CET Volume 86
DOI: 10.3303/CET2186111
Paper Received: 12 September 2020; Revised: 27 February 2021; Accepted: 9 April 2021
Please cite this article as: Njimou J.R., Tambe D.B., Nana A.S., Maicaneanu S.A., Noujep A.A., Tallab A., Elambo N.G., 2021, Sequential
Treatment of Municipal Wastewater and Valorization of Filtering Media, Chemical Engineering Transactions, 86, 661-666
DOI:10.3303/CET2186111
CHEMICAL ENGINEERING TRANSACTIONS
VOL. 86, 2021
A publication of
The Italian Association
of Chemical Engineering
Online at www.cetjournal.it
Guest Editors: Sauro Pierucci, Jiří Jaromír Klemeš
Copyright © 2021, AIDIC Servizi S.r.l.
ISBN 978-88-95608-84-6; ISSN 2283-9216
Sequential Treatment of Municipal Wastewater and
Valorization of Filtering Media
Jacques R. Njimoua,d*, Diana B. Tambeb, Annie S. Nanac, S. Andrada
Maicaneanud*, Armel A. Noujepe, André Tallabe, Nkeng G. Elambob
a
School of Chemical Engineering and Mineral Industries, University of Ngaoundere, P. O Box 454 Ngaoundere, Cameroon
b
Research Center, National Advanced School of Public Works, P.O. Box 510, Yaoundé, Cameroon
c
Center for Developpment Research, University of Bonn, P.O. Box Genscherallee 3, 53113 Bonn, Germany
d
Madia Department of Chemistry, Indiana University of Pennsylvania, Indiana, PA, 15705, USA
e
Energy, Water and Environment Lab., NASE, University of Yaoundé I, P. O. Box 8390 Cameroon
njimoujacques@gmail.com
Despite the wide availability of water in communities, sufficient water supply remains a major challenge in
developing contries. Most human activities, such as agro-industrial activities require enormous amounts of
water. Unfortunately at the tail end of such activities, large volumes of wastewater containing various
pollutants are released into the environment leading to its degradation.
This work aims to provide sustainable use of agro wastewater use in the city of Yaounde. With a source of low
cost agricultural waste available, corn cobs, this work proposes the development of a sequential filtrating
system for municipal wastewater treatment. A treatment process has been designed to recover C, N, P and to
remove hazardous microorganisms in the wastewater. With pollutant removal efficiencies between 51 and
95%, the proposed system allows the production of a water effluent readily to be used in agriculture, while the
waste filtering materials can be converted to compost and further used for biofarming.
1. Introduction
Water constitutes one of the most important factors of human as well as plant and animal lives. Its availability
is a crucial factor for global development. From an economic point of view, namely in developing areas and
particularly at the household level, the availability of drinking water saves time allocated for leisure, economic
activities, and childrens’ education (Singh, 2013). Although being the most precious component of the
environment, this gift is not always a reality in most developing communities. The issue of wastewater
contamination resulting from rapid population growth, agriculture, industries, and domestic waste has resulted
in high levels of pollutants (Beatriz et al., 2018; Rawlins, 2019) in water bodies making them unsafe for
consumption. Surface water sources are often highly polluted, and infrastructure to pipe water from fresh,
clean sources to arid areas is too costly endeavor. Groundwater is the best resource to provide clean water to
most African regions, especially in rural Africa. Groundwater has the benefit of being naturally protected from
bacterial contamination and is a reliable source during droughts. Unfortunately, they may be contaminated
with heavy metals, and bacteria introduced by leaking septic systems or contaminated wells (Gleick and
Pacific Institute for Studies in Development, 2002; Masindi and Foteinis, 2020).
It has been estimated that a minimum of 7.5 liters of water per person per day is required in the home for
drinking, preparing food, and personal hygiene, the most basic requirements for water. According to Gleick
and Pacific Institute for Studies in Development, (2002), 1.1 billion people around the world lacked access to
"improved water supply", and more than 2.4 billion lacked access to "improved sanitation." In Cameroon,
diarrheal diseases are the most prevalent waterborne diseases among children aged less than five years.
Studies conducted in the city among children aged less than five years showed that the prevalence rate
increased from 10.8% in 1998 to 13.1% in 2004.
