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America’s Authority in Membrane Treatment

Improving America’s Waters Through Membrane Filtration and Desalting

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n NORTH AMERICA’S LARGEST...CANTON MBR WATER RECLAMATION FACILITY UNDER CONSTRUCTIONBy Terry M. Gellner, P.E., TnT Engineering, LLC, 5900 SOM Center Road, STE 12 -133, Willoughby, Ohio 44094, Phone 440-478-5445, Email terrygellner5s@gmail.com

Project BackgroundConstruction began in March 2014 and initiation of membrane bioreactor activated sludge (MBR) process train No. 1 is underway at this writing. Six - 6.5 million gallon per day (MGD) average day flow (ADF) MBR trains operating in parallel will be constructed when the plant is completed. The project cost per gallon of treated wastewater is under $2.25 and significantly lower than most MBR plants. The design ADF is 39 MGD and the peak day flow is 88 MGD. The ADF was three to four times greater than any MBR operating at the time design began.

Construction of this MBR improvement at the Canton WRF will satisfy new and more stringent permit limits for phosphorus and total nitrogen. In addition to treating the new effluent limits the average day capacity of secondary treatment will be increased from approximately 35 MGD to 39 MGD, and the peak flow through secondary treatment and processes thereafter will be increased from approximately 70 MGD to 88 MGD. Experienced pumped peak instantaneous flows up to 110 MGD will continue to be processed through a new advanced preliminary treatment process with longitudinal grit/grease removal and two stage fine screening. Flows in excess of 88 MGD passing through the advance preliminary treatment process will be equalized in either of two stages. Accordingly, plant flow conditions, influent pollutant loadings and effluent permit limits for the final design are as follows:

Design Flow Parameters

Average Daily Design Flow 39 MGD

Minimum Day Flow 16 MGD

Maximum Month Flow 42 MGD

Peak Day Flow 88 MGD

Peak Instantaneous Flow 110 MGD

Pollutant Characteristics Influent Effluent

CBOD 160 mg/l 10.0 mg/l

TSS 170 mg/l 12.0 mg/l

Phosphorus 5 mg/l < 1.0 mg/l

NH3-N; Ammonia Nitrogen 17 mg/l 1.85 mg/l

TKN 26 mg/l

Total Nitrogen <8.0 mg/l

Dissolved Oxygen 6.0 mg/l

Plant Improvement OverviewThe existing wet stream process configuration begins with influent coarse screens and pumping from the southwest corner of the site to the elevated southeast end of the site. From this point flow across the site is by gravity. The pumped flow discharges to existing

FigureAerial View of Canton, Ohio WWTP

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IntroductionInnovative low-pressure membrane technologies are rapidly changing the municipal wastewater treatment (WWT) industry. In particular, projects involving water reuse, the retrofit of (aging) existing infrastructure and the replacement of older membrane equipment are becoming increasingly common. Over the last 13 years, The Running Springs Water District (RSWD) has successfully delivered all three types of projects and become an example for other communities.

Located in the San Bernardino Mountains of Southern California, The Running Springs Wastewater Reclamation Plant (WRP) was originally built as a package plant in 1968 before being converted to a conventional activated sludge (CAS) plant in 1980s. Thanks to creative, forward thinking operators, administrators and citizens, the Running Springs WRP is now arguably one of the best examples of an MBR retrofit in the country: ahead of its time and up with the times.

The Running Springs MBR: A Model for the Retrofit of Aging Infrastructure Using

Membrane TechnologyDennis Livingston, Director MBR Operations, Ovivo USA, LLC

Plant BackgroundThe RSWD, which serves the communities of Running Springs, Arrowhead, and County Service Area 79 (CSA 79), originally built a packaged wastewater plant to meet treatment needs. As the area population grew in the 1980s, a CAS plant was built consisting of two aeration basins and vacuum clarifiers. In 1999, The RSWD was advised by the United States Forest Service (USFS) to upgrade the plant in order to meet new discharge requirements. In particular, the USFS was concerned about the potential impact of (effluent) spray irrigation zones on local water quality.

In 2003, The District commissioned a membrane bioreactor (MBR) to meet pending USFS requirements including a new phosphorus limit. Ultimately the phosphorus limit was not imposed but The District took steps to ensure that system could meet more stringent limits if required. In fact, The RSWD MBR was the first enhanced biological phosphorous removal (EBPR) plant commissioned in the United States.

