It is obvious that also some of the suspended organic matter is biodegradable. It is probably more slowly biodegradable, however, since hydrolysis has to be involved in order to this organic matter to be biodegraded. We may analyse this matter by looking at the bOD/COD-ratio (see figure 3). There were, however, fewer BOD-data than COD-data and therefore the analysis becomes a bit uncertain 0,8 o Swed 0,8 ▲ Finland ▲ Finland 0,6 0,6 0.4 0.4 0 0 200 400 600 800 400 00 800 Total COD, mg/ Total COD, mg/ Figure 3 Ratio bOd/Cod and bod/CODe versus total COD Again we can see that the variation between the different countries is not so great and that th fraction is around 0, 4 in both cases. There is a tendency, however, that the fraction of biodegradable organic matter to that of total organic matter increases with increasing total COD. This is particularly evident in the filtered samples. This is also reasonable, since it may be expected that the amount of organic matter that is biodegraded in the network is relatively independent upon the concentration of biodegradable COd as long as there is no limitation with respect to the presence of biodegradable matter Nitrogen and phosphorus Nitrogen appears in wastewater mainly as ammonium and therefore the particulate fraction of nitrogen is quite low. In the survey, some plant owners have reported data on tot n on filtered samples, but most reported data on NH4-N and NO3-n(or only NH4-N)in addition to tot N. It was demonstrated in a survey of Norwegian plants(Osterhus, 1991)(Odegaard, 1992), that the organic N ily exi ded form(see table 2) Table 2 Nitrogen in wastewater from 10 Norwegian, chemical plants(Odegaard, 1992) Parameter Inlet Outlet Variation range Average Variation range 24.8 14,6-45,0 11,8-348 Tot N 19,6 11,7-326 NHA-N 9,1-45,0 18,3 6,5-326 0,1 0,1 NO2-N 0.3 0-14 0.65 It is obvious that also some of the suspended organic matter is biodegradable. It is probably more slowly biodegradable, however, since hydrolysis has to be involved in order to this organic matter to be biodegraded. We may analyse this matter by looking at the BOD/COD-ratio (see figure 3). There were, however, fewer BOD-data than COD-data and therefore the analysis becomes a bit uncertain. 0 0,2 0,4 0,6 0,8 1 0 200 400 600 800 Total COD, mg/l BO D/CO D Sweden Norway Finland 0 0,2 0,4 0,6 0,8 1 0 200 400 600 800 Total COD, mg/l BO Df/C O Df Sweden Norway Finland Figure 3 Ratio BOD/COD and BODf/CODf versus total COD Again we can see that the variation between the different countries is not so great and that the fraction is around 0,4 in both cases. There is a tendency, however, that the fraction of biodegradable organic matter to that of total organic matter increases with increasing total COD. This is particularly evident in the filtered samples. This is also reasonable, since it may be expected that the amount of organic matter that is biodegraded in the network is relatively independent upon the concentration of biodegradable COD as long as there is no limitation with respect to the presence of biodegradable matter. Nitrogen and phosphorus Nitrogen appears in wastewater mainly as ammonium and therefore the particulate fraction of nitrogen is quite low. In the survey, some plant owners have reported data on tot N on filtered samples, but most reported data on NH4-N and NO3-N (or only NH4-N) in addition to tot N. It was demonstrated in a survey of Norwegian plants (Østerhus, 1991)(Ødegaard, 1992), that the organic N primarily exist on suspended form (see table 2). Table 2 Nitrogen in wastewater from 10 Norwegian, chemical plants (Ødegaard, 1992) Parameter Inlet Outlet Average Variation range Average Variation range Tot N Tot Nf NH4-N NO3-N NO2-N 24,8 19,6 19,1 0,1 0,3 14,6 - 45,0 11,6 - 45,0 9,1 - 45,0 0 - 0,2 0 - 1,4 20,9 20,4 18,3 0,1 0,6 11,8 - 34.8 11,7 - 32,6 6,5 - 32,6 0 - 0,2 0 - 2,4