On-Site Wastewater Treatment: Turn Blackwater into a Green Opportunity

While greywater and rainwater harvesting are popular conservation strategies, blackwater remains a murky proposition for many properties. Until owners take the plunge, they can be hindered by concerns about odor, safety, performance, and occupant acceptance.

But don’t be fouled up by these misconceptions – you can save thousands, if not millions, of gallons of water by using a membrane bioreactor (MBR), an activated sludge system that treats wastewater. This tested technology will drastically reduce your utility and sewer costs while providing clean water that can be used virtually anywhere in your facility.

A Raw Deal
Building owners who adopt wastewater treatment are typically well on their way to water independence. Their facilities already use low-flow fixtures and irrigation controls and harvest rainwater and stormwater to reduce potable water demands. Blackwater recycling is simply the next step to closing the water loop.

While many areas of the country still enjoy inexpensive water, discharge rates and stormwater fees are driving up utility bills. Buildings pay for water twice – once for potable needs and again to discharge sewage – so there’s strong motivation to become part of the process. Even more so when you consider that very little water in your facility needs to be treated to drinkable standards.

“By taking on the cost of water treatment, you gain a level of control over your utility rates,” says Paul Schuler, engineered systems region executive for the Americas with GE Power & Water, a manufacturer of wastewater technology.

Reclaiming wastewater is also a powerful way to reduce your environmental impact and relieve pressure on your municipal infrastructure. Consider how far away your building is from your local treatment plant – every mile represents energy that’s required to pump water and sewage back and forth.

“One of the biggest advantages of water recycling is that it decentralizes the wastewater treatment process,” says Tracy Cort, operations manager for the firm Vision Engineering. “Water is harvested and reused where it’s needed the most: your building.”

Blackwater recovery can also help you earn green credibility. LEED, for example, offers up to six points for water reclamation and reduction strategies. Particularly if you are aiming for Gold or Platinum, water recycling is an important area to target. Blackwater treatment is also a necessary strategy for projects pursuing the Living Building Challenge, which requires net-zero water for certification.

Because wastewater recovery is such a clear signal of pushing the green envelope, it will make your property stand out from others in your market.

“The marketing message that a building reuses all its water can be a powerful differentiator when looking to increase occupancy,” says Josh Gleason, a business partner for Treatment Equipment Company (TEC), a supplier of water recycling systems.PageBreak

Make a Big Splash
Membrane bioreactors are a relatively straightforward technology, essentially a small-scale version of a municipal sewage plant. Unlike traditional settling methods that use gravity for separation, MBRs use micro- and ultrafiltration membranes to filter water more effectively and quickly, says Gleason.

Blackwater and greywater are collected from a variety of sources, typically toilets and urinals, lavatory sinks, laundry machines, showers, dishwashers, and kitchen drains. Stormwater and rainwater don’t need the same level of treatment as blackwater, explains Schuler, and are generally not included as they can be purified using less energy-intensive methods.

Once inside the treatment system, blackwater is cleaned using a series of processing tanks and filters:

1. An equalization or pretreatment tank is used for initial separation and settling. Depending on the system’s size, grinder pumps may also be included. Filters screen out nonbiological materials, such as plastics and paper fibers.
2. For large applications, the equalization tank contains a secondary aeration chamber that contains microbes. Sewage is broken down into a liquid state (effluent) by the bacteria, which simultaneously removes nitrogen and ammonia.
3. Pumps draw the effluent into the membrane, which contains fibers that trap suspended containments. The pores are typically 0.1-0.5 microns to inhibit bacteria, microorganisms, and insoluble solids, notes Toward Net Zero Water, a guide by the International Living Building Institute.
4. The resulting sludge is either pumped back into the aeration tank to replenish bacteria levels, picked up by a hauler, or released into the city sewer.
5. Because viruses may still be present, the leftover water is directed to a chlorine or UV touch tank. This process cleans the effluent for color and further purification. Some properties may include an air scrubber that uses charcoal to absorb any nuisance odors.
6. Treated water is held in storage tanks and then pumped back into the building. If capacity exceeds demand, however, reclaimed water is clean enough that it can be infiltrated into the ground or released into a nearby body of water.

