Sunday, August 16, 2015

American Society of Civil Engineers Water Treatment Competition 2015

The Water Treatment Competition (WTC) at the 2015 Mid-Pacific Regional Student Conference tasked students to design, develop, fabricate, and present a small-scale raw water treatment system. The influent contained 9 gallons of simulated agricultural run-off. Teams were allocated 30 minutes to construct a filtration system onsite. Water quality scores were determined by measured: turbidity, electrical conductivity, dissolved oxygen, free chlorine, pH, and recovered volume.

My team’s final design was a dual media filter with chemical amendments for oxygen and pH.
Cross section of dual media filter
The filter column is raised above the catchment to allow air entrainment by trickling.
Peroxide and acetic dissociation
Hydrogen peroxide and acetic acid were used to introduce O2 and H+. One of the most controversial decisions was to exclude chlorine. Without disinfectant, the design has no pathogen removal. This ignores the design scenario for making rinsing water for a lettuce farm.
Conductivity increasing with chlorine
The scoring rubric equally weighted all water quality parameters. Empirical data reflected a strong correlation between increasing chlorine and conductivity. Up to a point, chlorine increased score. Conductivity reduced score. The result is a one-for-one trade-off, or net zero.
6 points for both bleach and no-bleach scenario
Thus, the design omits bleach for simplicity. If the project specifications had emphasized the use of disinfectant, the team’s decision would have been different. However, point maximization supported this no-bleach approach. Much as the team was during design meetings, the judges at competition were leery of water treatment without disinfection. Although not technically improper within the scope of the rules, the spirit of the competition was to make washing water.

The team placed 4th of 14. Turbidity performance was significantly worse than in lab trials. A construction issue likely created a short circuit in the filtration column. This experience demonstrated two engineering lessons. First, specifications and requirements are the starting point for any design. Their interpretation drives the final output, so clear understanding between the client and consultant is essential. Second, preparation and research will be challenged by problems in the field. These lessons can be carried forward to make next year’s project even more successful.