A field study is done to analyze the effects of water reuse for irrigation with a focus on seed germination, crop morphology, crop yield, nutritional values of edible parts, fertilizer reduction, and benefit–cost ratio. For the study, three different crops, Lablab bean, tomato, and chilli, are considered and every crop type is irrigated with groundwater (GW), diluted treated wastewater (DTWW), and treated wastewater (TWW). The study reveals that the DTWW is optimal for seed germination. Crops irrigated with the TWW have the highest morphological characteristics. Crop yield is highest for the TWW-irrigated Lablab bean and DTWW-irrigated tomato. Chilli remains unproductive until the end due to thermal stress. Nutritional values of the edible parts of the DTWW- and TWW-irrigated crops are lower than the GW-irrigated crops. Crops irrigated with the DTWW and TWW are applied with the reduced quantities of N, P and K fertilizers. Indeed, even when the dosages are low those crops are able to produce higher yields than the GW-irrigated crops which are applied with full fertilization. As the crop yield is high and fertilizer cost is less, the benefit–cost ratio is higher for water reuse irrigation than the GW irrigation.

  • Water reuse, use of treated wastewater, for agriculture is one of the sustainable adaptations to combat the climate crisis.

  • This approach can ensure food security of people while conserving freshwater resources but the nutrient satiety of edible parts of crops irrigated with reclaimed water must be verified.

  • The study presented in this paper made an attempt to bridge the gap between the water–nutrient–food nexus of water reuse irrigation.

Water scarcity is one of the significant global issues, affecting most countries and gradually steering some of them to ‘Day Zero’. It arises due to many reasons such as population explosion, urbanization and industrial development, climate crisis, inadequate preparedness, and improper management of resources. Many countries are unable to cope with the rising water demand due to these factors and the persistence of resource-intensive economic development (UN Water 2021). Water scarcity and climate change are intertwined, resulting in extreme weather events and making freshwater availability highly unpredictable. Improper planning and management of water resources indeed results in economic water scarcity and impedes the developmental activities of a nation (Liu & Liu 2021). It is necessary to have an inclusive and integrated water resources management strategy to forestall this finite resource leaving only its footprint for the future.

Sustainable agriculture is essential to address the present and future needs of the communities in terms of food security, livelihood and living standards (FAO). Under water-scarce conditions, agricultural activities and their sustainability are challenging as this sector uses more than 70% of available freshwater (Urbano et al. 2017). In a developing country like India, agriculture is the central pillar of the nation's economy. Moreover, it is vital to ensure the food and nutrition security of the entire population, 1.428 billion, of the nation. Hence, it is necessary to develop a priority axis to search and categorize alternate adaptations to ensure sustainable agriculture (Baanu et al. 2022).

Various adaptations have been identified to reduce the pressure on freshwater resources and to improve agricultural practices (Haghi et al. 2020). Among them, water reuse, i.e., the use of treated wastewater (TWW) or reclaimed water can be seen as a sustainable as well as potential adaptation. It can not only conserve freshwater resources but also prevent environmental pollution by minimizing untreated wastewater discharge. Indeed, TWW can be seen as a source of nutrient supplements (Pereira et al. 2012; Kesari et al. 2021). In a nutshell, water reuse can revitalize agriculture (Djillali et al. 2020; Poustie et al. 2020).

Several literature works related to water reuse for irrigation and its effects on crop growth and yield (Tsadilas & Vakalis 2003; Kang et al. 2007; Libutti et al. 2018; Djillali et al. 2020; Hashmat et al. 2021), physicochemical and microbial properties (Balkhair et al. 2014; Helaly et al. 2018; Petousi et al. 2019; Perulli et al. 2021), and heavy metal accumulation (Gupta et al. 2010; Ghosh et al. 2012; Yaseen et al. 2017; Aftab et al. 2023) were reported. Fortunately, most of the earlier studies were concluded by highlighting the benefits of water reuse: a raise in soil fertility; improvement in crop growth and yield; reduction in energy utilization; and decrease in greenhouse gas emission. Unfortunately, a few studies were concluded with the following paradoxical effects: an increase in soil salinity and consequent reduction in fertility; microbial contamination of soil and its presence in crops; accumulation of heavy metals in soil and crop.

The quality of TWW primarily depends on treatment methods and for this purpose several methods have been developed. These methods include primary and secondary units, and an optional tertiary treatment unit. Primary and secondary treatment processes use physical forces, chemical reactions or microbial actions to treat wastewater, but they produce lower-quality effluent than the methods which include tertiary units (Halakarni et al. 2021). Tertiary treatment methods such as adsorption (El-Bassi et al. 2021; Kim et al. 2022) and membrane processes (Samage et al. 2022; Halakarni et al. 2023a, 2023b) are proven to be more efficient (Mallige et al. 2021).

The research gaps identified in the domain of water reuse for agriculture are: (i) no disquisition on the effect of reclaimed water on seed germination; (ii) no report on dilution of TWW by blending it with freshwater and analysing the effect on crop growth and yield; (iii) only a very few studies on the nutritive analysis of vegetables or fruits when water reuse is adapted; (iv) no studies on quantitative analysis on nutrients supplement by TWW; and (v) no documentation on economic analysis of yield considering the fertilizer reduction cost and augmented benefits of water reuse.

The research objective of the study presented in this paper is to address the above-mentioned grey areas in the domain so as to foster water reuse for agriculture. Considering GW irrigation as the benchmark, the study focused on analysing the effect of reclaimed water irrigation on (i) seed germination; (ii) crop morphological characteristics; (iii) crop yield; (iv) nutritional values of the edible parts; (v) fertilizer reduction; and (vi) benefit–cost (B–C) analysis.

The study was conducted in Sivakasi taluk of Tamil Nadu state, India for a period of 9 months, from June 2022 to March 2023. The study area is located to the East of the Western ghats and is characterized as a flat terrain. Black soil and red soil are the predominant soil groups in the taluk. The taluk experiences a hot and dry climate throughout the year with low rainfall and a low degree of humidity. The chief irrigation source is groundwater (GW) and is under a critical zone due to overexploitation and scanty rainfall. The area is being chosen as it is straggling with water scarcity and decreased agricultural practices. It is gradually transforming into a drought-prone zone primarily due to the climate crisis. Before implementing a potential sustainable adaptation to curb the impact on agriculture, it is imperative to perform a detailed study to know the facts behind closed doors.

