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.

Sunday, April 19, 2015

SWPPP

The California State Water Resources Control Board regulates the discharge of storm water associated with construction activities. The Construction General Permit requires the development of a Storm Water Pollution Prevention Plan (SWPPP). The purpose of the program is to limit erosion and sediment discharge, which could have ecological effects downstream.
Preparing for pH and turbidity measurement
Dischargers implement Best Management Practices (BMP) such as fiber rolls, gravel bags, and synthetic membranes to limit erosion and filter runoff.  Part of my duties at Shimmick Construction is to monitor storm water discharge from our job site. When it rains, I collect and test representative samples for pH (acidity) and turbidity (suspended solids).

I upload results from the portable meters to the State’s online tracking system. Exceedance of the legal limits indicates corrective action is necessary. Inspection of a problem area usually reveals the need for additional BMP.

Rain events by themselves reduce productivity on a construction site. An EPA fine of $75,000 per day per violation would make it that much worse. SWPPP implementation is a small but important part of the project.