industry and environment - DTIE

Chemicals management
Liquid waste
Wastewater quality and quantity vary considerably
(e.g. wastewater per tonne of dye produced is
very low compared with wastewater per tonne of
dye intermediate produced). In the case of major
dye intermediates, specific wastewater generation
is about 15-20 m 3 /tonne of product. The main
sources of wastewater generation are:
◆ mother liquor or filtrate streams from filtration
operations;
◆ wastewater streams from washing of filter cake
to remove salt impurities or residual filtrate adhering
to the cake;
◆ leakage and spillage;
◆ floor washing in the work area.
Typical characteristics of wastewater from this
sector are shown in Table 1.
Effluent discharged from this sector is highly
acidic. It contains toxic compounds, many of
which are carcinogenic. They can be very hazardous
to human health and the environment.
This is due to the presence in the wastewater of
benzene, naphthalene, and other nitro-aromatic
based compounds used as raw material in the production
of dye intermediates. Due to excessive
acid and alkali use, the wastewater also contains
high concentrations of inorganic salts, resulting in
high concentrations of total dissolved solids
(TDS). Because of the high level of TDS and toxic
aromatic compounds, effluent treatment is very
difficult and expensive.
Under the regulations prevailing in India, there
is currently no industry-specific effluent standard
for the dye industry. The general standard therefore
applies. According to this standard, effluent
discharged by an industrial unit must meet the
parameters in Table 2.
Management of liquid waste
Before 1994, many small and medium-sized units
in this sector did not treat their wastewater. It was
discharged directly to nearby surface water. Large
units and some medium-sized ones carried out
primary treatment, but almost none of these units
met pollution norms.
Following strict regulatory action, and intervention
by the High Court and Supreme Court,
industries began detailed wastewater treatment.
Today all units carry out primary wastewater treatment;
some also have secondary and tertiary treatment
systems. Nevertheless, it is still impossible
to meet the prescribed Pollution Control Board
norms. The reasons for this are:
◆Industrial units (especially if they are small-scale)
do not have enough land area to construct a treatment
plant with a capacity of about 50,000-
100,000 litres/day. Most plants are underdesigned;
◆ Treatment costs are very high. Units that are
small-scale economically cannot afford treatment;
◆ The wastewater is very difficult to treat;
◆ The expertise needed for proper treatment is not
available locally;
◆ Frequent product changes (based on demand)
and poor process control at the production plant
change effluent characteristics over time, thus disturbing
the treatment system.
End-of-pipe (EOP) treatment is a control strategy
to protect the environment from the
impact of waste and emissions discharged from
industries. The EOP treatment strategy incorporates
treatment of the waste and emissions
generated to bring them to a particular level
(considering the assimilative capacity of the
receiving bodies) before discharge. The EOP
strategy has existed since the establishment of
India’s Pollution Control Boards and the introduction
of the Air and Water Pollution Prevention
and Control Acts.
The Government and Industry Associations
have decided to build common effluent treatment
plants (CETPs) for primary-treated industrial
wastewater. The government has also taken steps
to fund the CETP projects, 3 as well as research
aimed at reviving the use of natural dyes, extension
of MODVAT 4 benefits to pollution control
equipment and other activities. It has also initiated
a ban on 190 textile dyes (in view of the German
ban on azo dyes) and emphasis is being given
to substitute dyes. Similarly to the CETP initiative,
steps need to be taken in the DDI industry
Table 1
Typical characteristics of wastewater
from dye and dye intermediate
production
Parameter
Value
pH < 1
Chemical oxygen demand
(COD)
50,000-1,00,000 mg/litre
Total dissolved solids
(TDS)
15,000-2,00,000 mg/litre
Ratio of biochemical
oxygen demand (BOD)/