Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>
5. Chemicals and Nutrients
The health risks associated with chemicals found in wastewater and
sludge may need to be given more attention, particularly as the pace of
industrialization increases in developing countries. In many areas, municipal
wastewater and industrial wastes are combined, creating a potentially dangerous
mixture of toxic substances that must be handled carefully (see table 2).
Municipal sludge may contain high concentrations of heavy metals such as
cadmium, lead, nickel and chromium.
When industrial wastewater is also present concentrations of these
metals can be 10 to 20 times higher (Chang, Page and Asano, 1995). In 1983, it
was estimated that incineration of sewage sludge worldwide introduced between 3
and 36 tonnes/year of cadmium into the atmosphere (Nriagu and Pacyna,
1988). This cadmium eventually is
deposited to terrestrial and aquatic environments. Heavy metals such as cadmium
and mercury concentrate in the tissues of many filter-feeding shellfish, fish,
and in some cases terrestrial plants (WHO, 1992; WHO, 1989) and thus can pose
significant health threats to consumers of these products. For example,
Grössman (1988 in WHO, 1991) found elevated levels of nickel in green
vegetables, cabbage, onions, beans and peas grown on soils contaminated with
nickel from sewage sludge application.
Organic chemicals found in wastewater and sludge may also cause adverse
health effects, but direct evidence is limited.
However, this does not mean that there are no serious health
effects associated with use of water contaminated with industrial wastes.
Rather, it is a reflection of the difficulty
of associating chronic exposure of chemicals and chemical mixtures to diseases
with long latency periods. In some parts of China where irrigation with
wastewater heavily polluted with industrial wastes has occurred for many years,
health effects have been observed. For example, wastewater irrigation was
associated with a 36% increase in hepatomegaly (enlarged liver), and a 100%
increase in both cancer and congenital malformation rates compared to control
areas (Yuan, 1993).
To minimize adverse health and environmental effects from these
components, industrial wastes should be adequately pre-treated to remove these
chemicals or should be treated separately from municipal wastewater and
Poor irrigation practices with untreated or partially treated wastewater
also impact the quality and safety of groundwater in shallow aquifers and
surface waters that may supply drinking water. Wastewater related nitrate
contamination of aquifers has been extensively documented in both developed and
developing countries. High concentrations
of nitrates in drinking water can cause methaemoglobinaemia (blue babyE
syndrome). Numerous cases of methaemoglobinaemia due to nitrate exposure in
bottle-fed infants have been reported in Eastern Europe and the United States
over the last ten years Eincluding several infant deaths (Knobeloch et al.,
2000). It has been suggested that
chronic exposure to nitrates in drinking water may also be linked to cancer,
thyroid disease and diabetes (Knobeloch et al., 2000).
Excessive nutrients (primarily nitrogen and
phosphorus), in wastewater, sludge and excreta, may contaminate surface waters
and can cause eutrophication.
Eutrophication of freshwater sources may create environmental conditions
that favor the growth of toxin-producing cyanobacteria.
Toxins produced by cyanobacteria can cause
gastroenteritis, liver damage, nervous system impairment, and skin
irritation. Chronic exposure to
cyanobacteria toxins has been associated with liver cancer in animals and may
cause similar effects in humans (Chorus and Bartram, 1999).
Health problems associated with cyanotoxins
have been documented in several countries including Australia, Brazil, Canada,
China, England, USA, and Zimbabwe. In China, Ling (2000) found that liver
cancer mortality was nearly six times higher in people who obtained their
drinking water from eutrophic ponds where high concentrations of cyanobacterial
toxins (microcystins) were present than in people who obtained their drinking
water from deep wells. Exposure to
these toxins has usually been through contaminated drinking water or
recreational contact with the water.
However, it is also likely that consumers of contaminated freshwater
fish or shellfish might be exposed to these toxins (Chorus and Bartram, 1999).
Table 2: Chemicals of Health Concern Found
in Untreated Municipal Wastewater and Excreta
Di and tri-chlorobenzenes
Skin irritation, nausea, embryo/fetotoxic
Nervous system damage, cancer (?)
Liver, kidney, and blood damage
Liver damage, nausea
Gastrointestinal, skin, and nerve damage, cancer
Gastrointestinal, kidney and lung damage
Lung and skin damage, cancer
Nervous and immune system, and kidney damage, embryo/fetotoxic
Brain and kidney damage, embryo/fetotoxic
Lung, brain, kidney, liver, spleen and skin damage, cancer
Brain and heart damage, shortness of breath, death
Dental and skeletal fluorosis
Nausea, vomiting, mucous membrane irritation
Cause eutrophication which facilitates the growth of toxin-producing cyanobacteria
and other harmful algae
Anemia, dizziness, leukemia
skin, eyes, and gastrointestinal tract, systemic toxicant
Brain and kidney damage
Confusion, dizziness, memory loss, embryo/fetotoxic
Reproductive/developmental effects in wildlife, various potential effects
effects in wildlife, various potential effects in humans
|Source: Chang, Page, and Asano, 1995;
National Research Council, 1998; WHO, 1999c; WHO, 1992; WHO,
1991; WHO, 1989; ATSDR, 2000.
