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African Journal of Biotechnology Vol. 3 (4), pp. 236-238, April 2004
Available online at http://www.academicjournals.org/AJB
ISSN 1684–5315 © 2004 Academic Journals
Full Length Research Paper
Nutrients requirements in biological industrial
wastewater treatment
Bashaar Y. Ammary
Water and Environmental Engineering Department, Balqa Applied University, Huson College, P.O.Box 50, Huson
21510, JORDAN. Phone: +962-2-7010400, Fax: +962-2-7010379. E-mail: bammary@yahoo.com.
Accepted 30 March, 2004
Wastewaters from olive mills and pulp and paper mill industries in Jordan have been characterized and
treated using laboratory scale anaerobic and aerobic sequencing batch reactors, respectively. Nutrient
requirements for these two industrial wastewaters were found to be less than what is usually reported
in the literature for C:N:P ratio of 100:5:1 for aerobic treatment and 250:5:1 for anaerobic treatment. This
was ascribed to the low biomass observed yield coefficients and relatively low removal efficiencies in
these wastewaters. It was found that for anaerobic treatment of olive mills wastewater COD:N:P ratio of
about 900:5:1.7 was able to achieve more than 80% COD removal. The observed biomass yield was
about 0.06 kg VSS per kg of COD degraded. For extended aeration aerobic treatment of pulp and paper
mill wastewater COD:N:P ratio of about 170:5:1.5 was able to achieve more than 75% COD removal. The
observed biomass yield was about 0.31 kg VSS per kg of COD degraded. In both these wastewaters
nutrients were not added. A simple formula is introduced to calculate nutrient requirements based on
removal efficiency and observed biomass yield coefficient.
Key words: Olive mill wastewater, anaerobic treatment, aerobic treatment, sequencing batch reactor, biomass
yield, nutrient requirement.
INTRODUCTION
Microorganisms involved in the removal of carbonaceous
contaminants from wastewater require nitrogen and
phosphorous for growth and reproduction.
Microorganisms require nitrogen to form proteins, cell
wall components, and nucleic acids (Maier, 1999a).
Biomass has been universally accepted to have the
chemical formula C5H7NO2P0.074 (Droste, 1997).
When treating wastewater, it is usually stated that the
ratio of COD:N:P in the wastewater to be treated should
be approximately 100:5:1 for aerobic treatment and
250:5:1 for anaerobic treatment (Metcalf and Eddy, 1991;
Abbreviations: COD, Chemical Oxygen Demand; BOD5, Five
days Biochemical Oxygen Demand; OMW, Olive Mill
Wastewater; VSS, Volatile Suspended Solids; MLVSS, Mixed
Liquor Volatile Suspended Solids Concentration; E, Chemical
Oxygen Demand Removal Efficiency; Yobs, Observed Biomass
Yield.
USEPA, 1995; Henze et al., 1997; Maier, 1999 a). For
anaerobic treatment, the required nitrogen and
phosphorous concentrations is lower than the case for
aerobic treatment due to the fact that anaerobic treatment
produces only 20% sludge compared to aerobic
treatment.
Henze and Harremoes (1983) based the COD:N
requirements for anaerobic treatment on loading rates.
For highly loaded processes (0.8-1.2 kg COD/kg VSS/d),
they recommended a value of 250:5. For lower loading
rates, the value can be increased from 250:5 by
multiplying it with a factor which equals to the loading rate
in kg COD/kg VSS/d divided by 1.2.
In the present study, the effect of both the removal
efficiency and observed biomass yield on nutrient
requirements for both aerobic and anaerobic treatments
is discussed. It is hypothesized that, for industrial
wastewater, more accurate determination of nutrient
requirements should be based on both removal efficiency
and biomass yield.
MATERIALS AND METHODS
The sequencing batch reactor used in this study had an active
volume of 2 L. For anaerobic treatment of olive mills wastewater
(OMW), it was mixed and kept at 30± 2
oC using a magnetic
stirrer/hotplate. After the mixing time was completed, mixing and
heating were turned off, and the reactor was kept quiescent for 2 h
to allow for anaerobic sludge to settle. After that the calculated
volume of the supernatant was removed from the reactor and
tested for a number of parameters following Standard Methods for
the Examination of Water and Wastewater (APHA, 2000). An equal
amount of raw wastewater was added and the whole volume
started a new phase of mixing under anaerobic conditions. After the
startup phase, the COD of the reactor was kept around 16,000 mg/l
by dilution. Sludge wastage was conducted to keep the volatile
suspended solids (VSS) concentration in the reactor as constant
and as close to 12,000 mg/l as possible. The hydraulic retention
time was kept equal to 3 days. pH of the reactor was adjusted to
around 7 as found necessary using sodium bicarbonate.
