The Altoona Water Authority is in the midst of a multi-year upgrade of its water plants’ ozonation and filtration systems, on which it has spent or intends to spend $43.5 million so far — with estimates for filtration replacements in three of the plants not yet calculated.

The operations of the six-plant system — there are seven, but Homers Gap has been offline for years — contrasts with authority operations 35 years ago, when water was merely chlorinated — except at the Horseshoe Curve plant, which is a special case, due to acid mine drainage, said Jim Balliet of Gwin, Dobson & Foreman, the authority’s consulting engineer, at a presentation recently.

The proposed new membrane filtration systems represent the second generation of filtration for the plants, replacing the old filter beds that purified water by percolating it through a layer of sand over top of a layer of coal.

The ozonation system replacements began in 2023 with Mill Run, Tipton and Plane 9, where the work is finished.

It continued with a project at Bellwood, which is nearly done.

And it will conclude in 2026 with Horseshoe Curve and Kettle, for which funding is expected this year — with a total ozonation replacement cost of about $18 million, according to Mark Glenn of Gwin, Dobson & Foreman.

The enhanced ozone preoxidation systems that have been or will be installed are designed to break down and enhance coagulation of organic matter, making it easier to remove it, according to online sources.

The membrane filtration replacements, coupled with new ultraviolet disinfection, will begin with the Bellwood plant, which is almost ready to go online after a $12.5 million project, coupled with a renovation of the dam.

The filtration replacement program will continue with a $13 million project at Plane 9 in 2027 and conclude with projects at the other plants between 2028 and 2032, with estimates of cost not yet made for those.

Membrane filtration is a more definitive process for pathogen removal than the current sand and coal filtration, according to Balliet.

The membrane filtration occurs within ultrathin hollow fiber tubes bundled together within cylindrical modules.

The tubes are closed only on the bottom, where there are spaces between the tubes that admit unfiltered water.

The semi-permeable tubes contain pores that are 0.1 micron in diameter, small enough that giardia, cryptosporidium and bacteria can’t fit through, according to Balliet.

Water is forced at low pressure into the bottom of the module containing the bundle of tubes, so that it enters the tubes, leaving contaminants outside them.

At the top of the module, where the tops of the tubes are open, but the spaces between the tubes are sealed, clean water wells up through and is taken off.

The water coming out the top of the modules is thus “guaranteed good quality,” Balliet said.

When individual tubes or “fibers” break, they can be capped in place, according to Balliet.

The “pore” size for the current filtration system that uses sand and coal is 50 to 70 microns, which requires that system operators feed alum into the water to get contaminants to “floc” together, so that they can be captured, according to Balliet.

That work is challenging, due to constantly changing water temperatures and raw water composition, including the presence of algae, Balliet said.

By contrast, the “fairly simple” membrane filtration process is “absolute,” he said.

The new systems allow for “recovery” of between 95% and 97% of the raw water that they handle, Balliet said.

The current systems allow for recovery of only between 85% and 90%, he said.

The new systems are guaranteed for 10 years, but can last 20, according to Balliet.

On average, they last about 15 years, he said. After that, they’re easy to replace.

It only takes about two days of work in a plant to effect the replacement, he said.

Like televisions over the years, the modules have become cheaper, he said.

The authority’s membrane installation projects will also include replacement of pumps and chemical feed and control systems, along with the plants’ electrical and HVAC systems, Balliet said.

The current sand and coal filtration systems were installed beginning in the early 1990s, with Plane 9, followed by Tipton, Mill Run, Bellwood, Kettle and Homers Gap, Balliet said.

That work was done in keeping with 1989 amendments to the Safe Drinking Water Act, Balliet said.

The water in those reservoirs, which are fed from forested watersheds, is generally high quality, which eliminates the need for large sedimentation basins, which are necessary in some systems with lower quality raw water, Balliet said.

Not having to build those saved millions of dollars and also saved on operations, he added.

The installation at that time of fully automated control systems that were manned only a few hours a day has also saved lots of labor costs over the years, Balliet said.

The new, ongoing upgrades are a reflection of the further tightening of water quality standards over the past couple of decades, according to Balliet.

Mirror Staff Writer William Kibler is at 814-949-7038.