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Article

Evaluation of the Characteristics of Pollutant Discharge in Tomato Hydroponic Wastewater (HWW) for Sustainable Water Management in Korea

by
Jinkwan Son
Research Institute of Environment Ecology & Green Space, Sanglimwon Co., Ltd., Seongnam 13590, Gyeonggi-do, Republic of Korea
Water 2024, 16(5), 720; https://doi.org/10.3390/w16050720
Submission received: 7 February 2024 / Revised: 23 February 2024 / Accepted: 26 February 2024 / Published: 28 February 2024
(This article belongs to the Special Issue Water, Wastewater and Waste Management for Sustainable Development)
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Abstract

:
In South Korea, the use of hydroponic cultivation has been on the rise. However, this system produces a large amount of wastewater. In this study, the amount of wastewater generated by hydroponic tomato cultivation is identified, and a management plan is proposed. Based on the analysis of 103 tomato HWW samples, it was found that the electrical conductivity (EC) was 4.25 ± 1.01 dS/m, the nitrogen (N) content was 411.21 ± 122.64 mg/L, and the phosphorus (P) content was 47.74 mg/L, which caused eutrophication. Therefore, agricultural reuse and HWW treatment were proposed. Regarding the annual HWW load, 1 ha of hydroponics discharges 964.26 kg/ha of N, 111.95 of P, 937.46 of K, 795.14 of Ca, 313.83 of Mg, and 405.40 of S. The trace elements were heavy metals, which were calculated as Fe—4.03, Mn—0.77, Zn—1.08, B—2.25, Cu—0.38, and Mo—0.05 kg/ha. Since wastewater is a national source of drinking water, it needs to be collected and treated. Inter-item correlation analysis showed that most of the fertilizer components were correlated with the EC concentrations. This study can be used to determine the concentrations required for agricultural reuse and to determine the treatment capacity in HWW management.

1. Introduction

South Korea is traditionally an agricultural country, with cropland accounting for 23% of the country’s land area in the 1970s [1]. Rice paddies are one of the country’s most important agricultural crops. South Korea has developed more than 1600 reclaimed land parcels to produce rice, converting them into paddy fields [2,3]. However, in recent years, rice consumption has declined due to increased imports and free trade agreements (FTAs), which have ultimately increased the consumption of fast food [4]. During the winter season in Korea, rice production is not possible, so the paddy fields are generally dormant. To address the instability of the rice market and difficulties in farm management, the Korean government has invested heavily in rural livelihood improvement and income enhancement (e.g., fostering successor workers, increasing farm income, regional revitalization projects, rural welfare projects, the cultivation of alternative crops, and the horticulture industry) [5,6,7,8,9,10].
Among the improvements, the horticulture industry has been able to grow a variety of vegetables and fruits even in winter by keeping them warm using horticulture greenhouses [11,12,13]. The horticulture industry in Korea has been recognized as a “white revolution” because it generates a lot of income [12,13]. It accounts for more than 40% of the horticulture industry, ranking third in the world in terms of area and significantly contributing greenhouse horticulture to the total agricultural income [11,14,15,16]. Various countries, such as China, Spain, the Netherlands, and Japan, are known as the world’s leading producers [17,18,19]. Due to the number of its advantages, including year-round production, automation, short production runs, labor savings, and fast income generation, the area of horticulture continues to increase [14,20,21]. However, a number of environmental and ecological problems have been reported, including rapid land use changes, groundwater depletion, waste disposal, and nonpoint pollution emissions due to the establishment of large-scale horticulture complexes [22,23,24,25,26,27]. Recent studies related to horticulture studies have focused on crop production, including environmental control, such as cooling and heating [28,29,30], energy efficiency [31,32,33], stability [34,35,36], and nutrient solution [37,38,39]; however, it is difficult to find studies on the creation of eco-friendly and ecological horticulture greenhouse complexes.
In a study by Son et al. [40], they identified 12 ecological functions that need to be considered when creating a horticultural complex. The main targets were analyzed in the following order: (1) water pollutant discharge measures, (2) groundwater depletion measures and cultivation measures, (3) securing surface water storage space, (4) flood control measures, (5) vegetation diversity space measures, (6) carbon emission reduction measures, (7) securing habitats for aquatic insects, and (8) securing habitats for amphibian reptiles. Among these, water pollution caused by HWW discharge, which was identified as the most urgent, hinders a sustainable global environment [41,42,43]. These discharges are uncontrolled nonpoint source (NPS) pollution. In fact, there have been cases where nutrient solutions discharged from horticulture cultivation have contaminated groundwater [44], rivers [45], fields [46], and dams [47]. For this reason, recycling technologies that reduce the off-site runoff of nutrient solutions continue to be promoted in countries such as the Netherlands, Spain, and Japan [48].
South Korea has more than 50,000 hectares of horticultural facilities, and hydroponic cultivation continues to grow [49]. The rise of hydroponics is not limited to South Korea; it is also occurring in Japan, the Netherlands, and China [50]. Hydroponics continues to grow in the form of plant factories [51], urban agriculture [52], and aquaponics [53]. Compared to soil cultivation, nutrient solution cultivation is an easy way to apply nutrients directly. However, overflowing fertilizers in nutrient solution cultivation is a unique horticultural technique [54,55,56] that generates up to 30% HWW [57,58]. This HWW contains large amounts of nutrients such as N, P, K, and Mg [55,56,59,60]. N and P are eutrophicating agents that affect rivers and even drinking water [61,62]. In Korea, newly constructed horticulture greenhouses are increasingly being equipped with circular nutrient solution reprocessing facilities for HWW reuse [56,63]. Various technologies, such as filtering [64,65,66], storage [67], sedimentation [68], and microbubbles [69,70], are being developed for the recycling of nutrient solutions. In addition, small-scale artificial wetlands [71,72], soil treatment [73,74], and natural remediation processes [75] have been studied for the treatment of HWW. In advanced countries, including the Netherlands, Canada, and Japan, 95%, 30%, and more than 45% of the horticultural facilities, respectively, have adopted circular hydroponic systems that reuse nutrient solutions [76,77,78]. It is expected that all water and nutrient solutions from hydroponic systems will eventually be prohibited from being discharged into the environment [78,79].
NPS pollution is a source of water pollution that is difficult to manage due to its unspecified origin, duration, and location [80,81,82]. The management of nonpoint pollution is a very important issue in water management, both domestically and internationally [83,84,85]. According to statistics in Korea, more than 68% of pollutants entering rivers and lakes are from nonpoint sources [86,87,88], and many reduction projects are being implemented by the national government, local governments, and basin units to improve the water quality of major rivers. The management of these nonpoint sources is considered very important because they are connected to national drinking water sources [83,89,90,91,92]. Agriculture and livestock farming are representative of nonpoint pollution, and to manage pollution sources, rural sewage facilities and pollutant discharge management are continuously promoted [93,94,95,96,97,98,99]. In Korea, awareness of the water environment is gradually increasing, and to manage NPS pollution, the government has set a goal at the national level to manage NPS pollution, which accounts for more than 68% of river pollution, with the Total Water Pollution Control System as the core policy [24,86,88,100,101].
Crops grown hydroponically include tomatoes [102,103], paprika [104], strawberries [105], cucumbers [106], peppers [107], lettuce [108,109,110,111], and Chinese cabbage [112]. Tomatoes have the highest nutrient solution requirements [49,113] and occupy the largest area under hydroponics worldwide [114,115].
This study was conducted to analyze the extent to which nutrients discharged from tomato horticulture are loaded into rivers, as well as their impact on rivers according to environmental standards, and to evaluate the economic cost of the water purification load through further research. The results of this study can be used as a basis for the improvement of horticulture for sustainable agriculture and to determine the necessity and feasibility of inputting water purification facilities when creating eco-friendly greenhouse horticulture complexes in the future.

