October 2012, Vol. 24, No.10

Problem Solvers

Attached growth treatment offers higher treatment at lower costs

Problem: Widespread failure of septic systems resulting in more-stringent permit requirements for a small town
Solution: Installing a gravity-fed sewer with an attached growth process system
 

With a population of 107, the small town of Mt. Union, Iowa, relied on individual onsite septic tanks for wastewater management, with no secondary treatment. But without regular maintenance, many of these outdated conventional systems failed, leading to widespread releases of untreated wastewater into a local creek.  

The Iowa Department of Natural Resources (DNR) cited Mt. Union for inadequate wastewater treatment and mandated that the community make improvements. The department issued permit requirements that the town meet specific concentrations for several parameters, including average biochemical oxygen demand (BOD) less than or equal to 25 mg/L, total suspended solids (TSS) less than or equal to 30 mg/L, ammonia–nitrogen of 2.6 m/L, total nitrogen of 14 mg/L, pH readings of 6 to 9, dissolved oxygen at 5 mg/L or greater, total residual chlorine less than or equal to 0.02 mg/L, and Escherichia coli less than or equal to 126 organisms per 100 mL.  

To meet these requirements for an anticipated 56,800 L/d (15,000 gal/d), the town sought an alternative wastewater treatment solution. When looking for new treatment options, minimizing capital and life-cycle costs was a priority because the small rural community has a median household income of just $27,500.  

Also, because the town had gone without a wastewater treatment system for many years, residents viewed any wastewater bill as excessive. The new treatment system also had to use minimal land area, because the town’s land is highly fertile and used to grow crops.  

   

Finding a system for a tight budget 

In 2007, the town retained French–Reneker–Associates (Fairfield, Iowa) to evaluate its options. Using a discharge lagoon was discarded because it would have required up to 4 ha (10 ac) of land that could be farmed. Other options were eliminated because of their inability to comply with the DNR-required limits or their operation and maintenance (O&M) requirements and costs.  

French–Reneker–Associates concluded that the best available technology would be a gravity sewer collecting flows from septic tanks followed by an Orenco (Sutherlin, Ore.) AdvanTex® treatment system. The technology would remove ammonia–nitrogen at an affordable up-front and long-term cost with low O&M and repair and replacement requirements, said Kent Rice, French–Reneker–Associates project engineer.  

   

Necessary treatment with additional benefits 

In February 2010, the town commissioned its solution, installing 34 septic tanks located throughout the town to feed into a gravity sewer system. The wastewater then is treated by the two-stage systemfor enhanced ammonia–nitrogen removal.  

The systemis a nonsubmerged attached growth system that includes recirculation/dilution (R/D) tanks and treatment media to provide biological nitrification. A timer-controlled pump in the tanks periodically doses effluent to a distribution system on top of the media. Pumps run intermittently, resulting in energy consumption of less than 2.5 kWh per 3785 L (2.5 kWh per 1000 gal). Each time the media are dosed, effluent percolates through and is treated by naturally occurring microorganisms. Effluent collects below and is conveyed back to the R/D tank. Effluent recirculates multiple times before final disposal.  

The system achieves unsaturated flow and sustained contact by distributing wastewater evenly over the surface of the medium and by keeping doses small and frequent. This also ensures that all of the media are used, preventing clogging. And because hydraulic, organic, and inorganic loads are distributed uniformly, biochemical interactions are more effective, according to Terry Bounds, Orenco’s executive vice president and the developer of the AdvanTex technology.  

The system’s medium has hydraulic loading rates of 0.4 to 2 m3/m2 d (10 to 50 gal/ft2 d), depending on permit requirements and organic and inorganic concentrations, Bounds said. It also features a solids retention capability of months or years and minimizes sloughing, which reduces solids management costs.  

The Mt. Union system provides reliable performance, and effluent quality exceeds the requirements. BOD is less than 10 mg/L, TSS is less than 10 mg/L, and ammonia–nitrogen averages between less than 1 and 2 mg/L (depending on seasonal temperature fluctuations), said Tyler Molatore, Orenco’s community systems program manager.  

“Performance is sustained with part-time operation and relatively low operational skills and maintenance requirements. Even with highly variable flows of [18,900 to 113,600 L/d] 5000 to 30,000 gal/d and part-time operation, the system is operating well within its permit limits,” Molatore said.  

The system requires no chemical additions, produces high-quality effluent that can be reused in various ways, such as for subsurface irrigation and groundwater recharge after disinfection, and for other nonpotable uses after disinfection.  

   

Calculating costs and savings to come out on top 

The system, funded in part by U.S. Department of Agriculture Rural Development grant and loan funds, included a collection system contract for $308,299 awarded to Jackson Creek Enterprises (Allerton, Iowa) and a treatment system contract for $419,275 awarded to Pilcher Construction (Ottumwa, Iowa).  

The system and its components are designed to provide cost-effective operation over its lifetime while energy requirements are minimized by the intermittent use of small-horsepower pumps.  