In the present study, water reuse is adapted as a supplement as well as a replacement for freshwater irrigation with a focus on the water–food–nutrient nexus approach. An experimental field is prepared and Lablab bean, tomato, and chilli are grown on it. These crops are selected because of their: (i) high intake in the daily diet; (ii) cultivation over a considerable percentage of the gross crop area of the taluk; and (iii) promising return monetary benefits. Each crop type is irrigated separately with GW, diluted treated wastewater (DTWW), and TWW in individual plots separately. The TWW for irrigation is taken from the decentralized sewage treatment plant (D-STP) of the institute, which is located in the Sivakasi taluk. The effects of different irrigation water quality on seed germination, crop morphological characteristics and nutritive values of the edible parts, reduction in fertilizer application and monetary benefits are analyzed. The outcome of the study brings to light that the irrigation water quality has a significant influence on seed germination, crop growth and yield, nutritional values of the edible parts and monetary benefits.

Agro-climatic conditions of the study area

The climate in Sivakasi taluk is semi-arid tropical monsoon type. The area is hot and dry with year-round temperatures between 39 and 22 °C (Figure 1(a)) and humidity between 65.6 and 79.2%. The annual rainfall is between 778 and 812 mm (Baanu et al. 2022). North-East monsoon is the predominant rainy season, which usually onsets from late September and continues till the end of December. The area receives a higher concentration of rainfall in certain months with moderate variations across the years (Figure 1(b)).
Figure 1

Temperature variation and rainfall pattern of the study area: (a) temperature variation and (b) rainfall pattern.

Figure 1

Temperature variation and rainfall pattern of the study area: (a) temperature variation and (b) rainfall pattern.

Close modal

Rabi is the primary agricultural cropping season, in which cultivation spawns from late August to the mid of January. The major crops cultivated in the taluk are rain-fed crops – including maize, cotton, red gram, black gram, Bengal gram, cowpea and millet. In addition, horticultural crops – including mango, guava, banana, amla, beans, tomato, chilli, brinjal, okra, onion and coriander – and flowers – including jasmine, oleander, and tuberose – are also cultivated significantly.

Daily rainfall data and daily minimum and maximum temperature data of the Sivakasi taluk are collected from the Public Works Department (PWD) of Tamil Nadu state for a period of 30 years (1991–2021). These daily data values are summed and averaged to obtain monthly data.

Experimental study

The study is carried out in an experimental field prepared in the institutional campus which is located in Sivakasi taluk. The institution has a D-STP that produces an effluent volume of about 1.5–2 lakh litres per day. The D-STP is a tertiary sewage treatment system which has a raw sewage collection tank, screen chamber, moving bed bio-reactor (MBBR), sand and carbon filter units, and TWW collection tank (Figure 2). The raw sewage is collected from the cafeterias, residential quarters and hostel zones, so it resembles a community domestic wastewater. The chemical oxygen demand (COD) of the raw sewage is 257 mg/l. The GW is pumped from the nearby bore-well available on the institute premises. The DTWW is obtained by mixing equal volumes of TWW and GW.
Figure 2

Process flow diagram of D-STP.

Figure 2

Process flow diagram of D-STP.

Close modal
The experimental field is prepared closer to the D-STP. The soil is sandy clayey loam. To precisely quantify the effect of reclaimed water irrigation on the different parameters of interest, the leaching effect of rainwater has to be prevented. This is obtained by covering the experimental field with transparent flexible polythene sheets but no provision is given for climatic condition control (Figure 3). This polyhouse of size 15 m × 5 m is supported by steel bars and wooden frames. The temperature within the polyhouse is 0.4–0.8 °C higher than the outside temperature; this has been monitored using a temperature sensor.
Figure 3

Outer view of the polyhouse.

Figure 3

Outer view of the polyhouse.

Close modal
The experimental study is conducted for a period of 9 months, from June 2022 to March 2023, as a single cycle crop produced with no repetition. The experimental field has nine plots, each of size 1.5 m × 5 m; lablab bean, tomato, and chilli are grown on them. Three experimental plots are reserved for each crop type; this is to irrigate every crop type separately with GW, TWW, and DTWW (Figure 4). Lablab bean seeds are sown directly in the experimental plots while tomato and chilli are transplanted as seedlings after 45 days of sowing. About 15 crops are grown in each experimental plot and are irrigated at a frequency of 4–7 days. The crop water requirement (CWR) for Lablab bean, tomato and chilli are calculated as 281.2, 474.8, and 393.2 mm, respectively, using Cropwat software. Border strip irrigation, a type of surface irrigation, is implemented to supply the CWR.
Figure 4

Top view of the experimental plot.

Figure 4

Top view of the experimental plot.

Close modal

Soil and water quality analysis

Soil sampling and testing are essential to ascertain the presence of macro and micro nutrients in the soil. In that way, it is an important diagnostic tool for identifying suitable crops for cultivation as well as assessing the fertility of soil (Nguemezi et al. 2020; Suchitra & Pai 2020). Soil samples from the experimental field are collected as per the standard procedure and tested in the soil laboratory for its physicochemical characteristics: electrical conductivity (EC), pH, organic carbon, nitrogen (N), phosphorous (P), potassium (K), nitrate (), nitrite (), ammonia (), calcium (Ca), magnesium (Mg), sodium (Na), iron (Fe), manganese (Mg), zinc (Zn), copper (Cu), boron (B), lead (Pb), mercury (Hg), cadmium (Cd), nickel (Ni), and arsenic (As) (Klimkowicz-Pawlas et al. 2019; Du et al. 2022; Koné et al. 2022; Sdiri et al. 2023).

The physicochemical and microbial characteristics of water are required to quantify the macro and micronutrients available in it and to verify its suitability for irrigation. Thus, the characteristics of the GW, DTWW, and TWW are also analyzed. The physiochemical parameters – including EC, pH, total nitrogen, , , phosphate (), K, Ca, Mg, Na, chloride (), Fe, Mg, Zn, Cu, borate (), Pb, Hg, Cd, Ni, and As – are analyzed (Perulli et al. 2019; Djillali et al. 2020; Biswas et al. 2021; Appiah-Brempong et al. 2022; Licata et al. 2022). The presence of microbes, including Escherichia coli, Coliform and Salmonella, are considered for microbial characterization (Hajji et al. 2022; Ma et al. 2022). In order to verify the suitability of the GW, DTWW, and TWW for irrigation, the laboratory test results are compared against the Food and Agriculture Organization standards (FAO 1985).

