ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT
AZOJETE - Centre for Satellite Technology Development Special Issue:

Space Science and Technology for Sustainable Development
AZOJETE, June, 2019. Vol. 15(SP.i2):160-171

Published by the Faculty of Engineering, University of Maidiguri, Maidiguri, Nigeria.

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160

ORIGINAL RESEARCH ARTICLE
ANALYSIS OF GROUNDWATER POLLUTION FROM AN UNLINED CONSTRUCTED

WETLAND SLUDGE DRYING BED

A. E. Adeniran1*, O. I. Ajibola2 and A. T. Aina3
1Department of Civil and Environmental Engineering, University of Lagos, Lagos, Nigeria

2Lagos State Building Control Agency, Ikeja, Lagos, Nigeria
3Works & Physical Planning Department, University of Lagos, Lagos, Nigeria

ARTICLE INFORMATION

Submitted: 10 May, 2018
Revised: 01 September, 2018
Accepted: 05 September, 2018

Keywords:
Groundwater pollution
Water quality monitoring
constructed wetland
Sludge drying bed.

ABSTRACT
Sludge drying beds (SBDs) are part of wastewater treatment processes
where dewatering and reduction of water content from the substrate
sludge take place to enhance caking and thus facilitate handling and
disposal. In this study, the effect of the operation of an unlined drying
bed of a constructed wetland for domestic wastewater treatment on the
adjourning groundwater was investigated. Experimental boreholes for
water quality monitoring were constructed downstream of the SBD prior
to its operation. Preliminary investigations of the quality of water in the
boreholes were carried out before the operation of the SBD. The
concentration levels of pH, Conductivity, Total Dissolved Solids, Colour,
Mn, Fe, SO4, NO3, Total Coliform and e-coli were used to empirically and
statistically determine the level of pollution of the ground water during
the operation of the SDB. The 2-way ANOVA at (�=0.05) showed that
the operation of the SBD had statistically significant impact on the
quality of the groundwater on all the observed parameters. For the
parameters observed, p<0.05 (p=0.00 for the averages of pH, EC, TDS,
Turbidity, Colour, Mn+2, Fe+2, SO4 and NO3), while p=0.0028 and 0.0018
for the averages of Total coliform and E.coli respectively in all the
boreholes. The distances from the discharge point of the SDB were at
15m, 20m, 25m, 30m, 35m, 40m and 50m for boreholes 1, 2, 3, 4, 5, 6
and 7 respectively. Also, comparison of the means of the quality
parameters with the allowable limits set by the Nigerian National
Environmental Surface and Groundwater Quality Control Regulations
(NSGQCR) indicated that the operation of the SBD rendered the quality
of the groundwater unacceptable

© 2019 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved.

1.0 Introduction
Pollution of water at any point in the hydrological cycle could prevent its availability in good
quality for other users in the cycle (Tundisi, 2008, Varade et al., 2017). Potential sources of
groundwater pollution include untreated wastewater effluent, seepage from leaking sewers;
shoddily built septic tanks, landfill leachate seepage, burial sites, unregulated animal husbandry
sites, farming practices and solid waste dumping on the ground. These pollutants include liquids,
organic substances, chemical substances and bacteria. Groundwater that is close to the surface,
as obtained in unconfined aquifers, is more susceptible to pollution (Naseh et al., 2018).

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Constructed wetlands are engineered systems that use natural functions of vegetation, soil, and
organisms to treat wastewater. Depending on the type of wastewater the design of the
constructed wetland has to be adjusted accordingly. Constructed wetlands have been used to
treat both centralized and on-site wastewater. Similar to natural wetlands, constructed wetlands
also act as a bio-filter and can remove a range of pollutants such as organic matter, nutrients,
pathogens, heavy metals from the water (Maiga et al., 2017). Constructed Wetlands (CW) have
emerged as a natural form of wastewater treatment. CWs operations mimic nature and research
has confirmed their suitability for effective and economic treatment of wastewater especially in
the tropical regions (Mairi et al., 2012; Olukanni and Kokumo, 2013 and de Anda et al., 2018).
Like all wastewater treatment processes, sludge is a by-product of CW wastewater treatment.
Sludge contains low concentration of solids compared to its much higher water content.
Dewatering aims at reducing the water content to enhance sludge handling for composting,
land application and disposal purposes. SDB are the oldest method of sludge dewatering and
are still used extensively in small to medium sized plants. This dewatering method easily
produces a sludge cake with 25 – 40 percent solids and can exceed 60 percent solids with
additional drying time (Qiao et al., 2010).