2. Materials and Methods

The methodology for assessing the water environment characteristics and discharge loads of HWW from a hydroponically operated horticulture complex was conducted in four phases. This study comprised the following stages: First, we selected study sites and sampled the discharged HWW by selecting tomato, which makes up the highest proportion of hydroponic farming in horticulture according to MAFRA [49] (Section 2.1). Second, the sampled HWW was analyzed for 19 major physicochemical parameters that are commonly analyzed when composing nutrient solutions for hydroponics (Section 2.2). Third, the discharge of tomato HWW was categorized into annual discharge amounts by applying the average of the discharge amounts mentioned in a previous study [55] (Section 2.3). Fourth, the results of the water quality analysis of the HWW were categorized through statistical analysis according to the type of horticulture greenhouse and monthly discharge characteristics of the studied sites (Section 2.4). Detailed materials and methods are discussed below.

2.1. Sampling HWW from a Tomato Hydroponic Horticulture Greenhouse

The study sites were based on the main production complexes for each crop, and 103 samples of HWW were collected from 24 tomato horticulture farmers (Gimje, Hongcheon, Jeong-eup, Jinju, Jangsu, Buyeo, Nonsan, Changnyeong, Changwon, Namhae, Hwaseong, and Geojae), as shown in Figure 1.
In addition, in order to identify the difference in water quality in the HWW according to the type of horticulture greenhouse, 61 points were collected from vinyl horticulture greenhouses, and 42 points were collected from glass horticulture greenhouses (Table 1). Vinyl and glass are Korea’s dominant greenhouse materials. They were classified to see whether the materials affected the emission of pollutants. Samples for this study were collected from the water collection tank in the case of farms with a water collection system (Figure 2) and directly from the outside in the case of farms without a water collection system. All samples were collected in 1 L sterilized collection bottles.

2.2. Analysis of Water Quality Items

The main analytes were the acidity (pH), electrical conductivity (EC), phosphate phosphorus (PO4-P), nitrogen nitrate (NO3-N), ammonium nitrogen (NH4+-N), chloride ions (Cl−), bicarbonate ions (HCO3−), sulfide ions (S2−), potassium ions (K+), calcium ions (Ca2+), magnesium ions (Mg2+), silicon ions (Si4+), sodium ions (Na+), iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), and boron (B). The pH and EC were analyzed using a pH meter (MP220, Mettler Toledo, Giessen, Germany) and an EC meter (S30, Mettler Toledo, Germany), respectively, and the HCO3− was measured using the bicarbonate method. The S−2, Cl−, NO3−, and NH4+ were analyzed using ion chromatography (Sykam GmbH 135, Germany). The former three were expressed as the nitrogen nitrate (NO3-N) concentration, and the latter as the ammonium nitrogen (NH4+-N) concentration. The PO4 -P was analyzed using the ascorbic acid reduction method, and the K+, Ca2+, Mg2+, Fe, Mn, Cu, Zn, Mo, B, Si4+, and Na+ were analyzed using an inductively coupled plasma analyzer (ICP-OES, Agilent Technologies, Santa Clara, CA, USA).

2.3. Assessing the Annual Discharge of Water Pollutants

The emission load per crop of hydroponic horticulture was assessed on an annual basis, focusing on nitrogen (N) and phosphorus (P). The emission load was evaluated by substituting the analyzed nitrogen and phosphorus contents per 1 L of HWW for the total amount of HWW discharged per year. The annual emissions of HWW from 1 ha of hydroponic horticulture were based on the findings of Son et al. [55].
In a previous study [55], the total amount of annual discharge from four sites was found to be 1867 ton/ha at the lowest site and 3025 ton/ha at the highest site, and the average of all four sites was calculated to be 2345 ton/ha per year (Table 2). Therefore, in this study, the total amount of HWW discharged from 1 ha of hydroponics was set to 2345 ton/ha, and the average result of the water quality analysis was substituted to evaluate the total annual load discharged to the outside.

2.4. Statistical Analysis

The results of the analysis were statistically analyzed by dividing the HWW analysis results of 103 sites collected at the study site by the type of covering material (glass or vinyl). The analysis was performed using SPSS 25.0 to analyze the differences in the trends of emission concentrations using a t-test and an F-test. Correlation analysis was applied to determine the relationships among the analyzed parameters. Origin Pro 2022b software (OriginLab Corporation, Northampton, MA, USA) was used, and 5% was used as the significance level.

3. Results and Discussion

3.1. Compositional Analysis of Tomato Hydroponic Wastewater (HWW)

The results of the main parameter analysis of the 103 tomato HWW samples are shown in Table 3. The acidity (pH) was found to be 6.19 ± 0.55 on average. This is within the range of 6.0 to 8.5 stipulated in the water quality environmental standard for Korean rivers [116], so it was determined that the discharged HWW did not exceed the standard.
Electrical conductivity (EC) is known to be one of the most important parameters in hydroponic crop management [55,56,117]. In practice, farmers are not able to analyze other nutrient solution components. Therefore, the concentrations of other nutrients in the nutrient solution and the degree of fertilizer application are calculated and inferred by measuring the concentration in real time through EC measurement equipment. In general, the EC is affected by Na, Cl, etc., and higher concentrations are measured closer to the coast [118]. If the fertilizer used for crop cultivation contains these elements, EC concentrations are known to increase due to soil accumulation [119]. The EC concentration in the HWW discharged from tomato hydroponics exceeded the water quality standard of 0.5 dS/m with an average of 4.25 ± 1.01 dS/m, and there was no difference between the VG (4.23 ± 1.04) and GG (4.27 ± 0.98). These values are high compared to the results of previous studies analyzing streams and groundwater [120,121].
In South Korea, the measurement used for the water quality environmental standard for lakes is the total nitrogen (T-N). If the concentration of T-N exceeds 1.5 mg/L, the water quality is rated as “very poor”. In addition, the discharge standard for sewage treatment plants specifies a discharge limit of 20 mg/L [116]. The average N concentration (sum of NH4+-N and NO3-N) of the studied samples was 411.21 ± 122.64 mg/L, which is 274.1 times higher than the very poor water quality standard of reservoirs and 20.6 times higher than the sewage treatment plant discharge standard. This is a very high concentration compared to the results of the concentration of total nitrogen (T-N) in Korean small streams and ponds [122,123]. In addition, it can be seen that the concentration of N (nitrogen) is higher than that of untreated domestic sewage, indicating that it is entering the river without any treatment [100].
The total phosphorus (T-P) content in the discharged HWW of a horticultural complex is also classified as very poor if it exceeds 0.5 mg/L, according to the water quality environmental standards for Korean rivers [116]. The discharge standard for sewage treatment plants is 8 mg/L or less. The average concentration of P in HWW discharged from the 103 samples of 24 sites in the study area was 47.74 mg/L, which is 95.5 times higher than the standard of “very poor” water quality and 23.9 times higher than the standard of sewage treatment plant discharge water. Considering that the average concentration of P in domestic sewage in rural areas is 10 mg/L, it can be seen that high concentrations of HWW are discharged into the river from the facility horticulture complex [100].
The average value of K+ was 399.77 ± 183.27 mg/L, that of Na+ was 114.42 ± 57.87 mg/L, that of Mg2+ was 133.83 ± 46.93 mg/L, and that of Ca2+ was 339.08 ± 109.83 mg/L. K+, Mg2+, and Ca2+ are essential nutrients for hydroponics and can be applied as potassium nitrate (KNO3), monopotassium phosphate (KH2PO4), calcium nitrate (5Ca(NO3)2·NH4 NO3·10H2O), monocalcium phosphate (Ca(H2PO4)2), and magnesium nitrate (Mg(NO3)2·6H2O) [124,125,126,127].
Si4+ was determined to have a mean of 41.44 ± 18.52 mg/L, that of Cl- was 75.13 ± 76.17 mg/L, and that of S2- was 172.88 ± 90.21 mg/L. HCO3- had an average concentration of 27.62 ± 31.50 mg/L. Sulfur (S) was found at high concentrations because it is an essential component for hydroponic crops [128] and plays an important role in regulating pH [129].
Heavy metals are also an essential requirement for hydroponics [130,131]. The mean value of Fe was 1.72 ± 1.08 mg/L, that of Mn was 0.33 ± 0.31 mg/L, that of Zn was 0.46 ± 0.32 mg/L, that of Cu was 0.16 ± 0.28 mg/L, that of B was 0.96 ± 0.50 mg/L, and that of Mo was 0.02 ± 0.02 mg/L. Of these, Fe had the highest concentration, which is due to its common use in hydroponics in the form of EDTA FeNa (C10H12N2O8NaFe) [124]. The large difference in Cu is caused by high concentrations of 1.51 and 1.53 mg/L in two of the glass greenhouse farms.
Based on these results, HWW has a very high fertilizer content and requires treatment, and its reuse can help prevent outflow nonpoint pollution and save valuable fertilizer. As no statistical difference was identified between the different types of horticulture greenhouse cover, it was not considered necessary to differentiate the assessment of pollutant emissions from hydroponics. It is expected that the concentrations analyzed in the study can be used to establish the concentrations required for agricultural reuse and to identify the treatment capacity for discharge water management.

