From distribution to wastewater, the costs associated with water treatment are rising. Budget-busting expenses include chemicals, maintenance, repairs, labor, and energy, and for wastewater plants, you can add the cost of getting rid of that sludge. However, there’s good news. We’ve got some products and technologies to help utilities reign in these rising costs. To cover all of them would take an encyclopedia-sized article, so rather than bog you down, we’ve gathered a shortlist of solutions that can address typical problems, and, a bonus: a look at Washington DC’s radically new anaerobic digestion treatment plant. It’s a first for a new technology from Europe, and it saves millions in sludge and energy; plus, it’s a marvel of engineering and design.
To start, let’s look at saving money on filters. According to Dane Madsen, CEO of Blue Earth Labs, Las Vegas, NV, utilities are faced with serious problems when filter media and underdrains become encapsulated and clogged. The results are higher head loss, shorter filter run times, frequent backwashing, lower water quality, and poor overall system performance. There are a number of methods to address the clogging problem. For example, chemical treatments, such as media cleaning through oxidization, and increasing prechlorine feed rates or adding chlorine on top of the filters. Others have tried using sodium hydroxide and simple acids, such as citric, phosphoric, hydrochloric, and sodium hypochlorite, with less than satisfactory results.
Many utilities have opted to economize by the use of simple cleaning with commodity chemicals and local personnel. Yet, although simple cleaning creates the appearance of proactive maintenance, it temporarily masks the real problems that ultimately lead to replacing filters. However, replacements are an expensive alternative that can be avoided. “Replacing filter media is a relatively popular method, but it introduces a lot of risks and problems,” says Madsen. “You have to take the filters out of service for a week or 10 days, and it’s not unusual to get damaged equipment. Furthermore, you’re not making water so there’s a loss of inventory, and a straight replacement won’t address some of the bigger issues that have to do with the biofilms that grow all around the filter walls and in the drains.”
An alternative to the problems stated above is to take the equipment offline and clean it in place. Blue Earth Labs offers the formerly Floran line of products, which are specifically formulated to quickly clean water infrastructure that can be taken offline, such as water tanks, filter bays, basins, air stripping towers, filter media, underdrains, and clearwells. This suite of products removes organic and inorganic deposits including iron, manganese and calcium scale, biomass, and algae.
“These products restore the equipment and remove the constituents that have gathered on filter media, and now you get runtimes that are back within spec,” says Madsen. “In one of the worst cases that we’re working on right now, their runtime should be from to 80 to 120 hours. But they’re getting runtimes of 12 hours. With this solution, for less than the cost of replacement, they get a full and complete cleaning and will see cost savings on the electricity and water because they won’t need to backwash so often. It’s not unusual for utilities to backwash as much water to clean their filters as they make in a day, and that’s a huge issue.”
Storage
Another huge issue occurs with the maintenance of storage tanks, which develop biofilms quickly. “Biofilms grow within seconds of water going into the container,” says Madsen, “and chlorine doesn’t take care of it. These structures in general have 100% of the utility’s daily production of water sitting in storage. So if it’s a 15,000,000-gallon system there’s 15,000,000 gallons of storage sitting around, and those tanks are generally ignored till there’s a problem. Currently, the leading solutions are remote-operated vehicles or a diver in the tank to vacuum up what’s on the floor. That’s okay for the loose material, but these biofilms attach themselves to all the surfaces, and divers and remote-operated vehicles can’t really deal with the walls. Yet, those have a much larger surface area than the floor of the tanks. We’ve done 5,000,000-gallon tanks in Houston where we happen to be at the moment, and we’re in and out in eight hours. These tanks are as clean as they can possibly be. And that allows the utility to actually look at the walls for the first time. In the past, they’ve seen those walls either be black or red, depending on whether it’s manganese or iron in the water.”
