废水处理系统

废水处理系统就是利用物理、化学和生物的方法对废水进行处理，使废水净化，减少污染，以至达到废水回收、复用，充分利用水资源。

按处理程度，废水处理(主要是城市生活污水和某些工业废水)一般可分为三级：
一级处理：
任务是从废水中去除呈悬浮状态的固体污染物。为此，多采用物理处理法。一般经过一级处理后，悬浮固体的去除率为70%~80%，而生化需氧量(BOD)的去除率只有25%~40%左右，废水的净化程度不高。

二级处理：
任务是大幅度地去除废水中的有机污染物，以BOD为例，一般通过二级处理后，废水中的BOD可去除80%~90%，如城市污水处理后水中的BOD含量可低于30毫克/升。需氧生物处理法的各种处理单元大多能够达到这种要求。

三级处理：
任务是进一步去除二级处理未能去除的污染物，其中包括微生物未能降解的有机物、磷、氮和可溶性无机物。

三级处理是高级处理的同义语，但两者又不完全一致。三级处理是经二级处理后，为了从废水中去除某种特定的污染物，如磷、氮等，而补充增加的一项或几项处理单元;高级处理则往往是以废水回收、复用为目的，在二级处理后所增设的处理单元或系统。三级处理耗资较大，管理也较复杂，但能充分利用水资源。有少数国家建成了一些污水三级处理厂。


Waste water treatment system is to use physical, chemical and biological methods to treat waste water, make waste water purification, reduce pollution, to achieve waste water recovery, reuse, full use of water resources. According to the degree of treatment, wastewater treatment, mainly urban domestic sewage and some industrial wastewater, can be generally divided into three levels: the first level of treatment: The task is to remove suspended solid pollutants from wastewater. To this end, the use of physical processing. Generally, after primary treatment, the removal rate of suspended solids is 70% ~ 80% , while the removal rate of biochemical oxygen demand is only about 25% ~ 40% . Secondary Treatment: The task is to substantially remove the organic pollutants in the waste water. In the case of Bod, generally after secondary treatment, the BOD in the waste water can be removed by 80 to 90 per cent, for example, the BOD content of the treated water can be less than 30 mg / l. Most of the treatment units of aerobic biological treatment can meet this requirement. Tertiary Treatment: The task is to further remove pollutants that can not be removed by secondary treatment, including organic matter, phosphorus, nitrogen and soluble inorganic matter that can not be degraded by microorganisms. Tertiary processing is a synonym for advanced processing, but they are not exactly the same. Tertiary treatment is the addition of one or more treatment units after secondary treatment in order to remove certain specific pollutants such as phosphorus and nitrogen from wastewater, while advanced treatment is often for the purpose of wastewater recovery and reuse A processing unit or system added after a secondary treatment. Three-stage treatment is expensive and complex, but it can make full use of water resources. A few countries have set up some tertiary treatment plants for sewage.