Water

Treating Wastewater Efficiently

Older and newer technologies can work together to improve plant operations and resource recovery.

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Credit: OVIVO
When it comes to waste­water treatment and processing, there are three challenges for operating plants, says Paul Rice, director of marketing for the Municipal Products and Services Division of Evoqua Water Technologies. One is getting more processing and capacity out of existing equipment, much of which is aging and requires retrofitting, rehabilitation, or upgrades.

New nutrient requirements present another challenge. “Those vary from state to state, whether it be nitrogen or phosphorus,” says Rice. “Wastewater plant operations have new limits that their permits are going to have to hit.” A third challenge: working to decrease operational-related energy costs.

While there are a number of new technologies on the market to meet the challenges, there are “tried and true technologies” which have been taken for granted that are “well-proven and well-demonstrated” and can be added into secondary clarifiers to improve operations, says Rice.

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Most of today’s secondary clarifiers were constructed 40–50 years ago and a lot of them have riser pipe in them, says Rice. For those facilities, the riser pipe clarifier can be converted to a use a Tow-Bro hydraulic sludge removal device to help remove settled solids within 30–40 minutes uniformly over the entire basin floor area without re-suspension of the solids, ensuring complete and positive control of the sludge blanket.

“It helps to handle higher concentrations of return activated sludge,” notes Rice, adding that it improves efficiency in an operation challenged with sufficient capacity.

Additionally, “there are a fair amount of clarifiers that have energy-dissipating inlets to slow down inlet water since any kind of currents mean that solids stay suspended longer,” says Rice. “The longer solids are suspended, the slower the process goes and the more space that is required for clarification.”

Evoqua Water Technologies has a Flocculating Energy Dissipating Well Arrangement (FEDWA) baffle system designed to help the flocculation efficiency of an operation. It is a relatively easy upgrade to a circular clarifier.

As with the other way around, new technologies can augment the benefits of existing ones, says Rice. Evoqua Water Technologies’ BioMag Ballasted Biological Treatment System helps flocculent settle faster through the infusion of magnetite as a weighting agent that attaches to the flocculent, says Rice.

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“The advantage of BioMag is it’s a system you can apply to the biological process at secondary clarifiers, allowing you to get much more treatment capacity in the same footprint,” he adds. “You can even free up tanks for other functions or do more processing in the same tank by applying this ballasted technology.”

BioMag is designed to double or triple biological treatment capacity and achieve enhanced nutrient removal limits within existing tanks. It is designed to routinely deliver total nitrogen less than 3.0 milligrams per liter, total phosphorous (TP) less than 0.2 milligrams per liter, and turbidity less than 1 NTU.

“It’s a drop-in to the plant, so you’re not requiring a new footprint for anything,” says Rice. “You’re just adding this ability to do ballasted settling into the secondary treatment, which meets the need to do more with less. It can help the existing process make better nutrient numbers, accommodate more flow, and add capacity to an existing plant or free up tanks for other uses.”

The CoMag particulate removal system is another magnetite ballasted clarification, but it’s used in primary clarifiers, tertiary treatment, and combined sewer overflows and stormwater management, says Rice. It performs similarly to other ballasted systems that use sand as a ballast instead of denser magnetite.

CoMag is designed to produce effluent nearly equivalent to ultra-filtration at capital and operating costs competitive with conventional alternatives. It also is NSF-approved for drinking water applications. The CoMag particulate removal system is designed to deliver TP less than 0.05 grams per liter, total suspended solids less than 2.0 grams per liter, and turbidity less than 1 NTU.

“In primary systems, it can help give you up to 10 times more capacity and it can help handle upsets and storm flow,” says Rice. “Many people are trying to figure out how they are going to get more water through their plant. A ballasted system at the front end of the plant can be a big help for that. On the back end of the plant, you can use this ballasted technology for nutrient removal.”

Evoqua Water Technologies also offers new approaches for advanced processing. The Captivator System is designed to improve a conventional anaerobic process by capturing and converting biochemical oxygen demand (BOD) to biogas that otherwise requires aeration energy.

