Pollution Load and Concentration
In most industries, wastewater effluents result from the following water uses:
- Sanitary wastewater (from washing, drinking, etc.)
- Cooling (from disposing of excess heat to the environment)
- Process wastewater (including both water used for making and washing products and for removal and transport of waste and by‐products)
- Cleaning (including wastewater from cleaning and maintenance of industrial areas)
Excluding the large volumes of cooling water discharged by the electric power industry, the wastewater production from urban areas is about evenly divided between industrial and municipal sources. Therefore, the use of water by industry can significantly affect the water quality of receiving waters. The level of wastewater loading from industrial sources varies markedly with the water quality objectives enforced by the regulatory agencies. There are many possible in‐plant changes, process modifications, and water‐saving measures through which industrial wastewater loads can be significantly reduced. Up to 90% of recent wastewater reductions have been achieved by industries employing such methods as recirculation, operation modifications, effluent reuse, or more efficient operation. As a rule, treatment of an industrial effluent is much more expensive without water‐saving measures than the total cost of in‐plant modifications and residual effluent treatment. Industrial wastewater effluents are usually highly variable, with quantity and quality variations brought about by bath discharges, operation start‐ups and shutdowns, working‐hour distribution, and so on. A long‐term detailed survey is usually necessary before a conclusion on the pollution impact from an industry can be reached. Because of the wide variety of industries and levels of pollutants, we can present a snapshot view of the characteristics. The values of typical concentration of conventional pollutants (BOD5, COD, TSS) and pH for different industrial effluents are given in Table 3.3. A similar sampling for nonconventional pollutants is given in Table 3.4.
Table 3.3 Comparative strengths of industrial wastewaters for conventional pollutants.
| Type of waste | BOD5 (mg/l) | COD (mg/l) | TSS (mg/l) | pH |
| Apparel | ||||
| Cotton | 200–1000 | 400–1800 | 200 | 8–12 |
| Wool scouring | 2000–5000 | 2000–5000a | 3 000–30 000 | 9–11 |
| Wool composite | 1 | — | 100 | 9–10 |
| Tannery | 1000–2000 | 2000–4000 | 2 000–3 000 | 11–12 |
| Laundry | 1600 | 2700 | 250–500 | 8–9 |
| Food | ||||
| Brewery | 850 | 1700 | 90 | 4–8 |
| Distillery | 7 | 10 | Low | — |
| Dairy | 600–1000 | — | 200–400 | <7 |
| Agriculture | ||||
| Citrus | 2000 | — | 7 000 | Acid |
| Pea | 570 | — | 130 | <7 |
| Slaughterhouse | 1500–2500 | — | 400–1 000 | 7–8 |
| Potato processing | 2000 | 3500 | 2 500 | 11–13 |
| Sugar beet | 450–2000 | 600–3000 | 800–1 500 | 7–8 |
| Farm | 1000–2000 | — | 1 500–3 000 | 7.5–8.5 |
| Poultry | 500–800 | 600–1050 | 450–800 | 6.5–9 |
| Industries | ||||
| Pulp; sulfite | 1400–1700 | — | Variable | |
| Pulp; kraft | 100–350 | 170–600 | 75–300 | 7–9.5 |
| Paperboard | 100–450 | 300–1400 | 40–100 | |
| Strawboard | 950 | — | 1 350 | |
| Coke oven | 780 | 1650a | 70 | 7–11 |
| Oil refinery | 100–500 | 150–800 | 130–600 | 2–6 |
a COD as KMnO4 mg O2/l.
Leave a Reply