Sustainable use of water in the Aegean Islands

Performance of a Micro-Scale Membrane Reactor for Greywater Treatment at Household Level

An aerated membrane reactor (25 L working volume) equipped with 1.5 m² hollow-fiber module was designed and operated using synthetic greywater for household water reuse. Activated sludge (MBR), activated carbon (PAC), zeolite (ZEO) and iron hydroxide (GEH) were added in separate experiments to optimize membrane hydraulic performance and removal efficiency of organics. The use of additives improved permeate quality (in terms of Chemical Oxygen Demand—COD) compared to the direct membrane filtration mode of operation. GEH and MBR were efficient for phosphorus removal, which was not the case for PAC and ZEO. No significant improvement of membrane flux was recorded when PAC, ZEO or GEH were added inside the membrane tank. The MBR system displayed optimum performance during medium-term operation, with COD removal efficiency 85% and permeate flux between 40 and 25 L m⁻² h⁻¹. The capital costs of the proposed technology were around 300 € and the operational costs below 80 € yr⁻¹, rendering the process feasible at household level. Greywater treatment systems for household applications are still on their infancy; however, this trend is expected to change due public perception towards circular economy, water conservation and reuse.

Challenges and Opportunities for Sustainable Management of Water Resources in the Island of Crete, Greece

Crete, located in the South Mediterranean Sea, is characterized by long coastal areas, varied terrain relief and geology, and great spatial and inter-annual variations in precipitation. Under average meteorological conditions, the island is water-sufficient (969 mm precipitation; theoretical water potential 3284 hm3; and total water use 610 hm3). Agriculture is by far the greatest user of water (78% of total water use), followed by domestic use (21%). Despite the high average water availability, water scarcity events commonly occur, particularly in the eastern-south part of the island, driven by local climatic conditions and seasonal or geographical mismatches between water availability and demand. Other critical issues in water management include the over-exploitation of groundwater, accounting for 93% of the water used in agriculture; low water use efficiencies in the farms; limited use of non-conventional water sources (effluent reuse); lack of modern frameworks of control and monitoring; and inadequate cooperation among stakeholders. These deficiencies impact adversely water use efficiency, deteriorate quality of water resources, increase competition for water and water pricing, and impair agriculture and environment. Moreover, the water-limited areas may display low adaptation potential to climate variability and face increased risks for the human-managed and natural ecosystems. The development of appropriate water governance frameworks that promote the development of integrated water management plans and allow concurrently flexibility to account for local differentiations in social-economic favors is urgently needed to achieve efficient water management and to improve the adaptation to the changing climatic conditions. Specific corrective actions may include use of alternative water sources (e.g., treated effluent and brackish water), implementation of efficient water use practices, re-formation of pricing policy, efficient control and monitoring, and investment in research and innovation to support the above actions. It is necessary to strengthen the links across stakeholders (e.g., farmers, enterprises, corporations, institutes, universities, agencies, and public authorities), along with an effective and updated governance framework to address the critical issues in water management, facilitate knowledge transfer, and promote the efficient use of non-conventional water resources.

Sustainable Water Generation on a Mediterranean Island in Greece

Population growth, increasing droughts, and high irrigation needs are all factors that create freshwater shortage problems on islands. The pressing needs of remote islands usually call for water transport from the mainland or other neighboring islands, at a high cost. This study evaluates the design and economic viability of an alternative, sustainable water supply network on the Mediterranean island of Skyros in Greece. The proposed water supply system provides the island with potable water from desalination units, as well as water for agricultural use from a wastewater treatment plant. The total investment cost of the project is found to be €9.8 million, accounting for the cost of transportation of the water between the different settlements (installation, operations, and maintenance), as well as for the required energy of the involved methods. It is found that 44% of the expenses are related to the transport of potable and residual water, and 52% of the cost corresponds to the production of the required desalinated water. As part of a sustainable water and energy network, all energy needs of water generation are assumed to be covered by a renewable power plant. The total cost of water generation on the island with the proposed system is estimated at 2.49€/m3, constituting a competitive and more sustainable solution, when compared to current practices.

