewer. These levels may vary, depending upon 17 Lead (as Pb) 0.1 mgll
18 Copper (as Cu) 2.0 mgll
19 Nickel (as Ni) 2.0 mg/l
Table A13.5 Average test results of effluent discharge (tank 20 Bio-assay Test 90% survival 96 hours
wash and spray booth mix of a medium-sized paint shoo
under consideration) before and after treatment Source Ministry of Environment and Forests, CPCB
SI: Pollutant Test results Tolerance the location of the plant. For sensitive or residential areas,
no. Before After level for instance, the levels may be more conservative, decided
treatment treatment by the local civic authorities. The effluent treatment will
depend upon these values.
BOD 58 mg/l 25 mg/l 30 mgll
COD 604 mgfl 242 mg/l 250 mgll
pH value 8.25 6.8 5.5-9.0 Effluent treatment and discharge of waste water
Total dissolved
solids 4208 mg/l 1950 mg/l - The appropriate method for effective effluent treatment
Total suspended is to segregate the strong wastes from the wastewater
solids 546 mg/l 25 mg/l 100 mgll and treat them separately, as shown in Figure A13.12.
Oil and grease 9 mgn 4 mg/l IO mg/l The strong wastes consist of discharges from electroplating
Phosphate as P 62.2 mg/l Nil 5 mgll plant, spray booth and spent passivation liquor etc.
Chloride as CI 1985 mgll 5 IO mg/l 600 mg/l Accordingly all the pollutants noted in Table A13.5 can
Zinc as Zn 3.5 mg/l Nil 5 mgll
be treated in the following manner: