Sewerage Treatment in an Integrated Constructed Wetland

Proceedings of the Institution of Civil Engineers Municipal Engineer 162 December 2009 Issue ME4 Pages 199–205 doi: 10.1680/muen.2009.162 .4.199 Paper 900038 Received 07/09/2009 Accepted 25/09/2009 Dan Doody Rory Harrington Mark Johnson Oliver Hofmann Don McEntee Keywords: Senior Engineer, Senior Scientific Officer, Senior Executive PhD student, Edinburgh Chartered Engineer, environment/groundwater/ Monaghan County Department of the Engineer, Monaghan Napier University, UK Dublin City Council, sustainability excavation/sewage Council, Environment, Heritage County Council, Ireland treatment & disposal Monaghan, Ireland and Local Government, Monaghan, Ireland Dublin, Ireland

Sewerage treatment in an integrated constructed wetland

D. Doody CEng MIEI, R. Harrington PhD, MFS (Yale) BAgSc, M. Johnson CEng MICE CEnv. MCIWEM MCIOB, O. Hofmann Dipl. Biol. and D. McEntee BE, MEngSc, MICE, MIEI

An integrated constructed wetland was constructed in humus tank. The effluent from the treatment plant discharged to 2006/2007 to treat combined sewage from the village of the nearby Glaslough Stream, a tributary of the Mountain Water Glaslough in North Monaghan, Ireland. With a design River. By the 1990s, the plant was heavily overloaded and a capacity of 1750 population equivalent, the plant became manifestly poor quality of effluent was being produced, leading operational in October 2007 and the current load is to prosecution of MCC by the Eastern Regional Fisheries Board around 800 population equivalent. Untreated influent is (ERFB). In 2001, the sewerage system was extended and a pumped directly to a receiving sludge pond; the liquid temporary package plant was installed with the treated effluent then flows by gravity through five sequential vegetated discharging directly to the Mountain Water River. By early ponds and the effluent discharges directly to the Mountain 2003, the temporary plant was in turn ‘experiencing difficulties’, Water River. The banks of the ponds feature equestrian leading to further written complaints from the ERFB. riding trails. Monitoring equipment has been installed in each pond and early results are very encouraging. In the During this period, MCC commissioned a preliminary report on first year of operation, effluent quality consistently the construction of a traditional treatment plant with a design surpassed the quality of the receiving river. The system capacity of 350 population equivalent (pe) and a final effluent can robustly cope with large variations in volumetric and standard of 20/30 (biological oxygen demand (BOD)/suspended biological oxygen demand loadings of the influent. The solids (SS)). The preliminary estimated cost (in October 1989) construction and maintenance of the wctland show was IR£205 000 (J260 000). By January 2002 the design significant cost savings compared with traditional sewage capacity had been revised upwards to 650 pe and the cost treatment plants in the county. The extensive monitoring estimate had risen to J950 000. Applying construction cost work being undertaken at Glaslough wctland will help inflation, this equates to an estimated 2008 cost of J1 530 000 promote the wctland concept and its application to a for a traditional plant of 650 pe capacity. range of water quality management issues such as leachate (from landfills), sewage sludges, drinking water 3. ICW CONCEPT source protection and flood amelioration. Initial work on the development of the ICW concept has been carried out on a number of farms in the Anne Valley, County Waterford over the last twenty years. By allowing liquid waste 1. INTRODUCTION streams (from a variety of sources) to flow sequentially through Glaslough is a historic village located some 10 km northeast of a number of vegetated ponds, ICWs (through a combination of Monaghan town in Ireland that has developed around the physical, chemical and biological processes) have the capacity to renowned Castle Leslie and the picturesque Glaslough Lake produce a high-quality effluent. In the Anne Valley during the (Figure 1). This paper describes the background, construction 1990s, a number of on-farm ICWs were constructed to treat dirty and early operation of the Glaslough–Castle Leslie pilot farmyard water. An ICW was also constructed to treat domestic integrated constructed wetland (ICW), constructed to treat effluent from the village of Dunhill. Prior to 1990, water in the domestic sewage effluent from Glaslough. This project is part of Annestown Stream was of very poor quality with little or no fish a unique initiative by the Department of Environment, Heritage life. Today the quality of the Annestown Stream is approaching and Local Government (DEHLG) in treating liquid waste streams good-quality status and sea trout have returned to the stream in shallow vegetated ponds. It is a cooperative undertaking by after an absence of many years.1 Monaghan County Council (MCC), Castle Leslie Estate, DEHLG and the University of Edinburgh. In August 2003, a delegation from the Castle Leslie Estate and MCC visited the Anne Valley to see the ICW concept in 2. BACKGROUND operation, and this resulted in the publication of an article in The sewerage collection system serving the village of Glaslough The Sunday Times supporting the use of ICWs for treating is a combined foul sewer and, until 2001, delivered flows to a municipal sewerage.2 The trustees of Castle Leslie were small treatment works (dating back to the 1940s) consisting of convinced of the benefits of treating the sewerage from primary settlement tanks, a single-pass biological filter and a Glaslough in an environmental manner and concurred with the

Municipal Engineer 162 Issue ME4 Sewerage treatment in an integrated constructed wetland Doody et al. 199 Glaslough

IRELAND Monaghan

N54 Belfast N2 Clones Monaghan Castleblaney Dublin

London MONAGHAN Carrickmacross

Figure 1. Glaslough location map

ecological standards being pursued by the Estate. The trustees of river water body is 0?025 mg/l for high status and 0?035 mg/l Castle Leslie agreed to lease some 6?5 ha of land within the for good status.3 The MRP of the effluent from Glaslough ICW walled estate to MCC for use as a treatment plant. during the first year of operation was 0?025 mg/l.

4. BENEFITS OF ICW 5. DESIGN, LAND LEASE AND PLANNING In Ireland over the past 10 years, the national parks and wildlife The site, enclosed within the black line in Figure 2, is located service of DEHLG has been uniquely developing a more robust within the Castle Leslie Estate walls on the banks of the and sustainable approach to the use of constructed wetlands. Mountain Water River. It is surrounded by woodland and Categorised as surface-flow type wetlands, they are similar to demanded sensitive development in terms of landscape fit, natural free surface water wetlands. The holistic approach, biodiversity, amenity and habitat enhancement. termed integrated constructed wetland (ICW), has been suc- cessfully applied to deal with a range of effluent types (e.g. The design capacity of the ICW was 1750 pe (current loading is farmyard runoff, industrial waste and sewage). <800 pe). This allowed a ‘footprint’ map to be drawn up and negotiations to commence on a 99-year lease of the 6?74 ha of The concept is based upon the free surface flow of water land required (the water surface of the constructed ponds covers through a series of sequential linked shallow ponds vegetated 3?25 ha). The lease agreement included the provision of with a range of emergent plant species. While the footprint of equestrian riding trails on the banks of the wetland ponds. the ponds is much larger than those usually used for similar Figure 3 shows the layout of ICW. hydraulic loadings in reed-bed type systems they are generally less costly to build and easier to maintain. ICWs consistently Site investigation works were carried out in September 2005. deliver better quality effluent than reed-bed wetlands due to Ground vulnerability maps prepared by the Geological Survey their long retention time (90–100 days). Where there are of Ireland (GSI) indicated that the site was located in an area of environmental constraints in the local receiving waters, an ICW low vulnerability to groundwater contamination. A planning can be designed to have zero discharge to the local waters. An application was submitted to MCC on 8 July 2005 and planning ICW comprises a diversity of plant species, facilitating permission was granted on 5 September 2005 of the same year. microbial and animal diversity, and is generally appealing for A land lease agreement was signed with the Trustees of Castle recreation and amenity. Due to the slow movement of water Leslie in September 2006 at an initial cost of J233 000 through the ponds, suspended matter is deposited and there is adequate time for both aerobic and anaerobic digestion of organic matter. ICWs also demonstrate good reduction of nitrates and phosphates (generally greater than 95%). Reduction of faecal indicators is of the order of 99% due to the long retention times and the complex ecology of the aquatic system. Furthermore, ICWs also remove endocrine disrupters such as oestrogen and testosterone, which are poorly removed in conventional wastewater treatment systems. An ICW effectively creates the important nexus between quality, quantity and amenity in a way that no other traditional sewerage treatment works can.

In rivers, phosphates are the controlling pollutants. High levels of phosphates create algal blooms, which deplete oxygen levels and kill fish and invertebrates. The level of molybdate reactive phosphorus (MRP) set out in the consultation paper on Figure 2. Aerial photograph of the Glaslough ICW site Environmental Objectives (Surface Water) Regulations 2008 in

200 Municipal Engineer 162 Issue ME4 Sewerage treatment in an integrated constructed wetland Doody et al. Pond 1

Discharge Mountain Water River to river

Pond 5

Sludge Sludge Pond 2 pond 1 pond 2 Stream diverted around edge of site Pumping station

