The use of tannery sludge vermicomposting in corn crop irrigated with sewage treated wastewater

The countless generation of waste (solid or liquid) by agro-industrial activities, has stimulated the development of researches aimed not only at the processing of these materials but also the possibility to take advantage of them in the agricultural environment. Therefore, this study aimed to evaluate the production of maize plants (Zea mays cultivar LG 6036) grown in pots containing Oxisol in addition to tannery sludge vermicompost and irrigated with treated wastewater from households. The treatments consisted of factorial 2x6 (two types of irrigation and six fertilization treatments) in a completely randomized design with five replications. At the end of the experiment, the following production components were evaluated: 100 grain weight (g) (13% moisture dry basis), total number of grains per spike, total weight of grains per spike and total weight of the spike (g). It was observed that plants grown in soil increased with tannery sludge vermicomposting and irrigated with treated wastewater had higher yields, which indicates that these residues are important sources of nutrients for growing corn.


INTRODUCTION
Currently, there is an increase in the development of researches aiming beyond treatment and the recovery of waste produced by agro-industrial activities.Environmental issues, in particular, have raised concerns and reflections, since the waste generated have the potential to cause environmental damage, if not properly treated (Kraemer, 2014).Therefore, in order to solve or minimize this issue, the reuse of this waste has emerged as an interesting and environmentally sustainable alternative since it can reduce the environmental problem, which is the disposal of these materials on the environment (Nunes et al., 2009).
Treated wastewater reuse for irrigation, landscape and surface or groundwater replenishment purposes is being widely implemented (Abourached et al., 2016;Fiorentino et al., 2016;Chen et al., 2016).Although, the reuse practice is accompanied by a number of benefits relating to the enhancement of water balances and soil nutrition by the nutrients existing in the treated effluents, a number of unanswered questions are still related to this practice (Fatta-Kassinos et al., 2011).
Besides the lack of knowledge in respect to possible elemental interactions that may influence the accumulation of heavy metals and other elements in the soil and the subsequent uptake by plants and crops, during the last several years, the technological progress in respect to analytical chromatographic methods has enabled the identification and quantitation of a number of organic xenobiotic compounds in treated wastewater.Therefore, it is now known that the effluents' remaining organic matter most usually expressed as chemical oxygen demand consists of a number of biorecalcitrant organic xenobiotic compounds including potential endocrine disrupting compounds (EDCs), pharmaceuticals, etc.It is also widely accepted that the currently applied treatment processes for urban wastewater abatement fail to completely remove such contaminants and this lead to their subsequent release in the terrestrial and aquatic environment through disposal and reuse applications.According to Fatta-Kassino et al. (2011), the number of studies focusing on the analysis and the toxicological assessment of such compounds in the environment is constantly increasing the aim being to bridge the various knowledge gaps associated with these issues.Thus, the existing knowledge in respect to the relevant existing legislation framework, the types of elements and chemicals of concern, the uptake of xenobiotic pollutants and also that of other neglected chemical elements along with their potential environmental interactions should be the focus of different studies.
According to Toze (2006), the reuse of water for agricultural irrigation is often viewed as a positive means of recycling water due to the potential large volumes of water that can be used.Recycled water can have the advantage of being a constant, reliable water source and reduces the amount of water extracted from the environment.In addition, in some cases, treatment requirements may need to be less than for water used in an urban environment due to less potential human contact.There are concerns and unknowns, however, about the impact of the quality of the recycled water, both on the crop itself and on the end users of the crops.Water quality issues that can create real or perceived problems in agriculture include nutrient and sodium concentrations, heavy metals, and the presence of contaminants such as human and animal pathogens, pharmaceuticals and endocrine disruptors (Toze, 2006).Thus, the minimization of human exposure to the practice of agricultural reuse is based on a set of mitigation measures that must be implemented by the authorities responsible for operating and monitoring systems for water recycling.
On the other hand, a generating activity of potentially toxic residue, very common in India and Brazil, refers to the bovine leather processing, through tanneries industries (Godecke et al., 2012).This brings several benefits in terms of jobs generation and income, however, they are faced with environmental problems, since the leather processing makes use of many potential polluting chemical (Godecke et al., 2012;Luersen et al., 2012).The problem becomes even worse when it was found that due to the great demand for products derived from tannery activity, large volumes of organic waste are generated (Godecke et al., 2012).Therefore, the agronomic use of these materials has been considered for reuse especially because most of these are compost of organic materials effective for fertilization and neutralization of acid soils (Godecke et al., 2012).However, the application of such natural wastes directly into the ground has caused controversy and widely varying results in different agricultural crops.
Thus, vermicomposting of waste tannery, biotechnological process that requires simple and low cost facilities, appears as an option for the recycling of this waste in the agricultural environment.As discussed by Vig et al. (2011), this process has been considered as a potential option in the hierarchy of integrated solid waste management, mainly because the unused solid waste can be transformed into noble organic compounds.According to Aquino et al. (1992), the use of vermicomposting in certain cultures may be more interesting than the use of natural waste, since vermicomposting can generate material with high agricultural potential.
Moreover, there are great demands for the use of treated wastewater coming from the domestic sewage produced daily.With the emergence of conflicts over water use and the fact that water consumption for irrigation is significant, the interest in the use of sewage to replace or complement the sources normally used for irrigation has increased.
As discussed by Leal et al. (2011), the prospects for irrigation in Brazil, with domestic treated wastewater, are promising considering the fact that agriculture plays an essential role in the economy, besides the fact that fresh water for irrigation of crops is scarce in some regions.Different studies have pointed to the potential use of this water in agriculture; this is due to the fact that the water has nutrients that are beneficial for plant growth (Andrade-Filho et al., 2013;Bonini et al., 2014;Leal et al., 2011;Silva et al. 2014).According to Hespanhol (2003), treated wastewaters from domestic sewage have nutrients whose content meets, if not all, at least most of the nutritional needs of plants in general.
Therefore, the present research aims to evaluate the development and productivity of maize in the soil with tannery sludge vermicomposting and irrigated with domestic treated wastewater.In addition, the authors sought to evaluate the nutritional quality of the crop by leaf analysis and the chemical impact of the combined use of such waste in the main characteristics of the soil.

