Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>
Biochemical oxygen demand domestic loads can be increased by 30 percent if
garburators are in use in a community. Stormwater runoff only accounts for about
5 percent of total BOD5 load in combined sewer systems. Septage pumpouts have
very high BOD5 concentrations, typically ranging from 2,000 to 50,000 mg/L.
Restaurants in resort areas can also be major contributors to plant BOD5 loads,
and oil and grease from such operations can be a nuisance in the treatment plant
Nitrogen and phosphorus
Besides human and culinary waste, other sources of nitrogen and phosphorus
are agricultural runoff into storm sewers, food processing industries and
fertilizer industries. These nutrients are a major problem in many areas of
North America, particularly when discharging to inland water bodies. Phosphorus
in laundry detergents was banned in some areas of the U.S. and Canada, and as a
consequence few detergents sold in North America now contain phosphates. Some
resort lakes, for example Okanagan Lake in British Columbia, surrounded by
increasing development began developing problems with nuisance weed and algal
growth. Stringent local requirements to limit nitrogen and phosphorus levels in
wastewater effluent were implemented to control the growth and maintain water
quality, requiring tertiary level wastewater treatment.
pH and Alkalinity
pH and Alkalinity are mainly a function of local geography and whether the
local water source is groundwater or surface water, with surface water tending
to be less mineralized. Although acid rain over much of the continent results in
many surface drinking water sources having pH as low as 5 or less, wastewater
tends to be roughly neutral or slightly basic pH. Industrial wastewater can have
extreme acid or basic pH. In the event nitrification is required to eliminate
effluent ammonia toxicity to fish, low alkalinity wastewater can result in low
pH levels. Consequently, it is often advisable to denitrify to recover some of
the alkalinity and energy used for nitrification. During denitrification,
bacteria use nitrate and nitrite as an electron source, reducing the overall
energy required for aeration.
Temperature of wastewater in North America varies widely, with larger seasonal
variations in Canada and the northern United States. Some low technology options
which would otherwise be appropriate, such as wetlands, cannot be used in some
northern areas because of freezing and thus only seasonal treatment. Biological
nitrogen removal is also affected by low wastewater temperatures, although nitrification
has been observed at plants with liquid temperatures as low as 4 oC.
Higher temperatures in the south, which can be as high as 30 - 35 oC,
result in year-round odour control issues.
Chlorides and sulphates
Wastewater chloride concentration may be high in communities with high
groundwater tables, and saltwater intrusion into groundwater or near shore
sewage pumping stations. Chlorides may also be high in communities with hard
water, where individual water softeners are in common use. The presence of
chlorides, in sufficiently high concentrations, can interfere with sewage
Sulphates formed in long, low slope sewers in warm climates have proven to be
a corrosion problem in older plants with concrete tanks, and in older sewers.
They can also contribute to severe odour problems. This condition is commonly
controlled by injecting ferric chloride upstream of the odour release point to
control hydrogen sulphide formation.
Toxic inorganics and priority pollutants
The EPA has identified a number of priority pollutants based on known or
suspected carcinogenicity, mutagenicity, teratogenicity or high acute toxicity.
Examples are heavy metals, halogenated organic compounds, and pesticides. The
main controllable sources of such contaminants are industrial users of the sewer
system. The implementation of Sewer Discharge Bylaws that levy charges for
contaminant loading is used to reduce this loading, as the bylaw makes it more
cost effective for industries to initiate source control measures and treat the
wastewater before discharge to sewer.
Contaminant loading from residential and commercial sources is more difficult
to control and regulate. When combined with low mineralization, low pH water
tends to leach metals from the water distribution system, resulting in
relatively high copper and iron loads at wastewater treatment plants. As well,
there are still some homeowners and small industries who find it easier to
dispose of hazardous wastes such as cleaning solutions to the sewer rather than
pay for proper disposal or take the hazardous waste to a collection site. Public
information and education programs have been used to reduce contaminants from
residential and commercial sources by educating people as to the environmental
effects of discharging materials such as latex paints and pesticides to the
Stormwater road runoff is another source of trace metals and petroleum
products. Public education programs have been effectively used to reduce the
discharge of toxic contaminants and hydrocarbons to storm drains. One of the
more effective programs is a community initiative to paint fish symbols next to
catchbasins to remind people that materials discharged to the storm drain affect
Many contaminants, especially ionic metals, tend to become adsorbed to fine
solid particles in the sewage and to bacteria in the waste treatment process,
and become part of the waste sludge stream. In some cases, the contaminant
concentrations in the sludge can be sufficiently high enough that they limit
disposal options for the biosolids generated by the wastewater treatment
process, and may even inhibit sludge digestion.