Agricultural Use of Biosolids Generated in Wastewater Treatment of a Food Industry

Biosolids generated as waste from a Wastewater Treatment Plant (WTP) are a pollution problem by the provision of large volumes in landfills and the waste of their potential as an agricultural input. The research conducted trials to analyze the agricultural use of biosolids in a food company's WTP, their effects on the germination and development of the vegetal plant species Coriandrum sativum were assessed through trials that mixed different amounts of biosolids, land soil and commercial fertilizer, and took into account: planting site characteristics, biosolid and Coriandrum sativum. A random block design was made to compare treatments understudy and resulted in the combination of 50% biosolids with 50% land soil was the best test by germination, height, mass and length of the roots of the plant studied. In the evaluation of results, the behavior of dependent variables was analyzed: 1 M. Sc. Unidad Central del Valle del Cauca (Tuluá-Valle del Cauca, Colombia). ssantacoloma@uceva.edu.co. ORCID: 0000-0002-7997-3512. 2 M. Sc. Unidad Central del Valle del Cauca (Tuluá-Valle del Cauca, Colombia). mbuitrago@uceva.edu.co. ORCID: 0000-0002-3242-9421. 3 Corporación Autónoma Regional del Valle del Cauca (Tuluá-Valle del Cauca, Colombia). ORCID: 0000-00019660-3743. 4 Eduambiental S.A.S (Palmira-Valle del Cauda, Colombia). ORCID: 0000-0002-5551-8742. 5 Ph. D. (c) Unidad Central del Valle del Cauca (Tuluá-Valle del Cauca, Colombia). mamartinez@uceva.edu.co. ORCID: 0000-0003-4545-4615. 6 M. Sc. Unidad Central del Valle del Cauca (Tuluá-Valle del Cauca, Colombia). lvillegas@uceva.edu.co. ORCID: 0000-0002-5423-6444. Agricultural Use of Biosolids Generated in Wastewater Treatment of a Food Industry Revista Facultad de Ingeniería (Rev. Fac. Ing.) Vol. 29 (54), e10666. 2020. Tunja-Boyacá, Colombia. L-ISSN: 0121-1129, e-ISSN: 2357-5328, DOI: https://doi.org/10.19053/01211129.v29.n54.2020.10666 germination, height, mass and length with respect to the four test types with their respective repetitions using ANOVA and Fisher's significant minimum difference (LSD) to determine the effect the biosolid had on the plant and to know the optimal dose for its development. The germination rate (GR) was also determined in the trials, and 98.3% was found for the best treatment indicating that the substrate does not contain phytotoxic elements.

germination, height, mass and length with respect to the four test types with their respective repetitions using ANOVA and Fisher's significant minimum difference (LSD) to determine the effect the biosolid had on the plant and to know the optimal dose for its development. The germination rate (GR) was also determined in the trials, and 98.3% was found for the best treatment indicating that the substrate does not contain phytotoxic elements.

