Engineered column treatment of greywater using raw and pyrolyzed coconut husk powder

Abstract

Reclaimed water from wastewater has become a prominent water source option to manage water scarcity. This study explores the potential of coconut husk biomass, a common waste material in Ghana, as a valuable low-cost resource for greywater treatment. Engineered column treatment was applied to investigate the influence of pyrolysis and biochar properties of coconut husk biomass waste on greywater treatment. Coconut husk biomass waste was pyrolyzed at 600°C and characterized using SEM, FTIR, and XRD. Three engineered columns with 1) raw coconut husk powder (RCHP), 2) charred coconut husk powder (CCHP), and 3) sand-gravel filters (control setup) were used. A hydrostatic head of greywater with a throughput of 8.0 ml/min and a hydraulic retention time of 45 min was maintained for engineered columns. The SEM image suggested an increased surface area and pores due to the pyrolysis of the husk biomass. RCHP and CCHP contributed to 63% and 95% turbidity removal, respectively. Experimental results showed high removal efficiencies of 71% COD for CCHP. The nitrate removal efficiency of 78.93%, 88.38%, and 28.65% was observed for RCHP, CCHP, and control respectively. The log removal of faecal coliform by CCHP was two orders of magnitude higher than RCHP. Faecal and total coliform removal was 2.87 log units for CCHP. Significant differences were observed between CCHP and RCHP, p < 0.05 for electrical conductivity and total dissolved solids of effluents. CCHP showed a promising potential for greywater treatment. Pyrolyzed coconut husk powder is a promising adsorbent applicable to greywater treatment.

Full text

Engineered column treatment of
greywater using raw and pyrolyzed
coconut husk powder
Theodora Sophia Taylor
1
*, Eugene Appiah-Effah
1
,
KofiAkodwaa-Boadi
2
,
3
, Ernest Obeng
1
and
Muriel Naa Lamiokor Ofei-Quartey
1
1
Regional Water and Environmental Sanitation Centre Kumasi, Department of Civil Engineering, Kwame
Nkrumah University of Science and Technology, Kumasi, Ghana,
2
Department of Environmental Health and
Sanitation Education, Akenten Appiah-Menka University of Skills Training and Entrepreneurial Development,
Kumasi, Ghana,
3
Department of Desalination and Water Treatment, Albert Katz International School for
Desert Studies, Zuckerberg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research,
Ben-Gurion University of the Negev, Beersheba, Israel
Reclaimed water from wastewater has become a prominent water source option to
manage water scarcity. This study explores the potential of coconut husk biomass, a
common waste material in Ghana, as a valuable low-cost resource for greywater
treatment. Engineered column treatment was applied to investigate the influence of
pyrolysis and biochar properties of coconut husk biomass waste on greywater
treatment. Coconut husk biomass waste was pyrolyzed at 600°C and
characterized using SEM, FTIR, and XRD. Three engineered columns with 1) raw
coconut husk powder (RCHP), 2) charred coconut husk powder (CCHP), and 3) sand-
gravel filters (control setup) were used. A hydrostatic head of greywater with a
throughput of 8.0 ml/min and a hydraulic retention time of 45 min was maintained
for engineered columns. The SEM image suggested an increased surface area and
pores due to the pyrolysis of the husk biomass. RCHP and CCHP contributed to 63%
and 95% turbidity removal, respectively. Experimental results showed high removal
efficiencies of 71% COD for CCHP. The nitrate removal efficiency of 78.93%, 88.38%,
and 28.65% was observed for RCHP, CCHP, and control respectively. The log
removal of faecal coliform by CCHP was two orders of magnitude higher than
RCHP. Faecal and total coliform removal was 2.87 log units for CCHP. Significant
differences were observed between CCHP and RCHP, p<0.05 for electrical
conductivity and total dissolved solids of effluents. CCHP showed a promising
potential for greywater treatment. Pyrolyzed coconut husk powder is a promising
adsorbent applicable to greywater treatment.