Agriculture does not only requires large amount of water but also hign amounts of fertilisers. This situation was
identified in Buea, an urban community in Cameroon. A study carried out by Toyoh et al. (2017) on the local
661
perceptions on chemical fertiliser application showed thatmost farmers used fertilisers even though some
agrochemical retailers disliked chemical fertilisers because of an inadequate and untimely application by
farmers, leading to different health problems (Toyoh et al., 2017). The release of nutrients (nitrogen,
phosphorus, and potassium) and agrochemicals from intensive agriculture and animal waste can further
accelerate the eutrophication of freshwater and coastal marine ecosystems and increase groundwater
pollution. Eutrophication can lead to potentially toxic algal blooms and declines in biodiversity (Bhattacharyya
et al., 2020; De Corato, 2020; Sánchez et al., 2017).
Towards remedying the impacts of wastewater in local communities, the Cameroonian government has
constructed wastewater treatment station to ensure effluent treatment before discharge in the natural
environment. Unortunately, most of them failed to deliver positive results in the later run due to the high
nutrient content of wastewaters. This is the case of the Biyemassi II wetland treatment station in Yaounde 1
which initially produced effluent with a 80% average efficiency (TSS: 95%, COD: 92%, turbidity: 90%, color:
88%, BOD5: 82%, phosphate ions: 55%, ammonium ions 54%, and conductivity 38%). Currently there are
days when the system is not functioning correctly, a scenario similar with other ponding treatment systems
(Kengne et al., 2014, 2003).
Considering the impacts of the use of synthesis fertilisers and the impacts of wastewater in communities, it
was deemed necessary to develop a sustainable wastewater system based on low cost and readily available;
materials such as sand, corn cob capable of removing heavy metals and recovering nutrients from wastewater
and using it agriculture and irrigation with little impact on the environment. Therefore, the aim of this study is to
propose an low cost feasible method to solve an important problem in developing regions.
2. Materials and methods
2.1. Location of the study site and Physico-chemical characterisation influent
Yaounde, Cameroon, Africa, Figure 1, enjoys a typical equatorial Guinean climate characterised by two rain
seasons (September to mid-November and mid-March to June) and two dry seasons (mid-November to mid-
March and July to August). The annual rainfall is around 1600 mm and daily temperatures vary between 23
and 27 °C (Kengne et al., 2003). Its surface area is 304 km² and occupies the Mfoundi Division in the Central
Region. The Yaounde metropolis is part of the western sector of the southern Cameroon Plateau, composed
of gentle rolling chains of hills and numerous valleys. All these topographic elements depict a contrasted relief.
Samples were collected from a river in Yaounde not far from the Biyemassi appartment buildings. The river
was selected because it contained wastewater from households and treated effluent from the wastewater
treatment station. In situ parameters such as temperature, pH, and conductivity were measured using a
Hanna multimeter. Samples were collected in 1 L containers, stored in an ice cube box to slow down chemical
change and 30 L bottles of raw wastewater were then transported in the laboratory for the analysis of physic-
chemical parameters.
Table 1: Physicochemical characteristics of corn cobs.
Figure 1: Location of Yaounde subdivisions in Cameroon.
2.2. Treatment and preparation of experimental setup
The samples of raw wastewater collected in 30 L bottles were transported to the laboratory and kept at - 20°C
for later use. The treatment process developed in the laboratory for wastewater processing is comprised of the
steps described in Figure 2A.
Parameter Unit Value
Length (average) cm 7.97±0.3
Diameter (average) cm 2.54±0.2
pH (average) - 6.11
Average moisture content % 58.6
Dry filled weight (average) g 192
Specific surface area cm
2
/cm
3
1.03
True density g/cm
3
1.18
Porosity (average) % 69.8%
C : H : N : S % 45.3 : 7.1 : 0 : 0
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Pre-treatment aimed to remove large particles from the raw wastewater as they can clog and reduce the
system's efficiency. In this study, a 300 mm sieve was used to prevent sticks, plastics and other large particles
from getting in the treatment system. Further, the wastewater was then channelled into a container serving the
role of a sedimentation tank, followed by the filtration steps (Figure 2B). The corn cobs used as filtrating
materials were collected from a farm in Biyemassi dried and transformed into charcoal locally in an iron tin.
Corn cobs are agricultural waste available in large amounts in Cameroon Central Region.
