RCAP’s Free Monthly Articles for Water and Wastewater Operators

A Drop of Knowledge is a monthly digital article from Rural Community Assistance Partnership (RCAP.) The articles focus on topics like infrastructure, capacity building, and economic development in rural America. It contains how-to’s, tips, and guidance from more than 300 technical assistance providers (TAPs) across the country. Some recent featured articles are linked below:

• Small South Dakota City Leverages Funds to Complete Expensive Sewer System Upgrade 
• Cross Connection Control – A Holistic Approach
• Are Your Utilities Prepared for the Upcoming Winter?
• Water Utility Digital Transformation
• Ohio Site Visit Shows Wastewater Potential of Sand Bioreactors
• Understanding Onsite and Decentralized Wastewater in America

Looking for something else? Find more articles and subscribe to A Drop of Knowledge.
 

A Look at Protozoa in Wastewater Treatment Systems

Wastewater treatment is fundamentally a biological process. When influent enters the microbial ecosystem of a treatment plant, nutrient removal is accomplished through the consumption of organic matter by microorganisms. The bulk of all nutrient removal is performed by bacteria, however protozoa and metazoa balance these bacterial populations and offer insight into wastewater conditions. Operators who understand the varying roles of wastewater microbes and the conditions that favor their growth can foster an ecosystem that promotes optimal treatment. In this week’s blog post we will review the niche protozoa fill in wastewater systems to enhance monitoring efforts and inform process control.

Roughly four percent of a wastewater system’s microbial ecosystem is made up of protozoa. Protozoa are single celled microbes both larger in size than bacteria and more complex. The most common types of wastewater protozoa include amoeba, flagellates, and ciliates. By consuming free bacteria and small, unsettled floc, protozoa enhance the clarity of the final effluent. Observing protozoa populations under a microscope can also alert operators of treatment conditions and sludge age.

Amoeba are predominant under a young sludge age because they require high nutrient levels or low competition to grow. Under shock loads of biochemical oxygen demand (BOD), high concentrations of particulate matter, toxic conditions, or low dissolved oxygen (DO), amoeba can also dominate. The latter two conditions generally trigger the amoeba to develop a protective gelatinous shell that gives them an advantage over other microbes. Furthermore, their slow movement reduces oxygen demand required for growth and reproduction.

Flagellates are typically present under a young sludge age as well. Since flagellates compete poorly with bacteria for the same soluble nutrients, their growth is favored at the younger sludge age before bacteria have had a chance to populate. As such, a wastewater sample relatively high in flagellates can indicate high soluble nutrient levels also known as a high food to mass (F:M) ratio.

Ciliates are favored under a healthy sludge age. While they do not consume organic matter, they do feed on bacteria making them excellent indicators of healthy floc formation and useful clarifying agents. Without ciliates, bacteria and algae populations can grow out of control in the wastewater microbial ecosystem. Among the three types of ciliates common to wastewater, each group has different conditions under which their populations are favored.

Swimming ciliates start to form as flagellates disappear. They may experience a spike in population when levels of free bacteria are abundant for predation. If too many free bacteria are present, the ciliate population surge can ultimately result in a cloudy effluent. Crawling ciliates dominate when those free bacterial populations begin to stick together forming floc through a secreted slime layer. This slime layer is produced when dissolved nutrients become limited. Since swimming ciliates cannot readily pick off bacteria within the floc, crawling ciliates begin to out-compete them. As they feed on bacteria, crawling ciliates can improve flock structure. A more mature sludge age with reduced BOD allows stalked ciliates to compete with crawling ciliates. Stalked ciliates anchor themselves to floc using the cilia surrounding their mouth structure to create currents that draw in bacteria. Once their food levels have diminished significantly more, stalked ciliates begin to branch into colonial units to acquire food more efficiently. If sludge continues to age, stentors and vaginocola protozoa grow in abundance.

For more information on wastewater protozoa and how to monitor them, we’d like to recommend the following documents. These resources and others like them can be found using our online, resource library.

Bacteria Protozoa – Toni Glymph
The guide overviews basic wastewater microscopy, slide preparation, sample collection, and the microbiology of activated sludge plants.

