Technical Resources

As much of what we do at Brentwood is highly technical. It is important that we share case studies, articles, and other research with our customers and contacts so you can be sure our products and systems have been designed and engineered for your application.



Biological Treatment Clarification Cooling Tower Stormwater Management

Biological Treatment

Effective Biofilm Control on High Surface Density Vertical-Flow Structured Sheet Media for Submerged Applications

This study was undertaken to investigate the mixing characteristics and establish aeration mixing criteria for a Vertical-Flow (VF) structured sheet media system. The results demonstrated that the optimized airlift pumping associated with the VF media system using fine bubble diffusers is capable of achieving effective biofilm control for enhanced process performance.

The media scouring velocities of 0.1–0.3 ft/sec obtained at aeration mixing criteria of 0.5–1.0 SCFM/ft2 – media plan view has been shown sufficient for the excessive biomass control in typical municipal IFAS retrofits. The identified scouring air requirements are often exceeded by the process air demand for the upgrade of a conventional activated sludge plant. Tapered aeration has been commonly implemented in the full-scale facilities, enabling a lower mixing air requirement and providing process kinetic benefits and energy savings. Engineering design parameters other than aeration as integrated in the VF media system for effective mixing were also discussed in the paper.

Biofilm Performance of High Surface Area Density Vertical-Flow Structured Sheet Media for IFAS and Fixed Bed Biofilm Reactor (FBBR) Applications

PVC structured sheet media has recently received increasing attention as a cost-effective alternative for IFAS applications. However, the impact of its type and configuration on the process performance has been less studied. This study was conducted to evaluate the biofilm performance of a high surface area density Vertical-Flow (VF) media in conjunction with a proprietary distribution media for IFAS and Fixed-Bed Biofilm reactor (FBBR) applications.

The study demonstrated that the VF media combined with the proprietary distribution media is capable of achieving complete nitrification and high-rate BOD removal for both IFAS and FBBR applications. As an essential element in the VF media system, the distribution media not only maximized the air and wastewater distribution over the entire surface area of the media, but also optimized the airlift pumping through the VF media for sufficient mixing and effective biomass control. Favorable kinetic rates (e.g. tertiary ammonia rates up to 1.4 g NH3-N/m2-day at 15°C, SCOD removal rate of 30 g SCOD/m2-day at a SCOD load of 45 g SCOD/m2-day, and predenitrification rates of 1.0–2.0 g NO3-N/m2-day) have been consistently observed in the VF structured sheet media system, mainly due to the intimate contact between thin biofilm and substrates/oxygen as promoted by the dedicated aeration associated with the media towers.

Compared to cross-flow (CF) media, the VF media provides an enhanced air/wastewater distribution and also offers significantly higher treatment capacity per unit media volume due to the increased specific surface area (e.g. 96 ft2/ft3 or 315 m2/m3) and comparable kinetic rates (e.g. concurrent 0.65 and 5.5 g/m2-day ammonia and soluble COD removal, respectively) in the IFAS application. Comparison of the VF media with other media systems (e.g. free-floating media and fabric media) is also discussed in the paper.

Full Scale Implementation, Operation, and Performance of a Structured Sheet Media IFAS System

This case study has shown that existing CAS facilities can be economically retrofitted with structured sheet media to achieve enhanced nitrification. Performance data collected for more than one year has confirmed that the structured sheet media IFAS system was able to consistently meet the ammonia discharge limits even in concurrent wet and winter weather (e.g. 7–9°C at over three times design flow). The IFAS system has also proven to operate similarly to the prior CAS process and requires little attention from the operator. In the typical plug-flow structured sheet media IFAS system, tapered aeration with fine bubble diffusers was utilized to minimize filamentous growth, improve solids settleability, optimize kinetic rates, and provide energy savings. Additionally, as a benefit for the system installation, the rigid and stackable media blocks allowed for a simple retrofit of the existing aeration basin without the need for constructing baffle walls or media retention sieves.

