在生活污水、食品加工和造纸等工业废水中，含有碳水化合物、蛋白质、油脂、木质素等有机物质。这些物质以悬浮或溶解状态存在于污水中，这种污染物可造成水中溶解氧减少，影响鱼类和其他水生生物的生长。水中溶解氧耗尽后，有机物进行厌氧分解，产生硫化氢、氨和硫醇等难闻气味，使水质进一步恶化。水体中有机物成分非常复杂，耗氧有机物浓度常用单位体积水中耗氧物质生化分解过程中所消耗的氧量表示，单位mg/L。一般用化学需氧量，即COD（Chemical Oxygen Demand）表示，是以化学方法测量水样中需要被氧化的还原性物质的量。其中一部分可通过微生物的生物化学作用而分解称为生化需氧量(BOD）表示。一般用20℃时，五天生化需氧量(BOD5）表示。
In industrial wastewater such as domestic sewage, food processing and papermaking, there are organic substances such as carbohydrates, proteins, oils, lignin and so on. These substances are suspended or dissolved in sewage, which can reduce dissolved oxygen in water and affect the growth of fish and www.dianzugui.com.cnwww.shoutao.org.cnwww.qibiji.org.cnwww.hrbzhoucheng.net.cnother aquatic shijiazhuang.71ix.cnwww.juanzhiji.com.cnorganisms. When dissolved oxygen in water is depleted, the organic matter is anaerobically decomposed to produce unpleasant odors such as hydrogen sulfide, ammonia and mercaptan, which further deteriorates the water quality. The composition of organic matter in water is very complex. Oxygen consumption in biochemical decomposition of Oxygen Consumption Organic Matter in unit volume water is usually expressed in unit mg/L. Chemical Oxygen Demand (COD) is generally used to measure the amount of reductive substances that need to be oxidized in water samples by chemical methods. Some of them can be decomposed by the biochemical action of microorganisms called biochemical oxygen demand (BOD). Normally, it is expressed by BOD5 (Biochemical Oxygen Demand) for five days at 20 C.