Reusing of Real Textile Wastewater After Treatment by Gamma Irradiation: Implications on the Growth of Capsicum Frutescens Plant

This investigation concentrates on the possibility of using gamma radiation for the decomposition of textile wastewater and reuse as irrigation water. The real wastewater sample was irradiated at four different radiation doses of 3, 5, 8, and 10 kGy. After irradiation at 8–10 KGy, physicochemical parameters, i.e., pH, turbidity, EC, total suspended solids (TSS), total dissolved solids (TDS), biological oxygen demand (BOD 5 ), and chemical oxygen demand (COD) have decreased sharply and approached to the expected value. At maximum 10 KGy radiation dose, 59.0 % BOD 5 and 71.6 % COD removal have been achieved, accelerating the enhancement in biodegradability index (BOD 5 /COD, 0.43). Ammonium and total nitrogen have improved up to 87.0 % and 94.5 % after irradiation at 10 KGy doses. These treated textile wastewater samples were reused to grow Capsicum frutescens plants to inspect the fertility responses. When Capsicum plants were nourished by textile wastewater irradiated at 8–10 kGy, the dry masses of the fruits, moisture content, root length, average plant height, average number of leaves, and total number of fruits were increased in comparison to those plants nourished by simply water and raw wastewater. The elemental analysis conrmed that the heavy metals concentration in Capsicum fruits decreased gradually with higher radiation doses. Helpful macro and micronutrients for plant production such as Na, K, and Mg were raised at a sucient level of 47.7 %, 23.5 %, and 63.8 % for 10 KGy, whereas the highest 50.0 % increase in Ca concentration was found for 8 KGy fruit samples. amounts, but vital macro and micronutrients for plant development and human wellness are obtained a superior level in Capsicum fruits, indicating fascinating and fruitful results.


Introduction
Like many other developing countries, textile industries play an integral role in creating economic development in Bangladesh (Masum 2016). Massive amounts of dyes have been produced to ful ll the annual requirements of these different textile industries (Lourenço et al. 2001). In the market, nearly 10,000 variations of synthetic dyes are found, whereas more than 700,000 tons are generated per annum all over the world. Almost 200,000 tons of synthetic dyes are absorbed yearly due to the incompetent dyeing operation in most textile industries. It has been reported by the World Bank that around 17-20% of wastewater is produced from the textile nishing and As a solution to this problem, industrial e uents require treatment in situ before discharging into the environment (Emongor et al. 2005). Existing conventional methods like physical or chemical treatments cannot destroy the poisonous organic pollutants; instead, contaminants are transferred from an aqueous to a solid phase by the chemical coagulation method (Rabby 2011). Thus, extensive sludge is generated from the coagulation process, creating secondary pollution if not properly handled (Al-Mamun et al. 2019). Several researchers have followed the adsorption techniques (Panda et al. 2009;Islam et al. 2013), although these techniques are lengthy, unable to generate a waste-free clear solution, and are not cost-effective. Reversely, biological processes are usually simple, environment friendly having economic bene ts, and often used to remove toxic waste from textile wastewater (Kim et al. 2004; Al-Mamun et al. 2019). However, typical biological methods (e.g., activated sludge process) cannot eradicate these organic pollutants rapidly due to their large size, complex molecular structure, and chemical nature that converts them as non-biodegradable in the environment (Kim et al. 2004). Advanced oxidation processes (AOPs) are also used to destroy wastewater dyes effectively, but their operation and maintenance costs are too high (Al-Mamun et al. 2019; Johnson et al. 2019). In this case, the application of gamma radiation, also known as ionizing radiation, can be used as a remedy for textile wastewater treatment as this is more powerful, economical, and environmentally favorable. Moreover, this treatment process gives some additional bene ts such as no extra usage of chemicals, no residual or sludge generation, high penetration capability in various matrixes of water, and also unresponsive towards the insoluble solids that existed in wastewater ( . The main advantages of radiation treatment over the conventional methods prescribe that this method is adaptable because of its easy management in a unit system as pollutants are destroyed by a rapid reaction mechanism and its capability of the simultaneous killing of pathogenic microorganisms along with destroying pollutants (Borrely et al. 1998).
Gamma radiation is one type of ionizing radiation with adequate energy to displace electrons from atoms and molecules, transforming them into electrically charged particles named ions (Selambakkannu et al. 2011). When gamma radiation is applied to the textile wastewater, radiolysis occurs in the water, producing excited and ionized water molecules with free electrons, highly reactive species.
The application of gamma radiation is highly effective in aqueous solutions because the dye molecules found in the wastewater solution become degraded by the operation of primary products (•OH, eaq . H + , •H, H 2 O 2 ) produced by water radiolysis (Solpan 2002;Wang et al. 2006;Selambakkannu et al. 2011;. Mainly the destruction of the conjugated system (N=N bonds) of the dye compounds occurs by the action of highly responsive hydroxyl radicals (•OH) (Sumartono 2008). Also, rapid addition occurs of this reactive species (•OH) to the unsaturated bonds of the benzene ring, which ultimately leads to the disintegration of aromatic rings and generates acetaldehyde, carboxylic acids with other species into the solution Takacs 2008, 2013;Wang and Chu 2016). Because of the radiation effect, the longer organic chain degrades into shorter chains, which are adjoining to the major dye or azo groups (Nickelsen et al. 1992).
Nowadays, scientists worldwide have given their attention to reusing textile wastewater because of the increasing pollution in the water bodies and groundwater depletion created by the textile industries . The wastewater can be recycled as irrigation water into the agricultural sector because it contains several amounts of inorganic and organic nutrients, which can input a handsome is the driving force for this present study on Capsicum frutescens. The speci c objectives for this work are (i) application of irradiation technology to disintegrate the dye compounds and organic pollutants as well as to increase the biodegradability (BOD 5 /COD ratio) of the textile wastewater, (ii) to investigate the changes of physicochemical parameters and level of heavy metals of the irradiated textile wastewater, (iii) doses optimization of gamma irradiation for the treatment of the textile wastewater by applying different irradiation doses ranging from 3 KGy to 10 KGy, (iv) to explore the recycling suitability of gamma-irradiated textile wastewater by applying into the vegetable species Capsicum frutescens and observing the growth rate and production effects of the plants and Capsicum fruits.