Wastewater Microbiology & Process Control - Wisconsin Wastewater Operator’s Association
Learn the about microscopes, slide preparation, and the microorganisms found during wastewater treatment.

Protozoan Count – Toni Glymph
This guide describes how to sample protozoa for observation under the microscope.

Managing Dissolved Oxygen in Activated Sludge Plants

Sustaining optimal dissolved oxygen levels in activated sludge plants is necessary for biological treatment of organic material and ammonia. While raw wastewater often contains some amounts of oxygen, aeration systems can increase dissolved oxygen (DO), mixing, and the suspension of microbes through mechanical agitation or diffused aeration. Aerobic microorganisms use this oxygen to breakdown organic waste into inorganic byproducts. The amount of dissolved oxygen consumed by microbes during biological treatment is referred to as biochemical oxygen demand (BOD). According to an article by Triplepoint Water, approximately 1.5 pounds of oxygen is consumed for every pound of BOD oxidized. To oxidize one pound of ammonia, that value increases to 4.57 pounds of oxygen. Most plants aim to maintain around 2 mg/L of DO which allows microbes contained within the center of floc to receive oxygen.

Wastewater operators should regularly monitor oxygen availability in the form of dissolved oxygen. Insufficient oxygen levels will allow aerobic and nitrifying microbes to die and floc to break up. At DO concentrations under 1 mg/L, the potential for filamentous growth increases. On the other end of the spectrum, too much oxygen increases power consumption and, at very high levels, inhibits settling. Research has estimated that aeration can use up to 45 to 75% of a treatment facility’s overall electricity use. With an online DO analyzer equipped to automated controls, the EPA reports that energy costs can be reduced by as much as 50%.

Where and when an operator samples for DO will be determined by the requirements written in the facility’s National Pollutant Discharge Elimination System (NPDES) permit and basic process control. To compare dissolved oxygen levels throughout the day, samples should be collected at the same location. The Ohio EPA’s Activated Sludge Process Control and Troubleshooting Chart Methodology recommends that systems sample within 1-2 feet of the surface water near the discharge of the aeration tank into the clarifier. By collecting multiple samples in the same location throughout the week, operators can reliably determine if DO concentrations are sufficient for treatment while developing a DO profile. In addition, measuring DO at multiple depths and locations in the aeration tank can help find dead spots.  

To supply adequate DO, the Ohio EPA manual includes how to determine blower runtime based on organic loading and system design. We should  still note that temperature, pressure, and salinity can all influence the solubility of oxygen. Additional sampling locations can include the raw wastewater, aerobic/ anaerobic digester, and final effluent. Final effluent with high dissolved oxygen can cause eutrophication in the receiving waters, however low DO can harm aquatic organisms. Some permits set a minimum DO level for effluent to ensure aquatic organisms have the necessary oxygen levels to sustain life.

While every technique and tool has its strengths and weaknesses, operators can measure DO through a Winkler Titration test (see Michigan DEQ Laboratory Training Manual pg.91), electrochemical sensor, or optic sensor. The two sensors mentioned can be purchased as portable handheld meters or stationary devices. For automated blower control and continuous sampling, an online sensor is used. For NPDES compliance monitoring, measurements must be taken through an EPA approved method at the frequency specified in the permit.

When using any DO sensor, the EPA’s Field Measurement of Dissolved Oxygen (SESDPROC-106) procedures require that the equipment be well maintained and operated per manufacturer instructions. Upon initial purchase, probes should be inspected, calibrated, and verified for accuracy. During each additional use the instrument should be calibrated and inspected again. The EPA recommends checking instrument calibration and linearity using at least three dissolved oxygen standards annually. All maintenance and sampling activities should be documented in a logbook per NPDES requirements. Any time a measurement is taken, the temperature of the water and any notable wastewater conditions should also be recorded in the logbook. 

Dissolved oxygen is a frequently monitored parameter in wastewater treatment systems. Operators should have a firm understanding of how dissolved oxygen is involved in wastewater processes and how they can manage DO to achieve compliance. Check out our online document library to find useful resources to learn more.