KEYWORDS
biochar, coconut husk biomass, engineered column treatment, greywater, pyrolysis, waste
1 Introduction
One of the very pressing global barriers to socioeconomic development is water scarcity (Liu
et al., 2017). Available water resources such as groundwater and open-bodied water are further
degraded and constantly under stress due to natural and anthropogenic occurrences (Ahuti,
2015;IWMI, 2019). In view of this global scarcity, wastewater (including greywater)
reclamation is thus an emerging water management technique that is fast becoming a
significant water source option (Singhal and Perez-Garcia, 2016;Yoshikawa et al., 2019).
With an annual global wastewater production of approximately 1,500 billion cubic meters and
daily domestic wastewater generation of 700–960 million cubic meters, it is estimated that
OPEN ACCESS
EDITED BY
Osnat Gillor,
Ben-Gurion University of the Negev, Israel
REVIEWED BY
Adewale George Adeniyi,
University of Ilorin, Nigeria
Titus Egbosiuba,
Chukwuemeka Odumegwu Ojukwu
University, Nigeria
*CORRESPONDENCE
Theodora Sophia Taylor,
theodorastaylor@gmail.com
SPECIALTY SECTION
This article was submitted to
Environmental Systems Engineering,
a section of the journal
Frontiers in Environmental Science
RECEIVED 22 October 2022
ACCEPTED 09 January 2023
PUBLISHED 23 January 2023
CITATION
Taylor TS, Appiah-Effah E,
Akodwaa-Boadi K, Obeng E and
Ofei-Quartey MNL (2023), Engineered
column treatment of greywater using raw
and pyrolyzed coconut husk powder.
Front. Environ. Sci. 11:1077379.
doi: 10.3389/fenvs.2023.1077379
COPYRIGHT
© 2023 Taylor, Appiah-Effah, Akodwaa-
Boadi, Obeng and Ofei-Quartey. This is an
open-access article distributed under the
terms of the Creative Commons
Attribution License (CC BY). The use,
distribution or reproduction in other
forums is permitted, provided the original
author(s) and the copyright owner(s) are
credited and that the original publication in
this journal is cited, in accordance with
accepted academic practice. No use,
distribution or reproduction is permitted
which does not comply with these terms.
Frontiers in Environmental Science frontiersin.org01
TYPE Original Research
PUBLISHED 23 January 2023
DOI 10.3389/fenvs.2023.1077379

greywater accounts for 70%–80% of household wastewater, and its
reuse can cut urban demand for potable water by 30%–70%.
Several physical, chemical, biological, and a combination of
techniques ranging from conventional to non-conventional
systems (Maimon and Gross, 2018) have been applied to
wastewater reclamation aimed at reducing treatment costs and
improving treatment efficiency (Gwenzi et al., 2017). Physical
techniques such as screening, gravity separation, dissolved air
flotation, filtration, adsorption, desorption, membrane filtration,
coagulation, flocculation, de-emulsification, and chemical
techniques such as pH adjustment, precipitation, ion exchange,
oxidation, reduction, electrolysis, resin-based processes, and
disinfection have all been applied (Meena et al., 2021).
Biological treatment options include aerobic and anaerobic
treatment and ion-exchange membrane bioreactors. The
treatment method usually depends on the end-use,
composition, and characteristics of the influent greywater,
pollutant or pathogen of interest, treatment costs, treatment
efficiency, energy, operations, and maintenance costs, among
others (Abdel-Shafy and Al-Sulaiman, 2014). Of all treatment
options, adsorption has proven to be a highly favorable and
much cheaper treatment option. Profound importance of
adsorption include high pollutant removal efficiency, ease of
operation and manipulation, tendency to eliminate multiple
pollutants concurrently as well as cost effectiveness (Egbosiuba
et al., 2020). Detoxification through adsorption is facilitated by the
presence of reactive functional groups in adsorbates as well as the
bonds formed between the adsorbate and adsorbent (Rashed,
2013). Adsorption has been used to remove many contaminants
from wastewater including textile dyes and heavy metals
(Egbosiuba et al., 2021). Depending on the contaminant of
focus, the type and dosage of adsorbent used and removal
conditions vary, i.e. pyrolysis conditions (time, temperature),
pH, contact time (Egbosiuba et al., 2021).