Groundwater pollution poses a major threat whilst employing the sludge drying bed method, as
the drained fluid percolates into the soil profile. Lagos State is increasingly dependent on
groundwater for domestic and industrial water supplies (Balogun et al., 2017). According to
Longe (2011), groundwater occurrence in the coast of Lagos can be classified as confined, semi-
confined to unconfined dominated by sand and clay formations. Sandy unconfined aquifers have
been reported to be susceptible to pollution (Odukoya et al., 2013, Naseh et al., 2018). The
University of Lagos, where this study was carried out, takes 60% of its domestic water supply
from groundwater aquifers both confined and unconfined (Adeniran, et al., 2013). The objective
of this study was to investigate the effect of the operation of an unlined drying bed attached to
a constructed wetland domestic wastewater treatment on the adjourning groundwater resources.

2. Materials and Methods
2.1 The study area
This study was carried out at the precinct of the constructed wetland located in the Service Area
of the University of Lagos, Lagos, Nigeria. The study area lies between longitudes 3o 23’ 44” E –
3o 23’ 48” E and latitude 6o 31’ 7” N – 6o 31’ 12” N (Figure 1). The area falls within the Dahomey
basin, which underlies a combination of inland, coastal and offshore regions that stretch through
Ghana, Togo, Benin and Southwestern Nigeria. The region is characterized by high water tables
within shallow aquifers with tropical weather conditions, lots of sunshine and excessive rainfall
(Obaje, 2009). The University is bounded on the East by the Lagos Lagoon which empties into
the Atlantic Ocean.

2.2 Constructed wetland wastewater treatment system
The SDB studied is part of the constructed wetland wastewater system for the treatment of part
of the domestic wastewater generated in the University of Lagos main campus. The wastewater
generated within the University community is conveyed through a network of sewers to the
central sewage pumping station. The wastewater is then processed through the various unit
operations including screening, aeration, anaerobic digestion, phytoremediation and slow sand

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Adeniran, et al: Analysis of groundwater pollution from an unlined constructed wetland sludge drying bed. AZOJETE,
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Corresponding author’s e-mail address: eadeniran@unilag.edu.ng, engrea54@gmail.com 162

filtration (Figure 1). Sludge dislodging operation was carried out fortnightly from the anaerobic
digester and the CW beds to the sludge drying bed and left to dry naturally by evaporation and
drainage through the underlying sand. The dried sludge cakes are evacuated for disposal and
land application. Prior to the introduction of the sludge drying bed and wetland treatment
system, the sludge from the anaerobic chamber were openly discharged, without treatment, on
the adjourning soil. The discharged sludge led to further degradation of the lagoon thus
endangering human and aquatic life as observed by Longe and Ogundipe (2010).

2.3 The sand drying bed and observation wells
The sand drying bed lies about 10m downstream of the anaerobic digester with dimensions 15 x
20 x 1.5 m (Figure 1). The sidewalls were constructed in concrete to ensure stability and prevent
collapse. A sand layer of 450 mm depth was placed over the bed. To monitor the groundwater
pollution (if any), seven (7) down gradient experimental boreholes of 150 mm diameter (with
screen casings) were drilled as part of the constructed wetland project by the University. The
depth of each of the experimental boreholes was 10 m. The distances from the discharge point
of the SDB were at 15m, 20m, 25m, 30m, 35m, 40m and 50m for boreholes 1, 2, 3, 4, 5, 6 and 7
respectively The constructed wetland and the observation boreholes were completely fenced to
avoid anthropogenic activities influence.

Figure 1: Contour Map of Study Area including Monitoring Boreholes

2.4 Collection and analysis samples
2.4.1 Experimental Boreholes
The experimental boreholes were monitored with preliminary samples collected for thirty (30)
days and analysed to determine the quality of the groundwater before the operation of the SDB.
During the operation of the SDB, groundwater samples were collected from the boreholes in

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accordance with US-EPA (2013) between the hours of 08.30 and 09.30 am. Sampling, at 5 m
depth, was done daily for 50 days for physicochemical parameters while sampling for
bacteriological parameters was carried out weekly for 8 weeks. The parameters monitored and
analysed were pH, Electrical Conductivity, Total Dissolved Oxygen, Turbidity, Colour, Manganese,
Ferrous, Sulphate, Nitrate, Coliform and e-coli.

