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Table 1.4: Currently used guidelines by the eThekwini Municipality (South Africa) for treated effluent being discharged into a receiving catchment
PARAMETER A B
Colour/ Odour/ Taste None None
pH 5.5 – 7.5 5.5 - 9.5
Dissolved Oxygen (mg/l) 75% saturation 75% saturation
Faecal Coliforms (CFU/100 ml) 0 0
Temperature (°C) 25 35
Chemical Oxygen Demand (mg/l) 30 75
Electrical Conductivity (mS/m) 250 250
Total Suspended Solids (mg/l) 10 90
Sodium Content (mg/l) 50 90
Soap/ Oil/ Grease None 2.5
Residual Chlorine (mg/l) 0 0.1
Free/ Saline Ammonia (mg/l) 1 1
Nitrate (mg/l) 1.5 None
Orthophosphate (mg/l) 1 1
Adapted from Government Gazette, 1984; (A): Guidelines for effluent being discharged into any catchment area/ river or a tributary (B): Guidelines for effluent being discharged into any area other than that specified by A.
1.9 Enteric viruses commonly detected in the water environment and associated
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inefficient wastewater treatment procedures result in their discharge in high numbers as well as increased persistence within the water environment. In addition, the discharge of inefficiently processed sludge may result in the persistence of viral particles within sediments and in the water column (Bosch, 1998). Infections occur as a result of swimming, canoeing or other related recreational uses of viral-contaminated waters. Viruses are shed in extremely high numbers from infected individuals with gastroenteritis patients excreting between 105 – 1011 viral particles per gram of stool. Transmission routes (Figure 1.2) may be diverse and includes consumption of shellfish grown in contaminated waters, consumption of contaminated drinking waters, food crops irrigated with contaminated wastewater, sewage polluted recreational waters or person to person contact (Wyn-Jones and Sellwood, 2001).
These viral agents cause a range of diseases such as gastroenteritis, meningitis, myocarditis, hepatitis, respiratory illness and diarrhoea with viral particles being shed in extremely high numbers in the faeces of infected individuals. Recent studies have detected the presence of human enteric viruses in groundwater intended for drinking purposes in Seoul, Korea with 4.8% of samples testing positive for rotaviruses whilst an additional 3.2% of samples were positive for human adenoviruses and noroviruses (Park et al., 2010).
1.9.1 Enteroviruses
Enteroviruses are naked icosahedral particles, stable within a pH range of 3 – 10 and generally present within the gastrointestinal tract as vaccine remnants and usually of low pathogenicity (Wyn-jones and Sellwood, 2001). They are usually transmitted via the faecal–
oral route and infection can be acquired through person to person contact, contaminated water and food sources (Figure 1.2). Most enteroviral infections are asymptomatic, however in certain cases, enteroviral symptoms range from the general cold and flu to more severe paralysis, meningitis and in certain instances, resulting in fatal diseases (Fong and Lipp,
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2005). Compared to most pathogens and bacterial indicators, the minimal infectious dose is extremely low with known cases of infection occurring with a single viral infectious particle.
Previous studies on the survival rate have shown varying rates ranging from 6 - 7 months in river waters; 2 - 6 months at temperatures between 4 – 10 ºC and approximately 4 - 6 months in frozen water samples such as ice and snow for poliovirus, coxsackievirus and echovirus depending on the temperature, pH, humidity and the enteroviral genus under investigation (Kocwa-Haluch, 2001).
1.9.2 Adenoviruses
Adenoviruses are members of the family Adenoviridae and have been classified into six groups (A-F), based on their physical, chemical and biological properties. They are non- enveloped viruses and possess a linear double stranded DNA genome (Benko and Harrach, 2003). Human adenoviral contamination via domestic sewage serves as one of the major sources of contamination due to these viruses being shed in extremely high numbers as well as low seasonal variability and persistence in the water environment (Jiang, 2006). In addition, human adenoviruses have shown resistance to current purification and disinfection processes such as chlorine and UV light, whilst host-cell DNA repair mechanisms may repair UV-damaged DNA using human adenoviral DNA strands as a template for replication thus prolonging survival rates (Van Heerden et al., 2005). Of the 51 serotypes, 30% are known to be pathogenic to man whilst only serotypes 40 and 41 cause gastroenteritis and are shed in large quantities in the faeces (Carter, 2005). These serotypes tend to survive longer than faecal bacteria in sewage and the surrounding environment, thus resulting in possible discharge with contaminated treated effluent that may already meet indicator bacterial standards (Jiang, 2006). In addition, previous studies have shown the occurrence of adenoviruses in 4% of 413 tested drinking water samples within South Africa, with additional
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research showing further detection in 4% of 204 and 30% of 198 finished drinking and tap water sources (Van Heerden et al., 2003; 2005; 2004).