Incoming raw sewage

Pond 3

Pond 4

Stream diverted around Stream edge of site

Figure 3. Layout of Glaslough ICW

(including legal fees) and a nominal annual fee thereafter. Six 6. SITE CLEARANCE, CONSTRUCTION piezometers were installed (using a hydraulic excavator) to AND PLANTING allow groundwater around and under the wetland system to be The chosen site, within the estate walls and straddling the monitored. Mountain Water River, presented a number of construction difficulties – not least being the felling of trees and removal of Tender drawings and documents were prepared by MCC and tree roots within the affected area. A tree survey was carried out advertised in the national press and the internet on 29 September during April 2005 and a tree-felling licence was granted to 2005. The tender documents were not comprehensive in that the Castle Leslie Estate by the Department of Agriculture on 13 May extent of the riding trails to be provided was still under 2005. The majority of good-quality trees adjacent to the estate negotiation with Castle Leslie. Likewise, requirements for walls and the river were retained. sampling and monitoring equipment were still being considered. Furthermore, subsequent to tender, an opportunity arose to secure Tree felling commenced in September 2005 and commercial approximately 5000 m3 of boulder clay material from construc- timber was stockpiled for use or sale by Castle Leslie. A tion works on the nearby N2 bypass of Monaghan town. This hydraulic wood-chipping machine was of limited success in allowed the area of the initial receiving ponds to be raised and dealing with tree roots. Roots and wood debris were subse- avoided secondary pumping across the Mountain Water River. quently stockpiled on site, creating a wildlife habitat. When the

Municipal Engineer 162 Issue ME4 Sewerage treatment in an integrated constructed wetland Doody et al. 201 lease was signed, earthworks commenced in October 2006 and, following a winter break, continued through 2007. Figure 4 shows the earthworks completed for pond 5.

Planting of a variety of wetland species commenced in November 2006 and continued through 2007. During dry spells water was pumped from the river to prevent the plants drying out. Figure 5 shows the completed pond 5. The ICW system was commissioned on 26 October 2007. Finishing works (including hardcore surfacing of riding trails) were completed during 2008.

7. SAMPLING AND MONITORING There is concern about the ability of clay liners to prevent infiltration into the subsoil and groundwater. The macrophytic Figure 6. Installing a lysimeter vegetation used in the ICW design essentially performs a variety of functions. Its primary function is the support of biofilms (slime layers) that carry out the principal cleansing functions of measure the vertical flow rate from the pond and provide a the wetland; it also facilitates the sorption of nutrients, acts as a sample of the liquid percolating into the subsoil. filter medium and, through the use of appropriate emergent vegetation, can control odours and pathogens. Biofilms seal the While the ICW concept is essentially a low-tech and low- interstices in the hydrated clay liner. To check percolation from maintenance system of water cleansing, the ICW at Glaslough a pond into the subsoil, a device called a lysimeter was includes a substantial suite of hi-tech sampling and monitoring developed as part of the ICW project in Waterford. A lysimeter equipment was installed under each pond in Glaslough (Figure 6) to (a) computer-linked Siemens Magmeters record all significant flows into, within and out of the wetland system (b) the Magmeters are linked to automatic samplers that sample the liquid as it progresses through the system (c) eight lysimeters installed before construction of the wetland ponds give an ‘upper-limit’ indication of infiltration through the subsoil (site investigation work in September 2005 indicated a soil coefficient of permeability of 9?07211 m/s) (d) a computer-linked weather station is located beside the inlet pump sump (e) six piezometers allow monitoring of the groundwater around and under the wetland system.

8. AS-CONSTRUCTED LAYOUT As stated earlier, the land take is some 6?74 ha while the water Figure 4. Pond 5 (May 2007) surface of constructed ponds covers 3?25 ha. The design capacity is 1750 pe, with a current load of approx 800 pe. No pre-treatment is carried out. The influent is pumped directly to a receiving sludge pond (the ICW contains two receiving sludge ponds that can be used alternately to allow for desludging when required). Thereafter, the liquid flows by gravity through five sequential vegetated ponds and the effluent discharges directly to the Mountain Water River.

Refinements to the original layout (Figure 3) included the following.