2.4.2 Analysis of Samples
2.4.2.1 Laboratory Analyses
Analyses of samples were carried out using the American Public Health Association (APHA, 2012)
Standard method for examination of water and wastewater (Eaton et al., 2012). All pH
measurements were made using an Accumet XL50, Dual channel pH/ion/conductivity meter.
Conductivity meter was calibrated with reference solution just prior to measurement of electrical
conductivity (EC). The materials for the reference solution were deionized water, calibration
standard, plastic cup and a thermometer. The temperature of the solution was adjusted to be in
conformity with the standard calibration value provided by the manufacturer. TDS was measured
using HM digital TDS meter. Turbidity was measured using Hach Dr 900 photometer. Colour was
measured using Hanna HI83200 multi-parameter photometer. The concentration levels of Mn+2,
Fe+2, SO4 and NO3 of the samples were measured with Thermo-Scientific X-Series2 ICP-MS
spectrophotometer. Coliform and e-coli count were enumerated with pour plate method and
identified using morphological and biochemical tests in accordance with APHA (2012).

2.4.2.2 Statistical Analysis
Data were analysed at α = 0.05 using a two-way analysis of variance (ANOVA) on EXCELR Data
Analysis to compare the means samples from preliminary investigation (samples obtained and
analysed prior to the operation of the SDB) with the means results obtained during the
operation of the SDB. The results obtained were compared with data in literature (where
available). The means of the groundwater quality parameters obtained during the operation of
the SDB were also compared with Nigerian National Environmental (Surface and Groundwater
Quality Control Regulations, 2011 (NSGQCR, 2011) for surface and groundwater discharges,
irrigation and reuse.

3. Results and Discussion
The results of means of the observed parameters before and during the operation of the SDB
are presented in Tables 1 and 2 respectively. The summary of means, deviations and range of the
observed parameters are presented in Table 3. In Table 4 the mean of the replicate
concentrations of the quality parameters during the operation of the SDB are presented along
with the maximum allowable limits by the Nigerian National Environmental (Surface and
Groundwater Quality Control Regulations, 2011 (NSGQCR, 2011) for surface and groundwater
discharges, irrigation and reuse. Table 4 shows that the observed concentrations of most of the
physical, chemical and bacteriological parameters were beyond the limits specified by the
regulatory authority. The operation of the SDB had seriously polluted the groundwater. Table 5
shows the output of ANOVA analysis of observed parameters (α=0.05). It is observed from the
ANOVA that the operation of the SDB significantly affected the groundwater quality statistically.

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Adeniran, et al: Analysis of groundwater pollution from an unlined constructed wetland sludge drying bed. AZOJETE,
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Table 1: Mean of quality parameters in experimental boreholes before the operation of SDB
Parameters Units BH1 BH2 BH3 BH4 BH5 BH6 BH7
pH 4.48 4.59 4.54 4.43 4.43 4.43 4.64
Cond. μS/cm 257.44 257.76 257.78 257.66 257.34 257.47 257.57
TDS mg/l 80.57 79.82 79.65 79.53 79.48 79.45 79.41
Turbidity FTU 0.51 0.42 0.52 0.55 0.48 0.45 0.45
Colour PCU 30.47 31.16 31.06 30.46 30.63 31.14 31.24
Mn+2 mg/l 0.51 0.60 0.53 0.52 0.55 0.41 0.47
Fe+2 mg/l 0.04 0.05 0.05 0.05 0.05 0.04 0.05
SO4 mg/l 2.89 2.87 2.88 2.88 2.88 2.88 2.87
NO3 mg/l 2.53 2.65 2.71 2.61 2.74 2.72 2.73
Coliform fu/100ml 2 1 2 1 1 1 0
e-Coli cfu/100ml 0 0 0 0 0 0 0
Note: BH1, BH2, BH3, BH4, BH5, BH6, BH7 are Experimental Boreholes 1, 2, 3, 4, 5, 6 and 7 respectively.

