for each were determined for the particular waste. The effects of chemical addition at
the primary settling tank, the aeration tank, and the final clarifier were studied. The
most effective location for adding the chemicals and the most effective chemical for
phosphate removal were the addition of alum at the final clarifier, but some chemical
savings could be achieved by addition to the aeration unit due to the return of some
of the chemical in the return activated sludge. Alum addition increased the sludge
generation in the range of 0.5 to 0.7 lb of dry sludge per lb of alum used. Chemical
addition aided sludge settling in the final clarifier and also increased BOD and TSS
removal.
The Federal Highway Authority has issued a report for the best management
practices for stormwater management [10]. A simple method is an alum injection
system that adds alum directly to a stormwater channel at a flow-controlled rate. The
precipitated chemicals are merely discharged to the receiving stream or lake where
thy settle to the bottom (under appropriate flow conditions). The added solids in lake
sediment are considered insignificant. Total phosphorus in Lake Ella, Florida, was
reduced by 89%, and total nitrogen by 78% [11]. Pitt [12] described a multichamber
treatment train that consists of a series of treatment units that mimic a conventional
wastewater treatment plant. In the first tank mild aeration separates the heavy solids
from the lighter ones. In the bottom of the second tank, most of the solids are settled
out by an inclined tray settler, and above this a DAF system lifts floatables and oil to
the surface. The final tank uses a sand/peat filter for final treatment. Total phosphorus
removal was determined to be 88%. Allard et al. [13] patented the StormTreat
System for treating stormwater. It consists of a circular holding tank 1.2 m deep
with discharge to the subsurface of a surrounding wetland. Overall the system
removed total phosphorus by 89%. Claytor and Schueler [14] have described a
constructed vegetated rock filter for biological treatment of stormwater, with application to the subsurface of the filter. This achieved 82% removal of total phosphorus.
Farming is a major source of nutrient discharges to streams and ultimately to
lakes. Runoff from fertilized fields carries the excess fertilizer off the field. This can
be controlled by establishing an unfertilized buffer zone between an active field and
the waterbody. Also the trend toward large feedlots has exacerbated runoff problems. A large combined animal and plant farm in the United Kingdom has installed
an environmentally sound water and wastewater system [15]. The collected liquid
wastes are treated in a DAF system before entering a reedbed treatment system. The
effluent flows into a lake whose overflow passes into a willow plantation. Water
from the lake is used for irrigation and pig wallowing. Seepage under the lake is
pumped out a sufficient distance away to allow for reuse. The lake also serves as a
fish and wildlife habitat.
In studies at the Lake George Village, NY, sewage treatment plant using trickling
filters and alum addition before the secondary clarifiers, with the final effluent being
dosed onto deep natural sand beds, Aulenbach [16] found that total phosphorus was
reduced to less than 1 mg/L within 7 m of vertical transport through the sand. In
another study of phosphate removal in the soil, Aulenbach et al. [17] traced a septic
tank effluent in shallow soil and found removal to less than 1 mg/L within 35 ft of
horizontal transport.
7 Lake Restoration
269
the primary settling tank, the aeration tank, and the final clarifier were studied. The
most effective location for adding the chemicals and the most effective chemical for
phosphate removal were the addition of alum at the final clarifier, but some chemical
savings could be achieved by addition to the aeration unit due to the return of some
of the chemical in the return activated sludge. Alum addition increased the sludge
generation in the range of 0.5 to 0.7 lb of dry sludge per lb of alum used. Chemical
addition aided sludge settling in the final clarifier and also increased BOD and TSS
removal.
The Federal Highway Authority has issued a report for the best management
practices for stormwater management [10]. A simple method is an alum injection
system that adds alum directly to a stormwater channel at a flow-controlled rate. The
precipitated chemicals are merely discharged to the receiving stream or lake where
thy settle to the bottom (under appropriate flow conditions). The added solids in lake
sediment are considered insignificant. Total phosphorus in Lake Ella, Florida, was
reduced by 89%, and total nitrogen by 78% [11]. Pitt [12] described a multichamber
treatment train that consists of a series of treatment units that mimic a conventional
wastewater treatment plant. In the first tank mild aeration separates the heavy solids
from the lighter ones. In the bottom of the second tank, most of the solids are settled
out by an inclined tray settler, and above this a DAF system lifts floatables and oil to
the surface. The final tank uses a sand/peat filter for final treatment. Total phosphorus
removal was determined to be 88%. Allard et al. [13] patented the StormTreat
System for treating stormwater. It consists of a circular holding tank 1.2 m deep
with discharge to the subsurface of a surrounding wetland. Overall the system
removed total phosphorus by 89%. Claytor and Schueler [14] have described a
constructed vegetated rock filter for biological treatment of stormwater, with application to the subsurface of the filter. This achieved 82% removal of total phosphorus.
Farming is a major source of nutrient discharges to streams and ultimately to
lakes. Runoff from fertilized fields carries the excess fertilizer off the field. This can
be controlled by establishing an unfertilized buffer zone between an active field and
the waterbody. Also the trend toward large feedlots has exacerbated runoff problems. A large combined animal and plant farm in the United Kingdom has installed
an environmentally sound water and wastewater system [15]. The collected liquid
wastes are treated in a DAF system before entering a reedbed treatment system. The
effluent flows into a lake whose overflow passes into a willow plantation. Water
from the lake is used for irrigation and pig wallowing. Seepage under the lake is
pumped out a sufficient distance away to allow for reuse. The lake also serves as a
fish and wildlife habitat.
In studies at the Lake George Village, NY, sewage treatment plant using trickling
filters and alum addition before the secondary clarifiers, with the final effluent being
dosed onto deep natural sand beds, Aulenbach [16] found that total phosphorus was
reduced to less than 1 mg/L within 7 m of vertical transport through the sand. In
another study of phosphate removal in the soil, Aulenbach et al. [17] traced a septic
tank effluent in shallow soil and found removal to less than 1 mg/L within 35 ft of
horizontal transport.
7 Lake Restoration
269