Pilot Testing of Structured Sheet Media IFAS for Wastewater Biological Nutrient Removal (BNR)

IFAS systems with various media have been increasingly implemented for enhanced nutrient removal. PVC structured sheet media have received little attention for IFAS applications despite their wide use for attached biomass retention in trickling filters. This pilot study was first conducted to evaluate the fabric media IFAS proposed for Springettsbury Township, Pennsylvania WWTP. Observations from the fabric media testing led to the following investigation of PVC structured sheet media IFAS to meet stringent nutrient limits.

The pilot results demonstrated that structured sheet media IFAS is capable of achieving complete nitrification with a surface nitrification rate of 0.88 g/m2-day. No media fouling was encountered. The unique shearing pattern from airlift pumping through structured sheet media creates thin and high-density biofilm for efficient oxygen and substrate mass transfer. The detrimental effects of red worm growth observed in this study with fabric media were not similarly observed with PVC structured sheet media.

Nitrifying Trickling Filter Provides Reliable, Low-Energy, and Cost-Effective Tertiary Municipal Wastewater Treatment of a Lagoon Effluent

The case study described in this paper demonstrates that the nitrifying trickling filter (NTF) is a reliable and robust bioreactor. The studied NTF was designed to oxidize ammonia-nitrogen (NH3-N) remaining in the effluent stream of an aerated lagoon that is located in Newton, Mississippi, USA. NTF performance data was collected during a period beginning in June 2007 and ending in January 2010. An analysis of the data demonstrated that the NTF consistently met, amongst other permitted criteria, a moderately stringent permit limit requiring an annual average NH3-N concentration less than 2.0-mg/L remaining in the effluent stream. Comparison of operating costs revealed that the NTF evaluated in this study required approximately one-third of the power required to meet the same treatment objective with a moving bed biofilm reactor (MBBR). However, the NTF required a slightly more foot print than the MBBR (e.g. 90 vs. 80 m2) to meet the treatment objective. The studied NTF was designed using generally accepted criteria defined throughout this paper. The NTF used medium-density modular plastic trickling filter media comprised of corrugated plastic sheets. The required biofilm surface area, and therefore bioreactor volume, was defined based on a 0.65 g NH3-N/m2/d zero-order nitrification rate and a 0.1 kg/m3/d five-day biochemical oxygen demand (BOD5) load at 12°C. The method for calculating NTF ventilation is demonstrated. Implementation of the NTF design and construction included some unique features: (1) the NTF influent pumps were located to provide NTF effluent recirculation (which provides proper media wetting, controls biofilm thickness and minimizes macro fauna accumulation), (2) use of influent pump(s) speed control to optimize the NTF superficial hydraulic application rate (or Spülkraft), (3) the ventilating area was conservatively designed to maximize airflow, and therefore process oxygen, for the nitrification process (i.e., 0.1 m2 (1.0 ft2) open area per 2.4 m (8.0 ft) of NTF periphery), and (4) the application of a column and pier support system to facilitate simple installation and increased air flow.

Meeting Stringent Discharge Levels with AccuFAS - Coldwater, MI Case Study

The wastewater treatment facility in Coldwater received tighter seasonal ammonia limits of 2 mg/L from May to November. Compounding this challenge, groundwater levels around the plant limited facility expansion and upstream industries caused organic shock. AccuFAS was selected as a retrofit solution for the existing solids contact aeration basins. The plant continues to consistently meet ammonia limits and has demonstrated improved resilience under hydraulic shock loads.


Performance Evaluation and Design Considerations of a Sludge Dredging Type Sludge Collection System

Sludge dredging (SD) systems have been widely used for sediment removal in lagoons, ponds and clarifiers in water and wastewater treatment plants. It is known to be more flexible in operation and better for confined space compared to other types of sludge collection systems, which also provides the opportunity for a packaged system within clarifiers. This paper will discuss a series of performance evaluation tests and the subsequent design improvements to a SD type sludge collection system.

The sludge collection system tested consisted of a wing design that removes settled solids from the bottom of the clarifier tanks. Either submersible pumps or vacuum were used to remove solids. The units were powered by either an integral motor drive (self-driven) or a cable drive (cable-driven). Four configurations were tested by pairing each solids removal mechanisms and drive types.

