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Treatment plant is beneficiary of value engineering.

A recent value engineering (VE) analysis will bring about significant cost savings during the upgrade of a 200-mgd secondary wastewater treatment plant in Pittsburgh, Pennsylvania. The study was performed by O'Brien Kreitzberg, a Dames & Moore Group company, based on a preliminary design. For the value engineering team, the focus was on aesthetic and performance characteristics deemed important by the facility owner, the Allegheny County Sanitary Authority (ALCOSAN).

In early 1994, the authority started planning for a 20-year, $392-million capital improvement program to meet current and future needs for liquid treatment, solids management, and odor/air pollution control. The program is divided into 10 design packages. The first phase will expand capacity to 250 mgd by 1999.

ALCOSAN's David Borneman, P.E., director of engineering and construction, is overseeing the development of the first expansion phase. At the project's onset, the authority retained two international firms to perform preliminary (30 percent) design on 10 design packages. The 30 percent designs later became the focus of three, 40-hour-long value engineering workshops. Suggestions emanating from the workshops were incorporated into the remaining design, which was completed by local firms.

Planned Capital Improvements. Located along the Ohio River, the ALCOSAN plant serves Pittsburgh and most of Allegheny County. With residential neighborhoods on the bluffs above the plant, odor control and aesthetics are major components of the upgrade. (Figure 1 is a plan view of the plant and major components.)

Final Clarifier Upgrade. The existing final clarifier mechanisms experienced structural corrosion and other signs of deterioration. They are being replaced with rapid sludge removal units using a continuous collection manifold with submerged components of stainless steel. The existing access bridges will be raised to protect drive mechanisms from 500-year floods.

Hypochlorite Disinfection. The plant currently uses gaseous chlorine for disinfection and odor control. Under the new program, a sodium hypochlorite system will replace the gaseous chlorine system.

Lime Building Improvements. ALCOSAN's staff recognized that a source of current off-site odor originates in the area where dewatered sludge is mixed with lime and loaded onto vehicles of varying size for transport to land disposal. To address these issues, improvements will include replacement of mixers conveyors, load-out bins, and the dust-control system. In addition, the loading area will be expanded to accommodate truck loading in a controlled environment with ventilation and scrubbing of the ventilated air.

Dewatering Building Ventilation Improvements. Ventilation and dewatering system modifications will improve the quality of air in the dewatering building. In addition, existing odor scrubbers will be modified to accommodate the ventilation system for air treatment.

Preliminary and Primary Treatment Odor Projects. The most odorous liquid processes are those units near the point where wastewater enters the plant. These processes accomplish screening, grit removal, preaeration, and primary clarification of the liquid waste. To eliminate a primary odor source, the preaeration process will be eliminated, and preaeration tanks will be converted to additional primary clarifiers. In addition, a new primary clarifier will be constructed adjacent to the Ohio River. This structure will serve as the base upon which the primary odor scrubbers will be placed. All preliminary processes will be in contained air spaces; ventilation air exceeding incinerator combustion air needs will receive a full two-stage chemical scrubbing to remove odors. The entire primary clarifier complex will be covered with precast concrete slabs and access structures.

Aeration Basin Covers. Odor containment will be accomplished by placing precast concrete covers on new and existing aeration basins and channels. Odors will be treated using single-stage chemical scrubbers that will be constructed on top of one of the new aeration basins.

Waste-Activated Sludge Thickening. The current plant configuration in which waste-activated sludge is co-thickened in the primary clarifiers will be changed. New gravity belt thickeners will be installed to provide an alternative to co-thickening before dewatering and disposal.

Expansion to 250 mgd. Additional plant capacity will be required by 1999. The first capacity expansion includes adding two new aeration basins on either side of the existing open basins, equipped with new air diffusion systems. Also included will be two new open circular final clarifiers with associated sludge pumping system improvements.

VE Applied. The value engineering process entailed a series of workshops that were coordinated with the completion of preliminary (30 percent) engineering. The workshops analyzed the program to achieve the essential functions at the lowest total cost (capital, operating, and maintenance) over the expected life of the project. The VE team used a systematic, organized approach to obtain the optimum value for each dollar spent.

O'Brien Kreitzberg (OK) contributed experience in civil, process, geotechnical, and hydraulics engineering. Each workshop started on a Monday morning and ran through a debriefing on Friday afternoon. At the start of each study, the design team made a presentation to familiarize the VE team with the background information, and provide items in each of the contract packages that were stipulated not subject to the analysis.

Unlike simple cost cutting using smaller quantities or cheaper materials, OK initially focused on analyzing the function of an item asking such questions as:

* What is it?

* What must it do?

* What does it cost?

* What is it worth?

* What other equipment or method could be used to perform the same function?

* What would the alternative cost be?

PARETO'S LAW

The most expensive items were selected for functional review. Experience indicates that Pareto's Law (20 percent of the items will control 80 percent of the budget) applies to construction programs. As a result, VE focuses on the 20 percent (more or less) of the items driving the project budget.

In combination with performing a function analysis, the workshops entail "brainstorming" to identify or speculate on alternate ideas or ways to achieve the desired function. A list of speculative ideas is prepared without consideration of practicality. The ideas then are given chronological numbers for identification only. Each is assigned a rating from 1 ("drop it") to 10 ("a good idea"). A cutoff threshold of 7 or 8 - depending on how many items are listed - is selected, and any ideas below the threshold are discarded. The remaining ideas are developed by various members of the team.

The most significant result of the function analysis was the conclusion that the function of the sodium hypochlorite building was to control temperature. Containment was not a required function, so the team recommended replacement of the building with a control room and a pump house. The savings accepted by the design team were $3.2 million.

Additionally, in reviewing as-built plant drawings, the VE team determined that the existing aeration tanks were not built on piles. It was recommended that piles be eliminated on three new treatment tanks (one primary treatment and two aeration).

After further analysis, the design team agreed that soil on the plant side nearest the bluffs was sound and eliminated piling on one aeration tank. The savings was $2.5 million.

Other ideas accepted regarding site work included:

* Remove unused sewers only as needed; abandon rest in place.

* Keep (rather than replace) an existing 6-in. PVC force main that was functional.

* Leave 900 ft of existing RCC pipe in place in lieu of installing new 18-in. pipe.

* Reuse existing 4160-V power where applicable and add new power lines at 13.6 kV.

* Eliminate paging system.

* Reduce the number of fire alarm control panels.

* The site work savings totaled $1.8 million. From 181 speculative ideas generated during the brainstorming sessions, 21 ultimately were implemented by the design team for a savings of $8.3 million.

All in all, the process proved to be very cost-effective, with a 100:1 ratio of savings implemented to workshop cost.

Jim O'Brien, P.E.

Mr. O'Brien is a founding partner of O'Brien Kreitzberg, Ewing, New Jersey.
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Title Annotation:wastewater facility in Pittsburgh, PA
Author:O'Brien, Jim
Publication:Public Works
Date:May 1, 1998
Words:1284
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