Removal of pharmaceuticals from municipal wastewater
3613
using Standard Methods (APHA-AWWA-WPCF, 2001). Obtained results are given in Table 3.
respectively. The mobile phase consisted of a mixture of aceto nitrile:water:orthophosphoric acid (70:30:0.1, v/v/v) for the analysis of diclofenac and salicylic acid, a mixture of metha nol:water:orthophosphoric acid (75:25:0.3) for the analysis of ibuprofen and a mixture of acetonitrile:water (30:70, v/v) for the analysis of acetaminophen. HPLC quality acetonitrile (CH 3 CN) from LabScan, orthophosphoric acid (H 3 PO 4 ) from Panreac and ultrapure water obtained by a Millipore System were used for the preparation of the mobile phase. Before use, each mixture was passed through a Millipore 0.45 l mpore size filter and degasified in an ultrasound bath during 30 min. For the chromatographic determination of concentration, four replicated injections were carried out under a mobile phase flow rate of 1 mL min 1 .
2.4. Adsorption experiments
Adsorption experiments were performed using a batch experi- mental approach. For each pharmaceutical, adsorption kinetic experiments were first carried out in order to determine the time necessary to attain equilibria ( t eq ). Then equilibrium experi- ments were done to determine the corresponding adsorption iso- therm. All experiments were carried out by shaking (250 rpm) a known mass of PS800-150 together with 100 mL of wastewater in 250 mL Erlenmeyer flasks. Initial concentration of each target pharmaceutical in wastewater was 100 ± 1 mg L 1 . All experi- ments were done in triplicate and at a constant temperature of 25±2 C by means of a thermostatically regulated incubator. Triplicate control experiments, with no adsorbent, were run in parallel with adsorption experiments in order to verify whether the concentration of the target pharmaceutical was stable throughout the duration of the experiments. In the kinetic experiments, Erlenmeyer flasks were progres- sively withdrawn from the shaker after pre-set time intervals. Then, from each flask, three aliquots were taken, filtered and chromatographically analyzed to determine the concentration of the target pharmaceutical. The amount of each pharmaceu- tical adsorbed onto PS800-150 at each time, q t (mgg 1 ), was calculated by a mass balance relationship as follows: q t ¼ð C 0 C t Þ V W ð 1 Þ where C 0 (mgL 1 ) is the initial liquid-phase concentration of pharmaceutical, C t (mgL 1 ) is the liquid-phase concentration of pharmaceutical at a time t (min), V is the volume of the solution (L) and W is the mass (g) of PS800-150. For equilibrium experiments, Erlenmeyer flasks were sha- ken during 1000 min in order to guarantee the equilibrium,
2.3. Wastewater from a municipal STP
Aiming the practical utilization of pyrolyzed primary pulp mill sludge in tertiary wastewater treatment, adsorption of pharmaceuticals from real wastewater was tested. Thus, for this work, the secondary effluent was collected from the STP of Leo´ n (Spain). This secondary effluent is directly discharged at the Bernesga river, a tributary of the Esla river that is 77 km long and goes through the town of Leo´ n. This STP consists of primary and secondary stage treatments. The primary stage comprises the following treatments: screening, sand removal, fat removal and primary clarification. Then, the secondary stage involves a plug-flow activated sludge with nitrification/ denitrification followed by secondary clarification. The plant was designed to treat the wastewater of 330,000 equivalent inhabitants and has an inflow of 123,000 m 3 day 1 with a hydraulic retention time (HRT) of about 6 h. Wastewater quality parameters, namely pH, conductivity, total suspended solids (TSS), biological oxygen demand at five days (BOD 5 ), chemical oxygen demand (DQO), NTK, N-NH 4 , N-NO 3 , N-NO 2 , total P-PO 4 , were determined by
Table 2
Physico-chemical properties of the pharmaceuticals used in this study. Source: ChemSpider
M w (gmol
a (mg L 1 )
1 )
2 )
Pharmaceutical (formula)
Structure
S
pKa
log K
PSA (A
HBAC
w
ow
Diclofenac Sodium (C 14 H 10 Cl 2 NNaO 2 )
318.13
50,000
4
0.57
52.2
3
Salicylic acid (C 7 H 6 O 3 )
138.12
2240
2.97 2.26
57.5
3
Ibuprofen Sodium (C 3 H 17 NaO 2 )
228.26
100,000
4.91 3.8
40.1
2
Acetaminophen (C 8 H 9 NO 2 )
151.17
14,000
9.48 0.46
49.3
2
PSA = Polar Surface Area. HBAC = Hydrogen Bound Acceptor Count. a S w = water solubility (25 C).
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