Hospital Wastewater Treatment through Horizontal Subsurface Flow Constructed Wetlands: The Case of Hawassa University Referral Hospital
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Date
2021-03
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Addis Ababa University
Abstract
A huge amount of water consumption in hospitals releases a significant volume of wastewater
loaded with complex mixtures of chemical and biological substances. The environmental and
public health consequences of the wastewater released in these healthcare setups isimmense unless
proper wastewater treatment system is in place. Among the treatment systems, constructed
wetlands as a reasonable option, have recently received considerable attention to treat a wide
variety of wastewater throughout the world. The aim of this study was to examine the potential of
subsurface flow constructed wetlands to treat hospital wastewater.
Different composite samples were collected from the inlet and outlet of wetlands, transported and
processed for physicochemical, heavy metal and drug analyses as well as enumeration of indicator
organisms, bacteriological identification and susceptibility testing were done following the
standard procedures. The Fisher's least significant difference (LSD) and Kruskal Wallis H test
were used to determine any significant differences in the mean influent and effluent values of
parameters, and to compare between planted and unplanted cells in broken brick and gravel bed
wetlands during the dry and rainy seasons.
The inlet wastewater of Hawassa referral hospital contained significant amount of organic matters
and nutrients. The average concentration of TSS, BOD5, COD, TKN, NH4
+
-N, NO3
-
-N and
PO₄³⁻were 535+22 mg/L, 221+31.3 mg/L, 713+86.5 mg/L, 86.3+11.7 mg/L, 0.9+0.2 mg/L,
13.4+4.9 mg/L during the dry season and 496+11.7 mg/L, 185+11.6 mg/L, 673+31.9 mg/L, 98+3
mg/L, 67.5+4.6 mg/L, 1.1+0.2 mg/L, 8+2 mg/L during the rainy season, respectively. The result
of the study indicated that the organic matter, ammonium, and phosphate concentration were
relatively higher during the dry season while TKN and nitrate were higher during the rainy season.
Heavy metal analysis of hospital wastewater demonstrated that the average concentration of
cadmium, chromium, nickel, lead, zinc, silver, arsenic, iron, manganese and copper to be
0.078+0.021, 0.1114+0.04, 0.162+0.082, 0.74+0.05, 0.134+0.009, 0.06+0.008, 0.021+0.007,
0.8+0.1, 0.21+0.03, and 0.06+0.008 mg/l, respectively. While the average concentration of
sulphamethoxazole and diclofenac were 22.9+2.25 and 1.94+0.06 µg/L, respectively. The
concentration of caffeine, salicylic acid, and ethinyl estradiol was below the detection limit.
Bacteriological analysis of samples from the hospital wastewater illustrated that the average
bacterial count of total coliforms and fecal coliforms was 1.3 x 107 + 1.2x103 and 1.4 x 105 + 5x102
xv
MPN/100 ml, respectively throughout the investigation period. The most frequently isolated
bacterial species were Staphylococcus sp 12 (26.6%), E. coli 11 (24.4%), Klebsiella sp 9 (20%),
Shigella sp 5 (11.1%), Salmonella sp 4 (8.9%), and others, such as Pseudomonas sp and
Citrobacter sp constitutes 4 (8.9%). Among bacterial isolates, 100% of Salmonella species were
found to be resistant to ampicillin and 75% to doxycycline, erythromycin, ceftazidime, cefoxitin,
and chloramphenicol. About 81.8% of E.coli isolates were also found to be resistant to ampicillin
and 72.7% to cotrimoxazole and amoxicillin-clavulanic acid. About 80% of ampicillin resistant
Shigella, as well as 77.8% ampicillin, amoxicillin-clavulanic acid, and ceftazidime-resistant
Klebsiella, were also frequently found.
The average percent removal efficiency of the constructed wetlands against TSS, BOD5, COD,
TKN, NH4
+
-N, NO3-N, and PO4
-3 were, respectively, 93.2%, 90.4%, 83.7%, 64%, 64.3%, 52.1%
and 56.1% in the dry season and 89.7%, 85.8%, 82.9%, 66%, 62.7%, 56.1% and 59.5% in the
rainy season. Broken brick bed wetlands gives better removal efficiency of TKN, ammonia, nitrate,
and phosphate with average removal rate of 73%, 71.3%, 79.6% and 77.1% in the dry season and
74.7%, 70.7%, 70.9% and 73.6% in the rainy season, respectively. Broken brick beds provide
better adsorption of ammonium, nitrate, and phosphate. Typha with broken brick bed was
significantly enhanced (P<0.05) the treatment performance of constructed wetland systems for the
removal of ammonia, nitrate, and phosphate. The seasonal variation couldn’t significantly
influence the removal of all the pollutants but a better performance of nitrate and phosphate was
achieved in a dry season. The use of locally available broken brick as a substrate media can
increase the nutrient removal efficiency of constructed wetlands with a cheaper cost when applied
in full scale constructed wetlands.
Among the examined wetlands for the removal of heavy metals, those planted wetlands were found
to be efficiently removed cadmium, chromium, and nickel with an average removal rate of 100%,
93.7%-100%, 56.8-99.4%, respectively. The average lead removal efficiency of planted and
unplanted wetlands was ranged from 75.7% to 100%. Planted broken brick bed wetlands removed
93.4 to 97.8% of lead while the unplanted broken brick bed wetland removed only 40.3%. The
average silver and arsenic removal efficiency of wetlands was 79.8% and 83.6%, respectively.
Vegetation plays a vital role in the removal of most heavy metals. Typha planted broken brick bed
wetland have a better performance in the removal of heavy metals. On the other hand, the average
diclofenac removal efficiencies of planted and unplanted reactors were 24%-100% and 8.2%-
xvi
34.2%, respectively. The Typha planted broken brick bed wetland removed all the diclofenac from
the wastewater. All planted wetlands were significantly removed diclofenac than unplanted gravel
bed wetland. There was also a significant difference between Typha planted broken brick bed
wetland with other planted and unplanted wetlands of both substrates.
Reductions of antibiotic-resistant bacteria were higher in the vegetated CW of both substrates than
the non-vegetated control gravel bed CW throughout the study period. Significantly (P<0.05)
higher removal (80.8% to 93.2%) of antibiotic-resistant bacteria was recorded in vegetated
wetlands. The overall isolated bacterial species in treated wastewater samples were E.coli
45(39.5%), Staphylococcus sp (35.1%) and Klebsiella sp 35 (30.7%). E.coli, Klebsiella, and
Staphylococcus sp were the most frequently isolated antibiotic-resistant species in treated
wastewater. The frequencies of resistant isolate from treated wastewater to ampicillin were 67/114
(58.8%) followed by cotrimoxazole 45/114 (39.5%), doxycycline 45/114 (39.5%) and
chloramphenicol 36/114 (31.6%). Higher removal rate (100%) of Salmonella and Shigella was
achieved in CW1, CW4, and CW5. A maximum removal (93.2%) of resistant bacteria was
recorded in CW2 and the least removal rate (42.4%) was observed in non-vegetated gravel bed
control wetland (CW8).
The overall pollutant removal efficiency of these constructed wetlands showed how much it is
effective to use CWs for the treatment of hospital wastewater. Typha plant with broken brick
substrate took part in the removal of heavy metals, nutrients and drug residual. Constructed
wetlands with broken brick substrate could help to solve the problem of hospital wastewater
treatment and can play significant role in the strategy to reduce water pollution in low-income
countries like Ethiopia.