Treatment performance of advanced onsite wastewater treatment systems in the Otsego Lake watershed, 2009 results update 1 Holly Waterfield 2 INTRODUCTION This report serves to document the treatment performance monitored for four systems installed in the Otsego Lake watershed, three of which were installed as part of a NYS DEC grant to demonstrate the use of advanced onsite wastewater treatment systems. These include two systems, OWTS 1 and 2, funded by the grant, and the UIC system (serving BFS Upland Interpretive Center), which have been monitored since 2008 (Waterfield and Kessler 2009). Another system, also funded by the grant, was installed in the spring of 2009 at the BFS Thayer Farm. This system serves three buildings; the Hop House, Boat House, and a rented residence. Treatment performance was assessed based on the following analyses: biochemical oxygen demand (BOD or CBOD), nitrate (NO 3 ), ammonia (NH 3 ), and total phosphorus (TP). An historical overview of Otsego Lake s nutrient loading and onsite wastewater treatment is provided in Waterfield and Kessler s 2008 results report (2009). METHODS AND MATERIALS Four onsite wastewater treatment systems (OWTS) were monitored in this study and are illustrated and described in Figure 1; these include the systems serving the SUNY Oneonta BFS Thayer Farm Upland Interpretive Center (UIC) and Hop House (HH) and two homeowner systems, which for the purpose of this study will be called OWTS 1 and 2. The UIC system has relatively high treatment capacity, as the UIC was built to accommodate large groups. However, water usage is relatively low due to the short duration of most events (<4 hours); actual flow has not been measured. The system was installed and use commenced in fall of 2005. The system has been in continuous operation, though the main tank was initially not sealed appropriately and as a result proper function did not begin until fall of 2007. Use of this facility increased during the summer of 2009, when typical BFS operations were moved temporarily to the Thayer Farm. OWTS1 and OWTS2 are located within 100 feet of the western shore of Otsego Lake off of State Highway 80, and are used mainly on weekends during the summer. Each system is shared by two adjacent residences and they are designed to receive daily flows of 440 gallons and 550 gallons respectively. Actual flow for OWTS1 was not measured. Flow through OWTS2 was measured by the service provider. OWTS1 has been in use since 1 June 2006. OWTS2 has been in use since 1 June 2007. The HH system installed at the BFS Thayer Farm to serve the Hop House (BFS temporary main offices and labs), the Thayer Boat House, and the Thayer Farm House (a residential rental) and operation began in April 2009 with waste from the Hop House and Farm House. Flow from the Boat House began in August 2009. The system receives consistent domestic flow from the Farm House, which is anticipated to be beneficial to the treatment system especially during the winter months, which is a low-occupancy period at the 1 Funding provided by NYSDEC grant #49298. 2 Research Support Specialist, Biological Field Station.
Figure 1. Onsite wastewater treatment system schematics. S# indicates a sampling point. A) The UIC system is comprised of a 2-compartment tank, a phosphorus removal unit, a pump tank, and gravel bed drainfield. Wastewater is circulated and aerated in the first chamber (UIC1 and 2), and settles in the clarification chamber for final solids settling (UIC3). It then flows through the phosphorus removal unit, on to a pump chamber (UIC4), from which it is pumped in to the drain field. B) OWTS1 provides primary treatment in a septic tank and processing tank (PTE) which flow into an equalization tank, then to a pump tank where the wastewater is pumped and sprayed over an open-cell foam media filter (BFE). In this case the foam media filter aerates the wastewater and provides surface area for beneficial bacteria, increasing organic digestion. 25% of flow is returned to the headworks of the processing tank to facilitate the removal of nitrogen from the waste stream, and 50% flows to the P removal unit (PRE) and on to the drainfield via gravity. C) OWTS2 provides primary treatment in 2 septic tanks which flow to a two-compartment processing tank. Effluent flows from the processing tank to a pump tank which periodically doses a textile media filter. Filter-effluent (AXE) is split between the processing tank (PTE) and the P removal unit (PRE). A portion of effluent from the textile media filter is returned to the processing tank to facilitate the removal of nitrogen from the waste stream. D) HH provides primary treatment in 2 septic tanks (STE) which flow to a two-compartment processing tank (PTE). Effluent is pumped from the processing tank to a textile media filter. Filter-effluent (AXE) is split between the processing tank (PTE) and the P removal unit (PRE). A portion of effluent from the textile media filter is returned to the processing tank to facilitate the removal of nitrogen from the waste stream.