Coconut husk, also known as coco peat or coconut coir, is the
fine spongy fiber left behind when coconut husk fibers are separated
from the shell during processing (Ifelebuegu and Momoh, 2015;
Suman and Gautam, 2017). It is also one material that has many
useful applications in water treatment (Parsons, 2014). It has been
used extensively to remove different pollutants from water and
wastewater streams (Marathe et al., 2021). It is also one of the
emerging adsorbents used for heavy metal adsorption and nitrogen
removal (Ifelebuegu and Momoh 2015;Clarence, 2016). When
converted to biochar, pyrogenic black carbon derived from
incomplete biomass combustion, the coconut husk is an effective
media for biofiltration in wastewater treatment (de Oliveira Cruz
et al., 2019;Halfhide et al., 2019) with a solid sorption capacity to
pesticides and natural contaminants. Its physicochemical properties
like surface area, particle size distribution, functional groups, pore
spaces, or volume contribute to its removal efficiency (Suman and
Gautam, 2017). Pyrolysis of biochar influences the surface functional
groups by rearranging structural bonds. An FTIR spectrum of the
biochar would reveal a disappearance of certain bands characteristic
of the carbonized raw materials (Tomczyk et al., 2020). Findings
from batch experiments suggested that the biochar’s maximum
phosphorus sorption capacity could reach >100 mg g
−1
(Yao,
2013). Biochar at a pH of 6 has also shown complete phosphate
removal from fertilizer wastewater. Sugar beet biochar pyrolyzed at
600°C shows the adsorption of phosphate ions on the biochar surface
(Chen et al., 2011). Similarly, orange peels produced at temperatures
between 250 and 700°Cgave80%–85% phosphate removal. Nitrates
are adsorbed by bamboo biochar with a concentration range of
0–10 mg/L. Biochar produced above 400°C was effective for organic
and inorganic pollutant sorption, whereas porous carbonized
fractions are dominant at high temperatures (Uchimiya et al.,
2010). Food waste biochar is also known to enhance Copper
coagulation and remove Chromium, Nickel, and organic dyes
from wastewater (Yang et al., 2021).
Meanwhile, coconut waste contributes significantly to the waste
management problem in developing economies like Ghana and other
coconut-rich countries. A large volume of waste is generated daily, and
in Ghana, the husks are not disposed of properly, becoming an
aesthetically objectionable breeding habitat for mosquitoes and
other disease-causing vectors. Although other studies have shown
that coconut husk biomass is suitable for water and wastewater
treatment, its application to wastewater in Ghana has not been
thoroughly investigated. With urban wastewater generation
expected to increase in countries like Ghana from about
530,346 m
3
/day (36%) in 2000 to about 1,452,383 m
3
/day (45%) in
2020, it is worthwhile to explore the use of locally available coconut
husk biomass for greywater treatment (Gyampo, 2012).
Therefore, this study will characterize locally available coconut
husk biomass waste, convert it to biochar through pyrolysis, establish
the influence of pyrolysis on its physical and chemical properties and
further investigate its potential for greywater treatment. The study will
contribute to the sustainable development goal (SDG) six on clean
water and sanitation by 1) complementing ongoing scientific studies
on low-cost wastewater treatment 2) improving the body of knowledge
on using coconut husk biomass for wastewater treatment 3) reducing
the burden of coconut husk biomass waste by re-using the husk,
towards a circular economy.
