Many industries in Bangladesh have effluent discharge levels above the Ministry of Environment’s (MoE) tolerance limits for discharge into inland surface water directly, or indirectly into soil and/or small channels leading to the nearby rivers. We have found that due to a lack of compliance monitoring almost all industries are violating the standards at all times, and are polluting nearby rivers, agricultural land and soil.
Background
Tannery wastewater originates from the tanning process. The waste may be classified as continuous and intermittent flow wastes. Continuous flow wastes consists of wash water after various processes and comprises a large portion of the total waste.
Spent liquors belonging to soaking, liming, bating, pickling, tanning and finishing operations are discharged intermittently. Although these are relatively small in volume, they are highly polluting and contain a variety of soluble organic and inorganic substances.
The spent soak liquor contains soluble proteins of the hides, dirt and large amount of common salts when salted hides are processed. The spent liquor undergoes putrefaction very rapidly as it offers a good amount of nutrients and favourable environment for bacterial growth. The growth of pathogenic anthrax bacteria in this waste is also reported.
The spent lime liquor contains dissolved and suspended lime, colloidal proteins and their degradation products, sulphides, emulsified fatty matters, and also carries a sludge composed of un-reacted lime, calcium sulphide and calcium carbonate. As such, the spent lime liquor has a high alkalinity, moderate BOD, and high ammonia-nitrogen content.
The spent bate liquor contains a high amount of organic and ammonia nitrogen due to the presence of soluble skin proteins, and ammonium salts used in deliming/bating.
The spent pickling and chrome tanning waste comprises a small volume, having a low BOD, and contains traces of proteinic impurities, sodium chloride,
mineral acids and chromium salts.
Chromium is known to be highly toxic to the living aquatic organisms in the hexavalent form and somewhat less toxic in the trivalent form. Tanning salts consist of the trivalent form.
In general, tanning industry wastes are of strong colour, have high salt content, high pH, high BOD, high COD, high dissolved solids, and a presence of
sulphides, lime and chromium.
Experimental
Materials and methods
A physico-chemical analysis of tannery effluents was carried out to monitor the compliance of the effluent standards set by the MoE. Wastewater samples were taken at the point of effluent
discharge into the ecosystem or environment, which resulted in soil and river pollution.
Sample analysis
The following parameters were considered for assessment: pH, colour, odour, electrical conductivity, N-ammonia, TDS, TSS, BOD, COD, Na and total Cr content. Effluent samples collections were performed by a standard grab sampling method and its physico-chemical parameters analyses were performed by the standard method.
Measuring tannery discharge
We have so far monitored four tanneries: Progoti Leather Complex, Bengal Leather Complex, Pubali Leather Industries, and Amin Tannery Industries situated in the western part of Dhaka. Tables 1-4 show the results of physico-chemical analysis for each company. Samples were taken in 2007/08 and were accurate at the time.
Results and discussion
As stated earlier the four tanning industries located on the bank of Buriganga river, near to dense public residential area produce tannery wastes that are characterised by high BOD, COD, high suspended solids and strong colour. These wastes when discharged as such deplete the dissolved oxygen of the stream very rapidly, due to both chemical and biological oxidation of sulphur and organic compounds. A secondary pollution of the stream may occur due to the deposition of solids near the discharge point and its subsequent putrefaction. The gas evolved during this process has a typical foul odour. The chromium is toxic to aquatic life and inhibits the growth of fish in the stream as also reported by the disappearance of fish from the Buriganga River. The presence of tannins in the untreated water renders it unsuitable for use in certain industries.
Chromium contents of the tested effluent samples are also found to be higher than the industrial effluents standards fixed by the government of Bangladesh. Sulphides are also toxic to the microorganism; however they are oxidized in the sewer before their arrival at the sewage treatment plant. Presence of lime also inhibits biological action in the sewage treatment plant. Though there is no permanent treatment plant setup by any of these industries, the natural water courses and rivers are getting more polluted day by day and the self purification power of these rivers will be definitely decrease further.
Conclusion
With an increase in industries, the industrial pollution is also increasing day by day in every country including Bangladesh. According to the Indian Prevention, Control and Abatement of Environmental Pollution, no industry, operation or process shall discharge or
permit to be discharged any
environmental pollution in excess of such standards as may be prescribed. From the conducted study of all the four tanneries, it could be inferred that none of the companies comply wholly with the standards set out by
the Bangladesh Ministry of Environment.
It is hoped that better standards, with their effective implementation and monitoring mechanism, could be strategically achieved through having in-house, competent, technical, professionals with an effective monitoring mechanism rather than the current limited process of hiring consultants for standard developments, and then handing over the responsibility of implementation to other institutions, which may have similar deficiencies of infrastructure and expertise. In this instant, the Government-NGO partnership in the compliance monitoring and evaluation should be promoted.
