Wastewater Reuse and Current Challenges

This volume offers an overview of current challenges related to the wastewater reuse practice, including analytical methodologies, bioassays, uptake of organic contaminants during crop irrigation, and antibiotic resistance-related issues. It also offers information on various wastewater reuse cases under various scenarios.

Presence of unregulated and not assessed organic microcontaminants in wastewater effluents represents a significant challenge to wastewater reclamation, especially if intended for human consumption or irrigation practices. Problems associated to the repeated release of treated wastewater in the environment for reuse applications, such as infiltration into the underground including pollution of ground water or accumulation in soil and plants, are still scarcely investigated. Consequently, comprehensive and high-throughput analytical methods have to be developed and validated to provide a comprehensive evaluation of these microcontaminants in water, soils and crops. This chapter aims to give an overview of the analytical strategies currently used in this field, its requirements and limitations.

Water deprivation with regard to quantity and quality is one of the most important environmental problems of the century. The increasing demand of water resources puts pressure on the utilization of alternative sources such as treated wastewater. In the context of “reduce, reuse, and recycle,” the inclusion of treated wastewater in the water cycle seems a promising practice for water management. The lack of general acceptance of stakeholders and public, however, still hinders the widespread application of wastewater reuse. A reason for this is, among others, the presence of contaminants of emerging concern in treated wastewater. This has led to an increased concern about direct and indirect effects to the environment and possible implications to human health. The development and application of bioassays able to identify and quantify the biological potency of treated wastewater is an ongoing research effort, especially when taking into consideration that a plethora of contaminants exist and interact in this complex matrix. This chapter summarizes available literature regarding the sensitivity of currently applied bioassays for assessing biological effects of treated wastewater and their correlation with chemical analysis. The focus is on pharmaceuticals since they represent one of the major groups of contaminants of emerging concern with many unanswered questions currently in place.

Organic contaminants occurring in reclaimed water can be incorporated in soil, where they can interact with humic compounds or anthropogenic organic matter depending on their physicochemical properties. In the soil water, a fraction of these contaminants can be biodegraded, particularly in the rhizosphere, where the process is enhanced by root exudates. Another fraction can be uptaken by plants and translocated by xylem. Once incorporated in the plant, a fraction of the incorporated contaminant is metabolized, while the rest remains unaltered. Three stages can be distinguished in the metabolization process: (1) oxidation, (2) conjugation, and (3) accumulation in the vacuole or cell wall.

The reuse of treated wastewater could be a promising measure to attenuate the water scarcity burden. In agriculture, irrigation with wastewater may contribute to improve production yields, reduce the ecological footprint and promote socioeconomic benefits. However, it cannot be considered exempt of adverse consequences in environmental and human health. Apart from the introduction of some biological and chemical hazardous agents, the disturbance of the indigenous soil microbial communities and, thus, of vital soil functions impacting soil fertility may occur. The consequences of these disturbances are still poorly understood.

This chapter summarises the physicochemical and microbiological alterations in soil resultant from irrigation with treated wastewater that are described in scientific literature. These alterations, which involve a high complexity of variables (soil, wastewater, climate, vegetal cover), may have impacts on soil quality and productivity. In addition, possible health risks may arise, in particular through the direct or indirect contamination of the food chain with micropollutants, pathogens or antibiotic resistance determinants. The current state of the art suggests that irrigation with treated wastewater may have a multitude of long-term implications on soil productivity and public health. Although further research is needed, it seems evident that the analysis of risks associated with irrigation with treated wastewater must take into account not only the quality of water, but other aspects as diverse as soil microbiota, soil type or the cultivated plant species.

Antibiotic resistance is considered to be one of the most significant public health concerns of the twenty-first century. Although traditionally the propagation of antibiotic resistance was considered to be limited to hospitals and other clinical environments, there is a growing realization that it is also associated with anthropogenically impacted environmental reservoirs. Wastewater treatment plants are considered to be significant reservoirs of antibiotic resistance because they combine extremely high levels of fecal- and environmental-derived bacteria with residual concentrations of antibiotic compounds believed to induce selection. These bacteria are primarily congregated in dense biofilms that are “hot spots” for horizontal gene transfer, which can facilitate inter- and intraspecies transfer of antibiotic genes, potentially resulting in the development of multidrug-resistant strains. Several studies have demonstrated that although wastewater treatment plants significantly reduce bacterial concentrations, relatively high levels of antibiotic-resistant bacteria and resistance genes are still present in effluents released to aquatic and soil environments and that under certain circumstances these resistance elements may persist for long periods of time in downstream environments. These elements may have significant epidemiological ramifications, especially when effluents enter drinking water and food webs; and henceforth, antibiotic resistance genes have recently been characterized as contaminants of emerging concern. This chapter summarizes current understanding of antibiotic resistance in wastewater treatment plants and downstream environments, presents knowledge gaps that need to be bridged in order to better understand the potential ramifications of this phenomenon, overviews the effect of disinfection treatments on antibiotic resistance elements, and finally discusses policy guidelines that should be implemented in the future to reduce the risks of antibiotic resistance from wastewater treatment plants.

