The
Portage Lake Water & Sewage Authority (PLWS&A)
was established in 1964 by the cities of
Hancock and Houghton for the purpose of
constructing and operating a joint use
wastewater treatment facility. The
facilities that were constructed
included a lift station for each city to
convey wastewater to a common site and a
wastewater treatment plant located on
the south shore of Hancock.
Planning was initiated by the PLW&SA in
1987 when it became evident that the
existing treatment plant was operating
at flows in excess of the design flow
and was not able to treat all of the
excess flow that was being generated by
both cities.
TKDA and U.P. Engineers and Architects
were retained to prepare a facility plan
to determine the rehabilitation and
possible expansion necessary to provide
treatment of all the wastewater flow
generated by the two committees. The
State DNR established the criteria that
all the wastewater generated must
receive treatment to meet the effluent
plant limits.
The facility plan determined that the
most cost effective and environmentally
sound long-term plan was to construct a
new treatment facility on the Houghton
sands site. Construction of this
facility is complete and it has been
placed into operation. This treatment
plant has the capacity to treat
wastewater flow up to 18 MGD during wet
periods of snowmelt and rainfall.
Wastewater Conveyance Components
Lift Stations and Forcemain. The Hancock
lift station at the old treatment plant
has been remodeled to serve as a lift
station to pump Hancock's wastewater
across the canal to the Houghton lift
station. The Houghton lift station was
also remodeled so that it pumps the
combined flow of both cities through a
24-inch forcemain to a 48-inch gravity
interceptor, which conveys all of the
wastewater to the new treatment plant.
Influent
Pumping
Wastewater that arrives at the treatment
plan is lifted by screw pumps through
the treatment units and to Portage Lake.
Pretreatment
Pretreatment consists of screening and
grit removal. The mechanically cleaned
bar screen removes coarse solids from
the flow. The aerated grit chambers
remove sand, gravel and heavy grit to
protect the downstream treatment units.
Primary Clarification
The primary clarifiers remove a
significant portion of the suspended
solids from the wastewater. These tanks
allow solids to settle slowly to the
bottom of the tank by gravity. Settled
solids are collected at the bottom of
the tanks and pumped as "sludge" to the
anaerobic digestors.
Secondary Treatment (Activated Sludge)
Secondary treatment is a biological
process that is used to remove organic
material present in the wastewater. The
biological process utilized is called
activated sludge. Aerobic
(oxygen-demanding) bacteria grow in
these tanks and consume the organic
materials in the wastewater. This
process is accomplished in the secondary
aeration tanks and the secondary
clarifiers. After aeration, the
bacteria-laden solids are separated in
the secondary clarifiers and a portion
is returned to the aeration tank. This
arrangment of "return sludge" allows the
operator to control the amount of
bacteria present in the process. Excess
solids are wasted to the primary
clarifiers where it is combined with the
primary solids.
Disinfection
Ultraviolet (UV) disinfection is the
final treatment of the wastewater.
Disinfection is accomplished by an
innovative process that utilizes high
dosages of ultraviolet light to
eliminate any potentially harmful
pathogenic organisms that could be
present in the wastewater. A specific
wavelength of ultraviolet light is
germicidal and is used to destroy nearly
all of the bacteria that are present.
Discharge
An underground pipeline carries the
treated effluent to discharge by a 100
foot long diffuser into Portage Lake.
Anaerobic Digestion
Anaerobic digesters process the sludge
removed from the clarifiers to produce
methane gas and biosolids fertilizer.
The Primary Digester is heated and mixed
to foster the growth of anaerobic
methanogenic bacteria. The Secondary
Digester separates the biosolids from
the liquid. Anaerobic digestion converts
most of the organic material in the
sludge to methane gas and produces
biosolids that are relatively odor free
and suitable for land application as a
fertilizer.
Biosolids
Dewatering and Storage
The biosolids are dewatered by belt
filter presses to a moist state
containing about 16% solid material by
weight. The dewatering step removes
water and reduces the volume to be
hauled to land application. A storage
facility provides storage of dewatered
biosolids between periods of land
application.
Land
Application of Biosolids Fertilizer
The processed biosolids are applied as a
soil fertilizer and amendment to assist
in vegetation of the Mason stamp sands .
Biosolids are also applied to assist in
fertilizing local agricultural and
wildlife areas in accord with MDEQ
requirements. |
