Grantee Research Project Results
Final Report: Improving TTHM Reduction Processing and Operational Efficiencies in Potable Water Distributions Systems Using Solar-Powered Circulation with Diffused, Near-Surface Aeration
EPA Contract Number: EPD12015Title: Improving TTHM Reduction Processing and Operational Efficiencies in Potable Water Distributions Systems Using Solar-Powered Circulation with Diffused, Near-Surface Aeration
Investigators: Tormaschy, Willard
Small Business: SolarBee Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2012 through August 31, 2012
Project Amount: $80,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2012) RFA Text | Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Drinking Water Treatment and Monitoring
Description:
SolarBee's Phase I research optimized our prototype Solar-Powered Circulation with Diffused Aeration (SPC-DA) system for trihalomethane (THM) reduction (Figure 1). The prototype system consisted of our existing Solar-Powered Circulation (SPC) unit that uplifts 10,000 gpm of water to the surface (3,000 gpm direct flow through the intake hose; 7,000 gpm induced flow external to the hose) with a new Diffused Aeration (DA) unit powered by a 7.5 hp blower. Optimization was defined as maximizing the total THM (TTHM) processing and energy efficiencies of the unit while minimizing capital and O&M costs. Processing efficiency was assessed by measuring TTHM removal rates during a single pass of all water in a tank through the treatment zone. A single pass was defined as the tank volume divided by the water upflow rate (the rate at which influent bottom water is transported through the DA treatment zone to the surface by the SPC unit). Energy efficiency was defined as the amount of power delivered to the air blower (directly related to electrical grid energy consumption) of the DA unit needed to achieve a set TTHM removal rate (no research was conducted to improve the energy efficiency of the SPC unit because this was done when the technology was first developed). Capital cost was defined as the cost of production plus a fixed profit margin. The operations cost was defined as the cost of electrical grid power for the DA air blower because there are no other operational costs. Maintenance cost was considered to be that required by the five original prototype units deployed in a Las Vegas Valley Water District tank for a 2-year period.
Figure 1. Illustration of the prototype SPC-DA unit. The two primary functions of the unit are circulation of all water in a tank through the treatment zone, and treatment with diffused aeration.
Summary/Accomplishments (Outputs/Outcomes):
The project was accomplished through systematic, internal research and development that addressed five research objectives. All objectives involved systematic variations of parameters involving the DA air manifold and DA airflow rate.
Relative to the prototype, the optimized system increased the THM reduction rate by almost 70% while power consumption declined by about 80%. This 70% improvement in processing efficiency resulted from multiple improvements in the DA manifold design. All optimal values were incorporated into optimized DA manifolds and tested with the SPC unit to assess additivity of effects. All processing and energy efficiency gains observed when the parameters were systematically varied individually were realized in the optimized system; the effects were additive.
The improvements in the DA manifold also reduced DA blower horsepower and amperage (proportional to air flow rate) requirements, resulting in the 80% improvement in operational efficiency. Charges for electrical-grid power to the DA blowers were the only operational cost of the five original prototype units deployed in a Las Vegas Valley Water District tank of mid-size (10 MG), moderate daily flow rate (2 MGD), and fill rate of 12,000 GPM. No maintenance was required. Therefore, O&M cost was limited to the cost of electrical-grid power for the five DA air blowers. Anticipated maintenance is replacing the SPC motor after about 10 years, the battery after about 5 years, and the DA air blower motor after about 5 years.
Conclusions:
Capital cost decreased by about 20%, primarily due to improvements in manufacturing process efficiencies. The project did not directly reduce capital cost because alternative TTHM reduction technologies were not investigated.
The original prototype SPC-DA system performed well in a Las Vegas Valley Water District tank. TTHM data were collected during the peak-THM quarter for 2 years in the treatment tank and the last tank in that distribution line. TTHM concentration was approximately 25% lower in the treatment tank, and 30% lower in the downstream tank, than during the mean of the previous 4 years. TTHM concentration was maintained well below the maximum contaminant level of 80 ppb in both tanks. The observation that TTHM concentration reduction was greater in the downstream tank than the treatment tank indicated that the TTHM formation potential was exhausted significantly during treatment.
During low THM seasons, the units DA components were turned off to save on operational expenses, but the SPC units remained on to continually circulate the water. Circulation prevents thermal stratification that results in aged water at the top, prevents short-circuiting of new influent water to the outlet and evenly distributes chlorine residual throughout the tank.
The prototype SPC-DA units in Las Vegas were recently optimized to incorporate the improvements identified in this SBIR project. SolarBee expects the processing and operational efficiency improvements that resulted from the Phase I project to be realized in the Las Vegas distribution system during the peak-TTHM quarter of 2012-2013.
Supplemental Keywords:
trihalomethane, TTHM, potable water, water distribution system, solar, near-surface aeration;The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.