Presently, The Running Springs WRP services about 5,000 connections and can treat average daily flows up to 0.5 million gallons per day (MGD) depending on the season. The present design capacity of the facility is 1 MGD with effluent discharge requirements of <30 mg/l 5-day biochemical oxygen demand (BOD

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<30 mg/l total suspended solids (TSS). The disinfected, treated effluent generally contains non-detectable amounts of TSS and registers a turbidity of <0.2 nephelometric turbidity units (NTU) and is sent to ponds about 2,000 feet below the plant on US Forest Service controlled property. Stored, reuse-quality, effluent is used for spray irrigation of forestland and fire suppression.

The RSWD figured out how to retrofit aging infrastructure and to maximize municipal investments through creativity, hard work and using membranes.

Retrofit & ReuseTo understand how the CAS system was retrofit requires a quick process explanation. Activated sludge (AS) systems rely on microbial activity to

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remove dissolved carbon, nitrogen and in some cases phosphorus from wastewater. In WW treatment terminology, microbes are often referred to as “bugs” and the bug-water slurry as “mixed liquor”. For a fixed volume, the concentration of mixed liquor suspended solids (MLSS) is directly proportional to treatment capacity up a limit that is usually determined by the capacity of clarifiers. This limitation can be overcome by using submerged, low-pressure membranes; the main reason that The RSWD upgraded to an MBR.

Once converted, plant performance dramatically improved and effluent quality has never violated permit. Today, effluent BOD numbers are typically reported as non-detect and TN measures less than 10 mg/l throughout the year. Since the phosphorus limit has not yet been implemented, the plant does not operate in an EBPR mode; but can with only minor process adjustments. Instead, alum is added to the MLSS to reduce influent phosphorus concentrations down from numbers as high 15 mg/l to less than 1 mg/l. In terms of reuse,

effluent fecal coliform concentrations are also generally reported as non-detect (<2.3 most probably number (MPN) per 100 ml).

Effluent from the MBR system is stored in a converted aerobic digester before being discharged to the pond system for irrigation. Regulations require that staff oversee irrigation and limits the use of effluent to eight hours per day. Membrane filtrate is disinfected with ultraviolet (UV) light and dosed with a small amount of chorine prior to storage. Waste biological sludge is dewatered using a screw press and then land applied.

The original MBR retrofit cost $4.4M and was designed to treat a maximum month flow (MMF) of 0.6 MGD. Thirteen years after commissioning the original membrane equipment was recently replaced with a new design that is nearly 400% more energy and space efficient. In addition to membrane equipment changes, multiple system improvements have increased capacity and reduced operating expenses (OPEX). The timeline in Figure 1 includes some of the more significant projects undertaken by The District and reflects the motivation of the crew running the plant. Common drivers behind most work have been energy optimization and membrane equipment innovation.

Energy OptimizationThe original retrofit cost about $7.33 per treated gallon. While that first project was extremely cost effective it did not specifically target energy efficiency; especially in terms of turndown. Turndown refers to the ability of equipment and systems to operate efficiently over a wide range of flows. Despite the plant not being designed for optimal energy efficiency from 200,000 gpd up to peak flows exceeding 2,000,000 gpd, The RSWD has consistently, and successfully, focused

Figure 1Running Springs WRP Improvement Timeline

Figure 2Normalized Energy Demand vs. Flow

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The Running Springs MBRContinued from page 15

on improving plant performance and in particular energy efficiency.

The strategies that had the biggest impact on energy bills included improved controls, the installation of a turbo fan and the replacement of older membrane technology with more efficient designs.

In 2009, The RSWD worked with the original MBR system supplier and the local power company to significantly increase energy efficiency. After replacing an old positive displacement blower with a high-speed turbo fan normalized energy demand decreased by nearly 40%. The results exceeded expectations and the power utility covered 30% of the new blower cost. The blower replacement project saved The District $30K/yr and paid for itself in four years.

Adding the turbo fan, and running the process efficiently, helped to reduce energy bills but turndown limitations are still clearly evident. As Figure 2 indicates, at low flows consumption can actually top 3.0 kWh/m3 whereas, at flows closer to design, normalized energy demand is cut in half to roughly 1.3 kWh/m3.

One knock against MBR technology is that it can be energy intensive. However, as is very often the case, optimized MBR systems can operate efficiently; especially if they are designed correctly, operated well and equipped with the latest membrane technology. At Running Springs, three generations of membrane equipment have been installed; the original units, additional units for expansion and most recently replacement units.

