Biochemical Oxygen Demand (BOD, CBOD) Testing

Biochemical Oxygen Demand (BOD, also called Biological Oxygen Demand) is the amount of dissolved oxygen which is consumed in the biochemical reaction of microbes and break down the biodegradable organic matter, and present in a given water sample under certain conditions ^[1]. BOD measures the oxidation of carbons and possibly nitrogenous compounds (i.e., incomplete conversion of ammonia (NH₃) to nitrate (NO₃^-)), but Carbonaceous Biochemical Oxygen Demand (CBOD) only measures oxidation of carbons. CBOD, and its cousins Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD), are often used as a kind of comprehensive index which reflects the content of the degree of organic pollution of water. BOD is usually measured within a period of 5 days (BOD5), and the value is most commonly expressed in mg/L, percentage and ppm. As we know, water is the origin of all things on the earth and there would be no life without water. However, there are ubiquitous pollutants such as pesticides, effluents and garbage, which contaminate drinking water supplies with their specific material properties. All of this means that it is imperative to determine the quality of a water source before water is consumed. Although the BOD results are not very accurate and reliable compared to the COD which the test is finished in just two hours rather than five days, BOD testing still has its widest application in the water treatment processes and the water quality monitoring, because it indirectly reflects the relative content of organic matter in water.

Alfa Chemistry is fully accredited at local and international level on testing the quality of water, and we aim to be the world leader in the technology of water detection. We can provide a broad range of methods and instruments to solve the problem that you are facing related to water quality.

• Instrument platforms

Fig. 1. BOD automatic detector.

There are two commonly recognized methods for the measurement of Biochemical Oxygen Demand (BOD), which are dilution and manometer method. Generally speaking, biodegradation of organic materials presented in water occurs in two phases. As shown in expression (1), the breakdown of carbons begins to be oxidized into carbon dioxide first. Then nitrification also needs the consumption of oxygen in the second phase. As shown in expression (2).

(1)Corg + O₂ → CO₂ + salts

(2) NH₄⁺ → NO₂ ^–→ NO₃^–

Normally, nitrification sets in after 10 days but may occur within 5 days. Therefore, if we want to detect the consumption of oxygen for carbon oxidation, nitrification inhibitors must be added to repress this undesirable occurrence. The BOD automatic detector has two standard procedures which are based on the two traditional methods respectively (Fig.1.). Unlike the general BOD automatic detector, here it uses the advanced micro pressure sensors, rather than traditional mercury sensors. When carbon dioxide is removed from the gaseous spectrum via the sample by means of a CO₂ adsorbent, usually potassium hydroxide (KOH), the resultant pressure drop can be measured in the closed system and is proportional to the volume of the consumed oxygen.

Alfa Chemistry is professional in the detection of Biochemical Oxygen Demand (BOD, CBOD). We provide a rapid and precise technique for high-quality water and wastewater tests. Feel free to contact us at any time. We will be glad to hear you and look forward to cooperating with you.

Reference

• J Zhan, W W Yang, Whole - Course Quality Control in Determining Water and Wastewater Biochemical Oxygen Demand after Five Days [J]. ENVIRONMENTAL SCIENCE AND MANAGEMENT, 2011, 36(7): 139 -145.