Project Name: Town of Mentone WWTP Upgrade
Location: Mentone, Indiana (United States)
Project Type: Municipal Wastewater Treatment
Completion Date: March, 2011
The Town of Mentone is an example of many a small community faced with stringent effluent limits for their aging lagoon based wastewater treatment facilities. Mentone's previous wastewater treatment facility was a seasonal discharge two cell facultative lagoon system providing secondary treatment. The facility was designed to meet effluent BOD5/ TSS limits of 25/70 mg/L, but it could not meet the NPDES limits for total ammonia nitrogen (TAN) of 9.6 mg/L in summer and 10.4 mg/L in winter.
Mentone, like majority of small communities in the United States and Canada, was left with no choice but to upgrade their WWTP. Until recently, mechanical plants were the only upgrade alternative that can meet low nutrients, BOD5 and TSS limits on a year round basis. Mechanical plants require a large infusion of capital for construction, operation and maintenance. The alternative to these cost prohibitive upgrades is to remain non-compliant. The latter of which is not an option.
In collaboration with the town's engineering consultant, Nelson Environmental Inc (NEI) designed an upgraded system utilizing the existing facultative lagoons in series followed by a SAGR® (Submerged Attached Growth Reactor). No changes were made to facultative lagoons' infrastructure. No aeration is required in the lagoons to meet the recommended lagoon effluent BOD5 feeding the SAGR® process.
Because the SAGR® is constructed with minimal components, the operations and maintenance aspect of the process is quite simple.
The only moving parts in the system are the blowers supplying oxygen to SAGR® process. A simplified control scheme manages the day to day operation of the blowers. Typically, an operator will perform a systems inspection using a simplified systems check list and on occasion change lubricating oil. Approximately every six months, the filters in the blower units will need changing (a process that takes just a few minutes). Process water sampling will be done in accordance to the State of Indiana's issued NPDES permit.
It is estimated that the Mentone's facility Operator will spend an average of 30 minutes per day on the system. On a bi-annual basis, the operator will initiate the step feed system by fully opening and fully closing two separate valves.
Mentone' s SAGR® system comprises of two gravel bed each capable of handling 100% in the rare case that maintenance would have to be performed within a single bed. The effluent quality from the Mentone facility is meeting and exceeding NPDES permit requirements at 10/15 mg/L BOD5/TSS and 1/5 mg/L TAN summer/winter. The design flow for the system is 0.12 MGD (454 m3/day).
The design of the treatment system allows for sufficient HRT (in the lagoons) to achieve the low BOD5 levels required to feed the SAGR® beds. This translates to significant energy savings that would otherwise be required to run blowers for a conventional aerated lagoon system.
It is estimated that 50% energy savings are realized with this design. The trade-off is the higher lagoon footprint required for the necessary residence time. Since the capacity was available at the onset of the system design, utilizing the existing infrastructure was deemed the most cost effective. Such a system would provide cost savings both in the construction and O&M phases of the project.