3.2. Differences in Monthly Analysis of Tomato HWW

The monthly analysis of the 103 tomato HWW samples is shown in Table 4 and Table A2. South Korea has four distinct seasons. Korean greenhouse horticulture was created to overcome the inability to produce crops in winter [11,12,13]. In addition, the hot weather in the summer makes it difficult to produce crops and the cost of cooling is high [132,133,134]. For these reasons, a typical crop-growing season starts in late August/early September at the end of summer and ends in June/July at the beginning of summer. The choice of these periods is subjective to the farmer. The analysis showed that NO3 -N was more than twice as high in August (503.56 mg/L) as it was in July (239.48 mg/L) and was the fertilizer component with the lowest concentration. Most of the fertilizer components, such as EC, PO4-P, K+, Ca2+, and Mg2+, were analyzed with higher contents in August. In general, in hydroponics, low fertilizer application is recommended in the early stages of crop growth [135]. However, the high water analysis results in August, which is early in the growing season, may be due to the flushing of the coconut coir peat. In fact, coconut coir peat is composed of fibers that contain large amounts of nitrogen, phosphorus, and other nutrients [136].
In Korea, tomatoes are grown hydroponically for about 10 months. However, the timing is adjusted according to the farmer’s choice. In the case of EC, it started at 5.06 in August and decreased to 3.34 in July the following year. By assessing the water quality analysis results of each item discharged by season and month, the appropriate utilization at that time can be determined. Another way to reduce HWW is to recycle it. However, this method creates an imbalance in fertilizer, which limits its recycling [124]. In addition, adopting a closed hydroponic system (recycling system) in Korea comes at a high cost [137,138].
Due to the high cost of recycling, it is necessary to find various applications. If it is used to grow leafy vegetables with low nutrient solution requirements, as a fertilizer for ecological restoration, or for rice cultivation, it may be worthwhile as a fertilizer. However, further research is needed to determine whether this is possible on a seasonal basis.

3.3. Assessing Pollutant Load through HWW Composition and Outflow Volume

The amount of HWW discharged from 1 m2 of a horticulture complex is presented in Table 2 based on previous studies [55]. The amount of HWW discharged per year was analyzed by month, and it was found that 1 m2 used as little as 11.5 L (Jul.) and as much as 28.6 L (May) (Table 5). The total amount of emissions was 234.5 L/m2. This was converted to the amount (kg) of each analyte in the HWW discharged from an area of 1 ha. The main purpose of this study was to determine the amount of fertilizer that is discarded and propose its management as a pollutant. However, since the HWW discharged from hydroponics contains water, it is considered necessary to study the reuse of HWW to conserve water resources at a time when global water shortage is emerging [56,139,140,141,142,143,144,145].
The results of the analysis (Table 5) show that the total amount of nitrogen (N) discarded from 1 ha per year is 964.26 kg/ha. Nitrogen is the main component of nutrient solution cultivation; only about 57–67% of it is used by crops in the supplied nutrient solution, and the rest is discharged to the outside. It has been reported that the loss of nitrogen content is large [63,137,138]. Therefore, if this amount is recovered and reused, or if the amount that can be used for other crops is identified and utilized, it can help reduce environmental pollutants and reduce the use of chemical fertilizers. The phosphorus (P) discharge rate was 111.95 kg/ha. Phosphorus is a cause of eutrophication and needs to be managed to avoid impacting streams [146]. The emission load of potassium (K) was assessed to be 937.46 kg/ha. This high concentration is attributed to the heavy use of potassium nitrate (KNO3) and monopotassium phosphate (KH2PO4) [124]. It was also calculated that 795.14 kg/ha of Ca, 313.83 kg/ha of Mg, and 405.40 kg/ha of sulfur (S) are emitted. Nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur are all components of fertilizers used in hydroponics. However, when they are disposed of outside, they become pollutants; therefore, it is important to try to clean them up. It would be more efficient to establish recovery and reuse beforehand.
In the case of trace elements, the doses are small, but it can be seen that they are essential in hydroponics because their deficiency affects crop growth. Based on the analysis of the HWW composition, the annual emissions were calculated as Fe—4.03 kg/ha, Mn—0.77 kg/ha, Zn—1.08 kg/ha, B—2.25 kg/ha, Cu—0.38 kg/ha, and Mo—0.05 kg/ha. Although these trace elements do not appear in large amounts, they are substances that need to be managed due to problems, such as heavy metals continuously flowing into people’s drinking water sources. In particular, they are substances that accumulate in river sediments and cause pollution and need to be recovered and reused or treated [147,148].
The pollutant load of HWW discharged from the above crop-specific horticulture greenhouses can be used to calculate the treatment capacity that should be reflected when introducing a water treatment facility. In addition, the results of evaluating the amount of fertilizer components, such as nitrogen and phosphorus, can be used for the economic evaluation of fertilizer. For water treatment, it is necessary to consider the area of the main industrial complex to ensure that an appropriate treatment plant is introduced and designed.

