Floating Floc Team Goals for Summer 2009

Summer 2009 Team Members

Tanya Cabrito, Team Leader
Adela Kuzmiakova
Shaina Khan

SETTING UP

Goal: Modify Experimental System to Develop Consistent Supersaturation in Inflow Water
(Changes were made to the sand filter experimental system to establish more consistent supersaturation of the water flowing into the sand filter. The existing aerator was replaced by a taller aerator that would allow for increased residence time of the bubbles.)

Approximate Timeline:

• June 8-11: Aerator was incorporated into the new system and leaks were fixed. (Adela, Shaina, Tanya)
• June 10-11: The water source of the system was changed from tap water to the white tub in the lab to allow for the removal of the hot and cold water valves. The cold and hot water valves were replaced with a flow control valve after the aerator and a water wasting valve was added to the aerator for better water level control. (Adela, Shaina, Tanya)
• June 11: Process controller methods for the experimental system were rewritten. (Adela, Tanya; Reviewed with Shaina)
• June 14 - June 30: Debug experimental system, debug process controller methods, and properly configure the system (determine set points for minimum and maximum water levels, etc), fix leaking problems. (Adela, Shaina, Tanya)
• July 1 - July 3: Verify that the new aerator functions properly and old results are replicable. Test DO out of the aerator and compare to theoretical results (Adela, Shaina, Tanya)
  
  

  EXPERIMENTS

  Descriptions of the experiments that will be conducted are available here.

  Approximate Timeline:

• July 5 - July 12: Experiment Bed Depth:
  Starting with 10 cm on June 24, experiments will be conducted with varying bed depths. Bed depth will be increased 10 cm daily. Final data analysis will occur on July 8-July 12. (Adela, Shaina, Tanya)
• July 12 - July 19: Experiment Bed Expansion:
  The range of expansions to be tested will be determined after the bed depth experiments are conducted. A bed depth that yields moderate gas removal will likely chosen and the physical limitations of the sand column will govern the expansion range. Like in Bed Depth Experiments, expansion will likely be increased incrementally by a certain percentage daily. Final data analysis will occur on July 15 - July 19(Adela, Shaina, Tanya)
• July 16 - July 21: Experiment DO Concentration:
  Starting with 20 kPa gage pressure on July 8, experiments will be conducted with varying aerator pressure and thus influent dissolved air concentrations. Pressure will be increased 20 kPa daily. Data analysis will begin July 19 - July 21. (Adela, Shaina, Tanya)
  
  

  MATHCAD

Literature Searches:

• June 26 - July 23: Literature searches for MathCAD modeling. After viewing data from each set of experiments, literature searches will be performed as necessary to explain the relationship between variables that are tested.
  June 26 - July 15: Bed Depth Research (Adela)
  July 19 - July 19: Bed Expansion Research (Shaina)
  June 26 - July 23: Dissolved Air Concentration Research (Tanya)

Modeling:

After collecting data, MathCAD models will be developed to quantify the relationship between the parameter of interest and the performance of the sand filter and also to find optimal values for each parameter.

• July 8 - July 26: Model Bed Depth (Adela, Tanya)
• July 15 - July 26: Model Bed Expansion (Shaina, Tanya)
• July 19 - July 26: Model Dissolved Air Concentration (Adela, Shaina)
  
  Note: Extra time will be used to continue modeling.

REFERENCES:

The articles detailed below were found in Spring 2009. References will be expanded during experiments, data analysis, and MathCAD modeling as the need arises.

Fundamentals of Bubble Formation during Coagulation and Sedimentation Processes

Gas bubbles can form in solution whenever the total dissolved gas pressure (TDG) is greater than the local solution pressure (supersaturation). Rapid mixers can also cause floating floc even in undersaturated water. This article outlines the experiments conducted to investigate the initial formation and then stability of floating floc during conventional coagulation-sedimentation processes. The volume of the bubbles formed and the equilibrium dissolved gas concentration in the water was estimated using a gas bubble equilibrium model based on the assumption of a closed system. This article also looks into the mass transfer rate of the dissolved gas into the gas bubbles. Factors such as water temperature and coagulant type are also discussed.

Scardina, P., and Edwards, M. (2006). "Fundamentals of bubble formation during coagulation and sedimentation processes." Journal of Environmental Engineering. 132(6):575-585. Available from <http://cedb.asce.org>. Accessed 2009 February 21.

An Improved Gas-Stripping Column for Deoxygenating Water

The article discusses gas-stripping columns and an experiment using a gas-stripping column. In the introduction, the article mentions the advantages of using such columns to deoxygenate water due to their simplicity and low cost. These columns generally involve a porous substrate in the column through which water flows downward and nitrogen gas flows upward. The methods section describes the setup of the experiment and how nitrogen gas was introduced into the compresses gas cylinder. They found that the amount of dissolved oxygen in the output water was inversely related to the rate of nitrogen gas flow.

Barnhart, M. (1995). "An improved gas-stripping column for deoxygenating water." Journal of the North American Benthological Society. 14(2):347-350. Available from <http://jstor.org/stable/1467786>. Accessed 2009 February 26.

Water Treatment Unit Processes: Physical and Chemical

This is a book describing water treatment processes, and in certain sections it mentions the stripping of dissolved oxygen from solution. The book briefly discusses gas transfer and the transport of gas from aqueous phase to gas phase, which is controlled by rate of interface area created. On page 956, there is the mention of using gas transfer to strip air in order to remove volatile compounds from the solution. On page 979, the book refers to an experiment in which nitrogen was used to strip oxygen from solution.

Hendricks, D.(2006). Water treatment unit processes: physical and chemical. Boca Raton, Florida: CRC Press. Available from <http://books.google.com/books>. Accessed 2009 February 25.

Expansion of Granular Water Filters During Backwash

Granular media filtration is a crucial unit operation in water treatment plants because of its high effluent quality standards. This paper studied the mathematical models for graded filter media with uniform and irregular sieve diameters. It points out that an increase in flow rate causes the bed to expand and accommodate the increased flow while maintaining the same pressure drop. It has been found that the log-log plot of the backwash velocity against bed porosity is linear for a fluidized bed of uniform grain size. Once the porosity of the media is known, the expanded bed height can be calculated with the formula given in the paper. From the paper, it reconfirmed that sand media with a size of 0.52 mm and uniformity coefficient of 1.43 results an effective backwashing at an expansion of 50% at 2.75 cm/s backwash velocity.

Akkoyunlu, A. (2003). "Expansion of Granular Water Filters During Backwash."Environmental Engineering Science. 20(6): 655-665, 2003. Available from <http://www.liebertonline.com/doi/pdf/10.1089/109287503770736168>. Accessed 2009 February 27.