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 is immense 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
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.
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Hospital Wastewater