Wastewater Reclamation and Reuse

Discussion Paper Series, 15(7): 139-148 Wastewater Reclamation and Reuse Vasileios Tsiridis University of Thessaly Athanasios Kougolos Associate Professor, University of Thessaly Angelos Kotios Professor, Department of Planning and Regional Development University of Thessaly e-mail: akotios@prd.uth.gr Panagiotis Plageras Professor, Technological Educational Institute of Larissa Yiannis Saratsis Researcher, Department of Planning and Regional Development University of Thessaly Abstract In Mediterranean area, several counties are regularly facing significant water demand and supply imbalances, particularly in the summer period, due to simultaneous occurrence of low precipitation, high evaporation and increased demands for irrigation and tourism. As the demand for water is constantly increasing and drought problems become more important, implementation of wastewater reclamation and reuse practices should be developed, in order to conserve and even extend water resources and constrain contamination of aquifers by seawater or wastewater and coastal water pollution. One of the objectives of ManWater Project was the investigation of the wastewater treatment potential in the context of reclamation and reuse of wastewater produced in the target areas. The application of an integrated wastewater management was evaluated aiming for the protection of water environment as well as for the conservation of water resources of the target areas. The wastewater reuse applications that were suggested included the agricultural and landscape irrigation and the enrichment of the groundwater bodies. Various collective data were evaluated including the wastewater treatment and disposal needs, assessment of the available water resources and the water demand as well as the analysis of the environmental and financial benefits resulting from a specific reuse application. Public acceptance was also evaluated by means of a questionnaire addressed to four different groups of people directly or indirectly affected by the water reclamation and reuse. These groups comprised tourists either from Greece or from abroad and entrepreneurs either native or temporal habitants. Key words: wastewater reclamation, water resources, reuse, irrigation, groundwater recharge January 2009 Department of Planning and Regional Development, School of Engineering, University of Thessaly Pedion Areos, 38334 Volos, Greece, Tel: +302421074462, e-mail: regiolab@prd.uth.gr, http://www.prd.uth.gr Available online at: http://www.prd.uth.gr/research/dp/2009/uth-prd-dp-2009-7_en.pdf

Wastewater Reclamation and Reuse 141 1. Introduction In Greece, water imbalance (imbalance between supply and demand) is often experienced, due to temporal and regional variations of the precipitation, the increased water demand during summer months and the difficulty of transporting water because of the mountainous terrain. Furthermore, in many southeastern areas, there is severe pressure for freshwater resources because of high water demand for tourism and irrigation. According to relative data more than 83 % of the treated effluents in Greece are produced in regions with a deficient water balance. Therefore, water reuse in these areas would satisfy the existing water demand (Angelakis and Bontoux, 2001; Angelakis et al., 2003). However, reuse of municipal wastewater has not been a common management practice in Greece, since no guidelines or regulations concerning water reuse have been adopted. On the contrary, direct disposal of treated effluents in rivers, lakes or sea is a frequent practice. Wastewater reclamation and reuse in various applications play an important role on the development of strategies for the utilization of water resources. Reclaimed wastewater may be used in various applications, most commonly in irrigation of agricultural and urban areas, industrial plants and in the enrichment of the groundwater reservoirs. Thus, wastewater reuse strengthens water savings and generates water sources, a practice exceptionally important in areas with limited rainfalls (Abdel- Jawad et al., 1999). The irrigation of agricultural areas is a valuable application of wastewater reuse, due to the conservation of water reservoirs and the natural enrichment of the fields and plants with nutrients, which reduces the demand for fertilizers. Other uses such as environmental enhancement (wetlands, wildlife refuges, riparian habitats and urban lakes), fire fighting, dust control, and toilet flushing have also been developed in many countries. This requires treatment of the effluent so that it meets the quality requirements for the intended use (Angelakis et al., 1999). Adequate infrastructure such as storage reservoirs and canals, pipelines and dual distribution systems are also necessary to ensure that waters of different qualities will be transported to different destinations. Aesthetics and public acceptance are important aspects of water reuse, especially where the public is directly implicated. Various advanced wastewater treatment technologies have been proposed for the production of high quality effluents, corresponding to specific applications of wastewater reclamation and reuse. The degree of treatment is mainly determined by the required use of the reclaimed water, i.e. if the water will meet agricultural or landscape irrigation, industrial reuse or groundwater recharge needs or if it will facilitate non potable or potable needs. The reuse of reclaimed wastewater in applications such as discharge into aquifers, unrestricted recreational impoundments, as well as the potable reuse, requires sewage effluents of high quality, essentially similar to drinking water quality Discussion Paper Series, 2009, 15(7)

