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.

Featured Video: Wastewater Treatment -Troubleshooting Aeration Basin

This week’s blog features a wastewater troubleshooting video by the YouTube account Wastewater Operations Channel. The account is run by Jon Kercher, an operator of 10 years who uploads educational videos filmed during the work day at his wastewater treatment plant.

In this video, Jon demonstrates how to troubleshoot a disparity between two air legs within an aeration basin that should be equal flow. The problem was noticed when the basin was put into lead position. This video not only demonstrates how to troubleshoot a flow disparity, but teaches a great methodology for troubleshooting any wastewater treatment issues. Jon notes that while we have a general tendency to gravitate our troubleshooting toward process parameters, we must also consider monitoring parameters as well. Watch his video to find out what was causing the flow disparity!

Nocardia Foam in Activated Sludge Systems

Nocardioforms are filamentous, Gram positive actinomycete bacteria that can cause persistent and excessive foaming in activated sludge plants during the summertime. There are nine main genus of nocardioforms. Two of these genera are involved in activated sludge foaming, Rhodococcus and Nocardia with the latter being the better known troublemaker. How to best control Nocardia foam is a highly debated topic.

Nocardioforms are known for their branch-like hyphae that extend from the cell wall similar to the hyphae found in fungi. These branches link together with other filaments and floc. Simple and complex organic material make up their diet which includes fats, oils, and grease (FOG). Nocardioforms are slow growing and utilize the aerobic conditions established by an aeration tank. These actinomycetes generally have difficulty out-competing other wastewater microorganisms, but once established they're a handful to remove.

Present in lower concentrations, Nocardia help to stabilize floc structure. The bacteria can rapidly breakdown biochemical oxygen demand (BOD) which can be beneficial to high strength wastewater. In higher concentrations, Nocardia can rip the floc apart and swiftly breakdown BOD starving out floc forming bacteria. The dense, brown foam that accompanies an outbreak forms when filaments float to the surface as a result of their low-density fatty acid membrane and the waxy, hydrophobic biosurfactant that coats their bodies. Bubbles from the aeration system can also help the filaments to float. Unlike Microthrix, nocardioforms are not often associated with sludge bulking.

Unfortunately, the conditions required for a nocardioform outbreak are still debated. In general, any change in temperature, pH, dissolved oxygen (DO), solids concentration, or nutrients might spur an outbreak. It’s believed that nocardioforms will be most favored under warm temperatures with a high concentration of FOG, low food to mass (F/M) ratio, and/or a high mean cell residence time (MCRT). Since nocardioforms grow slowly, they need ample time to proliferate, and under low F/M their larger surface area helps to secure nutrients easily. Some people theorize that anaerobic conditions in parts of the aeration tank or surfactants can encourage Nocardia growth as well.

Before deciding on a treatment solution, it helps to confirm that you are dealing with nocardioforms and not some other filament. Just because your foam is brown, doesn’t ensure that Nocardia is the culprit. Toni Glymph has developed a manual that describes how to identify filaments under the microscope. Nocardia is both Gram positive and Neisser positive, but after reading his guide you’ll find that only a Gram stain is really required for identification.

Treatment solutions for nocardioform foam are also highly debated. Using a high volume water spray will temporarily break down the foam, but be prepared for its return. A better solution is to skim off excess foam so the bacteria is not recycled back into the system. Chlorination is not highly recommended. The branching Nocardia filaments prevent sufficient disinfectant contact while healthy floc bacteria are killed. Many companies promote defoaming products, but the interlocking filaments are often too stable for these chemicals as well. Most resources recommend reducing your MCRT to under 8 days while increasing (F/M). Wastewater technician, Jeff Crowther, lists three of his own treatment recommendations on page 10 of the H2Oregon Springs 2016 Newsletter. Solids wasting may be the most common control method. Operators should learn about the life cycle of Nocardia to maintain a system that avoids future foaming incidents.

Featured Videos: Pump Curves and Pump Selection Basics

Pump curves inform operators to select and run pumps at optimal efficiency for their system. Whether preparing for a certification exam or looking to refresh your knowledge of pump hydraulics, this week’s featured videos will teach you how to read pump curves, calculate system curves, and use these curves to select an ideal pump for your system.

For any given pump, flow will impact pressure head, efficiency, horse power requirements, and vulnerability to pump damage. This video reviews three different pump curves starting with a very simple curve and moving to more complex curves with increasing pump information. Understanding performance, efficiency, horsepower, and net positive suction head (NPSH) curves is essential in selecting the proper pump for your system’s needs. After covering the basics, this video introduces concepts that will help operators to select and run pumps at recommended operating zones to maximize pump life and reduce operational costs.

Once you start to feel comfortable with these concepts, the next step is learning how to compare pump curves to your own system. For pump curves to be useful during selection, you must first have a system curve of your own. Prepare for a bit of math because this next video walks through the calculations needed to develop a simplified equation that graphs system pressure head (Hp) as a function of flow rate (Q) squared. When watching the video, remember that z1 is the starting elevation and z2 is the final elevation.

With a well developed knowledge of pump curves and system curves, selecting a new pump becomes much easier. This last video demonstrates how to compare the system curve to the pump curve . When comparing these two graphs, the pump’s best efficiency point should be fairly close to the system operating point. Other considerations include how much power is required to operate the pump and the net positive suction head available to avoid pump cavitation. 

