3.1 Preparation and Characterizations of Vermicompost
The limed fleshing (ANFL) is obtained by employing fleshing machines in tanneries, which are potentially alkaline-denatured. It is not financially feasible to use the same fleshing to make the glue due to the low molecular weight of protein. However, fleshing has a high percentage of sodium sulfide which are unsuitable for making glue. Generally, fleshing is disposed of through a landfill. The disposal of this fleshing is currently a major issue. Fleshing can be pre-boiled to separate the fat from the other ingredients before being used to make tallow. The method for obtaining tallow then proceeds like that used for green fleshing. The quality of the tallow is sufficient for cosmetic purposes, even though the acidity index generally is greater than the index of the tallow obtained from green fleshing [17]. Most fleshing wastes are disposed to land openly risking public health. For that reasons find out a green solution to this problem and vermicomposting is a sustainable approach. Treated lime fleshing contains 78–80% moister, ash 8.3%, and total nitrogen 15.2% which are suitable for vermicomposting [10].
Chrome shaving dust was washed with a solution of Potassium Carbonate and Hydrogen Peroxide to remove dangerous chromium from it. To convert the chrome shaving to collagen the following reaction might occur:
The chromium present in chrome shaving dust is in the chromium (III) state and is considered harmless. Under uncontrollable conditions, however, it can conceivably be oxidized to mutagenic chromium (VI). The chromium content in shaving waste before and after treatment was determined by Atomic Absorption Spectrometer and it was found untreated shaving waste was 148.37 mg/kg and treated at 1.95 mg/kg respectively. However, in the five times washing stage (Potassium Carbonate and Hydrogen Peroxide) chrome content was determined by AAS and found at 30.45, 26.45, 7.40, 5.25 and 1.95 mg/L respectively. The chromium content was under the limit of quantification which was much needed for the study. Working with chromium is risky as the project was based on chrome shaving waste the chrome content was to be checked. Excess chromium was removed with a solution as K2CrO4 which is more basic and removed by washing.
More number of worms indicates that the vermicompost is comfortable for the worms and that nutrition is adequate in the compost. The number of worms is expected to rise to some good margin within the time frame. After 30 days the release of earthworms exhibited different patterns of cocoon production with varying percentages of substrates in the feed mixtures. The cocoon production was found at 319, 310, 308, 65, and 52 in the field-1 (Control), field-2, field-3, field-4 and field-5 respectively. The cocoon production in vermi fields nos.2 and 3; was statistically significant with each other with control field-1. If the ratio of cow dung and solid waste is 1:1 cocoon production is statistically significant. The lesser cocoon in field-4 and 5 (cow dung and waste ratio 1:2) exhibits an increase in waste concentration with decreases the cocoon production in the feed mixture. It was concluded from the results that waste with a cow dung ratio of 1:1 served as a good feed for earthworms.
Figure 2 in supporting information showed the sieved and dried vermicompost after 90 days of composting. It was found control cow dung was 574 gm, treated fleshing (fleshing + cow dung) 426 gm, and treated shaving (shaving dust + cow dung) 446 gm respectively after dried sieved. Vermicomposting is a sort of composting where specific species of earthworms are employed to speed up the conversion of the organic waste and create a higher-quality final product. It is a mesophilic method that uses worms and microbes. Vermicompost is created when earthworms consume organic waste, process it through their digestive system, and then release it in the form of granules (cocoons). The earthworm castings include more nutrients that are readily available to plants because of the chemical secretions that help break down soil and organic material [18].
Nitrogenous substances create ammonia gas which increases the pH of the mixture and makes the bedding unsuitable for the earthworms. Earthworms are very sensitive to pH. Out of their suitable pH range, they are dead. For this reason, the regular stirring of the mixture is important so that gaseous substances can come out from the mixture. The moisture content has been maintained ranges between 34 to 66% and pH around 7 of every casting.
Figure 1
It has seen that; the pH is declined of the worm's bed over time. 0 to 30 days the decline effect is moderating, 60–90 days tending is neutral or slightly alkaline shown in Fig. 1. The results were reproducible within 3–7% error limits and Figure represents the maximum and minimum value of each experiment as in error bars. Worms can survive in a pH range of 5 to 9 found in other research [19] and most of the researcher feel that the worms favor a pH 7 or slightly higher. The pH was adjusted upwards by adding calcium carbonate in the cases if needed. The pH conditions always maintain between 6.5 and 8.6 and it is suitable for the cultivation of earthworms. A decrease in pH was observed over time in all waste, which might be occurred with the dissolution in water of the ammonia resulting from the microbiological metabolism of bacteria present in the substrates or the excrements of the earthworms, as suggested Edward [19].
