Recycling of Water Background: Traditional wet processing, when properly managed, leads to a high quality product but also requires large volumes of water. Improper treatment of this waste processing water can cause contamination of waterways. Various modifications of the process have been introduced with a view to reducing contamination and also to limiting water consumption. Dry pulping followed by mechanical mucilage removal has been developed in Latin America with the Penagos technology. Recycling of water during the process is also one of the possible solutions to meet both objectives. Water consumption in selected coffee processing systems: Location Authors Process description Central America Colombia Kenya m 3 /t cherries PEICCE (1994) 1 Whole wet process 2 7.6 Zambrano & Zuluaga (1993) 2 Pulping Full washing 7.2 4.8 Mburu et al. Whole process 17 20 (1994) 3 Kenya* Finney (1989) 4 Pulping Colombia Merchán & Henao (1976) 5 Pulp discharge Pre-washing/grading Transportation to tanks Washing-Grading Soaking (*) Plant cleaning Total One-stage pulping Full washing 4.5 0.8 8.3 0.6 3.1 0.3 0.2 19.0 1.2 1 Proyecto energético delistmo centroamericano (PEICCE). 1994. Por un café limpio: guía para el uso del beneficiador de café. Comisión Europea. 2 Zambrano, F. & Zuluaga, V. 1993. Balance de materia en un processo de beneficio húmedo del café. 44(2) : 45-55. Cenicafé, Colombia. 3 Mburu, J.K., Thuo, J.T. & Marder, R.C. 1994. The characterization of waste water from coffee processing factories in Kenya. Kenya Coffee 59(690): 1757-1763. 4 Finney. 1989. Technologie du traitement du café arabica "fully washed": 2- Technologie de dépulpage,fermentation, et lavage. Café, Cacao, Thé 23 (2): 117-124. 5 Merchán, V. & Henao, U. 1976. Normas para el diseño de beneficiaderos de café. Avances Técnicos 58. Cenicafé, Colombia. * In this process, there is a first fermentation (dry) for 12 to 36 hours followed by a fermentation (under water) for 16-24 hours, with a washing between these two steps. Page 1 of 7
Schematically, considering the recycling of water, wet processing can be divided in two broad steps: A pre-fermentation step which includes receiving, washing, pulping, pre-washing/grading, transport to fermentation tanks and water from pulp discharge; A post-fermentation step which includes washing/grading, occasionally soaking and transport to pre-drying/drying tables. These intermediate steps refer to traditional wet processing and, more especially, to Kenyan processing. It is clear that some of these may not be relevant in some applications. Main considerations in water recycling: Design and operation of coffee processing plants involving water recycling must take into account the following considerations: It must comply with all water quality requirements It is easier to deal with solid by-products than waste-water Prolonged contact between water and solids increase the organic load in waste water which makes the treatment more difficult Two types of recycling systems have been utilised: Partial recycling of water from pulping only Full recycling of water from both pulping and final washing Recycling of water at the pre-fermentation stage: Often, cherries are washed on receipt. Zuluaga & Zambrano 6 (1993), discourage the re-use of water which contains substantial quantities of soil dust. Nevertheless, water from pulping, pre-washing of parchment and transportation to tanks can be re-used. Criteria used to determine if recycled water is suitable for processing are more or less empirical and are generally based on clearness of water. During the first steps of the process, water in contact with parchment is loaded with organic matter, sugars, enzymes, thus the parchment is contaminated. When the parchment is heaped (e.g. fermentation tanks, drying tables), fermentation will start and then give off-flavours and brownish beans due to increase of temperature during fermentation. Presence of enzymes speeds up the beginning of fermentation. Water must be separated from coffee and pulp through grids at the outlet of pulpers, washing channels or fermentation tanks. 6 Zuluaga, V. & Zambrano, F. 1993. Manejo deagua en elprocesso de beneficio húmedo del café para elcontrol de la contaminación. Avances Técnicos 187. Cenicafé, Colombia. Page 2 of 7