The system utilizes a vertical loop reactor contact tank to help biomass maximize the soluble BOD absorption. A folded flow dissolved air flotation (DAF) applied to the liquid stream removes and thickens the majority of biomass and incoming sludge at high overflow rates.

The system is ideal for operations that have an anaerobic digestion plant and look to reduce the amount of net energy being used, or a plant that wants to convert the space tied up in primary clarifiers for other uses.

“The captivator system replaces primary clarification at the front end of the plant, so instead of having primary clarifiers, it takes solids out directly and uses a DAF at the front end of the plant and some aeration,” says Rice. “It pulls the solids—the more rich organics—right out and sends them to the digester. That offers more biogas out of the digester, so there is the potential to create up to 40% more energy.”

Secondary treatment can be an “energy hog,” notes Rice. “If you’re sending less organics there, you can reduce the energy used by aeration by 40%. If you’re thinking about an anaerobic plant and energy is an issue and you’re trying to drive to the concept of a net zero wastewater treatment plant, this is really a great thing to consider. It’s taking proven technologies and using them in a different way to save more energy and create more biogas.”

The process is ideal for operations looking to do renovations to primary treatment or for those entities seeking to convert gas to energy, says Rice. There is a current trend toward chemically enhanced primary treatment (CEPT) to limit BOD sent to secondary treatment. This requires a significant volume of chemicals and generates a lot of additional sludge.

Rice adds that the Captivator process from Evoqua can achieve the same or better results without the issues related to chemical addition.

Wastewater reuse is getting more attention now that California “is really stepping up their game,” notes Rice. “As California drives more reuse, the rest of the country is going to continue or step up efforts in that direction. There will be a lot of areas that are going to continue to increase what they’re doing and it’s going to go beyond mining water from collection pipes and using it for irrigation.”

Not-So-Flushable Wipes
One of the critical components in wastewater processing is the pump. “Our end users continue to be challenged by flushable wipes that seem to not be truly flushable,” notes Derek Alexander, municipal market manager for Crane Pumps and Systems. “Wastewater facilities are reporting this is a major issue and causing them big headaches with clogging. Although most debris is typically ground up and dissolves in the process, some municipal utilities are reporting the wipes form into strips during the treatment process and reform into larger balls, causing significant problems. This is causing a lot of repairs and service work which is costing municipalities a lot of money.”

Having a pump that can grind or shred flushable wipes is a very valuable resource municipalities are looking for immediately. Crane Pumps and Systems’ Barnes SH line of nonclog pumps offers up to 60 horsepower and has vortex impellers that can alleviate the flushable wipes concern, says Alexander.

The pumps have been used successfully in such installations as Salem, WI, a community that manages 25 lift stations for its population of 12,036. One of the lift stations, a triplex station, was clogging weekly, with the primary cause being flushable wipes. Brad Zautcke, utility district manager, says his team had to enter the station and unclog the pump by pulling out the rags with needle nose pliers.

The station’s design required entry into the station rather than removal of the pump, which meant a confined space entry with a three-person crew. Each clogging maintenance trip cost a minimum of $300. The problematic pump was located farthest from the influent channel. Operators switched the position of the pumps to no avail.

The municipality worked with Energenecs—a Crane Pumps and Systems channel partner—on potential solutions. Crane Pumps and Systems provided a Barnes 4SHVA 30HP Solids Handling pump as a demonstration replacement for the station in September 2013. The pump was installed a month later.

It wasn’t until October 2014 that the pump was pulled for its annual maintenance and it continued to be clog-free for more than a year. It is estimated that the pump had paid for itself within in the first six months of operation.

Crane Pumps and Systems is currently working on a new product development release that will provide municipalities a solution for challenging products advertised to be flushable, notes Alexander.

Regulations and Testing
Testing, as provided by such companies as Pat-Chem Laboratories, is a critical part of wastewater processing and regulations are the driving factor in what constituents of concern should be tested for in wastewater.

Pat-Chem is a California-certified environmental laboratory providing hazardous and non-hazardous testing to industrial, consulting, and governmental clients. The lab offers analytical services to support clients’ monitoring requirements under federal, state, and local environmental programs.

