Nitrogen and Carbon Characteristics of
Sludges from Formic Acid and Sodium
Hydroxide Pulping of Kenaf Stem
Chukwudebelu JA1* and Agunwamba JC2
1Department of Chemical, Fibre and Environmental Technology, Federal Institute of Industrial Research, Nigeria
2Department of Civil Engineering, University of Nigeria, Nigeria
Submission: November 24, 2020;Published: January 04, 2021
*Corresponding author: Chukwudebelu JA, Department of Chemical, Fibre and Environmental Technology, Federal Institute of Industrial Research, Oshodi, Nigeria
How to cite this article: Chukwudebelu J, Agunwamba J. Nitrogen and Carbon Characteristics of Sludges from Formic Acid and Sodium Hydroxide Pulping of Kenaf Stem. Int J Environ Sci Nat Res. 2021; 26(5): 556196. DOI:10.19080/IJESNR.2021.26.556196
Sludge is produced during paper manufacturing. In this study, kenaf stem was pulped with formic acid and sodium hydroxide at 20%, 60% and 90% concentrations for a cooking period of 1,2 and 3h at 96oC under atmospheric pressure. The effluent from the pulping processes was filtered to get the sludge. The sludge was analysed for carbon and nitrogen. The sludge content from 20% pulping has nitrogen and carbon from sodium hydroxide, sludge from 60% pulping has carbon and nitrogen from both chemicals with more nitrogen while 90% pulping has more carbon. Considering the pulped stem, it showed under pulped, normal and over pulped with respect to 20%, 60% and 90%. Therefore, looking at the normal pulp at 60% concentration with the two chemicals, formic acid has moderate values of carbon and nitrogen compare to sodium hydroxide that showed high nitrogen content. Formic acid pulping is considered here because it can easily be recovered after pulping and the sludge used as manure.
The paper mill and pulp industry produce enormous quantities of paper and pulp products each year. It is the sixth largest polluting industry after the oil, cement, leather, textile, and steel industries, and many environmental contaminants are associated with the discharge of paper and pulp mill sludge . Paper manufacturing is a complex industry involving multiple processes where different products are produced and large quantities of waste of primary, biological or de–inking origin are generated, waste water treatment sludge, primary sludge, and secondary sludge among them [2,3].
Pulp and paper mill production is growing every year worldwide. As a consequence, the amount of generated waste is increasing, along with increasing concern .
Sludge is the final solid waste recovered from the wastewater treatment process in pulp and paper mills. Sludge discharged from paper mills is divided into four categories:
a)primary sludge (PS), which comes from the production of virgin wood fiber;
b)de-inking paper sludge (DPS), which comes from the process of removing inks from recycled paper;
c)secondary sludge (SS; activated sludge), which comes from the secondary wastewater treatment system; and
d)combined primary and secondary sludge .
The sludge composition generally comprises organic matter, nitrogen and phosphorus, which can be used as macronutrient fertilizers in agriculture . Nitrogen is important for growth of plant, its food processing and creation of chlorophyll. Carbon is the main part of soil organic matter and it aids soil to have water-retention capacity, form and fertility.
The sources of solids in a treatment plant vary according to the type of plant and its method of operation [7,8]. The amount and chemical composition, as well as the geotechnical properties of paper mill sludge depend on the paper grade being manufactured, specific fresh water consumption, the wastewater cleaning technique applied and the type of raw materials (e.g. wood, fillers). Thus, the chemical composition of paper mill sludge produced by one mill is often significantly different from that of another [9,10].
Many parameters have been introduced and tests developed to measure specific properties of sludge in relation to particular methods of treatment. Conventional sludge characteristics can be
grouped in physical, chemical and biological parameters. Physical
parameters give general information on sludge processability and
handlability. Chemical parameters are relevant to the presence
of nutrients and toxic/dangerous compounds, so they become
necessary in the case of utilization in agriculture. Biological
parameters give information on microbial activity and organic
matter/pathogens presence, thus allowing the safety of use to be
Natural and anthropogenic environmental changes greatly
influence the behaviour of metallic pollutants in sludge, as the
form in which they occur may be change. Such external factors
can include pH, temperature, the redox potential, organic
matter decomposition, leaching, ion exchange processes and
microbiological activity .
The pulp and paper industry consumes enormous amounts of
water and natural resources and is also one of the largest effluents
generators. Before the 1970s, wastewaters from the pulp and
paper mills were normally discharged directly to the rivers or
lakes, without any treatment or even a rough primary treatment.
The high organic loads and solid content in the effluents affected
the aquatic ecosystem in several ways such as localized damage
to the benthic community, oxygen depletion in large areas and
numerous changes in fish reproduction and physiology .
This study sets out to find out the effects of chemical,
concentration and time interactions under laboratory conditions
on the quality of sludge considering nitrogen and carbon from two
chemical pulping processes.
