Advanced technologies stop plant bypasses
A recent $10.2-million upgrade at the regional wastewater treatment plant operated by the Portage (Pa.) Area Sewer Authority doubled the facility’s daily flow rating to 2 million gal per day (mgd) and brought the previously deficient peak rating up to 6 mgd. Added peak capacity was a primary goal of the project to correct hydraulic limitations that previously required repeated bypasses during heavy rainfall events caused by inflow and infiltration (I&I) into the collection system. The plant’s added peak capacity has proven to handle the collection system’s previous surges.
The engineers exercised additional foresight in designing the plant upgrade. Although the plant’s discharge does not reach Chesapeake Bay tributaries, they designed it to meet the effluent nitrogen and phosphorous limits set by the Chesapeake Bay Agreement. This instilled the added flexibility to comply with the agreement’s nutrient limits if Pennsylvania regulators expand them statewide or mandate the maximum daily loads on a site-specific basis, explained a design engineer for Gwin, Dobson & Foreman Inc., the project’s consultant, based in Altoona, Pa. Furthermore, the utility now can accept additional influent flows from future expansions of the service area.
The original plant utilized the contact stabilization activated sludge process (CSASP) as the logical design solution at the time for the community‘s size and regulatory requirements when the facility entered service in 1972. The initial construction produced a footprint that included two aeration tanks with individual clarifiers, digesters and pumps. Also included were a bar screen, grinders and a pump station to accept the gravity-feed delivery from the 6- to 18-in. mixed types of line comprising the collection system, some of which date back to the 1940s.
The plant effluent is received by the Little Conemaugh River, which flows through scenic mountainous areas and watersheds that were environmentally degraded over the years by drainage from abandoned coal mine operations and other pollution. Multiple jurisdictions currently are focusing on correcting the environmental damage.
By the time the service population had reached 5,800-plus residents and 3,000 connections, the plant bypasses had resumed and set the stage for the recent upgrade completed in 2010. The plant now embodies generations of advancements.
This scope included a new 9.44-mgd lift station, headworks, an aerated grit chamber, flow diversion channels, an auger screening system and conversion of the existing contact stabilization tanks to provide 0.6 million gal of equalization storage. Channel-type ultraviolet disinfection has replaced the chlorine disinfection that was used in the past. Sludge dewatering equipment and a polymer feed system also were provided to upgrade the solids-handling system.
The original CSASP has been replaced by an integrated Xylem wastewater treatment system featuring a Sanitaire ICEAS-NDNP (intermittent cycle extended aeration system with the nitrification/denitrification/phosphorous process feature) for secondary treatment and nutrient removal. The two basins for the ICEAS-NDNP system have individual Sanitaire Silver Series II fine-bubble diffused aeration grids with a total of 1,036 diffusers per basin served by 75-hp rotary blowers, a Flygt 140-gal-per-minute waste sludge pump and a total of four submersible Flygt mixers. A high level of automation and plant optimization is achieved from the Sanitaire SCADA system with an automated solids inventory management system (SIMS) to automatically control the rate of sludge wasting from the system and keep the biomass balanced for consistent, high-quality effluent. A YSI monitoring and control system instills automated supervision throughout the plant-wide process chain.
Gwin, Dobson & Foreman engineers evaluated various options before recommending the ICEAS-NDNP system, which favored the system’s smaller footprint requirement, directly translating into lower construction cost. The system also offered the flexibility to customize the continuous treatment cycle to respond to variable flows. Furthermore, the system’s modularity will facilitate incremental expansions at the Portage plant.
Evolution of a Basic Process
The ICEAS-NDNP system evolved from the conventional activated sludge process discovered a century ago in England. Activated sludge treatment became the cornerstone for wastewater treatment and the subsequent development of sequencing batch reactors (SBRs) years later in several configurations. In fact, initial activated sludge treatment first occurred utilizing batch-style processing. These SBRs all are similar in the basic process, applying two or more identically equipped tanks that receive raw wastewater (influent) at one end and discharge treated water (effluent) out the other as returned activated sludge is mixed to sustain the biological digestion process.
The ICEAS-NDNP system employs an advanced variant of SBR technology and is particularly effective in removing organic waste and denitrification during the anoxic mixing cycle. Of particular interest with ICEAS is that no sludge return systems or equipment are required.
The Portage plant’s ICEAS-NDNP system was designed to achieve 10 mg/L biological oxygen demand and 10 mg/L total suspended solids from effluent after a typical 30-day retention cycle. During peak flow conditions, the process automatically increases the number of cycles by 33%, explained Mark Stancovich, the utility’s superintendent.
The plant layout consists of two 146.7-by-58-ft basins that function in three automated, time-based phases. The initial react phase begins with raw wastewater entering the tanks and reacting with mixed liquor suspended solids. At this point, the influent is subjected to the desired aeration and anoxic mixing to stimulate biological oxidation and denitrification.
The agitation is suspended during the following settle phase so that the solids can stratify across the bottom of the basins and the clear water can build up across the top of the tanks. The decant phase then ensues, during which the clear treated water discharges by gravity into an effluent line and the sludge is wasted at a controlled rate by the SIMS operating feature.
Since the ICEAS-NDNP system began operation in October 2010, the Portage plant has successfully met nutrient removal goals (see Figure 1) and has withstood and successfully processed I&I-induced surges that reached a 10-mgd peak.
Effluent quality has been consistent, especially during the peak flows that challenged the facility in the past, Stancovich said.
The continuous flow ICEAS SBR process has gained widespread acceptance around the world because of its reliable operation and smaller workforce needs in comparison to other biological treatment infrastructure of similar scale. The Portage plant’s workforce includes only Stancovich; Kelly Randall, administrative assistant; Mario Dasilva Jr., assistant operator; and Brad Rousell, another plant worker. The six-member board is led by Chairman Don Squillario. The Pennsylvania Rural Water Assn. has recognized the plant for its operating excellence.
Stancovich admits that he still dreads a forecast calling for heavy storms across the area, but the upgraded plant has earned his confidence. The facility’s process now prevents the bypasses of the past by automatically responding to flow and load variations during all phases of the treatment cycle without compromised quality in the higher-capacity plant’s discharge.
http://www.wwdmag.com/sites/wwdmag.com/files/imagecache/article_slider_big/1-Photo.JPGOne of the two ICEAS-NDNP basins shows the aeration system churning the water during the react phase.
http://www.wwdmag.com/sites/wwdmag.com/files/imagecache/article_slider_big/2-Photo.JPGThe settle phase presents the calm surface of the tertiary water before discharge.
http://www.wwdmag.com/sites/wwdmag.com/files/imagecache/article_slider_big/3-Photo.jpgA grade-level view of the twin-basin ICEAS-NDNP system