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Wastewater reuse in irrigation
Context and issues related to the reuse of treated wastewater
Mediterranean countries, developing countries and arid regions are particularly vulnerable to wa-ter stress and suffer from most of the current global changes such as erosion of diversity, climate change, population growth, industrialization and especially the increasing degradation of water resources (over-exploitation, pollution, salinization, etc.). A continuation of the development trend will lead to a 55% increase of global water demand by 2050 (WRG, 2009; UNWWAP, 2015 1). By 2025, 1.8 billion peo-ple will live in countries or regions where water availability is less than 100 m3/ capita / year according to the International Water Management Institute (IWMI). As a result, humanity is facing a multitude of water-related problems and major improvements in water management strategies are indispensable for a sustainable future (Bagatin et al., 2014; Alnouri et al., 2015). Water recycling and especially wastewater reuse is becoming a critical element for managing our water resources for both environmental and economic reasons. Another reason to reuse wastewater is that its volume is constantly increasing with the expansion and intensification of urban planning. The U.S. Environmental Protection Agency (EPA) defines wastewater reuse as, ”using wastewater or reclaimed water from one application for another ap-plication. The deliberate use of reclaimed water or wastewater must be in compliance with applicable rules for a beneficial purpose (landscape irrigation, agricultural irrigation, aesthetic uses, ground water recharge, industrial uses, and fire protection). A common type of recycled water is water that has been reclaimed from municipal wastewater (sewage).” Agriculture, especially crop production, is the sector that consumes the biggest quantity of water. Water use for crop irrigation accounts for 70% and in some cases 90% of the water needs in the world (Kalavrouziotis et al., 2011; UNESCO 2003). To reduce the pressure on freshwater resources and preserve them for the supply of drinking water, many countries reuse treated wastewater for irrigation.
Figure I.1: Map showing areas of the world with water scarcity. Map by Mesfin M. Mekonnen and Arjen Y, 2016, courtesy Science Advances. CC-BY-NC-4.0 (National Geographic, 15/02/2016)
Worldwide application of wastewater in irrigation
Irrigation with wastewater even with no treatment or just primary treatment is a common practice in developing countries like China, India, Mexico, etc. due to high treatment costs (Lazarova and Bahri, 2005). In water scare regions of developed countries such as Australia, the Middle East, and coastal or inland areas of France and Italy, treated wastewater is used for irrigation (IWMI, 2007). In Spain, 408 million m3 of treated wastewater is reused; In Italy, ambitious projects are being created (22,000 ha of vegetable crops are irrigated with treated wastewater from a sewage treatment plant with a capacity of more than one million inhabitants). Cyprus has the most ambitious objective: to reuse 100% of treated wastewater (Lazarova and Brissaud, 2007).
For this reason, the selection of appropriate wastewater treatment at an affordable cost and adapted irrigation practices are the two main necessary measures to protect public health and prevent harmful conditions and damage to crops, soil and groundwater. Various reclamation technologies can be used to treat wastewater prior to irrigation, such as lagoon ponds, constructed wetlands, conventional wastew-ater treatment plants, membrane bioreactors, membrane filtration and others. However, these methods generally need large land areas and involve high investment costs (Norton-Brandao et al., 2013). More details are found in paragraph I.1.5 for the benefits and the disadvantages of the reuse of treated wastewater for irrigation.
Wastewater is all waters entering sewage pipes whose natural properties are transformed by do-mestic uses, industrial, agricultural and other enterprises. Rainwater that flows into these pipelines is also included (Bliefert and Perraud, 2001). There are several categories of pollutants:
– Particulate pollution, which refers to biodegradable and non-biodegradable mineral suspensions (MS or SS for suspended solids) or organic (VS for volatile solids).
– Organic pollution which includes biodegradable materials (BOD5), non-biodegradable materials, toxic substances, inhibitory material, dissolved and particulate matter.
– Nitrogen pollution consists of nitrogen in reduced form (organic nitrogen, ammoniacal nitrogen (NTK = nitrogen Kjeldahl)) or oxidized (nitrite (NO2 – ), nitrate (NO3 – )).
– Phosphorus pollution composed of mineral phosphorus (including PO43 – ) and organic phospho-rus.
– Microbiological pollution consisting of bacteria, viruses, protozoa and fungi.
For wastewater reuse and even for a rejection in nature, treatment series must be made. The concentra-tions of the input elements of the treatment plant are variable and depend on the size of the agglomer-ations and the origin of these waters. Table I.1 shows the flow of pollutants released per inhabitant per day according to the decree of 10/12/1991.