Pat-Chem Laboratories has been doing wastewater testing for such municipal entities as the City and County of Los Angeles and the City and County of Ventura for many years. A permit outlines what needs to be tested, notes Stephen Berentsen, general manager for Pat-Chem Laboratories.

“We come out, they give us the permit, we set up the compliance monitor, verify that’s what we’re testing for and do the testing,” he says, adding that some clients mistakenly believe they should only be testing for a few constituents of concern.

“A lot of people say, ‘I only need testing for COD and BOD and just the metals and that’s it,” says Berentsen. “We look at their permit and say, ‘You forgot about this, this, and this.’ As a policy, we always review their permit.”

Typically, testing occurs for the most prominent constituents of concern, such as chloride, cyanide, metals, oil and grease, pH, total organic compounds, and total toxic organics.

Sometimes, another constituent will present itself and require testing, such as hexavalent chromium. “That’s had a new resurgence. Everyone is looking for that kind of a test and we test for that,” says Berentsen. “We’re trying to be on the forefront of what needs to be done.”

The frequency of testing differs.

“Los Angeles County’s permit might be on an annual basis; another client we’re testing for has to test twice a month—every other week,” notes Berentsen, adding process manufacturing may require different time frames and testing for specific constituents such as metals. Testing can take place before, during, and after treatment.

“For an airline, we’re out on the runway when they’re taking their wastewater from their toilets and we test that there,” says Berentsen. “For other companies, we’re testing water before it goes into their system and they have a treatment plant where they’re treating their wastewater.

“Some large companies, such as breweries, have these anaerobic systems that are filtering out whatever they can and putting it back into wastewater discharge. We test before and after and during for some of them.”

There are instances in which a constituent of concern is involved in a permit and Pat-Chem’s testing hasn’t found it in several years. The company may advise the client to call the permitting authority to ask for a “pass” on testing that, says Berentsen.

With an upsurge in water reuse against the backdrop of drought, there will be an increased need for testing to ensure that the water is safe for the purposes for which it is being reused, he notes. “We can make some great changes in treating wastewater to be able to be reused as secondary reclaimed water, irrigate plants with it, or clean it up and drink it again,” notes Berentsen.

“If you think about it, all of the sewer water is processed, cleaned, and comes back to our taps. It’s weird in a way to think it’s coming from your toilet,” he adds. “But it’s clean and it’s tested. If the cities are able to test it on a daily or weekly basis or whatever is needed to be done, we should utilize that water. It shouldn’t go to waste.”

Resource Recovery
Given the growing appreciation of water as a precious resource, the practice of wastewater treatment and processing is undergoing a significant transformation, says Doug Owen, executive vice president and chief technical officer for the water division for Arcadis North America.

Arcadis North America is a consulting firm that provides services in planning, design, construction administration, and management for clients in municipal and private sectors.

“The traditional wastewater business is basically collecting wastewater and treating it prior to what historically has been a discharge to a receiving water,” he points out. “While it’s important for us to clean it, the end use is changing.”

The United States has largely accomplished the earlier goals of the Clean Water Act to make the country’s waters fishable and swimmable, says Owen. “But it was basically an environmental benefit rather than an immediate human benefit,” he adds. “Now we’re looking at the opportunity to see water as a resource in order to directly augment our water supplies. We’ve done that indirectly in some cases by putting it into rivers that downstream someone has taken as a resource, but it wasn’t planned for a certain urban environment.”

Another factor to consider is the blueprint developed by the National Association of Clean Water Agencies of utilities as resource “factories” instead of treatment facilities, says Owen.

“They produce water, energy, and nutrients,” he adds. “The technologies are moving now in the ability to recover water for the appropriate end use, whatever that end use might be. There are higher levels of treatment where we want to produce water that’s going to directly augment potable drinkable water sources. There’s a lot more focus on being able to recover energy from wastewater through a variety of means.”