Distribution
We’ve looked at the Blue Earth/Floran approach to addressing filters and storage tanks, but what about distribution systems? “You can’t take those offline,” says Madsen. “But a distribution system is a huge generator of disinfection byproducts that create issues when it comes to damage done by the bacteria.” To solve the unique problems of distribution systems, Madsen prescribes Clearitas, a formulation of oxidized chlorine specifically engineered to remove organic and inorganic deposits. Its oxidizing properties penetrate and remove the attachment mechanisms that start and hold inorganic and organic matrices together and to surfaces.
“To protect themselves from disinfection, biofilms secrete a polysaccharide layer over the top of the biofilm community, and it does a really good job,” explains Madsen. “This generates demand on the chlorine, and it generates disinfection byproducts. Clearitas removes all the organic-based scale and biofilms.” Clearitas is a nonhazardous, liquid formulation that works online in conjunction with a traditional disinfectant. It maintains its performance integrity within a wide range of water conditions and removes mineral deposits without changing water corrosivity. By controlling the dosing rate, deposits and scale are removed slowly, without adverse effects on water quality.
Disinfection Generators
Even in a clean system, chlorine is a considerable expense, but there are efficient methods for maximizing its production. For example, MIOX, based in Albuquerque, NM, produces onsite generators that make chlorine-based disinfectants by passing a solution of sodium chloride (salt and water) over an electrolytic cell. These systems also convert some of the oxygen in the water molecule into hydrogen peroxide. The combination of sodium hypochlorite and hydrogen peroxide creates a unique chemistry that addresses chlorine problems in distribution systems.
The Cedar Knox Rural Water Project turned to MIOX to solve its residuals problem. The project used 150-pound chlorine gas tanks to get the water plant’s levels to 3–3.5 milligrams per liter, but they couldn’t maintain a residual in the distribution system. To correct the issue, Cedar Knox installed a MIOX system that makes 50 pounds per day of free available chlorine, injected at a clearwell. Although the chlorine sits for eight hours of detention, it kept the plant around 2 milligrams per liter and still maintained the residual in the distribution system. The lower dose had an additional benefit: less disinfection byproducts, and less maintenance. The system automatically performs a self-clean at 700 hours of operation, eliminating manual cleanings.
Minerals and Metals
Disinfection byproducts are a growing concern for many water utilities that incorporate chlorination or disinfection processes. Also, considering all of the EPA-regulated drinking water parameters, one often can have multiple contaminants of concern, including iron, manganese, arsenic, uranium, or hydrogen sulfide, for example. In such cases, it’s necessary to consider an integrated treatment approach, according to Greg Gilles, vice president, AdEdge Water Technologies, Buford, GA. “There’s a full range of conventional and innovative treatment technologies that can be combined to meet or exceed regulatory standards,” says Gilles.
In the case of a site near Springfield, OH, arsenic was the primary problem, and an AdEdge Packaged Unit (APU) system was the answer; however, the site also had high levels of iron and manganese that required a second stage of treatment. The APU systems are designed, packaged, and assembled as a turnkey treatment solution, ready for simple installation and operation upon arrival. These systems can meet a variety of flow rates and configurations for groundwater, as well as surface water applications. AdEdge supplied two separate APU treatment systems for the EPA site in Springfield, OH, rated up to 200 gallons per minute. The lead system was for oxidation and filtration of high iron and manganese using the AD26 process. The polishing stage utilizes Bayoxide E33 granular ferric oxide media, with a three-vessel parallel flow configuration with PLC automatic controls and chlorine monitoring. Chlorine is injected prior to the system to aid in the iron and manganese removal, to convert arsenic (III) to arsenic (V), and for disinfection purposes. No other chemicals or regeneration are needed. Instrumentation on a control panel measures critical operating parameters. These systems can also be coupled with a 100% recycle backwash system that has zero discharge of wastewater.
With its turnkey design, an APU can solve problems quickly. When Spring Creek Utilities in Nevada needed arsenic treatment at three different well sites, they came to AdEdge in need of a solution, but within an unrealistic timeframe and shadowed by large fines from the NDEP if they didn’t meet stringent regulations. “We did a design build with a contractor and engineer to streamline the approach and put in our own arsenic treatment solution within containerized WaterPODs,” recalls Gilles. “The units are completely enclosed structures with treatment we built at our facility, so from design to installation to start up, it was done in six months. It involved a total capacity of a 2.5-MGD [million-gallon-per-day] system.”
