Featured Video: Sewer Cleaning in Los Angeles California with Kent Carlson

For roughly 30 years Kent Carlson worked for the City of Los Angeles to bring innovation and new technology to the Department of Public Works’ Bureau of Sanitation. When the Bureau observed that new technology was falling behind on their collections side, Kent was brought over to assist with tool development and the standardization of sewer cleaning procedures. Under the mission to reduce sewer overflows and recognize increasing drought in southern California, one of his favorite inventions featured a sewer nozzle designed to reduce water use and save time during cleaning.

In his article with CWEA Water News he offers his predictions on the future of the sewer profession asserting, “I think it’s an exciting future – technology is exploding in this sector – CCTV, GIS, computers on the trucks. Sewer workers of the future will be much better with technology. Rather than using rudimentary brute force for cleaning we’ll get smarter, more strategic and more efficient at what we do.”

Kent’s enthusiasm for tool development is demonstrated in this week’s featured video. The 5-minute video highlights the history of sewer cleaning in Los Angeles as well as a demonstration of how his team tests and develops their sewer cleaning tools. Back in the day, sewer cleaning featured manual removal of clogged pipes and sewer mains. Today, his team takes advantage of high-pressure tools and robotics. Kent says the best tools for sewer cleaning are designed or personally modified by the facility staff. These tools ultimately help the Bureau of Sanitation affordably maintain approximately 6,500 miles of pipe, some of which was originally installed as far back as 1883. We hope this week's featured video inspires your system to find new and innovative ways to help your utility operate more efficiently.

Opinion: Challenges Quantifying COVID-19 Cases Using Wastewater

Editor's Note: The views expressed in this post are the sole opinion of the author and not those of WaterOperator.org, our sponsors, or the University of Illinois.

In the May 5, 2020 edition of the WaterOperator.org newsletter, we highlighted ongoing research that uses wastewater-based epidemiology to monitor the spread of SARS-CoV-2, the virus that causes COVID-19. Especially in locations where no confirmed cases have been identified, any samples positive for SARS-CoV-2 viral RNA implies that there are people infected in that community excreting it. For that purpose, wastewater monitoring shows real promise as an approach to early detection. By monitoring wastewater influent, scientists hope we can develop an advanced warning system for outbreaks.

There has been significant buzz about using wastewater to quantify the actual number of people infected within a given service area, but there are some issues with quantifying cases I want to discuss. In our newsletter we highlighted MIT research aiming to quantify the number of infected from a large area in Massachusetts. In that article, the researchers point to concerns about meeting the litmus test of sound science.

The wastewater system they studied had 450 confirmed cases at the time of sampling. Results from this monitoring suggested the number of people infected could be much higher. They estimated somewhere between 2,300 and 115,000 infected people. A range this wide does little to help planners or health officials prepare for what might be coming during a pandemic.

Quantifying the number of people infected with COVID-19 using wastewater samples requires a much more comprehensive data set that we cannot gather today in any cost effective way. Here are a few of the problems I see in quantifying the positive COVID-19 population within a given wastewater system:

• Not everyone excretes the viral RNA:
  A recent study published March 30 in the American Journal of Gastroenterology found that some COVID-19 patients exhibit gastrointestinal symptoms, with those patients more likely to produce a positive stool test. In other words, COVID-19 positive patients may not have ANY viral RNA in their stool. How do we identify those people?
• Wastewater varies throughout the day and throughout the week:
  The influent coming through a plant varies based on the discharges from the users. A lot of variables can affect wastewater characteristics at the specific time a sample is collected. The time of day, time of week, and even the time of year can affect the flow into a plant depending on the types of users in the system.
• Every system has a variety of sources for their wastewater:
  What percentage of the wastewater is residential? Are there commercial or industrial facilities that are discharging to the community system? If so, how much, and what types of businesses? In some communities, commercial and industrial users could make up a significant portion of the wastewater treated. In a rural area, the regional hospital may be in a smaller community making it a significant source and contributor. Other communities could be almost completely residential.
• Sampling time and frequency can skew the results:
  Sampling time matters, as do the number of samples collected. How do we decide what is representative? Once an hour? Once a day? Sampling may need to be continuous to really understand the variability.
• Wastewater collection systems leak:
  Leaking can occur both ways. Some wastewater leaks into the environment through the collection system while, at other times, a high groundwater table may be leaking groundwater into the collection system. I looked at approximately 50 smaller systems in Illinois to compare the amount of wastewater discharge to the amount of groundwater they withdraw from drinking water wells. (You would expect the amount withdrawn from wells to be more than that treated at the wastewater plant because of consumptive use.) In many cases systems were treating more wastewater than the raw water being used for their community supply and, in some cases, it was 2-3 times a much. This would be significant factor when using any volumetric approach to evaluating COVID-19 sampling results.
• We have no benchmark to compare results:
  Without having data for a number of communities where the total number of residents with active COVID-19 infection is known, there is no way to validate assumptions and calibrate estimates built into the method. This would not be possible without a consensus understanding about the rate of asymptomatic cases.