Testing was conducted in a 70 ft long by 40 ft wide rectangular clarifier in a 3.4 MGD water treatment plant located in Tiffin, OH. Over 16 months, weekly test runs were performed to evaluate the sludge discharge rate, solids concentration and TSS for each configuration at various influent conditions. The same parameters along with sludge blanket depth were measured for settled sludge samples collected daily at the center of the tank in order to provide benchmark values. Special test runs were conducted during heavy runoff periods when turbidity was higher than 1000 NTU in order to pin-point the performance of the sludge collector at high solids loading events. Power consumptions were recorded.

Statistical analyses were performed to compare the performance of pump versus vacuum, as well as self-driven versus cable-driven configurations. In addition, Grit removal efficiency and solids thickening effect were also evaluated. The performance data were then combined with the clarifier influent/effluent conditions and the site specific conditions to determine the design recommendations for every one of the four configurations. Cost analyses and power optimization were generated based on these recommendations. The Wing design was further compared with another popular collector shape – the pipe design.

This study provided insights into the design considerations of the sludge dredging type of sludge collection systems. The study also suggests preferred system designs for various plant conditions, which may lead to cost reduction for the sludge removal process as well as the sludge disposal processes.

Pilot Study of Sediment Dredging System at Representative Drinking Water Plants

Dredging systems have been widely used for sediment removal in lagoons, ponds and clarifiers in water and wastewater treatment plants. Known to be flexible in operation, dredging systems with a low profile design also provide opportunities for packaged systems such as in combination with tube settlers. A previous study (Jin el al, ACE 2012, AWWA, Denver CO) described dredging system performance comparisons between different drive and sludge withdrawal mechanism designs. As a follow up, this paper will discuss a series of pilot tests performed with the previously identified, more reliable cable driven system at two representative water treatment plants (WTP).

The first plant is a 3.4 MGD WTP located in Ohio US, which is a typical US application. The second plant is a 980 MGD WTP located in South America representing the very large public water systems which are more common in international installations. Both plants have cable driven dredging units with wing headers installed in rectangular sedimentation basins. The OH site utilizes vacuum and pumping sludge withdrawal in two side by side bays, and the South America site utilizes pumping for sludge withdrawal only. The units were designed to handle flow capacity of 2 MGD at the OH site and 25 MGD at the South America site. The raw water turbidity at the South America site, which was influenced heavily by red clays from the nearby river source, was as high as 2000 NTU.

Settled sludge samples and discharged sludge samples at various locations along the tank length were collected at each site for test. Total Suspended Solids, Total Solids and Sludge Blanket Depth were analyzed. Results indicated that both vacuum and pumping units were able to remove settled sludge with concentration as high as 4%. The discharged sludge was generally found to be more concentrated than the settled sludge over a wide influent TSS range.

In addition, the effectiveness of grit removal was also investigated by comparing the wing header versus the conventional orifice pipe header side by side. This pilot study successfully assured the applicability of the dredging system under two very different drinking water plant conditions. The sludge removal process is flexible and robust, covers a wide range of sludge concentration, and exhibits potential to reduce loading to downstream residual handling processes.

Cooling Tower

Design Features and Their Effect on High Performance Fill (TP00-01)

In the design of a high performance cooling tower fill, many design features must be considered to produce optimum performance. This paper will show laboratory test data and detail the effect on fill performance of the following items: flute geometry (cross-corrugated, offset tube, vertical tube), cross-corrugated flute angle, sheet pitch (19 mm vs. 20 mm vs. 17 mm vs. 12 mm), microstructure (course, fine, none), material (PVC & polypropylene), module depth (12′ layers vs. 24″ layers vs. 48″ layers), and tip design (alternate tips vs. straight tips).

Evaporative Pre-Coolers for Air Cooled Heat Exchangers (TP06-07)

Evaporative precooling of air-cooled heat exchangers provides the thermodynamic advantages of water cooling towers with the reduced maintenance requirements of air-cooled heat exchangers. In areas where water conservation, cooling tower plume abatement, or water discharge permits are a problem, evaporative precooling of the air going to the heat exchanger can be the solution. This paper discusses the advantages of precoolers and presents some basic design considerations.