Peracetic Acid (PAA) in Wastewater Disinfection

Peracetic acid (PAA) has grown in popularity over the last several years for its use in the disinfection of wastewater and stormwater. Utilities use disinfectants as the primary mechanism to inactivate and destroy pathogenic organisms that spread waterborne disease. An appropriate disinfectant will sufficiently treat any disease-causing microbes including bacteria, spores, helminthes, and protozoa. While PAA technology has been employed in Canada and Europe for the last 30 to 40 years, this disinfectant has only become noticed in U.S. municipal wastewater treatment within the last 10 years. Competing with chlorine, an already well-established disinfectant, its use is still slow growing, however systems are discovering that PAA offers several benefits to wastewater treatment that chlorination does not.

What is peracetic acid? The alternative disinfectant is a clear, organic peroxide compound that readily hydrolyzes to acetic acid and hydrogen peroxide in water. It’s characterized as a strong oxidant and fast reacting disinfectant. Commercially available peracetic (CH₃CO₃H) is purchased in an equilibrium mixture of acetic acid (H₃CO₂H), hydrogen peroxide (H₂O₂), and water (H₂O). Manufacturers typically add a stabilizer as well. The following formula represents the equilibrium equation: CH₃CO₂H + H₂O₂ ←→ CH₃CO₃H + H₂O.

PAA can generally be purchased in concentrations of 5% to 22%. When PAA decomposes in water, free hydrogen peroxyl (HO₂) and hydroxyl (OH) radicals are formed. These radicals have significant oxidizing capacity that play an active role in microbial disinfection. According to the EPA, bacteria are destroyed through cell wall lysis and leakage of any cellular constituents.

Wastewater systems consider moving to peracetic acid for several reasons. Unlike chlorine, PPA decomposes into biodegradable residuals of vinegar (acetic acid) and hydrogen peroxide that can pass fish toxicity tests without removal. These residuals are not toxic, mutagenic, or carcinogenic. Bioaccumulation in aquatic organisms is also highly unlikely. Neither chlorinated compounds nor harmful disinfection by-products (DBPs) are produced with its use. As such, PAA has been considered the potential answer to tough DBP regulations. Peracetic acid can also disinfect over a wide range of pH and is unaffected by nitrate and ammonia concentrations.

Chemical handling of PPA is toted for being easier and safer than chlorination. The disinfectant can be stored for long periods of time exhibiting less than 1% decrease in activity per year when properly stored. Its use does not require any special risk management plans (RMPs) required by the EPA when handling certain toxic chemicals. For systems that operate under cooler conditions to prevent contamination or elevated temperatures, PAA has a low freezing point. Switching to PAA requires minimal retrofitting with the chemical itself being offered at prices competitive to other disinfectants.

There can be some disadvantages to peracetic acid. Depending on the formula purchased, PAA introduces varying amounts of acetic acid into the wastewater effluent. This can contribute to biological oxygen demand (BOD) and may not be appropriate for systems that are struggling to meet these limits. The biggest challenge wastewater systems face is regulatory approval. While PAA has been approved by the EPA as a primary disinfectant, each state regulatory agency must also approve its use. A WaterOnline guest column includes an infographic of states that have approved PPA as of 2017. The guest column discusses how systems can approach local regulatory agencies to seek approval on a case-by-case basis.

The overall effectivity of PPA will depend on wastewater characteristics, the PAA concentration, contact time, and the reactor configuration. Dosage will depend on the target organisms, wastewater quality, and level of inactivation required. When monitoring PAA residuals, operators can use the same analyzer and method as for chlorine residuals. A standard EPA sampling method does not yet exist. The lack of established methods and protocols for PAA makes approval difficult for local regulatory agencies. To help investigate the use and implications of PAA in wastewater, the Water Research Foundation (WRF) completed a study to evaluate effluent toxicity as well as dosage and contact times required to meet compliance. Metro Vancouver’s Northwest Langley WWTP in Canada has also published findings from a multi-year pilot program that used PAA as a disinfectant. More studies will have to expand on existing research until peracetic acid can become easily and widely adopted.