For aerobic treatment of pulp and paper mill wastewater,
dissolved oxygen concentrations were kept between 2 and 4 mg/l.
The treatment mode was extended aeration, because the yield
coefficient in this mode is lower than the conventional activated
sludge process. Average hydraulic retention time was 24 h. The
reactor was fed three times daily each with about 670 ml. Mixed
liquor volatile suspended solids concentration (MLVSS) was kept
about 2500 mg/l.
Table 1. Average olive mill and pulp and paper mill wastewater
characteristics during the study period.
Parameter Average
concentration/
value (Olive Mill
Wastewater)
Average
concentration/
value (Pulp
and paper mill
Wastewater)
BOD5 (mg/l) 30,600 230
COD (mg/l) 97,000 420
Total Nitrogen (mg/l) 532 13
Total-P (mg/l) 182 4
RESULTS AND DISCUSSION
Wastewater Characteristics
Wastewater from olive mills and paper and pulp
industries, have a wide range of characteristics. Table (1)
shows the average value of a number of wastewater
characteristics for these wastewaters. The table shows
that the COD value for olive mills wastewater is very high
and therefore anaerobic treatment is necessary for such
wastewater. The average ratios of COD to nitrogen
(COD: N) and phosphorous concentrations (COD: P) are
equal to about 180 and 530, respectively. The COD: N: P
ratio then equals 911: 5: 1.7. The maximum ratio that is
usually reported in the literature as the required ratio is
250:5:1 to 500:5:1 depending on the extent of loading or
COD influent concentrations (Droste, 1997; USEPA,
1995). The present ratio suggests that the concentrations
of nitrogen and phosphorous are lower than what is
Ammary 237
required for anaerobic treatment of such wastewater.
Therefore, and according to these figures, nutrients,
especially nitrogen, have to be added to the OMW.
Similarly, for the pulp and paper mill wastewater, the
ratio of C:N:P is lower than what is usually reported in the
literature. This suggests that both nitrogen and
phosphorous have to be added to the wastewater for
effective biological treatment.
COD Removal
Despite the low nitrogen and phosphorous
concentrations, the anaerobic reactor treating olive mill
wastewater performed at a high level of efficiency as was
observed from the low and stable concentration of fatty
acids (between 50-90 mg/l), and the high removal of
COD (about 80% at 3 days retention time).
Sludge wastage was conducted whenever the VSS
exceeded 13000 mg/l, about every 6 to 9 days. The
average sludge age at these conditions would be around
45 days. At 3 days retention time, the COD removal
efficiency averaged a value of about 83%. This was
achieved without the need for nutrients addition. At these
conditions, the observed yield was found to be around
0.06 kg VSS per kg COD removed.
Similarly, for pulp and paper mill wastewater, removal
efficiency of COD was higher than 75% without the
addition of any nutrients. The sludge yield coefficient was
found to be equal to about 0.31 kg VSS per kg COD
removed.
Nutrient Requirements
Nutrient concentrations in the wastewaters reported in
this study were lower than that reported in the literature.
However, they achieved high removal efficiencies without
the need for nutrient addition. So how were nitrogen and
phosphorous sufficient for the treatment at this low
concentration?
The C:N:P ratios listed in the literature (100:5:1 and
250:5:1 for aerobic and anaerobic treatments,
respectively) were based on the following theoretical
background. Carbonaceous organic matter is simplified
as glucose and is given the formula C6H12O6 while the
biomass is given the formula C5H7NO2. Upon degradation
of organic matter, biomass is produced. The mass of
biomass produced divided by the mass of the organic
matter is termed the yield coefficient. In the biomass
formula, the amount of nitrogen is 12.3% of the biomass.
The degradation is given in the following equation:
C6H12O6 + NH3 + O2 → C5H7NO2 + CO2 + H2O
In the above equation, the required ratio of C: N in the
wastewater becomes 100: 5 when the yield coefficient is
0.41. If phosphorous is introduced and assumed 20% of
nitrogen mass, the biomass chemical formula becomes
238 Afr. J. Biotechnol.
C5H7NO2P0.074 (Droste, 1997), and the required ratio
becomes 100:5:1. For anaerobic processes and
assuming that sludge production rate is 40 to 20% of
aerobic sludge production, the ratio becomes 250:5:1 to
500:5:1, respectively.
