Insight into a complex system: Cooperstown wastewater treatment wetland, 2011

T. Robb1

Overview The wastewater treatment wetland just south of Cooperstown, New York has been

operational for just over a year at the onset of this study. Beginning in June 2010, effluent from the Cooperstown Wastewater Treatment Plant was diverted to the wetland for additional treatment prior to its discharge into the Upper Susquehanna River (Albright and Waterfield 2010). In the summer of 2010, Olsen (2011) delineated and described the wetland in detail, including reasons for diversion of effluent and anticipated effects of pumping effluent through the system. This 2011 study attempts to characterize some of the effects of the processes occurring within the wetland. The components discussed within this paper are separated into four main topics; brightener survey, detention time (including bathymetric survey), dissolved oxygen survey, and nutrient survey. These topics will be discussed separately for clarity.

Current insights into physical processes within the treatment wetland are based largely on

visual observations and an understanding of the basic flow regime (Figure 1). There is a small intermittent stream with very low flow that enters the wetland on the western side. Just to the east of the stream mouth is a large area of overland flow that radiates from the inflow. This overland flow enters the open-water portion of the wetland at three separate channelized flow points, shown with arrows in Figure 1. The shaded area represents the area of overland flow between the point where the effluent is introduced and the wetland surface. Water level and outflow from the wetland are controlled by a weir located in a stand-pipe in the southeast corner of the wetland; flow enters a submerged drain pipe off-shore, flows over the weir, and is directed to a rip-rap channel for discharge to the Susquehanna River. This study will address characteristics of the open-water portion of the wetland.

Background One portion of this study investigated concentrations of optical brighteners throughout

the wetland and the Susquehanna River up- and down-stream of the wetland’s outflow. Optical brighteners are used in a variety of personal care and cleaning products including shampoo, cosmetics, cleaning agents and detergents. The result is an abundance of these compounds in wastewater effluent. Optical brighteners or fluorescent whitening agents are compounds that are excited (activated) by wavelengths of light in the near-ultraviolet range (360 to 365 nm) and then emit light in the blue range (400 to 440 nm) (Hagedorn et al. 2005). The chemical families that include the brightening formulations that are most widely used by the detergent industry are the carbocycles (mainly the distyrylbiphenyls) and the triazinylaminostilbenes (Ullmans Encyclopedia of Industrial Chemistry 2001). At the molecular level brighteners are fairly unstable and break down when exposed to sunlight. It is claimed that a reduction of more than

1 Biological Field Station intern, summer 2011. Current affiliation: Penn State University. Support provided by the Village of Cooperstown.

50% occurs over six months ( Hagedorn et al. 2005), however, there have been conflicting studies on this subject. According to Kramer et al. 1996, optical brighteners have displayed photo-decay in a matter of hours when exposed to UV light. In the context of the wastewater treatment wetland, optical brightener concentrations were used as a tracer for effluent, anticipating that higher levels of optical brighteners may correspond to preferred effluent flow paths.

Figure 1. An areal depiction of the wetland and surrounding area showing a small intermittent stream that enters the wetland on the western side. Just to the east of this streams mouth there is a large section of overland flow that radiates from the inflow. Water enters the wetland in three separate channelized flow points, shown with arrows. The checkered area represents a muddy section of the wetland. The drain for the system and the outflow are located in the Southeastern corner represented with circles.

Humic substances, also referred to as tannins, are a complex mixture of organic materials

released from decaying plant matter and soils (Dixon et al. 2005). Humic compounds also have a characteristic fluorescence signature, fluorescing in the entire range between 440nm and 550nm (Dixon et al. 2005). This places them close to the same range as optical brighteners and may lead to some error when interpreting results. Therefore, the levels in the lake were considered as natural background levels.

Detention time was estimated based on flow and wetland volume in order to determine

the amount of time the average molecule of effluent will reside in the wetland. This value

therefore gives an idea of the effectiveness of the wetland (Kadlec and Wallace, 2009). Both minimum and maximum estimates of detention time were calculated by manipulating the volume variables in the detention time equation based on a perceived difference between active flow volume and total wetland volume. Estimation of detention time is further complicated by the addition of precipitation to the catchment area. This variable adds flow to the system shortening detention time. Due to this combination of variables affecting detention time four calculations will be made. The actual detention time is projected to be between the resulting values.

