Page 26 - Industrial Wastewater Treatment, Recycling and Reuse

Industrial Wastewater Treatment, Recycling, and Reuse: An Overview 9

Figure 1.6 Water intensive industries most critical for water recycling and reuse.

3
amount of water up to 1000 m per ton of product and is one of the most
water-intensive in the industry sector (Chaphekar, 2013). Thus, among the
list of waste-generating industries, some of the most hazardous wastewater
comes from sectors such as mining, pulp mills, tanneries, refineries, sugar
production/distillery, and pharmaceuticals. The food and agriculture indus-
tries produce high biological oxygen demand (BOD) wastewaters. Typi-
3
cally, food industries generate 0.6 to 20 m wastewater/ton of product
such as bread/butter/milk or fruit juice. This is an order of magnitude less
than the chemical/petrochemical industries. The nature of pollutants and
levels of BOD/chemical oxygen demand (COD) also vary drastically in
these industry classes.
There have been process changes in the industry sector to minimize
wastewater generation. However, many times, this alters the quality of
wastewater so that it contains more refractive pollutants than the previous
process; for example, in the distillery industry, the conventional process gen-
erates 15 L of wastewater per liter of alcohol. With a process modification,
the industry can produce much less wastewater, to the tune of 5 L per liter of
alcohol; however, the BOD levels are significantly altered: 90,000 mg/L
compared to 40,000 mg/L previously. It is necessary that the process
changes be tuned not just to lower wastewater generation but also to reduce
the concentration of refractory pollutants in the wastewater to make it more
amenable to treatment.