There also is an effort on recovering nutrients such as nitrogen and phosphorous for two fundamental reasons, says Owen. “One is to keep them from being discharged into receiving streams and having all of the downsides of eutrophication, but also to be able to use them as valuable commodities for agriculture,” he adds. “That whole transformation in thinking about what is the role of the utility and what is the true value of wastewater is changing the industry and the technology that’s being applied.”

Opportunities abound to leverage the potential for wastewater, points out Owen.

“The real driver is how do we recover that water purposely and use it to augment drinking water sources because there just isn’t enough drinking water,” he says.

“In a lot of places that discharge to protected estuaries such as the Chesapeake Bay system on the mid-Atlantic coast—and there are others—a lot of it is driven around nutrient recovery, which is making sure we get those nutrients out that we can use as a product, but initially the driver is keep it out of the bay in order to protect the estuarine system that supports a lot of economy in that area.”

In “very-heavily” watered areas in the Northeast and the Midwest, traditional systems were designed to combine stormwater with wastewater collection, explains Owen. “Now we’re getting more intense storms with heavier rainfalls and a lot of combined sewer overflow from those systems,” he adds. “The big push is not only how do we separate those systems, but more importantly, how do we keep stormwater out of the wastewater systems from the beginning?”

Instead of collecting stormwater and bringing it into a single point of treatment or treatment with an end-of-pipe discharge, a more sustainable option would be to get it recharged into the groundwater or used in a riparian way in order to increase its value for an urban area, says Owen.

For example, billions of gallons of highly-treated wastewater in California that could be recycled are discharged into the ocean, Owen points out, adding that treated wastewater could yield more than one billion gallons of potable water daily, enough to meet the needs of more than eight million Californians.

Today’s purification technologies—combining micro- or ultrafiltration, reverse osmosis, ultraviolet disinfection, and advanced oxidation—are safe, reliable and leave the water cleaner than most bottled water, he adds, citing studies from the WateReuse Research Foundation.

Case in point: Orange County, CA, which is reusing 70 million gallons of treated wastewater per day to recharge its aquifer, and is poised to commission another 30 million gallons per day.

The barriers to reuse of wastewater have started to erode over the last four years, says Owen. “Historically, there have been legislative issues that may have prevented wastewater being used for this purpose, but those roadblocks are going,” he says. “For example, there has been a lot of legislation in California in the last five years mandating that criteria be developed to allow this to happen.” Regulators who are responsible for public safety in drinking water want to ensure the appropriate technology, operating criteria, reliability issues, and monitoring is in place, adds Owen.

The social aspect of recycling wastewater for potable water uses is another consideration. “It’s people really coming to grips with the fact that all of the water we have on the planet has been here since the beginning of time,” he says. “We are not creating water and we’re not destroying water. All water is recycled. It’s just whether we do it by a natural or man-made process.”

In arid regions such as west Texas and Orange County, there aren’t other choices, adds Owen.

Owen says he believes the social resistance will ease with younger generations who are more accepting of tech­nology as a solution.

Utilities that are not currently geared up to treat wastewater for reuse but envision doing so in the future should start by considering their entire water portfolio, says Owen. “Where do you get your water and what is the sustainability of those individual resources? When you look at that and how it plays out, you can make a decision about what portion of that portfolio should be associated with water reuse and reclamation,” he says. “There is an availability aspect and an economic aspect to that.”

While water may be imported from a long distance to an urban area, that may present reliability issues, he says. “There could be significant cost issues because you’re pumping and transferring water from long distances and the economics may be that it’s better off to use the water over which you have control that your population is generating.”

If wastewater is an important component of an entire portfolio approach as a water resource for an urban population, then it’s time to get all of the important stakeholders, political entities, NGOs, and others in place to “start to explain the story”, says Owen.

“Orange County is successful because they got started early,” he says, adding that it was an eight-year process of public engagement. “They explained the issues to their customers. During the entire time they developed that project they were meeting with stakeholders and working with health authorities.”

The technology is available for any utility to do so now, says Owen. “There are some monitoring issues and we continue to make sure that all of this is reliable, but it’s bringing the stakeholders along and putting together a long-term plan,” he says. WE_bug_web

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