Mt. Union’s system is monitored remotely with a telemetry control panel and visited periodically, generally requiring only part-time servicing with regular inspection of the main components, cleaning of pump screens and distribution nozzles, and adjusting timer settings as needed, Molatore said. Total annual onsite maintenance amounts to about 40 hours per year for about $1500.  

“Based on a 40-year present worth analysis, the total cost of ownership for the AdvanTex Treatment System was lower than the other technologies evaluated,” Molatore said. “Lower costs were largely attributed to low energy consumption and low O&M requirements.”  

According to the Water Environment Federation (WEF; Alexandria, Va.) Awards Subcommittee, “Orenco’s design is cost-effective, innovative and useful for small and decentralized wastewater treatment systems. As WEF members in small communities face ever-increasing regulatory requirements, Orenco’s cost-effective, reliable AdvanTex design comes along at the right time to help produce cleaner water and meet NPDES [National Pollutant Discharge Elimination System] permit requirements.” The committee selected the system to receive WEF’s 2011 Innovative Technology Award.


 

 

 

 

 

 

Cleaning up wastewater from nuclear contamination in Japan

Problem: Nuclear energy leaks contaminated wastewater after Japan’s tsunami.
Solution: Installing a treatment system using selective media extracted radioactive ions from wastewater at the Fukushima Daiichi Nuclear Power Plant.

On March 11, 2011, an earthquake and tsunami struck the east coast of Japan, killing thousands and causing billions of dollars in damage. The tsunami also cut the connection between the Fukushima Daiichi Nuclear Power Plant and the electrical grid that provides power to the plant’s control systems. Flooding from the tsunami knocked out the plant’s backup generators, stopping operation of pumps designed to circulate cooling water.

Between equipment ruptures caused by ensuing hydrogen explosions and seawater pumped over the nuclear reactors to provide emergency cooling, a large quantity of radioactive water accumulated. This water threatened to overrun the subbasement where it was being collected. If remediation didn’t begin by mid-June 2011, radioactive water would be released into the Pacific Ocean.

 

Instituting a temporary solution

On June 17, 2011, a water treatment system using various media coupled with coagulation, precipitation, and filtration was brought on-line to feed a reverse-osmosis system. This system enabled the already stored water to be recirculated for cooling but still required storage for future decontamination. This interim fix successfully reduced the water levels in the storage facility by 5% and maintained this level for several months, according to documents published by the Tokyo Electric Power Co., which owns and operates the Fukushima Daiichi plant.

Although the plant had limited success with the initial system, it began looking for a solution that would be easier to operate, produce less waste, and be safe and cost-effective, said Alan Greenberg, strategic marketing manager for UOP LLC (Des Plaines, Ill.), a company that creates technologies for the petroleum refining, gas processing, petrochemical production, and major manufacturing industries.

 

Implementing a long-term solution

The plant joined with Toshiba Corp. (Tokyo) and Shaw Global Services LLC (Baton Rouge, La.) to find a more effective solution to clean radiation-contaminated wastewater at the power plant. Toshiba, Shaw, and AVANTech Inc. (Columbia, S.C.) worked together to develop and implement the Simplified Active Water Retrieve and Recover System (SARRY) system to remove and reduce radioactive materials in water. The system uses the UOP LLC IONSIV R9160 and R9120 selective media to meet the plant’s water quality requirements.

The IONSIV ion-exchanger absorbents are crystalline materials able to selectively remove radioactive ions from liquids. They have been used commercially for more than 30 years to treat such liquids as radioactive wastestreams in commercial nuclear power plants, alkaline tank waste, and spent-fuel storage pool water.

IONSIV R9160 is an engineered zeolite previously used in the cleanup of the Three Mile Island nuclear power plant. It is designed especially to remove cesium relative to other cations. It has a distribution coefficient (Kd) of approximately 2000 relative to seawater; this led to its use for the primary bulk removal of cesium from the stored water at Fukushima.

IONSIV R9120 is a crystalline silicotitanate based on technology developed by Texas A&M University (College Station) and Sandia National Laboratories that is designed to have the highest combination of capacity and selectivity for cesium, with a Kd greater than 20,000. At Fukushima, it is being used as a polisher to reduce the radioactivity present, according to Greenberg.

Together, the IONSIV R9160 and R9120 reduce levels of cesium in treated water from 5×106 Becquerel/cm3 (Bq/cm3) to nondetectable levels of less than 1 Bq/cm3. This reduction translates to decontamination factors of more than 2 million relative to cesium.

Compared to the previous system, the SARRY system more effectively removes cesium between 1 and 2 orders of magnitude. The system also has proven to be more reliable and less complicated to operate.

The IONSIV’s high capacity enabled the system to reduce waste generated by a factor of 8 to 10 relative to either the media or precipitation systems that were installed initially. This leads to fewer media change-outs, a smaller waste-storage footprint, and lower costs of operation and disposal, Greenberg said. The system has removed radioactive ions from more than 227 million L (60 million gal) of contaminated water. 

 

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