Biofiltration integration with zeolite-biochar for removal of hospital wastewater contaminants from selected sites in Accra Metropolis, Ghana

¹Department of Biological, Environmental and Occupational Health Sciences, School of Public Health, University of Ghana, Legon, Accra, Ghana, ²Department of Environment, Sanitation and Health, Accra Technical University, Accra, Ghana, ³Department of Environment Health Sciences, University of Sharjah, Sharjah, United Arab Emirates, ⁴Department of Community Health, University of Ghana Medical School, Accra, Ghana

^&Corresponding author
Isaac Tetteh Mensah, Department of Biological, Environmental and Occupational Health Sciences, University of Ghana, Legon, Ghana

Introduction    

Pollutants in hospital wastewater comprise drugs, heavy and trace metals, microbial agents, physico-chemical compounds, among others [1,2]. Accumulated pollutants infiltrate the soil and surface water, and enter food chains, causing both acute and chronic toxicity to various organisms [3]. High concentrations of these pollutants in water sources have been linked to decreased fish fertility, growth, and reproduction [4]. Additionally, diversity loss in aquatic ecosystems, decreased immunity and growth rates in marine mammals, and changes in microbial community structure in soils have been documented [5,6]. Raw hospital wastewater (HWW) causes the death of crustaceans and zebrafish within 96 hours (4 days) of exposure, and it also contains a high concentration of antibiotic-resistant bacteria (ARB) and norovirus [7].

The modified biosand filtration system (MBFS) has been used to improve water quality in several settings before use or discharge. For example, Mensah et al. [8] and Thomson et al. [9] designed biosand filtration systems to improve the quality of septic tank effluent before discharge at a tertiary institution in Ghana and Vietnam, respectively. They had removal efficiencies of greater than 60% for various contaminants for both studies. However, no study has assessed the efficiency of a biosand filtration system in the removal of microbiological, physicochemical, and heavy metals occurring in hospital wastewater. This study aimed to evaluate the removal of microbiological, physicochemical, and heavy metals from hospital wastewater using biofiltration integrated with zeolite-biochar.

Research questions: do levels of contaminants in hospital wastewater pose a treat before biofiltration? do levels of contaminants in hospital wastewater treated with biofiltration exceed the maximum permissible levels set by WHO?

Methods     

Study site and design: a quasi-experimental study was employed to evaluate a biofiltration system integrated with zeolite-biochar for the removal of contaminants from hospital wastewater at three hospitals in the Accra Metropolis between December 2023 and December 2024. The samples were purposively drawn from a quaternary-level hospital (Hospital B), a tertiary hospital (Hospital A), and a primary hospital (Hospital C).

Data collection and analysis

Construction of the biosand filtration system: the biosand filtration system was constructed using a fibre-reinforced plastic (FRP) vessel and engineered media. The vessel comprised a seamless polyethylene (PE) liner encased in a fiberglass-epoxy composite, producing a lightweight, durable, and pressure-resistant tank with a 100-litre working capacity (NSF & CE certified). The biofiltration media consisted of biosand, zeolite, and coconut shell biochar. Biochar was prepared by carbonising dried coconut shells at 800°C for 60 minutes, followed by pulverisation. Zeolite and biochar were blended in a 70:30 ratio, which optimises adsorption capacity through the complementary ion-exchange properties of zeolite and the porous adsorption potential of biochar. Assembly followed CAWST (2008) guidelines: the distributor tube and riser were installed, under-bed gravel was layered, and filtration media were sequentially added. Cartridges were arranged into a composite multi-stage system, incorporating a clinoptilolite zeolite bed and filtrate receptacle, enabling effective removal of pharmaceuticals, organic pollutants, and ionic contaminants.

Experimental stage: the study conducted a field water quality analysis to determine the quality of wastewater before and after biofiltration. The output was used to assess the effectiveness of the biofiltration system in removing contaminants from wastewater.

Sample analysis: field sampling was conducted in three months (April-June, 2024) with a total of nine samples being collected (three samples per site). Physical water quality characteristics were measured using a pre-calibrated multimeter (YS1 Pro Plus & HI98194; Yellow Springs, OH, USA). Sampling protocols were designed to minimize sample contamination. In situ water temperature, pH, electrical conductivity (EC), and total dissolved solids (TDS) were measured using a multimeter (YS1 Pro Plus & HI98194; Yellow Springs, OH, USA). Water samples were collected using clean 1 L Nalgene bottles (Thermo Fisher Scientific, Whatman, MA, USA) and rinsed three times with site water before the final sample was taken. Samples were stored on wet ice until they were returned to the Ecological Laboratory of the University of Ghana, Legon (within 10 hours of collection) to preserve their integrity.

Statistical analysis: data were entered into Microsoft Excel and analyzed using Stata version 16.0 software. Microbiological and physicochemical characteristics were organized into mean and standard deviation (X±SD) for data of both before and after biofiltration in tables. Additionally, a one-sample t-test was used to compare test samples of each Hospital for various analytes to the maximum permissible limit. This was done for test values that exceeded the maximum permissible limits. P-values less than 0.05 were considered statistically significant.

Ethical approval and accordance: the study protocol was approved by the Ghana Health Service Ethical Review Committee with approval number [GHS-ERC: 014/08/23]. Written consent and permission were obtained from the management of the three hospitals before commencement of the study. Again, the study used codes for confidentiality of the study sites.