Seed germination analysis

The life of a plant begins with its successful seed germination and is followed by the growth of the seedling (Nonogaki et al. 2010; Rajjou et al. 2012). The physiological process – including imbibition of water, cell elongation, and increase in cell number – of seed germination primarily depends on favourable environmental conditions such as light, temperature, soil, and water (Wolny et al. 2018; Xue et al. 2021).

Water is a core element for seed germination; as a matter of fact, the process begins with water imbibition (Luna & Chamorro 2016). Also, water is essential for the enzymatic activities, transportation of the biological macromolecules and antioxidant defence system (Szczerba et al. 2021). Sluggish water could affect seed germination and subsequent crop growth and yield (Sghaier et al. 2022). Therefore, optimal quality as well as desired quantification of water is essential for successful seed germination. To address this, a comparative study is conducted to analyze the influence of the GW, DTWW, and TWW on seed germination of the crops considered for the study, Lablab bean, tomato, and chilli.

Crop morphology analysis

Crop morphology analysis encompasses the study of external features of a plant such as root length, stem diameter at the base, stem height, number of leaves, leaf area, number of fruits, and fruit size (Djillali et al. 2020). The stem diameter at the base, and pod and fruit diameter at the middle are measured using a digital slide vernier calipre (Hassan et al. 2022). The stem height, from the base to the tip of the stem, is measured using a measuring tape. Leaf area is measured using the graphical grid counting method (Datta & Chakroboarty 2018). Randomly five plants are selected from each experimental plot; their morphological characteristics are measured and averaged for comparison.

Crop edible parts analysis

The crop edible parts are hand-harvested periodically. After a harvest, the number of bean pods/fruits and their mass are recorded for every experimental plot. Randomly chosen representative pods/fruits are analyzed in the laboratory for their nutritional values, anti-diabetic and antioxidant capacities, heavy metal accumulation, and microbial quality. The nutritional values include carbohydrates, protein, fat, energy, fibre, cholesterol, and vitamins and minerals (FSSAI 2016).

Reduction in fertilizer application and cost savings

TWW is a rich source of plant nutrients and would be an incentive to farmers. It contains many macro and micronutrients required for crop growth and development (Hussain et al. 2002).

For the experimental study, the fertilizers, nitrogen:phosphorous:potassium (N:P:K), are applied to the crops in two split doses by broadcasting placement. The first dose is applied just after the first weed removal, 30 days from sowing/transplanting, for all the crop types. The second dose is applied at the onset of flowering stage. Conventional full N:P:K dose is applied to the crops irrigated with the GW as per the recommendation. On the other hand, recommended N:P:K doses are curtailed after accounting for the N:P:K supplement available in the corresponding irrigation water, and the reduced doses are applied for the DTWW- and TWW-irrigated crops (Equations (1) and (2)). The fertilizer supplement calculation is done as per the standard guidelines. The savings in fertilizer cost are estimated based on the quantitative reduction in N, P and K and their market prices (Equation (3)).
formula
(1)
formula
(2)
formula
(3)

B–C analysis

The efficiency of any project can be assessed by the B–C analysis. B–C analysis is useful to find a way to use limited resources with the most benefits out of them (Palmer & Torgerson 1999). B–C ratio () (Equation (4)), a profitability index expressed in terms of monetary values, has been used for the B–C analysis (Zangeneh et al. 2008). The project is economically efficient if the benefit outweighs the cost ().

The individual return benefits (income) of the crops irrigated with the GW, DTWW and TWW are calculated from their yield and market selling prices. The cost of cultivation is calculated by accounting for the field preparation, sowing/nursery, weeding, protection, fertilizers, wages and miscellaneous. The rates for these activities for the different crops considered are adopted as per the Tamil Nadu state guidelines.
formula
(4)

Soil and water quality

The topsoil layer is removed and the soil samples at the depth of 0–15 cm are taken from six different locations in the experimental field. The collected samples are thoroughly mixed and foreign materials like debris and stones are removed. Quartering and compartmentalization are done to obtain the desired quantity of representative soil samples for testing.

The test results reveal that the soil is fertile and suitable for agriculture (Table 1). The presence of heavy metals is within the permissible limits (Chary et al. 2008; Pramanik & Chakraborty 2014; Mawari et al. 2022). Lead content is relatively higher but still, its availability is within the permissible limit.

Table 1

Characteristics of the soil

ParameterUnitValuesIndian standards (Mawari et al. 2022)
EC dS/m 0.2 0–3.0 
pH – 8.1 0–9.0 
Organic carbon 0.2 – 
Nitrogen Kg/acre 65.8 – 
Phosphorus Kg/acre 14.0 – 
Potassium Kg/acre 173.2 – 
Nitrate mg/kg 10.5 – 
Nitrite mg/kg <0.1 – 
Ammonia mg/kg 4.6 – 
Calcium mg/kg 354.0 – 
Magnesium mg/kg 120.0 – 
Sodium mg/kg 640.0 – 
Iron mg/kg 1.4 – 
Manganese mg/kg 6.2 – 
Zinc mg/kg 0.2 300.0–600.0 
Copper mg/kg 0.9 135.0–270.0 
Boron mg/kg 0.5 – 
Lead mg/kg 5.8 250.0–500.0 
Mercury mg/kg <0.1 – 
Cadmium mg/kg <0.1 3.0–6.0 
Nickel mg/kg <0.1 75.0–150.0 
Arsenic mg/kg 0.1 – 
ParameterUnitValuesIndian standards (Mawari et al. 2022)
EC dS/m 0.2 0–3.0 
pH – 8.1 0–9.0 
Organic carbon 0.2 – 
Nitrogen Kg/acre 65.8 – 
Phosphorus Kg/acre 14.0 – 
Potassium Kg/acre 173.2 – 
Nitrate mg/kg 10.5 – 
Nitrite mg/kg <0.1 – 
Ammonia mg/kg 4.6 – 
Calcium mg/kg 354.0 – 
Magnesium mg/kg 120.0 – 
Sodium mg/kg 640.0 – 
Iron mg/kg 1.4 – 
Manganese mg/kg 6.2 – 
Zinc mg/kg 0.2 300.0–600.0 
Copper mg/kg 0.9 135.0–270.0 
Boron mg/kg 0.5 – 
Lead mg/kg 5.8 250.0–500.0 
Mercury mg/kg <0.1 – 
Cadmium mg/kg <0.1 3.0–6.0 
Nickel mg/kg <0.1 75.0–150.0 
Arsenic mg/kg 0.1 – 

