On-site wastewater treatment: investigation of rapid percolating subsoils, reed beds and effluent distribution

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Resource or Project Abstract

The safe disposal of on-site wastewater is essential for the protection of both groundwater and surface water resources in Ireland. This project reports the results from field trials carried out on three separate sites investigating the attenuation of chemical and microbiological pollutants in domestic wastewater through relatively fast percolating subsoil and also through reed bed treatment systems. In addition, the distribution performance of several different devices designed to split the on-site effluent evenly across the percolation areas was evaluated. Two sites with single houses were chosen with relatively fast percolating subsoil conditions, Site A in County Kildare with T-value of 3.7 and Site B in County Wicklow with T-value of 4.5. The on-site wastewater effluent was treated by a septic tank on Site A and secondary treatment RBC package plant on Site B and then the respective effluents split into two whereby half discharged into a standard percolation area on each site and the other half discharged to horizontal subsurface treatment reed beds. Samples of the respective effluents percolating through the subsoil were collected at different depths beneath the percolation areas for more than two year trial periods as well as monitoring the treatment performance of the reed beds alongside. A third site, Site C in Wexford, was also monitored to investigate the performance of packaged reed bed modules receiving secondary treated effluent. The results showed that higher permeability subsoil acted to reduce the biomat lengths and thus increase the areal effluent loading rate on the percolation areas. The effluent in the trenches receiving septic tank effluent was spread over a biomat length of roughly 10 m compared to the biomats in the percolation trenches receiving package plant secondary treated effluent which were considerably shorter and did not extend beyond 0.5 m. In general, however, the septic tank and percolation system provided a comparable treatment performance with respect to groundwater protection to the packaged secondary treatment system with the exception of nitrogen and viral indicators which underwent enhanced attenuation in the subsoil receiving septic tank effluent. The use of three different bacteriophage tracers (MS2, φX174, PR772) on the sites indicated that enteric viruses in on-site wastewater effluent are likely to be totally removed after a depth of 0.95 m of unsaturated subsoil underneath trenches receiving septic tank effluent. Some phage concentrations were still detected at this depth beneath percolation trenches receiving secondary treated effluent due to the much higher hydraulic loading - a result of muted biomat development. Although 0.95 m of unsaturated subsoil beneath the percolation pipes significantly reduced the enteric bacteria in both types of on-site effluent, there were isolated incidences of low concentrations of E. coli found in the subsoil on both sites at this depth. The horizontal flow subsurface reed bed receiving septic tank effluent was effective at reducing organic, suspended solids and bacteriological loads but not nutrients or the indicator viruses. The reed bed also acted to slightly enhance the hydraulic loading over the course of a year in an Irish climate. Equally, the tertiary treatment reed beds on Sites B and C achieved further polishing of the secondary effluent in terms of organics and enteric bacteria and some removal of nutrient loads. The microbiological quality of the final effluent however, still contained significant numbers of human enteric bacteria and high levels of phosphorus and the beds did not act to attenuate the bacteriophage indicator organisms to any significant extent. Finally, the investigation into distribution devices currently available in Ireland showed that they did not distribute the effluent effectively under real wastewater loading conditions from single houses. The on-site results suggested that the uneven deposition and biofilm growth were responsible for erratic distribution and therefore the long-term performance and sustainability of such devices is questionable for such a function where regular maintenance is rarely carried out by house owners. However, a low-head gravity distribution device has been designed during the project which proved to operate effectively under such low intermittent flow rates of varying effluent quality. Finally the wastewater generation in the three sites was much lower than the EPA guidance value of 180 litres per capita per day: a value of 150 L c-1 d-1 would seem to be a more reasonable design figure.

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Contact Information for This Resource

Mr. Laurence Gill
Department of Civil, Structural & Environmental Engineering

Mr. Paul Johnston
Trinity College Dublni

Mr. Bruce Misstear
Department of Civil, Structural & Environmental Engineering

Mr. Niall O'Luanaigh
Trinity College Dublin

Mr. Titiksh Patel
Trinity College Dublin

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Data, Files, Information Objects Related To This Project Resource

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Attachment Name and Download Link
Project Report Optimised For Online Viewing    STRIVE_28_Gill_onsiteWWT_epr_web.pdf  (18.65 Mb)
Offline Print Quality Version    STRIVE_28_Gill_onsiteWWT_syn_prn.pdf  (6.34 Mb)
Project Report Optimised For Online Viewing    STRIVE_28_Gill_onsiteWWT_syn_web.pdf  (1.19 Mb)
Att 4    Flows_(Site_A).xls   (0.78 Mb)
Att 5    Flows_(Site_B).xls   (0.05 Mb)
Att 6    Flows_(Site_C).xls   (0.07 Mb)
Att 7    Chem_&_Micro_results_(Site_A).xls   (0.65 Mb)
Att 8    Chem_&_Micro_results_(Site_B).xls   (0.21 Mb)
Att 9    Chem_&_Micro_results_(Site_C).xls   (0.07 Mb)
Att 10    Effective_Rainfall_(Site_A).xls   (0.93 Mb)