Figure 2: Scheme of the treatment process (A) and experimental setup (B) RWW-T: Raw WasteWater Tank.;
FW – T: Filtrated Water- Tank-T for filtering raw wastewater with corn cobs (Eniyavan et al., 2018).
The experimental setup to treat wastewater effluent presented in Figure 2B was modified from Eniyavan
(Eniyavan et al., 2018), which used a setup based on leafy husk (cut into 1-2 cm pieces, dried in sunlight and
blended into a powder). In our proposed proces, corn cobs are initially dried in an oven and cut into equal-
sized pieces having a length (h) and diameter (d) of 7.97 ± 0.30 cm and 2.54 ± 0.20 cm, respectively. They
were later washed and dried in an oven for 5 hours. The corn cobs specific surface area was determined by
dividing the surface area with a volume of the corn cob, which was 1.03 cm2/cm3. Carbonisation of the corn
cobs was done locally in an iron drum of 200 L. The corn cobs charcoal was chemically activated using
sodium hydroxide solution and thermally activated by the Eniyavan procedure (Eniyavan et al., 2018). In
line with Lalita Prasida's method (Eniyavan et al., 2018) the experimental setup sequence included: lateral
section of corn cobs, pieces of corn cobs, corn cobs powder, corn cob charcoal, and fine sand filtering steps,
Figure 2B.
The following parameters were determined: % mass of cob initial mass of cob present massinitial mass of cob 100 (1) % mass of charcoal cob 100 (2)
The flow rate Q (m3/s) of the river was calculated using the floating method. Q (3)
The adsorbed quantity per unit mass of the solid q (mg/g) and the removal efficiency E (%) were calculated
according to Eqs. (41) and (5) (Kengne et al., 2014; Njimou et al., 2016; Yangui et al., 2017): q Co Cem V (4) E % Co CeCe 100 (5)
where, C0 (mg/L) is the concentration of the influent in the liquid phase, Ce (mg/L) the effluent concentration at
equilibrium, m (g) the mass of the adsorbent, and V (L) the volume of the wastewater.
Raw Wastewater
Pretreatment
Clarification HNO3
Corn
cobs/charcoal/
Sludge collection
and drying
Heavy metal
removal
Effluent into
environment for
irrigation
Crushing and sorting materials
containing nutrients (N, P, K) for
biofarming
Filtering
media
recovery
A B
663
3. Results and discussion
3.1. Physicochemical characteristics
Physicochemical characteristics of corn cobs before filtering runs are presented in Table 1, while their
characteristics after heavy metals adsorption and matter recovery are presented in Table 2.
Physicochemical parameters of wastewater before and after filtering runs conducted in the laboratory are
displayed in Table 3. In line with the above physicochemical properties, raw wastewater composition exceeds
the recommended norms. The corn cobs and sand filter system used after pre-treatment permitted the
removal of the above composition with percentage efficiency ranging in between 51 and 95% (Table 3).
Results show that conductivity is high (1207 µS/cm) due to diverse activities in the appartment buildings
Biyemassi but as it passes through the filtration media, its value decreases (589 µS/cm). Cobductivity starts
increasing again due to human activities (poultry, pig farming, waste disposal) along the water body.
Table 2: Physicochemical characteristics of corncobs after heavy metals adsorption and matter recovery.
Parameters
Sampling zone
Norms before adsorption after adsorption
pH 7.5 5.5 6.5 -7.5
Temperature (°C) 20.5 21.2 nd
Cu (mg/kg) 8 36 53
Cd (mg/kg) 0.09 4.226 3
Zn (mg/kg) 27.308 159.65 200
Pb (mg/kg) 47.970 40.97 50
N (mg/kg) 1.65 152 0.1-1.8
Total Hydrocarbures (mg/kg) / / nd
Table 3: Physicochemical parameters of wastewater before and after adsorption runs.
Parameters
Sampling zone
Norms
Efficiency
E (%) Untreated sample Treated effluent
pH 7.7 7.8 6-9 /
Temperature (°C) 25.56 25.56 30 /
Turbidity (JTU) 85 4 5 95.3
Conductivity (µS/cm) 1207 589 / 51.20
COD (mg/L) 478.7 53.2 250 60
BDO5 (mg/L) 139.8 51.9 50 63
TKN (mg/L) 55.8 5.8 ≤ 20 89.6
TSS (mg/L) 199.3 20.9 50 89.5
NO3
- (mg/L) 80 15 / 80
PO4
3- (mg/L) 127 43 / 66.1
Cd2+ (mg/L) 1.2 0.4 0.5 66.7
Cu2+(mg/L) 3 0.3 1 90
Pb2+ (mg/L) 1.68 0.72 0.5 57
The influent BOD5 concentration is above the authorised standard (50 mg/L). The COD concentrations
recorded are also all above the standard, reflecting a strong presence of organic and biological materials in
this polluted water, hence the observed eutrophication phenomenon. The COD concentrations are relatively
higher downstream than upstream, reflecting the high degree of pollution happenind downstream due to the
inflow of water with high organic content.