2 Materials and method
2.1 Coconut husk powder (CHP) production
and characterization
Coconut husk was cut into chunks and dried at 105°C for 24 h
until complete drying as shown in Figures 1A,B. The dried husk was
milled to obtain Raw Coconut Husk Powder (RCHP). A fraction was
also charred at 600°C(Egbosiuba et al., 2020) for 2 h in a Nabertherm
2,345 muffle furnace and milled to obtain Charred Coconut Husk
Powder (CCHP). Optimum temperature range for pyrolysis is
between 500 and 800°C but 600°C in particular yields very high
microsurface area, pore volumes and a tremendous adsorption
capacity (Chartterjee et al., 2020). Both RCHP and CCHP were
sieved to obtain a particle size of 0.2–0.4 mm (Figures 1C,D). A
known volume of distilled water was mixed with the two fractions
separately in a ratio of 1:10, after which the pH of each mixture was
determined using a pH meter. The Fourier-Transform Infrared (FTIR)
Spectroscopy used Bruker Alpha II Platinum ATR-FTIR to study the
chemical composition and surface functional groups. The morphology
of the two forms of CHP was observed using Scanning Electron
Microscopy (SEM) under various voltages, beam sizes, and
magnifications ranging from ×50 to 2000X using a Nano-SEM
230 FEG. The SEM was run in low vacuum mode using the
variable contrast detector.
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2.2 Filter design and greywater sampling
The column filter bed consisted of a column of 40.0 cm in length, a
fixed bed depth of 14.0 cm, and a 7.0 cm internal diameter. Three beds
were designed for the Control, RCHP, and CCHP beds, each in
duplicates (Figure 2). A weight of 110.0 g of the CCHP
corresponded to a bed depth of 14.0 cm whilst 80.0 g of RCHP
corresponded to the same bed depth, RCHP was denser than
CCHP. Each filter bed was supported by 2.0 cm sand and gravel
layers at the bottom and a 1.0 cm sand layer at the top to prevent
channelling. The influent flow rate was set at 8.0 ml/min at a retention
time of 45 min.
FIGURE 1
(A) Fresh coconut husk (B) Dried coconut husk (C) Raw coconut husk powder (D) Charred coconut husk powder.
FIGURE 2
Schematic diagram of experimental Setup (not to scale).
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The influent feed was domestic greywater collected from students’
residential facilities at the Kwame Nkrumah University of Science and
Technology campus in Kumasi, Ghana. The effluents were collected
from the filters over time and analyzed for physicochemical and
biological properties using standard methods for the examination
for water and wastewater (APHA 2005) where applicable. pH, electric
conductivity, and TDS were measured by immersing the Palintest
Micro 800 MULTI electrode in a known volume of solution. Colour
was determined using the Lovibond Comparator. Equal volumes of
sample and distilled water were pipetted into separate test tubes and
inserted into the comparator and measurements taken. The HANNA
Turbidimeter HI 93414 was used to measure the turbidity of samples.
Empty vials were filled with a known sample volume and placed in the
vial holder for measurements. DO and BOD
5
were analyzed by mixing
a known volume of sample with standard nutrient pillows and
subsequently measuring the DO using HACH HQ 30d meter.
COD was analyzed by the digestion method. Nitrates were
measured using HACH DR3900 spectro photometer at a
wavelength of 500 nm. Microbial analysis was done by the Serial
Dilution Method using chromocult agar, membrane filtration and
plate counting.
3 Results and discussion
3.1 Physical characteristics of RCHP and
CCHP
The physical properties of CCHP are presented in Table 1. The
pH of the RCHP was determined to be 4.67, an indication of the acidic
nature of the adsorbent. Conversely, the pH of the CCHP was 10.61,
being basic. The basic pH of the CCHP may be due to the pyrolysis of
the CCHP, which modified the structural morphology and increased
the ash content. Carbonization also favors the formation of carbonates
and inorganic alkalis while decreasing acidic functional groups
(Tomczyk et al., 2020). The pH values are within ranges found in
similar studies of coconut husks (Samaniego and Tanchuling, 2019).
The bulk density and porosity of the RCHP were higher than the
CCHP, suggesting that the RCHP has relatively better throughput.
Kalaivani and Jawaharlal (2019) reported bulk density slightly higher
than that obtained in this study. The RCHP recorded a moisture
content of 5.7% and the CCHP, 5.6%. The relatively lower moisture
content of the CCHP could be attributed to the temperature effect on
the CCHP, which contributes to the loss of water and volatile organic
compounds.