Sample collection and gamma irradiation
The combined actual textile wastewater samples were collected from the wastewater collection vessel from a knit dyeing textile industry, namely "Radial International Ltd.-Radiance Group" at Zirani Bazar, Kashimpur, Gazipur, Bangladesh. The samples were a composition of natural wastewater generated from different actions such as knitting, washing, and dyeing. The wastewater samples were gathered and sealed tightly in a 100 L clean and dry HDPE container and then sent for irradiation by gamma rays from the Cobalt-60 gamma source of the Institute of Radiation and Polymer Technology (IRPT), Atomic Energy Research Establishment, Savar, Dhaka, Bangladesh. The gamma radiation source was in batch irradiation mode, and the combined textile wastewater was irradiated at various radiation doses (3, 5, 8, 10 kGy) at a dose rate of 13 kGy/h. An Amber Perpex dosimeter (type 3042F) has been used to measure the given dose values throughout the irradiation process.

Physicochemical analysis of raw and irradiated wastewater
The textile wastewater samples (both treated and untreated) were subjected to physical and chemical characterization, i.e., pH, turbidity, TSS, TDS, EC, DO, BOD 5 and COD, to determine the optimum dose for decontamination. pH, TDS, and EC for irradiated and unirradiated samples were determined using a portable Multimeter (Model no. sension TM 156, HACH, USA, 2000) not over 30 minutes of the sample collection. The DO meter HQ40d from HACH, USA, was used to determine the DO values. BOD 5 of the wastewater samples were analyzed by ve days BOD 5 test at 20 °C operating HACH DBR200 system following the standard procedures (APHA 2017). A single beam UV-spectrophotometric system, model: DR/4000U, HACH International, Colorado, USA, with the help of reactor digestion method, was used to measure the COD values. The turbidity was measured by portable turbidity meter WTW TURB 350 IR. An oven dried (30 min at 103-105 ºC) ber pad lter paper was weighed by analytical balance after cooling in desiccators for TSS measurement. Then 1000 mL samples were thoroughly shaken and ltered through the lter paper, followed by drying of the lter paper in the oven (30 min at 103-105 ºC), cooling in the desiccators, and then take the dry weight of the materials . The total nitrogen and ammonium (NH 4 + ) concentration of the treated and raw wastewater samples were also measured by the Kjeldahl and Kjeldahl distillation techniques (Mulvaney 1996).
Experiments for the fertilizing effects by reusing of irradiated textile wastewater Tabasco peppers (Capsicum frutescens) plants were irrigated three times a week by the irradiated and unirradiated wastewater to inspect the scope of reusing of gamma-ray irradiated textile wastewater as irrigation water and its fertility impact. Twelve pots had
This study revealed that the pH values in the textile wastewater were gradually decreased with the rise of the irradiation doses from 3 to 10 KGy. At an irradiation dose of 10 KGy, the pH value in wastewater was found to be 8. 19, which was enough for reuse as irrigation water since it satis ed the standard range of irrigation water (DoE 1997 (Miyata 1993).
