What is COD?

COD is an important indicator of water treatment control and it is the three letters that concern water treatment operators concern. "Effluent COD anomaly" is undoubtedly the most concerned issue in operation management.

There are three common reasons for the abnormal COD in the effluent: first, the abnormal content of reducing inorganic matter. In order to figure out this problem, we should first understand what COD means. In view of this concept, the interpretation of professional books is: Chemical Oxygen Demand (COD) refers to the consumption of oxidation dose under certain conditions, using a certain strong oxidant to treat water samples. It is said the water reducing agents an indicator of how much. The concept is accurate, but the question is, isn't COD used to represent organic pollutants in sewage? What concept of said is reducing agents? This is a critical issue because, in general, the reducing substances in sewage are mainly organic substances, so in the field of water treatment, the two are regarded as the same thing. In fact, the COD measurement also includes nitrite, sulfide, ferrous salts and other inorganic substances, which are greater than the amount of real reducing organic matter in sewage. This link contains a cause of abnormal COD in the effluent, that is, the content of reduced inorganic matter in the influent or middle section is abnormal, resulting in the determination of COD is not accurate enough, and the actual situation of organic matter does not fluctuate.

In addition to a few cases of abnormal organic matter content, the most common is the abnormal situation of biochemical system. The common factors are:

1, temperature fluctuations, cause changes in sludge activity, and then affect the decomposition of COD;

2, the proportion of nutrients is not balanced, such as the proportion of C, N and P is unbalanced for a long time, the sludge activity decreases, and the decomposition of organic matter is affected;

3, dissolved oxygen in water, sludge activity affected, make the efficiency of COD sewage treatment is abnormal;

4, biochemical system into toxic substances, sludge poisoning, affecting the treatment efficiency;

5, too much salt into the biochemical system, microbial activity, metabolic abnormalities, effluent COD increases;

6, sludge aging, degradation performance of living system decreased, effluent COD increased;

7. The hydrolysis effect of the anaerobic pool in the front segment becomes worse, the water degradability of the aerobic pool segment becomes worse, and the effluent is abnormal;

8. The aeration is too intense, the gum pellets are broken, and the small particles are released, causing the COD to increase;

Three, impact load in addition to the above situation, the water inlet water quality, water quantity fluctuation can also lead to water COD anomalies.

1. As the water intake increases, the regulating pool does not effectively buffer the impact, resulting in shorter residence time of the biochemical section, less effective removal of organic matter, and abnormal effluent;

2. The influent water quality fluctuates, the biochemical system does not enter a stable state in an emergency, or the system is abnormal, affecting the degradation of organic matter, and the effluent water quality is abnormal.