3.2 SEM imaging
The SEM images in Figure 3 reflect differences between the
morphology and pore structure of the RCHP and CCHP. The
RCHP shows a distinct fibrous structure with heterogeneous
cylindrical pores. After carbonization, it is observed that the
linkages of the carbon-bearing adsorbent in the microstructure are
split. This follows observations by Suman and Gautam (2017). The
CCHP shows relatively higher pores and increased surface area due to
the breakdown of lignin and cellulose compounds at elevated
temperatures under pyrolysis. Maximum surface area have been
reported to occur at 600°C(Egbosiuba et al., 2020). Higher pores
provide adequate receptacles within the interstices of the adsorbents
TABLE 1 Physical characteristics of CHP.
Sample pH Bulk density (kg/m
3
) Pore volume (cm
3
) Particle density (kg/m
3
) Porosity (%) Moisture content (%)
Raw CHP 4.67 875.00 32.00 250.00 80.00 5.70
Char CHP 10.61 760.00 37.50 253.00 75.00 5.60
FIGURE 3
(A) SEM image of RCHP (B) SEM image of CCHP.
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for adsorbates. Increased surface area is equally necessary for increased
sites for the adsorption of contaminants. The SEM images
demonstrate that the properties of the RCHP are enhanced after
charring and based on the pore sizes and surface area, the potential for
contaminant removal of the CCHP is relatively higher as compared to
the RCHP.
3.3 Functional group characteristics of CHP
The infrared spectra of the RCHP and CCHP are presented in
Figures 4,5respectively. The peak observed at 3,340 cm
−1
(Figure 4)is
characteristic of an O-H stretch of carboxylic acids (Egbosiuba et al.,
2020) or hydroxyl vibrations of phenolic groups of lignin within the
coconut husk powder, similarly observed by Etim et al., 2016 and
Mishra and Basu, 2020. At 2,913 cm
−1
the medium peak indicates a
C-H stretching motion of alkane groups (Malik et al., 2017;Suman
and Gautam, 2017). The C=O intensity stretch at 1722 cm
−1
is
characteristic of carboxylic acids, and 1,605.4 cm
−1
represents the
C=C bonds observed for RCHP (Wang and Sarkar, 2018;Bello
et al., 2019). The C-C bonds in aromatic compounds in the lignin
of coconut husks are observed at 1,515 cm
−1
in the RCHP spectrum.
Lignin itself shows bands at 1,242 to 1,514 cm
−1
resulting from
aromatic C=C and C=O stretches of carboxylic acids (Qambrani
FIGURE 4
Infrared spectrum of raw CHP.
FIGURE 5
Infrared spectrum of char CHP.
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et al., 2017). The N-O symmetric bond shows the presence of the nitro
group at 1,368 cm
−1
. At 1,440 cm
−1
, the broad intensity at 1,032.45 cm-
1 indicates symmetric C-O stretching movements in cellulose (Chen
et al., 2011).
The spectrum observed for the CCHP (Figure 5) does not align with
the bands of known functional groups. This may be due to pyrolysis that
modified the structural integrity of the CHP. The decomposition of
cellulose and lignin polymers during carbonization facilitates the
disintegration of bonds. The characteristic O-H band observed for
the RCHP was absent in the spectrum of the charred sample
because temperatures above 400°C have been known to decompose
lignin present in coconut husk (Wang and Sarkar, 2018) hence, the
absence of the characteristic O-H vibrations in the IR spectrum of CHP
calcined at 600°C(Suman and Gautam, 2017). The C=O peak is also not
observed in the spectrum of the charred CHP because, during the
carbonization of coconut husk, carboxyl and carbonyl groups are
broken down to yield carbon monoxide and dioxides (Wang and
Sarkar, 2018). The peaks in the spectrum are due to incomplete
degradation that occurs at 600°C of which higher temperature
carbonization would produce relatively smoother IR curves.