At 10 KGy radiation dose, the EC value became 1690 µS/cm, which was comparatively lesser than the EC value found in raw wastewater (4010 µS/cm) but not close to the standard value (1200 µS/cm) for irrigation water (DoE 1997). However, higher radiation doses were required to reduce the EC value because of ionized constitutes in the wastewater. EC has an approximate correlation with TDS (Rouse 1979), which was consistent with our Pearson's correlation data between EC and TDS (Table 3) having a strong positive correlation (r = 0.992, p < 0.005, α = 0.01). This study has been suggested that with the increment of irradiation dose, both EC and TDS values reduced signi cantly. A similar reduction tendency was also found for TDS (Table 1), which was 1540 mg/L at 10 KGy, lower than the recommended value of 2100 mg/L for irrigation quality of the water (DoE 1997). The suspended solids content of the wastewater readily lowered after the gamma-ray irradiation ( Table 1). The TSS value was 486 mg/L for unirradiated wastewater and 217 mg/L for 10 KGy radiation dose, almost near to the standard TSS value (200 mg/L) for irrigation water as per DoE (1997). There are two probable causes of TDS and TSS reduction; the rst is the deterioration of suspended dye molecules persuaded through the reaction with oxidative agents from hydrolysis of water (Getoff 1996;Somasiri et al. 2006). The second cause is the destruction of bigger organic molecules into tinier ones by radiation (Nickelsen et al. 1992). In the case of biological oxygen demand (BOD 5 ) and chemical oxygen demand (COD), a notable reduction in BOD 5 and COD values of the wastewater is observed with increasing radiation doses (Fig. 1). The recommended standard limit of BOD 5 and COD for irrigation water is 100 mg/L and 400 mg/L, respectively set by DoE (1997) which were duly achieved for the wastewater irradiated at 8-10 KGy in this study. The present study also revealed that at the highest radiation dose of 10 KGy, 59.0% and 71.6% of BOD 5 and COD removal were obtained. A strong positive correlation (r = 0.992, p < 0.005, α = 0.01) between BOD 5 and COD was observed (Table 3). It could happen because the reason that the ˙OH radicals are produced by the radiolysis of wastewater reacting with suspended solid materials and degrade the organic contaminants (Selambakkannu et al. 2011). As a result, the degradation of these organic pollutants also reduces the bulk of biodegradable matters in wastewater, which results in the lowering of BOD 5 and COD values .
The decline in COD values of the wastewater samples after radiation treatment could increase the biodegradability index (BOD 5 /COD) ratio, which is evident from Fig. 1. However, the BOD 5 /COD ratio value elevated to 0.43 from 0.3 after irradiation. Also, 32.3 % to 44.4 % biodegradability of the wastewater samples increased after irradiation at 8-10 KGy (Fig. 1).

Effect of irradiation doses on total nitrogen and ammonium in textile wastewater
This study revealed that the radiation treatment signi cantly improved the amount of total nitrogen (N) and ammonium (NH 4 + ) contents in wastewater samples (Fig. 2). The unirradiated wastewater contained only 32.6 mg/L and 18.5 mg/L of total nitrogen and ammonium, but when the wastewater was irradiated at 10 KGy, total nitrogen and ammonia increased 63.4 mg/L and 34.6 mg/L, respectively. However, the total nitrogen content increased 68.7% at 8 KGy and 94.5% at 10 KGy. Again, 77.3% and 87.0% increase were observed for ammonium content in wastewater irradiated at 8 KGy and 10 KGy, respectively (Fig. 2). The nding for applying irradiation dose on total nitrogen and ammonium in wastewater was completely reverse to changing of pH value, which can be seen in the Pearson's correlation data ( Table 3)