MATERIALS AND METHODS
This research was conducted in a greenhouse, from April to August 2014, at the Experimental Station of the Instituto Federal Goiano (IF Goiano) -Campus Urutaí (GO, Brazil).The soil used in the experiment was taken from the surface layer, 0-20 cm, of an area next to the greenhouse, having been classified as Oxisol soil (Table 1).The vermicomposting used were those produced from substrates compost of 20% liming and primary tannery sludge types, and 80% of cattle manure, which were produced as described by Malafaia et al. (2011).It is noteworthy that the liming sludge used in this research refers to the waste produced in the waxing phase of the skin and the primary sludge from the primary treatment to the tannery station industry.The grantor company for sludge treats the effluents generated in the bovine leather tanning stage, separately from other waste and produced effluents.Therefore, the tannery sludge used in this research did not contain the element Cr.Table 1 shows the characterization of such compounds done according to Tedesco et al. (1995).
The dose of NPK used in treatments T2 (A) and T2 (R) was calculated based on the nutritional needs of the crop, the nutrient concentrations in the soil and culture yield expectation of 10 Mg ha - 1 , according to Souza and Lobato (2004).NPK sources were urea (CH4N2O), superphosphate (P2O5) and potassium chloride (K2O), respectively.The doses of tannery sludge vermicomposting for the soil were calculated based on the concentration of K, high concentration element in vermicomposting used (Table 1) and the supply of 50 kg ha -1 K2O at the base.The amount of 60 kg ha -1 K2O was provided by fertilizing two plots of 30 kg ha -1 , at 40 and 60 days after sowing (DAS).Thus, the dose of liming sludge vermicomposting (VLc20) added to the soil corresponded to 6.1 Mg ha -1 and primary sludge vermicomposting (VLp20), 5.5 Mg ha -1 .It was not necessary to adjust the soil pH.
The soil previously mixed with vermicomposting (VLc20 and VLp20) and inputs were put in polyethylene vessels (volumetric capacity of 15 L) in a total of 12.5 kg.After the installation of the experimental units, the vessels were sown with three corn seed (Zea mays L.) cultivar LG 6036 (LG Seed®) and 15 days later, thinning was realized when one plant was kept by vessel.The phytosanitary treatment was performed when necessary and the nitrogen fertilization (total of 130 kg ha -1 ) was performed on the surface, in two equal plots (65 kg ha -1 ), at 40 and 60 DAS.
The water used in irrigation were those from the IF Goiano -Campus Urutaí water supply system, treated in a water treatment plant (WTP), and treated wastewater from a domestic wastewater stabilization pond, also located on the facilities of the institution.For the characterization of irrigation, water samples were collected monthly within the experimental period (n = 4) for evaluation of physical, chemical and physico-chemical parameters according to the methodology proposed by APHA (1997).
The management of crop irrigation was realized from an evaporimeter tank, developed by Salomão (2012), with a circular shape of 52 cm internal diameter and 24 cm height (internal), installed over a pallet of wood (height, 15 cm) and installed inside the greenhouse, between the treatments.To keep the soil water retention capacity in 70% (243.1 mL.kg -1 ) during the experimental period, the volume of daily irrigation water was based on the vessel area to be irrigated (0.06 m 2 ) and crop evapotranspiration (ETc).It is noteworthy that the volume of water to be replaced was measured in a graduated cylinder.The soil water holding capacity (C100% = 347.4mL.kg -1 ) was determined by calculating the power of the soaking soil according to the methodology recommended by Embrapa (2007).
At the end of the trial period, the following production components was evaluated: 100 grain weight (g) (13% moisturedry basis), total number of grains per spike, total weight of grains per spike and total weight of spike (g).
All the data were subjected to analysis of variance according to the factorial model (two-way ANOVA), and the factors were the treatments (six levels) and irrigation (two levels), with five replications.In cases of significant F, the Tukey test at 5% probability was performed.It is noteworthy that the analysis of variance was performed using the ASSISTAT software, version 7.7 beta (copy distributed for free).

