| dc.description.abstract | Endocrine disrupting chemicals (EDCs) cause adverse health effects to biota. They are
not effectively removed by conventional wastewater treatment options and advanced
methods are costly. This study investigated the levels, mass loadings, removal efficiency,
and associated ecotoxicological risks of selected EDCs, namely, dibutyl phthalate (DBP),
diethylhexyl phthalate (DEHP), dimethyl phthalate (DMP), linuron (LNR) and
progesterone (PGT) in wastewater, sludge, and untreated dry biosolid (UDBS) samples
from twelve wastewater treatment plants (WWTPs) in nine major towns in Kenya.
Analysis was done using high-performance liquid chromatography coupled with triple
quadrupole mass spectrometry (HPLC-MS/MS). All the wastewater influents had
quantifiable levels of EDCs with DBP being the most abundant (37.5%) with a mean range
of 4.3 ̶ 9.7 μg L-1. DEHP was the most abundant in sludge and accounted for 48.2%
ranging between 278.7 and 9243.5 ng g-1 dry weight (dw). In the UDBS samples, DEHP
was also the most abundant (40%) of the total EDCs detected with levels ranging from
78.8 ̶ 3938.5 ng g-1 dw. The average removal efficiency per pollutant was as follows: DMP
(98.7%) > DEHP (91.7%) > PGT (88.3%) > DBP (77.9%) > LNR (72.2%). The mass
loadings were as high as 373.3 g day-1 of DBP in WWTPs in densely populated cities.
DEHP and PGT had their Risk Quotients (RQs) > 1, posing a high risk to biota. DMP,
DBP, and LNR posed medium risks as their RQ values were between 0.1 and 1. Removal
of these toxicants was carried out via adsorption using chemically activated fat-free
powdered Moringa oleifera seed biomass (MOSB) which was pretreated, characterized,
and used as a low-cost biosorbent for the abstraction of PGT and LNR from synthetic
wastewater. The process parameters, contact time, pH, adsorbate concentration,
temperature, and adsorbent dosage were set and optimized using central composite design
(CCD) and response surface methodology (RSM) in Design Expert Software. For
biosorption of both PGT and LNR, the proposed model was quadratic. The optimum
parameters for PGT adsorption to MOSB were: 86.8 min, 500 µg L-1 adsorbate
concentration, 298 K and 0.1 g adsorbent dosage while for LNR were: 154 min, 500 µg
L-1 adsorbate concentration, 298K and 0.1 g adsorbent dosage. pH was not a significant
factor in the removal of both PGT and LNR. The kinetics, isotherms, and thermodynamics
were analyzed further using OriginPro. The equilibrium data were best described by the
Langmuir isotherm for PGT and Sips model for LNR, with maximum monolayer
adsorption capacities of 135.8 µg g-1 and 144.0 µg g-1, respectively. Adsorption kinetics
followed pseudo-first order (PFO) for PGT and pseudo-second order (PSO) for LNR
predicting physisorption and chemisorption rate-determining steps, respectively. The
thermodynamics functions (PGT: ΔG < 0, ΔH = -9.3 kJ mol-1 and ΔS = +44.2 J mol-1 and
LNR: ΔG < 0, ΔH = -10.3 kJ mol-1 and ΔS = +41.5 J mol-1) confirmed that the adsorption
of PGT and LNR onto MOSB was a spontaneous and exothermic process with randomness
and affinity experienced at the surface of the adsorbent. The adsorption mechanism was
non-electrostatic and may have involved π-π interactions. The results from this study show
that the MOSB is a promising alternative for an ecofriendly, low-cost biosorbent that can
effectively remove PGT and LNR from aqueous solutions. Phytoremediation of LNR and
PGT using Eichhornia crassipes was also carried out. The concentrations of EDCs
abstracted using phytoremediation were however below the quantification levels. | en_US |