Another portion of this study was to gain an understanding of the dissolved oxygen

concentrations and diurnal variations occurring within the waste water treatment wetland. Dissolved oxygen (DO) is of interest in treatment wetlands for two principal reasons: it is an important participant in some pollutant removal mechanisms, and it is a regulatory parameter for discharge to surface waters (Kadlec and Wallace 2009). For these reasons several diurnal cycles of DO have been recorded across the surface of the wetland and at depth. The DO is the driver for nitrification and aerobic decomposition; also it is critical for the survival for aquatic organisms in receiving water bodies (Kadlec and Wallace 2009). The amount of DO present in water results from photosynthetic and respiratory activities of aquatic biota and from diffusion at the air-water interface (Odum 1956). The many factors contributing to DO complicate analysis of observed levels and may warrant further study to fully understand the implications of the data recorded.

The primary purpose of the wastewater treatment wetland is to sequester nutrients prior

to the discharge of treated effluent to the upper Susquehanna River. To assess the effectiveness of the wetland, 20 grab samples were taken throughout the system. These samples were analyzed to determine the concentrations of total phosphorous, total nitrogen, ammonia, and nitrate+ nitrite.

METHODS

a. Brightener survey Surveys of Otsego Lake, upper Susquehanna River, and the wastewater treatment

wetland were conducted on 19 July 2011. Data were collected to determine background levels, concentrations within the wetland itself, and impacted concentrations within the stream to which the wastewater treatment wetland empties. Measurements were made at many points throughout the wetland; the same locations were used for the development of bathymetry used in detention time calculations (Figure 2). The Upper Susquehanna was surveyed several hundred meters above and below the outflow of the wastewater treatment wetland to determine the concentration of brighteners in the river.

Brightener concentrations were measured using a CYCLOPS-7® fluorometer

manufactured by Turner Designs. This instrument measures relative concentrations of optical brighteners using fluorescence, or emission of light. This device was calibrated to zero using ultra pure de-ionized water in the lab and was evaluated using several concentrations of commercially available detergent advertised as having optical brighteners, to determine efficiency in detection. This device gives concentrations in relative brightener units or RBUs, a value representative and proportional to the amount of brighteners in the water.

Waste water treatment wetland- Relative Locations of Brightener and Bathometric Data Points

Figure 2. A representation of the relative locations of data points collected to assess brightener concentration and bathymetry. Triangles represent the shoreline, squares represent the shoreline of the island, and diamonds indicate points of data collection.

b. Detention Time There are two variables associated with detention: volume and flow. The volumes used to

calculate retention time were the result of intensive mapping at the wastewater treatment wetland. Materials included a row boat, inflatable raft, meter stick, Speed Tech® depth finder, Garmin Rino® GPS, and Global Mapper® GIS software. There were many data points collected throughout the wetland in three separate excursions; these locations have been displayed using Excel® using an arbitrary origin (Figure 2). The water level on banks was defined as zero and all the information was plotted as x, y, z point data in Global Mapper®. Global Mapper® was also used to generate contours, calculate volumes, and display bathymetry (Figure 3).

The data collected during the brightener survey implies that a portion of the wetland’s

volume is not involved in active flow, as indicated by lower brightener readings. Considering that there may be “inactive” areas within the wetland, two estimates of volume in the wetland should be calculated in relation to detention time; total and active flow (Figure 4).

Figure 3. A bathymetric map of the wastewater treatment wetland. Contours in 0.1 m intervals. Figure 4. Areas used to calculate the total volume (left) and active flow volume (right) are indicated by horizontal line striping. Background shading indicates bathymetry, contours show brightener concentrations in 25 unit increments.

The second variable associated with detention time is the flow; this can be accounted for at times with precipitation as well as during dry times. The outflow has been recorded at a standard 90o weir constructed at the outflow of the wetland (Albright and Waterfield 2011). A Reconyx Hyperfire® HC 600 Trail Camera has been used for observing weir measurement values every 15 minutes. Visual observation of the weir allowed for calibration of a Logger Pro Depth® sensor provided a means by which to recognize periods of obstructed flow (due to animal interference). The depth sensor readings were found to be inaccurate, so visual gauge readings were used to determine outflow for this study. Animals, including muskrats and beaver, freqently plugged both the outlet pipe and the weir, preventing accurate outflow estimates. Debris blockages artificially raised the water level in the outflow weir structure and created inconsistent flow patterns int eh pipe; these blockages introduced error to the estimation of water volume outflow at a given point in time. Over the course of the study almost 5000 data points were recorded to document the outflow of the system.