(a) The Glaslough Stream, which originally flowed through the site, was diverted (and substantially widened) around the perimeter of pond 4, with the excavated material being used to construct the banks of the pond. By slowing the flow in the stream and planting with wetland plants, an improve- ment in water quality in the stream (which is otherwise independent of the wetland system) will be achieved. Figure 5. Pond 5 (November 2008) (b) A dam was constructed upstream with a valved and metered

202 Municipal Engineer 162 Issue ME4 Sewerage treatment in an integrated constructed wetland Doody et al. Cost 9. CAPITAL COSTS J Item ( incl. VAT): The total capital cost of providing and constructing the Land lease (incl. legal fees) 233 000 Glaslough ICW (including land lease and monitoring equipment) was J770 000 including value added tax (VAT) (see Table 1). In Site works addition, MCC has entered a contract with Edinburgh University Preliminary items (site survey, tree survey, 27 000 to provide one full-time and one part-time PhD student (under aerial photos, site investigation, tree clearance. the direction of Dr Miklas Scholz) to conduct research on the etc.) J Earthworks, pipework and planting 206 000 project at a total cost of some 165 000 over three years. Hardcore riding trails 115 000 2 No. footbridges 35 000 10. RESULTS Monitoring Early results for Glaslough ICW are summarised in Tables 2 and Communication ducting, manholes etc 48 000 3 and in Figures 7, 8 and 9. These are very encouraging, with Broadband connection 4 000 effluent quality during the first year of operation consistently Lysimeters 3 000 matching the quality of the receiving Mountain Water River. Siemens Magmeters & samplers 90 000 The system can robustly cope with large variations in volumetric Weather station 2 000 Marker posts and signs 3 000 and BOD loadings of the influent. Piezometers 4 000 Total 770 000 11. COMPARISON OF TWO RECENTLY CONSTRUCTED TREATMENT PLANTS Table 1. Capital costs of Glaslough ICW In 2007/2008, two wastewater treatment plants were constructed in North Monaghan. The plant at Emyvale is an upgrade of an existing plant using a conventional treatment system for a pipeline installed to link with pond 3. This allows the pe of 2000. The Glaslough plant uses the ICW system for a pe of wetland system (ponds 3, 4 and 5) to be kept hydrated in 1750. Table 4 shows performance results from the two plants, prolonged dry spells when the volume of influent could taken in June to August 2009. evaporate before reaching the outfall. (c) A valved and metered pipeline was installed linking pond 3 The estimated cost of a traditional treatment facility of 650 pe back into the inlet pump sump. This allows partially treated capacity for Glaslough was J1 530 000 at 2008 prices. The final liquid to be re-circulated through the system and is the cost of the Glaslough plant was J770 000, including monitoring subject of further study. equipment costs (for additional research and development) and

ICW Glaslough

UWWD*: mg/l Influent: mg/l Effluent: mg/l Removal efficiency: %

Biochemical oxygen demand (BOD) 25 837 5 99 Chemical oxygen demand (COD) 125 1179 37 97 Suspended solids (SS) 35 2544 9 99 Total nitrogen (N) 15 43?36 1?69 96 Total phosphorus (P) 2 7?91 0?31 96 Ammonium — 34?04 0?34 99 Nitrates — 9?81 0?19 98 Molybdate reactive phosphorus (MRP) — 4?28 0?04 99

*Urban Waste Water Directive4

Table 2. Performance of ICW Glaslough (February 2008 to August 2009)

ICW Glaslough Mountain Water River

Influent: mg/l Effluent: mg/l Upstream: mg/l Downstream: mg/l

BOD 837 5 4 3 COD 1179 37 35 34 SS 2544 9 11 9 Total N 43?36 1?69 1?87 1?93 Total P 7?91 0?31 0?14 0?13 Ammonium 34?04 0?34 0?51 0?48 Nitrates 9?81 0?19 0?95 0?95 MRP 4?28 0?04 0?08 0?08

Table 3. Quality of receiving watercourse as of February 2008 to August July 2009 (upstream/downstream meaning from discharge point of wetland)

Municipal Engineer 162 Issue ME4 Sewerage treatment in an integrated constructed wetland Doody et al. 203 14.0 Total phosphorus Molybdate reactive phosphorous 12.0

10.0

8.0

6.0

4.0 Phosphorous: mg/l 2.0

0.0 Area: % 00.9 15 29 68 96 100

Area: m2 0 285 4949 9449 22109 31279 32739

Input Pond 1 Pond 2 Pond 3 Pond 4 Pond 5 Output Figure 7. Phosphorous concentration/reduction with cumulative wetland area at Glaslough ICW (values and standard deviation shown, n 5 27–36)

BOD _ COD n=25 37 8000 TSS 7000

6000

5000

4000

3000

Concentation: mg/l 2000

1000

0 Area: % 00.9 15 29 68 96 100

Area: m2 0 285 4949 9449 22109 31279 32739

Input Pond 1 Pond 2 Pond 3 Pond 4 Pond 5 Output Figure 8. The effect of cumulative wetland area on biological oxygen demand (BOD), chemical oxygen demand (COD) and total suspended solids (TSS) at Glaslough ICW (values and standard deviation shown, n 5 25–37)