These videos simplify many of the factors that go into a real system, however they offer a good foundation for operators to better understand the theory behind pump curves and pump selection.

What's on the Drinking Water Radar for the Year Ahead: 2019

Being a small-town water operator is not easy; it is up to you to ensure the quality of your community's water day-in and day-out, often with very limited resources. Let WaterOperator.org help you meet the challenge head-on with this list of tools and resources to put on your radar for the year ahead:

• Have you gotten in the groove yet with the new RTCR requirements? Here are two new documents from the USEPA designed to help small public water systems: Revised Total Coliform Rule Placards and a Revised Total Coliform Rule Sample Siting Plan with Template Manual. Additional compliance help, including public notification templates, a RTCR rule guide, a corrective actions guidance and more can be found here.
• While we know your hands are full just getting the job done, there are new and emerging issues you may have to deal with in the year ahead. For example, this past year many communities have been dealing with PFAS contamination issues. This ITRC website provides PFAS fact sheets that are regularly being updated on PFAS regulations, guidance, advisories and remediation methods. Especially of interest is this excel file that has begun to list the different state standards and guidance values for PFAS in drinking water as they are developed. Be sure to check back often for updates.
• Your utility may also have to adjust to new compliance rules in the coming year. In Michigan, for example, a new Lead and Copper Rule arising from the water crisis in Flint has gone into effect, making it the strictest in the nation. Other states, such as Ohio, have also adopted tougher standards, or are now requiring schools to test for lead. Oregon has established temporary rules that will require drinking water systems in the state using certain surface water sources to routinely test for cyanotoxins and notify the public about the test results.
• With a warming climate, these incidences of harmful algal blooms in surface water are on the increase, causing all sorts of challenges for water systems that now have to treat this contaminant. This cyanotoxin management template from the EPA can help assist you with a plan specific to your location.
• Worker turnover and retirements will still be an issue in 2019. According to this article, the median age for water workers in general (42.8 years) and water treatment operators specifically (46.4 years) are both above the national average across all occupations (42.2 years). You can keep transitions as smooth as possible by using EPA's Knowledge Retention Tool Spreadsheet and/or this Electronic Preventive Maintenance Log.
• New Tech Solutions: A UMass lab focusing on affordable water treatment technologies for small systems will be rolling out its Mobile Water Innovation Laboratory in 2019 for on-site testing. In addition, the facility is testing approaches to help communities address water-quality issues in affordable ways. "Early next year, in the maiden voyage of the mobile water treatment lab, UMass engineer David Reckhow plans to test ferrate, an ion of iron, as a replacement for several water treatments steps in the small town of Gloucester, MA.

But even without all these challenges and new ideas for the future, simply achieving compliance on a day-to-day basis can be tricky - if this sounds familiar, you may want to check out our recent video on how operators can approach the most common drinking water compliance issues.

Focus on Chemical Feed Control

Chemical dosing at the water treatment plant is a critical, but often underrated step in producing safe drinking water. Historically, process control points have focused on the hazards present in incoming source water - with emphasis on the filtration and disinfection steps to minimize microbial risks. But while many hazards do indeed enter the plant with the raw water, it is just as important to identify the multiple risks associated with treating this raw water.   

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

What's New in our Document Library: Fall 2018

Every day, staff members at WaterOperator.org search the internet to find events, resources and tools that have the potential to make a water operator's job easier and more effective. Here is a selection of our most recently-entered resources of interest to small system operators. 

Have we missed anything especially helpful recently? Let us know! 

Biosolids

• Comparison of Options for Biosolids Dewatering (slide presentation, ORWEF) 

Cyanobacteria/Harmful Algal Blooms

• Cyanobacteria and Public Water Systems (guidance manual, MassDEP)

Emergency Response

• Santa Rosa: Response and Recovery from 2017 Fires (slide presentation, ACWA)
• Disaster Management for Water Utilities - What is Your Emergency Response Plan (slide presentation, Iowa Rural Water Association)
• Guidance for Building Field Capabilities to Respond to Drinking Water Contamination (guidance manual, US EPA)

Financial Management

• Water Cost of Production (spreadsheet, Iowa Rural Water Association)

Inflow/Infiltration

• Newberg Inflow and Infiltration Study (slide presentation, ORWEF)

Non-community Systems

• Small Water System Management Program Guide for Noncommunity Systems: An Operations and Management Tool for Owners of Nonresidential Water Systems (manual, WDOH)

Safety

• Safety Issues in the Treatment Plant (slide presentation, NAWT)

Sampling/Monitoring

• How to Develop a Sample Siting Plan (video, Alaska DEC)

Test-Prep Resources

• Water Treatment and Distribution Operator Math Reference Sheet (factsheet, AWWA)
• Water Treatment and Distribution Operator Chemistry Reference Sheet (factsheet, AWWA)

Wastewater

• Current Trends in Digester Mixing Technologies (slide presentation, ORWEF)
• Handling Flushable Wipes in Wastewater (slide presentation, RUSA/UCC/PNCWA)

Water Security

• Enhanced Security Monitoring (video, USEPA)
• Wastewater Systems Security Vulnerability Assessment & Emergency Response Template (form/template, Minnesota Rural Wastewater)

Featured Video: A Day in the Life of a Water Treatment Plant Operator