142 Vasileios Tsiridis, Athanasios Kougolos, Angelos Kotios, Panagiotis Plageras, Yiannis Saratsis standards (Asano and Levine, 1996). Among the most common processes that are used for the advanced treatment of secondary activated sludge effluents are filtration (depth, surface or membrane filtration), use of membrane bioreactor, adsorption, reverse osmosis or ion exchange, followed by disinfection with chlorine or ozone (Hamoda et al., 2004; Jimenez et al., 2000; Abdessemed and Nezzal, 2002; Xu et al., 2002; Jolis et al., 1996; Metcalf and Eddy, 2003). Filtration processes have been used for the removal of substantial amounts of particulate matter from secondary treated effluents, improving the performance of the other advanced treatment steps such as carbon adsorption, ultrafiltration and disinfenction (Metcalf and Eddy, 2003). In addition, filtration may be regarded as an additional polishing step for producing an effluent of constant quality that is not affected by the performance of the activated sludge unit and the variations in the effluent quality (Hamoda et al., 2004). 2. Planning of Wastewater Management System 2.1 Main considerations The application of an integrated wastewater management was evaluated in the present work aiming to the protection of water environment as well as to the conservation of water resources of the target areas. The main data required for the planning of wastewater management included the quantity of wastewater produced in the target area, the water consumption, the existing treatment facilities, the population growth and the minimal treatment requirements for discharge or for reuse for a specific application. The evaluation of the wastewater treatment technologies that could be applied in the target areas focused on decentralized wastewater treatment systems. These systems can be applied in small communities enabling the collection, treatment and potential reuse of wastewater at or near the point of generation. The treatment technologies evaluated included the activated sludge systems, septic tanks, sand filtration, constructed wetlands, stabilization ponds, membrane bioreactors and compact biofilters. For the selection of treatment technology for each specific location, several variables were evaluated, such as topography, land use, distance of water receivers, existence of environmentally protected areas, wastewater effluent characteristics and flow rate variations as well as the potential local reuse applications of reclaimed wastewater. Cost variables as well as the feasibility of the suggested wastewater treatment management system were also evaluated. The wastewater reuse applications that were evaluated included the agricultural and landscape irrigation and the enrichment of the groundwater bodies. Various collective data were evaluated including the wastewater treatment and disposal needs, assessment of the available water resources and the water demand as well as the analysis of the environmental and financial benefits resulting from a specific reuse application. Generally, the main concerns in wastewater reclamation and reuse application are related to the reliable treatment of wastewater which should meet strict UNIVERSITY OF THESSALY, Department of Planning and Regional Development

Wastewater Reclamation and Reuse 143 water quality requirements for the intended reuse, to the protection of public health and finally to the reassurance of the public acceptance. These issues were also evaluated by means of a questionnaire addressed to four different groups of people directly or indirectly affected by the water reclamation procedure. These groups comprised tourists either from Greece or from abroad and entrepreneurs either native or temporal habitants. The results between groups were statistically compared. 2.2 Data of the wastewater management system The required data for wastewater management system were collected by local surveys and interviews of public administration agencies, hotel owners and commercial and agricultural sectors of the target areas. A template, including population data, wastewater management data and solid waste management data, was filled and the results for Skiathos island are presented in Table 1. The population of Skiathos island was estimate about 6000 in January, while in August the estimated population was about 50000. The quantities of water consumption were obtained by the hydrometers of drinking water network. Although the population was increased about one order of magnitude from January to August, the quantities of water consumption for August was only three times higher than from January. The drinking water network services only the municipality of Skiathos, while for the other part of the island, the requirements for dinking water (including hotels and other business activities) are covered by drilling water. This water supply system explains the specifically low quantities of water consumption resulted by the hydrometer for the summer period. The entire water consumption can be estimated by multiplying the population by average water consumption per person of 0.2 m 3 /persone/day. An average solid waste quantity produced per person corresponds to 1 kg/person/day. This estimation is in accordance with the population data for winter and summer period. There is one wastewater treatment plant located in Xanemos of the municipality of Skiathos, while a second wastewater treatment plant located in Koukounaries. The wastewater treatment plant in Xanemos has a treatment capacity equal to 4800 m 3 /day and it serves the wastewater produced in the municipality of Skiathos. According to the interviews with the public authorities involved with the wastewater management in Skiathos, 90 % of the wastewater produced in the municipality of Skiathos is collected to the wastewater treatment plant in Xanemos, through the drainage system. The quantity of wastewater collected in wastewater treatment plant in Koukounaries is equal to 500 m 3 /day. The relative percentage of the wastewater collected to either a wastewater treatment plant or to a sewage tank was difficult to be estimated: Most of the hotels Discussion Paper Series, 2009, 15(7)