The following equation, taken from Kadlec and Wallace (2009), has been modified to

account for different variations of detention time: total volume and active volume, under dry and wet conditions.

In Global Mapper software, the

total volume and active flow volume, wrespectively. Figure 4 depicts the areas findicates bathymetry (bottom depth) whbrighteners. The dry outflow rate (Tabletreatment wetland during periods withourecent rain event. The wet outflow rate (received notable precipitation.

Table 1. Volume and outflow rates used

Total volume (m3), (figure 4 ) Active volume (m3), (figure 4)

Dry outflow rate (m3/day) Wet outflow rate (m3/day)

V=Qi=

II. III.

IV. Results

Equation 1: detention time τn = detention time, days

volume of water in cubic meters. Daily average out-flow, cubic meters/ day.

bathymetric profile was used to calculate estimates of hich were estimated to be 4564 m3 and 3357 m3 (Table 1) or which volumetric calculations were made. Shading ile contour lines illustrate the concentrations of optical 1) is an average of daily outflows from the wastewater t precipitation occurring at least one day after the most Table 1) refers to an average outflow of days that

to calculated the various estimates of detention time.

4564.18 3357.14 2311.4 2503.7

c. Dissolved Oxygen survey Before the initiation of this study, ten Eureka Midge® dissolved oxygen loggers were

rigorously calibrated and tested five times for competence, resulting in seven seemingly accurate and functional probes. The eight units that seemed most reliable were selected for use, though one, Midge® E, performed marginally; it displayed repeatedly that it was functional at recording changes in magnitude similar to the other probes, however these changes were at different concentrations.

On 14 July 2011 the eight Midges® were placed across the wetland at 14:15 in the afternoon (Figure 5). The Midges® were deployed to record data for several days in order to observe the dynamics of dissolved oxygen conditions over a continuous period of time. This time period was selected in order to limit variables influencing DO in that there was no rain for several days previous, limiting the amount of atmospheric mixing. The midges that were designated surface monitors were placed suspended from floats approximately .08 meters from the surface of the wetland. The units that were designated deep monitors were also suspended from floats but were placed approximately .08 meters from the bottom of the wetland. All of the units were programmed to sample temperature and DO at the same fifteen minute intervals throughout the day.

Figure 5. A map showing the sample locations for the dissolved oxygen probes placed around the wetland, both at the surface and at depth at two locations.

d. Nutrient survey Twenty locations were identified to characterize the spatial distribution of nutrient concentrations through the wetland (Figure 6). These points represent six transects perpendicular to perceived flow and one end point in the shallows, G1. Grab samples were taken from the surface and at depth using a VanDorn water sampler on 12 June at 14:00, preserved and stored in 125 ml containers. Samples were analyzed for Ammonia, nitrate +nitrite, total phosphorous, and total nitrogen according to automated methods using a Lachat QuikChem FIA+ Water Analyzer. Concentration data were plotted in Global Mapper at the location in which it was collected. Concentration data points are displayed with proportional symbols.

F

D

E

A B

C

G

Figure 6. A map depicting the data points and point IDs used in the nutrient analysis of the wetland.

RESULTS

Brightener survey A survey of optical brighteners in Otsego Lake indicates that average levels are around18

RBUs, with slightly higher concentrations (24 RBUs) in close proximity to populated areas. Brightener concentrations in the Susquehanna River downstream of the Village of Cooperstown are elevated to 50 RBUs. Effluent leaving the wastewater treatment plant contains about 350 RBUs, while concentrations in the treatment wetland’s outflow range from 300 to 350 RBUs. 150 meters downstream in the river, after adequate mixing, optical brightener concentration decreases to 70 RBUs. Figure 7 displays brightener concentrations across the wastewater treatment wetlands. Contours of 25 RBUs have been generated via interpolation using Global Mapper; “m” represents the relative measurement.

Figure 7. A graphic display of brightener concentrations across the wastewater treatment wetland. Contours of 25 RBUs have been generated via interpolation using Global Mapper®; “m” represents the relative measurement.

Detention Time Estimates of detention time range from 1.2 to 2 days (Table 2). The minimum detention time

was calculated for the estimate of active flow volume under rainy conditions. The maximum detention time (2 days) was estimated for the total volume of the wetland during dry conditions. See Figure 4 for the delineation of total volume vs. active flow volume.