BFS. The system is configured so that Boat House waste flows to a septic tank, then flows to a processing tank, where it mixes with treated effluent from a textile filter. Wastewater is pumped from the end of the processing tank to the textile filter. Following a final pass through the textile filter, effluent flows via gravity to a nutrient removal unit (primarily phosphorus) containing a commercially-available iron-oxide based reactive media and is then pumped to the drainfield. Preliminary sampling efforts were conducted during the summer of 2007 in order to assess the concentrations of various chemical and nutrient parameters. Regular grab samples were collected between May and August 2008, and were collected in 2009 on a bi-weekly basis from 10 June through 2 September. During each sampling event, approximately 600 ml of wastewater were taken following each treatment component of all systems. Each sample site is shown in Figure 1 as S#. Samples were tested for BOD 5 using methods summarized by Green (2004). This method involves determining initial dissolved oxygen (DO) concentration of the sample and nutrient buffer followed by incubation at 20 C for five days and determination of the final DO concentration. Samples were diluted to obtain target DO values such that the 5-day DO concentration would be lower than the initial by at least 2 mg/l but with a final concentration greater than 1 mg/l. These conditions were not always achieved, thus valid BOD values were not obtained for every sample collected. Because a nitrification inhibitor is used during incubation, results are presented as values of CBOD, as they are associated with the carbonaceous oxygen demand rather than the total oxygen demand (APHA 1992). Overall CBOD reduction rates for each secondary treatment unit (OWTS 1 and 2 and HH filters, UIC 1-3) were calculated based on the average CBOD concentrations observed over the monitoring period, presented in Table 1. Total phosphorus concentrations were determined using the ascorbic acid following persulfate digestion method run on a Lachat QuikChem FIA+ Water Analyzer (Laio and Marten 2001). Nitrate and ammonia concentrations were also determined for each sample, using Lachatapproved methods (Pritzlaff 2003, Liao 2001). All reduction and transformation rates are calculated based on average concentrations observed over the monitoring period. Total nitrogen concentrations were not determined and are not presented here due to incomplete oxidation of ammonia to nitrate during the digestion process, which results in underestimation of TN concentrations. Biochemical Oxygen Demand (Carbonaceous) RESULTS AND DISCUSSION Table 1 summarizes CBOD and TP concentrations at each sampled stage of the treatment process for each system monitored. The overall performance of the systems can be assessed by comparing the first stage with the last. These values are demonstrated graphically in Figure 2. Typical CBOD concentrations associated with raw wastewater vary greatly (100 600 mg/l) depending on per capita water usage and inputs of solids to the system (i.e. garbage grinder waste) (Crites and Tchobanoglous 1998). The average CBOD concentrations observed in the UIC system (Table 1; Figure 2) are substantially lower than those generally encountered in raw wastewater, and the reduction rates averaged 57% (Table 2). It is likely that the system would achieve greater rates of reduction if