3.4. Correlation Analysis among Items for Reuse of HWW

It was found that it is necessary to find a way to manage and utilize tomato HWW containing a large amount of these fertilizer components so that it does not become a nonpoint source of pollution at various levels, such as horticulture reuse and other agricultural and forestry industries. For such utilization and the immediate determination of discharge concentrations, water quality analysis should be conducted quickly. However, there is a disadvantage in that it is difficult to perform at farms and utilization sites. Therefore, there is a need for a basis to estimate other analytes by utilizing pH and EC sensors that can easily analyze water quality.
The 103 tomato HWW samples collected in this study were statistically analyzed (Figure 3) to determine the correlation between the items and whether the concentration could be estimated using a trend line. The most common sensors used by farmers are pH and EC sensors. The analysis showed that the pH was correlated with phosphorus (p, −0.37**) and sodium (Na, 0.29**). However, the correlation coefficients were not high. It is very difficult to determine the relationship between pH and fertilizer composition [149], and more research needs to be carried out.
Based on the EC concentrations, most fertilizer components were correlated. NH4+-N (0.613**), NO3-N (0.846**), PO4-P (0.441**), K+ (0.414**), Na+ (0.214*), Ca2+ (0.858**), Mg2+ (0.792**), Si4+ (0.198*), Cl− (0.226*), and S2− (0.658**) were correlated with the EC. In addition, many correlations were found to be in the heavy metal category, such as Mn (−0.228*), Mo (0.206*), and B (0.470**).
Based on the correlation analysis, we checked whether the concentration of the analytes could be estimated through the trend equation (Table 6). As a result of the analysis, the concentration of NH4+-N relative to the EC concentration is y(NH4+-N concentration) = 99.465x(EC concentration) − 18.569, so the concentration of NH4+-N can be interpreted as 80.896 mg/L at EC of 1.0 ds/m, 180.361 mg/L at 2.0 ds/m, etc. For Ca2+, Mg2+, and S2−, with such high coefficients of determination, it is expected that the analyte concentration of the item can be estimated by simply measuring the EC concentration. In fact, a number of studies have been conducted on the estimation of other components using EC [150,151]. However, for PO4-P, K+, etc., where the correlation is recognized but the trend coefficient is rather low, further research is needed to analyze the complex correlation between fertilizer prescription criteria and other items. Based on these results, the HWW discharged from hydroponics contains very high fertilizer content and needs to be treated, and its reuse can help prevent the outflow of nonpoint pollution and save valuable fertilizer. Therefore, based on the concentrations analyzed above, it is expected that it can be used to determine the concentration required for agricultural reuse and to identify the treatment capacity for discharge water management.

3.5. Comprehensive Discussion of HWW Analysis Results

According to the analysis of the main parameters of the 103 tomato HWW samples, the pH did not exceed the Korean water quality environmental standard. However, the electrical conductivity (EC) was very high compared to the water quality standard of 0.5 dS/m. The concentration of nitrogen was 274.1 times higher than the very poor water quality standard of reservoirs and 20.6 times higher than the sewage treatment plant discharge standard. The phosphorus (P) content was 95.5 times the standard for very poor water quality and 23.9 times the standard for sewage treatment plant discharges. It can be said that the management of nitrogen and phosphorus, which are the causes of eutrophication, is urgent. The K+, Mg2+, and Ca2+ are essential nutrients for hydroponics and were determined to be related to the products used. The highest concentration of heavy metals was Fe, which is often used in hydroponics in the form of EDTA FeNa (C10H12 N2O8NaFe). These results suggest that the HWW discharged from hydroponics has a very high fertilizer content that requires treatment, and its reuse can help prevent the outflow of nonpoint pollution and save valuable fertilizer. No statistical differences were found between the different horticulture greenhouse cover types. Based on the concentrations analyzed in the study, it is suggested that the data for agricultural reuse potential and HWW treatment capacity are used.
Typical crop cultivation in South Korea begins in late August/early September at the end of summer and ends in June/July at the beginning of the subsequent summer. The monthly HWW analysis showed that NO3-N was more than twice as high in August (503.56 mg/L) as in July (239.48 mg/L), the lowest month. Most of the fertilizer constituents, including the EC, PO4-P, K+, Ca2+, and Mg2+, were high in August. The high concentrations at this time of year were attributed to the flushing of coir peat. Care should be taken when reusing HWW. The monthly analysis results are shared to suggest the cultivation of leafy vegetables with low fertilizer requirements, use as ecological restoration fertilizer, and rice cultivation.
The annual HWW load was analyzed monthly to determine the amount of fertilizer and propose its management as a pollutant. In addition, recycling this HWW can respond to water shortages. In one year, the amount of nitrogen (N) discharged from 1 ha of hydroponics totaled 964.26 kg/ha, and the discharged phosphorus (P) totaled 111.95 kg/ha. They are causes of eutrophication, so it is necessary to manage them so that they do not affect the rivers. It was calculated that potassium (K) was emitted at 937.46 kg/ha, Ca was emitted at 795.14 kg/ha, Mg was emitted at 313.83 kg/ha, and sulfur (S) was emitted at 405.40 kg/ha. Nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur are all components of fertilizers used in hydroponics. However, they become pollutants when disposed of outside. It is suggested that HWW from hydroponics should be legally managed and treated. We also suggest further research on recovery and reuse methods. The trace elements, which are heavy metals, were calculated as Fe—4.03 kg/ha, Mn—0.77 kg/ha, Zn—1.08 kg/ha, B—2.25 kg/ha, Cu—0.38 kg/ha, and Mo—0.05 kg/ha. Since rivers are a source of drinking water for people, it can be said that it is necessary to recover and reuse the HWW or treat it. The pollutant load of HWW discharged from the above crop-specific horticulture greenhouses can also be used to calculate the treatment capacity that should be reflected when introducing a water treatment facility. In addition, the results of evaluating the amount of fertilizer components, such as nitrogen and phosphorus, can be used for the economic evaluation of fertilizer. For water treatment, it is suggested that it is necessary to consider the area of the main industrial complex to ensure that an appropriate treatment plant is introduced and designed.

4. Conclusions

In South Korea, the horticulture industry generates a lot of income, making up a large percentage of agricultural income. For this reason, the use of hydroponic farming has been on the rise. The increase in hydroponics is responsible for the generation of large amounts of HWW. In this study, the amount of HWW generated from hydroponic tomato cultivation was determined and a management plan was proposed.
Since rivers are a source of drinking water for people, it can be said that it is necessary to recover and reuse HWW or treat it. The pollutant load of HWW discharged from the above crop-specific horticulture greenhouses can also be used to calculate the treatment capacity that should be reflected when introducing a water treatment facility. In addition, the results of evaluating the amount of fertilizer components, such as nitrogen and phosphorus, can be used for the economic evaluation of fertilizer. For water treatment, it is suggested that it is necessary to consider the area of the main industrial complex to ensure that an appropriate treatment plant is introduced and designed.
The immediate determination and estimation of discharge concentrations is necessary for the reuse of tomato HWW. The correlation analysis of the 103 tomato HWW sample items showed that most of the fertilizer components were correlated with the EC concentration. Therefore, for Ca2+, Mg2+, and S2−, which have high coefficients of determination, it is expected that the analyte concentrations of these components can be estimated by simply measuring the EC concentration. However, for PO4-P, K+, etc., it is suggested that further research should be conducted to analyze the complex correlation between fertilizer prescription criteria and other items. The HWW from greenhouse horticulture contains a very high fertilizer content and requires treatment, and its reuse can help prevent NPS pollution and save valuable fertilizer. Therefore, it is expected that the concentrations analyzed above can be used to establish the concentration required for agricultural reuse and to identify the treatment capacity for discharge water management.