If researchers must accept such a high degree of uncertainty, how can this method ever be accurate or useful? Many factors would have to be considered to quantify the number of positive cases for a given community and these would be unique to the individual system. That said, these are not likely new considerations for the talented researchers working on this effort. 

In the future I hope an approach to accurately quantify an infected population using wastewater-based epidemiology becomes a reality. It would be a tremendous asset. In the meantime, however, I believe our focus should be on evaluating the pitfalls mentioned above and working toward technologies/protocols needed within a wastewater plant to reduce uncertainty and move us closer to our common goal of protecting public health.

Managing Sanitary Sewer Overflows (SSOs)

The U.S. EPA estimates that approximately 23,000 to 75,000 sanitary sewer overflows (SSOs) occur in the United States each year. An SSO is defined by the release of untreated sewage into the environment through an overflow, spill, basement backup, or unpermitted discharge before completed treatment at the sewage plant. These overflows can degrade water quality, cause property damage, and pose serious threats to public and environmental health due to the release of harmful pollutants, disease causing microorganisms, metals, and nutrients into the environment. 

Section 301 of the Clean Water Act prohibits the discharge of pollutants to any Water of the United States from a point source without a National Pollutant Discharge Elimination System (NPDES) permit. To address compliance challenges associated with SSOs, the EPA recently completed a National Compliance Initiative that first began in 2000 to reduce the discharge of raw sewage in national water ways.

SSOs occur through debris or grease blockages, root intrusion, vandalism, inflow and infiltration, improper design, aging infrastructure, operational mistakes, and structural, mechanical, or electrical failures. Typically, the most frequent culprit takes the form of blockages. After an overflow, clean up and response is not only expensive, but traumatic for the impacted communities.

In Queens, NY a sewage backup on the Thanksgiving holiday weekend of 2019 flooded the basements of approximately 100 homeowners creating a putrid odor and exposing the community to harmful pathogens. Liability for residential damages and repairs to the pipe was projected to reach millions of dollars.  The culprit for the backup? While operators initially theorized a grease induced fatberg was to blame, investigation later revealed a collapsed sewer pipe instigated the SSO.

In New England and around the country, many communities maintain collection systems of 100 years old or more. Aging infrastructure exacerbates SSO prevention challenges. As years of wear on system equipment increases, the likelihood of mechanical or electrical failures as well as the opportunity for inflow and infiltration increases. Pipe deterioration due to natural freeze-thaw cycles, environmental conditions, water flow, and water chemistry can also increase the likelihood of structural failures. When this deterioration is not routinely inspected and maintained, resulting failures will only add further hydraulic stress to the system.

The frequency of SSOs can be reduced significantly through preventative maintenance and the implementation of an appropriate asset management program. To upgrade your preventative maintenance program, an article from the March 2017 Kansas Lifeline discusses the basics of lift station maintenance. The Georgia Association of Water Professionals provides a more comprehensive guide of collection system maintenance practices in its 2016 guide Wastewater Collection System Best Management Practices.

Developing an asset management program will allow systems to plan for the replacement or rehabilitation of aging pipes, pumps stations, valves, manholes, and collection system infrastructure. During program development systems can predict and plan for population changes, capacity objectives, equipment deterioration, and more. To encourage proper asset management of collection systems, the EPA developed the CMOM program. CMOM stands for Capacity, Management, Operations, and Maintenance.  The information-based management approach encourages dynamic collection system management through the prioritization of activities and investments. Utilities can access how well their current practices meet the CMOM framework using this Self Assessment Checklist and the EPA Evaluation Guide for CMOM at Sanitary Sewer Collection Systems. Follow up this evaluation by integrating CMOM best practices into a new or updated asset management program using this blog post.