I. INTRODUCTION
Any human activity that requires water generates liquid waste known as wastewater, which is classified according to its origin in industrial, agricultural-livestock and domestic. This wastewater must be treated in order to partially or fully being rejoined [1]. Such treatment generates by-products known as waste sludge, which are solid, semi-solid or liquid residue [2]; its composition depends mainly on the characteristics of the effluent wastewater and the treatment process used in the plant that generates it [3].
The volume of sludge produced depends on the characteristics of wastewater, pretreatment, sedimentation time, solid density, and moisture content, type of sludge removal equipment or method, and frequency of removal [4,5]. The sludge can contain a large number of pathogens, depending on the treatment processes used [6]. The most important pathogens that exist in water and have been found in sludge are bacteria (such as Salmonella), viruses (mainly enterovirus), protozoa, trematodes, baskets and nematodes [7] that can spread diseases if you have direct contact with them.
As for the composition of biosolids, it is a mixture of nitrogen-rich organic compounds, and commonly present a low carbon-to-nitrogen ratio (C/N) [8]. In addition, there are factors that influence their quality as is the case of metals, these being mainly: Zinc (Zn), Copper (Cu), Nickel (Ni), Cadmium (Cd), Lead (Pb), Mercury (Hg) and Chromium (Cr) [9]. Its potential for accumulation in human tissues and its biomagnification are characteristics that generate concern; metals are present in low concentrations in domestic wastewater, but high concentrations are mainly found in industrial wastewater [10].
The current concern, in relation to sludge is to try to reduce their volume and that the compounds and elements they contain are in concentrations that allow them to be managed without problems or negative environmental impacts [3,11]. Estimates of the global production rate of biosolids are in the order of 25 to 60 million tons of dry solids per year [12] with much of this applied to soil [13]. Because biosolids are rich in nutrients, their application in the soil as fertilizer is an attractive option for sustainable soil nutrient management and carbon sequestration [14].
As for the agronomic composition of the sludge, characteristics similar to those usual in a commercial fertilizer are taken into account, with the nutrients and trace elements necessary for the correct development of plants [15]. The elements that confer these properties are Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), some metals in certain amounts (Zinc (Zn) and Copper (Cu)) and humid organic compounds [16,17].
From a practical point of view, sludge is a source of organic carbon, N, P, as well as some inorganic compounds such as silicates, aluminates, and so on, which can be recycled and used for industrial or agricultural purposes [12].
The term biosolid is the product resulting from the stabilization of the organic materials (sludges) generated in the treatment of wastewater, with physical, chemical and microbiological characteristics that allow being reused with restriction according to with the regulations of each country. An example of reuse is its return to the ground for the supply of nutrients and organic matter [18].
The quality of biosolids depends mainly on four groups of contaminants: Pathogens, Heavy metals, Nutrients and organic pollutants [19]. Agricultural use has become the main method of removing sewage sludge [20]. Statistics show that between 40% and 50% of dry sludge is used in agriculture [21]. Approximately 7% to 22% of the dried sludge produced by the European Union and the United States respectively are treated with incineration or thermal drying. Between 14 and 17% of sludge produced is use for landfill [22], while 12% is used in other areas such as forestry, soil recovery, among others. The use of the sludge as input for growing vegetables becomes the best option, because, due to its properties, it gives agricultural practices management of nutrients in their crops that allow reducing the environmental impact that is generated with the use of chemical fertilizers [23]. In addition to those mentioned, there are other possibilities, some of them derived from the above, such as the restoration of quarries, and others such as the use of sludge, after different treatments, in the manufacture of building materials and even, as an animal feed by obtaining proteins [24].
Currently, it is common to incorporate waste sludge in agricultural soils, as it reduces the addition of commercial fertilizers, improves their fertility, increases water retention capacity and reduces soil erosion [25]. Sludge acts as a soil conditioner to facilitate the transfer or provide nutrients, increase water retention and improve soil fitness for cultivation [26]. Sludge also serves as a partial substitute for expensive chemical fertilizers [4]. Sewage sludge is a renewable resource that contains important nutrients that can be used to replace fertilizers made from fossil fuels [27] but need to be treated in advance appropriately.
The main objective of this work was to study the use of sludge generated in wastewater treatment when used as an agricultural input in various concentrations.
It was used for the planting of a fast-growing plant and compared its development in terms of germination, mass and length of the plant and roots with the use of fertilizer for commercial use and with a control sample.

II. MATERIALS AND METHODS
For the development of this research, the following actions were carried out:

A. Identification of the Physical, Chemical and Microbiological Characteristics of Residual Sludge
The following analyses were performed in a certified laboratory: • Nitrogen Characterization (N-NH4, N-NO3, N-NO2) • COT, N-total, Ca, Mg, K, Total Mn, Total Cu, Total Zn, Total B, Total S.

B. Implementation of the Pilot Trial
The choice of the plant was made considering factors such as the ease of obtaining the seed, the climate which the study area counts with and the time which the plant germinates and grows in.
To start the test, the terrain is searched and the exact area where the blocks will be made is chosen, for this, it was taken into account that all the blocks were exposed to the same conditions of temperature, shadow, and slope, among others. The terrain is shown in Fig. 1. A planting area was selected, taking a bearing in mind the environmental factors of the site, such as; temperature, humidity, sun exposure, soil type, etc. Based on these factors, the type of plant was Coriandrum sativum [28].
The effect of 3 independent variables (50% and 100% biosolid concentration and NPK fertilizer known as Triple 15) was studied on the dependent variables (% germination, height, number of leaves, root length, and mass). This design sought to make constant all environmental factors that could affect dependent variables to be certain of the effect that independent variables cause. For the addition of sludge, the phenology of the plant (germination and harvesting period) was taken into consideration. Different amounts of sludge were used, indicating four types of treatment: • Treatment 1 (T1): Composed of the soil of the ground (test control).
• Treatment 4 (T4): Composed of the soil of the ground + commercial fertilizer NPK.

C. Random Block Design
The use of this design allows comparing the treatments under study. The selection of each treatment was the sort to define its respective location in each block [29,30,31]. Table 1 shows the random complete block design that was used.