Suggested Citation Information

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Author(s)Gill, L. Johnston, P. Misstear, B. O'Luanaigh, N. Patel, T.
Title Of WebsiteSecure Archive For Environmental Research Data
Publication InformationOn-site wastewater treatment: investigation of rapid percolating subsoils, reed beds and effluent distribution
Name of OrganisationEnvironmental Protection Agency Ireland
Electronic Address or URL http://erc.epa.ie/safer/resource?id=7cd68383-a2fd-102c-9c91-0a68ec663af0
Unique Identifier7cd68383-a2fd-102c-9c91-0a68ec663af0
Date of AccessLast Updated on SAFER: 2018-05-27

An example of this citation in proper usage:

Gill, L. Johnston, P. Misstear, B. O'Luanaigh, N. Patel, T.   "On-site wastewater treatment: investigation of rapid percolating subsoils, reed beds and effluent distribution". Associated datasets and digitial information objects connected to this resource are available at: Secure Archive For Environmental Research Data (SAFER) managed by Environmental Protection Agency Ireland http://erc.epa.ie/safer/resource?id=7cd68383-a2fd-102c-9c91-0a68ec663af0 (Last Accessed: 2018-05-27)


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Access Information For This Resource

SAFER-Data Display URL http://erc.epa.ie/safer/iso19115/display?isoID=117
Resource KeywordsReed beds, percolation, subsoils, effluent, distribution devices, viruses, septic tanks, nitrogen, phosphorus
EPA/ERTDI/STRIVE Project Code2005-MS-15
EPA/ERTDI/STRIVE Project ThemeWater Quality
Resource Availability: Any User Can Download Files From This Resource
Limitations on the use of this ResourceAttachments (if any) connected to this resource can be used in journal article or other means of publication provided the original authors are informed of this usage and an appropriate acknowledgement or citation is included within the published article. The EPA advise that this acknowledgement should take one of the following forms dependent upon how heavily the published work relates to the downloaded report: * Co-Authorship(s) for the original author(s)* Written acknowledgement within the body of the article* Written acknowledgement by means of the inclusion of a bibliography entry which clearly cites the original authors. The EPA as a/the primary funder of the research should be acknowledged.
Number of Attached Files (Publicly and Openly Available for Download): 10
Project Start Date Friday 1st April 2005 (01-04-2005)
Earliest Recorded Date within any attached datasets or digital objects Monday 10th April 2006 (10-04-2006)
Most Recent Recorded Date within any attached datasets or digital objects Friday 13th June 2008 (13-06-2008)
Published on SAFERFriday 5th June 2009 (05-06-2009)
Date of Last EditThursday 26th November 2009 at 08:30:04 (26-11-2009)
Datasets or Files Updated On Thursday 26th November 2009 at 08:30:04 (26-11-2009)

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Geographical and Spatial Information Related To This Resource

Description of Geographical Characteristics of This Project or Dataset
The project investigated three seperate sites consisting of a single house with on-site wastewater treatment system: (1) Kilrainy, Co. Kildare (2) Redcross, Co. Wicklow (3) Riverchapel, Co. Wexford. See bounding boxes below for a map of the locations.

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Supplementary Information About This Resource

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Lineage information about this project or dataset
This project is a stand-alone project on three new sites but follows on from the previous MS-15 project (2000-2004) which condidered 4 separate sites. The work feeds into the Code of Practoce for Single House Wasetwater Treatment Systems. The link to the previous work is also available on SAFER.
Supplementary Information
The following is a summary of the technical characteristics of the project:

Flow; chemical water quality (BOC, COD, NH3, NO2, NO3, Total-N, org-N, ortho-P, Cl, pH); microbiologcal water quality (Total coliforms, E.col, MS-2 phage, X174 phage, PRD1 phage); pore water pressure; meterological variables (precipitation, temperature, wind speed & direction, humidity, solar radiation). N15 isotopes were also measured for nitorgen cycling trials in the reed beds. Rhodamine concs were also measured using fluorometers fro RTD studies on reed beds. X-ray diffraction analysis was used to investigated the minerology of the subsoil. Note, all details of sampling and analysis techniques are contained in the final report.
Links To Other Related Resources
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