3.4 Influent greywater quality
Table 2 shows the result of the physicochemical and biological
parameters of the influent greywater. The pH range of the greywater
sampled in Kumasi was determined to be 6.5 to 7.4. The mean pH and
BOD are comparable to similar studies of grey water in Kumasi
(Dwumfour-Asare et al., 2020). The total suspended solids
concentration (TSS) range corroborates the values reported by
Chaillou et al. (2011). The influent Chemical Oxygen Demand
(COD) concentration was lower than domestic greywater
characteristics in Kumasi (Dwumfour-Asare et al., 2020). However,
the concentrations are comparable to studies conducted by Pillai and
Vijayan (2012). Empirical data from Casanova et al. (2001) also
support the turbidity value of the influent observed in this study.
However, Anim et al. (2014) reported a relatively higher turbidity of
90 NTU. The difference in turbidity values of the greywater influent
may be attributed to the variations in water use of consumers.
Microbial cultures of Salmonella spp and Escherichia coli were
identified in the influent greywater.
3.5 Effect of charred husk powder on effluent
quality
3.5.1 pH
From an influent pH of 6.73, the greywater effluent from the
RCHP column bed dropped to 5.27, and the effluent through the
CCHP column bed increased to 8.8, a reflection of the acidity and
alkaline nature of the RCHP and CCHP, respectively.
Biochar is generally alkaline as carbonization has been found to
increase the pH of the biomass feedstock due to the formation of
carbonates and inorganic alkalis. Carbonization also decreases acidic
functional groups (Belhachemi et al., 2019). Thus, releasing OH ions
from biochar when in contact with water and increase pH. The
carbonization process favors the formation of carbonates and
inorganic alkalis while decreasing the acidic functional groups of
the feedstock (Tomczyk et al., 2020).
TABLE 2 Physicochemical and biological characteristics of influent greywater.
pH TDS
(ppm)
TSS
(ppm)
Conductivity
(µS/cm)
Colour Turbidity
(NTU)
DO
(ppm)
BOD (ppm) COD
(ppm)
NO
3
−
(ppm)
PO
4
3-
(ppm)
Total coliform
(CFU/100 ml)
Faecal Coliform
(CFU/100 ml)
Mean ±
SD
6.86 ±
0.24
146.35 ±
14.79
68.66 ±
71.82
299.58 ± 29.97 60 ± 25 70.11 ± 27.86 0.86 ± 0.5 169.36 ±100.84 237.46 ±
125.01
6.31 ± 1.52 1.153 ± 0.80 3.32 x 10
6
2.87 × 10
6
Range 6.56 - 7.4 123.7 -
168.7
10.0 - 215.0 253.4 - 346.2 25 - 100 41.6 - 154.0 0.44 - 1.72 77.4 - 460.0 84 .0 - 483.0 2.5 - 8.4 0.15 - 3.34 5.00 × 10
4
-7.03×10
6
2.3 × 10
4
-2.40×10
6
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Depending on the intended use, pH adjustment may be required
for effluents from both RCHP and CCHP. Considering the adsorbent
pH of 4.67 for the RCHP, 10.61 for the CCHP, and the effluent pH, it
can be concluded that the adsorbents adjusted the acidity and
alkalinity during the treatment of the effluents based on their
prevailing pH. Thus, the pH of effluents from biochar treatments
tends to have increased pH compared to non/biochar treatments
(Emslie, 2019).
3.5.2 Dissolved oxygen (DO)
Both RCHP and CCHP improved the dissolved oxygen
concentration of the greywater exponentially. Influent DO was
0.86 mg/L, effluent DO from the CCHP was 7.37 mg/L, the RCHP
was 5.21 mg/L and the Control was 4.84 mg/L. The DO concentration
of the effluents establishes a possible reduction in the organic matter
content of the influent as greywater was filtered. Biochar is also rich in
oxygen-containing compounds, which may serve as oxidizing agents
for water flowing through the adsorbents (Qambrani et al., 2017). The
effluent flowing through the Control recorded an appreciable level of
DO. This is consistent with studies by Yaseen et al. (2019), where a
30%–50% increase in the DO of laundry greywater through sand-
gravel filters was observed. The effluent DO’s were within guideline
values for discharge and reuse by the World Health Organization
(WHO), which is >1 mg/L. However, stricter limit of >2 mg/L is
recommended in some countries (World Health Organization, 2006).
