Metals in wastewater and effluents
- The Association tests for metals concentrations at various stages of treatment.
- Tests for metals are performed on the raw sewage, effluent and sludge by an outside laboratory.
- The source of metals in raw sewage is usually industrial wastewater discharged into the sewage collectors of the cities in the Association’s service area.
- The wastewater treatment plant is designed to treat organic materials and nitrogen in the wastewater and is not designed to treat metals in the raw sewage.
- Some of these metals may undergo chemical reactions during treatment or bind with larger molecules, both organic and inorganic. Furthermore, some of these metals may undergo physical processes of adsorption, settlement and accumulation in sludge.
- It is important to emphasize that high concentrations of metals in raw sewage may harm treatment processes of the wastewater, which are based primarily on bacterial action that is sensitive to the presence of heavy metals.
- According to the results of analyses of the metals in wastewater entering the treatment plant, there are no deviations in levels permitted according to public health regulations.
- Results of analyses of heavy metals in plant effluents and sludge (see the attached table) show that the concentration of metals in these effluents is very low since most of the metals reaching the treatment plant in the raw sewage are absorbed into the sludge during treatment and are removed with the sludge.
Metals in treatment plant effluents (annual averages)
|
Parameter |
Units |
2015 |
2016 |
2017 |
Standard |
|
Silver |
mg/l |
0 |
0 |
0 |
– |
|
Arsenic |
mg/l |
0 |
0 |
0 |
0.25 |
|
Cadmium |
mg/l |
0 |
0 |
0 |
0.025 |
|
Chromium |
mg/l |
0 |
0 |
0 |
0.25 |
|
Copper |
mg/l |
0 |
0 |
0 |
0.5 |
|
Mercury |
mg/l |
0 |
0 |
0 |
0.005 |
|
Nickel |
mg/l |
0.007 |
0 |
0 |
0.5 |
|
Lead |
mg/l |
0 |
0 |
0 |
0.25 |
|
Zinc |
mg/l |
0.09 |
0.07 |
0.032 |
5 |