The GW, DTWW, and TWW which have been used for the irrigation of the experimental plots are sampled and tested; results are compared against the irrigation water standards and found that all are suitable for agriculture (Table 2). The concentrations of macro and micronutrients in the DTWW and TWW are higher than in the GW. They can be considered a good source of nutrients for crop growth and yield. The presence of sodium and chloride is significantly higher in the TWW. This can accelerate the salt accumulation in mains and laterals besides promoting microbial growth, so it is not suitable for micro-irrigation (Zaman et al. 2018; Zhangzhong et al. 2018). The availability of heavy metals and microbes is in trace amounts yet below their threshold limits.

Table 2

Characteristics of the GW, DTWW, and TWW

ParameterUnitGWDTWWTWWFAO standards
NoneSlight to moderateSevere
EC ds/m 0.790 0.910 1.042 <0.7 0.7–3.0 >3.0 
pH – 7.200 7.800 8.000 6.5–8.4   
COD mg/l – 13.600 34.000 –   
Total nitrogen mg/l 30.000 34.400 37.500 –   
Nitrate mg/l 8.200 7.900 8.600 –   
Ammonia mg/l 0.300 0.800 1.200 –   
Phosphate mg/l 0.100 0.200 0.500 –   
Potassium mg/l 2.200 3.800 4.400 –   
Calcium mg/l 84.000 78.000 89.000 – – – 
Magnesium mg/l 1.900 1.000 1.500 – – – 
Sodium mg/l 0.913 4.045 16.747 <3.0 3.0–9.0 >9.0 
Chloride mg/l 3.934 6.206 6.603 <4.0 4.0–10.0 >10.0 
Sulphate mg/l 112.000 145.000 189.000 – 
Iron mg/l BDL 0.050 0.240 5.00 
Manganese mg/l BDL BDL BDL 0.20 
Zinc mg/l BDL BDL 0.160 2.00 
Copper mg/l BDL BDL 0.050 0.20 
Borates mg/l BDL BDL 0.120 – 
Lead mg/l BDL BDL 0.020 5.00 
Mercury mg/l BDL BDL BDL – 
Cadmium mg/l BDL BDL BDL 0.01 
Nickel mg/l BDL BDL BDL 0.20 
Arsenic mg/l BDL BDL BDL 0.10 
E. coli CFU/ml Absent Absent 100.000 – 
Coliform CFU/ml Absent 100.000 500.000 – 
Salmonella CFU/ml Absent Absent Absent – 
ParameterUnitGWDTWWTWWFAO standards
NoneSlight to moderateSevere
EC ds/m 0.790 0.910 1.042 <0.7 0.7–3.0 >3.0 
pH – 7.200 7.800 8.000 6.5–8.4   
COD mg/l – 13.600 34.000 –   
Total nitrogen mg/l 30.000 34.400 37.500 –   
Nitrate mg/l 8.200 7.900 8.600 –   
Ammonia mg/l 0.300 0.800 1.200 –   
Phosphate mg/l 0.100 0.200 0.500 –   
Potassium mg/l 2.200 3.800 4.400 –   
Calcium mg/l 84.000 78.000 89.000 – – – 
Magnesium mg/l 1.900 1.000 1.500 – – – 
Sodium mg/l 0.913 4.045 16.747 <3.0 3.0–9.0 >9.0 
Chloride mg/l 3.934 6.206 6.603 <4.0 4.0–10.0 >10.0 
Sulphate mg/l 112.000 145.000 189.000 – 
Iron mg/l BDL 0.050 0.240 5.00 
Manganese mg/l BDL BDL BDL 0.20 
Zinc mg/l BDL BDL 0.160 2.00 
Copper mg/l BDL BDL 0.050 0.20 
Borates mg/l BDL BDL 0.120 – 
Lead mg/l BDL BDL 0.020 5.00 
Mercury mg/l BDL BDL BDL – 
Cadmium mg/l BDL BDL BDL 0.01 
Nickel mg/l BDL BDL BDL 0.20 
Arsenic mg/l BDL BDL BDL 0.10 
E. coli CFU/ml Absent Absent 100.000 – 
Coliform CFU/ml Absent 100.000 500.000 – 
Salmonella CFU/ml Absent Absent Absent – 

BDL, below detectable limit.

Seed germination

Soil from the experimental field is collected in nine small containers; three for every crop type. The seeds of each crop type are sown in the respective containers and watered with the GW, DTWW, and TWW separately, and the progress is monitored (Figure 5). The seeds watered with the DTWW germinate first and indeed develop at a faster pace than the rest for all the three crop types, followed by TWW and GW. The higher salinity of TWW and lower nutrient concentration of GW would have decelerated the seed germination process.
Figure 5

Effect of water quality on seed germination: (a) Lablab bean, (b) tomato, and (c) chilli.

Figure 5

Effect of water quality on seed germination: (a) Lablab bean, (b) tomato, and (c) chilli.

Close modal

Crop morphology

The crop morphology analysis (Figures 6 and 7) shows that the crops irrigated with the TWW possess the highest morphological characteristics such as root length, stem height, number of leaves, and leaf area. However, the basal stem diameter and pod/fruit size are almost the same for all the irrigation water quality.
Figure 6

Crop morphology: (a) Lablab bean, (b) tomato, and (c) chilli.

Figure 6

Crop morphology: (a) Lablab bean, (b) tomato, and (c) chilli.

Close modal
Figure 7

Morphological characteristics of the crops: (a) Lablab bean, (b) tomato, and (c) chilli.

Figure 7

Morphological characteristics of the crops: (a) Lablab bean, (b) tomato, and (c) chilli.