Table 2. A summary of results for detention time, comparing total and active flow and wet compared with dry conditions. The values were derived from equation 1 combined with Table 1.

Total volume

detention time (days) Active volume

detention time (days) Wet detention time (days) 1.6 1.2

Dry detention time (days) 2.0 1.5

Dissolved Oxygen (DO) survey

Dissolved oxygen concentrations recorded by the deployed Midges are displayed in Figure 8. As noted earlier, the absolute concentrations presented are suspect, as problems were encountered when attempting to calibrate the probes. However, the relative differences between the readings may provide some insight into the daily fluctuations in concentration. The majority of the sample sites (A, E, F, and J) represented classic diurnal cycling, with lower values at night and higher values during the day. Kadlec and Wallace (2009) state that photosynthetic and respiration cycles are the cause of such variations. Sample sites B and D showed signs of diurnal cycling, though the peak times are offset from the norm, in that they were elevated at night. Midges H and I are the probes that were monitoring the deepest portions of the wetland (~2 m deep). Waters there were essentially anoxic. Midge E has recorded classic diurnal cycling, though recorded concentrations were substantially elevated in comparison to the rest of the Midges in the wetland.

Wastewater Treatment Wetland DO Over Time

Calendar Decimal Days

Figure 8. Wastewater treatment wetland dissolved oxygen concentrations over two days of samples recorded by eight probes every 15 min. The positions of these probes throughout the wetland are depicted in Figure 5.

The amplitudes of the two day DO diurnal cycle are represented in Table 3. Midges H and I positioned on the bottom of the wetland show very little variation in oxygen, whereas Midge D displayed the largest variation over the course of the sample period.

Table 3. The values represented in this table account for the amplitude of change that the midges recorded over a two day period in the waste water treatment wetland.

Midge DO (mg/L)A 3.2B 4.26D 12.5E 7.34F 2.38H 0.3I 0.31J 2.58

Amplitude of Diurnal Cycle

Nutrient survey

Total phosphorous In general phosphorus concentrations decreased from the effluent inflow to the wetland outflow, excepting the area near the outflow, which had high TP concentrations. The lowest concentrations of phosphorous are found along transect F and at point G, in areas which were thought to be outside of the wetland’s active flow path. Phosphorus concentrations in mg/L are depicted in Figure 9, with the symbol size being proportional to concentration values.

F

G

A B

C

D

E

Figure 9. Total phosphorous concentrations (mg/L) in the wastewater treatment wetland. Symbol size is proportional to the TP concentration at each sampling location. Total nitrogen Figure 10 depicts concentrations in mg/L numerically as well as with symbols proportional in size to the nitrogen concentrations. Total nitrogen appears to initially increase as effluent enters the wetland. The concentrations decrease slightly along transect D and then rise again along E, near the drain pipe. Transect F and point G exhibited lower concentrations, again, outside of the active flow path. The highest concentrations were found along transect E, near the drain pipe.

G

A B

D

C

F

E

Figure 10. Total nitrogen (mg/L) concentrations in the treatment wetland. Symbols are sized proportionally to the N concentration, which is also given numerically, for each sampling location. Nitrate + nitrite In Figure 11, concentrations of nitrate + nitrite are shown in mg/L with stars sized proportionally to the concentrations determined for each sample site. These concentrations display similar patterns to those of ammonia (see below), with concentrations initially increasing and then decreasing as the effluent moves through the wetland. The highest concentrations in the wetland were found along transect C. The lowest concentration values were again found to be along transect F and at point G.

G

A B

C

D

E

F

Figure 11. Nitrate+nitrite (mg/L) concentrations in the treatment wetland. Symbols are sized proportionally to the nitrate concentration, which is also given numerically, for each sampling location. Ammonia The concentrations of ammonia initially increased from transects A through C and then dropped off considerably by transect E. Figure 12 shows concentrations of ammonia in mg/L with circles proportionally sized to concentrations at collection points. The highest values were observed along transect C and the lowest were found at point G.

E

F

C

D

A

B

G

Figure 12. Ammonia (mg/L) concentrations in the treatment wetland. Symbols are sized proportionally to the ammonia concentration, which is also given numerically, for each sampling location.

Nutrient concentrations were also measured at depth and appeared to be similar to those concentrations measured at the surface locations, with the exception to this being ammonia, for which the highest levels were recorded in the deepest portions of the wetland along transect D. Higher ammonia levels would be expected in this reducing, anoxic environment. Average surface and at-depth nutrient concentrations are displayed in Table 4.