There is also some evidence to indicate that nutrient enrichment of marine
waters is partially responsible for other (i.e. non-cyanobacterial) toxic algal
blooms (Epstein, et al. 1993). Toxins produced by these algae accumulate in
the flesh of filter-feeding shellfish. When the toxins in the shellfish are
consumed a variety of illnesses may result, including; paralytic shellfish poisoning,
diarrhoeic shellfish poisoning, amnesic shellfish poisoning, ciguatera poisoning
and neurotoxic shellfish poisoning (Hallegraeff, 1993). Several of these toxins
can cause serious health effects - even death in certain circumstances (WHO,
In the last several years chemicals that mimic hormones or have
anti-hormone activity, and interfere with the functioning of endocrine systems
in various species have been identified in municipal wastewater.
Endocrine disruptors as they are known,
derive from many sources including pesticides, persistent organic pollutants,
nonionic detergents and human pharmaceutical residues.
Many of these substances are resistant to
conventional wastewater treatment and may persist in the environment for some
time (National Research Council, 1998).
Human health effects potentially linked to exposure to these chemicals
include: breast, prostate and testicular cancer; diminished semen quantity and
quality; and impaired behavioural/mental, immune and thyroid function in
children. Although direct evidence of
adverse health effects in humans is lacking, reproductive abnormalties, altered
immune function, and population disruption potentially linked to exposure to
these substances has been observed in amphibians, birds, fish, invertebrates,
mammals, and reptiles (WHO, 1999b).
6. Treatment and Risk Management
There are many
ways in which adverse health effects to humans from the release of
untreated/inadequately treated municipal wastewater and excreta into the
environment can be minimized. Some of
the most important methods include proper wastewater and excreta treatment and
disposal, waste minimization (e.g., reducing the volume of the wastes or the
use of toxic chemicals), providing separate treatment or diversion of
wastewater and sludge with high concentrations of toxic chemicals (industrial
wastes), protection of water sources, restriction of shellfish harvesting and
bathing in polluted waters, safe water handling and storage, and improving
personal hygiene including hand washing with soap and safe disposal of
will focus on the proper treatment and disposal of wastes (i.e., the removal or
significant reduction of harmful components from wastes and disposal of wastes
so that humans will not be exposed to harmful substances) and improving
6.1 Treatment options (see table 3)
in municipal wastewater and excreta generally pose the greatest threat to human
health. Wastewater and excreta should
be effectively treated to reduce threats to human health.
Most of the world's population does not have access to adequate sanitation.
Conventional sanitation relies on centralized sewerage systems and requires
large amounts of water to carry the wastes away. This type of approach may work
well in developed countries and large cities but is impractical for many other
locations. The cost of a sewerage system (which is usually more than four times
that of on-site alternatives) and its requirement of a piped water supply preclude
its adoption in the many communities in developing countries that lack adequate
sanitation (Franceys, et al. 1992). On-site disposal, can effectively protect
public health, facilitates the reuse of valuable waste components (nutrients,
organic matter, and water), keeps the waste where it is produced, reduces contamination
with toxic chemicals, and generally is the least expensive alternative. On-site
disposal alternatives range from simple composting latrines to complex bioreactor
systems. Refer to Source Book.
Where land is available at low cost and sewerage is conveyed to centralized
locations, well-designed waste stabilization pond (WSP) systems have proven
to be very effective in treating wastes. The advantages of WSP systems are that
they cost little to run, are simple to maintain, produce small volumes of sludge,
facilitate waste reuse and are good at removing pathogens - especially helminths
which are not adequately removed in most primary and secondary treatments.
wastewater and excreta treatment strategies (primary and secondary levels) in
developed countries have traditionally focused on the removal of suspended
solids and pollutants that used oxygen in the receiving waters to decompose
(Biological Oxygen Demanding substances or BOD) and less on the reduction of
pathogens and nutrients. These processes usually are expensive to operate due
to the large energy, skilled labor, infrastructure, and maintenance
requirements. Tertiary treatments must
be added to the process to effectively reduce pathogen and nutrient levels.
Frequently different tertiary treatments may be used in combination to reduce
pathogen levels to very low or undetectable levels.
