Wastewater quality
Composition of raw sewage
- Raw sewage contains 99.9% water and only 0.1% solids.
- Out of the solid materials, 30% are inorganic, primarily salts, and 70% are organic materials.
- The organic materials in the wastewater contain an average of 50% proteins, 40% carbohydrates and 10% fats.
- The principal role of the treatment plant is to remove these organic materials from the water.
- The solids in the wastewater are comprised of suspended materials and dissolved materials.
- The suspended materials are removed using mechanical methods while the dissolved materials are treated using biological methods as explained in the previous sections.
Average composition of raw sewage discharged into the treatment plant
The following table presents the typical characteristics of raw sewage over the last few years:
|
Parameter |
Units |
2015 |
2016 |
2017 |
|
BOD |
mg/l |
426 |
394 |
301 |
|
COD |
mg/l |
1105 |
1216 |
982 |
|
Suspended solids |
mg/l |
627 |
667 |
560 |
|
Total nitrogen |
mg/l |
91 |
87 |
93 |