The Hydrosocial Cycle in Coastal Tourist Destinations in Alicante, Spain: Increasing Resilience to Drought

Tourism, and particularly residential tourism, has led to a change in the urban and demographic model of towns along the European Mediterranean coastline. Water as a resource limited and limiting for the growth of tourism is a popular topic in the scientific literature. However, the incorporation of non-conventional resources (desalination) has meant, in theory, that this limitation has been overcome. The aims of this paper are: (a) to identify the different tourism models existing in coastal towns in Alicante province and characterize them according to their water consumption from 2002–2017; and (b) analyse the hydrosocial cycle, highlighting the measures aimed at satisfying water demand and identifying the limitations related to these hydrosocial systems. To this end, different types of information have been processed, and various basic indicators have been analysed. The results revealed the increase in the resilience of this region to natural aridity and drought events. This was possible because the demand management and the use of desalinated water. However, this has generated other problems associated (energetics, environmental) due to maintenance of a non-sustainable territorial model based on an accelerated real estate development.

Sustainable Water Resources Management in Small Greek Islands under Changing Climate

Five different water resource management scenarios are examined on eight dry islands of the Aegean Sea in Greece, pitting the current practice of water hauling via ship against alternative water supply schemes in delivering a sustainable solution for meeting water demand. The first scenario employs current water supply practices along with the operation of domestic rainwater harvesting systems. Desalinated water, provided through the operation of wind-powered desalination plants, is considered the main source of potable water in the rest of scenarios. Wind-powered desalination may be combined with rainwater harvesting as a supplementary source of water and/or seawater pumping and an additional source of energy that is supplied to the system. All different alternatives are evaluated for a 30-year lifespan, and an optimal solution is proposed for each island, based on a life cycle cost (LCC) analysis. The performance of this solution is then assessed under six climate change (CC) scenarios in terms of the rate of on-grid versus off-grid renewable energy that is required in order to achieve a certain reliability level. Overall, the examined scenarios show a decreasing performance in terms of reliability under CC for the eight islands.

A new framework proposal, towards a common EU agricultural policy, with the best sustainable practices for the re-use of olive mill wastewater

The disposal of olive mill wastewater (OMW) is a serious environmental issue for the Mediterranean countries. However, there is still no common European legislation on the management and the re-use of OMW in agriculture, in the frame of sustainable crop management and the standards for the safe OMW disposal and re-use are left to be set by each EU country, individually. This review paper presents the most effective and sustainable practices for OMW, (treatment, application and management), which can maximize the benefits of OMW on crops and soils, while minimizing the potential hazards for public health, thus promoting environmental sustainability. The findings of this synthetic work suggest that there is enough information and proven sustainable practices to go ahead with the initial formulation of a new consensual framework, environmentally acceptable, socially bearable and economically viable, that could hopefully help to set the standards for the re-use of olive mil wastewater and can lead to a common EU policy on the management and re-use of OMW.

Preliminary analysis of the decrease in water level of Vrana Lake on the small carbonate island of Cres (Dinaric karst, Croatia)

A strong and potentially dangerous decreasing trend in the level of water in Vrana Lake over the last three decades was analysed. This freshwater lake is a unique karst hydrology feature located on the small Adriatic island of Cres (405.71 km2), which is entirely composed of carbonate rocks. The lake is situated in a large cryptodepression and its base reaches a depth of 61.3 m below mean sea-level. The lake is a complex hydrological–hydrogeological system with an average water volume of c. 220 × 106 m3. The larger geographical region has been affected by an increase in air temperature over the last c. 40 years. This exceptionally clean freshwater lake is the only source of potable water for the whole Cres archipelago. A dangerous drop in the water level of the lake started in 1983. This decreasing trend is driven by both global climate change and anthropogenic (the overexploitation of water) factors.

Performance of the biosorptive activated sludge (BAS) as pre-treatment to UF for decentralized wastewater reuse

A biosorptive activated sludge (BAS) was operated at lab-scale with diluted and concentrated municipal wastewater to study the efficiency of removal of organics (particulate and soluble COD) and recovery of nutrients (TKN, ammonia, phosphorus). The system performed significantly better with concentrated wastewater, where COD removal efficiency was 80% at organic loading rates between 10 and 20kg m(-3)d(-1). Supplementation of ferrous iron at 20mg L(-1), significantly improved both the removal of particulate, soluble COD and phosphorus. The effluent from the BAS was further treated using an ultrafiltration process with backwashing. The average permeate flux (at constant TMP=0.3bar) increased from 23 to 28 and 34L m(-2)h(-1) when raw sewage, BAS without iron, and iron respectively were tested. The proposed technology is compact, efficient and suitable for decentralized water reuse, while the capital and operational expenses were calculated as 0.64 and 0.43€ m(-3), respectively.

