Mastering water quality parameters for wastewater ensures community health

Water quality parameters for wastewater

Substrate water quality parameters

Effluent water quality parameters

In-stream water quality parameters

Biochemical oxygen demand (BOD):

The amount of oxygen needed by bacteria to break down organic material in water. High BOD levels indicate more pollutants, which can deplete oxygen needed by aquatic life, thus harming our waterways. 

Influent BOD for municipal wastewater is typically 100-500 mg/L and significantly higher if strong industrial BOD sources are present.

BOD can be between 0-30 mg/L in treated municipal sewage.

In-stream water with BOD up to 5 mg/L is considered moderately clean. 

Chemical oxygen demand (COD):

The total number of pollutants in the water. It determines the overall cleanliness of water and the effectiveness of treatment processes. 

Influent COD for municipal wastewater is typically two to four times higher than BOD and potentially higher if significant industrial COD sources are present. 

COD in waters receiving effluents can be greater than 200 mg/L. 

COD concentrations in unpolluted surface waters are typically 20 mg/L or less. 

Total suspended solids (TSS):

The number of particles in water that affect clarity and quality. High TSS can cloud water, hinder aquatic plant growth and complicate water treatment, affecting aesthetics and ecosystem health. 

Influent TSS for municipal wastewater is typically 100-500 mg/L and significantly higher if strong industrial TSS sources are present.

TSS in treated effluents is typically less than 30 mg/L.

In-stream TSS levels vary by season, water flow and weather events. In most situations, in-stream water appears clear with TSS concentration of 20 mg/L or less. 

Total Kjeldahl nitrogen (TKN):

The total nitrogen in water. It’s vital for assessing how well our wastewater treatments control nitrogen, which in excess can lead to eutrophication – over-fertilization of water bodies that harms aquatic life. 

The TKN content of influent municipal wastewater is typically 15-75 mg/L. 

Total nitrogen (TN) is the sum of TKN, ammonia and nitrate-nitrite. Effluent TKN typically ranges from 2-30 mg/L, depending on the effluent permit limits. 

Nitrogen concentrations in streams and rivers should not exceed 0.3 mg/L.

Total phosphorus (TP): 

The measure of phosphorus in the water. High levels can cause algae blooms, which deteriorate water quality and disrupt aquatic and human life. 

Wastewater influent can contain 3-20 mg/L of total phosphorus. Values in the 6-7 mg/L range are most common.

TP limit for WWTPs discharging into impaired streams and rivers is typically 1.0 mg/L or less. 

The natural background levels of total phosphorus in-stream are generally 0.1 mg/L or less, depending on the stream. 

pH:

The level of acidity or basicity of the water. If within the 6-9 range, wastewater can support healthy aquatic ecosystems when discharged into natural bodies of water.

The acceptable pH range for substrate, effluent and in-stream is 6-9. 

Fecal coliform:
The coliforms and fecal streptococci are two bacteria groups used as indicators of sewage contamination of a waterway. E.coli is a subgroup of fecal coliform. 

NPDES permits typically specify that the fecal coliform bacteria limit in effluent wastewater should be 400 colonies per 100 ml. 

Chlorine residual:
It refers to the low level of chlorine remaining in treated water after a certain period or contact time after its initial application. 

Free chlorine residual of 0.5 mg/L in wastewater effluent ensures sufficient disinfection. 

Dissolved oxygen: It refers to oxygen concentration incorporated in water. Oxygen enters water through direct absorption from the atmosphere. 

DO content in domestic wastewater influent is typically 1 mg/L or less. 

A dissolved oxygen (DO) level of 2.0 mg/L is maintained to ensure efficient wastewater treatment. 

DO in surface waters may vary from 0-18 mg/L.