Assessing Reclaimed Urban Wastewater for Reuse in Agriculture: Technical and Economic Concerns for Mediterranean Regions

Appraising water and nutrient recovery for perennial crops irrigated with reclaimed water in Mediterranean areas through an index-based approach

The use of reclaimed water for agricultural irrigation is among the agronomic practices being increasingly valued by policy-makers, water planners, and regulators to pursue more sustainable resource management in many arid and semi-arid agricultural production areas worldwide. This practice can make additional supply available in water-scarce areas, provide crop nutrients, and reduce the disposal of wastewater to the environment, thus providing considerable agronomic and environmental benefits. However, the process for treated wastewater reuse is complex because of multiple interactions among technical, economic, environmental, and public health related aspects. In this context, the application of quantitative indices capturing agronomic, engineering, and environmental factors and their possible inter-relations enable to appraise the potential benefits and risks of treated wastewater reuse at individual project's scale and for regional policies. The present article describes a quantitative approach that utilizes a set of proposed indices to characterize various aspects affecting water and nutrient recovery for specific combinations between the characteristics of the treatment facility and the attributes of the irrigation district supplied with reclaimed water. The proposed index-based approach was tested on datasets collected for 11 pilot reuse schemes located in the Apulia region of southern Italy with the aim to evaluate the potential for water and nutrient recovery resulting from irrigation with reclaimed water. Results from the data analysis and interpretation showed that the proposed indices enabled to quantify the environmental benefits of irrigation with RW that leads to divert less freshwater from conventional sources and dispose less reclaimed water into natural water receptors, as well as the agronomic advantages of using RW, which can partially fulfill the irrigation and nutrient requirements for the supplied districts' service areas. Overall, the proposed set of indices can provide valuable information for the successful implementation of water reuse policies for irrigated agriculture.

Improving the Performance of the Reverse Osmosis Process with Fiber Filter and Ultrafiltration: Promoting Municipal Sewage Reclamation and Reuse for Industrial Processes

Wastewater reuse presents a promising solution to the growing need for the sustainable use of available water resources. The reclamation of municipal sewage through reverse osmosis can be applied for diverse uses to alleviate chronic water scarcity. In this study, a pilot plant was fabricated to measure the efficiency and the costs that are associated with pretreatment by the fiber filtration and ultrafiltration of secondary effluent from a water resource recovery facility in Taiwan. The results of this dual-membrane process meet the quantity and quality standards for industrial reuse. The pretreatment produced feedwater with a silt density index (SDI15) lower than 4.1, and with average turbidity removal rates of 42.7% (fiber filtration) and 99.2% (ultrafiltration). Following reverse osmosis, a 97.9% rejection of the electrolyte conductivity was achieved in the reclaimed water. The fouling of the membranes was controlled through the application of intensive backwash, chemically enhanced backflushing, and cleaning in place. The proposed system improves the feasibility, reliability, and economy of the dual-membrane process as a tertiary treatment for safe water reuse, and it thereby demonstrates that this technology has reached maturity for the full-scale implementation of sustainable water reuse.

Heavy metal accumulation and genotoxic effect of long-term wastewater irrigated peri-urban agricultural soils in semiarid climate

Water scarcity is becoming an alarming issue in the Mediterranean countries. Therefore, using the treated wastewater in the irrigation is considered as a valuable option. However, uncontrolled and long-term irrigation by wastewater leads to human health and environmental damages, mainly related to some specific pollutants. The assessment of the availability and toxicity of the heavy metals after long term irrigation, under semi-arid climate, is not yet well documented. In this study, physicochemical properties, genotoxicity (Vicia faba micronucleus test), total and available (CaCl₂-extractable) concentrations of Cr, Pb, Cu, Zn, Co and Cd in eight soils of peri-urban farms irrigated with wastewater were examined to evaluate their accumulation. The results indicated that long-term irrigation with wastewater induced significant increase of electrical conductivity, organic matter, calcium carbonate equivalent and nutrient availability. Total and available concentration of heavy metals were significantly higher (P < 0.05) in irrigated soils by wastewater. The total concentrations of Zn, Pb, Cu, Cr, Cd and Co in irrigated soils by wastewater at 0-40 cm depth were 85.69, 43.94, 34.86, 14.62, 9.94 and 7.17 mg kg^-1, respectively. Furthermore, the increase of the available metal fraction in irrigated soils by wastewater at 0-40 cm depth followed the following order: Co (1270.1%) > Cd (914.5%) > Cu (881.5%) > Cr (471.2%) > Pb (230.8%) > Zn (223.8%). The micronucleus assay indicated significant increase of micronucleus frequencies (41.25‰, 35.48‰, 21.66‰, 16.23‰ and 13.62‰ respectively for P1, P2, P3, P4 and P7) which were higher than the negative control (0‰) and the irrigated soil by fresh water (3.29‰). The micronucleus induction was significantly correlated with the high available fraction of Cd, Co and Zn at P1, P2 and P7. The genotoxicity can be a powerful test to assess the ecological effects associated with the interactions of heavy metals with other pollutants.