2007 Plant ExpansionAt an elevation of 5,000ft wastewater temperatures can plummet to less than 8oC during the winter. In addition to cold temperatures, rain and snowmelt can increase peak flows to 2 MGD for short periods of time (the WRP is actually permitted to treat flow up to 4.0 MGD).

Early efforts to increase peak capacity, especially during winter/spring season included the use of flux enhancing polymer (MPE50TM) and the use of shorter relax cycles (micro-relax) where filtration is temporarily suspended for seconds instead of minutes. However, these optimization steps did not address the long-term need to increase capacity from 0.6 MGD to 1.0 MGD. In order to nearly double throughput new, taller membranes were added and permeate pumps installed (see Figure 3). The pump-assisted gravity (P.A.G.) configuration increased peak flows without having to increase pipe sizes making the expansion quick and seamless.

2015 Replacing Original Membrane EquipmentThe original MBR system included 16 membrane units. Each unit was equipped with 2,583 ft2 of microfiltration (MF) membrane area and required roughly 75 SCFM of air scouring for stable operation. The equipment ran well for over a decade with 80% of the plates lasting longer than 8 years and 50% of the plates lasting over

Figure 3Adding Permeate Pumps

Figure 4The OV960

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10 years. However, when it came time to replace the equipment, plant operators opted for new technology.

The newest membrane units (see Figure 4) have 10,332 ft2 of ultrafiltration (UF) membrane material in the form of 240 flexible flat sheets and take up about ¼ of the space the original units needed. They require a minimum of 72 SCFM (up to 100 SCFM) for air scouring and are equipped with non-clogging, medium bubble diffusers.

Overall the MBR system has worked well since commissioning but there has been some concern about maintenance and energy usage. For example, about once a year, operators needed to drain the tanks in order to clean the coarse bubble diffusers and to remove accumulated (dewatered) solids from between the rigid plates. These concerns were addressed with the new technology but ultimately the selection process came to energy and return on investment.

The taller design of the new units and the higher packing density reduced air scour from 1,200 SCFM to 360 SCFM. Moreover, the oxygen transfer efficiency of the integral diffusers is roughly 300% greater than what it was with the coarse bubble technology. While this improvement in efficiency is helping to reduce energy bills, it is interesting to

note air scour requirements are expected to decrease even further to 160 SCFM with the next upgrade. Looking at the trend from 2003 to 2016, the overall reduction in air scouring represents a decrease in volumetric air flowrate of almost 8 fold (see Figure 5).

Wrap UpEarly adopters like The Running Springs Water District started a retrofit trend that has become increasingly common today. From projects as small as 30,000 GPD in Pembroke, MA to massive plants like the one in Canton, OH treating 42,000,000 GPD, using MBR technology to retrofit existing infrastructure is often the best, if not the only, solution to wastewater treatment problems. In addition to being one of the first to use MBR technology in the United States, The Running Springs WRP is also a reuse facility that turns a nuisance (wastewater) into a resource (irrigation and fire suppression).

The original Running Springs upgrade to MBR cost $4.44M or roughly $7.33/gal. Since the plant was commissioned in 2003 there have been numerous upgrades nearly doubling both the treatment capacity and the energy efficiency of the facility. Programming changes, new operational strategies, turbo fans, the addition of filtration pumps and the use of new generations of

Dennis is responsible for membrane bioreactor (MBR) business at Ovivo, USA, LLC. A licensed engineer, most of his professional career has involved membrane technologies starting with high purity reverse osmosis and ultra-high purity water production. For the last 13 years Dennis has focused on biological processes and in particular the optimization of MBR related solutions. His experience includes working with hundreds of industry professionals during the design, construction and operation of nearly 300 MBR facilities. Dennis has authored several patents, published numerous papers and been a contributing author to three industry texts on membranes and MBR specifically.

Dennis Livingston

Figure 5Air Scour Demand of Running Springs Membrane Equipment

membrane equipment have all helped to drive down energy demand (< 1.3 kWh/m3) and decrease overall OPEX.

With the replacement of older membrane technology, nearly 13 years after the MBR upgrade, Running Springs is now also an example of how far membrane technology has come in a relatively short period of time. Equipment is now more reliable and easier to maintain than in years past. New designs are also nearly 4 times more energy and space efficient than the first generation model.

The RSWD story is a model for the retrofit of old infrastructure using MBR technology to meet today’s needs while preparing the future. n

The Solutions newsletter is the property of the American Membrane Association (AMTA) and a members-only benefit.Rights to electronic distribution have been granted to the authors of this Edition and their representatives. For more information, contact www.amtaorg.com