Even with the implementation of these programs, systems should still prepare for the event of an unexpected overflow. As in Queens, NY, preventative maintenance and asset management did not stop the SSO on the Thanksgiving weekend. Systems must be prepared to respond swiftly with a Sanitary Sewer Overflow Response Plan. These emergency response plans will limit potential damages and reduce community distress. By combining preventative maintenance, asset management, and emergency response planning, systems can ensure that their community and its environment have the best protection from SSOs.

ISAWWA COVID-19 Utility Impact Survey

To assess management approaches and concerns utilities have adopted in response to the COVID-19 pandemic, the Illinois Section of the American Water Works Association (ISAWWA) released a utility survey to their membership via email on April 3, 2020. Available for one week, 141 members responded with 139 of these respondents representing public water or wastewater systems. Eleven survey questions focused on operational, managerial, and financial changes implemented in response to the pandemic as well as system concerns and needs moving forward. Three additional questions gathered information on utility demographics. Results from the survey can be found in the report: COVID-19 Impact on Utilities. In this blog we will highlight some of the key findings below.

The report indicates that the primary concerns for Illinois utilities focus on maintaining staff health, staff availability, and the continuity of operations. To respond to the pandemic, many systems have implemented staff scheduling changes, split shifts, and the reduction of staffing hours. The survey report goes on to note how other changes are being implemented and how those changes are impacting operations. Regarding revenue, many systems believe it is still too early to understand the full financial impact of the pandemic and have not begun planning for worst-case scenarios. Of those who have noticed changes in revenue, few have witnessed a positive impact on finances. The majority note that they are experiencing lowered commercial water use, an increase in non-payments, cuts to capital projects, or hiring freezes. Emergency response plans offer an effective way to mitigate many pandemic challenges, however the survey notes that only 56% of respondents are developing plans.

Additional questions from the report elucidate the training needs identified by respondents and how utilities are complying with an order by the Illinois Commerce Commission to discontinue water shutoffs.

Of notable interest to small systems, the report includes a section to highlight how system size impacts pandemic response and concerns. To develop these size related trends, the ISAWWA asked respondents whether they represented a small system serving a population of 5,000 or fewer, a medium system serving between 5,001 to 50,000, or a large system serving greater than 50,001. The report reflects that small systems generally have less capacity to respond to the pandemic likely as a result of fewer employees, fewer resources, and the use of a single staff member to maintain a large portion of the system. On the other end, though large systems may have a greater capacity to address the pandemic, they must also overcome the challenges that result from managing a greater number of staff members. Small systems may have fewer challenges related to staff management, however they must also plan for absenteeism more carefully.

For a more detailed review of the survey results, we recommend reviewing the report for yourself. Reading utility responses, concerns, and approaches to managing the virus may assist your system in planning for future challenges and concerns. Visit our web page COVID-19 Resources for Water Systems to find clear and concise information, tools, and resources to make managing these pandemic challenges a little easier.

Challenges Developing an Asset Management Program

Developing and maintaining an asset management program benefits the short and long-term operations of any utility. During operational, financial, and managerial decision making, choices can be backed by quantifiable data and knowledge gathered from asset inventories, condition assessments, and risk assessments. Furthermore, the maps, spreadsheets, and reports generated for asset management programs can improve communication between board members and utility staff. Asset management programs allow utilities to shift their operations to preventative maintenance and long-term planning.

The recommended methods to develop asset management programs are well documented, however implementation of such methods in the real world generates a slew of both predictable and unpredictable challenges. Fortunately for all communities, it is the responsibility and the nature of any utility to problem solve and overcome these challenges.

In October of 2017, the Michigan Water Environment Association (MWEA) and the Michigan Section American Water Works Association (MI-AWWA) hosted a roundtable seminar on asset management plan development. The results of this roundtable highlight how communities and their consultants developed their own plans in response to new regulatory requirements in Michigan. The Spring 2018 Edition of MWEA Matters summarizes the actual approaches undertaken by these facilities and how they overcame individual challenges in developing an asset management program. These approaches and challenges were divided into six categories:  inventory, condition assessment, risk, O&M/ capital planning, rate integration & level of service, and software.

