Category: Lesson Learned

Lesson Learned: Technology Selection

7/11/2016

Problem: A greenhouse facility wants to reuse water from a flood floor which is used to water potted plants. The water collected has vermiculite and organic matter clouding the water which would clog nozzles and settle in pipes.

Solution: The operator looked at two different technologies, a self-indexing filter and a parabolic filter screen (Figures 1 & 2). Both are recommended units that filter coarse material from water.

Figure 1: Diagram of a self-indexing filter [level sensor is tripped when water rises due to clogged paper and roll is unspooled]

Figure 2: Diagram of a parabolic filter screen [(a) inflow; (b) flows onto screen; (c) waste remains on screen and treated water falls through; (d) waste exits through tray; (e) treated water exits through (f); (g) water overflows if screen becomes clogged and exits through (f)]

Discussion: The infrastructure required for either technology is similar; both will need some plumbing and a pump to move water through the treatment system. The technologies are compared in the table below. Both systems will complete the task; the self-indexing filter is more hands-off but requires more inputs. The parabolic filter screen must be supervised but has minimal on-going costs.

Decision: The operator choses the self-indexing filter as it requires less regular supervision. The additional energy costs, on-going need of paper rolls, and disposal of paper was preferable to increased labour requirements and disposal of waste.

Lesson Learned: When there are multiple technologies that could fit in a treatment system it is important to investigate all aspects. Decisions should be made based on more factors than merely cost.

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Lesson Learned: Drum Filter Optimization

8/4/2015

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For more information on the drum filter test, see Drum Filter Demonstration Site.

Filtration systems are not always a simple installation. Technologies require some manipulation to ensure that they are functioning at their maximum efficiency. The drum filter that was installation is one example. It succeeded in taking in washwater and filtering it through the screen. It was successful in rotating the barrel and spraying off the waste into a collection tray. However, initially the output of the collection tray contained excessive amounts of water. As the goal is to have a sludge-like material with the least amount of water possible to limit amounts of waste to dispose, adjustments were in order. The drum filter is able automated to rotate and spray on a regular schedule; the purpose of the optimization process is to find the setting that produces the most concentrated waste stream.

Table 1: The time between each spray cycle, approximate volume of waste output, volume of waste output per minute, and solids (depth in sample bottles) for each spray cycle setting

The first step was to investigate the settings that were most appropriate for the solid load and flow rate of the washwater. The drum filter was run at each of those settings for a few cycles and sludge samples were taken along with waste output volumes, spray cycle time, and time between rotations was recorded (Table 1). The samples were left to settle so the solids portion of the sludge could be observed (Figure 1).

Figure 1: Illustration of waste output at a spray cycle setting of (left to right) 5 seconds, 10 seconds, 15 seconds, 20 seconds, and 3 samples at 25 seconds.

Based on the results outlined in Table 1, the samples taken from the 5 second and 15 second rotation had the highest amount of solids in the sludge. The 5 second spray cycle has the lowest overall waste output. It was determined that this setting was the most efficient out of those tested.

Prior to optimizing the cycle setting, the change in total suspended solids between pre and post drum samples was 46%. The drum filter was run using the 5 second spray cycle setting and samples of the pre drum, post drum, and sludge were taken. After changing the setting, the change pre and post drum was 71%. Through manipulating the spray cycle, the efficiency of the system was greatly increased.

Figure 2: Total suspended solids in pre drum, post drum, and sludge samples prior to optimization on day 1 and after on day 2

Lesson Learned: As with many technologies, it takes time and careful measurements to set equipment to operate at optimal levels.

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Lesson Learned: Bottom-up Aerator to Treat Washwater in Settling Tanks

11/11/2014

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Not every solution implemented results in success. Those various mistakes and failures are discussed here as well as the lessons learned from them.

Goal: Decrease Total Suspended Solids (TSS) while increasing Dissolved Oxygen (DO) concentrations in a settling tank

Solution: Installation of a Bottom-up Aerator.
A Bottom-up Aerator works by pumping compressed air down to a diffuser (Figure 1) situated on the bottom of the tank. The air is released through the diffuser as bubbles which work their way to the surface. As the bubbles rise, the oxygen is dissolving into the water.

Figure 1: A Bottom-up Aerator diffuser (left) and the surface disturbance caused by the system (right)

Problem: The primary goal of the settling tank is to remove suspended particles by sedimentation and removal of clear water at the surface. The bubbles surfacing from the aerator interrupted this process by keeping the particles in suspension (Figure 2). Also, water testing results showed that there was no significant positive impact on the DO (Figure 3).

Figure 2: Total Suspended Solids in a settling tank over time before and after Bottom-up Aerator installation, as shown by the green line

Figure 3: Dissolved Oxygen concentration in a settling tank over time before and after Bottom-up Aerator installation, as shown by the green line, with a target level of 7-10 mg/L (CCME, 1999)

Discussion: The system failed to increase the DO in the water and had a negative impact on the TSS. While a Bottom-up Aerator is suitable in other situations where particle settling is not a concern, it was not appropriate for resolving this problem. It was removed and replaced with a Surface Aerator.

References

Canadian Council of Ministers of the Environment (CCME). 1999. Canadian water quality guidelines for the protection of aquatic life: Dissolved oxygen (freshwater). In: Canadian environmental quality guidelines, Canadian Council of Ministers of the Environment, Winnipeg, MB.

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Lesson Learned: Technology Selection

Lesson Learned: Drum Filter Optimization

Lesson Learned: Bottom-up Aerator to Treat Washwater in Settling Tanks

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