How Water Quality Is Measured And Assessed in Sewage treatment plant?

How Water Quality Is Measured And Assessed in Sewage treatment plant?

9 major water quality chemical indicators and their meanings for sewage treatment

1.BOD5

Average sewage concentration/(mg/L)       The abbreviation of biochemical oxygen demand, which indicates the amount of dissolved oxygen consumed by microorganisms to oxidize and decompose organic matter in 5 days at 20°C. The first stage is carbonization (C-BOD), and the second stage is digestion (N-BOD).

The significance of BOD: a. The amount of organic matter decomposed by biological oxidation; b. Reflects the degree of pollution of sewage and water bodies; c. Determines the effectiveness of treatment plants; d. Used in treatment plant design; e. Sewage treatment management indicator; f. Emission standard indicator; g. Water quality standard indicator.

2.CODMn / CODCr

Average concentration of sewage/(mg/L)

Abbreviation for chemical oxygen demand (CHD), indicating that the oxidants are KMnO4 and K2Cr2O7. COD determination is simple and fast, not limited by water quality, and can be used to determine industrial wastewater containing biological toxicity. It is a substitute indicator for BOD. It can also be regarded as the amount of reducing substances.

CODCr can be approximately regarded as the total amount of organic matter. The CODCr-BOD difference represents the organic matter in the sewage that is difficult to be decomposed by microorganisms. The BOD/CODCr ratio represents the biodegradability of the sewage. When BOD/CODCr ≥0.3, the biodegradability of the sewage is considered to be good; when BOD/CODCr ＜0.3, the biodegradability of the sewage is considered to be poor and biological treatment is not suitable.

3.SS

Average concentration of sewage/(mg/L)

Suspended soild is abbreviated as suspended soild. The suspended soil in water is measured by passing through a 2mm sieve and retained by a glass fiber filter paper with a pore size of 1μm. Alternating substances are contained in both the filtrate (soluble substances) and the retained suspended soil, but most people believe that colloidal substances are retained by filter paper like suspended substances.

4.TS

Average concentration of sewage/(mg/L)

Total solid is the abbreviation of the amount of water sample left after evaporation and drying. The amount of dissolved matter is equal to the amount of evaporation residue minus the amount of suspended matter.

5. Soda ash content (VTS) (VSS)

Average concentration of sewage/(mg/L)

The evaporation residue or the suspended matter volatilized at 600±25 for 30 minutes at high temperature represents the amount of organic matter (the former is VTS, the latter is VSS). The difference in the amount of evaporation residue after burning is called the burning residue, which represents the inorganic part.

6. Total nitrogen Organic nitrogen Ammonia nitrogen Nitrite nitrogen Nitrate nitrogen

Average concentration of sewage/(mg/L)

Nitrogen is cyclically converted in various forms in nature. Organic nitrogen such as protein is hydrolyzed into amino acids, which are decomposed into ammonia nitrogen under the action of microorganisms. Ammonia nitrogen is converted into nitrite nitrogen (NO2-) and nitrate nitrogen (NO3-) under the action of nitrifying bacteria; in addition, NO2- and NO3- are converted into N2 under the action of denitrifying bacteria under anaerobic conditions.

Total nitrogen = organic nitrogen + inorganic nitrogen

Inorganic nitrogen = ammonia nitrogen + NO2— + NO3—

Organic nitrogen = protein nitrogen + non-protein nitrogen

Kjeldahl nitrogen = organic nitrogen + ammonia nitrogen

Nitrogen is an indispensable material element for bacterial reproduction. When the amount of nitrogen in industrial wastewater is insufficient, biological treatment requires artificial nitrogen supplementation; on the contrary, nitrogen is also one of the elements that cause eutrophication pollution in water bodies.

7. Total phosphorus Organic phosphorus Inorganic phosphorus

Average concentration of sewage/(mg/L)

There is a lot of phosphorus in feces, detergents, and fertilizers. There are inorganic phosphorus salts such as phosphates, polyphosphates, and polyphosphoric acid, and organic phosphoric acid compounds such as phospholipids in sewage. Phosphorus, like nitrogen, is also an element necessary for sewage biological treatment. Phosphorus is also one of the elements that cause eutrophication pollution in closed water bodies.

8. PH value

Average value of sewage   6.5~7.5         The PH value of domestic sewage is about 7. The PH value of industrial wastewater discharged with strong acid or strong alkaline will change; abnormal PH value or large PH value change will affect the biological treatment. In addition, when using physical and chemical treatment, PH value is an important operating condition

9. Alkalinity (CaCO3)

Average concentration of sewage/(mg/L)

Alkalinity indicates the ability of sewage to neutralize acid, usually expressed as CaCO3 content. Sewage contains mostly Ca(HCO3)2 and Mg(HCO3)2 alkalinity. Higher alkalinity has stronger buffering capacity and can meet the consumption of alkalinity in sewage nitrification reaction. In sludge digestion, there is acidification caused by buffering overload operation, which is conducive to the stability of the digestion process.

In addition to the above indicators, there are also indicators of activated sludge, such as: MLSS (mixed liquor suspended solids concentration), MLVSS (mixed liquor volatile suspended solids concentration), SV% (sludge settling ratio), SVI (sludge volume index), SDI (sludge density index), Ns (sludge load), Fr (volumetric load), organic load, sludge age, etc. to judge the activity and survival of sludge.

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