Table 2: Weekly means of quality parameters in experimental boreholes during the operation of
SDB
Parameters Units BH1 BH2 BH3 BH4 BH5 BH6 BH7
pH 6.83 6.88 6.81 6.66 6.68 6.42 6.82
Cond. μS/cm 617.28 664.66 651.30 548.60 555.22 512.14 477.12
TDS mg/l 543.90 551.98 533.04 527.58 495.66 496.74 395.56
Turbidity FTU 24.48 26.78 25.55 24.15 24.70 23.69 21.89
Colour PCU 335.76 368.32 362.76 273.50 284.04 345.96 242.12
Mn+2 mg/l 2.37 2.46 2.30 1.88 1.58 1.70 1.13
Fe+2 mg/l 36.63 39.15 31.01 24.67 21.26 20.88 10.90
SO4 mg/l 61.93 67.01 60.52 58.43 57.99 56.97 46.83
NO3 mg/l 65.55 71.04 46.77 49.07 40.24 28.26 23.65
Coliform cfu/ml 942 1047 975 960 984 1036 776
e-Coli cfu/100ml 14 13 18 16 19 14 12
Note: BH1, BH2, BH3, BH4, BH5, BH6, BH7 are Experimental Boreholes 1, 2, 3, 4, 5, 6 and 7
respectively

Table 3: Summary of observations before and during operation of SDB
Parameters

Mean Before SDB
Mean
During SDB

pH 4.51±0.09 6.73±0.16
Cond. μS/cm 257.57±0.17 575.19±71.03
TDS mg/l 79.70±0.41 506.35±53.44
Turbidity FTU 0.48±0.04 24.61±1.61
Colour TCU 30.88±0.34 316.07±49.16
Mn+2 mg/l 0.51±0.06 11.54±3.81
Fe+2 mg/l 0.05±0.00 26.30±9.17
SO4 mg/l 2.88±0.01 58.53±6.15
NO3 mg/l 2.67±0.08 46.22±16.16
Total Coliform cfu/100ml 1±0.05 960±83
e-Coli cfu/100ml 0.0±0.0 15±2

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Table 4: Comparison of observed parameters with Nigerian standard for drinking water

Parameters Units
Observed
Pollutant Level

NSGQCR, 2011
Comments

pH 6.73±0.16 6.5-8.5 Acceptable
Cond. μS/cm 575.19±71.03 1000 Acceptable
TDS mg/l 506.35±53.44 500 Marginally Acceptable
Turbidity FTU 24.61±1.46 5 Not Acceptable
Colour TCU 316.07±49.16 5 Not Acceptable
Mn+2 mg/l 11.54±3.81 40 Acceptable
Fe+2 mg/l 26.30±9.17 0.5 Not Acceptable
SO4 mg/l 58.53±6.15 500 Acceptable
NO3 mg/l 46.22±16.16 40.0 Not Acceptable
Total Coliform cfu/100ml 960±83 10 Not Acceptable
e-Coli cfu/100ml 15±2 0 Not Acceptable

Table 5: Output of ANOVA analysis of observed parameters (α=0.05)

Parameter SS df MS F
P-
value F crit

Observatio
n Inference

pH 82.548 1 82.548 487.852 0.0000 4.1830 F>Fcrit; P<α
Statistically
Significant

EC 1782476.355 1 1782476.355 303.070 0.0000 4.1830 F>Fcrit; P<α
Statistically
Significant

TDS 2393786.247 1 2393786.247 678.072 0.0000 4.1830 F>Fcrit; P<α
Statistically
Significant

Turbidity 8408.549 1 8408.549 70.876 0.0000 4.1830 F>Fcrit; P<α
Statistically
Significant

Colour 1414055.224 1 1414055.224 317.001 0.0000 4.1830 F>Fcrit; P<α
Statistically
Significant

Mn 1793.557 1 1793.5566 313.953 0.0000 4.1830 F>Fcrit; P<α
Statistically
Significant

Fe 11377.843 1 11377.8427 29.814 0.0000 4.1830 F>Fcrit; P<α
Statistically
Significant

SO4 50672.420 1 50672.4202 201.470 0.0000 4.1830 F>Fcrit; P<α
Statistically
Significant

NO3 33075.1899 1 33075.1899 147.902 0.0000 4.1830 F>Fcrit; P<α
Statistically
Significant

