What is Sludge in Environmental Engineering?
Sludge is a semi-solid substance formed during water and wastewater treatment that is removed by settlement. It is a substance that requires further treatment; unless this is done it may pose harm to the environment and public health.
Why further treatment is needed for sludge?
Because sludge includes; large amounts of organic matter, nurients, pathogenic microorganism, huge amount of water.
Sludge production amounts
In order to calculate the amounf of sludge produced in a conventional domestic wastewater treatment plant, dry solid matter content is assumed as roughly 0.09 kg per capita per day in wastewater treatment. For instance, for a residential area with 1.000.000 population, 90-100 tons sludge production can be expected in a day.
| Sludge | Conc.of Solids (%) | Characteristics |
| Raw Primary | 4-8 | Bad odor, gray-brown color, does not drain well on drying beds, can be dewatered mechanically |
| Anaerobic Primary Digested | 6-10 | Black color, produces gas, dewaters well on drying beds |
| Wasted Activated Sludge | 0.5-1.5 | Little or no odor, yellow-brown color, flufly, biologically active, difficult to dewater |
| Mixed Digested (Primary and Waste Activated) | 2-4 | Black-brown color, produces gas, not as easy to dewater as digested primary |
| Aerobic Digested | 1-3 | Yellow-brown color, biologically active, generally difficult to dewater |
| Waste Alum | 0.5-1.5 | Grey-yellow in color, odorless, very difficult to dewater |
