Procedures

1. The separation of particular and solubilized fractionThe separation of particular and solubilized fraction was realized by centrifuging the sample of sludge at 6000g during 20 minutes, followed by a filtration in vid with a filter paper whose porosity was of 0.45µm. Solubilized fraction was prelavated in vials and maintained in the fridge at the temperature of for further analyses. Particular fraction was used for dry matter, volatile and mineral matter. The concentration of all the analyses regarding particular fraction will be realized by difference of concentration of total fraction and concentration of soluble fraction.

%particular=%total-%soluble

2. The determination of dry matter, mineral and volatile matterThe content of dry matter and of volatile matter from the sludge helps us to understand the reparation Instruments necessary for the procedure: porcelain crucibles, two ovens(105°C and 550°C ), digital balance.

For this procedure the crucibles are kept in a desiccator for 24 hours before the manipulation for removing all traces of water. After this they are weighted (Wc) and a certain volume of sludge (Vs)is taken and put in them. These are maintained in the oven at 105°C during 24 hours for evaporating the water, and weighted again for the determination of dry matter(DM).The next step is to insert the crucibles in the second oven, at 550°C during 2 hours for volatilize all the organic matter. The content of mineral matter (MM) is determined by measuring the weight of the crucibles and the organic matter (VM) by difference, the results are being reported at the volume of sample (Vs).

DM=Wc105 ˚ C−Wc

Vs

VM=Wc550 ˚ C−Wc

Vs

MM=DM-VM

3. Chemical oxygen demand(COD)Chemical oxygen demand(COD) is defined as the amount of a specified oxidant that reacts with the sample under controlled conditions. The quantity of oxidant consumed is expressed in terms of its oxygen equivalence. Because of its unique chemical properties, the dichromate ion (Cr2O7

2-) is the specified oxidant that is used in this test, and it is reduced to the chromic ion (Cr3+).Both organic and inorganic components of a sample are subject to

oxidation, but in most cases the organic compounent predominates. COD test is a defiens test; the extent of a sample oxidation can be affected by digestion time, reagent strength, and CAD sample concentration.Cod tests were realized for total and particular fraction, in triplicates for each sample.

Total COD = chemical oxygen demand including both particulate or soluble COD;

6) Soluble COD = chemical oxygen demand of soluble compounds.

7) Particulate COD = chemical oxygen demand of particulate compounds: estimated as the difference between total COD and soluble COD.