Wastewater Treatment Plant profile:
City of Caldwell Idaho WWTP, operated by the City of Caldwell
Service Population:
47,500
System Type:
Class IV: BNR System
The Caldwell WWTP is currently treating all of its wastewater through the activated sludge system.
The Caldwell WWTP treats wastewater by screening and grit removal; two primary clarifiers accomplish
solids removal. The effluent from the clarifiers proceeds to the intermediate pump station where three
100 hp pumps are available to lift the wastewater up to the new facilities. An organic treatment and
nitrification system comprised of a selector basin with for individual cells, in the first cell of the selector
basin we are currently denitrifying and have some phosphorus removal. The flow from the selector
basin then proceeds to two aeration basins where nitrification then takes places (removal of ammonia)
the basins are operated in the plug flow mode. The basins are equipped with over 1,500 fine bubble
diffusers in each basin. Air to the basins is supplied by any of three 250 hp aeration blowers. Depending
on the time of year we operate the system with MCRT from five days in the summer up to eleven days
during the winter months. The solids inventories range from 20,000 lbs volatile in the summer to 40,000
lbs volatile during winter operation. Flows from the aeration basins then proceed to three Westec final
clarifiers, which incorporate the COP package (Clarifier Optimization Package) this consists of a new
mechanical scraper system, which continuously moves the sludge towards the hoper resulting in a
fresher and denser sludge. RAS pumps then return this sludge back to the activated sludge system. The
effluent from the final clarifiers then proceeds to the UV system, which uses ultra violet light to disinfect
disease-causing bacteria than survive previous treatment processes.
Thickening of waste solids is accomplished with a DAF and/or GBT unit; currently solids are being
thickened to 4 - 5% with an efficiency of 99%. The concentrated solids are then pumped to the
anaerobic digesters. Improvements have been made which include a heat pump, mixing pump, heat
exchanger and associated piping. To ensure that the system will continue to operate in the event of a
power failure, an emergency power generator (1500 kV) was installed to supply power to all essential
processes. A central computerized monitoring system (SCADA) for the facility is located at the
Operations building, giving us the ability to monitor and control the operations process and vital
equipment needed to run the plant.
The solids removed during the treatment process are digested in anaerobic digesters and are stored and
thickened in two sludge lagoons. These lagoons are drawn down by a sludge press. The press thickens
and presses water out of the sludge cake. The cake is then disposed of via landfill.
Flows:
Peak Flow Design: 18.5 mgd
Average Daily Flow: 5.50 mgd
Expansions/Upgrades:
Currently in the planning stages of Phase V WWTP improvements – New digester and filter building
Industrial Dischargers:
Darigold – SIU – Dairy industries
Fiber Guide – CIU – Fiber optic assembly, nickel electroplating
Inspire Technologies – CIU – Silicone disks assembly
Plant Personnel:
Salvador Arreola, Superintendent
 25 years experience
 Class II Wastewater
 Class IV Collections
 Certifications in several states
Brendan Clemens, Assistant Superintendent
 21 years experience
 Class IV Wastewater Operations
Scott Baity, Collection System Operator
 5 years experience
 Class II Wastewater Collections
 Class I Water Distribution
Brad Bartrop, Mechanic
 2 years experience
Daniel Cross, Collection System Operator
 2 years experience
 Class I Wastewater Collections
Aaron Ford, Wastewater Treatment Operator
 2 years experience
 Class I Wastewater Collections
 Class I Wastewater Operations
Rodger Hawker, Lab Technician
 25 years experience


Class I Wastewater Operations
Class I Laboratory
Tom Hendry, Collection System Operator
 5 years experience
 Class II Wastewater Collections
Chris Johnson, Wastewater Treatment Operator
 13 years experience
 Class III Wastewater Collections
 Class I Wastewater Operations
Kerry Johnson, Wastewater Treatment Plant Lead Operator
 12 years experience
 Class II Wastewater Collections
 Class II Wastewater Operations
Marissa Rider, Lab Technician
 2 years experience
 Class I Wastewater Operations
 Class I Laboratory