Using Reed Beds for Sludge Treatment

The use of reed beds in both central and decentralized wastewater treatment systems can offer a low cost and energy efficient opportunity to process sludge. Originally developed in Germany, the practice was brought to the United States in the 1980s. Under this technology, a variety of marsh grass, also known as Phragmites, is planted in reed beds built with concrete walls and lined with an impermeable layer to protect groundwater. TPO magazine suggests using a concrete bottom because PVC liner can be easily damaged during maintenance. The beds themselves contain a porous, finely aggregated media such as sand or recycled glass (pg. 12). This media allows the reeds to grow and excess liquid to pass through an underdrain system connected to the head of the plant for recycling. Risers can help distribute and load the sludge.

After the reeds have been established during a period of roughly three months, sludge can be loaded into the beds every three weeks. As the plants’ extensive root structure absorbs sludge moisture, water will be released through leaves and into the atmosphere via evapotranspiration. The microbes found in the root rhizome will help the sludge continue to break down. During the winter months when the reeds are dormant, the freeze-thaw cycle will allow liquid to easily separate from sludge to continue dewatering. When spring arrives, the reeds will return to their active growing cycle.

According to TPO Magazine, reed beds can adequately manage facilities that treat up to two million gallons per day provided that the required land is available. The reeds themselves can handle climates that experience several weeks of freezing temperatures during the winter. Before temperatures drop too low, operators will typically burn off the reeds in the fall. Alternatively, the reeds can be composted or disposed in a landfill. After approximately 8 years, the solids must be removed. At this time, the beds will be taken out of service in the summer and given an additional 90 days to dry out. Once the sludge is removed, the reeds will need to be re-established. A presentation by the Constructed Wetland Group provides a detailed overview of how to perform maintenance on reed beds.

While this technology is low maintenance and energy efficient, there are still pros and cons. As an advantage, reed beds can help to remove heavy metals from sludge. This should be considered during reed harvesting. As a drawback, constructing new beds requires significant capital costs, however utilities may be able to convert existing sand pits or drying beds to reduce costs. TPO Magazine notes that unpleasant odors can emerge during the spring when winter ice melts. Many scientists also worry that wastewater facilities using non-native grasses can encourage the establishment of invasive species. Phragmites spread predominantly through their underground rhizomes, laterally growing stems with roots. Furthermore, when non-native grasses escape into a new area, they can easily take over since their native competitors aren’t present. Facilities should practice careful harvesting and monitor the integrity of their bed structures to ensure containment. Despite these drawbacks, reed bed systems can be a successful and efficient form of sludge treatment even in comparison to conventional treatment methods.

Spooky Sewers and Things That Go Bump at the Treatment Plant: 2018 Edition

Featured Video: Using Decommissioned Wastewater Tanks for Fish Farming

Just when you think you've seen it all, someone comes up with a crazy idea that holds some promise. This just might be true in the case of a local aquaculture businessman, who, along with a Kentucky State University researcher, looked at outdated wastewater treatment plants and source water reservoirs and envisioned profitable fish farms! 

This week's featured video explains how Steve Mims and Tim Parrott used a USDA grant a few years ago to turn decommissioned wastewater plants into working aquaculture farms (pg. 8) using treated effluent in digester tanks and daphnia (as fish food) from upgraded facilities that are often just next door. The tanks don't generate waste because the water cycles right back to the treatment plant.  

His big idea? To establish regional fish hatcheries through public-private partnerships, with young fingerlings sold to local farmers to raise in their own ponds all the while adding commercial-level fish and caviar production to the rural economies of Kentucky. So add fish farming to all the creative ways to recycle wastewater that people have been coming up with recently!  

Featured Video: Wastewater Treatment Series

Wastewater Treatment - Introduction from RCAP on Vimeo.

1. Wastewater Treatment - Collection System
2. Wastewater Treatment - Preliminary Treatment
3. Wastewater Treatment - Primary Treatment
4. Wastewater Treatment - Secondary Treatment
5. Wastewater Treatment - Solids and Sludge Handling
6. Wastewater Treatment - Effluent Disinfection
7. Wastewater Treatment - Effluent Disposal

For more on wastewater treatment for non-operators, see RCAP's A Drop of Knowledge handbook for wastewater systems. (There's one for drinking water systems too!)