3.5.3 Electrical conductivity (EC) and total dissolved
solids (TDS)
Significant differences were observed between CCHP and RCHP
(p<0.05) in terms of electrical conductivity (EC) and Total Dissolved
Solids (TDS) of effluent. Generally, effluents from the CCHP showed
an increase in EC and TDS concentrations from 298.19 μS/cm to
FIGURE 6
Effect of pyrolysis on organic matter removal.
FIGURE 7
Effect of pyrolysis on nitrate removal.
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411.74 μS/cm and 145.36 to 200.76 mg/L respectively. The RCHP
effluents recorded a reduction in EC and TDS concentrations from
298.19 to 207.81 μS/cm and 145.36 to 101.18 mg/L respectively. The
relatively higher EC of the CCHP effluent suggests the release of water-
soluble ions from the biochar into the greywater as suggested by
Belhachemi et al., 2019. It has been asserted that pyrolysis increases the
EC of biochar (Hoffman et al., 2019) probably as a result of the
breaking of bonds which further enhances the release of free ions in
the CCHP into the effluent. The findings compare positively with
other studies that have reported an increase in EC after carbonization
(Suman and Gautam, 2017). Effluents from the Control showed a
decrease in both TDS and EC like Yaseen et al. (2019), consistent with
the fact that sand filters are known to reduce the EC of water due to ion
exchanges between the finer particles of sand and the water.
3.5.4 Turbidity and colour
Effluents were generally less turbid after filtration. Turbidity
values declined from an influent value of 67.30 NTU to 3.62 NTU,
24.61 NTU, and 41.27 NTU for CCHP, RCHP, and Control
respectively. This corresponds to 95% removal for CCHP, 63%
for RCHP, and 39% for the Control. The increased surface area and
porosity of the biochar due to pyrolysis enhances the removal of
solids and adsorption of molecules that impart color and turbidity
(Enaime et al., 2020;Fu et al., 2020). Turbidity values for the RCHP
were relatively lower than CCHP due to the adsorbent’slow
porosity and surface area. Turbidity removal by the Control is
consistent with the available literature on turbidity removal by
sand filters (Saad et al., 2016) in that sand and gravel grains are
known to remove suspended matter in greywater, thereby making
wastewater less turbid (Samayamanthula et al., 2019). From an
influent of 58 TCU, results obtained for color in the treated effluent
were 10 TCU, 69 TCU, and 63 TCU for CCHP, RCHP, and Control.
The Control and RCHP showed an increase in the color of
greywater after filtration. This could be attributed to microbial
activities on both the greywater and the adsorbent, which will
impart some turbidity and color.
3.5.5 BOD, COD, and TSS removal
The removal efficiency of organic matter by CCHP was relatively
higher than by RCHP (Figure 6).ThepercentageremovalofCODand
BOD was 71% and 16%, respectively, for CCHP. COD removal efficiency
for RCHP was 1.7% but was relatively poor for BOD removal. CCHP
showed significant differences (p<0.05) in COD removal compared to
RCHP and Control. Though RCHP successfully removed suspended
solids, it was not effective for BOD and COD removal. The negative BOD
recorded for the RCHP could be attributed to nitrogenous oxygen
demand in the presence of nitrifying bacteria over the incubation
period. Cocopeat supports microbial communities’growth (Thomson,
2014) and over time, microbial breakdown of lignocellulose in cocopeat
and pine barks occurs as reported by (Dalahmeh, 2016)significantly
reducing their ability for BOD and COD removal. In the case of CCHP,
there was no observed microbial breakdown of the biochar because
pyrolysisaltersbiocharcarbons’chemical nature, making them
relatively stable and resistant to biological decomposition (Qambrani
et al., 2017).