144 Vasileios Tsiridis, Athanasios Kougolos, Angelos Kotios, Panagiotis Plageras, Yiannis Saratsis have private wastewater treatment facilities, while the wastewater produced by various apartments and bungalows is discharged into septic tanks. Table 1. Identification of the wastewater management system on Skiathos island A. Population data Population registered according to the last census 6160 Estimated population in January 6000 Estimated population in August 50000 B. Wastewater management data Quantities of water consumption in January 1300 m 3 /day Quantities of water consumption in August 3500 m 3 /day Are there any wastewater treatment plants How many wastewater treatment plants Two Skiathos, Xanemos Koukounaries, Aghia Eleni Capacity of the existent wastewater treatment plants (in m 3 /day) Skiathos, 4800 m 3 /day Koukounaries, 500 m 3 /day The existent sewage tanks are mainly: Sorptive Septic X Percentage of wastewater that is discharged in: Wastewater treatment plants 60 (%) Sewage tanks 40 (%) The applied wastewater systems are: YES NO Activated sludge X Decentralised (bio-disks, compact ) X Natural systems (constructed wetlands) X C. Solid waste management data Tons of solid wastes produced in January: 8 10 tn/day Tons of solid wastes produced in August: 45 50 tn/day Is any waste recycling program applied? If yes, please specify: --- 2.3 Evaluation of the treatment technologies for wastewater reclamation and reuse The treatment technologies that have be evaluated included the activated sludge systems, septic tanks, sand filtration, constructed wetlands, stabilization ponds, membrane bioreactors and compact biofilters. For the selection of treatment technology for each specific location, several variables were evaluated, such as topography, land use, distance of water receivers, existence of environmentally protected areas, UNIVERSITY OF THESSALY, Department of Planning and Regional Development

Wastewater Reclamation and Reuse 145 wastewater effluent characteristics and flow rate variations and the potential local reuse applications of reclaimed wastewater. Cost variables as well as the feasibility of the suggested wastewater treatment management system were also evaluated. A pilot-scale advanced wastewater treatment plant was used as a basis for a treatment process for the production of high quality reclaimed water that could be used for crop irrigation or for ground water recharge (Petala et al., 2006). The advanced treatment unit included three treatment steps: i) sand filtration ii) activated carbon adsorption and iii) ozonation. For a treatment of 1000 m 3 /day secondary treated effluent the cost of the reclaimed water has been evaluated equal to 0.25 /m 3 reclaimed water (Petala et al., 2006). The investment cost for the construction of such type of advanced treatment unit is about 300000,00. Considering a minimum advanced treatment of secondary treated effluent of wastewater treatment plant located in Koukounaries, a sand filtration process is suggested, while the reclaimed water can be used either for irrigation of olive trees or for ground water recharge, preventing the salination of ground water. 3. Public Acceptance - Questionnaire Aesthetics and public acceptance are very important aspects for the implementation of a water reclamation and reuse application, especially where the public is directly implicated. A questionnaire to four different groups of people was applied for a preliminary evaluation of their sensitization towards environmental issues as well as for the public acceptance of wastewater reclamation and reuse. These groups comprised i) tourists from Greece and ii) tourists from abroad, iii) entrepreneurs from Skiathos and iv) entrepreneurs who are not permanent residents of Skiathos island. Subsequently we compared the results of the questionnaires between the different groups. The purpose was the application of hypothesis-testing procedures to make relative comparisons between two population percentages. The null hypothesis was that the two parameters are equal- i.e., there is no significant difference between the two parameters. In our example we are only concerned about the two tailed test because we were only interested in the equality or nonequality of opinions between the two groups (Sanders et al., 1985). The evaluation of the public acceptance of a wastewater reclamation and reuse application is a very complicated task, related with various social, economical and health effect issues. A preliminary estimation took place by posing to the two main groups the question: Would you ever reuse treated municipal wastewater for the garden irrigation of your hotel? The obtained results for entrepreneurs and tourists are presented in Figure 1 and 2, respectively. Discussion Paper Series, 2009, 15(7)

146 Vasileios Tsiridis, Athanasios Kougolos, Angelos Kotios, Panagiotis Plageras, Yiannis Saratsis As shown in Figure 1, the majority of both groups of entrepreneurs are willing to try wastewater reclamation and reuse for irrigation, with entrepreneurs permanent residents on Skiathos to be more decisive regarding their opinion. However a percentage (equal to 20 % and 23 % for entrepreneurs temporal residence and for entrepreneurs permanent residence on Skiathos, respectively) have not yet been convinced that this kind of irrigation is safe to use. Figure 1. Results of the question: Would you ever reuse treated municipal wastewater for the garden irrigation of your hotel? (A: Entrepreneurs temporal residents on Skiathos; B: Entrepreneurs permanent residents on Skiathos). 5% (A) 15% Maybe Do not know 23% (B) 0% Maybe 20% 60% 77% Figure 2. Results of the question: Would you ever reuse treated municipal wastewater for the garden irrigation of your hotel? (A: Foreign tourists; B: Greek tourists). 13% (A) Do not know 26% 19% (B) 8% Do not know 61% 73% A strikingly different picture is revealed regarding the same question in the tourist group (Figure 2). Foreign tourists are less willing to accept reclaimed wastewater for irrigation whereas Greek ones gladly accept this use. Further investigation into the reasons for this discrepancy will be an interesting challenge in the future. UNIVERSITY OF THESSALY, Department of Planning and Regional Development

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