Michael Richard, Ph.D.
Presented at the Rocky Mountain American Waterworks Association / Water Environment Association Annual Conference, Sheridan Wyoming September 11th, 1995
A coming problem in the Rocky Mountain region is the requirement for ammonia removal during municipal wastewater treatment. Many small communities in the Rocky Mountain region that use aerated lagoons are getting effluent ammonia limits in their renewed NPDES permits. A major problem exists in that aerated lagoons in the Rocky Mountain region have to operate at a low winter time temperature where ammonia removal by nitrification is minimal or ceases. this makes meeting low effluent ammonia standards almost impossible for these systems. A great need exists to find a way for the continued use of small community aerated lagoons to meet effluent ammonia limits in the cold time of the year.
The Grand County Water and Sanitation District (GCWSD), Winter Park, Colorado uses an aerated lagoon system to treat an average flow of 300,000 gpd of domestic wastewater that contains 15 - 25 mg/l ammonia-N. New effluent ammonia discharge limits are coming into to effect for this system which change monthly, but may reach low values of 1 - 2 mg/l ammonia-N in the winter time. Historically, little ammonia removal occurs in this system during the wintertime due to cold temperatures.
GCWSD in cooperation with RBD and Ringlace Products, Inc. has undertaken a two year full scale evaluation of wintertime enhanced ammonia removal by nitrification using a ringlace fixed film system installed in the GCWSD aerated lagoon. Ten thousand meters of Ringlace material ( special 1/2 inch diameter "rope" ) held in six 8 x 4 x 6 foot frames were placed in one of two identical aerated lagoons in July of 1994. The second lagoon cell was unchanged to serve as a control.
The first years results showed a 25% increase in nitrification (ammonia removal) in the ringlace lagoon compared to the control lagoon in the winter of 1994-95 at operating temperatures of <1 C. Nitrification was significantly increased by the Ringlace system at low temperature. An unforeseen benefit of the Ringlace system has been a reduction in TSS and algae growth, often a summertime problem for this lagoon system.
The Ringlace system is very cost effective compared to replacing lagoons systems with activated sludge systems. costing about 10% of the cost of an activated sludge system with almost no operational costs. If the ringlace system proves of benefit for ammonia removal at low temperature, many small communities that use an aerated lagoon system may benefit.
A coming problem in the Rocky Mountain region is the requirement for ammonia removal during municipal wastewater treatment. Many small communities in the Rocky Mountain region that use aerated lagoons are getting effluent ammonia limits in their renewed NPDES permits. A major problem exists in that aerated lagoons in the Rocky Mountain region have to operate at a low winter time temperature where ammonia removal by nitrification is minimal or ceases. This makes meeting low effluent ammonia standards almost impossible for these systems. A great need exists to find a way for the continued use of small community aerated lagoons to meet effluent ammonia limits in the cold time of the year.
The Grand County Water and Sanitation District's need for increased ammonia removal:
The Grand County Water and Sanitation District (GCWSD ), Winter park, Colorado uses and Inca Grid aerated lagoon system to treat an average flow of 300,000 gpd of domestic wastewater that contains 15-25 mg/l ammonia-N. This system, shown in figure 1, consists of 2 primary aeration lagoons (east and west lagoons of 7.5 and 7.1 million gallons capacity, respectively ) operated in parallel and a final settling lagoon of 10.88 million gallons capacity. The total system capacity is 25.4 million gallons which results in a hydraulic detention time of 30 to >200 days at seasonally fluctuating influent wastewater flows of 0.1 to 1.0 mgd (averaging about 0.3 mgd) due to substantial I/I in the springtime. Influent wastewater flows for the study period are shown in figure 2.
New effluent ammonia discharge limits are coming into effect for this system which change monthly, but may reach low values of 1 - 2 mg/l ammonia-N in the early springtime. Historically, ammonia removal in this lagoon system varies seasonally with good ammonia removal in the warmer months but little ammonia removal in the wintertime due to cold temperatures ( shown in figure 3 ). A comparison of modeled future effluent ammonia limits to recent lagoon effluent ammonia concentrations, shown in figure 4, illustrates the need for further ammonia removal in the lagoon system to meet the future ammonia limits.
Ringlace Fixed-Film Media
Ringlace material was developed in Japan in the 1980's and consists of a rope like material of high surface area and a chemical composition conducive to bacterial attachment and growth. Biomass densities on the ringlace material approximate that found on trickling filter media or other high rate attached growth systems.