Close modal

For Lablab bean, root length and leaf area are lower for the crops irrigated with the DTWW than the GW; however, the stem height and number of leaves are greater for the DTWW. In case of tomato, all four parameters – root length, stem height, number of leaves, and leaf area – are higher for the crops irrigated with the DTWW than the GW. The growth rate of chilli more or less resembles the pattern of Lablab beans. However, chilli is more sensitive to the thermal stress induced by the polyhouse. Stunted growth, poor pollination, very little flowering, and drying and falling of flower buds are the results of the thermal stress and it remains unproductive until the end.

When compared to the GW and DTWW, the TWW has higher micronutrients as well as macronutrients. In fact, the presence of iron, zinc, copper, and boron in the TWW can eliminate the foliar spray application for feeding the micronutrients. The crop morphological characteristics lead to the conclusion that TWW irrigation provides more vital nutrients for crop growth and development; thereby considerably improving their morphological characteristics. Fortunately, plants irrigated with TWW are in good health condition; this is ensured by the absence of leaf and root diseases.

Crop yield

The harvesting started after 3 months of the sowing and planting for Lablab bean and tomato, respectively, and thereafter lasted for a period of 5 months, from October 2022 to February 2023. More than 20 pod/fruit pickings are done at an average interval of 3–5 days. For the Lablab bean, the total number of pods and cumulative mass yielded are significantly higher for the TWW irrigation than the other two (Table 3). On the other hand, for tomatoes, the crops irrigated with the DTWW produced a higher yield than the other two. This proves that the presence of higher macro and micronutrients in the reclaimed water significantly improves crop yield. Unfortunately, the yield from the TWW-irrigated tomato is even lower than the GW-irrigated crops. This manifests that TWW has some detrimental effects on yield in some types of crops. Interestingly, dilution works in a better way for this case. More importantly, crops irrigated with DTWW and TWW are able to produce higher yields than the GW irrigation in most cases, even when reduced quantities of fertilizers are applied for these fields.

Table 3

Number of pods/fruits and their mass

IrrigationLablab bean
Tomato
No. of podsMass (g)No. of fruitsMass (g)
GW 397 2,673 380 12,999 
DTWW 422 2,727 412 14,073 
TWW 1,006 7,098 340 10,064 
IrrigationLablab bean
Tomato
No. of podsMass (g)No. of fruitsMass (g)
GW 397 2,673 380 12,999 
DTWW 422 2,727 412 14,073 
TWW 1,006 7,098 340 10,064 

Crop edible parts quality

There is no yield from the chilli plants grown in the polyhouse, hence, only the edible parts of Lablab bean and tomato are analyzed for their quality: nutrient values, vitamins and minerals, anti-diabetic and antioxidant capacities, and lycopene content in tomato (Table 4); heavy metal accumulation (Table 5); microbial quality (Table 6).

Table 4

Nutritive values of edible parts of the crops

Lablab beans
Tomato
ParametersUnitsGWDTWWTWWGWDTWWTWW
Carbohydrates 9.55 9.17 7.42 5.17 4.67 5.09 
Protein 4.36 3.14 3.28 1.60 1.14 1.20 
Total fat 0.40 0.38 0.30 0.23 0.20 0.21 
Energy kcal 59.20 52.70 45.50 29.20 25.04 27.05 
Fibre 4.18 3.05 3.10 1.52 1.38 1.46 
Cholesterol mg 0.00 0.00 0.00 0.00 0.00 0.00 
Iron mg 0.85 0.76 0.71 0.57 0.48 0.52 
Calcium mg 17.60 14.80 15.20 5.60 5.00 5.20 
Phosphorus mg 80.00 71.00 68.00 31.00 27.00 27.00 
Potassium mg 106.00 94.00 115.00 166.00 160.00 166.00 
Magnesium mg 20.40 15.20 12.40 6.40 5.90 6.50 
Zinc mg 0.60 0.40 0.27 0.14 0.10 0.12 
Copper mg 0.02 0.02 0.02 0.04 0.05 0.05 
Folic acid μg 75.00 65.00 60.00 30.00 27.00 27.00 
Vitamin A μg 12.50 9.70 10.60 85.00 80.00 80.00 
Vitamin C mg 1.80 1.30 1.50 17.50 16.80 17.50 
Anti-diabetic property (IC50mg 56.90 70.30 66.00 86.30 90.50 90.20 
Antioxidant property (IC50mg 54.20 62.10 59.50 51.80 54.70 53.00 
Lycopene content in tomato (mg) 3.50 3.00 3.20 
Lablab beans
Tomato
ParametersUnitsGWDTWWTWWGWDTWWTWW
Carbohydrates 9.55 9.17 7.42 5.17 4.67 5.09 
Protein 4.36 3.14 3.28 1.60 1.14 1.20 
Total fat 0.40 0.38 0.30 0.23 0.20 0.21 
Energy kcal 59.20 52.70 45.50 29.20 25.04 27.05 
Fibre 4.18 3.05 3.10 1.52 1.38 1.46 
Cholesterol mg 0.00 0.00 0.00 0.00 0.00 0.00 
Iron mg 0.85 0.76 0.71 0.57 0.48 0.52 
Calcium mg 17.60 14.80 15.20 5.60 5.00 5.20 
Phosphorus mg 80.00 71.00 68.00 31.00 27.00 27.00 
Potassium mg 106.00 94.00 115.00 166.00 160.00 166.00 
Magnesium mg 20.40 15.20 12.40 6.40 5.90 6.50 
Zinc mg 0.60 0.40 0.27 0.14 0.10 0.12 
Copper mg 0.02 0.02 0.02 0.04 0.05 0.05 
Folic acid μg 75.00 65.00 60.00 30.00 27.00 27.00 
Vitamin A μg 12.50 9.70 10.60 85.00 80.00 80.00 
Vitamin C mg 1.80 1.30 1.50 17.50 16.80 17.50 
Anti-diabetic property (IC50mg 56.90 70.30 66.00 86.30 90.50 90.20 
Antioxidant property (IC50mg 54.20 62.10 59.50 51.80 54.70 53.00 
Lycopene content in tomato (mg) 3.50 3.00 3.20 
Table 5