Funding

This study was supported by the RDA Fellowship Program (in 2019~2021) of the National Institute of Agricultural Sciences, Rural Development Administration, Republic of Korea.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

Author Jinkwan Son was employed by the company Sanglimwon Co., Ltd. The author declares no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Appendix A

Table A1. Classification of survey samples and site locations.
Table A1. Classification of survey samples and site locations.
MaterialLocationCodeSamplesJan.Feb.Mar.Apr.MayJun.Jul.Aug.Sep.Oct.Nov.Dec.
Vinyl Buyeo, ChungnamV12 1 1
Buyeo, ChungnamV221 1
Changnyeong, GyeongnamV35 111 1 1
Changwon, GyeongnamV4511 1 1 1
Gimje, JeonbukV54 11 1 1
Hwasun, JeonnamV63 1 1 1
Jangseong, JeonnamV741 1 1 1
Jangsu, JeonbukV83 11 1
Jangsu, JeonbukV93 1 1 1
Namhae, GyeongnamV1031 11
Nonsan, ChungnamV113 1 1 1
Wanju, JeonbukV124 1 111
Buyeo, ChungnamV13101 1 1 11 1 11 1 1
Jinju, GyeongnamV14101 1 1 1 1 1 1 111
Vinyl Greenhouse Total61665555345566
Glass Buyeo, ChungnamG12 1 1
Changnyeong, GyeongnamG23 1 1 1
Geoje, GyeongnamG34 1 111
Gimje, JeonbukG43 1 11
Hongcheon, GangwonG521 1
Jeongeup, JeonbukG631 1 1
Jinju, GyeongnamG72 1 1
Jangsu, JeonbukG83 11 1
Nonsan, ChungnamG9101 1 1 11 1 11 1 1
Hwaseong, GyeonggiG10101 1 1 1 1 1 1 111
Glass Greenhouse Total42444444224433
Study Sample Total 10310109999789999
Table A2. Water quality analysis results of 103 study samples (mg/L).
Table A2. Water quality analysis results of 103 study samples (mg/L).
TargetMonthpH
(1:5)		EC
(dS/m)		NH4+-NNO3-NPO4-PK+Na+Ca2+Mg2+Si4+Cl−S2−HCO3−FeMnZnBCuMo
Gg127.026.1017.46676.8022.85367.8893.68551.50151.0043.6041.19432.0044.544.300.120.533.560.400.04
Gg166.262.648.05212.6442.92394.5215.29155.2350.901.914.6842.6613.120.830.500.350.360.050.02
Gg2107.635.8920.89366.6019.85376.53255.88374.31176.0354.02396.22312.03151.370.440.481.230.430.110.06
Gg255.422.293.21225.4024.06225.4136.53213.3159.1725.703.4548.292.322.200.480.360.460.030.02
Gg276.082.633.98237.0231.81312.5721.45185.6150.6210.5121.9839.3312.240.680.110.160.290.040.03
Gg3107.503.443.93326.4212.17199.92140.88278.28161.5554.41120.60141.12121.350.140.010.060.420.020.03
Gg336.004.5112.63466.8136.64444.96139.32348.90140.9521.15147.50140.9948.880.530.020.371.230.040.02
Gg395.846.6425.61640.27119.27757.3738.72492.18256.3926.556.95213.823.720.580.090.131.460.480.02
Gg436.313.497.21347.8550.70376.6173.77235.39120.4045.0823.2670.568.492.290.160.320.620.050.01
Gg476.283.889.22332.0425.80444.5798.08312.94110.6314.307.27205.0913.670.970.100.200.670.040.03
Gg486.254.7415.10417.7430.97440.1657.80376.79109.8224.3028.86293.282.220.260.010.290.460.040.02
Gg496.774.7212.99417.2536.33559.5280.97318.80172.7950.4240.77279.6525.140.340.030.280.570.040.02
Gg515.395.8013.96685.4987.58735.4758.60564.73186.8449.3015.31221.7923.222.590.150.751.620.110.01
Gg546.174.024.02341.0848.28439.48118.67303.77105.8725.37107.56195.422.871.460.100.161.230.020.02
Gg616.835.124.06573.9843.05512.6094.37488.98187.8031.71130.11258.6225.871.800.130.680.960.150.02
Gg666.014.7210.41415.3364.36801.9425.70348.17123.7214.6135.27317.4420.010.650.200.200.700.390.01
Gg685.595.2411.72556.94130.54616.61187.64385.17185.3721.97233.87138.085.871.130.230.221.010.030.05
Gg7125.613.4915.75343.0752.37409.7738.03267.4591.7026.4012.55124.389.980.640.220.260.540.040.02
Gg725.426.0813.45644.9381.92789.8248.46512.62170.8744.07123.54245.2515.232.330.330.491.620.070.01
Gg8117.414.053.64333.8359.38423.84121.98352.46157.4047.72119.32189.1830.212.610.180.301.110.010.03
Gg846.065.9712.86640.2127.69376.61139.39505.01187.2741.01117.41248.32198.000.860.200.240.800.050.04
Gg855.903.932.96368.0262.71516.51113.66323.61111.5422.4489.16145.3144.902.360.130.261.550.040.02
Gg915.474.320.30512.0666.34487.97142.63439.68190.8658.9669.84285.7425.692.980.861.941.611.010.02
Gg1015.554.285.05362.6830.35290.24196.61400.84227.9163.0640.31416.4213.731.740.260.781.541.590.01
Gg926.163.752.59387.4551.26472.72141.94249.0699.0646.9939.10141.7432.702.730.470.670.960.310.00
Gg1025.793.870.86384.9047.29436.75142.31290.70110.2544.139.5055.2926.722.850.920.991.580.620.00
Gg936.343.623.88354.4937.57383.81147.92245.01101.8243.5126.34124.8920.382.460.430.530.790.240.00
Gg1036.083.658.33392.6340.14348.97107.87264.4593.6039.3879.3096.936.102.820.730.331.240.170.00
Gg946.603.551.93362.9256.24257.12129.41303.4197.9554.1322.0993.100.002.110.350.731.190.350.01
Gg1046.953.830.16329.3141.19346.97114.51289.62103.7739.8358.56153.9414.952.110.560.311.180.130.00
Gg956.003.741.20448.2658.29420.72112.44333.1098.9947.6720.4875.3815.862.100.490.460.940.290.00
Gg1055.713.465.54313.6446.18279.1797.09287.1382.2637.4238.3967.6044.111.320.410.330.890.100.00
Gg966.023.110.00316.3841.65228.1596.97304.2592.1945.2852.5066.473.781.960.290.661.310.040.01
Gg1066.333.851.90313.4334.59299.86146.15246.33105.1646.550.0093.2148.990.630.090.140.350.360.00
Gg996.464.820.00446.4834.75179.90168.10348.38131.6564.1033.39299.706.653.190.200.611.100.090.00
Gg1096.884.192.76374.1632.30425.80146.42357.87125.0152.56161.30232.5335.510.850.060.210.380.050.01
Gg9106.264.342.35354.2365.4193.10210.11392.58182.0355.2810.22302.8366.861.540.070.170.670.040.01
Gg10105.514.402.85542.3948.5629.33155.04432.26195.2767.920.00158.2421.962.720.380.440.951.530.01
Gg9116.954.101.90387.4915.7919.63145.53342.20179.4455.871.03158.2820.862.300.110.351.010.030.00
Gg10116.254.981.17499.5151.22327.97122.51404.01170.8473.2913.15194.0123.982.090.380.581.131.510.02
Gg9126.454.282.90399.5929.51102.68235.88364.29150.4282.7311.45116.9120.742.160.050.291.030.020.01
Gg10126.243.803.33353.6468.16547.7982.76356.71102.3541.7740.06131.180.004.011.271.010.940.570.00
Vg1116.225.2817.27577.1180.49561.4872.30424.85197.804.417.16132.1018.360.310.130.320.750.050.03
