Increasing the contact time means the amount of time to digest the available biodegradable carbon is three time longer. Generally, that is a good thing. The impact also depends on your reactor design. A completely mixed reactor may take a 3:1 increase in load with a 3:1 increase in digestion time better than a plug-flow reactor. If you have, for example, a plug flow reactor that receives 3 times the concentration of substrate, the oxygen demand at the head end of the process could overwhelm and exceed the oxygen supply. Also, you need to determine the nature of the increased COD. Whether it is organic or inorganic can greatly affect the process response to the high concentration. Hope that makes sense.
Published by Troy Vassos, Senior Environmental Engineer
Increasing the contact time means the amount of time to digest the available biodegradable carbon is three time longer. Generally, that is a good thing. The impact also depends on your reactor design. A completely mixed reactor may take a 3:1 increase in load with a 3:1 increase in digestion time better than a plug-flow reactor. If you have, for example, a plug flow reactor that receives 3 times the concentration of substrate, the oxygen demand at the head end of the process could overwhelm and exceed the oxygen supply. Also, you need to determine the nature of the increased COD. Whether it is organic or inorganic can greatly affect the process response to the high concentration. Hope that makes sense.