Evaluating two infiltration gallery designs for managed aquifer recharge using secondary treated wastewater

As managed aquifer recharge (MAR) becomes increasingly considered for augmenting water-sensitive urban areas, fundamental knowledge of the achievable scale, longevity and maintenance requirements of different options will become paramount. This paper reports on a 39 month pilot scale MAR scheme that infiltrated secondary treated wastewater through unsaturated sand into a limestone and sand aquifer. Two types of infiltration gallery were constructed to compare their hydraulic performance, one using crushed, graded gravel, the other using an engineered leach drain system (Atlantis Leach System(®)). Both galleries received 25 kL of nutrient-rich, secondary treated wastewater per day. The Atlantis gallery successfully infiltrated 17 ML of treated wastewater over three years. The slotted distribution pipe in the gravel gallery became clogged with plant roots after operating for one year. The infiltration capacity of the gravel gallery could not be restored despite high pressure cleaning, thus it was replaced with an Atlantis system. Reduction in the infiltration capacity of the Atlantis system was only observed when inflow was increased by about 3 fold for two months. The performance of the Atlantis system suggests it is superior to the gravel gallery, requiring less maintenance within at least the time frame of this study. The results from a bromide tracer test revealed a minimum transport time of 3.7 days for the recharged water to reach the water table below 9 m of sand and limestone. This set a limit on the time available for attenuation by natural treatment within the unsaturated zone before it recharged groundwater.

Soil pollution under the effect of treated municipal wastewater

Soil heavy metal pollution due to wastewater reuse was assessed by means of the concentration factor (CF) and/or pollution load index (PLI).In this respect, a greenhouse pot experiment was conducted, using a completely randomized block design, including five treatments of treated municipal wastewater (0%, 25%, 50%, 75%, and 100%), in four replications. Brassica oleracea var. Capitata was used as a test crop. The optimum CFs were expressed as a function of maximum dry matter of cabbage plant parts yield, and the values obtained per plant part were as follows: stems-Zn-CF 2.96, Co-CF 0.85, Ni-CF 0.92; whole plant-Cu-CF 3.90, Ni-CF 0.87, and Pb-CF 11.52; and leaves-Pb-CF 11.78. The PLI was calculated as the geometric mean of the CF of each metal, and was related to the maximum dry mater yield of cabbage stems and heads. The optimum values found were: stems PLI 1.99-2.55 and heads 2.25.

Hotel water consumption at a seasonal mass tourist destination. The case of the island of Mallorca

While it is true that tourism is one of the main driving forces behind economic growth in several world regions, it is also true that tourism can have serious negative environmental impacts, especially with regard to water resources. The tourist water demand can generate big problems of sustainability, mainly in those regions where water is scarce, as occurs in most coastal and small island destinations where a large part of world tourism is concentrated. Given the shortage of literature on the subject, further research into the tourist water demand is required, with particular attention to the hotel sector, since hotels are the most popular option for tourists, displaying higher levels of water consumption. The main purpose of this study is to develop a model to analyse hotel water consumption at a mature sun and sand destination with a strong seasonal pattern and scarcity of water; characteristics shared by some of the world's main tourist destinations. Our model includes a set of different hotel variables associated with physical, seasonal and management-related factors and it improves on the capacity to explain water consumption at such destinations. Following a hierarchical regression methodology, the model is empirically tested through a survey distributed to managers of a representative sample of hotels on the island of Mallorca. From the obtained results, interesting recommendations can be made for both hotel managers and policy makers. Among these, it should be highlighted that the strategic move contemplated by many mature destinations towards a higher quality, low-season model could have significant negative effects in terms of the sustainability of water resources. Our results also conclude that managerial decisions, like the system of accommodation that is offered (i.e. the proliferation of the "all-inclusive" formula, both at mature and new destinations), could give rise to the same negative effect. Development of water saving initiatives (usually introduced in response to demand-based factors), also reveals significant effects over water consumption. Finally, other key factor in explaining hotel water consumption is the management system under which the hotel is run.