Vg185.854.3612.51469.1887.55575.1654.26335.87125.6428.2924.43105.315.321.330.350.180.390.030.02
Vg276.453.629.09280.7039.67585.3370.26234.9994.8641.0732.19173.2523.551.740.190.240.550.040.02
Vg216.374.039.57441.8239.77448.4843.70354.5599.4222.1622.5194.5620.800.900.190.560.450.040.05
Vg3116.394.063.88457.2877.80505.9565.68319.88147.5326.0712.8741.6612.211.210.150.590.640.060.03
Vg345.774.6614.13423.0771.35602.14117.78372.70136.7528.03194.48205.128.120.730.130.150.920.030.02
Vg355.252.463.85287.5736.76305.4519.86192.9566.774.8612.6637.508.300.630.260.150.430.030.01
Vg366.193.397.31260.0237.32631.47131.7855.3559.0724.63304.2720.7428.130.260.050.440.300.080.04
Vg397.584.3010.02326.2613.75387.95136.31315.11150.3277.67135.63260.7479.311.390.020.021.250.020.06
Vg417.652.9215.83197.4019.88408.99267.14125.2158.6951.38173.67155.42132.520.200.040.070.240.020.03
Vg426.385.4117.09501.9581.33515.73137.80424.45173.4792.30200.26149.5033.980.510.160.240.560.070.02
Vg446.785.2416.58599.9737.44262.4887.89632.06174.8456.993.97258.5924.950.660.030.231.040.040.02
Vg466.912.645.12182.1645.71538.02110.12140.0866.0322.3692.17143.6219.830.400.180.100.460.050.03
Vg485.916.5028.07700.49116.11917.6842.85498.60249.3021.40122.21208.063.540.110.200.301.170.250.02
Vg5126.173.714.94330.5026.01210.51113.13383.33158.3653.51212.70188.707.321.120.720.541.510.080.02
Vg525.223.574.53405.5720.50245.0844.95387.1795.7031.0113.8396.9622.412.740.310.370.500.050.01
Vg536.026.0225.22609.94128.12840.65127.53516.23182.2351.77103.51208.0028.352.850.370.531.920.310.03
Vg556.046.585.71322.0039.60152.65321.86593.58132.1237.47159.88216.1645.511.250.070.092.280.220.08
Vg6116.315.8023.86609.0266.40436.4572.14438.88157.2862.8936.87201.8218.881.560.190.950.640.190.02
Vg656.573.5911.54421.0832.02293.76112.05312.0698.0345.3954.8165.3425.751.460.200.360.940.040.03
Vg677.022.993.38191.3926.70501.65141.87137.5981.6243.09175.76133.8917.570.480.460.760.240.180.02
Vg715.505.5519.22508.9355.56491.88140.51589.98184.7433.23176.47291.9470.252.140.300.321.200.050.02
Vg7127.315.8222.21480.3427.87491.48128.70407.21174.8732.22177.54362.8845.450.680.321.080.390.210.03
Vg736.585.4220.51499.4469.31838.70106.90447.29181.7031.7477.71306.409.332.920.150.811.320.150.02
Vg786.365.4112.77546.1153.67615.4382.60379.76199.658.34154.23272.1318.363.470.170.730.610.050.02
Vg8123.234.4011.05416.6338.90428.1597.64313.55132.6035.67128.44131.2328.883.651.201.180.880.400.05
Vg825.612.574.82212.2521.68245.0418.53194.0365.967.644.1879.3326.170.760.270.150.440.020.04
Vg836.553.769.29357.5160.89519.2563.94294.91102.6325.98108.02104.7432.153.751.950.430.910.130.06
Vg9105.925.222.96539.0961.60419.5483.45469.34153.3875.76133.43107.233.422.540.140.290.980.140.03
Vg926.264.233.60417.6065.28434.7980.03357.35125.7449.6655.16117.6318.062.440.530.431.690.120.03
Vg976.292.223.94156.2329.73197.3812.92139.3621.841.0190.8920.5177.911.510.480.670.760.090.01
Vg1016.345.195.97417.9535.84353.67243.11367.80190.4135.6160.95323.2331.121.910.200.491.380.210.08
Vg10106.355.236.17412.7534.67347.46250.75365.20193.3836.30260.65336.0931.851.990.210.481.420.220.09
Vg1096.055.585.91438.8177.92725.3159.87432.06157.2025.00217.31303.6510.740.620.060.250.570.040.02
Vg1146.752.781.90278.6726.51328.2481.43204.4568.7941.2659.1387.8765.771.540.250.440.560.060.05
Vg1167.672.502.04138.1815.61233.90172.98160.0058.9237.53261.0576.9397.620.190.560.450.170.080.03
Vg1195.434.011.76426.2174.58606.0549.73359.36122.7327.648.90154.431.591.890.300.400.460.020.01
Vg12105.624.3811.93434.3986.56464.9072.33390.66177.3241.8514.96120.5128.883.050.630.801.040.090.01
Vg12115.904.6514.55435.5556.86705.3654.35369.38147.7319.7265.41252.100.850.370.230.641.110.060.03
Vg12126.575.7819.40633.0125.24326.29154.72563.93125.9256.85109.04226.881.111.560.030.251.630.320.04
Vg1285.904.0810.88330.9053.08625.2143.08333.63130.4015.9098.66192.679.560.620.060.271.130.050.02
Vg1315.954.640.00487.3831.87339.58173.11433.26189.3963.5132.58189.1319.580.360.971.471.580.030.02
Vg1415.714.873.16467.1229.27267.99179.37399.16164.1964.8939.42256.1116.351.810.320.521.280.070.00
Vg1325.944.172.64407.4932.08245.59162.86270.14128.1746.3543.11188.7428.673.140.370.620.930.160.00
Vg1426.034.012.57411.1455.53424.24111.25290.62114.5345.0826.13120.740.000.360.871.091.130.020.09
Vg1335.983.992.48356.2529.73232.84117.23328.22114.1249.3314.75143.0720.382.490.340.520.800.100.01
Vg1435.903.554.81397.6438.65344.1699.39310.9491.7333.90109.9094.581.102.530.850.241.190.020.01
Vg1346.053.650.00322.2043.54179.66125.80371.86104.8860.2871.43100.840.005.350.581.171.440.060.01
Vg1445.703.462.95312.0239.27336.49104.47201.5282.3834.27101.71138.8416.722.590.790.271.100.020.01
Vg1355.983.520.10317.7655.84283.32128.58218.7281.9358.0618.9754.9015.313.090.310.821.540.040.00
Vg1455.823.524.09368.7234.47206.49102.70253.7189.2638.8838.4680.4744.842.710.340.250.790.050.00
Vg1365.373.691.93327.1537.04473.89145.11285.9795.7242.5867.9286.8424.473.020.710.411.030.030.03
Vg1465.703.520.00308.1160.45318.55107.02300.44105.8049.8333.18119.699.821.680.570.320.870.210.02
Vg1396.003.113.17327.2141.07289.89104.21266.41124.3539.78118.01217.9822.150.830.510.210.330.060.03
Vg1495.903.091.91347.4435.37258.4199.94220.20118.9138.7439.05184.5913.460.750.050.110.460.020.02
Vg13106.004.180.39410.8039.95184.12178.29276.31172.5964.809.57244.8843.561.050.030.070.680.050.00
Vg14106.203.980.00448.6532.58135.70155.57416.43170.6163.0325.49321.2115.922.000.220.500.970.060.01
Vg13115.904.230.04355.2825.27174.60118.21282.80137.4649.971.31140.5625.503.300.180.390.940.030.01
Vg14116.003.940.00340.5940.10177.01171.09310.42170.9566.406.77166.5334.531.370.200.490.970.090.01
Vg13125.904.630.14405.7852.43221.23139.30324.01208.6171.3518.68237.3821.842.090.250.231.150.020.04
Vg14125.404.483.29398.9758.84255.71131.85281.80188.1564.3010.17187.333.602.120.450.471.210.020.00

