Page 69 - Energy from Toxic Organic Waste for Heat and Power Generation

Toxic Waste From Leather Industries 57

Although the leather processing industry is economically significant, it
leads to negative environmental impact by producing solid waste and waste-
water effluent containing hazardous chemicals such as chromium, synthetic
tannins, oils, resins, biocides, and detergents [5,11–13].

5.3.1 Waste Water
Huge amount of water and pollutants are discharged during the entire tan-
ning process [14]. The details of water consumption for several steps and the
characteristic pollutant loads for each operation are presented in Table 5.1 [1].
Conventional pretanning and tanning processes account for nearly 90%
of the total pollution from a tannery [15]. Pretanning process results in
variations in pH and causes increase in chemical oxygen demand (COD),
total dissolved solids (TDS), chlorides, and sulfates in tannery wastewaters
[16]. The conventional dehairing process with sodium sulfide and lime ac-
counts for 84% of biochemical oxygen demand (BOD), 75% of COD, and
92% of suspended solids (SS) from a tannery [17]. The use of sodium sulfide
not only gives rise to unfavorable consequences on environment, but also
affects the efficacy of effluent treatment plants [18]. The poor uptake of
50%–70% of chromium during commercial chrome tanning method results
in material wastage on one hand and creates ecological imbalances on the
other [19]. The posttanning process also results in modifications in TDS,
COD, and heavy metal pollution significantly [20]. Highly polluted sedi-
ments resulting from discharge of chemicals adversely affect the ecological
functioning of waterbodies [21].

5.3.2 Solid Wastes
A great deal of sludge generated from the tannery plants [22] renders the
solid waste management system highly inactive due to nonbiodegradabil-
ity of the tanned leather [23,24]. Leather itself is slow biodegradable and
treatment of different chemicals during tanning process makes it resistant
toward chemical, thermal, and microbiological degradation [25]. This, in
turn, affects the agro-based activities and degrades groundwater system [26].
These wastes are a threat to ecology and aquatic system in vicinity of tan-
nery plants [27].

5.3.3 Volatile Organic Compounds
Pollutants such as ammonia, hydrogen sulfide, volatile hydrocarbons, amines,
and aldehydes are emitted to the atmosphere from tannery plants as efflu-
ents [28]. Ammonia emissions may occur during deliming, unhairing, or