Guidelines for Selecting the Proper Film Fill (TP06-19)

For many years PVC film fills have been the most popular choice of heat transfer media for use in cooling towers. Throughout this history, design features of these fills have continued to evolve from the first cross corrugated products through vertical flow fills to today’s popular combination designs. Some of these features are not obvious to the casual observer and if not chosen correctly can adversely affect tower performance, product cost, lifespan, or ease of installation. This paper traces the history of these fill designs while providing guidelines as to the proper fill selection.

Current Fouling Problem of PVC Film Fills and Research into New Designs to Eliminate Fouling

The fouling of film fills in power plant cooling towers represents a major problem in loss of performance of the cooling tower and loss of efficiency of the power plant. The results of this loss of performance is higher energy consumption to drive the fans to move air through the cooling tower in mechanical draft towers. Higher fuel consumption in plant operations or reduced peak load output and the discharge of warmer water which poses environmental concerns to our rivers and lakes. This paper discusses the effects of fouling on cooling tower performance and the current knowledge to how this fouling may occur, industry practices of controlling cleaning and eliminating the problem using new film fill products.

Simultaneous Comparison of the CTI HBIK and the EPA 13A Isokinetic Drift Test Procedures (TP93-07)

Cooling tower drift is defined as the percent of circulating water flow that exits from the cooling tower fan stack in the form of fine water droplets and aerosols entrained in the exhaust air. For cooling tower drift tests, the CTI recommended Heated Bead Isokinetic (HBIK) procedure is the most commonly used procedure and is close to being accepted as a code by CTI, whereas regulators prefer the EPA Method 13A procedure. In theory both procedures (if properly operated, recovered and analyzed), should give the same results. This paper examines and compares the two-isokinetic methods and their proper operation, recovery and analysis so as to obtain accurate and repeatable results.

The testing services of Midwest Research Institute (MRI) were retained by Brentwood Industries, Inc. to conduct a series of 18 drift tests by using both the CTI recommended HBIK drift test procedure and the EPA Method 13A drift test procedure. The tests were conducted simultaneously using both test procedures on two types of Brentwood drift eliminators at two water loadings and several air velocities at the Ceramic Cooling Tower Company’s test facility located in Fort Worth, Texas.

The drift from the test cell was determined by isokinetically sampling a representative fraction of the test cell airflow above the drift eliminators. Lithium was added to the test cell circulating water prior to starting the series of tests to serve as an analysis tracer. Inductively coupled argon plasma spectroscopy (ICP), an extremely sensitive detection technique, was then used to measure the concentration of lithium in the circulating water and in the collected drift samples. The total drift rates were calculated from the ratio of the concentration of the lithium in the sampling train to the concentration of the lithium in the circulating water.

The CTI HBIK and the EPA 13A methods of isokinetic drift collection were found to yield nearly identical results in the series of tests.

Evaluation of Anti-Fouling Replacement Fills in Utility Cooling Service

Many utilities with power stations served by cooling towers are considering fill replacement due to deterioration of the original fill media. Often this allows an opportunity to reevaluate the unit’s thermal requirements and seek improvement on return cold water temperature, increasing unit performance. In the past, this meant specifying high efficiency, PVC packing as the most cost-effective path to improved thermal performance. Vendors’ submittals were typically evaluated based on capital cost plus energy cost savings due to more economical operation of the turbine/condenser allowed by the colder than originally specified return water temperature.

With recent discoveries of significant fouling in these highly efficient fills, utilities are incurring added costs to treat their circulating water to maintain their fills’ cleanliness. In a recent paper, one utility reported that their water treatment expenses have increased by a factor of six since the replacement of the original asbestos cement fill with high-efficiency PVC packing. This significantly reduced the economic advantage that the utility expected from the supplier’s guaranteed cold water temperature. New to the marketplace are anti-fouling fills that by design prevent or sharply reduce foulant buildup. However, this improvement in fouling resistance is accompanied by a modest drop in thermal performance. This may be more than offset by avoiding the high cost of aggressive water treatment required to maintain the cleanliness of higher performing fills.