The pH values recorded in all the samples are included in the authorised pH range (6 -9). The values of
turbidity and suspended matter which are clearly higher in the effluent are brought into the norms after the
filtering sequence. The presence of TKN in this river water can be explained by the fact that people use
nitrogen fertilisers to increase their crops, but the system used lead to a decrese of this value into the norms.
The results obtained from the effluent and the corn cobs residues collected for biofarming show that they do
not contain a high content of heavy metals harmful to the environment and agriculture. Still, some cadmium
and zinc traces are present in proportions slightly above the recommended standards.
664
3.2. Discussion and recommendations
The obtained results showed high removal efficiency for COD, 60% and BOD 63% removal, displaying
showing that the proposed filtering system rapidly reduces COD and BOD concentrations. It was observed
that this is close correlation with the formation of a slime layer onto the corn cobs filter media. If these norms
are followed, raw water quality will contain these effluent composition amounts, not too far from standards.
For the effluent with more than 100% bed volume, the filter bed is saturated with the feed. At this stage, the
filtering media in the column was analyzed in order to decide its possible usage as compost material. The
results in Table 2 showed the presence of nutrients and some traces of metals in proportions slightly above
the recommended standards, showing promising application of this solid as compost. The composting is
recognised as a viable alternative and beneficial use of end-product for waste management. Composting is
the biological degradation of highly concentrated biodegradable organic wastes in the presence of oxygen
(aerobically) to carbon dioxide and water. The final product of composting is a stable humus-like material
known as compost (Eniyavan et al., 2018; Vilpas and Santala, 2007).
To obtain the compost from the effluent, saturated filtering material will be removed from the columns, dried,
crushed, and sieved using a 40 mm sieve as shown in Figure 3. Compost will be constantly turned using a
rake to ensure moisture evaporation and when dried will be stored in bags made from plastics. Its pH,
temperature and other necessary parameters will be continuously checked. Water resulting from the treatment
system will eventually be used for the irrigation of crops such as cereal and vegetables. Hence a control
quality of bio-products will be obtained from the farms.
Figure 3: Schematic diagram for nutrients and water recovery for biofarming usage.
4. Conclusions
This study aimed at providing a sustainable wastewater treatment that could ensure water reuse in the sense
of recovering nutrients and valorising the water for irrigation. Towards achieving the main goal, wastewater
was characterised. The characterisation showed that pH and temperature were within the norms of
wastewater in the environment. Unfortunately, other parameters such as BOD, COD, TSS, N and P
components were far above admissible values for the environment. Two systems were proposed to remedy
the situation: the first for wastewater treatment and recovery for irrigation while the second system aimed at
providing a composting system from sludge recovery.
Following initial parameters and studies done in the scientific domain, this work will go a long way to achieve
wastewater reuse if present design parameters are implemented in Cameroon's study site. More so, different
parameters such as TOC, COD and an ideal rainy season study should be done.
This system has proved that "use of secondary resources" in the treatment of wastewater and the treated
wastewater has a wide range of applications as a replacement of water resources for irrigation uses. It is very
helpful for people to use this technique to recycle water resources since it is economical and simple in
construction. This method is eco-friendly, a facile protocol, thus it is suitable for both developed and
developing countries without the use of special equipment and electricity and maintenance cost.
Acknowledgements
We wish to acknowledge the support for EXEED workshop funded by the German Academic Exchange
Services (DAAD). The authors are grateful for the Fulbright grant PS00301505 that offered data sharing
between University of Ngaoundere and Indiana University of Pennsylvania.
Recovered sludge + corn
cob medium and water
Drying of sludge for
3 days
Crush and mix the
dry sludge
Compost with nutrients (N, P, K)
ready for biofarming usage
Recovered water for
irrigation in farms
665
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