Featured Videos: Small On-Site Wastewater Treatment Systems

Sometimes wastewater treatment doesn't involve clarifiers or even treatment buildings big enough to walk around inside. Approximately 25 percent of homes in the United States are not connected to centralized sewer systems. These homes and businesses collect and treat their wastewater on their own property using systems that are referred to as onsite wastewater treatment systems, septic systems, or decentralized systems.

In some rural and suburban areas, everyone uses decentralized systems. Even in communities with sewers and a centralized treatment facility, there are often areas the sewer does not reach and where homes or businesses are on septic systems. If a community wants to manage all of its wastewater, it is necessary to address both centralized and decentralized systems.

This video is for small, rural communities that are looking for wastewater treatment options. You'll hear about the benefits of onsite systems and get a "tour" of one community's system.

Small On-Site Wastewater Treatment Systems from RCAP on Vimeo.

Small, on-site treatment systems are an innovative way to treat water. They come in a variety of types and are often found in housing subdivisions, schools and small commercial centers. They have advantages for a variety of situations, especially for locations that are distant from or isolated from centralized sewer systems.

For more on operating decentralized wastewater systems, visit our documents database and search by the category Decentralized WW Systems and document type Manuals/Handbooks.

What's That Smell? Eliminating Wastewater Treatment Odors

With all this talk about public awareness of hidden water system infrastructure, it is important to point out that there are times when public awareness is definitely NOT on your side. And one of those times is when there is a stink that just doesn't go away.

Odors are generated from every phase of wastewater management including collection, treatment, and disposal, and they can cause all sorts of public relations issues, putting pressure on an utility to resolve the problem in a timely way. Certainly, managing odors is one of the most important - and yet most challenging - aspects of wastewater treatment. 

Why so challenging? Because in part there are many odor control technologies available but no single ideal solution. Some systems, like this Brownsville Public Utilities Board plant in Texas, solve odor problems by placing covers over wastewater tanks and channels and then blowing the smelly hydrogen sulfide gas through a biological tower. Others such as this Bridgeport, CN Water Pollution Control Authority plant, capture odorous offgas with coated fabric covers and treat it with a carbon system. Still others use a combination of  different measures, such as activated sludge diffusion, carbon adsorber sytems, pump station chemical feed systems, coverings and plant operation modifications. 

But fixes like these don't come easily, or cheaply. And sometimes, the problem is even more complex. Consider this story of a system in Saline, MI that has been the subject of neighbor complaints for years. Even after odor studies and abatement work, the smell just keeps getting worse. 

How can a smaller system then, with its limited funding and manpower, address odor problems effectively? The cheapest way to control odors is at their source, according to this Science Daily article, but sometimes that is simply not possible. Fortunately, researchers from the University of British Columbia may have recently developed a solution. 

Many wastewater facilities use anaerobic digestion, but is is expensive to acquire and maintain the associated odor control and biogas safety equipment needed. A much more cost-effective way to mitigate odors, these UBC researchers have discovered, is to revisit metal salts treatment. Simply adding new combinations of these common commercial metal salts during the fermentation process dramatically improves offensive odors, and also improves their ability for remove water from digested sludge. It is these unique doses/formulas and point of addition during the fermentation process that really amplifies the effectiveness of this new approach. Moreover, the cost of adopting their technique is minimal, so smaller systems can afford to test it out. 

In the meantime, if you need a quick primer on odor generation and management, the Water Environment Federation (WEF) has a 7-page factsheet explaining the problem and outlining advantages and disadvantages of various mitigation strategies. 

You can also keep an eye out for odor events right here on WaterOperator.org. For example, this Iowa training later in the month troubleshoots lagoon odor issues. Just type "odor" in the keyword search box on the event calendar page. 

Want to brainstorm with other wastewater professionals? Attend WEF's Odors and Air Pollutants Conference 2018 in Portland, Oregon in March, 2018. With sessions ranging from "Optimizing Hydrogen Peroxide Dosing" to "Odor Control Scrubber System Planning and Design," there will be many opportunities to learn in-depth solutions to any smelly situation.