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A sustainable source of water

A sustainable source of water

Hampton Roads Sanitation District’s eight-step process includes flocculation and sedimentation, ozone contact, biologically active filtration, granular activated carbon contractors, ultraviolet disinfection, chlorine contact, chemical addition, and aquifer recharge. Photo: Hampton Roads Sanitation District

Virginia project finds innovative reuse of wastewater.

By Thomas Renner

A recently opened research center could be the centerpiece toward solving vexing and critical water issues facing Virginia’s Hampton Roads region. The innovative water treatment program — Sustainable Water Initiative for Tomorrow (SWIFT) — is a critical first step in that it is designed to ensure a sustainable source of groundwater while addressing environmental challenges.

The $25 million research center, located on the grounds of Nansemond Treatment Plant in Suffolk, is capable of producing 1 million gallons of SWIFT Water (water treated to meet drinking quality standards) daily. The SWIFT Water is treated to match existing groundwater and used to charge the Potomac Aquifer.

The eventual goal is to build five facilities by 2030 to recharge the Potomac aquifer with more than 100 million gallons of SWIFT water daily by 2030. The project aims to have the first full-scale SWIFT facility built by 2020, and four more added by 2030. The total output from each facility will range from 9 to 45 million gallons per day.

“This is a great project because 90 percent of what we currently discharge will no longer go into the Chesapeake Bay,” said Ted Henifin, general manager of the Hampton Roads Sanitation District (HRSD), the Virginia agency that is managing the project. “It will be treated, purified, and put into the ground where it can provide other benefits.”

An eight-step process

The Hampton Roads Sanitation District’s Sustainable Water Initiative for Tomorrow (SWIFT) is designed to ensure a sustainable source of groundwater while addressing environmental challenges. Photo: Scott Lau, Marcor Associates

The system to clean wastewater revolves around an eight-step process that completes three primary objectives. “One goal of this project is to treat without the large environmental footprint of membrane systems,” Henifin said. “The SWIFT Recharge is a first of its kind treatment, recharge, research, and public education facility.”

The eight-step process includes flocculation and sedimentation, ozone contact, biologically active filtration, granular activated carbon contractors, ultraviolet disinfection, chlorine contact, chemical addition, and aquifer recharge.

When wastewater enters an HRSD treatment plant, it first flows through a bar screen that removes large floating objects such as trash, sticks, and rags. The captured material is properly disposed of in a landfill and the wastewater flows to a grit chamber and a sedimentation tank. These devices slow the flow of the water and allow sand, grit, human waste solids and other small particles to settle to the bottom. These solids are then removed along with any scum or grease floating on top.

The wastewater then travels to secondary treatment facilities that speed up the processes of nature, allowing microorganisms (bacteria and other organisms) to consume 80 to 90 percent of the organic matter — human, animal, and plant waste.

The most commonly used secondary treatment technique in HRSD plants is the activated sludge process. The process speeds up the work of the microorganisms by pumping oxygen-rich air and sludge into close contact with the wastewater in an aeration tank. Over several hours, the organic matter is broken down into harmless by-products.

The wastewater is then sent to a final clarifier, where the microorganisms that grow during the activated sludge process sink to the bottom and are recycled back to the aeration tanks, and the remaining water moves on to the final treatment process.

Advanced treatment systems remove additional pollutants such as nutrients, heavy metals, and chemical compounds. These systems may use microorganisms that differ from those in secondary treatment, additional chemicals, or an effluent filtration system. This significantly increases plant construction and operation costs but improves the final quality of HRSD’s highly treated water.

Finally, the water is disinfected. Some wastewater treatment plants use chlorine, while others expose the water to high levels of ultraviolet light. HRSD facilities remove excess chlorine before discharging the cleaned water to local rivers. These processes kill 99 percent of disease-causing pathogens such as bacteria and viruses. That step allows the water to support the intended use of the area waterway and can be released back into the environment.

Cost-effective pump stations

Two underground pump stations and several vaults are key parts of the process. “Building the pump station was the most cost-effective option, both from a capital perspective and operations and maintenance, allowing gravity to feed to the stations,’’ Henifin said. “Additionally, building the pump station underground allows for site circulation above the pump station, which was important to conserve land and minimize footprint.”

The vaults and pumps are protected by channel frame doors manufactured by The BILCO Company of Connecticut that prevent water and other liquids from entering the access opening. There are seven doors protecting the valves and pumps in the sophisticated system, along with three LadderUP Safety Posts, also manufactured by BILCO. The posts provide easier, safer access through floor doors, roof vents and manholes. Two BILCO roof hatches were also used in the project. Marcor Associates of Midlothian, Va., delivered the doors, hatches, and safety posts. Crowder Construction and Hazen and Sawyer served as general contractors on the project.

In improving its infrastructure for SWIFT, HRSD built a new $12.4 million pump station designed to pump as much as 16.6 million gallons per day (mgd) of wastewater. The Bridge Street Pump station, which replaces a station that had been in operation for longer than 70 years, will be resistant to tidal flooding as well as the effects of long-term sea level rise.

The station includes walls that extend more than 300 feet into the ground, five pumps at the bottom of the pump station, pipes that range from 8 to 48 inches in diameter, and 14 concrete walls, each of them 3 feet thick. The station includes the latest in technology and will be able to handle the wastewater of a growing population in Hampton, one of the largest cities within the HRSD.

Fighting subsidence

There are many benefits associated with SWIFT, but among the most crucial are replenishing the area’s dwindling groundwater supply, fighting sea level rise, and protecting groundwater from saltwater intrusion due to a shrinking aquifer.

“Once we were seriously considering treating to drinking water standards, we needed to find a beneficial use for the valuable water we would be producing,” Henifin said. “That led to the idea that we should put it back into the already stressed groundwater aquifer. Using the aquifer to redistribute the water to anyone in Eastern Virginia would eliminate the need to build expensive pipelines to move water to specific areas or customers. We see this as a ‘wireless’ solution to water distribution.”

Land subsidence has been observed in the Chesapeake Bay region at rates of 1.1 to 4.8 millimeters per year since the 1940s, according to a government report (https://pubs.usgs.gov/circ/1392/pdf/circ1392.pdf). The aquifer system in the region has been compacted by extensive groundwater pumping, accounting for more than half of observed land subsidence. The report said, “Glacial isostatic adjustment, or the flexing of Earth’s crust in response to glacier formation and melting, also likely contributes to land subsidence in the region.”

Increased water use in the region is a direct result of its surge in population. The Hampton Roads region population swelled from slightly less than 600,000 residents in 1960 to more than 1.7 million in 2016, according to estimates. In Virginia Beach alone, the population increased from about 8,000 in 1960 to more than 450,000 in 2016.

The SWIFT project is critical in many respects and could be a template for many areas of the country to follow to fight similar issues with wastewater and land subsidence. “There are many elements that can be applied in other areas, but for the most part, SWIFT requires some geological features to be fully successful that are location specific — a confined thirsty aquifer being the primary requirement,” Henifin said. “But large-scale success with a carbon-based process — eliminating the need to deal with a waste brine stream — opens the possibility of recycling wastewater throughout the country.”

Thomas Renner writes frequently on construction, manufacturing, building, and other topics for trade publications in the United States and Canada.