Figure 1: Diagrams of a pulp drainer and screen separator. Water is then directed to sedimentation tanks which are also supplied with fresh water, the flow of which being adjusted to optimize residence time of reusable water. Meanwhile, water consumption is reduced by using dry pulping and endless screws for transportation of parchment and pulp. Vásquez 7 (1994) in Costa Rica experimented pulping with recycled water on the most common varieties grown in the country. Water from pulping was recycled for different periods, up to 3 days for Caturra and up to 4 days for Catuai (the quantities of pulp and mucilage being different). The organoleptic analyses of coffee did not show any off-flavours, and best samples came from two days recycled water. In this paper, Vásquez does not give an equivalent in tons of cherries which were processed in the stated periods. Finney (1989) considers that recycling of water from pulping operations must not exceed 5 or 6 hours, which might correspond to processing 20 to 25 tonnes of cherry. After this period, the water is directed to sedimentation ponds for treatment, prior to disposal. There are some unsubstantiated reports that recycling of water from pulping gives an advantage because the water is loaded with enzymes which allow a faster fermentation. 7 Vásquez, M. 1994. Influencia deldesmucilaginado mecánica del café de diferentes períodos de espera al secado sobre lacalidad. Revista del Instituto del Café 6 (64): 3-5. Page 3 of 7
Recycling of water at post-fermentation stage: At this stage, the parchment is washed and sent for drying and thus it must not be recontaminated by organic matter which can later cause unexpected fermentation during drying. Finney (1989) recommends using waste water from the previous washing and soaking. During the first five minutes of washing the water is heavily loaded with organic matter and must be channelled to sedimentation tanks. Mencia et al. 8 (1994) reiterate that water be recycled cautiously from washing, and water from the second washing be used only once, and then only for carrying out the first washing. Final washing must be done with clean water. This generally involves only a visual assessment. Three schematic diagrams of water re-cycling systems used in coffee processing, showing water and coffee flows, are provided at the end of this document: Diagram 1: Coffee flow and recycling of water, from Finney (1989) Figure 2: Schematic plan, according to Bending (Costa Rica) Figure 3: Schematic plan, according to PEICCE (1994) Conclusion: According to the findings of various investigations, water from pre-fermentation stage can possibly be recycled for few hours but some fresh water must be added in the process. Water from post-fermentation can be used cautiously and only once. Sedimentation tanks or ponds, for a plantation producing 200 t of green coffee might be sized at 1000 to 1500 m 3 capacity (Finney 1989). Systems of water recycling require considerable investments for pipes, pumps, screen separators, pulp drainers and ponds, especially in mountainous countries. These costs can be prohibitive - particularly when world coffee prices are low. However, in order to protect the environment many countries implement policies to reduce water use and water recycling is one approach. Equipment innovations such as dry pulping and the Penagos systems also address this need. 8 Mencia, A. et al. 1994. Recirculación de las aguas del lavado en el tren húmedo del beneficaido del café y su influencia enlacalidad. IICA-PROMECAFE/IHCAFE, Seminario regional sobre el mejoramiento de la calidad del café. San Pedro Sula, 1993, Tegulcigalpa, Honduras. Page 4 of 7
Diagram 1: Coffee flow and water recycling in the fully washed process Source: Finney (1989) Reception of cherries Sedimentation pond Fresh water Pulping and pre-grading Recycled water Water / Pulp separation Fermentation and washing Sedimentation pond Washing and grading Sun drying of lights Soaking of heavy parchment Recycling of water from last washing Transportation of wet parchment Recycling of water from soaking pre-drying on table or mechanical Sun drying on table Page 5 of 7
Figure 2: Schematic plan of wet processing unit with water recycling Source: Bending (Costa Rica). Page 6 of 7
Figure 3: Schematic plan of wet processing unit with water recycling Source: PEICCE (1994). Page 7 of 7