Biological Treatment
With emerging contaminants creating new requirements for utilities, AdEdge is launching biottta, a fixed-bed biological treatment process with dual stages. biottta treats nitrate, perchlorates, a variety of VOCs, hexavalent chromium, and other contaminants. “biottta is an exciting technology,” says Gilles. “It uses biological means and treatment for potable drinking water wells to remove things like nitrate, perchlorate, and VOCs from water. It’s not the typical chemical means or filtration process. We’re using biological methods to convert constituents like nitrate into harmless nitrogen gas. It’s a very environmentally friendly technology that has a lot of interest in the marketplace because it doesn’t generate hazardous waste residuals or waste byproducts. This is something new for drinking water, though the basic technology of biological treatment has been employed for many years in the wastewater industry.”
The biottta biological process works fast. In about a 5–10-minute period of time, the water passes through the treatment system, and contaminants are converted from forms that don’t currently meet safe or acceptable drinking water standards to non-harmful and non-toxic forms that meet all drinking water requirements. “Conventional technology would often take hours, and perhaps days, to do that type of conversion,” notes Gilles. “The technology creates a great environment for naturally occurring microorganisms and non-harmful bacteria to remove or transform these contaminants.” The system is modular and scalable with packaged systems capable of serving wells with 100–200 gallons per minute of capacity to systems producing several MGD.
APU ready to ship
Thermal Hydrolysis
Now let’s head to Washington DC, where the district of Columbia Water and Sewer Authority (DC Water) has entered the commissioning stages of a revolutionary wastewater treatment plant that introduces thermal hydrolysis to North America, in a project that’s currently the world’s largest facility of its kind. The Blue Plains Advanced Wastewater Treatment Plant employs a thermal hydrolysis treatment system manufactured by Cambi, Asker, Norway. The system is well-known and proven throughout Europe, but getting it approved as the first such system in the US took some research and groundwork, according to Chris Peot, biosolids manager for DC Water.
“We work in a very conservative industry when it comes to new technologies,” says Peot. “We have to meet our permit [requirements] every day, and if we don’t, there are dire consequences. For us, it’s tens of thousands of dollars a day in fines, and if an investigation finds negligence, there is a potential for jail time—because this is a felony for whoever signs that permit.” To ensure that the choice of a new treatment system could meet regulations, DC Water had a requirement stating that the technology had to have operated in a plant treating at least 20 MGD for five years, consecutively and successfully in North America. The Cambi system didn’t meet either specification, but its success in Europe, and the economics of the process, were persuasive arguments.
Improved Pumping for Complex Water Systems
Water distribution treatment plants are also taking advantage of variable frequency drive (VFD) pumps, and manufacturers are improving the technology. For example, Pentair, Minneapolis, MN, recently released its next-generation Aurora IntelliBoost constant-pressure variable-speed booster system to manage complex water systems in commercial, industrial, and municipal buildings. The IntelliBoost uses state-of-the-art Pentair VFDs for pumps, plus a Programmable Logic Controller (PLC) with a Proportional Integral Derivative (PID) Loop. The system can stage up to four pumps, based on the pressure and flow needs of the building.
“It allows users to simply select how they want the pumps to be utilized, such as programming sequence pumps by time or selecting a permanent lead pump, without the need to physically change the controller or require special programming,” notes Robert Mueller, systems product manager for Pentair’s Aurora Pump. “As another added bonus for our users, the new controller comes equipped with an auto-detect function that will automatically adjust the pumps’ start and stop times to maximize the booster system’s efficiency, while increasing the life of the pumps and saving both time and money.”
For convenience and flexibility, the IntelliManager’s ethernet connection allows operators to configure settings and control the system with a computer or mobile device, by accessing a built-in webpage that displays the statistics and information needed to properly monitor the booster system. Intelli-Manager provides security by constantly monitoring performance. It sounds an alarm when predetermined tolerances are reached, and automatically shuts down the system if tolerances are exceeded.
