Wastewater wetlands on display

June 2012 » Features » PROJECT CASE STUDY
Compact onsite systems provide biological treatment to reclaimed water standards.
David Maciolek, P.E.
Living Machine System wetland cells in a greenhouse at Evergreen Elementary School treat as much as 7,000 gallons per day of wastewater with low energy and no odor.
Photo: Guy Cali Associates Inc.

Current wetland technology can provide energy-efficient wastewater treatment in a compact footprint. Fill-and-drain wetland technology provides a reliable, high level of treatment with minimal energy input. The systems are cost effective, attractive, and have no odor, making them ideal for a variety of applications.

Project
Port of Portland headquarters, Portland, Ore.
Evergreen Elementary School, Scranton, Pa.

Product application
Living Machine Systems tidal flow wetlands provide compact, onsite, energy-efficient wastewater recycling and reuse.

Recent installations include a Living Machine Systems tidal flow wetland integrated into the main entrance and in the lobby of the Port of Portland's LEED Platinum-certified headquarters building at the Portland (Oregon) International Airport. At the Evergreen Elementary School outside of Scranton, Pa., the Living Machine System is located in a greenhouse structure adjacent to the school that will provide educational opportunities, as well as ease of operation.

In these systems, the effluent from the tidal flow wetlands is polished with a 20-micron pleated fabric filter, then disinfected and stored for pumping into reclaimed water plumbing systems to flush all toilets in the buildings or homes. At the Evergreen Elementary School, effluent not used for toilet flushing is disposed of via spray irrigation of surrounding forested areas.

Tidal wetland cells enhance the main entrance of the Port of Portland headquarters building while treating the sewage from the building for toilet flushing reuse.
Photo: Living Machine Systems, L3C

The two engineered subsurface flow wetland wastewater treatment systems described in this article treat wastewater onsite and produce very high quality effluent for reuse. These operational systems receive different types of wastewater and are located in very different settings but have similar overall design. The primary biological treatment component is a tidal flow wetland. The Living Machine System is a technology developed and patented by Living Machine Systems, LC3.

In each of the systems, most of the wastewater treatment takes place in the tidal flow wetland system. The systems' components are wetland cells, pump stations, and a control system that uses a programmable logic controller (PLC) to activate pumps and control valves in the proper sequence based on water levels in the various tanks and cells. Influent is pumped into the cells receiving influent flow at the beginning of a fill cycle. That cell is then filled with water from the previous cell or the recirculation tank.

When the wetland cells are filled, wastewater is brought into contact with the treatment media covered with microbial biofilms. As the cells drain, air is drawn into the voids in the wetland, effectively providing oxygen without aeration equipment and diffusers. This tidal flow wetland process has proven effective in a wide variety of applications (Lohan et al., 2011; Pier and Behrends, 2010), and energy use with these systems is a fraction of comparable activated sludge systems (Maciolek and Austin, 2006).

The wetland cells consist of watertight basins filled with engineered media supported by an underdrain system. They are planted with selected vegetation with roots that grow down into the engineered media, which consists of manufactured lightweight expanded shale aggregate (LESA). Numerous properties make LESA an excellent material for engineered wetlands including a high surface area-to-volume ratio and low contamination risk from fines.

Microbial biofilms grow on the surfaces of the LESA and clean the water by typical bacterial processes. Because biofilms are attached and there is a very large surface area relative to loading, this process provides stable and reliable treatment over variable flows and loads. The microbial ecology in these wetland cells is very resilient, with little or no reduction in treatment when fully loaded after two weeks of very low or no loading.

No sludge is generated because of the very low mass loading relative to the microbial biomass. Additionally, the consumption of biomass by "grazing" organisms in several trophic levels includes microbial predators, worms, snails, and insects. Effluent from the tidal flow wetland system is very low in biochemical oxygen demand (BOD), total suspended solids (TSS), total Kjehldahl nitrogen (TKN), and ammonia. The effluent quality is such that minimal further treatment is required to achieve reclaimed water standards.

Port of Portland headquarters building
In 2010, the Port of Portland, Ore., completed construction of a new office building, located at Portland International Airport, to serve as its headquarters. Although sewer was available, the architects and owners wanted to incorporate into the project a wastewater recycling system designed to demonstrate onsite treatment and reuse of building wastewater. This would also maximize water efficiency and be an asset in achieving LEED Platinum certification. To provide educational opportunities for staff and visitors, the design team wished to incorporate the wastewater system into the first floor lobby of the 11-story office building. To achieve this, the Living Machine wastewater system needed to be aesthetically appealing, odor free, and relatively compact.

Because the building design incorporated low-flow fixtures and water efficiency throughout, it was projected that the wastewater from the office building would be fairly concentrated with a high proportion of nitrogenous compounds compared with residential or municipal wastewater. A tidal flow wetland system provided an ideal solution to meet these challenges.

Figure 1: Port of Portland Living Machine System schematic

After solids are removed in the septic tank with an effluent filter, wastewater is pumped from a flow equalization tank to the first wetland cells (see Figure 1), which are located outside the main entry of the building. The remaining wetland cells, encompassing about 70 percent of the total area, are located in the entry lobby of the headquarters building.

Evergreen School
The Western Wayne School district outside of Scranton, Pa., constructed a new elementary school in 2010-2011 to replace several outdated facilities. The school is projected to attain LEED Silver certification. Available land parcels for the new school were not served by sewer and thus required onsite wastewater management. Because area soils had low infiltration capacity, traditional land disposal of wastewater was not feasible. The Pennsylvania Department of Environmental Protection (DEP) suggested a wastewater system that allowed recycling and had a reduced disposal area, making the desired parcel feasible for onsite management. A Living Machine System delivered necessary effluent quality in a modest footprint, provided educational opportunities, and fit overall sustainable design objectives.