Nonpotable purposes include urinal and toilet flushing, fire protection, vehicle and window washing, landscape irrigation (including green roofs), laundry machines, dust control for construction, and cooling tower or boiler water makeup.

A Pipeline to Efficiency
Properties of all types are compatible with bioreactors, including high-rise buildings, office parks, casinos, resorts, shopping malls, stadiums, multifamily complexes, and golf courses. Even a small business can benefit, though the higher your blackwater volume is, the more likely you are to see significant savings.

Installation costs range from $7-20 per gallon treated, according to the EPA in its Wastewater Management Fact Sheet: Membrane Bioreactors. Expect to pay anywhere from $100,000-500,000 for an average system, estimates Schuler.

Each system is custom-built according to your capacity requirements, which can be estimated from your sewage discharge volume on your utility bill. A commercial installation is typically less than 100,000 gallons per day, notes Schuler. Gleason has even designed systems as small as 2,500 gallons per day.

Treatment plants are ideal for new construction because you can anticipate layout ahead of time, says Schuler, including piping requirements, energy costs, and reuse strategies.

But it’s not uncommon for MBRs to be added to existing buildings. One of the most famous examples is Fallingwater, a Frank Lloyd Wright home in Pennsylvania that added a system in the early 2000s to keep up with increased visitor traffic and preserve the environmental integrity of the site.

MBRs also have the smallest footprint of any advanced commercial wastewater treatment options. For example, one of the small-scale systems TEC offers can treat up to 60,000 gallons per day in a 40-foot by 8-foot space, says Gleason. Plants are often located at low levels on a property to take advantage of gravity and decrease pump use. Other out-of-site locations include basements, underground parking garages, and mechanical rooms.

If there isn’t space internally, an MBR can be housed in a small outbuilding, says Gleason. These are often located near a delivery or freight area or the edge of a property. This can be a tasteful way to hide your plant in plain sight while providing easy access for inspection and maintenance. PageBreak

Teeming with Success
Because MBRs have to abide by the same permit and monitoring standards as a public treatment plant, you need a licensed operator to oversee the system. A 30,000 gallon-per-day system, like the one Oregon Health & Science University has, may only require 8-10 hours per week to operate, says Gleason. Larger installations, such as the Vancouver Convention Centre, will likely need a full-time staff member for plant management.

Private contractors and consultants can also be used, particularly as remote monitoring makes it easy to stay on top of performance. Schuler suggests finding professionals who work at your city’s waste treatment plant who are interested in doing work on the side. They can also be an invaluable resource when designing your system.

Because you’ve taken on the full responsibility of water treatment, you need to plan ahead for how you will dispose of your waste solids. Plastics and nonbiologicals that have been caught in the filters simply go in the trash, but it’s the activated sludge that must be handled carefully.

As long as the connections are in place, you can always discharge the waste solids to the sewer. You will still incur disposal fees, but they will be far less than if water hadn’t been extracted beforehand. You can also contract with a waste hauler, such as a septic tank company, and schedule daily, weekly, or monthly pickups, says Gleason.

To avoid safety concerns and loss of performance, MBRs require routine maintenance. Because the equipment is in daily use, it is prone to wear and tear at higher rates than other building systems.

For example, the membrane needs to be replaced periodically, just like a furnace filter. Membranes have an expected life of seven to eight years on average, notes the EPA. Pumps, air compressors, and blowers will eventually need to be replaced as well.

Other items that will require replenishment are chlorine levels, corrosion control, and lubrication. Pressure logs and readings should be taken routinely to monitor performance, notes Mike Garcia, senior manager of facility operations and engineering with the Vancouver Convention Centre. He also recommends testing for biochemical oxygen demand (BOD) to check for broken tubes or leaks.

While water treatment may seem like a big responsibility, the benefits and tradeoffs are no different than adding your own energy generation. While it’s a more independent way of operating your facility, reclaiming blackwater will flood your operations with success.

Jennie Morton is senior editor of BUILDINGS.