Beyond Greywater: On-Site Wastewater Treatment at Emerald Bay
By Peter Kraut
With the explosion of LEED and the advent of green building codes, greywater treatment has become more common in plumbing design. Many homeowners and building operators are excited about the idea of saving water. The effort to separate sewer flows and the expense of the equipment often is not considered as they head down the design path and into construction. They are dismayed when they find out that the only use for greywater is as below grade drip irrigation and that, in order for it to be used for toilet re-flush or cooling tower makeup, it must be treated to a higher standard. The cost of “going green” suddenly becomes too much, and our most precious resource is flushed down the drain.
The Western Los Angeles County Council of the Boy Scouts of America took a different path. Faced with water costs exceeding four cents per gallon at Camp Emerald Bay on Catalina Island, they had to find a way to reuse every precious drop. They contacted wastewater treatment expert Steve Braband of BioSolutions Inc., who began outlining a program for onsite wastewater treatment.
The camp serves over 7,000 campers each year, most residing for a full week, and the collection points are spread out over 88 acres. The camp’s central dining facility is not far from the beach and is surrounded by staff cabins, a marine center and support buildings. The main circulation corridor heading inland is flanked by several buildings, including a general store, a craft building and the future Environmental Learning Center.
The rest of the land is divided into 19 smaller camps surrounding six toilet and bathing facilities. These are currently discharging into four septic systems, each comprised of a tank and a leach field. Numerous historical septic systems also exist throughout the camp, most of them abandoned. To centralize the collection in a facility this vast, the design utilized the significant slope to minimize trenching and carry all of this waste to a new waste treatment plant.
To get a better understanding of the flow rates, water usage was analyzed. Fortunately, the camp had already begun a program to conserve water. Patty Breech of UHG Consulting helped put this conservation plan together. It included the use of low flow fixtures, finding and fixing leaks and metering to determine where the water was being used. With these meters and a head count of the campers each month, it was soon demonstrated that the camp used 40,000 to 200,000 gallons of water per month. As much as 50,000 gallons per month may have been used for irrigation. The remainder equated to 25 gallons per person or about half of what the codes and standards suggest for sizing septic systems. Armed with this information, the new wastewater treatment equipment could be cut in half. It was then assumed that 19 gallons per person per day was used in toilets/bathing and six gallons per day per person in meal preparation.
The design begins with the majority of the solids being separated into a local settling tank, much like a septic tank. In waste treatment, however, the process begins here, so the tank is sized for 2 ½ days of retention. Simply multiplying 19 gallons times the peak number of campers times 2 ½ days yielded the tank size. The result called for nine tanks, ranging from 1,500 to 25,000 gallons, plus an 8,000 gallon grease interceptor serving the dining hall. To maximize the solids retention in these tanks, a Biotube® filter manufactured by Orenco Systems® Inc. was used. It allows effluent flow from the clear zone of the tank, between the sludge and scum layers. Using vertical flow and small orifices, these filters remove about two thirds of the total suspended solids before the effluent leaves the septic tank.
The effluent from all of these septic tanks is then collected in two 15,000 gallon holding tanks. These create a surge volume to level out the peak flows and allow for a system sized closer to the average flows. For this purpose, Biotube® pump vaults with effluent filters and effluent pumps deliver a metered quantity of effluent to the treatment system. Unlike a septic system, waste treatment relies on the aerobic process of digestion. These two words, aerobic, meaning “with oxygen” and digestion, meaning “the mechanical and chemical breakdown of food,” establish the natural process of treating waste. Through retention, this process has already begun, but a much more sophisticated approach is needed if the water is to be used for toilet re-flush.
Several characteristics of the wastewater must be known for the final system configuration. Among them are CBOD5 (five-day carbonaceous biochemical oxygen demand), TSS (total suspended solids) and TKN (total kjeldahl nitrogen or the sum of organic nitrogen, ammonia NH3 and ammonium NH4+). Water softener backwash is prohibited, and greases and oils must be removed through pre-treatment. Although the wastewater should be tested prior to installation, the design for a camp of this nature can begin with common residential strength wastewater characteristics, as shown in Table 1.
The goals for this project were to reduce CBOD and TSS to 5 mg/L and to reduce nitrogen by 90%. For this purpose, an AdvanTex® treatment system was selected. This modular, fully-plumbed wastewater treatment system incorporates a special textile filter media below recirculating spray nozzles in a fiberglass tank with telemetry-enabled controls.
Waste treatment relies on aerobic digestion; the textile filter media provides a place for the aerobic bacteria to thrive. The recirculating spray nozzles use a process called micro dosing. This method of wetting the textile at regular intervals allows the bacteria to feed and then starve, ultimately consuming them. The tanks are installed in series; each tank passes the effluent on to the next tank, where the cleaner water continues the same process for greater refinement. The controls monitor the levels in the surge tanks, regulate the effluent pumps, control the micro dosing and even monitor and record the quality of the final product.
Even with a sophisticated treatment system such as this, nitrogen and ammonia can be difficult to remove. For this process, the Western Los Angeles County Council of the Boy Scouts of America turned to Will Kirksey of the Living Machine®. Similar to the waste treatment system described above, this process is controlled by pumps regulating water levels and moving it back and forth between several tanks. The tanks are filled with a gravel aggregate, specially engineered films of beneficial microorganisms and plants working together in a living, highly complex ecosystem. These establish one of three wetland types. For Emerald Bay, a horizontal subsurface flow wetland was selected. In the end, an ultraviolet system is used to kill any pathogens that are left in the water.
The culmination of the process occurs at the site of the future Environmental Learning Center. This landmark building, along the main path through camp, will house classroom and conference space, with exhibits explaining the waste treatment system, rainwater harvesting system and other sustainable practices incorporated into the camp. From here, the effluent will be used to feed toilet re-flush as well as for drip irrigation, with the goal of reducing potable water demand by 50% or more.
The Western Los Angeles County Council is pursuing a significant number of grants and donations for this project. Meanwhile, a solid operating budget has allowed continual progress towards its goals. Rob Jernigan, Richard Hammond and Peter Barsuk of Gensler have created a master plan for the camp that includes capacity for over 1,100 people. It focuses on sustainable design and includes photovoltaic solar arrays on the hill behind the new Marine Biology Center. All of these measures may add up to huge cost savings. In a small community on an island off the coast of Los Angeles, the cost of “going green” may actually have a return on its investment.
Peter A. Kraut, P.E., is a licensed Mechanical Engineer in 23 states. He founded South Coast Engineering Group, near Los Angeles in 2001. He can be reached via email at pkraut@socoeng.com.