D. Technical Specifications of the Test
• Each block had the following dimensions: Width: 1 m; Length: 5.5 m.
• Each block was divide into 4 rows, and each row had the following dimensions: Width: 1 m; Length 1 m.
• The space between each row is call groove; each groove had 0.50 m, with three grooves per block.
• The distance between each block was 0.50 m, to have space when making the respective observations.
• Each row had four rows per treatment, the distance between each of the rows was 0.25 m, and the distance between plants (hole) had about 0.05 m.
• The seeds chosen had % germination of 70% and because they were a little low, 3 seeds were used for each planting hole.
• For each treatment, ground beds were made, about 0.10 m wide, as the seeds are small.
• Each treatment was marked, indicating the type of treatment (T1, T2, T3, T4). As shown in Fig. 1 • Irrigation was performing daily, with the use of a hose.

Sativum
The evaluation frequency was as follows: one at 5 days after planting and then every 15 days for a 1-month time period. The parameters to be determined were as follows: • Percentage (%) germination: In each experimental unit, the number of seeds germinated on the total sown was assessed.
• Plant height: Height from the base of the stem to the highest branch.
• Root Length: The length of the roots of each plant is measured.
• Number of leaves: at 15 dap (days after planting), 30 days after planting were counted the number of leaves per plant.
The number of data taken at 15 dap was as follows: -% Germination: 10 data per treatment, 40 data per block and 120 data in total.
-Height: 5 data per processing, 20 data per block and 60 data in total -Number of sheets: 5 data per processing, 20 data per block and 60 data in total.
At 30 days after planting, five data per processing took for 20 data per block to the following dependent variables: -Height -Number of sheets -Root length -Seedling mass

F. Assessment of Information
Photographic record (Fig. 1), observations were made and analysis of a factor's ANOVA variance, means table, and data dispersion was performed.
The hypothesis on which work was made was that the variation between sludge concentrations affects the test-dependent variables.
The ANOVA analysis raises two hypotheses: Ho: null hypothesis and Ha: an alternative hypothesis. The Ho states that there were no effects of the independent As an interpretation of the results, it is that when P<0.05 the alternative hypothesis is accepted and when P>0.05 the null hypothesis is accepted.
The Germination index (GI) of Zucconi was also determined to evaluate the germination and growth of fast response plant seeds that was obtained by multiplying the germination percentage and the percentage of root growth, both relative to control (Equation 1).
According to [32,33] when the GI values are greater than 80%, the substrate does not contain phytotoxic elements; GI values between 80 and 50% indicate moderate presence, while values below 50% reveal a strong presence of phytotoxins.

III. RESULTS
The chemical and microbiological characteristics of the sludge were identified and the results presented in Tables 2, 3, 4 y 5.     All results were analyzed by using ANOVA of one factor (Treatments 1, 2, 3 and 4) for the analyzed variables: -Dependent variables: % germination, height, mass, root length -Factor: Type of test Treatments 1, 2, 3 and 4.
In the analysis of variance of a factor for % germination, height, root length and mass of seedlings are compared with the 4 different levels of Test Type.
The F-test in the ANOVA table determines whether there are significant differences between the means (Table 10).  Table 11 shows the average of the measurements of the dependent variables for each type of test.  It is note that T3, yielded the best values on average in terms of germination, mass and height of plants. Those results were also above the control test (T1).
The intervals obtained are based on Fisher's Low Significant Difference (LSD) procedure and are included in Fig. 3.
The Fig. 3 shows that germination was favored in T3 with more than 10 percentage points from Control.
In terms of height, the mean values for T2 and T3 were very similar, but when analyzing the dispersion of the obtained data, the T2 data are dispersed between 7.5 and 16 while the T3 data disperse between 8 and 13.5 and turns out to be more reliable because it is not so scattered.   As for the microbiological composition of sludge, it could be observed that the levels obtained are too high which became an unfavorable aspect and that it is necessary to consider in case the use of the sludge as an agricultural input is implemented.

V. CONCLUSIONS
The characterization of sludge allows to establish their potential use according to the concentration of contaminants that affect their biodegradability depending on their toxicity; in this case, the analysis showed its feasibility as an agricultural input.
The use of completely random block design helped reduce and control the variance of experimental error; experimental units (T1, T2, T3 and T4) were relatively homogeneous with respect to factors that could affect response variables (germination, height, mass, and root length).
The use of wastewater treatment sludge is a favorable environmental aspect because it decreases the large amount that is carried to the landfill while taking advantage of its nutritional content.
In the case of the studied sludge, which is generated in wastewater treatment, its use as an agricultural input is a viable option and offers good results provided that it can be controlled that its nutrient content, its ecotoxicity, its microbiological conditions and Its content of corrosive and dangerous elements are below the maximum admissible levels for this use.
The combination of soil with raw sludge from wastewater treatment provides a stable, hummus-like organic material that can be used as a nutrient source for plant growth and development. It was found that the mixture of 50% soil + 50% sludge is the option that produced the best results for the growth and development of seedlings of the species Coriandrum sativum.