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Water 16 00720 g001
Figure 1. The sampling sites and locations of greenhouses.
Figure 1. The sampling sites and locations of greenhouses.
Water 16 00720 g001
Water 16 00720 g002
Figure 2. HWW emission status of greenhouse (a–m) and collection facility (n,o) in greenhouse horticulture.
Figure 2. HWW emission status of greenhouse (a–m) and collection facility (n,o) in greenhouse horticulture.
Water 16 00720 g002
Water 16 00720 g003
Figure 3. Correlation analysis results among water quality analysis items.
Figure 3. Correlation analysis results among water quality analysis items.
Water 16 00720 g003
Table 1. Classification of HWW 103 samples.
Table 1. Classification of HWW 103 samples.
MaterialSamples20202021
Aug.Sep.Oct.Nov.Dec.Jan.Feb.Mar.Apr.MayJun.Jul.
Vinyl Greenhouse61455666655553
Glass Greenhouse42244334444442
Study Sample Total 10389999101099997
Table 2. The drainage amount of HWW from tomato greenhouse horticulture (unit: L/m2).
Table 2. The drainage amount of HWW from tomato greenhouse horticulture (unit: L/m2).
SiteJan.Feb.Mar.Apr.MayJun.Jul.Aug.Sep.Oct.Nov.Dec.Total
Vt118.9 18.1 10.9 9.3 26.1 2.3 13.8 28.3 27.6 47.4 41.1 58.9 302.5
Vt219.4 20.0 20.5 20.9 21.3 19.9 15.9 9.6 16.6 24.5 16.0 19.4 223.8
Gt113.4 19.7 30.4 32.5 48.4 28.1 7.8 14.4 8.6 9.4 6.9 5.4 224.9
Gt222.9 19.4 18.3 16.2 18.4 17.8 8.5 2.8 14.0 18.3 15.8 14.2 186.7
Ave.18.7 19.3 20.0 19.7 28.6 17.0 11.5 13.8 16.7 24.9 20.0 24.5 234.5
S.D3.9 0.8 8.0 9.8 13.6 10.8 4.0 10.8 8.0 16.2 14.7 23.7 48.7
Table 3. Analysis results of wastewater at 103 study samples (unit: mg/L).
Table 3. Analysis results of wastewater at 103 study samples (unit: mg/L).
ParametersVinyl Greenhouse (n = 61)Glass Greenhouse (n = 42)Total Greenhouse (n = 103)t-Test *
Mean S.D.Mean S.D.Mean S.D.t-ValuePost Hoc.
pH (1:5)6.11 a0.656.23 a0.576.160.620.004N.S
EC (dS/m)4.23 a1.044.27 a0.984.251.010.403N.S
NH4+-N7.77 a7.286.72 a6.247.346.861.341N.S
NO3-N396.60 a118.59414.41 a119.72403.86118.790.018N.S
PO4-P47.69 a23.2647.81 a24.2447.7423.550.161N.S
K+404.50 a184.20392.89 a183.92399.77183.270.521N.S
Na+113.84 a59.46115.26 a56.19114.4257.870.000N.S
Ca2+334.06 a119.48346.36 a95.01339.08109.831.849N.S
Mg2+132.38 a46.91135.94 a47.44133.8346.930.098N.S
Si4+41.16 a19.3441.83 a17.4841.4418.520.525N.S
Cl−84.99 a75.8360.81 a75.2675.1376.171.132N.S
S2−167.87 a83.84180.17 a99.33172.8890.211.574N.S
HCO3−25.76 a24.5830.30 a39.6427.6231.502.516N.S
Fe1.67 a1.131.78 a1.031.721.080.218N.S
Mn0.35 a0.330.29 a0.270.330.310.246N.S
Zn0.46 a0.310.46 a0.350.460.320.208N.S
B0.92 a0.451.01 a0.570.960.500.183N.S
Cu0.09 b0.080.27 a0.410.160.2830.577 ***VG < GG
Mo0.03 a0.020.02 a0.010.020.022.805N.S
Notes: * Significantly different according to Duncan’s multiple range test. N.S, *** indicate non-significant or significant at p ≤ 0.001, respectively; Result is according greenhouse types: a < b.
Table 4. Monthly discharge analysis result and F-test of greenhouse HWW (unit: mg/L).
Table 4. Monthly discharge analysis result and F-test of greenhouse HWW (unit: mg/L).
Parameters20202021F-Test *
Aug.Sep.Oct.Nov.Dec.Jan.Feb.Mar.Apr.MayJun.Jul.F-ValuePost Hoc
pH (1:5)5.98 a 6.32 a 6.33 a 6.37 a 5.88 a 6.08 a 5.98 a 6.20 a 6.31 a 5.85 a 6.27 a 6.42 a 0.870N.S
EC (dS/m)5.06 d 4.50 cd 4.56 cd 4.57 cd 4.49 cd 4.67 cd 4.38 cd 4.22 bcd 4.13 bcd 3.68 abc 3.34 abc 3.07 ac 2.776 **7 < 6 < 5 < 4, 3 < 2, 12, 9, 10, 11, 1 < 8
NH4+-N15.18 b 7.13 a 5.72 a 7.37 a 9.22 ab 7.71 a 6.96 a 10.48 ab 6.06 a 4.24 a 4.09 a 5.92 a 1.466N.S
NO3-N503.56 c 416.01 bc 426.15 bc 443.96 bc 417.95 bc 465.48 c 445.01 bc 420.28 bc 401.05 bc 341.38 ab 274.82 a 239.48 a 3.879 ***6,7 < 5 < 4, 9, 12, 3, 10, 11, 2 < 1, 8
PO4-P78.65 b 51.70 a 44.59 a 52.59 a 42.15 a 43.95 a 47.97 a 54.64 a 43.50 a 43.32 a 42.18 a 30.74 a 1.584N.S
K+631.71 c 465.58 bc 250.07 a 370.25 ab 332.62 ab 433.69 ab 417.76 ab 481.10 bc 347.69 ab 298.16 ab 435.59 ab 408.30 ab 2.584 **10 < 5, 12, 4, 11, 7, 2, 1, 6 < 9, 3 < 8
Na+78.04 a 98.25 ab 166.92 c 104.87 abc 124.67 abc153.92 bc 98.18 ab 109.32 abc 113.26 abc 116.09 abc 105.68 abc 68.92 a 1.996N.S
Ca2+384.97 b 345.60 b 377.26 b 360.54 b 362.48 b 416.42 b 352.76 b 332.37 b 353.82 b 303.13 ab 221.76 a 202.10 a 3.014 **6, 7 < 5 < 3, 9, 2, 4, 11, 12, 10, 8, 1
Mg2+166.70 f 151.04 def 175.80 f 162.94 ef 148.11 def168.02 f 123.48 cd 125.46 cde 118.06 bcd 91.12 bc 84.17 b 71.91 a7.644 ***7 < 6 < 5 < 4 < 2 < 3 < 12, 9 < 11 < 8, 1, 10