3.5.6 Nitrate removal
Nitrate removal was 78.93%, 88.38%, and 28.65% for RCHP, CCHP,
and Control respectively (Figure 7). The percentage removal of the CCHP
was 10% higher than the RCHP and 60% higher than the Control. The
differences could be attributed to the carbonization of the husk which
possibly increased the adsorptive sites and capacity of the husk, improved
the C: N ratio, and the activity of denitrifying bacteria (Halfhide et al.,
2019).TheremovalratewashigherthanpredictedbyYao (2013) biochar
carbonized at 600°C. However, the removal rate was consistent with
studies by Halfhide et al. (2019) who reported nitrate removal from stock
solution and wastewater between wastewater 74%–90%.
3.5.7 Microbial populations
The biochars effectively reduced microbialloadsinthewastewater
stream (Figure 8). The log removal of Faecal Coliform (FC) by the RCHP
wastwoordersofmagnitudelessthanthatoftheCCHP.Faecalandtotal
coliform removal was 2.87 log units for CCHP compared to 0.31 log units
FIGURE 8
Microbial population of treated effluent.
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Taylor et al. 10.3389/fenvs.2023.1077379

for Total Coliform (TC) removal recorded for the control filter. This
supports the assertion that biochar filters increase the removal of
coliforms (E. coli)fromwater(Maurya et al., 2020). Previous studies
reported log removal between 0.1 and 1.0-log units for E. coli removal
depending on initial counts. Though the findings from this study agree
with the reported values, the log removal observed is relatively higher. The
higher removal observed for this study may be attributed to biochar
properties and the varying nature of biochar feedstocks (Afrooz and
Boehm, 2016). The particle sizes of the biochar also facilitate microbial
removal by adsorption due to the larger surface area and increased contact
with the wastewater (Guan et al., 2020). A significant difference was
observed between the CCHP and the Control (p<0.05). The log removal
recorded in the control filter was 0.31-log units forTotalcoliforms.The
reductioninthemicrobialpopulationinthecontrolfilter could be due to
straining aided by biofilm formation on the sand and gravel surfaces.
4 Conclusion
Coconut husk biomass showed great potential as a filter material for
greywater treatment. Pyrolysis was successfully applied to the coconut husk,
which significantly improved greywater treatment. CCHP contributed to
95% of turbidity removal. High removal efficiencies of 71% COD by CCHP
were observed. The CCHP had a relatively higher nitrate removal efficiency
of 88.38%, as compared to 78.93% and 28.65% for RCHP and Control
respectively. Empirical evidence demonstrates that CCHP was more
effective in removing color, turbidity,COD,BOD,andnitrates.The
SEM image suggests that the carbonization of the raw coconut husk
increased the surface area and number of pores of the adsorbent. The
log removal of faecal coliform by CCHP was two orders of magnitude higher
than the RCHP. The CCHP was also efficient in the treatment of microbial
loads. The results demonstrate that pyrolyzed coconut husk biomass waste is
a promising adsorbent applicable to the treatment of greywater.
Data availability statement
The original contributions presented in the study are included in
the article/supplementary material, further inquiries can be directed to
the corresponding author.
Author contributions
All authors listed have made a substantial, direct, and intellectual
contribution to the work and approved it for publication.
Funding
This study was funded by the Regional Water and Environmental
Sanitation Centre Kumasi (RWESCK) at the Kwame Nkrumah
University of Science and Technology (KNUST), with funding
from the Ghana Government through the World Bank, under the
Africa Centres of Excellence project. The views, however, expressed in
this paper do not reflect those of the World Bank, Ghana Government,
or KNUST.
Acknowledgments
ETH Zurich for Development (ETH4D) and Eawag is duly
acknowledged for providing financial and technical support.
Conflict of interest
The authors declare that the research was conducted in the
absence of any commercial or financial relationships that could be
construed as a potential conflict of interest.
The handling editor OG declared a shared affiliation with the
author KA-B at the time of review.
Publisher’s note
All claims expressed in this article are solely those of the
authors and do not necessarily represent those of their affiliated
organizations, or those of the publisher, the editors and the
reviewers. Any product that may be evaluated in this article, or
claim that may be made by its manufacturer, is not guaranteed or
endorsed by the publisher.
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