水和废水监测试卷.ppt

These two reactions can be considered as nitrifying process that is brought about by nitrifying bacteria. The nitrifying bacteria are usually present in relatively small numbers in untreated domestic wastewater or other nitrogen-containing wastewater, and their reproductive rate at 20℃ is very slow. So their populations do not become too large to show obvious oxygen demand through this nitrifying process until 8 to10 days after incubating. Generally the nitrifying process can accomplish completely after 100 days. BOD5 is the 5 days biological oxygen demand. The consumed oxygen within 5 days is mainly used to oxidize most of the organic-carbon and organic-nitrogen to carbon dioxide, water and ammonia. In the case of domestic and many industrial wastewaters, it has been found that the 5-day BOD value is about 70 to 80 percent of the total BOD. BOD20 is 20 days biological oxygen demand. The consumed oxygen within 20 days is used to oxidize almost all the organic-carbon and organic-nitrogen to carbon dioxide, water and ammonia, and to oxidize part of the ammonia to nitrite and nitrate. In order to measuring the amount of decomposable organic-carbon matters in water samples, we often test 5-day BOD value. BOD5与BOD20的区别 微生物在对有机物降解时，分两个阶段：一是将有机碳转化成CO2和H2O；二是将有机氮转化为 或 ，第二阶段，一般在5－7天，才有明显的反应迹象，有时10天后才有明显的好氧。 BOD5是指，在20℃，五日培养后水样中溶解氧的消耗量，所以BOD5不包括第二阶段的耗氧量，只包括反应水中可生化的C、H，转化成CO2和H2O所需的氧。 BOD20是在20℃，20日培养后水样中溶解氧的消耗量，所以BOD20包括C、H、N转化为CO2、H2O等消耗的溶解的含量。 （3）BOD5的测定方法： ①稀释法 A 准备稀释水或接种稀释水 氧饱和的蒸馏水：中20℃下，通O2（或空气）使O2饱和，需平衡24h。 微量元素：临用前加入Ca2＋、Fe3＋、Mg2＋ 微量元素。 确定微生物：水样无微生物或很少，且易降解：生活污水上清液，或花园土浸出液； 有毒、难降解水样：驯化获得接种微生物； 水样有微生物，且易降解：一般不用接种微生物。 B 确定稀释倍数：用CODCr值、CODMn 确定，参见课本P83表2－13讲解。 C 稀释水样并分装成两瓶（溶解氧瓶或用碘量瓶） 2.8.3 biochemical oxygen demand 例：取5ml废水样800ml， 即取50ml废水样＋750ml稀释水800ml混匀，分装到两个碘量瓶中，其中一个用于测定当天的溶解氧，另一个水封好后，五天以后，取出来测溶解氧。 常需要做一个空白：只是将水样用蒸馏水代替其它操作与样品相同。 如果要同时做三个稀释倍数，并且微