Figure 1.2: Transmission routes of human enteric viruses
(Adapted from WHO, 1979; Charles et al., 1975; Gerba et al., 1979; Bosch et al., 2006)
1.9.3 Caliciviruses
Caliciviruses include norovirus, sapovirus, lagovirus and vesivirus, with only the first two genera being comprised of human pathogens. These viral agents are included on the U.S Environmental Protection Agency’s Contaminant Candidate List (CCL) (Table 1.5). They are small non-enveloped RNA viruses that have characteristic cup-shaped depressions on a spherical capsid surface and range in size between 27 – 35 nm. Outbreaks associated with this virus generally occur within the colder months of the year (Mounts et al., 2000). Noroviral symptoms differ from others in that it is the most significant cause of viral diarrhoea and
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induces a high level of explosive vomiting. Furthermore, due to the multiple noroviral serotypes, immunity in humans is generally short-lived. Sapoviruses on the other hand induce infections mainly in children, with most being infected between the ages of 3 months and 6 years. Norwalk-like and Sapoviral human pathogens have been differentiated based on their morphology, size, nucleic acid content and protein profile. However, one of the major challenges associated with this group of viruses is their inability to be cultured in a laboratory setting (Blacklow, 1996). Numerous studies have confirmed their presence in a range of faecal samples from infected individuals as well as surrounding environmental samples. A study conducted in Japan using qPCR to determine the presence and distribution of human sapoviruses in wastewater by Kitajima et al. (2011) confirmed their presence in 100% and 58% of influent and final effluent samples respectively.
1.9.4 Rotaviruses
Rotaviruses are RNA viruses, approximately 60 – 80 nm in diameter, belonging to the family Reoviridae. Infection with this virus is generally characterized by diahorrea and vomiting after an incubation period of 4 – 7 days, with infectious particles being shed in extremely high numbers (109 per gram of stool) in faeces, where infectivity can be maintained for up to one week (Table 1.6). Rotaviral infections are one of the major leading causes of diahorroea in children leading to approximately 40% of child-related diahorreal hospitalizations and approximately 600 000 child-related deaths in developing countries (Hashizume et al., 2008).
Rotaviruses have been shown to survive for long periods in a range of water sources – from treated sewage to surface water to groundwater sources - in some cases, surviving longer than poliovirus whilst survival rates in surface waters range between 8 – 32 days and in tap water for greater than 64 days (Kocwa-Haluch and Zalewska, 2002).
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Table 1.5: Microbial contaminants on the United States Environmental Protection Agency Contaminant Candidate List and associated infections
Microbial contaminant Waterborne associated infections
Adenovirus Respiratory and gastrointestinal illnesses
Caliciviruses (including Noroviruses) Mild self-limiting gastrointestinal illnesses Campylobacter jejuni Mild self-limiting gastrointestinal illnesses Enterovirus (including poliovirus,
coxsachievirus and echovirus)
Mild self-limiting respiratory illnesses
E. coli O157 Gastrointestinal illnesses / kidney failure
Helicobacter pylori Colonizes the human gut, causing ulcers / cancer
Hepatitis A Virus Liver disease, jaundice
Legionella pneumophila Lung diseases
Mycobacterium avium Lung infections
Naegleria fowleri Primary amoebic meningoencephalitis
Salmonella enterica Mild self-limiting gastrointestinal illnesses
Shigella sonnei Mild self-limiting gastrointestinal illnesses / bloody diarrhea
Adapted from USEPA, 2012
1.9.5 Hepatitis A and E viruses
Hepatitis A (HAV) and E (HEV) are distinctly recognised from other types of human viral hepatitis, namely hepatitis B, C and D. Being non-enveloped viruses, they are transmitted mainly via the faecal-oral route whereas the latter types frequently progress to chronicity and are enveloped viruses, transmitted principally via blood (Purcell and Emerson, 2001). HAV is a member of the Picornavirus family, containing an icosahedral particle of 28 nm in diameter, composed of 30% RNA and 70% protein. It contains a single stranded RNA genome of 7.48 kb, possesses no envelope, and replicates in the cytoplasm. The surface proteins VP1 and VP3 serve as major antibody-binding sites. Previous studies have shown the virus to be stable to disinfection, acid and heat treatments, being able to withstand temperatures up to 60 ºC
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(Melnick, 1992). HAV is generally transmitted via the faecal oral route either by direct contact with an HAV infected individual or by consumption of HAV-infected food or water and is characterised by symptoms such as anorexia, fever, nausea, vomiting and jaundice (Fiore, 2003).