The elimination of contaminants of emerging concern (CECs) during conventional wastewater treatment is not complete, and therefore, different amounts of these compounds are continuously released via wastewater effluents into the aquatic environment. This constitutes a major issue for water reuse, because these compounds can undergo transformation in the environment or during disinfection if reclaimed water is used for drinking water production. Different emerging contaminants, e.g., perfluorinated compounds, pharmaceuticals, antibacterials, plasticizers, and preservatives, and transformation products, which are in some cases more toxic than original compounds, have been occasionally found in finished drinking waters. The present chapter reviews the CECs detected in drinking water and the disinfection by-products generated by different CECs present in the aquatic environment. Moreover, the potential toxicologic effects that these pollutants and their transformation products pose for human health are also reviewed. Levels of these compounds in treated waters, and therefore exposure, could be reduced by the use of advanced removal technologies.

Water is commonly used in the process industries as raw material and utility systems as well as for washing operations. In recent years, stricter environmental regulations and water scarcity issues have led to the growing need for better water management. Concurrently, the development of various process integration tools for resource conservation has become very established in recent years. This chapter presents one of the important process integration tools, known as water pinch analysis, for the design of a water recovery system. A water recovery case study of a steel plant is used for illustration.

Irrigation is the largest practice of water reuse worldwide. In North African countries, both formal and informal uses of wastewater were practiced for a long time thus exposing users and consumers to microbiological and chemical health risks. Negative environmental impacts are also of concern because secondary biological treatment is not effective in removing ubiquitous and persistent contaminants like some emerging micropollutants. Based on research findings during the last decades, the presence of micropollutants in reclaimed water has gained interest in developed countries, and the release of some of them into water bodies has been regulated. In North African countries, in view of the prevailing quality of reclaimed water and its current usage for growing crops, the occurrence of such contaminants has recently raised concern with an increasing number of research works and publications. However, it remains challenging to identify, quantify, and prioritize the most relevant to be regulated. This paper aims at shedding light on the usage of reclaimed water for irrigation in Algeria, Egypt, Libya, Morocco, and Tunisia while pinpointing the potential sources of micropollutants in wastewater. It discusses the extent to which some micropollutants could be relevant and challenging to public health and environmental quality.

Pulp and paper industry is still an intensive water consumer, although fresh water use by this sector has decreased by 90% along the last three decades, which currently shows its long water reuse tradition. Sustainable water management has been achieved by following the principle of water fit for use, which has mainly been developed through the optimization of water circuits, the cascade use of water, the implementation of internal water treatments, the optimal treatment of effluents to be reused and the use of alternative water sources, such as reclaimed water from municipal wastewater treatment plants. In fact, this sector is nowadays regarded as a reference for water reuse. Paper mills need to use fresh water to compensate evaporation losses and in critical applications. In addition, the final degree of circuit closure depends on the quality of the final product. For example, whereas unbleached paper grade mills may work with highly closed circuits, this is not usually possible for virgin pulp and bleached paper grade mills. Filtration and dissolved air flotation are the most common treatments applied to internal water reuse. Otherwise, the combination of physicochemical, biological and filtration technologies is generally considered to enable the reuse of mill effluents. Finally, tertiary effluent from municipal wastewater treatment plants must be further treated by filtration technologies and disinfection stages to be finally reused within the papermaking process safely.

The possibility of reusing leachate substances for agronomical purposes might be of interest, especially in arid areas when used in addition to the leachate water content. This study presents a simple procedure for the revegetation of the walls of closed landfills, reusing the leachate as a fertigant. The results demonstrated the real possibility of employing blended leachate as a fertigant for the revegetation of the walls of closed landfills. The native plants Lepidium sativum, Lactuca sativa and Atriplex halimus, which suit the local climate, were chosen for this study in Southern Italy. The methodology was structured into three phases: (i) early-stage toxicity assessment phase (apical root length and germination tests), (ii) adult plant resistance assessment phase and (iii) soil properties verification phase. The rationale of the proposed approach was first to look at the distinctive qualities and the potential toxicity in landfill leachates for fertigation purposes. Afterwards, through specific tests, the plants used were ranked in terms of resistance to the aqueous solution that contained leachate. Finally, after long-term irrigation, any possible worsening of soil properties was evaluated. In particular, the plants maintained good health when leachate was blended at concentrations of lower than 25% and 5%, respectively, for Atriplex halimus and Lepidium sativum. Irrigation tests showed good resistance of the plants, even at dosages of 112 and 133.5 mm/m², at maximum concentrations of 25% and 5%, respectively, for Atriplex halimus and Lepidium sativum. The analysis of the total chlorophyll content and of aerial parts dried weight confirmed the results reported above.