Table 4. Average nutrient concentrations for surface and at-depth samples collected throughout the wetland.

ammonia

(mg/L) nitrate+nitrite

(mg/L) total nitrogen

(mg/L) total phosphorus

(mg/L) Surface average 0.85 6.33 7.58 1.33 Depth average 1.84 6.06 7.64 1.72

DISCUSSION

Brightener survey

Higher concentrations of optical brighteners in close proximity to populated areas along Otsego Lake are perceived as being the result of humic and fabric materials leeching fluorescent compounds into the water. Dynamics within the Susquehanna River are interesting and should be investigated further.

The observed concentrations of optical brighteners in the wastewater treatment wetland

indicate what is assumed to be the preferred pathway for effluent flow. The higher concentrations approximately follow the shortest pathway from the inflow to the outflow. These concentrations helped to determine the location of the drain pipe and imply that only a portion of the wetland is involved in active flow, as effluent is taking the shortest pathway from in flow to outflow. This likely results in reduced effectiveness of the wetland as a tertiary treatment for wastewater effluent, though it seems there is potential for further treatment if the entire wetland was utilized.

Other research has indicated that no optical brighteners should be produced by waste

water treatment plants using disinfection procedures such as chlorination and UV light (Tavares 2008). However slightly higher levels of RBUs after UV filtration have been observed during the course of this study. This is believed to be caused by the excitement of the brightener compounds, due to their absorption of UV radiation, leading to heightened level detection by the fluorometer.

Detention Time

Concentrations of brighteners and nutrients indicate a preferential flow path through the

wetland; this shortened flow path reduces the area of the wetland that contributes to effluent treatment. The bathymetric survey revealed that the treatment wetland is considerably deeper than recommended by Kadlec and Wallace (2009); this text indicates that a treatment wetland should be designed to accommodate and foster plant growth at all depths. The treatment wetland has an average depth of 0.7 meters (2.3 feet) which may encourage a large amount of plant growth due to the availability of sunlight. However, the maximum depth is 2.4 meters (almost 8 feet). Most of the wetland’s open-water area appears to lack rooted plants. The detention time is greatly increased by the depth of the wetland, though this may not be as important as encouraging plant growth throughout the system. It seems likely that the wetland would greatly benefit from shallower depths.

Dissolved Oxygen survey

Oxygen is released into the water as the result of photosynthetic primary production

during the day, and is taken up throughout both the night and the day by autotrophic and heterotrophic organisms and by chemical oxidation (Cronk et al. 2001). These factors directly impact the productivity of the wetland and its ability to mitigate effluent. The DO concentrations and daily fluctuations overall are fairly low. DO concentrations may be reduced due to the thick

coverage of Lemna (duckweed) isolating the wetland from atmospheric deposition of oxygen. The suppression of the diurnal DO cycle is characteristic of all wetlands receiving moderate to high loads of nutrients (Kadlec and Wallace 2009). The extremely low values persistent at the bottom of the wetland indicate persistent stratification. This stratification indicates that there is little vertical mixing throughout the wetland. Case studies indicate that there are several approaches to mitigate these effects including aeration with compressed air bubbles and controlled intermittent vertical flow.

Nutrient survey

Overall it appears that the treatment wetland is indeed retaining nutrients. Ammonia as

well as nitrate and nitrite concentration values increased initially and then decreased as the flow progresses through the wetland. Total nitrogen and total phosphorous show similar trends initially but indicate elevated levels near the drain pipe. In all cases the lowest concentrations were found to be at point G. This section of the wetland is positioned after the projected flow has passed the drain pipe and outside of the preferential flow path indicated by the brightener survey. These results indicate that perhaps the whole wetland is not being utilized to sequester nutrients.

CONCLUSION

The data presented here provide insight into the processes that occur within this treatment wetland. Several unexpected things were found that may warrant further research. The dissolved oxygen readings were considerably different than what was be expected (though some problems existed with the probes used). Also the total nitrogen and total phosphorous concentrations are elevated near the drain pipe. There may be several explanations for this phenomena, further research is required to formulate adequate conclusions. The nutrient data, as well as the brightener survey, indicate that only portions of the wetland are acting as nutrient sinks (that is, there are some preferential flow paths through the system). The active flow volume calculated implies that about 1,200 m3 of the wetland (25% of its volume) receives less flow than the rest of the system.

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