HEV was originally considered to be a Calicivirus due to similar genome organization but is now, however, currently declassified due to studies showing differentiation of HEV’s viral genes. It is a self-limiting virus, found worldwide, with the highest prevalence being in the East and South Asia. Genotype 1 is usually found in developing countries, resulting in outbreaks within various communities whilst genotype 3 is generally found in developed regions. Transmission of HEV is usually via the faecal-oral route with low socioeconomic regions exhibiting the highest serovalence rates, mainly due to poor sanitation and excessively contaminated water (Grabow, 2002).
1.9.6 Astroviruses
Human astroviruses are non-enveloped, small, circular shaped viruses, with an icosahedral symmetry of approximately 28 nm in diameter and a total genome length of approximately 6800 – 7900 nucleotides. They are noted for lacking a capsid and their characteristic star-like appearance when viewed under the electron microscope. Infection results predominantly in gastroenteritis, with incidence of infections spiking in winter months. A range of sero- prevalance studies suggest that more than 80% of children between the ages of 5 – 10 possess antibodies to the virus (Wyn-jones and Sellwood, 2001).
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Table 1.6: Examples of waterborne viruses detected from various sites and common methods used for their detection
SAMPLE SITE VIRUS NUMBERS
(CU/litre)
DETECTION
METHOD REFERENCE
Freshwater
Loire river
France Entero 1.39 Cell culture Le Bris et al. (1983)
Besos River
Spain Entero 15.5 Cell culture Bosch et al. (1986)
Tiber river Italy
HAV + ELISA Divizia et al. (1989)
Umgeni River South Africa
Presumptive
Adenovirus + Microscopy Olaniran et al. (2012)
Food
Lettuce HAV 2.03 RT-PCR Croci et al. (2002)
Cabbage Polio 6.15 Cell culture Ward et al. (1982)
Lettuce HAV Less than 1.00 Cell culture Bidawid et al.(2001) Assorted
vegetables Rota +
Cell culture RT-PCR
Van Zyl et al. (2006)
Seawater
Italy Entero 0.4 – 16 Cell culture De flora et al. (1975)
USA Entero 0.01 0.44 Cell culture Goyal et al. (1979)
France Entero 0.05 - 6.5 Cell culture Hugues et al. (1980) Spain Entero 0.12 - 1.72 Cell culture Finance et al. (1982) Drinking
water South Africa Entero +a Cell culture and
RT-PCR Ehlers et al. (2005)
South Africa Rota +a
Cell culture RT-PCR
Van Zyl et al. (2006)
Korea Entero/
Adeno +a
Cell culture/
RT-PCR
Lee and Kim. (2002) CU/litre – cytopathic units of virus per litre; (+) virus detected; a: molecular detection of viral RNA only
37 1.10 Scope of the present study
The escalating rates of urbanization, industrialization and population growth have contributed to the increase in water pollution and degradation of water quality. The Durban Metropolitan Area produces over 1.8 million tons of waste a year, the majority of which is disposed of in landfill sites with approximately 261 mega litres of treated wastewater being discharged into the sea daily. A further 242 mega litres are discharged into rivers (State of the Environment Report, 2007/8). Stresses such as chemical pollution, salinity, acid mine drainage, alteration of flow and eutrophication, especially when acting together, can have a significantly negative impact on river bodies, resulting in large amounts of organic matter and nutrients being discharged into waterways thereby affecting aquatic life as well as disrupting the biotic community structure and function (Wakelin et al., 2008). Furthermore, the failure of large numbers of existing wastewater treatment plants to comply with national water standards as well as inefficient management and monitoring of these water treatment services, poorly maintained infrastructure, capacity problems and budget constraints have resulted in an increased decline in the effluent quality from treatment plants (DWA, 2012). This study therefore aims at assessing the microbial (bacterial and viral) and physico-chemical quality of treated effluent being discharged from two wastewater treatment plants in Durban as well as to assess their impacts on the quality of the receiving water bodies.