50 _ 0.9 Ammonia n=35 37 _ . 45 Total oxidised nitrogen n=4 7 0 8 . 40 0 7 0.6 35 0.5 30 0.4 25 0.3 20 0.2 15 . Ammonium: mg/l as N 0 1 10 0.0 Total oxidised nitrogen: mg/l as N 5 _0.1 _ 0 0.2 Area: % 00.9 15 29 68 96 100

Area: m2 0 285 4949 9449 22109 31279 32739

Input Pond 1 Pond 2 Pond 3 Pond 4 Pond 5 Output Figure 9. The effect of cumulative wetland area on ammonia and total oxidised nitrogen at Glaslough ICW (values and standard deviation shown)

the cost of additional amenities including the surfacing of horse 12. ICW BIODIVERSITY AND AMENITY riding trails (Figure 10). Compared with a traditional treatment The shallow emergent vegetation (and stable food supply) of the facility, the ICW thus provides approximately three times the pe wetlands provides an ideal habitat for microbes to thrive. The capacity at half the price. The cost of upgrading the Emyvale plant long residence time (of the order of 80 days in Glaslough; indeed to a design of comparable capacity (pe of 2000) was J1 400 000. in dry spells there is no surface discharge at all) allows ample

204 Municipal Engineer 162 Issue ME4 Sewerage treatment in an integrated constructed wetland Doody et al. Glaslough ICW Emyvale

Effluent to Removal Removal Influent: mg/l river: mg/l efficiency: % Influent: mg/l Effluent: mg/l efficiency: % UWWD*: mg/l

Total N 46?60 1?42 97?073?75 16 78?015 Ammonia 37?83 0?29 99?210?70 2?70 75?0— Nitrates 8?15 0?33 96?06?15 10?00 — — Total P 7?33 0?03 99.6 3.32 1.63 51 2 MRP 5?02 0?01 99?86?00 4?99 17?0— COD 1377 47?14 96?6 687 86 87?5 125 Total SS 4542 2?48 99?9 231 30?44 87?035 BOD 1147 5?12 99?6 389 25?594?025

*Urban Waste Water Directive4

Table 4. Comparative results of the performance of a conventional treatment system for a pe of 2000 (Emyvale) and the Glaslough ICW for a pe of 1750 (June–August 2009)

(a) leachate (from landfills) (b) sewage and drinking water sludges (c) drinking water source protection (d) flood amelioration and sustainable drainage systems (SuDS).

This work was presented at a joint meeting of ICE and Engineers Ireland in November 2008 in Dublin. Further information on ICWs is available in the literature.1,5

ACKNOWLEDGEMENTS The participation of Monaghan County Council (for supporting the project), Sammy Leslie (Castle Leslie), Dr Miklas Scholz (University of Edinburgh), Eamon Sherry (Contractor), Aila Carty (VESI Environmental), and Paul Carroll and Sue Cook (Waterford County Council ) is noted in the Castle Leslie ICW Figure 10. Horse riding trails around the ponds of project. Glaslough ICW REFERENCES 1. See http://www.dublincity.ie/WaterWasteEnvironment/ time for the necessary aerobic and anaerobic processes to occur WasteWater/Pages/SustainableDrainageSystems(SuDS) and insulates the wetland system from the effects of shock andIntegratedConstructedWetlands(ICW).aspx (accessed 30/ loadings that would overwhelm a traditional plant. Although a 09/2009). fascinating, vital and little understood realm, the microbial 2. MILLER S. Scientist uses nature for waste treatment. The world is beyond the scope of this paper. Sunday Times, 31 August 2003, Section 1, p. 11. 3. See http://www.environ.ie/en/Environment/Water/ The large footprint area required is sometimes quoted as a WaterQuality/ConsultationDraftSurfaceWaterRegulations/ downside of ICWs. However, in Glaslough, the amenity value of FileDownLoad,18286,en.doc (accessed 30/09/2009). the affected area has been greatly enhanced and complements 4. EUROPEAN UNION. The Urban Waste Water Treatment the tourist-based activities of Castle Leslie and the equestrian Regulations, 2001 (S.I. 254 of 2001), dated 14 June 2001 and centre. The detritus in the beds of the ponds provides a amended on 15 July 2004. The original Regulations EU storehouse of carbon, phosphorus and other nutrients. Council Directive 91/271/EEC of 21 May 1991. 5. SCOTTISH ENVIRONMENTAL PROTECTION AGENCY. Constructed Farm Extensive monitoring work being undertaken at Glaslough ICW Wetlands Design Manual. See http://www.sepa.org.uk/land/ will help promote the ICW concept and its application to a range land_publications.aspx for further details (accessed 30/09/ of water-quality management issues such as 2009).

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