Impact of irradiation doses on metals concentration in textile wastewater
This present study observed that the analyzed raw and irradiated wastewater samples carried a lower concentration of heavy metals ( Table 4). The textile industry from where the wastewater samples were collected mainly consumes reactive and disperse dyes for dyeing. Shore (2002) reported that metal complex groups are not found in disperse dyes, and reactive dyes contain only 12-15 % of metal complex azo groups. Hence, it is expected to found a lower concentration of heavy metals in the studied wastewater samples.
Heavy metals like Cr, Pb, Ni, and Cu are crucial because of their bio-accumulation solid capability, which could harm humans when introduced into the food cycle (Fisseha 1998;Itanna 2002). Among the heavy metals Pb, Cr, Zn, Co, Ni, Cu, Mn, and Hg showed higher values in the wastewater samples irradiated at 3, 5, 8, and 10 KGy doses than in unirradiated wastewater samples (Table 4). However, arsenic (As) and cadmium (Cd) were found less than the detection limit in elemental analysis. An increase in the metal contents in the irradiated wastewater may be due to the freeing of metals from trapped or chelating forms within the organic compounds that exist in the wastewater solution (Parvin et al. 2015). These obtained metal values were within the tolerable limits for using the wastewater as irrigation water (DoE 1997; Ayers and Westcot 1985; USEPA 2012). Only copper (Cu) and manganese (Mn) concentrations were higher, according to Ayers and Westcot (1985), but they were found well below the maximum allowable limit set by DoE (1997). Also, a higher concentration of potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), and iron (Fe) were found in the irradiated wastewater than the unirradiated (Table 4), which could be helpful for plant growth as these are the vital micro and macronutrients for plants (Begum et al. 2011;). In addition, heavy metals analysis of the soil used for plant cultivation was presented in Table 5. Almost all the heavy metal concentrations in the soil samples were within the maximum allowable limit (   Evident effects were also found on the dry mass, moisture content (%), fruit growing time, and the total number of fruits of Capsicum plants (Fig. 4) after implementing gamma-ray irradiated textile wastewater. The Capsicum fruits grew after 29 days on the plant nourished by wastewater radiated at 10 kGy. On the other hand, the plants fed with only water and raw wastewater, the fruits grew after 41 days and 59 days, respectively. Maximum 40 fruits and 3.02 g dry mass of these fruits were gained from the Capsicum plants treated by 8 kGy gamma-irradiated textile wastewater. The dry mass for the control sample was 2.25 g (total 25 fruits), and the plants treated with raw textile wastewater were 0.17 g (total two fruits only). According to Fig. 4, the other plants treated with 3, 5, and 10 kGy gamma-ray irradiated textile wastewater showed a better result than the plants treated with only raw textile wastewater. Contrariwise, the highest moisture content (93.2%) was found for the fruits collected from the plants treated with raw wastewater, and 92.62% moisture content was found for 8 KGy fruit samples, which showed comparatively better performance among the irradiated and control fruit samples. Gamma irradiated textile wastewater possessed a higher concentration of nitrogen and ammonia, which ultimately in uenced the increase in dry mass and moisture content of the Capsicum fruits (Parvin et al. 2015;.

Metals concentration in Capsicum fruits
The analysis of Capsicum fruit samples for heavy metals concentration and the macro and micronutrients was done and presented in Fig. 5a and 5b, respectively. The outcomes show that heavy metals concentration (Pb, Cr, Hg, Ni, Cu, and Zn) in Capsicum fruits decreased progressively as higher doses of treated wastewater were implemented (Fig. 5a)

Conclusion
From this present comprehensive investigation, it has been observed that gamma radiation can e ciently break down the textile dyes and large organic contaminants in wastewater solutions which eventually reduce the pH, BOD, COD, turbidity, EC, TDS, and TSS of textile wastewater. Signi cant improvements have been noticed in DO, ammonium, and total nitrogen content. The decline in COD values has in uenced the increase in the biodegradability index of irradiated wastewater. This outcome reveals an impressive sign of the irradiated textile wastewater that could have been recycled as irrigation water with fertilizing characteristics. After implementing gamma-ray irradiated textile wastewater, the growth and production rate of the Capsicum frutescens have been reinforced in contrast to that of the plants cherished with unirradiated wastewater and only water. According to the elemental analysis report, the heavy metals exist in negligible amounts, but vital macro and micronutrients for plant development and human wellness are obtained at a superior level in Capsicum fruits, indicating fascinating and fruitful results.
The outcome of this research will develop a convenient way of wastewater treatment and reusing irradiated wastewater for irrigation purposes by which environmental threats can be removed effectively. The physicochemical features of the irradiated wastewater, the plants' morphological characteristics, and the Capsicum fruits production approach to a decent level at the radiation doses of 8-10 KGy. So, irradiation of textile wastewater by gamma-ray at 8-10 KGy doses could be an alternative solution for wastewater treatment.
Besides, due to having fertilizing properties of the treated wastewater, it can be reused as irrigation water, and the extra cost of fertilizer could have been reduced. Therefore, it has been suggested that textile wastewater can be converted into water resources by applying gamma radiation which may solve the existing and rising environmental problems. Figure 2 Changes of total nitrogen and ammonium level in raw and irradiated textile wastewater.

Figure 3
Comparison of average plant height (cm) per week, average number of leaves (per week) and root length for control, unirradiated/raw and gamma ray irradiated Capsicum plants.
Page 17/18 Figure 4 Variation in dry mass, moisture content (%), fruit growing time and no. of fruits for control, unirradiated/raw and gamma ray irradiated Capsicum plants.