Heavy metal accumulation in edible parts of the crops

Heavy metals (mg/kg)Lablab beans
Indian standardsTomato
Indian standardsa
GWWDWWTWWGWWDWWTWW
Lead <0.01 <0.01 0.40 0.20 <0.01 <0.01 0.15 0.10 
Mercury <0.01 <0.01 <0.01 1.00 <0.01 <0.01 <0.01 1.00 
Cadmium <0.01 <0.01 <0.01 0.05 <0.01 <0.01 <0.01 0.10 
Nickel <0.01 <0.01 <0.01 1.00 <0.01 <0.01 <0.01 1.00 
Arsenic <0.01 <0.01 <0.01 1.10 <0.01 <0.01 <0.01 1.10 
Heavy metals (mg/kg)Lablab beans
Indian standardsTomato
Indian standardsa
GWWDWWTWWGWWDWWTWW
Lead <0.01 <0.01 0.40 0.20 <0.01 <0.01 0.15 0.10 
Mercury <0.01 <0.01 <0.01 1.00 <0.01 <0.01 <0.01 1.00 
Cadmium <0.01 <0.01 <0.01 0.05 <0.01 <0.01 <0.01 0.10 
Nickel <0.01 <0.01 <0.01 1.00 <0.01 <0.01 <0.01 1.00 
Arsenic <0.01 <0.01 <0.01 1.10 <0.01 <0.01 <0.01 1.10 

aIndian standards for food safety and standards, 2011 (FSSAI 2011).

Table 6

Microbial quality of edible parts of the crops

Microbes (CFU/g)Lablab beans
Tomato
Indian standardsa
GWWDWWTWWGWWDWWTWW
E. coli Absent 2,000  250 Absent 1,500  400 To be absent 
Coliform Absent 4,700 1,000 Absent 5,000 1,800 <10 
Salmonella Absent Absent Absent Absent Absent Absent To be absent 
Microbes (CFU/g)Lablab beans
Tomato
Indian standardsa
GWWDWWTWWGWWDWWTWW
E. coli Absent 2,000  250 Absent 1,500  400 To be absent 
Coliform Absent 4,700 1,000 Absent 5,000 1,800 <10 
Salmonella Absent Absent Absent Absent Absent Absent To be absent 

aIndian standards for microbial food safety and standards (IS 5402 2012).

The edible parts of both Lablab bean and tomato crops, irrigated with the GW, have considerably higher nutrients than those crops irrigated with the DTWW and TWW (Table 4). While taking the nutrient values of GW-irrigated crops as the benchmark (100%), the availability of all the nutrients is considerably less for both DTWW- and TWW-irrigated crops of Lablab bean and tomato (Figure 8). Relatively, the reduction is higher on Lablab beans than on tomatoes except for protein, for which it is more or less the same on both of them. This throws light on the fact that the reduction in nutrient values varies based on the crop type.
Figure 8

Nutrition, vitamins, and mineral availability of crops with respect to GW-irrigated crops: (a) nutritional availability of Lablab bean, (b) nutritional availability of tomato, (c) vitamins and mineral availability of Lablab bean, and (d) vitamins and mineral availability of tomato.

Figure 8

Nutrition, vitamins, and mineral availability of crops with respect to GW-irrigated crops: (a) nutritional availability of Lablab bean, (b) nutritional availability of tomato, (c) vitamins and mineral availability of Lablab bean, and (d) vitamins and mineral availability of tomato.

Close modal

The majority of the vitamins and minerals are available in relatively higher levels in the edible parts of the crops, both Lablab bean and tomato, irrigated with the GW (Table 4). However, the availability of potassium is higher in the TWW-irrigated Lablab bean; magnesium is slightly higher in the TWW-irrigated tomato; copper is higher in the DTWW- and TWW-irrigated tomatoes (Figure 8). Like major nutrients, the reduction in vitamins and minerals, especially vitamins, is also relatively more in Lablab beans.

The anti-diabetic and antioxidant capacities are generally expressed in terms of Inhibitory Concentration (IC50) values. IC50 refers to the amount of drug required to suppress the biological process by half (Aykul & Hackert 2016). Anti-diabetic property is assessed using α-glucosidase inhibition activity and antioxidant capacity is assessed using α, α-diphenyl-β-picryl hydrazyl (DPPH) assay (Kedare & Singh 2011; Baliyan et al. 2022). A higher value of IC50 represents a lower capacity and vice versa. The anti-diabetic and antioxidant capacities are more for the Lablab bean and tomato crops irrigated with the GW. When comparing the DTWW- and TWW-irrigated crops of Lablab bean and tomato, the capacities are more for the TWW-irrigated crops. Lycopene content, one of the potential natural antioxidants of tomato, is the primary reason for the brightest red colour and all of its positive health effects (Imran et al. 2020). It is assessed using the UV-Vis spectrophotometric method (Barba et al. 2006; FAO 2006; Alda et al. 2009). Tomato irrigated with the GW has the highest level of lycopene, followed by TWW and DTWW.

Accumulation of heavy metals except lead (only for the crops irrigated with TWW) is within the permissible limits of Indian standards for vegetables and fruits (Table 5). Lead content is significantly higher in Lablab beans and slightly higher in tomatoes than the allowable limit. Accumulation of heavy metals is higher in reclaimed water irrigation and the results are in agreement with the earlier studies (Gupta et al. 2010; Hussain & Qureshi 2020; Othman et al. 2021). In a nutshell, heavy metal accumulation is higher in TWW irrigation, followed by DTWW and GWW.

The microbial quality analysis reveals that the edible parts of the GW-irrigated crops are germ-free (Table 6). Whereas, Escherichia coli and Coliform make their presence in the TWW- and DTWW-irrigated Lablab bean and tomato. Unfortunately, their presence is more on DTWW-irrigated crops than the TWW-irrigated crops for both Lablab bean and tomato. This demands further research to bring out the logical reason. Fortunately, none of the crops contains Salmonella bacteria, a highly infectious disease-causing pathogen that affects human health.

The prime factor for the reduced nutritive values could be biotic stress resulting from the excess microbial activities. The microorganisms affect metabolic activities and induce physiological stress, ultimately impacting plant development (Perulli et al. 2021). Again, the presence of microorganisms in an edible part breaks down the components such as protein, carbohydrate, amino-acid, and sugar by excreting lytic enzymes, thereby altering the biochemical reactions (Tournas 2005). Also, the microorganisms break the plant cell wall by softening it and utilizing the starch, carbon sources, lipids, vitamins, and minerals for their survival development, which in turn reduces the nutritive values of the vegetables or fruits (Alegbeleye et al. 2018).