Most challenges in asset inventories arose around the question of how and where to organize data so that information could be related to other data sources. Challenges in condition assessment were often rooted in cost limitations, evaluating underground infrastructure, and weighting the data available from equipment history, maintenance history, age, condition scores, visual inspections, engineering judgement, and operational institutional knowledge. During risk assessment difficulties emerge when estimating risk for uninspected equipment or considering system redundancies. The final challenge lies in determining how to make maintenance program and financial decisions by balancing institutional knowledge with system modeling.

Utilities can find expertise in avoiding or overcoming these common program develop challenges through the Rural Community Assistance Partnership (RCAP) or the National Rural Water Association (NRWA). We also recommend searching through our online resource library to find program develop manuals, spreadsheets, and tips to get started. For a general overview of the program development process, review the 13 Session Asset Management Training Slides by the U.S. Environmental Protection Agency.

RCAP Advocacy and Policy Update: COVID-19 Response

Over the last two weeks, the National Office has been active in promoting the needs of rural water systems and small communities during this ongoing COVID-19 crisis. In the last two weeks, Congress has approved and President Trump signed into law Phase 1 (H.R. 6074) and Phase 2 (H.R. 6201) legislation addressing the COVID-19 crisis in a variety of ways. Phases I, II, and III are the three parts to COVID-19 legislation so far. 
 
Phase I, enacted into law March 6. Provides $8.3 billion in emergency funding for federal agencies to ensure vaccines developed to fight the coronavirus are affordable, that impacted small businesses can qualify for Small Business Administration (SBA) Economic Injury Disaster Loans (EIDLs), and that Medicare recipients can consult with their providers by telephone or teleconference, if necessary or desired.
 
Phase II, signed into law on March 18. This package includes provisions for paid sick leave, free coronavirus testing, expanded food assistance, additional unemployment benefits, and requirements that employers provide additional protection for healthcare workers. 
 
Phase III, signed into law on March 27. The Trump administration struck a deal with Senate Democrats and Republicans on a package providing an estimated $2 trillion in spending and tax breaks to strengthen the U.S. economy and fund a nationwide effort to curtail the coronavirus. The price tag of this package is enormous, unprecedented, and is roughly equal to 10% of the country’s economic output. The plan includes approximately $500 billion that can be used to back loans to distressed companies, including $50 billion for loans to U.S. airlines, as well as state and local governments. It also contains more than $350 billion to aid small businesses. While stipulating the airlines as eligible for a special fund of money available for loans, the legislation is otherwise broad in its approach, recognizing that the coronavirus has affected almost every sector of the economy. 
 
It provides payment to states to reimburse nonprofits, government agencies, and Indian tribes for half of the costs they incur through December 31, 2020 to pay unemployment benefits; and funding to support “short-time compensation” programs, where employers reduce employee hours instead of laying off workers. Employees with reduced hours receive a pro-rated unemployment benefit. This provision would pay 100 percent of the costs they incur in providing this short-time compensation through December 31, 2020.
 
Under Phase Ill, all U.S. residents with adjusted gross income up to $75,000 ($150,000 for married couples) would get a $1,200 ($2,400 for couples) "rebate" payment. They are also eligible for an additional $500 per child. The payments would start phasing out for earners above those income thresholds and would not go to single filers earning more than $99,000; head-of-household filers with one child, more than $146,500; and more than $198,000 for joint filers with no children.

Thank you to Ted Stiger, Senior Director of Government Relations and Policy at the Rural Community Assistance Partnership for providing this update on enacted legislation related to the pandemic.

WaterOperator.org Recommends Agencies Postpone Operator Certification Renewals During COVID-19

As communities tackle the COVID-19 pandemic, the critical services that water and wastewater utilities supply are ultimately pulled into the spotlight. While reliable drinking water and wastewater services remain essential to public health, they also sustain adequate hygiene practices to prevent the spread of illness.

Central to the continuity of operations for every utility lies our water and wastewater operators. Under normal operating conditions, operators, especially those of small or rural systems, must juggle the challenges of aging infrastructure, regulatory compliance, customer communication, board collaboration, and regular operations and maintenance. During the pandemic these challenges can be exacerbated by handling COVID-19 customer concerns, cross training staff, updating contingency and emergency response plans, connecting with critical suppliers, acquiring backup equipment and parts, reaching out to neighbors or mutual aid groups, etc. Operators must take on this workload while sustaining personal health and safety.

