**5.10 C.O.D removal by a pure culture and by a heterogeneous culture (sludge) of tannery wastewater not subject to physical–chemical treatment**

Two sterilized samples of untreated tannery wastewater collected in two flasks have been adopted as substrate for B1 strain. The two samples have been inoculated at 5% with the strain and with sludge respectively. Following exactly the procedure illustrated previously, after 24 hours, 50 ml of substrate have been extracted, transferred into sterile Falcon polystyrene tubes and centrifuged at 10,000 rpm for 10 minutes, to remove microbial cells. Supernatant, collected in sterile medium, has undergone C.O.D test with potassium bichromate 0.0417 M [35]. The protocol utilizes a solution 0.25N of FAS (ferrum(II) ammonium sulphate) as titrant, and C. O.D has been calculated according to the formula:

$$C.O.D. = DF \bullet (V\_b - V\_s) \bullet M \bullet 800\tag{1}$$

where:

• Vb is the average volume (ml) of iron(II) ammonium sulphate solution used in the titration of blank solution

*Experimental Investigation of Biomass Attachment to Wastewater Reactors DOI: http://dx.doi.org/10.5772/intechopen.94426*