the incoming wastewater were of a higher strength. OWTS 1 also has initial CBOD concentrations (prior to aerobic treatment) that are at the low end of the typical range. Following aerobic treatment CBOD concentrations ranged from 5.66 mg/l at HH to 57.34 mg/l at OWTS 2. This average concentration for OWTS 2 reflects all samples collected throughout the monitoring period, which included a discrete episode of poor performance which required system maintenance; prior to said episode, CBOD concentration was less than 10mg/L (with 95% CBOD reduction). OWTS 1 foam filter reduced CBOD by 59% across all samples, which is an increase over the 2008 average of 34%, though the final concentrations are still higher and more variable than the manufacturer considers typical for the treatment unit, based on monitoring of the systems at the Massachusetts Alternative Septic System Testing Center, during which the systems averaged 94.7% BOD removal, with an average effluent BOD concentration of 9.3 mg/l (Jowett personal communication 2010, MASSTC 2004). However, the system installed here (OWTS 1) differs from the norm in terms of usage and configuration, making it difficult to directly compare the results obtained here; OWTS 1 experiences only seasonal, mainly weekend use from late May through September. More than half of this relatively short period of operation is comprised of the start-up period; results documented here correspond with those observed during the start-up period at the MASS Testing Center, which lasted about 8 weeks (MASSTC 2004). In terms of configuration, OWTS 1 does not include a sump to capture filtrate beneath the foam filter unit, making it difficult to collect a representative sample without manipulating the operation of the system to induce flow. A sample was collected on June 25 by the manufacturer indicating a BOD concentration of 14 mg/l; lower than any sample result during BFS monitoring. Results prior (25 mg/l) and subsequent (87 mg/l) to this sample indicate the variability encountered. Issues surrounding sampling protocol are addressed further in the conclusions at the end of this report. Initial CBOD loading and overall CBOD reduction are greatest in OWTS 2, at 238 mg/l and 74%, respectively. This system is receiving wastewater of typical strength for US households, and is generally producing wastewater of high quality, though there was an episode between July and September where high CBOD and ammonia concentrations were observed in textile filter effluent (CBOD >110mg/L, NH 3 > 60mg/L). During periods of typical performance, this system achieved about 95% reduction of CBOD, as is typical for textile filters of this design. 2010 monitoring will document the effectiveness of the maintenance provided by the manufacturer s certified service provider. The system at the HH achieved 97% reduction in CBOD over the monitoring period, producing effluent containing 5.66 mg/l CBOD on average. Total Phosphorus Total phosphorus concentrations at each sampled stage of the treatment process for each system are summarized in Table 1 and presented graphically in Figure 3. TP removal rates are summarized in Table 2. Average total phosphorus concentrations in untreated wastewater ranged from 9.4 mg/l at HH to 15.9 mg/l at OWTS 1, which is similar to the range typically seen in residential wastewater (Crites and Tchobanoglous 1998). Final effluent concentrations at OWTS 1 and 2 averaged 0.89 and 0.61 mg/l respectively (Table 1; Figure 3). In terms of phosphorus removal rates, OWTS 1 and 2 each achieved 95% removal over the course of the monitoring period (Table 2). This removal rate is above the manufacturer s performance claim
Table 1. Average Biochemical Oxygen Demand (CBOD) in mg/l, and Total Phosphorus in mg/l with standard error (SE) and sample size (n) for samples collected from June through September 2009, grouped by treatment system. Site UIC1 UIC2 UIC3 UIC4 OWTS1 PTE OWTS1 BFE OWTS1 PRE OWTS2 PTE OWTS2 AXE OWTS2 PRE HH STE HH PTE HH AXE HH PRE CBOD Total Phosphorus Avg mg/l SE n Avg mg/l SE n 22.16 6.90 7 10.18 1.49 6 8.31 2.46 6 9.98 1.57 6 9.43 2.30 5 10.64 1.91 6 n/a - - 5.25 1.37 6 109.76 19.86 6 15.96 1.99 6 44.68 8.82 7 18.80 1.69 6 24.78 9.02 4 0.89 0.14 6 237.84 17.57 7 11.64 1.96 6 57.34 19.33 5 12.73 1.81 6 7.16 4.22 6 0.61 0.23 6 185.88 20.59 6 6.28 2.21 4 21.74 5.60 6 7.49 2.10 5 5.66 2.35 7 9.59 2.55 5 3.35 1.10 3 6.55 1.96 5 Carbonaceous Biochemical Oxygen Demand CBOD (mg/l) 250 200 150 100 50 0 UIC OWTS1 OWTS2 HH Site Figure 2. Average CBOD in mg/l across all sampling sites and dates. Error bars indicate standard error, as presented in Table 1.