Coliform 3680938.373 1 3680938.373 20.2609 0.0028 5.5914 F>Fcrit; P<α
Statistically
Significant

e-coli 894.952 1 894.952 23.5641 0.0018 5.5914 F>Fcrit; P<α
Statistically
Significant

3. 1 pH
The mean pH of 4.51±0.09 was observed before the operation of the SBD. During the operation
of the SDB, the mean pH values in the observation boreholes ranged from 6.42 to 6.88 (Table 2)
with a mean of 6.73±0.16 (Table 3). The pH values in the observation boreholes were consistent
with each other and ranged between 4.43 and 4.64 (Table 1). The pH level of the groundwater
was altered through the operation of the SDB from an initial acidic level ranging from 4.51±0.09
to an almost neutral level of 6.73±0.16. This may be due to the alkalinity of the sewage sludge

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(Table 3). A two-way ANOVA returned F=487.85 while F-critical=4.18; p=0.000<0.005, hence
statistically significant (Table 5). The operation of the SDB altered the level of the ground water
pH, though the observed levels are within acceptable limits recommended by the NSGQCR
(Table 4). This is consistent with Kengne et al. (2014) who reported groundwater pH level of 6.91
after unplanted drying bed leachate percolation.

3.2 Electrical Conductivity (EC)
Electrical conductivity (EC) is a measure of the capacity of water to conduct electric current. It is
an indication of the presence of high level of organic and inorganic nutrients in the water body.
The conduction of current through a water solution is primarily dependent on the concentration
of dissolved ionic substances such as salts. High amounts of dissolved substances can prevent
the use of waters for irrigation and drinking, hence conductivity ranks as one of the most
important inorganic water quality parameters. The lower the EC of a water sample, the better the
quality of the water. Mean conductivity value of 575.19 ± 71.03μS/cm was obtained during the
operation of the SDB, while a mean value of 257.64 ± 0.17μS/cm was obtained from preliminary
investigations (Table 3). The deviation in the EC values were significant; F=303.07>F-critical (4.18),
p=0.000<0.05 (Table 5). The levels of EC during the operation of the SDB were acceptable by
NSGQCR standards (Table 4). The results are consistent with results obtained by Kengne et al.
(2014), Sanko et al. (2014) and Pande et al. (2015) who obtained after pollution ground water
qualities ranging from 6.61 to 523.6 μS/cm.

3.3 Total dissolved solids (TDS)
Total Dissolved Solids (TDS) are the total amount of inorganic salts and organic matter dissolved
in a given volume of water. A high level of TDS is an indication of inorganic salts and organic
matter pollution. A mean TDS value of 506.35±53.44 mg /l was obtained during the operation of
the SDB while a mean value of 79.70±0.41 mg/l prior to the operation (Table 3). The initial
values of TDS in the boreholes range from 79.41 mg/l to 80.57 mg/l and were acceptable by
NSO standards (Table 1). The TDS values ranging from 395.56 mg/l to 551.98 mg/l observed
during the operation of the SDB (Table 2) were slightly higher than the regulatory value of
500mg/l (Table 4). Pande et al. (2015) reported TDS pollution values ranging from 789.6-811.4
mg/l. The concentration TDS in the observation boreholes during the operation of the SDB was
marginally acceptable within the limits recommended by the NSGQCR standards (Table 4)
though the analysis of variance indicated the change in the level of TDS that occurred during the
operation of the SDB was statistically significant (Table 5).

3.4 Turbidity
Turbidity is the measure of relative clarity of a liquid, as turbidity makes water cloudy or opaque.
Materials that caused turbidity include clay, silt and microscopic organisms. The mean turbidity
value was 0.48±0.04 FTU before the operation of the SDB, whereas the level during operation
was 24.61 ± 1.46 FTU (Table 3). The Turbidity level of the groundwater during the operation of
the SDB was observed to be higher than the regulatory value of 5 FTU (Table 4) hence the
aesthetic quality of the groundwater has been altered by the operation of the SDB. Analysis of
variance showed that the Turbidity level was statistically significant (Table 5). The turbidity level
of the groundwater was significantly altered due to the operation of the SDB. Pande et al. (2015)

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obtained values that ranged from 11.1 to 12.5 for groundwater quality after leachate percolation
for the city of Dhanbad.

