Ask the Expert Question-and-Answer Archive
by Mike McGinness, EcoShield Environmental Systems, Inc.
COD Increase After Wastewater Treatment
I'm using two white rot fungi for the biotreatment of simulated effluents containing textile dyes. The treatment is performed at small scale inoculating the fungus (50ml of a fungal preculture)in 450ml of wastewater in 1L flasks. I've found that the treatment is more effective (in terms of percentage of decolourisation) when the wastewater is supplied with nutrients (malt extract). This, obviously increases the COD value of the starting wastewater, but after treatment, despite a high reduction of colour (up to 70% decolourisation)I measured an increased COD value! How do you think it is possible? Could I suppose that fungal growth (the fungal can grow in this conditions) release some organic compounds in the wastewater? I'm confident on the sperimental procedure, the data have been repeated three times.
The fungi only need to remove one or more atoms or re-arrange the existing atoms of the dye molecule, to remove the dye color, non of which will reduce the COD, Chemical Oxygen Demand. The nutrients added to support the Fungi increase or add to the COD. The Fungi themselves also have a COD. Once the color has been removed by the fungi, the COD can be removed, barring any toxic constituents, by treating the waste water with a typical aerobic or biological oxidation process that converts COD and BOD into dense, easy to gravity settle biomass (fat, happy dense bacteria).