Ringlace systems are widely used in Japan and have recently been used extensively in the eastern US to upgrade municipal activated sludge plants to provide nitrification. To our knowledge, the use of Ringlace in the GCWSD lagoon system is the first Ringlace use in a lagoon system and the first Ringlace installation in the US west of the Mississippi River.
Ringlace is currently being installed or considered for use by RBD for additional wastewater treatment needs in Colorado including: BOD removal and nitrification upgrade for activated sludge systems: BOD treatment capacity upgrade for aerated lagoons: and pretreatment for brewery wastewater. The use of Ringlace for enhanced nitrification in aerated lagoons is being examined at this time (this study).
Study Rationale and Goals
The GCWSD needs to find a way to improve ammonia removal during wastewater treatment to be able to meet future effluent ammonia limits. One obvious solution is abandonment of the lagoon system and construction of an activated sludge system, proven to control ammonia concentrations to the extent needed even at cold temperature. However, this option would involve a major capital expense ($3 - 5,000,000). RBD joined with the GCWSD to explore potential ways to improve ammonia removal in the existing aerated lagoon system.
Ammonia removal is primarily accomplished in biological wastewater treatment through conversion to nitrate by nitrifying bacteria. These specialized bacteria occur in lagoon systems, however, at low concentration. Typically an aerated lagoon contains 50 - 100 mg/l biomass concentration of which only a small amount is nitrifying bacteria. This low nitrifier population in combination with seasonably cold temperatures in Colorado usually results in a loss of nitrification in lagoons in the wintertime.
One approach to increase nitrification in lagoons is to increase the biomass concentration, analogous to increasing the MLSS concentration in activated sludge systems to maintain nitrification at colder temperature. Ringlace fixed film media was selected as a possible way to increase the biomass concentration in the GCWSD lagoon system, in the hope the nitrifier population would also be increased and provide better nitrification at cold temperature. A major question addressed by this study was whether nitrification could be maintained in the lagoon system at temperatures of 1C or less.
The Ringlace Study
GCWSD in cooperation with RBD and Ringlace Products, Inc. has undertaken a two year full scale evaluation of wintertime enhanced ammonia removal by nitrification using Ringlace fixed film system installed in the GCWSD aerated lagoon. Ten thousand meters of Ringlace material (a special 1/2 inch diameter "rope" held in six 8x4x6 foot frames were placed in one of two identical aerated lagoon cells in July 1994. The second lagoon cell was unchanged to serve as a control.
The Ringlace system was installed in the west aeration lagoon to span the are between the center baffle and the lagoon sidewall as close as possible to the influent wastewater entrance to the lagoon as shown in figure 1. This was done to take advantage of an increased temperature at this location due to the warmer influent wastewater during the wintertime.
Analytical testing done by the GCWSD included weekly analyses of influent, east and west lagoon effluents, and final effluent for BOD5, TSS, pH, alkalinity, dissolved oxygen, temperature and ammonia, Nitrite, nitrate. Additionally, samples of the ringlace material were removed and analyzed by RBD for biomass development and the presence of nitrifying bacteria at approximately two month intervals. Algae counts and their contributions to the east and west lagoons' TSS were performed periodically through the study.
This paper reports the initial performance of the Ringlace system at increasingly nitrification in the GCWSD lagoons through the first year of the two year study. Final conclusions must await completion too the study in 1996. The mo they average lagoon operating temperatures ranged from<1C to 18C with a three month period of <1C temperature in December through February.
Monthly average values for BOD5 concentration in the east and west lagoon effluents are shown in figure 6. BOD5 in both lagoons was generally similar with no apparent rends. It is not known why the west (Ringlace) lagoon BOD5 was higher than the BOD5 in the east lagoon in December and January.
Monthly average TSS values in the east and west ( Ringlace ) lagoon effluents are shown in Figure 7. After an initial acclimation period, the west ( Ringlace ) lagoon had a lower TSS concentration that the east lagoon during the warmer times of the year (fall and late spring-summer). Microscopic examination showed lower suspended biomass in the west versus the east in the fall and spring-summer periods. An example of this is shown by east and west lagoons algae counts on 6/1/95 which were 1.26 X 105/ml in the east lagoon and half this amount, 7.00 x 104 / ml, in the west lagoon. Prior studies before Ringlace installation had shown equal algae growth in both lagoons.
