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Filtration

Evoqua – WateReuse Project of 2017

Evoqua Water Technologies and Air Products, a Los Angeles based hydrogen production facility, installed a brine recovery reverse osmosis technology to reduce water and wastewater impact by up to 75 million gallons a year.

UF System Design

UF municipal application example (direct filtration, no coagulation)

Design a pressurized Ultrafiltration (UF) system capable of supplying 20 MLD (5.28 MGD) of drinking water (net permeate) from a lake water source characterized by low levels of dissolved organics (< 2 mg/L) and low turbidity (1 NTU typically, with spikes up to 10 NTU).

The system should have a minimum of two (2) trains. One (1) of the trains shall be redundant.

Minimum interval between CIP events shall be 30 days (monthly frequency).

Minimum interval between Maintenance Clean (MC) events shall be 2 days.

The first step is to select a suitable flux rate given the raw water quality and cleaning frequencies at design conditions.

Based on experience, piloting and full scale applications, on similar water quality, a typical flux rate (instantaneous) at design conditions is 50 gfd (85 lmh).

Assuming a UF module with a filtration area of 500 ft^2, each module can process 50 gfd x 500 ft^2 = 25,000 gpd (gallons per day) which is equivalent to 25,000 gpd : 1440 minutes/day = 17.36 usgpm/module (US gallons per minute per module).

In order to supply the desired net capacity of 20 MLD or 5.28 MGD, at least 212 modules are required, per the following:

5,280,000 gpd : 1440 mins/day : 17.36 usgpm/module = 3,666.6 usgpm : 17.36 usgpm/module = 211.2 ~ 212 modules.

The above calculation assumes the system is online 24 hours per day and no additional water has to be processed (filtered) for cleaning (backwash and maintenance clean).

In order to estimate the actual online time (OLT), the following assumptions are made:

a) backwash frequency is once every 30 minutes and takes 2 minutes b) maintenance clean frequency is once every two days and takes approximately 1 hour c) CIP downtime is not included in calculations, as one extra train is provided for redundancy d) 20 minutes are required for the daily integrity test (IT).

The online time can be calculated as follows: OLT = 1,440 minutes – 60 minutes (MC) – 2 x 2  x 23 (BW) – 20 (IT) = 1,440 – 60 – 92 – 20 = 1,440 – 172 = 1,268 minutes per day (approximately 21 out of 24 hours).

The online time percentage (OLT%) is therefore: 1,268 : 1,440 = 88%.

Assuming a recovery rate of 95%, approximately 2.5% (half of the reject or backwash water) represents permeate used for backwash and maintenance clean (MC) operations.

The number of modules would have to increase in order to maintain the same design flux rate (50 gfd), while producing 2.5% more permeate in a shorter amount of time, 1,268 minutes, rather than 1,440.

N_required = 212 x 1.025 : 0.88% = 247 modules (a 16.5% increase).

Next, the above number of modules would have to be divided over the number of duty trains, minimum 2.

The goal is to reduce the number of trains to a minimum, keeping in mind that minimizing the number of duty trains would result in a larger redundant train (more modules overall and higher cost).

My preference would be for a 3 duty + 1 redundant (4 x 33%) design to minimize the number of modules and the flow fluctuations when trains is taken offline for cleaning.

Since it is preferable to choose the number of modules per train in multiples of four, one could select either 80 modules per train (3 x 80 = 240, resulting a 3% higher flux rate), or 84 modules per train (3 x 84 = 252, 2% lower flux).

Considering N_selected84 modules per train, the total number of modules, including those installed on the redundant train, would be: 4 x 84 = 336 modules. Should we have selected only two (2) duty trains, the total number of modules would have been: 252 : 2 x 3 = 378 (42 extra modules).

In actual production, all four trains are online producing permeate (drinking water). Based on an average flow rate, usually half of the design capacity (10 MLD or 2.64 MGD), the average flux rate becomes approximately 18 gfd (36% of our original design flux of 50 gfd).

In the next post, we will evaluate the capital and operating cost of such system, along with the life cycle analysis over a 20-year horizon.

Should you have any questions regarding UF sizing and design, please feel free to drop me a line at:

cornell.evans@watertechnologiescanada.com

 

 

Vortisand®

EcomuseumZoo: High Efficiency Filtration Reduces Turbidity & Maintenance Costs
The Project

​The Ecomuseum Zoo is home to the most impressive ambassadors of Quebec’s wildlife. All residents of the Ecomuseum Zoo are there for a special reason: orphaned, injured or born under professional human care, each of them could not return to the wild. Hence, they have found a forever home at the zoo.

The $1.4 million 6,000 square foot river otter habitat, first of its kind in Canada, is made up of vast land, river banks and a 250,000 litre (66,000 gallon) water basin; includes two port holes, an underwater tunnel and a 15 meter (50 foot) viewing window. In order to improve water clarity, a high efficiency submicron performance filtration system was required to fit in a 3 meter by 4 meter (10 foot by 14 foot) mechanical room.

With the need to filter contaminants and fine particles, engineering consultants had specified Vortisand® cross-flow filtration technology as the go to side stream filtration system.

Download PDF version of the case study here.

Montreal Ecomuseum Zoo Otter Water Basin

​The footprint of the mechanical room presented itself as one of the first challenges the Ecomuseum Zoo was faced with. With only a portion of the mechanical room space being dedicated to the water filtration system, the Vortisand team of application engineers were mandated to design a customized configuration. The natural outdoor environment of the habitat posed a second challenge for the Ecomuseum Zoo and engineering consultants. Over time the water basin acts as an air scrubber, absorbing airborne contaminants and debris as they brush along the surface of the water. These contaminants can buildup and create a film on various types of hard surfaces, potentially covering the viewing window and other surfaces found within the otter habitat. The airborne contaminants and debris also increase the risk of experiencing higher levels of water turbidity. Such high levels of turbidity will result in reduced water clarity, further limiting the learning experience for Ecomuseum Zoo visitors. Routine water basin cleaning would be costly, and the use of harmful chemicals are prohibited; ultimately requiring the removal of the fine particles before they have the chance of creating a concern. The Vortisand system was required to handle various types of contaminants and fine particulates, while yielding minimal maintenance and operational related costs.

The Solution

​Thanks to its compact design, the Vortisand H2F® system was installed within the current parameters of the maintenance room. Its submicron filtration performance and high efficiency capabilities helped remove the fine particles that would otherwise make it impossible for visitors to see the otters through the viewing glass, portholes and underwater tunnel. Most importantly, the Vortisand® system made it possible for the otters to go about their daily activities comfortably. With minimal maintenance and manual intervention required, the Ecomuseum Zoo employees were able to focus on nurturing and growing their family.

Upon start up a particle analysis test was conducted, showing that particles of 5 micron and less in size made up the vast majority of the particles within the otter water basin. The Vortisand system delivered 94% removal of particles less than 5 micron in size.

“Every effort is made to provide an exceptional level of care. Here at the Ecomuseum Zoo, we make animal welfare our number one priority, and this habitat is a faithful reflection of that choice. Nothing has been neglected to ensure that the River Otters in our care have a safe, soothing and stimulating environment. We are deeply satisfied with the work achieved by Vortisand systems. Being able to work with such a high level product means a lot for our team’s efficiency and our animals’ well-being, two of our main concerns.”

David Rodrigue, Executive Director of the Ecomuseum Zoo

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