3.5 Colour
Colour is an aesthetic requirement for water. The initial perception of the consumer and
acceptability of water for consumption or use will normally derive from the colour. Before the
operation of the SDB, the colour of the groundwater of the study area was acceptable at a level
of 30.88± 0.34 PCU and is less than the regulatory standard of 50 PCU (Table 1). The colour
variation in of the groundwater was consistent and ranged between 29.5 and 31.9 PCU. During
the operation of the SDB, the colour of the groundwater became clouded and not aesthetically
acceptable. The trends of colour in the observation boreholes (BH) ranged between 93 PCU and
497 PCU with peak points around dislodging days. The mean value of colour was an
unacceptable figure of 316.07±49 PCU in accordance with NSGQCR standard (Table 4). Analysis
of variance showed groundwater was significantly polluted (in respect to colour) as a result of
the operation of the SDB (Table 5). Pande et al. (2015), using visual observation, reported
alteration of groundwater from “very clear” to “pale yellow” and “light brown.”

3.6 Fe
High presence of iron ions (Fe+2) in water causes discolouration of sanitary wares and stains
laundry. Iron concentrations in naturally occurring surface waters are normally low (< 0.1 mg/l)
but can be higher in groundwater. A mean iron value of 26.30±9.17 mg/l was obtained from the
experimental boreholes during the operation of the SDB, while a mean value of 0.05 ± 0.00 was
obtained from preliminary investigation (Table 3). The concentration of Fe+2 of the groundwater
before the operation of the SDB was between 0.0 and 0.10 mg/l. The iron concentrations
changed significantly during the operation of the SDB and ranged from1.5 and 14.7 mg/l.
ANOVA analysis (Table 5) showed significant alteration to the iron concentration in the
groundwater during the operation of the SDB. These concentration values in the groundwater
during the operation of the SDB exceeded the NSGQCR maximum permissible level of 20.0 mg/l
(Table 4) hence not acceptable. Pande et al. (2015) and Ohwoghere-Asuma and Aweto (2013)
reported groundwater pollution levels for iron ranging from 17.28 to 18.60 due to sludge
leachate.

3.7 Manganese (Mn+2)
Manganese ions (Mn+2) is a chemical quality parameter in water. High concentration of Mn+2 in
water has health implication including neurological disorder. The mean Mn+2concentration of
the experimental boreholes during the operation of the SDB was 11.54 ± 3.81 mg/l, while a
mean of 0.51 ± 0.06 mg/l was obtained from preliminary data (Table 3). The levels of Mn+2
during the preliminary investigation were within the limits of NSGQCR standards and ranged
between 0.0 and 0.99 mg/l while the observed. Manganese values from the experimental
boreholes during the operation of the SDB varied widely between 2.40 and 29.70 mg/l and were
below the NSGQCR standard of 40mg/l (Table 4). Krithika et al. (2017) obtained similar results.
Analysis of variance, however, indicated statistical significance (Table 5) in view of the wide
difference that occurred between the observation before and during the operation of the SDB.

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3.8 Sulphate (SO4)
Sulphate minerals can cause scale build up in water pipes similar to other minerals and may be
associated with a bitter taste in water that can have a laxative effect on humans and young
livestock. High level of sulphate is not desirable in water for domestic and industrial uses. A
mean sulphate value of 58.53 ± 6.15 mg/l was obtained from the experimental boreholes, while
a mean value of 2.88± 0.11 mg/l was obtained prior to the implementation of the sludge drying
bed (Table 3). Before the operation of the SDB the observed concentrations of SO4 ranged from
2.83 to 2.92 mg/l and were within the NSGQCR specified standard (Table 4). During the
operation of the SDB, high values of 117, 119, 121, 125, 129 mg/l which were observed, though
these were below the NSGQCR standard of 500 mg/l (Table 4), the operation of the SDB altered
the level of SO4 in the groundwater significantly (Table 5). Lower figures that ranged from 43.36-
47.99 were reported for sludge leachate percolation by Pande et al. (2015).

3.9 Nitrate
Unpolluted natural waters usually contain only minute amounts of nitrate (Jaji et al., 2007). In
essence, nitrate is responsible for eutrophication. A mean Nitrate value of 46.22 ± 16.16 mg/l
was obtained from the experimental boreholes during the operation of the SDB, while a mean
value of 2.67 ± 0.08 was obtained from preliminary investigation (Table 3). The experimental
borehole samples displayed show high fluctuation of NO3 concentration reaching peak values
during dislodging operation. The mean value of 46.22 ± 16.16 mg/l is not acceptable by
NSGQCR standard (Table 4) and it is an indication of groundwater pollution. Analysis of variance
showed that the operation of the SDB had statistically significance on the nitrate level of the
groundwater (Table 5). Łuczkiewicz and Quant (2007) obtained NO3 value in groundwater of 80
±10.0 after land application of sewage sludge.

