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Case Study for Customer Location
ND47:
System Overview:
Municipal wastewater treatment system. Periodic discharge.
Population 16,000. Most critical discharge permit limits are 25
mg/l BOD, 30 mg/l TSS, and stringent ammonia limit that varies
from 5 to 10 mg/l depending on river flow.
Flow, Type of Discharge, System Detention Time:
Flow rate: 1.4MGD, Originally 50% to aeration basin A1 then Cell
1, then Cell 2. Other 50% to aeration basin A2 then Cell 2. Then
100% to Cell 3, then Cell 4, then Overland Flow, then 88% to
irrigation system and 12% discharged. Current system is 100% to
A1, then Cell 1, then Cell 2, then Cell 3, then Cell 4, then
100% periodically discharged. Total system detention time 240
days.
Reservoir Information and Loading:
Aeration Basins A1 and A2: each 1 acre, 11 ft deep, Design
loading was 935 lbs of BOD5/acre/day in each, with installed 60
hp of grid aeration operating 24 hours per day. (SolarBees in
the primary cell allowed both of these aeration cells to be
bypassed in 2002. But starting in spring, 2003, due to heavy
incoming surfactants and the need to volatize them, one aerated
cell was put back into service at about 2500 lbs of
BOD5/acre/day, with 60 hp of aeration).
Cell 1: primary cell, 43 acres, 3.5 ft deep, 42M gallons,
has installed 0 hp of grid aeration operating 0 hours per day.
Cell 2: 43 acres, 3.5 ft deep, 42M gallons, has installed
0 hp of grid aeration operating 0 hours per day.
Cell 3: 58 acres, 12 ft deep, 151M gallons, has installed
0 hp of grid aeration operating 0 hours per day.
Cell 4: 29.7 acres, 20 ft. deep, 145M gallons, has
installed 0 hp grid aeration operating 0 hours per day.
Reported Problem Before Installation:
High energy costs of 500 hp including irrigation, could not get
rid of enough water, only 12% could be discharged due to ammonia
limits and the rest had to be irrigated, some odor problems. The
Overland Flow was causing the river bank to cave in. A $15M
mechanical plant was contemplated.
Installation:
(These machines were installed by PSI between 1998 and 2003):
Cell 1: 6 solar only units equal to SB2500, and 3 solar
only SB4000
Cell 2: 6 solar only units equal to SB2500
Cell 3: 5 solar only SB10000 dual mix units, as of 2003
Cell 4: 4 solar only SB10000 dual mix units, as of 2003,
and 1 original test machine equal to SB2500.
Results:
Excellent results. Eliminated 400 hp of aeration, irrigation,
and transfer pumping equipment at energy savings of over $50K
per year. All water can be discharged within permit limits and
irrigation is now used only when desired by farmers. Cell A2 and
the Overland Flow are all still functional but are being
bypassed. Better odor control has been achieved. The BOD in Cell
3 and Cell 4 is usually less than 5 mg/l. Cell 3 and Cell 4 are
usually discharged when ammonia is 5-7 mg/l. The city lagoon
system now appears adequate for the town to double in population
without any increase in capital expense or annual operating
expense. The city sewer rates have not changed since 1983 and
will not have to change far into the forseeable future.
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