It appears that biomass growth on the Ringlace medium occurred at the expense of suspended biomass growth. the reason for the reduced algae growth in the ringlace lagoon is not currently known. A possible explanation is the more successful competition of the attached nitrifying bacteria on the ringlace medium foot low and often growth limiting alkalinity at the expense of algae growth.
Weekly values for east and west ( Ringlace ) lagoon dissolved oxygen, pH, and alkalinity for the study are shown in Figures 8, 9 and 10, respectively. There was no significance difference in these parameters between the east and west lagoons during the study to date. Both lagoons dissolved oxygen values were consistently high during the study with no oxygen limitation for nitrification (always well above 2.0 mg/l). Influent wastewater alkalinity is low in the GCWSD system and lime was added (100 pounds/day) to try to maintain at least 60 mg/l alkalinity in each lagoon. Alkalinity below this amount was previously shown to inhibit nitrification in the GCWSD system.
Influent wastewater ammonia concentrations for the study period, shown in figure 11, ranged from 2 to 25 mg/l NH3-N. Influent wastewater ammonia concentration was fairly constant for most of the year with a much reduced ammonia concentration in the spring due to snowmelt and substantial I&I (see influent wastewater flows shown in Figure 2). Ammonia removal in the lagoons was best assessed by nitrate formation and not ammonia removal, due to some uneven flow split between the 2 lagoons and the long detention time in the lagoons.
The monthly average east and west (Ringlace) lagoon effluent nitrate concentrations along with the lagoon temperatures are shown in figure 12. After about a 2 month acclimation period, the west (Ringlace) lagoon effluent had a nitrate concentration typically about 25% higher than the east lagoon effluent. This finding indicates significantly increased nitrification in the Ringlace lagoon compared to the control lagoon. Microscopic examination of the ringlace material through the study showed nitrifier development on the ringlace material, but at a low density prior to the summer of 1995 due to cold temperature. Both lagoons maintained nitrification at wintertime temperatures of <1C for three months duration.
Nitrification was decreased in both lagoons in the springtime by high I & I flows and low influent ammonia concentration. Comparison of nitrification between the east and west lagoons for the summertime period has not yet been completed and will be presented at a later time.
Incorporation of Ringlace material into the aerated lagoon system at GCWSD increased nitrification about 25% compared to the control lagoon through the first winter of operation. This increase in nitrification is significant as it occurred at a low operating temperature of <1C.
The first winters Ringlace nitrification performance may not have been optimal, due to installation of the Ringlace system at the end of the summer with insufficient time allowed for nitrifier development on the Ringlace material before cold lagoon temperatures occurred. Nitrification performance is expected to be improved in the upcoming second winter of operation, due to better nitrifier development on the Ringlace medium over the warm summertime period.
Ringlace addition to one of the lagoons significantly reduced the lagoon TSS concentration (suspended biomass concentration). This presumably occurred due to the growth of the biomass on the Ringlace material at the expense of suspended biomass growth. An unforeseen effect of Ringlace was reduced algae growth in the lagoon during the warmer times of the year. This effect of Ringlace could be important in helping to control algae overgrowth in the lagoons, a common problem in Colorado lagoon operation.
The first years result showed a 25% increase in nitrification ( ammonia removal ) in the Ringlace system in the winter of 1994-1995 at operating temperatures of <1C. Nitrification was significantly increased by the Ringlace system. An unforeseen benefit of the Ringlace system has been a reduction of TSS and algae growth, often a summertime problem for this lagoon system.
The Ringlace system cost about $25,000 to purchase
and install in one half of the GCWSD lagoon system. Addition of Ringlace to the
second lagoon cell would increase this cost to $50,000. Given the cost of a
mechanical plant $3-5,00,000, the Ringlace option appears to be a very low cost
upgrade for increased ammonia removal in aerated lagoons in the cold climate of
the Rocky Mountain region. Ringlace appears to increase nitrification at cold
temperature, however, the suitability of this upgrade would be dependent on the
degree of ammonia removal required. Very low effluent ammonia requirements in
the wintertime probably will require an activated sludge process as no
biological treatment process will function at peak efficiency at wintertime low
temperatures below <5C. Ringlace may find its greatest use in systems that can
seasonally store effluent and discharge intermittently when treatment is best
through the year.