Reclaimed Water for Vineyard Irrigation in a Mediterranean Context: Life Cycle Environmental Impacts, Life Cycle Costs, and Eco-Efficiency

The agricultural sector in the Mediterranean region, is increasingly using reclaimed water as an additional source for irrigation. However, there is a limited number of case studies about product-based life cycle analysis to ensure that the overall benefits of reclaimed water do indeed outweigh the impacts. The Life Cycle Assessment (LCA) and Life Cycle Costing (LCC) methods are used in this study to investigate the environmental impacts and costs of vineyard cropping systems when tertiary reclaimed water is used as a supplementary source of irrigation water (integrated system). The conventional production system utilizing 100% groundwater was used as a reference system. As a proxy for sustainability, eco-efficiency, which combines economic and environmental performance, was assessed. The LCA revealed that the integrated system could reduce the net environmental impact by 23.8% due to lower consumption of irrigation water (−50%), electricity (−27.7%), and chemical fertilizers (−22.6%). Nevertheless, trade-offs between economics and the environment occurred as an integrated system is associated with higher life cycle costs and lower economic returns due to lower crop yield (−9.1%). The combined eco-efficiency assessment (ratio of economic value added to total environmental impact) revealed that the integrated system outperformed in terms of eco-efficiency by 12.6% due to lower environmental impacts. These results confirmed that reclaimed water could help to ensure an economically profitable yield with net environmental benefits. Our results provided an up-to-date and consistent life cycle analysis contributing to the creation of a valuable knowledge base for the associated costs and benefits of vineyard cultivation with treated wastewater.

Treated wastewater reuse for irrigation: Pros and cons

The appropriateness of using treated wastewater for crop or agricultural irrigation remains a bone of contention among experts and policymakers. Here, we outline and analyze not only the benefits but also the drawbacks of such a practice in order to suggest a way forward. To ensure that our review reflects the state-of-the-art in terms of technological advances and best practices, only literature published in the last decade is considered except for literature on the history of reuse. The review begins by highlighting growing water scarcity, the history of wastewater reuse in agriculture, and the limitations of existing studies. A short overview of the approach used in the write-up is outlined after the introduction. It then proceeds with an in-depth look at three broad areas: environmental impacts, public health impacts, and economic impacts. In terms of environmental impacts, effects on soil quality, water resources, plant growth, and soil microbial communities are analyzed. For each sub-area, the positive effects are described before the negative ones. The same approach is then applied to public health impacts, the focus of which is on human exposure to heavy metals and pathogens, and economic impacts, which are assessed with particular reference to investment cost, financial benefit to wastewater treatment plants (WWTPs), farm expenditure and income. Having weighed the advantages and disadvantages in each area, innovative measures are proposed for optimizing the benefits and mitigating the drawbacks of using treated wastewater for crop irrigation. Special consideration was given to contaminants of emerging concern and the known or perceived environmental and health risks associated with these contaminants.

Responsible Water Reuse Needs an Interdisciplinary Approach to Balance Risks and Benefits

Freshwater is a precious resource, and shortages can lead to water stress, impacting agriculture, industry, and other sectors. Wastewater reuse is increasingly considered as an opportunity to meet the freshwater demand. Legislative frameworks are under development to support the responsible reuse of wastewater, i.e., to balance benefits and risks. In an evaluation of the proposed European regulation for water reuse, we concluded that the proposed regulation is not practically feasible, as the water provider alone is responsible for the risk assessment and management, even beyond their span of control. The required knowledge and resources are extensive. Therefore, without clear guidance for implementation, the regulation would hinder implementation of reuse programs. As a consequence, the current practice of uncontrolled, unintentional, and indirect reuse continues, including related risks and inefficiency. Therefore, we provide an outline of the interdisciplinary approach required to design and achieve safe, responsible water reuse. Responsible water reuse requires knowledge of water demand and availability, quality and health, technology, and governance for the various types of application. Through this paper we want to provide a starting point for an interdisciplinary agenda to compile and generate knowledge (databases), approaches, guidelines, case examples, codes of practice, and legislation to help bring responsible water reuse into practice.