Data from three vermicompost were taken after 0 and 90 days and the parameters were TOC, TKN, TK, TP, and C/N. All samples were analyzed in triplicate and the results were presented on average. The results were reproducible within 3–5% error limits. The three vermicompost specimens were also tested for the presence of heavy metals (Cr, Pb, Fe, Ni, and Cu) before the plantation of grass. After plantation, various body parts of the Napier Grass were tested for any possible uptake of heavy metals from the fertilizers and compared with the minimum standard set by WHO. At the same time, data for growth and other visual observations were collected.
Table 1
Table 1
Nutrient parameter (%) (mean ± SD) analysis of 0- and 90-day vermicomposting (n = 3).
Parameter (weight in %) | Days | Cow dung (%) | Fleshing waste (%) | Shaving waste (%) |
TOC | 0 | 21.85 ± 0.508 | 55.12 ± 2.82 | 45.11 ± 1.62 |
90 | 12.47 ± 0.06 | 16.3 ± 0.912 | 17.27 ± 0.523 |
TKN | 0 | 0.95 ± 0.05 | 0.81 ± 0.0321 | 0.71 ± 0.008 |
90 | 1.45 ± 0.076 | 1.99 ± 0.042 | 1.73 ± 0.032 |
TK | 0 | 0.319 ± 0.015 | 0.168 ± 0.003 | 0.468 ± 0.002 |
90 | 0.539 ± 0.032 | 0.275 ± 0.008 | 0.281 ± 0.002 |
TP | 0 | 0.124 ± 0.021 | 0.275 ± 0.007 | 0.127 ± 0.002 |
90 | 0.556 ± 0.0424 | 0.604 ± 0.0142 | 0.849 ± 0.032 |
C/N | 0 | 23.65 | 68.04 | 63.54 |
90 | 8.6 | 8.19 | 9.98 |
Table 1 shows the Total Organic Carbon (TOC), Total Kjeldahl Nitrogen (TKN), Total Pottasium (TK), Total Pospurus (TP), and carbon-nitrogen ratio (C/N) analysed nutrient data from 0- and 90-day vermicomposting. The TOC parameter shows organic carbon significant decline, which is in congruence with the other studies' vermicomposting [20, 21]. There are two main reasons why TOC decreases after the vermicomposting process: the mineralization of the organic matter (a process that happens when earthworms and microorganisms work together), and the annelids' diet, as they use some of the carbon in their diet to build their biomass. A drop in TOC at the end of the vermicomposting procedure indicates that the original material degraded. However, after the vermicomposting procedure, C/N (one of the most common indices of compost maturation) significantly decreased in all treatments. These findings corroborate those of other studies that also showed that the acceleration in humidification promoted by earthworms during vermicomposting results in a decrease in the C/N ratio [22]. These findings are related to the decrease in TOC and increase in N concentrations observed after vermicomposting.
Total Kjeldahl Nitrogen (TKN) is the sum of organic nitrogen, ammonia (NH3), and ammonium (NH4+) in the chemical analysis of soil and vermicompost. A significant increase in nitrogen concentration occurred at the end of the experiment in all treatments and those composed of tanning waste of the fleshing and shaving types. At the end of the trial, N concentrations significantly increased in all treatments, particularly those containing fleshing and shaving tanning waste. A linear rise in N concentration was seen as the doses of primary waste and lime were increased in the cattle dung. Even though these statistics don't match with other reports [21], they are consistent with other research that used vermicomposting on substrates other than tanning sludge [20, 21]. The mass reduction during vermicomposting is associated with an increase in nitrogen (N) due to the nitrogenating of the earthworms' byproducts and the release of carbon through their metabolic processes [21]. Given that 65–75% of earthworms' bodies are made up of proteins, these substances may originate from excrement, urine (as ammonia and urea), mucus proteins, and the tissues of dead earthworms [22].
