POTABLE WATER FROM RAINWATER HARVESTING

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1 POTABLE WATER FROM RAINWATER HARVESTING Potential for Reuse in Seafood Processing Several fish processors have expressed an interest in potable water from rainwater harvesting. There are a number of key issues that must be considered in this case, and may be summarised as: 1) Regulation governing use of water in food preparation/processing (Dept. of Agriculture, Fisheries and Food. Food Safety Authority) 2) Volume of water available (roof area, rainfall) 3) Rainwater collection. Single or multiple storage points. 4) Rainwater treatment and storage 5) Quality control and quality assurance (incl. HACCP, S.I. No. 106 of 2007 European Communities (Drinking Water) Regulations Water testing. 6) Cost of installation and operation (payback on investment vs. continuing use of mains water only) 7) Planning Permission. Rainwater harvesting tanks may require planning permission. Objective: Size and cost a water treatment plant to produce potable water from the rainwater. Treatment Plant Sizing Storage capacity is based on plant demand and rainfall profile. Key parameters are the roof area and geographical location (see rainfall map). Above ground or underground storage, single storage point or multiple collection/storage locations influence cost. Figure 1: 1961 to 1990 mean annual rainfall in Ireland (Source: Met Eireann)

2 According to Met Eireann most of the eastern half of the country has between 750 and 1000 millimetres (mm) of rainfall in the year. Rainfall in the west generally averages between 1000 and 1250 mm. In many mountainous districts rainfall exceeds 2000mm per year. The wettest months, in almost all areas are December and January. April is the driest month generally across the country. However, in many southern parts, June is the driest. Hail and snow contribute relatively little to the precipitation measured. Sample Calculation Fish factory in South West Ireland Example roof dimensions: Flat roof 49,000mm x 22,000mm (1,078m 2 ) and the domed roof: 49,000mm x 13,000mm (637m 2 ). Total roof area = 1,715m 2 Table 1:Total rainfall in millimetres for 2010 at Valentia Observatory (source Met Eireann) Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Based on annual rainfall of 1,331.7mm for 2010 this meant that 2,283m 3 of rain fell on the factory roof. Not all of this 2,283m 3 is available for use. A more detailed analysis should consider variables including amount and intensity of rainfall, storage capacity, and yield. To calculate the potential collectable rainwater the following equation should be used 1 : W = (A x P x e)/ 365 Where: W = Average daily Collectable rainwater (m 3 ) A = Roof area (m 2 ) P = annual Rainfall (m) e = Yield coefficient For example: For a roof area of 1000m 2, with an annual rainfall of 1100mm the maximum daily collectable rainwater is: = (1000 x 1.1 x 0.81)/365 = 2.44m 3 or 2440 litres. So the minimum tank size required for this unit is 2440 x 7 = 17,080 litres and the maximum tank size is 43,920 litres. The actual size of the tank installed depends upon the water demand. In cases where demand is greater than supply, then the 1 S171 Minimum specification for rainwater harvesting equipment. Dept. of Ag. And Food; March 2011

3 tank size shall be towards the shorter storage period. There is no value in constructing a large tank to hold 18 days rainfall if the rainwater supply is only half or less of the actual demand. Using this equation W = (A x P x e)/ 365 W = (1078 x x 0.8) / 365 W = m 3 /d Therefore, based on current demand and the cost paid for water a cost benefit for the installation of an appropriately sized system can be completed. Note: Other potential catchment areas (process yards, car parks etc.) were not factored into this example. Capital Cost The cost can be broken down into two areas: i) Cost of collection and storage ii) Cost of treatment equipment Running Costs Depends partly on treatment technology(s) chosen (filtration, UV, chlorination, etc.). Energy costs associated with pumped distribution system. Quality Issues As rainwater may be contaminated, it is not considered suitable for drinking without treatment. Rainwater harvested from roofs can contain animal and bird faeces, mosses and lichens, dust, and other deposited pollutants. The highest concentrations occur in the first rain immediately after a dry spell. The concentration of contaminants is reduced significantly by diverting the initial flow of water to waste. Devices to achieve this are commonly known as 'firstflush' diverters, and are used to increase the chance that the large-particle residue that might accumulate on the collection surface is washed away from (and not into) the storage tank. Such a system also compensates for the fact that the initial minutes of a rainfall can include airborne pollutants being washed from the sky, and likewise minimizes contamination of the captured supply. Some Quality Issues: Risk assessment for food processing, part of HACCP. Bacteriological and viral contamination (bird and animal faeces). Deposition from boiler stacks (heavy metals, ph issues). Leaching from catchment area materials of construction (lead flashing, copper roofing etc.). Water quality standards (Drinking Water Regulations 2007). Testing regime.

4 Water Treatment Water will have to be treated to meet drinking water standards. It is envisaged that this may consist filtration for physical removal of suspended solids and chlorination and/or UV treatment for pathogen removal. Table 2: Some common uses for rainwater harvesting projects and associated treatments (source: Envirowise Guide EN896, Reducing Mains Water Use Through Rainwater Harvesting; Collecting A Valuable Free Resource And Reducing The Impact Of Runoff) WATER USE QUALITY REQUIRED TREATMENT OPTIONS Nurseries, sports grounds, gardens Toilet flushing Cooling (boilers) General cleaning Filter backwashing LOW: Water is not used for consumption, and there is a very low risk of contact. Water should look clean and be odour free. First flush diverted Coarse filter Laundry Cleaning of equipment or process cleaning Food processing Cleaning food processing equipment Substitute potable supply Water Testing MEDIUM: Water is not used for consumption, and there is a low risk of contact. Water must be clean and odour free, but not necessarily sterile. HIGH: Water may be used for consumption, water must be clean, odour free and sterile. All of the above, plus Fine filter (possibly membrane filter) All of the above, plus Pathogen removal and/or inactivation (eg UV treatment) There are up to 48 parameters to be tested in accordance with the Drinking Water Regulations Check samples are taken frequently but require a small number (13) of critical parameters to be tested. Audit samples are taken infrequently but are tested for the full range of parameters. Conclusion While the treatment of rainwater to potable standard is technically feasible, the cost of on-going analysis of the water for parameters specified in the Quality of Water for Human Consumption Regulations is a barrier. This cost is currently borne by the local authority in the mains water charge. The price paid for mains water significantly influences whether the capital cost of harvesting equipment and water treatment plant has an acceptable payback to the client.

5 Appendices SI 106 of 2007 (extract from Drinking Water Regs.) Point of compliance. 5. Subject to Table B in Part 2 of the Schedule, measurement of compliance with the parametric values specified in Part 1 of the Schedule shall be made in the case of (a) water supplied from a distribution network or a private source, at the point within a premises at which it emerges from the tap or taps that are normally used for the provision of water for human consumption; (b) water supplied by tanker or similar means, at the point at which it emerges from it; (c) water used in a food-production undertaking, at the point where the water is used in the undertaking.!

6 Rainwater Harvesting at IPPCL Facilities 1. In 2008 Shannonside Galvanizing, Drombana, Co. Limerick, actively practiced rainwater harvesting at its Plant (ref. AER 2008, EPA IPPCL No ). This collected water was used primarily in the cooling tank and process tanks. 2. Pfizer Ireland Pharmaceuticals, Dublin Sterile Operations (ref. AER 2009, IPPC Licence P ): Rainwater Harvesting Project: Investigate the potential for collecting rainwater on-site and re-using it as a supply of service water so as to result in the potential annual savings of approximately 22,000m3 of water.