Water treatment in a Wastewater Treatment Plant (WWTP)
Developed countries have generated techniques and guidelines for safe reuse of wastewater in irrigation for the purposes of health and environment. Water treatment represents a technological and economic challenge with the common goal of preserving biodiversity and protecting water resources. Depending on the degree of elimination of pollution and the processes implemented, several treatment levels are generally defined: pretreatment, primary treatment and secondary treatment. In some cases, tertiary treatment is applied, particularly when treated water must be disposed of in particularly sensitive areas. There are also extensive treatments known as lagoons, which combine biological, physical and natural. Table I.2 shows the different stages of water treatment in a WWTP from pretreatment to tertiary treatment.
According to French regulations, the discharge levels of urban effluents into non sensitive zones for WWTPs treating a gross load < 120kg BOD5 / day (< 2000 inhabitant equivalents “IE”) and > 120kg BOD5 / day (> 2000 inhabitant equivalents “IE”) are presented in Table I.3 (decree of 22 June 2007).
Beneficial and negative impacts of the reuse of treated wastewater for agricultural irrigation
The reuse of wastewater in irrigation results in both positive and negative impacts on soil, crops and health. This practice can benefit soil and farmers, while at the same time posing a risk of contami-nation to the ecosystem.
Benefits of wastewater reuse
The use of treated wastewater in irrigation can positively influence crop production and improve physico-chemical characteristics of soil (Kiziloglu et al., 2007). The presence of nitrogen, phos-phorus, organic matter, and other trace elements in the water provides a good source of nutrients for the growth, yield and quality of crops, minimizes soil degradation, improves fertility and restores the nutrient contents of soil (Benitez et al., 2001; Plauborg et al., 2010; Abusam and Al-Anzi, 2011; Khurana and Singh, 2012; Christou et al., 2014; Almuktar et al., 2015; Almuk-tar and Scholz, 2016). The extra supply of organic carbon or the addition of micro-organisms via wastewater increases the soil microbial activity. This increase in microbial activity of the soil brings benefits to both agriculture and the development of flora and fauna in the soil ecosystem (Friedel et al., 2000). Wastewater reuse can also have an economic benefit since it has limited costs compared to other techniques developed to obtain fresh water. Production of treated wastewater may cost less than the supply of deep groundwater, water import and desalination (Veolia, 2006). A cost-benefit analysis was done in 2014 on treated wastewater reuse by IRSTEA for ONEMA. One focus was the sport of golf in the city of Sainte Maxime, France. Golf consumes 12% of total water volume issued in Sainte Maxime. Using treated wastewater instead of drinking water, golf has an additional cost of 2 million e for the new watering system but it is largely offset by the 5.9 million e of savings in terms of re-grassing, fertilizer and especially water purchase (Loubier and Declercq, 2014).
Negative impacts of wastewater reuse in agriculture
The main downside of reusing treated wastewater in agriculture is the pollution of soil, the po-tential contamination of crops (Khan et al., 2008) and water sources (Batarseh et al., 2011). Municipal wastewater contains a huge quantity and variety of pathogenic agents, such as bacteria, pro-tozoa and viruses. The study of microbial contamination is focused on the pollution of crops rather than the soils receiving wastewater. This is because a greater number of people are exposed to pathogenic microorganisms through consumption of contaminated crops. It also has a significant risk of helminth, bacterial/viral and protozoan infections for farm workers and their families, causing diarrhea and hook-worm disease (Blumenthal and Peasey, 2002). Crops are polluted by direct contact with wastewater during irrigation. Pollution of the edible parts of plants depends not only on the quality of water, but also on the quantity applied to soil, the irrigation method and the type of crop. Other risk factors have only measurable effects over longer periods and increase with the continued use of wastewater, such as the salinity of the soil (Levy et al., 2011; Muyen et al., 2011), the accumulation of toxic chemicals (Kukul et al., 2007) heavy metals and organic compounds (Mapanda et al., 2005; Rattan et al., 2005) . Different levels of risk are perceived for different heavy metals. While some of them are nutrients for plants at trace concentrations (Cu, Fe, Mn, Mo, Zn, Ni) others have been shown to produce harmful effects on exposed organisms or are absorbed by plants and accumulated through the food web (Cr, As, Pb, Hg, Al, Cd). Pollution of soil by organic polluants (pesticides, polyaromatic hydrocarbons, organochlorides, paraffin, organic solvents, etc.) can have different effects in soil organisms depending on the compound. For example some antibiotics (chlortetracycline, etc.) can decrease crop growth and inhibit the microbial activity of the soil. Figure I.2 shows the 20 countries with the highest use of un-treated wastewater for agricultural irrigation. China is the country with the highest volume of untreated wastewater in agriculture (Jimenez et al., 2008), followed by Mexico then the United States. We can also see in this figure sites where monitoring studies are aimed at determining the occurrence of organic pollutants in soils after irrigation with wastewater.