of 50% removal and produces effluent with an average concentration below the claimed final concentration of less than 2 mg/l (Noga 2007). The media canister within each of these units was replaced in late September 2008 and provided sufficient removal of phosphorus through the treatment season. Contrary to the OWTS 1 and 2 systems, the phosphorus removal unit in the UIC system produced final effluent of 5.2 mg/l, removing 50% of the phosphorus on average. The reactive media component in the phosphorus removal unit of the UIC system has not been replaced since system operation began; this sampling indicates that the media has reached its capacity to reduce final phosphorus concentrations to acceptable levels and needs replacement. Phosphorus removal within the HH system changed drastically between 2 July (87% reduction) and 17 July (24% reduction) leading to an average reduction of 31% (7.9 mg/l final concentration) over the course of the monitoring period. It should be recognized that this system likely receives higher flows than the other systems monitored, as such, the total load of phosphorus was likely greater and has exhausted the removal capacity of the media. Actual flow through this system is monitored by the manufacturer, and will be taken into consideration when it becomes available. 25 Total Phosphorus TP (mg/l) 20 15 10 5 0 UIC OWTS1 OWTS2 HH Figure 3. Average total phosphorus concentrations in mg/l for all sampling sites across all sample dates. Error bars indicate the standard error, as presented in Table 1. Site Table 2. Average percent reduction and sample size (n) of biochemical oxygen demand (CBOD), total phosphorus (TP), percent of ammonia reduced (NH 4 reduction), and percent of nitrogen removed (N reduction) from the waste stream for each treatment system sampled from June through September 2009. Sample sizes n/n indicate sample numbers of influent and effluent. Site CBOD TP NH 4 Reduction N Reduction % n % n % n % n UIC 57 6/5 51 6 80 5/4 2 5/4 OWTS 1 59 6/7 95 6 63 6/6 36 6/6 OWTS 2 76 6/7 95 6 61 6/6 50 9/7 HH 97 6/7 32 6 99 5/3 37 5/3
It is important to consider that the quality of influent to any treatment unit directly affects the treatment performance of that unit. The concentration of wastewater constituents (alkalinity, CBOD, ph, available carbon, etc.) may inhibit or decrease the efficiency of treatment processes within a given unit. In terms of the phosphorus removal units, high concentrations of incoming CBOD may cause growth of a biofilm on the media in the treatment unit, thus coating the reactive surfaces. Theoretically, this could greatly reduce the treatment capacity of the unit, as it isolates the adsorptive surfaces from the wastewater. Another factor that influences the treatment performance of the unit is the life-expectancy of the media canister. Given that adsorption of P onto active sites of the media is the mechanism for P removal from the waste stream, the length of time the unit has been in service and the loading that it receives determine its effectiveness at a given point in time. Because of this characteristic, the media s performance decreases over time as active adsorption sites become occupied by phosphorus compounds. The rate at which this decrease occurs is dependent on the use of each system and must be determined on a case-by-case basis. For these reasons, additional research efforts have been focused on P removal capacity of various media (Albright 2010) in hopes of developing a costeffective long-lasting solution to phosphorus