The higher K concentration observed at the end of the experiment is related to a decrease in volume resulting from the vermicomposting process. These data differ from those studies in which a decrease in K was observed at the end of the vermicomposting process of tanning sludge mixed with cattle dung [20]. This decrease could be related to K consumption by the earthworms [21]. It is important to note that in all treatments, K concentrations were much higher at the end of the trial than they have been at the beginning. This decline could be attributed to the earthworms' consumption of K. However, it might be the high K concentration found at the end of our study is connected to a volume reduction brought on by the vermicomposting procedure.
In the treatments where an increase in P concentration was observed at the end of the experiment, this was probably a consequence of the reduction in volume resulting from the vermicomposting process. A significant decrease in the C/N ratio (which is one of the most traditional indicators of the maturation of a compost) after the vermicomposting process in all treatments was observed. These results are related to the decrease in TOC and increase in N concentrations observed after vermicomposting which corroborates with the results of different studies that also demonstrated that the acceleration in humidification promoted by earthworms during vermicomposting causes a decrease in the C/N ratio [21]. In the treatments where an increase in P concentration was observed at the end of the experiment, this was probably a consequence of the reduction in volume resulting from the vermicomposting process. However, it was observed that the compost volume of the pots containing tanning sludge of the liming type was smaller at the end of the experiment.
Figure 2
Figure 2 shows the comparison percentage of vermicomposting nutrients. TOC found in the prepared vermicompost was higher than the normal vermicompost and farmyard manure [23] for both fleshing wastes and treated shaving dust. But cow dung is below normal and farmyard vermicompost. TKN, TK, and TP were lower than normal vermicompost for both three composts. But C/N was higher than normal vermicompost in the prepared composts. The normal and farmyard comparison was done with a UNIDO publication [23].
The number of worms is expected to rise but some good margin within the time frame. Initially, the number of earthworms released was 40 for every bowl. Finally, it was found 319, 52, and 65 in cow dung, fleshing waste and shaving waste vermicompost respectively. More number of worms indicates that the vermicompost is comfortable for the worms and that nutrition is adequate in the compost.
Figure 3
Before the plantation of Napier Grass, the heavy metal Cr, Pb, Cu, Fe, and Ni were determined by AAS of three resultant vermicompost and normal soil. The comparison chart shown in Fig. 3, indicates that the concentration of chromium found in vermicompost as prepared from chrome shaving dust is similar to the standard limit sets by WHO [24]. In the others fleshing and cow dung vermicompost, the heavy metals are found below the permissible limits set by WHO.
Figure 4
The FTIR spectra were recorded in the spectral region of 4000–500 cm-1 and their frequency assignment were discussed. The FTIR spectra were studied to measure wavelength and intensity which have characteristics of specific types of molecular vibration and stretching that help to identify functional groups of samples on the surface as shows in Fig. 4. An intense broad band centred between 3300 and 3500 cm-1 indicating a strong hydrogen band of OH − stretch in a carboxylic group which strongly appeared in treated fleshing and shaving dust. A symmetric band at 2925 and 2854 cm-1 occurred due to aliphatic C–H group stretching of fatty acids. The highly intense peak of treated waste and compost at 1600 cm− 1 can be ascribed to the C = C skeletal vibration of compost carbon. In addition, the spectra band from 1070 cm− 1 can be ascribed to the presence of oxygen moieties, C = O carbonyl groups. Peak at 2921, 2849 and 700 cm-1 have confirmed the presence of C-H (Alkanes) groups in treated waste and compost. Furthermore, Amide bands (I and II) are also appeared in the frequency range 1540 and 1230 cm-1, these are originating from amide groups. The above-indicated stretching frequencies are the evidence for the presence of protein, polysaccharides, lipids and fatty acids.
The composting shows a relatively decreasing peak intensity of the aliphatic region at 2925 and 2850 cm-1 and of polysaccharides at 1090 cm-1. These results were the evidence for degradation and condensation reactions of organic compounds present in compost mixtures [25]. These aliphatic methylene groups were eliminated during the composting period [26]. On other hand, deformations of peaks were found at 1100 cm-1. A strong reduction in the intensity of the bands of lignin at 1400 cm-1, cellulose at 1420 cm-1 and hemicellulose at 1460 cm-1 in the final compost. Amide II and III peaks were disappearances in IR spectrum of compost. This result was closely related to the observations recorded by Ravindran and Sekaran [27]. During composting, the protein containing intrinsic hydrogen bonding structure was disrupted and structures were broken up, at the time those carbonyls and amides were easily consumed. A Sharp nitrate band at peak 1384 cm-1 occurs on the final day of composting, indicating stable, reproducible and well-composted or maturity of manure. These results would confirm the complete mineralization of polypeptides, polysaccharides, aliphatic methyl groups and lignin.