Kenaf stem was pulped with formic acid and sodium
hydroxide at 20, 60 and 90% concentrations for a cooking time
of 1, 2 and 3h at 95°C under atmospheric pressure. At the end of
each period, the sample was filtered with a fine mesh sieve of size
0.027mm to get effluent and the effluent was filtered with a filter
paper to get the sludge used in the analyses. The sludge samples
were then air-dried and screened to remove other contaminating
materials. The screened raw materials were ground and placed
in an airtight container to balance the moisture content and then
used for chemical analysis. The tests were carried out in triplicate
and each value is an average of three samples.
Determination of nitrogen content
Nitrogen content of the sample was determined by using
Kjedahl technique . The method involves digestion of samples,
distillation of digests and titration of distillate.
Where T = (sample titre – blank titre)
Determination of carbon content
Colorimetric method of  was used to calculate the total
carbon (Figure 1).
Table 1 presents the values of carbon and nitrogen from
sludge obtained from pulping kenaf stem with 20% concentration
of FA and NaOH. The sludge from formic acid pulping with 20%
formic acid at three-hour intervals did not show any presence of
carbon and nitrogen. Carbon and nitrogen were detected in the
sludge from sodium hydroxide pulping at three-hour intervals in
a decreasing concentration. The highest concentrations of carbon
(0.17%) and nitrogen (1.67%) were obtained after 1-hour pulping
while the lowest (0.07 & 0.63) were after two hours pulping. The
increase of carbon content after three hours pulping may be as a
result of esterification reaction as reported by .
Nitrogen content of sludge from NaOH has close values and
showed a little increase from 2 hours (0.63%) to three hours
(0.67%). According to , the little increase in nitrogen may be
due basic character of amine and hydrogen as triethylamine which
took part in the reaction.
Table 2 shows the values of carbon and nitrogen in the
sludge from pulping kenaf stem at 60% formic acid and sodium
hydroxide. Carbon was detected throughout the 3-hour pulping
with 60% formic acid, but the value did not follow a particular
pattern because the highest value (8.7%) was obtained at 2 hour
pulping followed by 3 hour (3.57%), while the lowest was at 1
hour (1.77%). With sodium hydroxide, carbon did not show a
significance difference but only a minimal increase (0.03%) at
3-hour pulping. Nitrogen content in the sludge from formic acid
is lower than that from sodium hydroxide which shows high
percentage of nitrogen. The nitrogen values increased (18.1
-39.77) with time during sodium hydroxide pulping which may
be due to the presence of triethylamine as reported by ,
while nitrogen in formic acid pulping sludge shows low values
with minimal variations throughout the pulping period with the
highest (0.29%) recorded after 2 hours pulping.
Table 3 reported the values of nitrogen and carbon contained
in the sludge obtained during pulping of kenaf stem with 90%
formic acid and sodium hydroxide at three-hour period. The
values of carbon from both chemicals during the three-hour
pulping were higher than those obtained from 20% and 60%
pulping with sludge from formic acid pulping having the highest
values (3.37-8.73%). The highest carbon (8.73%) was obtained
after 3-hour pulping with formic acid while sodium hydroxide
gave highest value (4.3%) after 1-hour pulping. Nitrogen content
from both formic acid and sodium hydroxide pulping have close
values (0.13 - 0.28) with formic acid showing a little higher value.
This result has a little similarity with  that reported 0.9% for
nitrogen Table 4.
The Table 5 & above shows Anova table that all the factors and
interactions were significant (p < 0.05) except time.
Table 6 & above shows Anova table that both all the factors
and interactions were significant (p < 0.05).
The sludge content from 20% pulping has nitrogen and
carbon from sodium hydroxide, sludge from 60% pulping has
carbon and nitrogen from both chemicals with more nitrogen
while 90% pulping has more carbon. Considering the pulped
stem, it showed under pulped, normal and over pulped with
respect to 20%, 60% and 90%. Therefore, looking at the normal
pulp at 60% concentration with the two chemicals, formic acid
has moderate values of carbon and nitrogen compare to sodium
hydroxide that showed high nitrogen content. Formic acid pulping
is considered here because it can easily be recovered after pulping
and the sludge used as manure. However, further research is
recommended with more focus on other sludge parameters.
Pearson D (1976)The Chemical Analysis of Foods. (7thedn), Churchill Living stone, London.
Nelson D, Sommers L (1996)Total carbon, organic carbon, and organic matter. 961-1010.In: DL Sparks et al. (Eds.), Methods of soil analysis. Part 3. Chemical Methods. SSSA Book Series No. 5, SSSA and ASA, Madison, WI.
Gary M, Said A, Amy S (1995)Sludge Characteristics andDisposal Alternatives for the Pulp and Paper Industry.In: Proceedings of the 1995 International environmental conference; 1995 May 7-10; Atlanta, GA. Atlanta, GA: Tappi Press: pp. 269-279.