removal in onsite systems. Nitrate and Ammonia Nitrate and Ammonia concentrations are summarized in Table 3. Figure 4 provides a graphical comparison of average ammonia and nitrate concentrations for each sampling site. Nitrate concentrations in OWTS 1 and 2 primary-treated effluent were very low (Table 3), as would be expected for raw wastewater; nitrogen enters the system in the ammonium form (NH 4 ) and bound in organic compounds (Crites and Tchobanoglous 1998). UIC nitrate concentrations were much higher in the first chamber, with 97% of nitrogen occurring in the nitrate form. This difference is due to the configuration of the UIC system; the chambers of the tank are not hydraulically isolated, and so water can circulate between the first two sampling points, resulting in aeration and thus nitrification of ammonia. The secondary treatment steps of OWTS 1and 2 reduced incoming ammonia by 63 and 61%, and reduced nitrogen overall by 36 and 50%, respectively (Table 2). Final effluent from OWTS 1 contained an average of 32.3 mg/l of nitrate and 26.9 mg/l of ammonia (Table 3), which is a decrease in ammonia concentration from 2008 averages (Waterfield and Kessler 2009). Final effluent from OWTS 2 contained 7.5mg/L of nitrate and 24.5 mg/l of ammonia on average, which is a lower average nitrate concentration than observed in 2008 (22 mg/l). The HH system reduced ammonia almost entirely, with final effluent containing only 0.24mg/L. Of the total nitrate+ammonia in the treatment unit effluent, 93% was in the form of nitrate, indicating exceptional nitrification during the aerobic treatment step. Overall, N was reduced by 37% in the HH treatment system. Environmental Technology Verification (ETV) testing was conducted by the US EPA and National Sanitation Foundation (NSF) on the type of foam filter unit incorporated in the OWTS 1 system (ETV 2003). Similar to issues documented in the Verification Report, start-up period performance issues were encountered during the 2008 start-up period. The ETV report associates poor nitrification rates following a cold-weather start-up test with settling of the foam media, which seemed to inhibit growth of the nitrifying bacterial community. Following adjustment of the media during spring 2009 maintenance performed by the manufacturer, nitrification and CBOD reduction rates improved dramatically, though still not to rates observed
during MASSTC s evaluation of the system (ETV 2003). Such maintenance has proved effective in improving the treatment performance of the unit. Table 3. Average nitrate and ammonia concentrations in mg/l with standard error (SE) and sample size (n) for samples collected from June through September 2009, grouped by treatment system. Sample Nitrate (mg/l) Ammonia (mg/l) average +\- SE n average +\- SE n UIC1 43.81 6.30 6 1.05 0.44 5 UIC2 38.81 6.86 6 0.97 0.49 5 UIC3 38.44 6.61 6 1.02 0.55 5 UIC4 35.13 5.50 6 8.53 4.14 4 OWTS1 PTE 22.46 1.14 4 73.47 6.10 6 OWTS1 BFE 54.28 10.37 6 46.16 4.40 6 OWTS1 PRE 32.31 4.71 6 26.87 7.00 6 OWTS2 PTE 0.46 0.16 6 63.27 7.03 6 OWTS2 AXE 24.63 8.83 5 50.44 9.74 6 OWTS2 PRE 7.52 1.35 6 24.53 4.20 6 HH STE 0.15 0.04 5 63.99 9.96 5 HH PTE 32.82 5.36 6 16.12 2.08 6 HH AXE 39.17 3.51 6 3.00 1.79 3 HH PRE 39.97 3.61 5 0.24 0.06 2 Nitrogen Concentration as Ammonia and Nitrate Concentration mg N/L 100 80 60 40 20 0 Site Ammonia (mg/l) Nitrate (mg/l) Figure 4. Proportion of the average nitrogen concentration reported as ammonia and nitrate. Error bars indicate standard error, as presented in Table 3.