IntelliManager also features maintenance alarms that deliver notifications to the user, providing ample time to schedule maintenance appointments in advance. Other new innovations include a touchscreen color display for easy-to-use systems management and full system access and password protection for increased security.
The IntelliBoost system is all about efficiency and lower operating costs, and ultimately, that sums up the benefits for the other products we looked at in this article. Whether it’s something as simple as cleaning filters, or as complex as engineering a wastewater treatment plant with a biogas-driven CHP system for heat and electricity, the solutions are available. And they’ll save money on operating costs.
Before choosing the Cambi system, the design for a new plant specified large egg-shaped digesters, at a cost of $600 million. “That was $200 million over what we had budgeted,” recalls Peot. “So the board of directors asked us to spend two years to try to get under budget. We mentioned removing the three words [about North American operations] because we had our eye on this technology, and it was proven. We did the math and found that if we made an investment of $20 or $25 million for the thermal hydrolysis, it could cut the digester volume in half, because you feed it at twice the normal percent of solids. Then you save $200 million for digester vessels, and that helped us come in under budget.”
According to Perry Schafer, vice president of the project’s design build manager, Brown and Caldwell (based in Walnut Creek, CA), the savings don’t stop with the digester vessels, because the Blue Plains Project reduces the amount of biosolids produced by the anaerobic process, and also boosts the quality. Then, the biogas produced by the process fuels a combined heat and power plant (CHP) that provides a number of benefits.
“These digesters are very large and unique in terms of their design. They take a very high level of loading and are efficient for large gas production, so we have large-diameter piping to transport all that gas,” says Schafer. “The combined heat and power uses a combustion gas solar Mercury 50 turbine. It’s a great machine and fits really nicely because we need steam production of 175 psi for the Cambi system’s cooking process. So, overall efficiency with combined heat and power will be in the 73% range, which is very high.” The CHP plant will generate 13 MW of electricity, cutting DC’s grid consumption by about a third, and saving about $10 million annually.
Earlier, we mentioned that the Cambi process produces less biosolids of higher quality, and the savings are significant. With DC Water’s legacy system, it takes 65 semitrucks a day to haul the solids to Virginia for land application, at a cost of $20 million a year. The lower volume will require about 28 truckloads per day, and the quality of that material is much better.
“It will be a pathogen-free material and dewatered with about 30% solids, which is a very nice bulk material,” explains Schafer. “It’s very moist, but it doesn’t look like it has a lot of water. It will stand up in a pile and can be spread easily on agricultural land. That’s the initial usage, but over time, we want to turn that material into other products and mix it into urban and metropolitan use products. It’s screened of debris and hair, and it will be a much-improved product that you can actually handle and use in urban areas. So we’re anxious to get started on developing those products.”
Although a 30% solid consistency makes an attractive product, Schafer notes that moving up to 450 tons of sludge per day is a complex process. “Sometimes you don’t know at the start of a project what the pumping head will be. Sludge slurries are thixotropic, which means that the viscosity changes as you pump it. So it’s a very difficult process to nail down what the pumping head will be. Sludge slurries require some variability and flexibility in the pumps, and variable frequency drives are common for what we’re doing here. We have dozens of systems, and the digester mixers on each of the four digester tanks also use variable frequency drives. That’s a common approach to match the needs of the system and conserve energy.”
With so much capacity, it would be reasonable to expect a large footprint for the plant, but Brown and Caldwell had to fit the entire operation into just 6 acres of land. The solution involved developing a vertical design to save space. But the plan also provided additional benefits. “The small footprint pushed us to think a little bit better about making things efficient,” says Schafer. “You can pump water and liquids fairly easily, but once solids are dewatered, it’s more difficult, so we wanted to eliminate that because transferring cake material has been a nemesis at this plant for many years. We’ve done a lot to reduce the conveyance, and the operators are very anxious to turn off some of the old existing cake conveyance equipment and use the new system.”