Reduction in fertilizer application and cost savings

The physiochemical characteristics of the DTWW and TWW make it clear that they have more potential for supplementing the soil nutrient requirements when compared to the GW as they have relatively higher concentrations of macro and micronutrients (Table 2). When compared to the GW, excess N, P, and K available in DTWW are 14.7, 100 and 72.7%, respectively; TWW are 25.0, 400, and 100%, respectively. Iron is available in the DTWW and TWW but its availability is below the detectable limit in the GW. It is noteworthy that zinc, copper, and borates are available only in TWW.

The conventional fertilizer dose estimated for Lablab bean, tomato, and chilli are 10.0:15.0:7.5, 60.0:30.0:15.0, and 66.0:16.0:25.0, respectively. To meet these requirements, fertilizers, namely urea, Single Super Phosphate (SSP), and Muriate of Potash (MOP), are applied in the experimental field. The crops irrigated with GW are applied with a conventional dose of fertilization, and the dosage for the crops irrigated with the DTWW and TWW are curtained after accounting for the supplemental fertilizer availability (Baanu et al. 2022) in the reclaimed water (Table 7). The reduction in the requirement of N is significant, followed by a considerable reduction in K and a marginal reduction in P for all the crops.

Table 7

Fertilizer reductions of the DTWW and TWW irrigation

CropConventional dose of N:P:KN:P:K supplement by DTWWN:P:K supplement by TWWReduced dose of N:P:K for DTWW irrigationReduced dose of N:P:K for TWW irrigation% reduction in N:P:K for DTWW irrigation% reduction in N:P:K for TWW irrigation
(kg/acre)(kg/acre)(kg/acre)(Equation (1))(Equation (1))(% N:%P:%K) (% N:%P:%K)
Lablab beans 10.0:15.0:07.5 39.36:0.22:4.32 42.66:0.43:3.79  0.00:14.77:3.17 0.00:14.43:2.49 100.0:1.5:58.0 100.0:3.8:67.0 
Tomato 60.0:30.0:15.0 66.49:0.38:7.30 72.06:0.96:8.45  0.00:29.61:7.69 0.00:29.03:6.54 100.0:1.3:49.0 100.0:3.2:56.0 
Chilies 66.0:16.0:25.0 55.01:0.31:6.04 59.62:0.79:6.99 10.98:15.68:18.95 6.37:15.20:18.00  83.3:2.0:24.0  90.3:5.0:28.0 
CropConventional dose of N:P:KN:P:K supplement by DTWWN:P:K supplement by TWWReduced dose of N:P:K for DTWW irrigationReduced dose of N:P:K for TWW irrigation% reduction in N:P:K for DTWW irrigation% reduction in N:P:K for TWW irrigation
(kg/acre)(kg/acre)(kg/acre)(Equation (1))(Equation (1))(% N:%P:%K) (% N:%P:%K)
Lablab beans 10.0:15.0:07.5 39.36:0.22:4.32 42.66:0.43:3.79  0.00:14.77:3.17 0.00:14.43:2.49 100.0:1.5:58.0 100.0:3.8:67.0 
Tomato 60.0:30.0:15.0 66.49:0.38:7.30 72.06:0.96:8.45  0.00:29.61:7.69 0.00:29.03:6.54 100.0:1.3:49.0 100.0:3.2:56.0 
Chilies 66.0:16.0:25.0 55.01:0.31:6.04 59.62:0.79:6.99 10.98:15.68:18.95 6.37:15.20:18.00  83.3:2.0:24.0  90.3:5.0:28.0 

When compared to GW irrigation, the use of DTWW and TWW for irrigation reduces the fertilizer cost significantly (Table 8). The reduction in fertilizer application not only reduces its cost but also could bring down the magnitude of fertilizer production and associated energy requirements and greenhouse gas emissions. Also, the use of reclaimed water for agriculture curtails the GW pumping and thereby conserves freshwater resources.

Table 8

Savings in fertilizer cost of the DTWW and TWW irrigation

Cost of conventional N:P:K fertilizerCost of fertilizer for DTWW irrigationCost of fertilizer for TWW irrigationNet savings in fertilizer cost for DTWW
Net savings in fertilizer cost for TWW
Crop(₹)(₹)(₹)(₹)(%)(₹)(%)
Lablab beans  828.0  617.0  591.0 211.0 25 237.0 25 
Tomato 2,116.0 1,264.0 1,219.0 852.0 40 897.0 42 
Chilies 1,860.0 1,087.0 1,003.0 773.0 41 853.0 46 
Cost of conventional N:P:K fertilizerCost of fertilizer for DTWW irrigationCost of fertilizer for TWW irrigationNet savings in fertilizer cost for DTWW
Net savings in fertilizer cost for TWW
Crop(₹)(₹)(₹)(₹)(%)(₹)(%)
Lablab beans  828.0  617.0  591.0 211.0 25 237.0 25 
Tomato 2,116.0 1,264.0 1,219.0 852.0 40 897.0 42 
Chilies 1,860.0 1,087.0 1,003.0 773.0 41 853.0 46 

B–C analysis

For the B–C analysis, income is calculated for the typical minimum (₹20 per kg) and maximum (₹40 per kg) market prices of Lablab bean and tomato (Table 9). The B–C analysis brings out that the ratio is highest for the TWW-irrigated Lablab bean, followed by the DTWW irrigation. The ratio for the maximum selling price is 1.5 times the value corresponding to the minimum selling price for Lablab bean. On the other hand, the yield is higher for the DTWW-irrigated tomato and thereby the ratio is also highest for it. The ratio for the maximum selling price is twofold the value of the minimum selling price for tomatoes. Relatively, tomatoes yield better monetary benefits than the Lablab beans.