In deriving these ratios, it was assumed that the
efficiency of removal is 100%. The fact that different
wastewaters have different biomass yields was not taken
into account. Therefore when addressing nutrient needs,
one should take into account both the microbial yield and
the efficiency of COD removal. Giving a ratio between
COD:N:P is misleading as this does not take into account
the previously mentioned factors (biomass yield and
efficiency). This is especially true for industrial
wastewaters that have low removal efficiency and yield.
For example, biomass treating pentachlorophenol
aerobically has a very low cell yield of approximately 0.05
(Maier, 1999b). On the other hand octadecane has a cell
yield as high as 1.49 (Maier, 1999b).
As mentioned above, for aerobic treatment, the
required ratio of C:N:P in the wastewater should be
100:5:1 when it is assumed that COD removal is 100%,
that nitrogen content of biomass is 12.3%, and that the
observed yield coefficient is 0.41. In case the observed
yield (Yobs) is different than the 0.41, and removal
efficiency (E) is different than 100%, the COD: N ratio
required in the wastewater would be 0.41(100)/EYobs:5, or
41/EYobs:5. If phosphorous content is assumed 20% of
nitrogen content then the required ratio of COD: N: P in
an aerobic reactor should be calculated from the
following formula 41/EYobs:5 :1.
For anaerobic treatment, the value of C: N: P ratio of
250: 5: 1 is observed at an observed yield value of 0.16
and 100% removal efficiency. At an observed yield value
of 0.08, the ratio becomes 500: 5: 1 at 100% removal
efficiency. For different observed biomass yield and
different than 100% removal, the same formula
(41/EYobs:5 :1) can be used.
In the present study, the observed yield factor for
aerobic biomass treating pulp and paper mill wastewater
was equal to 0.31 while the removal efficiency was about
75%. For such treatment, the required C:N:P ratio should
be (41/0.75(0.31)): 5:1, which is equal to 176:5:1. The
COD:N:P ratio in the present study was a little bit higher
than these values (161:5:1.5).
The observed yield for the anaerobic biomass treating
olive mills wastewater was found to be equal to 0.06 and
efficiency of COD removal was equal to 83%. The
required COD:N:P ratio will then be equal to
(41/(0.83)(0.06)): 5: 1, which is equal to 823:5:1. The
concentration of nitrogen in the olive mills wastewater is
lower than what is required by this formula. It should be
noted, however, that for industrial wastewater, the usual
sludge age used is very high, especially with low
degradable wastewater. For this reason, the usual
nitrogen content in biomass is lower than 12.3%
(Eckenfelder, 1989). This suggests that in anaerobic
treatment even lower nitrogen and phosphorous
concentrations can be used than those calculated by the
above formula. If nitrogen content is assumed 11%
instead of 12.3%, the nitrogen content in the wastewater
would then be sufficient. However, the above formula still
gives a conservative value and therefore should be used.
This formula should be used instead of using a constant
value such as 250:5:1 or 500:5:1 for all wastewaters
regardless of the removal efficiency or biomass yield.
In applying Henze and Harremoes (1983) criteria for
COD:N requirements for the present study, the following
were obtained. For a loading rate of 0.44 kg COD/kg
VSS/d, for the olive mills wastewater, the COD:N ratio
required would be 682:5 ((1.2/0.44)250:5). According to
their method, nitrogen should be added to the
wastewater. This method also depends on influent COD
concentration, and does not differentiate between
different removal efficiencies. Biomas yield is also not
considered. Therefore, the use of loading rates for
nutrient requirement determination is as misleading as
the use of constant ratios of COD to nitrogen and
phosphorous. More accurate determination of nutrient
requirements should be based on both removal efficiency
and biomass yield as suggested above.
The following conclusions can be drawn from the
present study: (1) Olive mills wastewater and pulp and
paper mill wastewater in Jordan have sufficient nitrogen
and phosphorous concentrations that addition of such
nutrients was not necessary, and (2) the COD:N:P ratio
required for aerobic and anaerobic treatment of industrial
wastewater should be calculated from a formula that take
account of the removal efficiency and observed yield for
the wastewater in concern (41/EYobs:5:1) instead of using
a constant value for all different wastewaters, or based
on loading rate.
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Droste R L (1997). Theory and Practice of Water and Wastewater
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Eckenfelder W. W., Jr. (1989). Industrial Water Pollution Control,
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