Increasing the Productivity of Salt through HDPE Geomembrane— Indonesian Case History in Salt Evaporation Pond Andryan Suhendra Lecturer of Civil Engineering Bina Nusantara University, Indonesia e-mail: [email protected] ABSTRACT In Indonesia, the application of HDPE geomembrane is generally for waste liners such as industrial waste, hazardous waste, landfill etc. A new application of HDPE geomembrane in Indonesia is as a liner for salt evaporation ponds introduced on 2011. For the initial phase of the trial, as many as 25 percent of the total area of 406 ha salt evaporation ponds were to be covered using 20 mil HDPE geomembrane. The trial showed that the area covered by HDPE geomembrane had its productivity increased to 460 percent. After 1 year (2012), the numbers suggest that productivity of the salt evaporation ponds with HDPE geomembrane was almost double of ones without. The lifetime of HDPE geomembrane of more than 10 years (HDPE geomembrane can be used repeatedly) added to the benefit. It can be concluded that HDPE geomembrane application in salt evaporation ponds provide many benefits and positive impact on productivity increment of salt, so the officials extended the project in subsequent years. This paper will present a case history of HDPE geomembrane application in salt evaporation ponds located at Madura island, East Java Indonesia and will cover the technical aspects of the project i.e. site condition, technical criteria of HDPE geomembrane, installation process, and productivity of ponds with and without HDPE geomembrane. KEYWORDS: HDPE Geomembrane, Salt Evaporation Pond, Productivity INTRODUCTION Madura Island is the largest salt producer in Indonesia, located at northeastern coast of Java and part of East Java Province. Madura Island has a unique characteristic, with longer dry seasons and limited river and fresh water source, making the Madura Island an area of good quality and largest producer of salt in Indonesia. Mostly the salt production is carried out by independent farmer since the 19th century using conventional methods; therefore the productivity of salt is low. The farmers would drain the sea water to the salt farm/pond through channel by pump or due to high tide, then the water was left for evaporation process. After 25 – 28 days of evaporation process, the salt crystals are transferred to the salt table for drying process. The drying process will take 4-10 - 4273 - Vol. 21 [2016], Bund. 11 4274 days depending on the weather conditions (Prijono, 2013). When using conventional methods, the farmer could produce and harvest the salt three times a year. PT Garam is a state-owned salt producing and marketing firm, which has 5700 hectares of land in the districts of Sumenep, Pamekasan and Sampang on Madura Island, used for salt production. Since 2012, the government has provided several hectares plot of land for trial to increase salt production on Madura Island. After detailed studies, the geomembrane then was chosen to be applied on several ponds (Figure 1) and in year 2012 about 115 hectares of evaporation ponds were be covered by geomembrane, then the productivity of salt ponds with and without geomembrane was evaluated and discussed as presented in this paper. Figure 1: Layout of salt evaporation ponds The area range of a pond varies from 800 m2 to 2000 m2 with typical cross section as shown in Figure 2. Vol. 21 [2016], Bund. 11 4275 Bamboo Mattress HDPE Geomembrane Figure 2: Typical cross section of pond with geomembrane GEOMEMBRANE MATERIAL Geomembrane is a very low permeability synthetic liner, usually made from synthetic polymer i.e. Polyethylene (PE), polypropylene (PP), or Polyvinyl Chloride (PVC). The main criteria of geomembrane as a liner in salt evaporation ponds are durability, economic value and resistance to degradation by chemical, biological and Ultra Violet. There are some accepted publication that Geomembrane application in the exposed environment such as at salt ponds has a shorter lifespan compared to the buried or covered environment due to adverse degradation mechanisms such as rich natural presence of oxygen, UV degradation from photo-oxidation and increase temperature degradation due to thermo-oxidation (Rowe et. al. 2002, Koerner et. al. 2012, Denis et. al. 2013). Carbon black and antioxidants are the additives which are generally used to retard and inhibit the UV degradation and temperature degradation of Geomembranes (Denis et. al. 2013). HDPE geomembrane that includes by carbon black and antioxidants additives was chosen to be applied in this project. The HDPE geomembrane had to fulfill the requirements as shown in Table 1. Vol. 21 [2016], Bund. 11 4276 Table 1: Requirement of HDPE Geomembrane properties No. Properties Test Method Unit Required Value 1 Colour - - Black 2 Thickness ASTM D5199 mm 0.5 3 Density ASTM D1505 gr/cm2 >0.93 4 Tensile Properties ASTM D6693 -Strength at Yields kN/m 8 – 9 -Strength at Break kN/m 14 -Elongation at Yields % 13 -Elongation at Break % 700 5 Tear Resistance ASTM D1004 N >65 6 Carbon Black Content ASTM D1603 % 2 – 3 INSTALLATION PROCESS The total area to be covered by HDPE geomembrane during 1 period of the project in year 2012 was about 900,000 m2. A team of 4 technicians and 10 local labours to enable the rate of geomembrane installation of about 15,000 m2 per day and the installation of geomembrane was to be completed within 2 months barring any complications during the installation. The process of the HDPE geomembrane installation was carried out like a common practice of geomembrane installation, started by delivering the HDPE geomembrane rolls to the nearest ponds location using heavy equipment like excavator or bulldozer (see top left picture in figure 3). To unroll the HDPE geomembrane, a simple tool is used with the assistance of human power as shown in top right picture in figure 3. The bottom pictures of figure 3 show the process of laying and seaming of the HDPE geomembrane panels. Vol. 21 [2016], Bund. 11 4277 Figure 3: Installation Process of HDPE Geomembrane The main constraints during the HDPE geomembrane installation were rains and wind. The works had to wait until the rain stopped, pump the inundated ponds from rain water and put some sand-bags on the HDPE geomembrane panels to keep it from blowing out (see figure 4). a. The HDPE geomembrane panels blow out by wind b. Pumping process Figure 4: The constraints and its solution during installation process of HDPE Geomembrane Vol. 21 [2016], Bund. 11 4278 EVALUATION OF HDPE GEOMEMBRANE PERFORMANCE TO SALT PRODUCTIVITY The evaluation of the HDPE geomembrane performance was carried out by comparing the productivity of salt evaporation ponds with and without HDPE geomembrane for 3 different sections. The prediction of salt ponds productivity in case of the whole area covered with HDPE geomembrane was also carried out to show the potential difference it could make. Table 2 shows the production of ponds with and without HDPE geomembrane during year 2012 in real condition, and table 3 shows the comparison between no liner and if all ponds were covered by HDPE geomembrane. Table 2: Comparison of ponds productivity in real condition Section Soil Table Geomembrane Table Area (ha) Productivity (t/yr) Area (ha) Productivity (t/yr) 1 150.00 33.305 62.00 85.220 2 62.93 26.846 27.07 37.864 3 77.70 25.654 26.30 25.241 Total 290.63 85.805 115.37 158.325 Table 3: Comparison of the productivity of all the ponds combined with and without HDPE geomembrane *) Section Soil Table Geomembrane Table Area (ha) Productivity (t/yr) Area (ha) Productivity (t/yr) 1 212.00 47.071 62.00 291.397 2 90.00 38.394 27.07 125.887 3 104.00 34.337 26.30 139.356 Total 406.00 119.802 115.37 556.640 *) The productions are determined by linier interpolation per each section Note for table 2 and 3: - Soil table: salt pond without HDPE Geomembrane - Geomembrane table: salt pond with HDPE Geomembrane Figure 5 shows that the 25% of the area covered by HDPE geomembrane had their production increased becoming almost double that of 75% of the area without HDPE geomembrane. By interpolation, we can see that if the whole area covered by HDPE geomembrane, the salt ponds productivity will increase to about 460 percent. Vol. 21 [2016], Bund. 11 4279 Figure 5: Productivity of salt ponds The main reasons of this increase in production (the advantages of ponds with HDPE geomembrane) are: 1. The evaporation process are shorter, from 25 days of conventional system to 14 days with HDPE geomembrane. 2. The turnaround time is improved. 3. The harvest and the quality of salt is improved (contamination by subsoil can be avoided) 4. The long lifetime of HDPE geomembrane will reduce the preparation works. CONCLUSION REMARKS The application of HDPE Geomembrane on salt pond would increase the salt production in multiple compare to salt pond without HDPE geomembrane, therefore the application of HDPE geomembrane in salt ponds is expanded in subsequent years. ACKNOWLEDGEMENTS The research is supported by PT Tetrasa Geosinindo – Indonesia as a supplier and installer of HDPE Geomembrane and PT Garam – Indonesia as owner of the project. REFERENCES 1. Koerner R.M., Koerner G.R. and Hsuan Y.G. 2012. Lifetime Prediction of Laboratory UV Exposed Ge-omembranes: Part I - Using a Correlation Factor. GRI Report #42, Geosynthetic Institute, Folsom, PA, U.S.A Vol. 21 [2016], Bund. 11 4280 2. Magnetic Method Used In Geothermal Exploration in Ie-Seu ‘Um, Aceh Besar (Indonesia)” Electronic Journal of Geotechnical Engineering, 2015 (22.22) pp 12345- 12351. Available at ejge.com 3. M.M. Nordiana, Muhammad Syukri, Rosli Saad, Marwan Ebubakar, and Nur Aminuda Kamaruddin: “The Identification of Fault Zones in Krueng Raya, Aceh Besar (Indonesia) Using Magnetic Method” Electronic Journal of Geotechnical Engineering, 2014 (19.Z) pp 9331-9338.