increasing energy efficiency at the allegan wwtp mwea/awwa joint annual conference august 19, 2010
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Increasing Energy Efficiency at the Allegan WWTP
MWEA/AWWA Joint Annual Conference
August 19, 2010
Project Background
Current treatment plant built in the early 70’s
Headworks, manual 1 ½” bar screen, grit removal system has not been operation for 25 years.
Freezing at headworks during winter months.
Project Background
Aeration basin 2 inoperable due to failed air header, failing air header and extensive weed growth the in grit and sludge in basin.
Fine bubble diffuser in aeration basins and underground sludge storage tank added in 1992
Aeration basin 3 and clarifier added in 1995 for addition BOD capacity.
Project Background
(3) 150Hp Hoffman blowers for 3 aeration basins.
No auto controls on blowers to track D.O.
Blowers and motors were in needed new bearings.
Aeration basin 3 utilized existing blower designed for basin 1/3 its size.
(2) 75hp centrifugal blowers were used on the aerobic digester, no timer or automated controls.
Project Background
Centrifugal wasting pumps held together with wooden wedges, pumped 50gpm above rated capacity.
Centrifugal sludge transfer pumps were unable to move thickened sludge over 3% solids.
Significant Industrial flow from Perrigo Corporation with no pretreatment other than pH adjustment.
Project Goals/Constraints
Rehabilitate/replace existing process equipment Modify/improve activated sludge process to
improve performance, increase efficiency and add organic treatment capacity for Perrigo
Accomplish improvements on existing site which is surrounded by floodplain, old municipal dump and Rockwell Superfund site (utilize existing tankage or build structures primarily above grade).
Aeration Energy Efficiencies
1. Diffusers Replaced fine bubble
diffusers with new, more efficient diffusers in aeration basins 1 and 2.
Aeration Energy Efficiencies
Energy Savings from Diffuser Replacement
Aeration Energy Efficiencies
Energy Savings from Diffuser Replacement
Aeration Energy Efficiencies
Energy Savings from Diffuser Replacement
Aeration Energy Efficiencies
2. Sensors Dissolved oxygen sensors were installed at the
end of aeration tanks 1 and 2 to provide automatic feedback/control of blower inlet valves based on operator set D.O. control point.
Aeration Energy Efficiencies
Design Point: 114 HP
Operating Point: 70 HP
Energy Savings from Automatic Blower Control Savings of just over $5,000/yr for every 10 HP reduced
Aeration Energy Efficiencies
3. Biological Nitrogen Removal If nitrification is occurring in the aeration basins,
nitrates (NO3) can be returned to the anoxic zone (no or low dissolved oxygen).
Bugs utilize oxygen in nitrates. Nitrogen (N2) is released as a gas and oxygen needs
are reduced in aeration basin.
Aeration Energy Efficiencies
Basin configuration made returning nitrates very simple, and anoxic zone was already in place due to new divider wall.
External carbon source is sometimes required (in addition to raw sewage) for de-nitrification reaction to be optimal.
Aeration Energy Efficiencies
We may not optimize this process, just get some added benefit at a low up-front cost.
After system is more fully loaded will test BNR process to determine if further optimization is desired.
Septage/Treatment Energy Efficiency
Mix septage in aerated tank with waste-activated sludge.
Pump contents to sludge storage tank.
Decant from sludge tank back to liquid end of plant is treated in liquid process.
Load to the aeration system is reduced due to less flow and lower organic loading.
Septage/Treatment Energy Efficiency
Energy Savings from Septage Treatment System Sludge Decant: 140 mg/l CBOD Septage: 4,550 mg/l CBOD Estimated Annual Septage: 3,000,000 gallons
Miscellaneous Efficiencies
Biological phosphorus removal system results in less sludge produced (less chemical deliveries).
Automatic flow control system for high flows routes flows to either the EQ tank or aeration tank 3 (standby tank) to maintain treatment efficiency of main treatment tanks.
Miscellaneous Efficiencies
New Headworks ¼” automatic fine screen Self-cleaning wet well High efficiency grit removal
Miscellaneous Efficiencies
New clarifiers with energy dissipating influent well and stamford baffles
New RAS pumps with VFDs
Miscellaneous Efficiencies
Replaced gaseous chlorine disinfection system with Ultraviolet Disinfection (no more chlorine gas or sodium bisulfite deliveries).
Building Systems Efficiencies
New natural gas fed Pulse Boiler Indoor lighting
Replaced all fluorescent bulbs (T12 to T8) Occupancy sensors installed in new areas of building Option to control multiple bulbs in each fixture
Outdoor lighting Replace mercury vapor lights with 2 stage induction
lighting with motion detector (10 pole mounted fixtures)
Treatment Results
Average effluent results: CBOD: 8 mg/l SS: 17 mg/l T. Phos. .6 mg/l
Septage receiving: 250,000 gallons per month CBOD: 4,500 mg/l SS: 20,000 mg/l
Decant from aerated sludge storage: CBOD: 140 mg/l SS: 218 mg/l
Operational Efficiencies
New SCADA system provides full automation of plant Automatic sludge wasting Automatic sludge pumping PD Sludge Blower control UV control pacing Automated headworks (fine screen control, grit collection, raw
sewage pumps)
Personnel requirements More duties (e.g. septage operation), less personnel 1990’s: total of 5 staff Present: total of 3 (possibly 4) staff
Original POTW Found
The wastewater plant that was built in the 1930’s was located during construction.
It was supposed to have been removed and filled.
Increasing Energy Efficiency at the Allegan WWTP
MWEA/AWWA Joint Annual Conference
August 19, 2010