Halifax Harbour Cleanup Inc. - Halifax Regional Municipality

Issues 41
• Treatment of all flows by advanced primary treatment. This
would require more chemicals, and hence would be more
expensive than the second option.
0 Treatment of part of the flows by advanced primary treatment.
Since the maximum concentrations of all pollutants
are normally expected during dry weather flow, this option
would provide advanced primary treatment to a volume of
influent comparable to average dry weather flow. The balance
of the flow (up to three times average dry weather
flow) would bypass advanced primary treatment and be
treated by plain sedimentation, as originally proposed by
HHCI. A very rough schematic is shown in Figure 11.
HHCI should examine both options, conduct laboratory-model
treatability studies, commission a predesign study, and subject
the results to a value engineering audit before reaching a
conclusion.
29. The Panel recommends that HHCI give serious
consideration to designing the sewage
treatment plant/Oil-from-Sludge (STPIOFS)
facility to include advanced primary treatment
at the initial stage, irrespective of site
location. The analysts should consider Initial
capital Investment, operating costs, effects
on sludge-management technology, and lmpacts
on and benefits to human and natural
environments.
The recommendation to consider advanced primary treatment
is also supported by concern expressed by review participants
over the proposed disinfection method, as described in the
following section. The inclusion of advanced primary treatment
would also allow consideration of alternative disinfection
methods.
However, much concern was registered by participants over
the potential negative impacts of chlorination on both human
and environmental health. It was felt that alternative disinfection
methods should be considered, including ultraviolet light
and ozonation.
The Panel is aware that chlorine and chlorinated wastewater
discharges are currently being evaluated on the Priority Substances
List under the Canadian Environmental Protection
Act. Chlorine is considered by many to be an unacceptable
disinfectant due to the production of organochlorine compounds
during treatment and the potential for their bioaccumulation
in the marine food chain. This has the ultimate
potential of impacting the health of top levels of the food
chain, including humans.
Recent toxicity tests with freshwater fish demonstrated that
certain non-chlorinated wastewater treatment plant effluents
were not toxic to fish, but chlorinated effluents from the same
sources were toxic when above certain concentrations.
Threshold levels of effect varied with the nature of the effluent
tested (GM Szal, et a/. Research Journal Water Pollution
Control Federation 63, SeptIOct. 1991). The effects of disinfection-generated
organochlorines in the marine environment
are relatively undocumented.
It should be noted that dechlorination procedures are capable
of removing free chlorine but do not to remove the organochlorines
associated with suspended particulates.
Chlorination could conceivably be limited to the swimming
season, since the main reason to chlorinate the effluent is to
protect swimmers and others engaging in body-seawater contact
sports such as windsurfing. Provincial regulations may
have to be altered to allow for this.
4.8.3 Disinfection
HHCI proposes to use chlorination (sodium hypochlorite derived
from sea water) to disinfect the primary treated effluent
before discharging it into the Harbour. The Panel agrees with
HHCl’s assessment that given the characteristics of primary
treatment, few other disinfection technologies are appropriate.
Table 6
Advanced Primary
If chlorine is deemed unfit for effluent disinfection in the future,
the proponent may have to consider alternatives. Also, the
initial costs ($4.7 million) associated with the chlorine-based
technology (chlorine contact chambers) indicates the need to
consider other options. HHCI should be prepared to participate
in directed research for developing alternatives to chlorine-based
disinfection.
Comparison of Advanced Primary and Primary Sewage Treatment Levels:
Contaminant Removal Efficiency
Primarv
• Up to 90% of suspended sotids
• Greater levels of toxic organics associated with
suspended solids
. Up to 90% of heavy metals
• 80-90% of bacteria, greater levels of removal of
other pathogens associated with suspended solids
• Greater levels of phosphorous and other nutrients
• Greater levels of biochemical and chemical oxygen
demand (BOD and COD)
. 4&60% of suspended solids
• Lesser levels of toxic organics associated with suspended
solids
. 15% of heavy metals
• Lesser levels of bacteria and other pathogens associated with
suspended sdids
0 Lesser levels of nutrients
. Lesser levels of BOD and COD