3.10 Total Coliforms
Coliforms are a large group of bacteria that inhabit the intestinal tract of humans and animals
that may cause disease. Coliform presence is an indicator of faecal or sewage pollution in water,
which impact negatively on odour, taste and turbidity. A mean coliform value of 960 ± 83
cfu/100ml was obtained from the experimental boreholes during the operation of the SDB, while
a mean of 1.00±0.05cfu/100ml was obtained from preliminary observations (Table 3). Before the
operation of the SDB the Total Coliform concentration in the ground water was acceptable and
was between 0 and 5.0 cfu/100ml. The experimental borehole Coliform levels, during the SDB
operation, ranged from 105 to 1,800 cfu/100ml, which exceeds the NSGQCR limits (10 cfu/100ml)
for drinking and recreational purposes (Table 4). Valenzuela et al. (2009) and Adeyemi et al.
(2007) reported Total Coliform groundwater pollution raging from a mean of 225 to 440
cfu/100ml and 140 to 271 cfu/100ml respectively due to sludge leachate. As shown in Table 5,
ANOVA showed that the operation of the SDB significantly altered the Total coliform level of the
groundwater. The implication is that the groundwater has become unsuitable for use or
discharge into

3.11 E. Coli
E. coli is a species of diseases causing coliform bacteria specific to faecal material from humans
and other warm-blooded animals. E.coli is widely preferred above other coliform as an indicator
of faecal contamination of water sources. A mean E-coli value of 0±0 cfu/100ml was observed
during the preliminary investigation before the introduction of the SDB. However, during the

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169

operation of the SDB an unacceptable high level of E.coli pollution was observed in all the
monitoring boreholes (Table 2). The value of E.coli during the operation of the SDB is consistent
with dislodging operation and ranged from 3 cfu/100ml to 31 cfu/ml. The E.coli in the
observation wells during the operation of the SDB was 15.0±2.0 cfu/100ml (Table 3). Mendoza et
al. (2017) obtained similar results of (3.6-23 cfu/100ml E.coli groundwater pollution due to
leachate percolation. The concentration of E.coli in the ground water exceeded the NSGQCR
limits of 0 cfu/100ml (Table 4). Analysis of variance showed that the operation of the SDB had
statistically significance E. coli concentration level in the groundwater (Table 5). As a result of its
operation, the groundwater at the precinct of the SDB was no longer safe for discharge into
water bodies or for direct usage.

4.0 Conclusion
Groundwater pollution induced by the operation of the sludge drying bed attached to the
constructed wetland domestic sewage treatment plant of the University of Lagos was
investigated. Samples were taken from seven down gradient boreholes downstream of the
sludge drying bed for various physicochemical and biological analyses. The obtained water
quality parameters were compared with the results from preliminary data obtained from the
boreholes before the implementation of the sludge drying bed. Increase in the various
parameters was observed in the borehole samples when the SDB was in operation. Analysis of
variance was carried out for each of the water quality parameters investigated. It was observed
that, statistically, the operation of the SDB significantly altered the ground quality parameters. In
almost all the parameters investigated, the values were in excess of the Nigerian regulatory body
(NSGQCR) standard for drinking water. The concentration values of the parameters during the
operation of the SDB were much higher than those obtained from the boreholes prior to the
operation of the SDB. The NSGQCR standards for the parameters were exceeded (indicating
groundwater pollution), with the exception of pH, Mn and SO4. It is recommended that a layer of
well compacted clay should be provided to avoid groundwater pollution. Also, before the
construction of drinking water boreholes in the precincts of sludge drying beds, septic tank soak
pits etc., thorough groundwater quality investigations including physical, chemical and biological
analysis should be conducted.

Acknowledgement
The authors wish to express our gratitude to the Department of Works and Physical Planning,
University of Lagos for making available the facilities under its control for this study. Our sincere
appreciation also goes to Surveyor Tunde Ramon for producing the topographic survey of the
study area under short notice.

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