Small communities face very tough decisions today regarding the resolution of wastewater treatment problems. Stricter treatment requirements result in hardships, particularly, for public facilities like schools.
In such applications, an important balance between environmental compliance and a feasible operation becomes critical. When Leroy (Ala.) High School, serving a rural population in the central part of the state, encountered the problem of maintaining effluent compliance, a cost-effective solution was required and sought.
Primary factors
A review of the high school’s wastewater treatment plant revealed two primary factors in the plant’s poor performance: the flow variation and the lack of proper operation and maintenance.
The former is not unusual for a school application, which generally experiences flows only eight hours a day and often contain high concentrations of nitrogen. At Leroy, the flow variation was compounded by the lack of adequate flow equalization tankage to support suspended growth. The latter problem was a result of the school’s insufficient budgeted resources for proper treatment plant maintenance. McFadden Engineering sought a solution that would reduce operation and maintenance attention and still meet the strict effluent criteria. As they evaluated viable alternatives, the engineering firm opted for the Modular FAST process manufactured by Smith & Loveless, Inc.
The patented Modular FAST treatment system consists of a tank–which was donated to the school–filled with fixed, fully submerged media. The submerged media provides more surface area for bacterial growth while air distribution provides sufficient oxygen and mixing. Bacteria exist in both the suspended and attached growth phases, providing the benefits of both a Complete Mix Activated Sludge process and an attached growth system.
For the school’s wastewater treatment plant, the benefit of attached growth was fundamental to counter the variation of flow, both in terms of preventing washout and maintaining sustained biological activity during the low flow periods. Continual bacterial growth results in higher levels of bacterial concentration, which ensures a high level of treated effluent. The higher bacterial concentration also produces a longer sludge age, making nitrification and denitrification much easier to achieve.
Instead of requiring a clarifier, a zone underneath the media provides a settling area for biological solids that slough off the media. Consequently, this zone has as much surface area as the aeration zone, which allows for a conservative settling rate of the biological solids that slough off. The settling sludge anaerobically decomposes in the underneath zone.
The result is high quality influent as seen in the post-installation testing.
In the seven months after start-up and throughout the school year, the new wastewater system achieved satisfying results. With an incoming BOD of 152 mg/L and TSS of 170 mg/L, the seven month effluent data average was 3 mg/L BOD and 12 mg/L TSS with an ammonia (NH3-N) figure of 0.5. The plant has been in complete compliance with the ADEM Permit limits, stopping the citations generated previously by the original system.
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