It can be seen that the particulate fraction of the tot n was around 20%, and that the filtered Tot N was about equal to the inorganic N. Consequently the organic n was mainly on particulate form This can also be seen from the fact that the amount of n left after coagulation was very close to the sum of the inorganic N In table 3 the results of the survey of the Scandinavian plants are shown with respect to nitrogen as well as phosphorus Table 3 Average values on N and p in raw wastewater from Scandianvian plants Country N TotN NH -N F-Nss Tot P PO -P F-Pss Sweden 1733,124,4 0, 6.14 8.1+7.6 +0.13 +165+142 +0.15 12 0 13.7 0,29 3.00 1.10 0.65 +4.2 +0.08+1.12+0.62+0.09 Finland 743828,7 0.33 7.473.29 +10.4+7.6 +007 +134 Based on the assumption that the organic n is suspended 2 Based on the assumption that the soluble p is equal to soluble PO4-p As it is shown i figure 4, the suspended fraction of tot n varies between 0, 2 and 0, 5, but is in most cases around 30 % It seems to decrease a bit with increasing tot N concentration. Generally it seems from the data that the plants with a higher fraction of soluble COd had a lower fraction of particulate N. This seems reasonable, since the particulate n to a large extent is organically N bound in biomass In oxygen- rich systems with considerable biodegradation, inorganic, soluble N(NH4-N is used in the assimilation process producing biomass, i. e particulate, organic N 日0.8 ay 08 0.6 ▲ Finland 0.6 0.4 o Swede ▲ Finland 0 0102030405060 2 6 Total N, mg N/ Total P, mgP/ igure 4 Fraction of N and P on suspended form In the survey, some plant owners gave data for filtered tot P and some only on PO4-P. The difference was not great. However, filtered tot P is on average somewhat higher than PO4-P. There were large variations from plant to plant with respect to the particulate fraction of phosphorous(30 80%). This may be caused by the fact that the sludge water may influence in some cases on inlet concentrations since the inlet sampling point in some cases may be downstream the introduction point of the sludge water. It was a bit surprising, however, that in most of the plants the fraction of particulate P was higher than 50 %. Again, it is the plants with a low fraction of soluble COD, that has a high fraction of particulate P. As mentioned for nitrogen, this indicates again that a considerable fraction of the particulate P is in fact present in biomass
6 It can be seen that the particulate fraction of the tot N was around 20 %, and that the filtered Tot N was about equal to the inorganic N. Consequently the organic N was mainly on particulate form. This can also be seen from the fact that the amount of N left after coagulation was very close to the sum of the inorganic N. In table 3 the results of the survey of the Scandinavian plants are shown with respect to nitrogen as well as phosphorus. Table 3 Average values on N and P in raw wastewater from Scandianvian plants Country N Tot N NH4-N F-NSS 1 Tot P PO4-P F-PSS 2 Sweden 17 33,1 +8,1 24,4 +7,6 0,28 +0,13 6,14 +1,65 3,26 +1,42 0,49 +0,15 Norway 12 22,0 +6,2 13,7 +4,2 0,29 +0,08 3,00 +1,12 1,10 +0,62 0,65 +0,09 Finland 7 43,8 +10,4 28,7 +7,6 0,33 +0,07 7,47 +1,34 3,29 +1,36 0,56 +0,19 1 Based on the assumption that the organic N is suspended 2 Based on the assumption that the soluble P is equal to soluble PO4-P As it is shown i figure 4, the suspended fraction of tot N varies between 0,2 and 0,5, but is in most cases around 30 %. It seems to decrease a bit with increasing tot N concentration. Generally it seems from the data that the plants with a higher fraction of soluble COD had a lower fraction of particulate N. This seems reasonable, since the particulate N to a large extent is organically N bound in biomass. In oxygen-rich systems with considerable biodegradation, inorganic, soluble N (NH4-N) is used in the assimilation process producing biomass, i.e. particulate, organic N. Figure 4 Fraction of N and P on suspended form 0 0,2 0,4 0,6 0,8 1 02468 1 Total P, mgP/l Fr a ction s u s p e nded P Sw eden Norw ay Finland 0 0 0,2 0,4 0,6 0,8 1 0 10 20 30 40 50 60 Total N, mg N/l Fr a ctionsuspended N Sw eden Norw ay Finland In the survey, some plant owners gave data for filtered tot P and some only on PO4-P. The difference was not great. However, filtered tot P is on average somewhat higher than PO4-P. There were large variations from plant to plant with respect to the particulate fraction of phosphorous (30- 80 %). This may be caused by the fact that the sludge water may influence in some cases on inlet concentrations since the inlet sampling point in some cases may be downstream the introduction point of the sludge water. It was a bit surprising, however, that in most of the plants the fraction of particulate P was higher than 50 %. Again, it is the plants with a low fraction of soluble COD, that has a high fraction of particulate P. As mentioned for nitrogen, this indicates again that a considerable fraction of the particulate P is in fact present in biomass