This paper will describe an economic evaluation using the annual cost method that considers the difference in two repack alternatives: anti-fouling fills and standard, cross-corrugated fills. Differences in project capital costs, net plant heat rate, and water treatment costs will be computed. Using station specific economics, the least costly alternative is shown to be the use of lower efficiency anti-fouling fills with an existing water treatment program as opposed to high efficiency fills with an aggressive water treatment program.

Best Practices for Minimizing Drift Loss in a Cooling Tower (TP12-21)

There are many factors associated with the drift loss potential of a cooling tower. With the greater restrictions on drift emissions that are now required in many locales, it is important to know all of these factors to make sure that the drift loss of a tower is minimized. This paper will explore the various factors involved for both counterflow and crossflow cooling towers.

Rising Interest in Sea-Water Cooling

Using evaporative cooling systems saves resources, protects the environment, and provides economic benefits.

Locking in to Cooling Tower Fill Assembly

Film fill increases heat rejection and reduces air resistance, but also adds to the cost of cooling tower construction. Mechanically assembled film fill offers the same benefits with less labor costs while providing environmental benefits.

Getting Your Fill

Not all cooling tower fills will meet your application’s performance and environmental requirements, so choose carefully. Here’s a primer to help you out.

Improving Cooling Tower Performance

This article highlights innovations in film and splash fill technology. These approaches offer new product selections that can be used in applications with poor water quality or process contamination and still provide the benefits of optimum thermal performance. These products are used in the more desirable counterflow towers and some can be employed in both counterflow and crossflow applications.

Stormwater Management

Dickinson College Kline Fitness Center Expansion – Carlisle, PA StormTank Case Study

Dickinson College is located in the heart of the small Pennsylvania town of Carlisle and was established in 1773. Since then, the student population has grown at an ever-increasing rate, forcing the need for major renovation and expansion of the school’s Kline Fitness Center. With tight space constraints and stormwater permitting required, the large void space and modular, subsurface design offered by Brentwood’s StormTank provided an innovative solution. Due to be completed in the summer of 2014, the StormTank system will permit the necessary mitigation to meet regulatory needs while expanding usable land and providing the necessary cleanability.

Spring Ridge Corporate Center – Wyomissing, PA StormTank Case Study

Once a sprawling 636-acre farm, the Spring Ridge Corporate Center in Wyomissing, PA, now houses a shopping center, a hotel, a medical center, and several office buildings. When Kohl’s Department Store purchased the final plot of available land, site designers needed to meet stormwater regulations in a creative way: incorporating above-ground stormwater facilities with underground detention. Brentwood’s StormTank was utilized to mitigate the remaining runoff the above-ground bio-filtration basins could not handle within the site’s dimensional constraints. The strength of the StormTank system allowed for the installation of two subsurface detention basins beneath the store’s parking facilities.

Sheetz Gas Station – Mechanicsburg, PA StormTank Case Study

The 3-mile stretch of U.S. Route 11 (Carlisle Pike) that runs through Mechanicsburg, PA, has become a commercial and residential hub within a rural landscape, making it a prime location for gas stations. Sheetz, Inc., unable to acquire an undeveloped site along the highway, purchased two small properties available for repurposing. In order to incorporate a full-service drive-through, a convenience store, an automated car wash, and gas pumps into the site design, Sheetz opted to upgrade the site’s stormwater mitigation facilities by choosing a subsurface system. Brentwood’s StormTank offered an ideal solution because it met the regulatory requirements for volume and rate without impacting buildable land.

Sweet Street Cafe Terrace – Reading, PA StormTank Case Study

Once a company designed solely to bake chocolate chip cookies, Sweet Street Desserts in Reading, PA, has transformed into an internationally renowned supplier of frozen desserts and pastries. The company’s success has required expansion, including the addition of Cafe Sweet Street and a terrace to provide outdoor eating. The site’s tight space constraints and decorative landscaping called for the incorporation of a subsurface stormwater storage system to provide rainwater harvesting. Brentwood’s StormTank system provided a cost-effective solution and ensured that runoff captured by the modules could be utilized for landscape irrigation.