Table of contents :
I Context and Objectives
I.1 Wastewater reuse in irrigation
I.1.1 Context and issues related to the reuse of treated wastewater
I.1.2 Worldwide application of wastewater in irrigation
I.1.4 Water treatment in a Wastewater Treatment Plant (WWTP)
I.1.5 Beneficial and negative impacts of the reuse of treated wastewater for agricultural irrigation
I.2 Irrigation generalities
I.2.1 Irrigation systems
I.2.2 Clogging problems in micro-irrigation systems
I.2.3 Types of drippers
I.2.4 Hydrodynamics and flow behavior of drippers
I.2.5 Parameters influencing clogging in micro-irrigation
I.3 Biofilm 44
I.3.1 Definition of Biofilm
I.3.2 Advantages and disadvantage of biofilms development
I.3.3 The different stages of biofilm development
I.3.4 Factors influencing the different stages of biofilm development in micro-irrigation systems
I.4 Characterization of chemical and biological clogging
Conclusion and thesis objectives
II Materials and Methods
II.1 Characterization of chemical precipitation
II.1.1 Chemical precipitation in batch reactors
II.1.2 Precipitation modeling with PHREEQC
II.2 Effect of shear stress on biofilm development
II.2.1 Taylor-Couette Reactor generalities
II.2.2 Hydrodynamic conditions inside TCR
II.2.3 Choice of the shear stress
II.2.4 TCR speed rotation and parameters
II.2.5 TCR experimental set-up
II.2.6 Experimental protocol
II.2.7 Wastewater Treatment Plant (WWTP) of Mauguio
II.2.8 Analyzing the water quality inside the TCR
II.3 Effect of calcium carbonate on biofilm development
II.3.1 Experimental set-up
II.3.2 Method of fouling analysis
II.3.3 Synthetic effluent quality
II.3.4 Characterization of the fouling material
III Characterization of chemical precipitation
III.1 Experimental characterization
III.1.1 Chemical precipitation
III.1.2 Precipitate characterization by X-ray diffraction (XRD)
III.1.3 Precipitate characterization by thermogravimetric analysis (TGA)
III.1.4 Effect of pH and temperature on calcium carbonate precipitation
III.2 Numerical characterization
III.2.1 Treated wastewater speciation
III.2.2 Calcite saturation index in function of pH and temperature
III.2.3 Experimental and numerical calculation of pH and SI
III.2.4 Numerical precipitation of calcite
III.2.5 Effect of CO2 partial pressure on calcite precipitation
IV Characterization of biological fouling
IV.1 Effect of shear stress on biofilm development
IV.1.1 Validation of the protocol for monitoring the biofilm development kinetics
IV.1.2 Evolution of the fouling in the TCR
IV.1.3 Characterization of fouling chemical composition inside the TCR
IV.2 Effect of calcium carbonate precipitation
IV.2.1 Interaction between calcium carbonate precipitation and biofilm development in irrigation
IV.2.2 Characterization of the fouling by DRX and TGA
IV.2.3 Effect of calcium carbonate precipitation on biofilm development and dripper clogging
V R´esum´e d´etaill´e en Franc¸ais
V.1 Contextes et Objectifs de la th`ese
V.2 Mat´eriels et m´ethodes 162
Qualit´e de l’eau
Pr´ecipitation chimique au laboratoire
Mod´elisation de la pr´ecipitation avec PHREEQC
Effet de la contrainte du cisaillement sur le d´eveloppement du biofilm
Effet du carbonate de calcium sur le d´eveloppement du biofilm
Caract´erisation de l’encrassement
V.3 Caract´erisation de la pr´ecipitation chimique
Pr´ecipitation chimique au laboratoire
Caract´erisation num´erique de la pr´ecipitation chimique
V.4 Caract´erisation du colmatage biologique
D´eveloppement du biofilm en fonction des contraintes de cisaillement
Interaction entre carbonate de calcium et d´eveloppement du biofilm
Conclusion et perspectives
List of Figures
List of Tables