Si4+20.03 a 44.72 bcd 57.04 d 45.15 bcd 51.64 cd 47.38 bcd 45.08 bcd 37.98 abc 42.35 bcd 35.32 abc 31.70 ab 22.00 a 3.211 ***8, 7 < 6 < 5, 3 < 4, 9, 2, 11, 1 < 12 < 10
Cl−110.38 a 84.59 a 107.90 a 29.32 a 80.07 a 76.12 a 55.60 a 76.70 a 81.82 a 48.47 a 94.56 a 65.62 a 0.798N.S
S2−201.59 cde 238.57 e 227.13 de 164.03 abcde 189.65 bcde249.30 e 162.72 abcde 143.35 abcd 164.67 abcde 87.88 a 107.51 ab 114.41 abc3.814 ***5 < 6 < 7 < 3 < 2, 11, 4 < 12 < 8 < 10 < 9, 1
HCO3−7.48 a 22.03 ab 53.91 b 20.60 ab 15.44 ab 37.91 ab 24.85 ab 19.46 ab 36.82 ab 27.43 ab 29.53 ab 28.99 ab 1.247N.S
Fe1.15 a 1.16 a 1.72 ab 1.68 ab 2.00 ab 1.64 ab 2.22 ab 2.52 b 1.94 ab 1.90 ab 1.07 a 1.08 a 1.685N.S
Mn0.17 ab 0.15 a 0.24 abc 0.19 ab 0.50 bc 0.34 abc 0.44 abc 0.56 c 0.33 abc 0.30 abc 0.35 abc 0.27 abc 1.592N.S
Zn0.33 a 0.25 a 0.45 ab 0.51 ab 0.59 ab 0.76 b 0.56 ab 0.45 ab 0.41 ab 0.34 a 0.34 a 0.41 ab 1.860N.S
B0.79 abcd 0.73 abc 0.84 abcd 0.92 abcd 1.03 abcd 1.19 cd 1.30 d 1.11 bcd 1.05 bcd 1.09 bcd 0.62 ab 0.50 a 2.041 *7 < 6 < 9 < 8, 10, 11, 12 < 4, 5, 3 < 1 < 2
Cu0.08 a 0.09 a 0.25 a 0.22 a 0.19 a 0.33 a 0.18 a 0.13 a 0.08 a 0.09 a 0.14 a 0.08 a 0.685N.S
Mo0.03 a 0.02 a 0.03 a 0.02 a 0.02 a 0.03 a 0.03 a 0.02 a 0.02 a 0.02 a 0.02 a 0.02 a 0.260N.S
Notes: * Significantly different according to Duncan’s multiple range test. N.S, *, **, *** indicate non-significant or significant at p ≤ 0.05, 0.01, 0.001 respectively; Result is according monthly difference: a < b < c < d < e < f.
Table 5. The pollutant load analysis results of hydroponic wastewater.
Table 5. The pollutant load analysis results of hydroponic wastewater.
ContentsJan.Feb.Mar.Apr.MayJun.Jul.Aug.Sep.Oct.Nov.Dec.Total
Drainage Amount (L/m2)
4 Sites’ Mean18.719.320.019.728.617.011.513.816.724.920.024.5234.5
Pollutant load of fertilizer components (kg/ha)
Nitrogen88.49 87.23 86.15 80.20 98.85 47.41 28.22 71.59 70.66 107.53 90.27 104.66 964.26
Phosphorus 8.22 9.26 10.93 8.57 12.39 7.17 3.54 10.85 8.63 11.10 10.52 10.33 111.95
K81.10 80.63 96.22 68.49 85.27 74.05 46.95 87.18 77.75 62.27 74.05 81.49 937.46
Ca77.87 68.08 66.47 69.70 86.70 37.70 23.24 53.13 57.71 93.94 72.11 88.81 795.14
Mg31.42 23.83 25.09 23.26 26.06 14.31 8.27 23.00 25.22 43.77 32.59 36.29 313.83
S46.62 31.40 28.67 32.44 25.13 18.28 13.16 27.82 39.84 56.55 32.81 46.46 405.40
Pollutant load of heavy metal components (kg/ha)
Fe0.31 0.43 0.50 0.38 0.54 0.18 0.12 0.16 0.19 0.43 0.34 0.49 4.03
Mn0.06 0.08 0.11 0.07 0.09 0.06 0.03 0.02 0.02 0.06 0.04 0.12 0.77
Zn0.14 0.11 0.09 0.08 0.10 0.06 0.05 0.05 0.04 0.11 0.10 0.14 1.08
B0.22 0.25 0.22 0.21 0.31 0.10 0.06 0.11 0.12 0.21 0.18 0.25 2.25
Cu 0.06 0.04 0.03 0.02 0.03 0.02 0.01 0.01 0.02 0.06 0.04 0.05 0.38
Mo0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.05
Table 6. Results of statistical analysis of EC concentration vs. component concentration in tomato HWW.
Table 6. Results of statistical analysis of EC concentration vs. component concentration in tomato HWW.
ParametersRegressionR2Correlation Analysis
NH4+-Ny = 4.1592x − 10.3230.37560.613 **
NO3-Ny = 99.465x − 18.5690.71630.846 **
PO4-Py = 10.286x − 4.0540.19490.441 **
K+y = 75.094x − 80.8360.17150.414 **
Na+y = 12.272x + 62.3000.04590.214 **
Ca2+y = 93.22x − 56.8350.73610.858 **
Mg2+y = 36.764x − 22.3030.62710.792 **
Si4+y = 3.633x + 26.0660.05110.198 *
Cl−y = 17.033x + 2.79110.03930.226 *
S2−y = 58.737x − 76.5760.43320.658 **
Notes: * Significantly different according to Duncan’s multiple range test. *, ** indicate at p ≤ 0.05, 0.01, respectively.
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Son, J. Evaluation of the Characteristics of Pollutant Discharge in Tomato Hydroponic Wastewater (HWW) for Sustainable Water Management in Korea. Water 2024, 16, 720. https://doi.org/10.3390/w16050720

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Son J. Evaluation of the Characteristics of Pollutant Discharge in Tomato Hydroponic Wastewater (HWW) for Sustainable Water Management in Korea. Water. 2024; 16(5):720. https://doi.org/10.3390/w16050720

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Son, Jinkwan. 2024. "Evaluation of the Characteristics of Pollutant Discharge in Tomato Hydroponic Wastewater (HWW) for Sustainable Water Management in Korea" Water 16, no. 5: 720. https://doi.org/10.3390/w16050720

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