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Cases > Equipment and Engineering > Geotube Technology
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Geotube Technology
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Case Study - Field Examination of a Dewatering, Volume Reduction, and Contaminant Reduction Solution for Animal Slurry
With the implementation of existing and impending legislation under the Nitrates Directive and IPPC legislation, the current scenario where slurry is spread directly to land will be severely restricted going forward.
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| Due to an over-abundance of phosphorus in Irish soil and groundwater, the derogation restricting the amount of phosphorus nutrient that can be spread to land is due to be implemented in 2010. This will seriously restrict the availability of Irish land banks for conventional slurry spreading, while also drastically increasing the costs of spreading slurry in Ireland. In addition, reduction of phosphorus losses from grassland is a requirement under the Water Framework Directive, which will also impose restrictions in relation to where slurry can be spread. |
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| If operations within the agricultural sector do not have an economic alternative for dealing with animal slurry, their ability to operate and expand will be severely curtailed. In view of this concern facing the agricultural sector, environmental solutions provider, Enva were approached by RJ Mooney Ltd (who had already began looking at sourcing potential methods of overcoming this issue) to assist in the development and integration of a potential solution. |
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Following on from trials conducted in 2005 /06 at Teagasc Grange and Teagasc Moorepark, an on-site study was initiated at the McCrea farm in Cookstown, Co. Tyrone in August 2007. The overall aim of this study was the production of a solid free liquid organic fertiliser, with little or no phosphorus content, and a dewatered solid fraction that can be stored and transported away from the farm if necessary.
The McCrea farm operates a pig unit with 750 sows and 4,000 weaners to 35kgs. This generates up to 18m³ per day of pig slurry, which needs to be stored on-site and spread during the months of February to October in accordance with the Nitrates Directive limits of 170 kilos of organic nitrogen per hectare.
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Solution Details
The solution being examined needed to consist of two main constituents; mixing and treatment, and dewatering.
Through its research and engineering functions, Enva set about designing and manufacturing a mobile dewatering unit specifically for this application, as well as specifying and sourcing a range of necessary support equipment. These included batch and continuous polymer make-up systems, a coagulant dosing system for coagulation and phosphorus removal, a submersible pump for transferring and re-circulating the pig slurry, a control panel, and all necessary pipe-work.
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| Geotube® Technology was then evaluated in terms of allowing dried solid and liquid separation. |
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| It offers a low-cost high-volume dewatering solution, which is used worldwide for the dewatering of various different types of sludge, in such industries as pulp and paper, power generation, mining and mineral processing, and water and wastewater. |
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| The first stage in putting together a suitable solution involved mixing and treating in order to reduce contaminant levels. Mixing was required to remove gases such as hydrogen sulphide and methane from the slurry, while chemical addition was minimised to allow successful coagulation (change into a thickened mass) and flocculation (separating the solid from the solution) further on in the process, as well as successful phosphorus removal for this particular application. |
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| This treatment generated a low solid content liquid, with significant contaminant level reductions, and which is commonly referred to as organic fertiliser. Laboratory tests showed the following results: |
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98.5% reduction in total phosphorus. |
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95.4% reduction in biological oxygen demand. |
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95% reduction in suspended solids. |
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94.4% reduction in chemical oxygen demand. |
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60% reduction in total nitrogen. |
| As can be seen from these results, this liquid has a high total nitrogen value and a low total phosphorus value, which therefore make it ideal for land-spread. Recent studies carried out by the Irish EPA recommend that effluent displaying the above characteristics seems far more suitable for land-spread in comparison to conventional slurry. This is due to the significant overall reduction in pollutant matter, and the easier overall uptake by the soil due to the lower solid content of the effluent. |
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Geotube® Technology
Geotube® Technology provides an ideal high volume low-cost solution specifically designed for liquid solid separation in remote areas. The Geotube® bag comprises of a geo-synthetic moulded plastic, with fine membrane pores, which allow excess liquid to drain through the small pores and into the receiving tank. Several types of Geotube® bags are available, and are manufactured in various widths and lengths to be custom utilised for solids separation.
A number of key attributes make it an ideal technology for the agricultural sector. These include:
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Low capital costs. |
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No moving parts, such as belts or gears, etc. |
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Hydraulic capacity as well as a dewatering mechanism. |
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Bags can vary greatly in size and capacity. |
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Unlike a lot of substitute technologies, it does not have high maintenance costs or very high depreciation costs. |
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It is easily/simply run when installed and does not require extensive supervision when operating. |
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Low running chemical costs as it is not a moving/spinning dewatering device. |
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By storing the sludge (can be up to 20+ years), Geotube® reduces capital costs on storing dewatered material, while also significantly reducing the risk of cross contamination by insects back to the herd. |
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No electrical costs required to run its technology. |
| Slurry entering the Geotube® bag had an average dried solid content of 3.7%. After 48 hours, this had increased to 17% on average dried solids, with the expected figure after six months to be 25%. The Geotube® bag prevents moisture entering the bag, even in periods of heavy rainfall. |
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| Subsequent dry solids tests were completed on a Geotube® bag in-situ at Teagasc in Moorepark, Co. Cork, whereby the solids were left in a Geotube® bag for six months. All final dry solids and bacteriological tests were carried out on this bag, which found dry solids at 25%.This represents over an eight fold reduction in dry solids over the lifetime of the bag, and is in alignment with previous research papers done on Geotube® Technology. The bag itself can last between 20 to 50 years on-site when filled. |
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| Jar tests showed the average removal of: |
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65% of total ammonia. |
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Up to 60% of total nitrogen (previous research on Geotube® indicates that this can vary between 40 and 60%). |
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55% of potassium. |
| Based on the performance of the bag during the case study, and with relevant mixing, Enva have undertaken to guarantee the bag to remove a minimum of 95% dried solids for over a commissioning period of 21 days before handover. |
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| The results outlined in this case study show that this solution can provide an efficient and high volume solution for dealing with animal slurry, while facilitating compliance with existing and impending legislation under the Nitrates Directive, IPPC legislation, and the Water Framework Directive. |
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| Combined with Enva’s expertise in effluent treatment, dewatering through Geotube® technology can become a passive event creating options and opportunity for operations within the agricultural sector. This solution also offers a more cost-effective and less technical system than other conventional dewatering mechanisms, and is the most suitable solution for the agricultural sector in terms of capital cost, revenue cost, technical input, storage requirements, depreciation and maintenance costs and labour input. |
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