As operators manage the ongoing challenges associated with the Novel Coronavirus and Stay-at-Home orders, we have observed that several certifying agencies are extending or postponing their deadlines for continuing education requirements and the recertification of licenses expiring during this pandemic. WaterOperator.org believes that the focus of our operators should remain on continuity of operations and customer outreach without having to manage renewal and recertification requirements at this time. Our concern for small system operators, especially those of rural communities, is that some do not have access to reliable internet. Internet access that may have previously been obtained through public libraries or recreational centers is no longer accessible as a result of community shutdowns leaving operators with no alternative locations to complete online training for certification renewal. Given the extent of these shutdowns, online trainings do not offer a reliable substitute for in-person training sessions at an equal opportunity to all operators.

Many agencies are already working to address the accessibility and burden of licensing renewal. Among the certification programs who have provided relief for operators, agencies in Montana, Oklahoma, Texas, and Wisconsin as well as the Inter Tribal Council of Arizona are working to suspend or extend the time period for licensing renewal and continuing education requirements. In Ontario, Canada an emergency order offers relief to utilities by allowing operators with recently expired licenses to continue work while temporarily allowing non-certified, but qualified individuals to perform operational duties if deemed necessary. Taking a different approach, the drinking water program in Kentucky is currently waiving late fees for renewals until August 31, 2020. While licenses can still expire, the Kentucky Operator Certification Program will consider this grace period when performing inspections or alternate staffing plans. At this time other agencies are actively considering similar measures to the examples we’ve highlighted.

Where these actions are not possible, we ask that agencies consider supplementing other educational resources to operators in need. The Ohio Environmental Protection Agency notes on their website that correspondence courses are available for operators to earn continuing education credit. They recommend reaching out to local training providers to find these courses and other training alternatives. The Inter Tribal Council of Arizona is also researching self-guided distance learning and the loaning of training books distributed via mail.

For some operators, achieving educational requirements and licensing renewal through the duration of the pandemic will create an added burden that may impact their ability to protect and serve the citizens of their communities. Other operators may be left unable to run their facility due to an expired license. We are grateful to the primacy agencies that have taken positive action to support their operators. WaterOperator.org believes that these measures will help utilities of all sizes to protect their communities.

Featured Video: Disinfection Byproducts in Tap Water: 5 Things To Know

The challenge of disinfection byproduct (DBP) control in drinking water lies in balancing the varying health risks of over 600 known DBPs with the benefits of microbial waterborne illnesses prevented via disinfection. While DBPs can originate from industrial sources, they generally form in water treatment systems when natural organic matter reacts with a disinfectant, usually chlorine-based. Ongoing studies have suggested that the toxicity for any given DBP can range from having no known health effects to exhibiting links between exposure and cancer, birth defects, or reproductive disorders. Disinfectant type and dose, residual chlorine, inorganic and organic precursor concentrations, pH, temperature, and water age can impact DBP formation.

The management of DBPs in drinking water is enforced through the Stage 1 and Stage 2 Disinfection Byproduct Rule (DBPR). Collectively, the rules set maximum contaminant levels (MCLs) for total trihalomethanes (TTHM), 5 haloacetic acids (HAA5), bromate, chlorite, chlorine/chloramines, chlorine dioxide, and DBP precursors.

According to a 2019 report by the U.S. Environmental Protection Agency (EPA), the Stage 2 DBPR invoked the largest number of community water system violations between 2017 and 2018, accounting for approximately 30% of all drinking water violations. Consecutive water systems, those with surface water sources, and systems serving populations of 501 to 10,000 people experienced violations more frequently. A greater compliance challenge is experienced by consecutive systems because they have little control over the water that they receive. While treated water may have achieved compliance at the system’s interconnection, DBP concentrations can rise through the receiving distribution system.

Non-consecutive utilities experiencing compliance challenges for the Stage 1 or 2 DBPR can start by troubleshooting the system using our previous blog post on The Disinfection By-Product Challenge. Consecutive systems should coordinate with their wholesale system following the approaches suggested in the 2019 report discussed above. The preferable methods of control often lie in prevention and optimization. As your system troubleshoots the cause of high DBP concentrations, keep the community informed on your efforts as well as some basic information on the health effects and sources of DBPs. Operators can find a general overview on DBP challenges in this week’s featured video. We recommend using this video to provide customers with answers to the following questions:

• What are disinfection byproducts?
• How are DBPs regulated?
• How do I know if my water has high levels of DBPs?
• How are people exposed to DBPs?
• How do I remove DBPs from my home’s water?
  