Table 9

Benefit–cost analysis

Cost of cultivation per hectareLablab beans
Tomato
GWDTWWTWWGWDTWWTWW
Field preparation 6,000 6,000 6,000 6,000 6,000 6,000 
Sowing/Nursery 7,000 7,000 7,000 7,000 7,000 7,000 
Weeding 10,000 10,000 10,000 10,000 10,000 10,000 
Plant protection 12,000 12,000 12,000 12,000 12,000 12,000 
Fertilizers 6,000 4,500 4,320 8,000 4,800 4,640 
Wages 5,000 5,000 5,000 13,000 13,000 13,000 
Miscellaneous 5,000 5,000 5,000 5,000 5,000 5,000 
Total 51,000 49,500 49,320 61,000 57,800 57,640 
Benefit (per hectare)       
Yield from experimental plot (g) 2,673 2,727 7,098 12,999 14,073 10,064 
Projected yield per hectare (kg) 3,605 3,678 9,573 17,531 18,980 13,573 
Selling price @ ₹ 40/kg 108,150 110,334 287,185 701,253 759,191 542,919 
Selling price @ ₹ 20/kg 72,100 73,556 191,457 350,626 379,596 271,460 
for maximum market price 2.12 2.23 5.82 11.50 13.13 9.42 
for minimum market price 1.41 1.49 3.88 5.75 6.57 4.71 
Cost of cultivation per hectareLablab beans
Tomato
GWDTWWTWWGWDTWWTWW
Field preparation 6,000 6,000 6,000 6,000 6,000 6,000 
Sowing/Nursery 7,000 7,000 7,000 7,000 7,000 7,000 
Weeding 10,000 10,000 10,000 10,000 10,000 10,000 
Plant protection 12,000 12,000 12,000 12,000 12,000 12,000 
Fertilizers 6,000 4,500 4,320 8,000 4,800 4,640 
Wages 5,000 5,000 5,000 13,000 13,000 13,000 
Miscellaneous 5,000 5,000 5,000 5,000 5,000 5,000 
Total 51,000 49,500 49,320 61,000 57,800 57,640 
Benefit (per hectare)       
Yield from experimental plot (g) 2,673 2,727 7,098 12,999 14,073 10,064 
Projected yield per hectare (kg) 3,605 3,678 9,573 17,531 18,980 13,573 
Selling price @ ₹ 40/kg 108,150 110,334 287,185 701,253 759,191 542,919 
Selling price @ ₹ 20/kg 72,100 73,556 191,457 350,626 379,596 271,460 
for maximum market price 2.12 2.23 5.82 11.50 13.13 9.42 
for minimum market price 1.41 1.49 3.88 5.75 6.57 4.71 

₹, Indian rupees.

In fact, even if the ratio for TWW irrigation is less than freshwater irrigation, its value is greater than one, so water reuse for irrigation can be considered as a successful adaptation. This is because water reuse reduces the existing pressure on freshwater resources; water reuse makes agriculture possible in an area where otherwise it would be abandoned due to the unavailability of water.

This paper presented an experimental field study focusing on the effect of water reuse, i.e., the use of reclaimed water on three crops, namely Lablab bean, tomato, and chilli in a polyhouse experimental field. For the study, three types of irrigation were used: GW, TWW, and DTWW (50% GW and 50% TWW). The specific outcomes of the research objective are as follows:

  • The seed germination is fastest when it is watered with the DTWW, followed by the TWW and GW watering. The high salinity of the TWW and the low nutrient concentration of the GW would be the reason for the slower germination. Thus, DTWW is recommended for seed germination; however, the optimal mixing ratio of GW and TWW for dilution may vary for different crop types and soil conditions. Further study shall be devoted to this area to arrive at the optimal blending ratio for a particular scenario.

  • The crop morphological characteristics – root length, stem height, number of leaves, and leaf area – were maximum for the crops – Lablab bean, tomato, and chilli – irrigated with the TWW. However, the size of the Lablab bean pods and tomato fruits neither increased nor decreased when using the reclaimed water, both DTWW and TWW irrigation.

  • The TWW-irrigated Lablab bean was able to produce about 2.7 times the yield of the GW-irrigated crops but the increase is meagre in the DTWW-irrigated crops. On the other hand, DTWW-irrigated tomatoes produced about 1.1 times the yield of the GW-irrigated crops and indeed the TWW-irrigated crop yield is the least. This output highlights the need for optimal blending of GW and TWW for higher yields of certain crops. Further study shall be devoted to addressing this issue as well.

  • Concerning the nutritive values of the edible parts of the crops, both DTWW and TWW irrigation could not reach the corresponding values associated with the GW-irrigated crops. This would be due to the biotic stressors, the presence of microorganisms, in the edible parts. The marginal presence of microorganisms in the pods and fruits of the DTWW- and TWW-irrigated crops would not pose any serious health risk to the consumers, but it is necessary to prevent the raw consumption of such edible parts and is required to be boiled.

Analyses on crop yield and nutritional values of the edible parts lead to a conclusion that a greater number of studies have to be done with different – including crop types, soil types and TWW quality – conditions with a prime focus on nutritional values as well as yield. One has to choose crops that can produce high yields without losing the nutrient values much when using reclaimed water for irrigation. The farmers may be interested in the crops which yield more when using the reclaimed water but the government has to take initiatives to develop frameworks in order to ensure the nutritional security of the people.

  • The reduction in fertilizer quantity for the DTWW- and TWW-irrigated crops was done after accounting for the N, P, and K values available in the reclaimed water. The N fertilizer reduction is the maximum while the reduction in P is the minimum. Thus, reduced dosage of fertilizer application by careful accounting of the fertilizer supplement available in the reclaimed water is recommended for water reuse agriculture.

  • The B–C analysis brought out that the use of TWW for the irrigation of crops would be an alternative and sustainable adaptation to combat climate crises in water-scarce regions with a high B–C ratio neglecting the associated energy cost.

This research throws light on the fact that the quality of irrigation water plays a pivotal role in agricultural productivity in terms of food and nutritional values. This water–nutrient–food nexus approach shall be disseminated by highlighting the need for resource recovery, promoting food security, and creating awareness of nutrient availability to mitigate the climate crisis. These three factors ultimately contribute towards the achievement of Sustainable Development Goals (SDGs), especially SDGs 2 and 6. However, it is imperative that water reuse for agriculture must be subjected to varietal assessments as well as periodic monitoring in order to avoid any possible health hazards. Furthermore, good agronomic practices are also essential, to ensure the triple bottom line of sustainability: social, environmental, and economic development.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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