CONCLUSIONS Treatment performance in 2009 showed variation from that observed in 2008. OWTS 1 increased in BOD reduction and nitrification efficiency while OWTS 2 had an episode of lessthan-ideal treatment. TP removal increased dramatically in OWTS1 and 2 following the fall 2008 replacement of the reactive media. Treatment performance of the phosphorus removal units in UIC and HH systems is outside acceptable criteria, suggesting that the media canisters are in need of replacement. Overall, the onsite treatment systems are producing high-quality effluent with a portion of the total phosphorus removed, though some final TP concentrations remain within the range expected from primary treated residential wastewater. Additional research on phosphorus removal media are presented in Albright and Waterfield 2010. Sampling protocols can influence the observed treatment performance; this influence varies with the type and configuration of each system. Samples are either collected to represent the performance at a single point in time, referred to as a grab sample, or to represent treatment over the course of a period of time (typically 24 hours), referred to as a composite sample. Treatment performance assessments based on grab samples are more likely to incorporate error if the quality of effluent is variable over the course of a day; composite samples capture the range of conditions encountered throughout the day, providing flow-weighted results of effluent quality produced by the system. The potential for sampling protocol to influence results will vary with the configuration of the system; some systems, such as UIC, continuously mix wastewater and yield more consistent results over the course of a 24-hour period, whereas a system with discrete treatment components will experience variation over the course of a day, depending on use of the system, in which case a grab sample may yield non-representative results if such factors are not considered. The timing of a sampling event may coincide with dosing of the filter unit, allowing one to obtain a sample without manipulating the cycling of wastewater within the system. However, in the case that the system is between dosing events, flow must be induced in order to capture water between the treatment components; in the case of an absorbent media (becomes saturated during dosing), induced wastewater may displace that previously saturating the media or may short-circuit the media; in either case, the effluent leaving the treatment unit is partially treated at best. Sufficient sample size should allow for a range of conditions to be encountered, providing an average that is representative of the effluent quality that typically leaves the system, though this cannot be guaranteed. Comparisons between monitoring and assessment efforts must acknowledge such details. Communications with service providers and manufacturers resulted in remedied issues and increased treatment performance. Vigilance in the maintenance of advanced treatment systems is of the utmost importance if these systems are to be relied upon to reduce human impacts to sensitive environments, especially considering that the vast majority of systems are not monitored once they are installed, as they are with this project. REFERENCES Albright, M.F. and H.A. Waterfield. 2010. Evaluation of phosphorus removal media for use in onsite wastewater treatment. In: 42 nd Ann. Rept. (2009). SUNY Oneonta Bio. Fld. Sta. Cooperstown, NY.
APHA, AWWA, WPCF. 1989. Standard methods for the examination of water and wastewater, 17 th ed. American Public Health Association. Washington, DC. Crites, R. and G. Tchobanoglous. 1998. Small and Decentralized Wastewater Management Systems. McGraw-Hill, p183 Environmental Technology Verification Program (ETV). 2003. ETV Joint Verification Statement: Waterloo Biofilter Model 4-Bedroom. National Sanitation Foundation and US Environmental Protection Agency. Green, L. 2004. Standard Operating Procedure 011: Biochemical Oxygen Demand (BOD) Procedure. University of Rhode Island Watershed Watch. Jowett, C. 2010. Personal Communication. February 2010. Liao, N. 2001. Determination of ammonia by flow injection analysis. QuikChem Method 10-107-06-1-J. Lachat Instruments. Loveland, Colorado. Liao, N. and S. Marten. 2001. Determination of total phosphorus by flow injection analysis (colorimetry acid persulfate digestion method). QuikChem Method 10-115-01-1-F. Lachat Instruments. Loveland, Colorado. MASSTC. 2004. US EPA Environmental Technology Initiative Onsite Wastewater Technology Testing Report: Waterloo Biofilter. Massachusetts Alternative Septic System Test Center, Cape Cod, MA. Noga, M. 2007. The knight nutrient removal device. Knight Treatment Systems. http://www.knighttreatmentsystems.com. Accessed October 2009. Pritzlaff, D. 2003. Determination of nitrate/nitrite in surface and wastewaters by flow injection analysis.quikchem Method 10-107-04-1-C. Lachat Instruments, Loveland, Colorado. Waterfield, H.A. and S. Kessler. 2009. Treatment performance of advanced onsite wastewater treatment systems in the Otsego Lake watershed, 2008 results. In: 41 st Ann. Rept. SUNY Oneonta Bio. Fld. Sta. Cooperstown, NY.