Results     

The general characteristics of wastewater at the study sites before biofiltration are summarized in Table 1. For physicochemical characteristics, some study sites had levels beyond the maximum permissible level for conductivity, total dissolved solids, turbidity and alkalinity. In Hospital C, the wastewater exceeded the maximum permissible levels for both conductivity (2357.5 ± 3.54) and total dissolved solids (1186 ± 11.31), whilst other sites had levels within the reference ranges. Concerning turbidity and total alkalinity, maximum permissible levels were exceeded at Hospital A (155.5 ± 23.34) and (238.6 ± 23.48) and Hospital B (84.30 ± 39.17) and Hospital C (163.60 ± 10.75), respectively.

For heavy and trace metals, lead and copper exceed the permissible limit for all the study sites i.e., Hospital A (0.15 ± 0.03) and (3.36 ± 0.42), Hospital B (0.01 ± 0.03) and (3.21 ± 0.71), Hospital C (0.15 ± 0.03) and (1.68 ± 0.04), respectively. Total coliforms and E. coli were determined to be high for all three study sites i.e., Hospital A (11975 ± 58.03) and (5975 ± 47.21), Hospital B (10950 ± 70.71) and (6175 ± 54.10), Hospital C (1.68 ± 0.04) and (176 ± 5.66), respectively. Shigella spp. had elevated levels in wastewater at Hospital C (162.50 ± 10.60).

Table 2 presents the general characteristics of wastewater at study sites following the biofiltration intervention. All microbial indicators, such as total coliforms, E. coli, Shigella and Salmonella, had at least one study site with values exceeding maximum permissible limits. The total coliform count and E. coli were reportedly high for Hospital A (6510 ± 17.34) and (510 ± 12.84), Hospital B (6000 ± 21.82) and (400 ± 11.40), respectively. E. coli concentration was also high for Hospital C (20 ± 5.07). Lastly, both Shigella (400 ± 24.57) and Salmonella (400 ± 19.43) exceeded maximum permissible limits after biofiltration intervention for Hospital B.

Discussion     

Hospital wastewater presents as an important public health concern due to its potential harm [10]. This study was conducted to assess the removal of microbiological, physicochemical, and heavy metals occurring in hospital wastewater with biofiltration integrated with zeolite-biochar. At least one study site presented with values exceeding maximum permissible limits for all microbial indicators, such as total coliforms, and specifically E. coli, Shigella spp. and Salmonella spp. The presence of coliforms like E. coli, Shigella spp. and Salmonella spp. has implications for human health. For instance, E. coli concentration was reportedly high for all study sites. E. coli, when ingested, causes gastrointestinal infections, urinary tract infections, sepsis/ bacteremia, and extraintestinal infections [11,12]. Lastly, both Shigella spp. and Salmonella spp. exceeded maximum permissible limits after biofiltration intervention for Hospital C. Studies have found both Shigella spp. and Salmonella spp. to contribute to a wide array of gastrointestinal disorders like diarrhoea, vomiting, among others [13,14]. These could contribute to dehydration and loss of essential nutrients, which could be life-threatening [15]. E. coli is an indicator organism, and its presence implies the presence of other faeco-orally transmitted pathogens.

Implications for public health and development: the inability to remove pathogens from wastewater and improve water quality has implications for human health and development. The persistence of faecal-oral pathogens in the environment facilitates the spread of diarrhoeal diseases in the absence of good sanitation and hand hygiene. Estimates of the cost of treating diarrhoeal illness among children aged below five years in northern Ghana were reported for the outpatient and inpatient care as ranging between US$3.86 to US$4.35 and US$65.14 to over US$133.86, respectively [16]. In comparison, the national minimum wage in 2025 is GHS 539.19 or US$43.46 monthly. Thus, diarrhoeal diseases place a high financial burden on families. Ensuring adequate treatment of wastewater can help avert this preventable cost to households. SDG target 6.3 calls for the improvement of water quality by reducing pollution, eliminating dumping, and minimising the release of hazardous chemicals, halving the proportion of untreated wastewater and increasing recycling and safe reuse globally. The main indicators of the target are: the proportion of wastewater that is safely treated and the proportion of water bodies with good ambient water quality. Biofiltration with zeolite biochar has proven less effective in the removal of pathogens in wastewater in the present study, and continual discharges into the environment potentially place downstream communities at risk of diarrhoeal illness and financial hardship.

Conclusion     

The study demonstrates that although biofiltration integrated with zeolite biochar improved the quality of hospital wastewater, microbial contaminants, particularly E. coli, Shigella spp, and Salmonella spp, still exceeded permissible limits. For optimum efficiency of the zeolite biochar, there should be initial treatment by disinfection for instance with sodium hypochlorite. Additionally, hydraulic conditions and biofilm maturity should be ensured prior to zeolite biochar usage.

Competing interests     

The authors declare no competing interests.

Authors' contributions     

Isaac Tetteh Mensah, Mawuli Dzodzomenyo, Prudence Tettey, Paul Kingsley Botwe and Emilia Asuquo Udofia: research conception, design, coordination and drafting of the manuscript. Isaac Tetteh Mensah, Paul Kingsley Botwe and Albert Abaka-Yawson: data collection, analysis and statistical support. All authors have read and approved the final version of the manuscript.

Acknowledgments     

The authors are grateful to the entire staff of the various health facilities where data was collected.

Tables     

References