  

Controlling Legionella in Drinking Water Systems

Photo Credit: CDC Public Health Image Library ID #11148 by Janice Haney 2009; Edited with cropping.

The prevalence of Legionella bacteria in drinking water and distributions systems has gained notice over the past several years due to its increasing rate of infection in the United States. Inhalation or aspiration of small aerosolized Legionella bacteria from water can cause Pontiac fever and Legionnaires’ disease most frequently in sensitive or immunocompromised populations. Between 2000 and 2015, the National Notifiable Diseases Surveillance System (NNDSS) reports that the incident rate of Legionnaires’ disease in the U.S. increased from approximately 0.42 cases per 100,000 persons to 1.89 cases per 100,000 persons. According to the Ohio Department of Health, potential reasons for this change in rate might include increased monitoring and awareness, higher population susceptibility, climate change, water-saving fixtures, and/or aging infrastructure. As of 2019 Legionnaires’ disease is reported to afflict and kill more people in the U.S. than any other waterborne disease.

Existing research indicates that, though Legionella bacteria can be found in all parts of the water treatment system, they amplify best inside protozoan hosts and near the biofilm typically found within premise plumbing or drinking water systems. The resiliency of biofilm to disinfection acts as a protective barrier for Legionella while creating an environment abundant in nutrients. Protozoan hosts also offer defense against extreme temperatures and treatment technologies. A 1994 study by Kramer and Ford found that hundreds of Legionella bacteria can be contained within a single amoeba vesicle. L. pneumophila, the species responsible for most human infections, can also differentiate into various life cycle forms that alter susceptibility to water treatment. This symbiotic relationship with other microorganisms complicates Legionella disinfection.

Hot spots for growth include showerheads, faucets, plumbing systems, cooling towers, hot tubs, fountains, and distribution systems where water stagnation, insufficient disinfectant residual, warm temperatures (77-124°F), or excess nutrients foster biofilm formation. As a result, the most frequent outbreaks from Legionella have been documented in hotels and healthcare facilities. Management of outbreaks can start at the site of these impacted buildings as well as the treatment plant. Drinking water utilities can participate in prevention by understanding the conditions that favor propagation and the methods to control growth.

The U.S. EPA established a Maximum Contaminant Level Goal (MCLG) for Legionella at zero microorganisms. While this is not an enforceable limit, the Agency believes that if Giardia and other viruses are removed or inactivated as required under the Surface Water Treatment Rule, Legionella will also be controlled. Requirements to manage bacterial contamination under the Revised Total Coliform Rule and Ground Water Rule also contribute to Legionella management. Though some systems may routinely monitor for Legionella bacteria, testing methods can often yield both false positives and false negatives. Given the complications of environmental monitoring as well as the cost, management generally starts in response to outbreaks or sporadic cases.

Ongoing research has identified that potential drinking water treatment methods for Legionella include chlorination, copper-silver ionization, ultraviolet (UV) light, ozonation, and thermal disinfection. Among these technologies, chlorine, chlorine dioxide, chloramine, and ozone are the most widely used disinfectants. A combination of these techniques offers the most effective defense against recolonization and biofilm formation. To inactivate individual bacteria as well as those contained within biofilm, operators should also pay attention to the contact time and concentration of disinfectant used during treatment. Equally important to contact time is the maintenance of disinfectant residuals throughout distribution. The National Academy of Sciences’ Management of Legionella in Water Systems details the recommendations for proper disinfection using free chlorine, chlorine dioxide, monochloramine, and technologies more commonly used by building water systems.

To effectively manage Legionella in drinking water, utilities must also collaborate with impacted buildings. Facilities that have experienced outbreaks can develop their own management plan using the Center for Disease Control’s (CDC) Developing a Water Management Program to Reduce Legionella Growth & Spread in Buildings and the World Health Organization’s Legionella and the Prevention of Legionellosis. This literature, along with the CDC training on Legionella Water Management Programs and the other resources linked within this guide will ensure that your community members, especially those at greater risk to illness, are protected from Legionella.

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.