For example, a filtration step (i.e., microfiltration,
ultrafiltration, multimedia filtration) or reverse osmosis may be combined with
disinfection. Addition of further treatment steps however, significantly
increases the cost and complexity of the process.
Table 3: Removal Efficiencies of Excreted Microbes
|Primary + chemical coagulation
|Activated sludge + 2B
|Aerated lagoon + settling pond
|Waste stabilisation ponds
|Effluent storage reservoirs
|ND= No Data
Sources: Feachem et al., 1983; Rose et al., 1996; Rose et al., 1997; National
Research Council, 1998; Karimi, et al., 1999; Clancy et al., 1998; Lazarova et
al., 2000; Sobsey, 1989
6.2 Treatment of excreta and sludge
Sludge that is
produced from municipal wastewater treatment processes also must be treated
carefully before it can be safely disposed of or used as a fertiliser.
Many of the organic and inorganic chemicals
as well as the pathogens are concentrated in the sludge.
When industrial wastewater is mixed with
municipal wastewater high concentrations of toxic chemicals may be found in the
sludge turning it into a hazardous waste that requires special disposal to
limit adverse health and environmental effects.
Additionally, toxic chemicals can interfere with the biological
processes that are used to treat the wastes thus reducing the effectiveness of
the treatment. Therefore, it is
imperative to separate toxic industrial wastes from municipal wastes before
treatment to preserve sludge reuse options and protect public health.
are extremely durable and can remain viable for long periods of time.
Therefore, excreta and sludge treatments
usually require storage periods for many months to ensure helminth egg
inactivation. Storage times can be
reduced when the excreta and sludge are allowed to digest at higher
temperatures. WHO recommends each of
the following procedures for the treatment of sludge, excreta, and nightsoil to
minimise adverse health effects prior to sludge disposal or use of sludge or
excreta as a fertiliser (Mara and Cairncross 1989, Helmer and Hespanhol, 1997):
- Storage for 12 months at ambient temperatures (warm climates), or
- Batch thermophilic anaerobic digestion at 50 - 55°C for 13 days, or
- Forced-aeration co-composting of excreta with domestic refuse for one month
(temperature should rise to 55 - 60°C), followed by 2 - 4 months of maturation,
- Raw sludge and excreta can be safely
applied to the land by subsurface injection, or placed in trenches and covered
with at least 25cm of soil before crops are grown (where soil conditions and
the depth to the water table permit), or
- Liquid nightsoil can be stored for one
week and applied to land but the settled sludge which may contain high
concentrations of helminth eggs should be stored for at least a year or
digested as above.
Improving personal hygiene generally requires major behavioural changes (and
an adequate supply of water), but is one of the most important steps in minimising
adverse health effects from municipal wastewater and excreta. Numerous epidemiological
studies have documented the importance of washing hands with soap and water.
This act alone, can cut the transmission of diarrhoeal disease by a third (WHO,
1993b; Esrey et al., 1985; Esrey and Habicht, 1986; Huttly, 1990; Esrey et al.,
1991). Additionally, it is critically important to dispose of faeces, particularly
children's faeces, in a safe manner. Children frequently are the victims of
diarrhoeal disease and other faecally/orally transmitted illnesses, and thus
may act as sources of pathogens. Getting children to use sanitation facilities
(or designing child-friendly toilets), and implementing school sanitation programmes,
are important interventions for reducing the spread of disease associated with
waste and excreta (WHO, 1993b).
Poor wastewater and excreta disposal continues to be responsible for a significant
proportion of the world's infectious disease burden. This burden is not distributed
equally, waterborne illnesses predominantly affect the poor and the young. However,
when basic water, sanitation, and hygiene interventions are applied, waterborne
illnesses can be effectively reduced. Moreover, low cost interventions can be
implemented to reduce the transmission of many diseases. For example, the safety
of drinking water can be improved by protecting sources from faecal contamination
and disinfection. Wastewater and excreta can be treated in waste stabilization
ponds to reduce pathogen concentrations and facilitate the reuse of nutrients.
Hygiene education and the promotion of hand-washing is also extremely effective
in reducing faecal-oral disease transmission. As poor countries industrialize,
it is important to minimize the production of toxic chemicals and to treat industrial
wastes separately when high concentrations of dangerous chemicals are present.
Reducing the adverse health effects associated with wastewater, sludge and
excreta is possible but takes sustained effort at the individual, community
and national levels. Additionally more emphasis must be found on finding sustainable
approaches for reducing health hazards associated with wastewater, sludge and
excreta, and at the same time, closing the nutrient cycle and protecting limited
fresh water sources and the environment.