Eliminating the COD or TOC

In the second instance, according to some practice in the U.S. petrochemical industry, powdered activated carbon (PAC) is added directly into the aeration tank in amounts that may vary from 10 to 50 mg l . At the same time, however, advanced activated sludge age (40 to 45 days) is maintained and considerable reductions (from 10 to 20%) in TOC have been achieved. 

Filtration on granular activated carbon (GAG) is also practiced in North America, but development comes up against the cost of regenerating the activated carbon. Tlie GAG may fix only 90 to 250 kg of COD per cubic meter and so its turnover time is short. When no (thermal) regeneration is done, the filters ensure only physical purification of the SS or even a biological purification of the soluble BOD. 

A chronic shortage of available fresh water has prompted studies on reusing treated MWW or refinery WW, especially in the U.S. The situation has recently worsened with the drought and so reuse now needs to be reconsidered more in-depth. 

In fact, reuse requires a certain escalation in equipment of increasingly complex design and operation, which can be chosen since needs are more sophisticated (boilers, for example). In contrast, when seawater is conveniently available it can be used to cool heat exchangers if they have been specially designed. 

---