RESULTS AND DISCUSSION
The results of analysis of variance indicated a high difference in the interaction between the sources of variation, "irrigation" and "treatments", for all yield components evaluated at the end of the experiment (100 grain weight (g), total number of grains per spike, total weight of grains per spike, and total spike weight (g) (Table 2).The interaction between the types of irrigation water × fertilization treatments for the production components that were evaluated can be seen in Table 3. Figure 1 shows images of ears of corn cobs for different experimental treatments.
The number of spike produced per plant was similar to the treatments (n = 1), and the total weight of grains per spike was taken as productivity, which is the total weight of grain produced per plant.For this variable, it was observed that the T6R treatment was higher than the T1R, T4R and T5R treatments and equal to the T2R and T3R treatments.It is noteworthy that the T3, T4, T5 and T6 treatments, irrigated with treated wastewater or not, had similar productivity with that observed in the T2 group (Table 3), which received chemical fertilizers.This indicates that the use of tannery sludge vermicomposting in the proportion used in this experiment can be an interesting alternative to reduce the use and cost of chemical fertilization, when it is aimed at producing maize.
Regarding the 100 grains weight, it was observed that there was difference only between the treatments irrigated with water supply (from T2A to T6A) when compared with its control (T1A) (Table 3).It is noted that the average number of grains for the last treatment was less than 100; therefore, the variable weight of 100 grains was estimated by a simple rule of three.Regarding the treatments irrigated with treated wastewater, no differences were identified (Table 3).Also, the grains produced have similar quality, state of maturity and sanity  with the treatments.As for the number of grains per spike produced by plants irrigated with the water supply, difference between the T2A to T6A treatments, compared to its control (T1A) was also observed.The treatments irrigated with treated wastewater also did not differ (Table 3).
Regarding the total weight of spikes produced by plants with treatments irrigated with the water supply, it was observed that the T2A to T6A treatments showed higher values for the variables as compared to their control, T1A.Also, the T3A, T4A, T5A and T6A treatments were similar to the treatment that received mineral fertilizers, T2A, (Table 3).Furthermore, with regards to the treatments irrigated with water supply, all the groups irrigated with treated wastewater, except T4R treatment, produced spikes with the highest total weight (Table 3).
The data obtained in this study, regarding the yield components evaluated, also allow us to infer that the combined use of tannery sludge vermicomposting and irrigation with domestic treated wastewater can be an interesting alternative for agricultural practice that reduces the amount of chemical fertilizer used in maize crops, embedding environmental benefits and human health.
Previous studies, such as the works by Panoras et al. (2004), Azevedo et al. (2007) and Costa et al. (2012) showed that the use of treated wastewater from sewage provides greater or similar productivity to maize cultivation held in conditions of high chemical fertilization.Similarly, studies by Chamle et al. (2006), Kalantari et al. (2010), Tejada and Benítez (2011), Manyuchi et al. (2013) and, more recently, Chamle (2014) and Pandurang (2014) evaluated the impact of the use of vermincomposting in maize and also showed positive effects on the crop.However, no study to date, had evaluated the effect of combined use of treated wastewater with tannery sludge vermicomposting on production parameters.

Conclusion
Based on the results and according to the experimental conditions, it can be concluded that both the tannery sludge vermicomposting and the treated wastewater from households, are important sources of nutrients for the cultivation of maize and helps in providing conditions that provide improved productivity in maize.

aA*Figure 1 .
Figure 1.Images of corn cobs (Zea mays L. -LG 6036) produced by plants in the different experimental treatments.

Table 1 .
Main characteristics of the initial soil and tannery sludge vermicompost used in this study.Urutaí,GO, 2014.

Table 2 .
F test analysis of variance for 100 grains weight, number of grains per spike, yield and total weight of the corn spike (Zea mays L. -LG 6036), depending on the type of water irrigation and fertilization treatments.Urutaí,GO, 2014.

Table 3 .
Mean values of interaction type of irrigation water x fertilization treatments for 100 grains weight, total number of grains per spike, yield and total weight of the corn spike (Zea mays L. -LG 6036).Urutaí,GO, 2014.
aA Total weight of the spike (g)