The COD of the gasified wastewater is high

In the case of Texaco gasification, the high COD levels in the wastewater are mainly due to excessive ammonia nitrogen levels in the wastewater; this is a problem faced by most Texaco gasification plants. Many of them have added ammonia stripping towers in the sludge-water treatment section to reduce the ammonia nitrogen content in the water!

Does ammonia nitrogen have such a significant impact on COD levels?

Ammonia nitrogen and COD shouldn’t be related, right?

COD has little to do with ammonia nitrogen; COD mainly comes from coal

This post was last edited by xklcj on 2015-8-10 22:31. Chemical oxygen demand (COD or CODcr) refers to the amount of oxidizing agent consumed when reducing substances in water are oxidized and decomposed under strict conditions, using an external strong oxidant, and is expressed in mg/L of oxygen. Chemical oxygen demand reflects the degree of contamination in water by reducing substances, including organic matter, sulfites, ferrous salts, sulfides, etc. However, the amount of inorganic reducing substances in water and wastewater is generally low, while contamination by organic matter is quite common. Therefore, COD can serve as a comprehensive indicator of the relative content of organic matter. Let’s first understand what COD is before discussing anything! The wastewater from the Texaco gasification unit contains very little organic material; most of it is inorganic. Ammonia nitrogen is an inorganic reducing substance, and among the reducing substances present in the wastewater from Texaco gasification, ammonia nitrogen is the most abundant!

This phenomenon also occurs in four-nozzle gasifiers, mainly due to the addition of high-COD waste liquid from later stages during slurry preparation, which accumulates during the gasification process.

I agree with the above statement: there is a direct and inevitable connection between ammonia nitrogen and COD. Chemical oxygen demand – ammonia nitrogen is a reducing substance that can be oxidized; therefore, when ammonia nitrogen levels are high, the chemical oxygen demand will necessarily be high as well

In my opinion, potassium dichromate used for COD testing is unable to oxidize ammonia nitrogen; therefore, measuring only CODcr doesn’t tell much about the relationship between the two

We analyzed that the ammonia nitrogen level is within the acceptable range, but the COD level exceeds the limit

So you didn’t take samples for analysis to determine which reducing substance has a high content? The Texaco gasification process has been in use for many years. Due to the high reaction temperature and the fact that it involves partial oxidation, the combustion chamber has a reducing atmosphere. The organic content in the slag water is virtually zero, and among the inorganic substances, there are only a few that are reducing in nature: carbon dioxide, silicon oxide, calcium oxide, and magnesium oxide. None of these are reducing substances. The main reducing substances are ammonia, carbon monoxide, ferrous oxide, and hydrogen sulfide. In theory, the concentrations of ferrous oxide, hydrogen sulfide, and carbon monoxide are not very high; therefore, ammonia is the most likely candidate.