C/N-ratios and C/P-ratios In table 4 are given calculated C/N-and C/P-ratios. The C/N-ratio is often taken as an indication of the availability of carbon source for pre-denitrification. One has to remember, however, that it is the biodegradable organic matter that counts, and that particulate nitrogen may be hydrolysed during the process(extent depending on which process). The C/N-ratios that tell us most, therefore, is probably the bod tot N-ratio or the bscod tot N-ratio Table 4 Average values calculated C/N-and c/P-ratios from Scandinavian plants Country N COD/ CODf/ BOD/ BOD/ BSCOD/ BSCOD/ COD/ COD/ NHg-N NHA-N Tot n NHI-N TP POk-P Sweden 17 14.7 2.6 79,555,5 3.3 +10 6 +4.0 23.9 Norway 1211,5 6.3 3,3 86.7 93,2 +14 +23 +249+48.3 Finland 7 13.5 5.3 2.8 75.4 +5,0±1,8 +14 +1,3 +0.9 +1.6 29.3+52.1 It is interesting to note that even of there are great variations between the C/N- ratios when comparing the three countries, the differences are smaller than one could expect, even though the Norwegian waters generally seem to be less suitable for pre-denitrification than the ones in Swedish and Finland. Based on the COD/Tot N-ratio alone one might draw the conclusion that the available carbon source is more than sufficient for pre-denitrification in most cases. When considering the cases(see figure 4), especially when there is not time available for hydrolysis(as in some biofilm BSCOD/Tot N-ratio, however, one may fear that the available carbon source is insufficient in many processes ). One has to remember, however, the carbon source that will be needed for oxygen assimilation. Especially in the Norwegian wastewater the oxygen concentration in the inlet water is normally high, making this wastewater even more unfavourable for pre-denitrification o Sweden a Norw ay a Norw ay 64▲ Finland ▲ Finland 0 200 600 800 Total COD, mg/l mg Po4-P/ Figure 5"BSCOD"/TotN versus Figure 6"BSCOD"/PO4-P ratio versus COD concentration PO4-P concentration
7 C/N-ratios and C/P-ratios In table 4 are given calculated C/N- and C/P-ratios. The C/N-ratio is often taken as an indication of the availability of carbon source for pre-denitrification. One has to remember, however, that it is the biodegradable organic matter that counts, and that particulate nitrogen may be hydrolysed during the process (extent depending on which process). The C/N-ratios that tell us most, therefore, is probably the BOD/Tot N-ratio or the BSCOD/Tot N-ratio. Table 4 Average values calculated C/N- and C/P-ratios from Scandinavian plants Country N COD/ TN CODf/ NH4-N BOD/ TN BODf/ NH4-N BSCOD/ Tot N BSCOD/ NH4-N COD/ TP CODf/ PO4-P Sweden 17 14,7 +3,3 7,1 +4,2 5,2 +2,1 2,6 +1,0 3,8 + 2,6 5,5 + 4,0 79,5 +7,2 55,5 +23,9 Norway 12 11,5 +1,4 6,3 +1,4 5,2 +2,3 2,2 +0,7 2,1 + 0,8 3,3 + 1,3 86,7 +24,9 93,2 +48,3 Finland 7 13,5 +5,0 5,3 +1,8 6,1 +1,4 3,3 +1,3 2,8 + 0,9 4,2 + 1,6 78,2 +29,3 75,4 +52,1 It is interesting to note that even of there are great variations between the C/N-ratios when comparing the three countries, the differences are smaller than one could expect, even though the Norwegian waters generally seem to be less suitable for pre-denitrification than the ones in Swedish and Finland. Based on the COD/Tot N-ratio alone one might draw the conclusion that the available carbon source is more than sufficient for pre-denitrification in most cases. When considering the BSCOD/Tot N-ratio, however, one may fear that the available carbon source is insufficient in many cases (see figure 4), especially when there is not time available for hydrolysis (as in some biofilm processes). One has to remember, however, the carbon source that will be needed for oxygen assimilation. Especially in the Norwegian wastewater the oxygen concentration in the inlet water is normally high, making this wastewater even more unfavourable for pre-denitrification. 0 1 2 3 4 5 6 0 200 400 600 800 Total COD, mg/l "B S COD"/ T ot N Sw eden Norw ay Finland 0 20 40 60 80 100 0 2 4 6 8 10 mg PO4-P/l "B S COD"/ P O4- P Sw eden Norw ay Finland Figure 5 "BSCOD"/TotN versus Figure 6 "BSCOD"/PO4-P ratio versus COD concentration PO4-P concentration