Effluent that is not recycled for toilet flushing is land applied to sports fields and forested areas on the property. Irrigation of the sports fields with the effluent also makes use of the remaining nitrogen and phosphorus in the effluent.

In August 2011, the school opened and the system began treating wastewater. Monitoring of influent and effluent began in October 2011, after the treatment system biology had matured. Performance data shows that effluent met the reuse criteria since monitoring started. Due to some mechanical issues, use of toilet flushing effluent started in April 2012.

Wastewater characteristics and system flows
Because both projects were new construction, influent wastewater characteristics had to be estimated for each site during the design process based on literature values and previous experience. These estimated flows and concentrations were used to compute mass loading rates for BOD, TSS, and TKN in the flow from primary treatment to the tidal flow wetland system.

Characteristic  
Port of Portland
Evergreen School
Influent (gpd) Design (a)
5,000
7,000
  Observed
Avg.: 2,630(b)
Max: 3,304(b)
Avg.: 2,779(b)
Max: 5,045(b)
Per unit Flow, (gpd) Basis
Per capita
Per capita
Design
10.0
7.0
Observed
5.6(c)
3.0(d)
BOD (mg/L) Design
140
185
Observed
209
415
COD (mg/L) Design
300
355
Observed
467
Not measured
TSS (mg/L) Design
55
1.6
Observed
93
Not measured
TKN (mg/L) Design
90
125
Observed
159
125
Table 1: Comparison of design and observed influent wastewater characteristics
a) Maximum monthly average flow allowable at design influent characteristics.
b) Based on weekday flow only, excluding holidays.
c) Estimated occupancy of 450 staff.
d) Based on estimated occupancy of 750 students and staff.

The actual wastewater flow rates of the operating systems were generally much lower than design values, but concentrations were correspondingly higher (see Table 1). The primary reason for this appears to be the very low-flow plumbing fixtures used in these buildings. Reduced water use due to project design and user awareness appears to contribute as well.

The systems are designed based on mass loading rates, thus influent flow rates are not the most important factor to consider in evaluating them. At both Port of Portland and Evergreen School, the observed BOD loading is approaching the design (peak monthly) value. At Port of Portland, the TKN loading is actually exceeding the design value. The TKN loading to the Evergreen School System is just under half of the design loading but still quite substantial.

Overall, both of the systems have performed as designed and effluent has generally been of excellent quality. The BOD and TSS in the effluent are consistently below 5 milligrams per liter (mg/L) and often below the detection limit. Effluent ammonia averages less than 1.0 mg/L for both systems and the final effluent turbidity in all the systems is very low. These low levels are achieved with minimal filtration after the tidal flow wetland. Port of Portland system operators report having to clean or change the small filter at six-month intervals once the system had fully matured. The Evergreen system has not yet required routine cleaning of the filters, indicating very low suspended solids leaving the tidal wetland portion of the treatment system.

Considering the high-concentration waste input and the variable loading, the two Living Machine Systems have performed very well and met all design criteria. In light of the very high effluent quality produced by these systems, operator input has been very low. Aside from sampling requirements, the operators report spending less than one day per week in operation and maintenance activities.

Conclusion
The Living Machine System provides high levels of treatment in a compact space with very little operations and maintenance required. With efficient performance in a variety of applications, these tidal flow wetland systems offer an opportunity for wastewater recycling and reuse. The onsite systems are also outstanding for public education regarding wastewater treatment. Energy efficient, the Living Machine System can also be a strong asset to any project slated for LEED certification.

References

  • Lohan, E., Muñoz, P.A., Salthouse, G., Fisher C., and K.Reid Black, 2011, Performance of decentralized wastewater systems for green building projects in North America and Australia, Greenbuild International Conference and Expo Research Track Conference Proceedings, 2011, Toronto, Canada, Oct. 4-7.
  • Maciolek, D. and D. Austin, 2006, Low energy biological nitrogen removal by cation exchange, thin film oxygen transfer, and heterotrophic nitrification in sequencing-batch, packed-bed reactors, Water Environment Federation Technical Conference, Dallas, Oct. 2006.
  • Pier, P.A. and L.L Behrends, 2010, Reciprocating wetlands for wastewater treatment: A commercial-scale demonstration, Oahu, Hawaii, 12th International Conference on Wetland Systems for Water Pollution Control, Venice, Italy, Oct. 4-8, pages 826-831.

David Maciolek, P.E., principal engineer, Aqua Nova Engineering PLC (www.aquanovaengineering.com), Earlysville, Va., has more than 21 years of experience primarily related to water and wastewater management, including treatment systems for municipal, commercial/industrial, and small-scale wastewater and stormwater flows. He is recognized as a co-developer and the lead engineer of the Living Machine Systems advanced wetland systems for wastewater and stormwater treatment. He can be contacted at david@aquanovaengineering.com.
Eric Lohan, LEED AP, general manager, Living Machine Systems, Charlottesville, Va., has been involved in the development of Living Machine technology and the design and installation of Living Machine projects for 11 years. He is coauthor of six patents on ecological wastewater treatment technology, and author of a number of papers and book chapters on ecological wastewater treatment and reuse. He can be contacted at elohan@worrellwater.com
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