By: Kate
Email:kate@aquasust.com
Date: 24th December 2024
The phenomenon when the sedimentation performance of activated sludge decreases mainly has the following manifestations:
1, the effluent COD, SS value rises significantly, BOD removal efficiency decreases;
2, DO value in the aeration tank fluctuates abnormally, sludge concentration decreases, and SVI value increases;
3. microscopic examination of bacterial colloid loosening, protozoa reduction, filamentous bacteria increased;
4, floating mud in the effluent of the secondary sedimentation tank;
5.Activated sludge color is abnormal and fine. Activated sludge settling performance decline, often accompanied by the above phenomena together, if this phenomenon continues for a long time, there will be a gradual decrease in the concentration of reflux sludge in the two-sinking tank, the two-sinking tank mud surface position is gradually increased, ultimately resulting in the two-sinking tank turning mud phenomenon.
Reasons for the decline in the settling performance of activated sludge
1,Adverse flocculation of activated sludge
In this case, microscopic examination of activated sludge, the indicator microorganisms are mainly dominated by swimming protozoa, such as echinoderms, bean-type worms, grenadier worms, the reason for this feature is that the activated sludge consists of many dissociated bacteria, which provide a food source for swimming protozoa. After 30 min of sludge standing, the sludge still showed a dispersed state, and there was no obvious interface between the supernatant and the settled sludge. This situation occurs in both high BOD load and low BOD load, high BOD load sewage into the aeration tank, under the action of oxygen so that the rapid growth of bacteria, the amount of newborn sludge grows very fast, in the process of activated sludge from newborn to maturity, this phenomenon is bound to happen; and in the case of low BOD load, sludge is in a starvation state, at this time, the organisms will produce selective, the fittest survive, the microorganisms that are not suitable for this environment are naturally scattered, no obvious interface between the settling sludge and the swimming protozoa. Microorganisms that are not suitable for this environment will die out naturally, resulting in sludge disintegration, which will also lead to a decline in the settling performance of activated sludge.
2,Decrease in density of activated sludge
(1)Decrease in density caused by N2
The density decrease caused by N2 is mainly due to the role of denitrification in the process of nitrogen cycle, the reaction formula is as follows
NO3- + cBOD ─ (strain) → NO2- + CO2 + H2ONO2- + cBOD ─ (strain) → N2↑ + CO2 + H2O
The final product of denitrification is N2, which will be adsorbed by the sludge in the process of N2 release, and the adsorbed N2 sludge rises along with N2 in the process of N2 rise, which leads to the phenomenon of sludge floating.
(2)Decrease of sludge density caused by over-exposure
In the high aeration condition, the sludge is in the state of violent agitation, this situation bacterial colloid is easy to adsorb oxygen, thus rising in the sedimentation tank; in the high aeration state, the sludge oxidation speed accelerated, at this time the sludge will be partially oxidized, from the point of view of the color of the sludge, it will show the phenomenon of slight whitish, the sludge itself is oxidized will also make the density drop.
(3)Decrease of sludge density caused by low inorganic matter
The determination of inorganic quality can be analyzed by MLSS and MLVSS two indicators, general municipal wastewater MLVSS accounted for the proportion of MLSS between 65% and 70%, higher than this value, indicating that there are too many organic components, prone to mud running phenomenon.
Solution measures for the decline of settling performance of activated sludge
1, for the performance decline caused by flocculation in the positive growth of water temperature and gradually increase the BOD load, municipal wastewater BOD load can generally be maintained at 0.05~0.10kgBOD/MLSS/m/d, control sludge age in winter>18 days. Summer is greater than 12 days can be.
2,For the performance decline caused by the low inorganic quality can be fixed by adding powdered carbon, diatomaceous earth or lime in the case of unit sludge age, gradually increase the amount of inorganic quality to gradually improve the sludge settlement. Improvement of sludge settleability is a very slow process, often taking a year or more, and therefore requires a combination of emergency and routine operations.