Figure 5
TGA profiles for the initially treated waste and final stages of compost are shown in Fig. 5. A weight loss represents the dehydration reaction observed in the temperature range of 50–100°C treated with initial fleshing and weight sharply losses 60% and finally 80% at 700°C. The decomposition process occurred in treated shaving waste and compost samples in the range of 200 and 700°C. The initial treated shaving sample showed a weight loss of 65% dry matter, while it was only 45% in the final compost sample in the temperature range of 200–700°C. The weight losses at this temperature are attributed to the combustion of carbohydrates and the thermal degradation of aromatic structures. The results support the evidence for the destruction of carbohydrates in mature compost manure. Immature compost was characterized by high carbohydrate components which tend to disappear in the stabilized compost. Weight losses occurring at 310°C can be associated with the thermal degradation of proteins and also the thermal degradation of cellulose catalysed by sodium and potassium [28].
The four tubs were filled with vermicompost and tagged as soil (S), treated shaving dust (TSD), cow dung (CD), and Fleshing (F). The first tub was filled with 1 kg of sandy loam soil as a reference. The second tub was filled with 0.5 kg of soil and 0.5 kg of shaving dust vermicompost (1:1 proportion). The third tub was filled with 0.5 kg soil and 0.5 kg cow dung vermicompost (1:1 proportion). The fourth tub was filled with 0.5 kg soil and 0.5 kg fleshing vermicompost (1:1 proportion). The soil and compost were mixed evenly before filling the tubs. Two healthy Napier Grass cuttings were planted in each tub, in such a way that at least one knot is under the soil and one is above the soil. Adequate water was sprayed and the tubs are placed in the same condition of light and air available for each tub. When the cuttings seemed to be spirited, then one cutting was removed from every tub, and observation was carried out on one cutting.
The cuttings were watered every day in the morning and the afternoon and observed for 45 days. The observations were carried out in two stages. In the first stage, the leaves were measured for 30 days with a gap between each observation of at least 2/3 days. Then the plants were cut. After further germination, the second stage started and the leaves were measured for 15 days in the same way. The growth rate was found fastest in cow dung and faster in Shaving dust as shown in Table 2.
Table 2
Measurement of leaf area increment of 30- and 45-day vermicompost.
Day | Shaving Dust (cm) | Fleshing Waste (cm) | Cow Dung (cm) | Soil (cm) |
30 (1st stage cutting) | 39.5 | 37.0 | 41.0 | 37.0 |
45 (2nd stage cutting) | 35.5 | 18.5 | 20.0 | 16.5 |
Table 2
A linear increase in leaf area was observed in the Napier grass which was cultivated using shaving dust compost. But in the end, cow dung provided better nutrition and so the increasing rate of leaves of the latter one sailed the former one. The growth rate of plants in the fleshing waste was lower than in shaving dust. The deficiency of nitrogen in the fleshing waste can be the reason for lower growth as nitrogen plays a significant role in plant growth.
The rate of death was found higher in the soil and lower in the cow dung compost. This is because in the soil nutrition was not available which was necessary for the plant. As the composts were treated specially to make them able to provide nutrition, the plants live longer. The other reason can be the limitation in choosing healthy cuttings. Also, root development was found higher in cow dung for the same reason. So, the prepared composts were more suitable for plant growth than soil singly.
3.2 Application and effect of Ecological Plant growth
High levels of heavy metals are released into the surface and groundwater, soils, and the biosphere by human activities such as industrial production, industrial pollution, mining, transportation, and agriculture. The possibility of food contamination through soil root contact makes the buildup of heavy metals in crop plants extremely concerning. Despite not being necessary for plant growth, heavy metals such as Cr, Cd, Pb, and Ni are easily absorbed and accumulated by plants in poisonous forms. Vegetables cultivated in heavy metal-contaminated soil and irrigated with wastewater may pose a risk to both human health and wildlife. Metal bioavailability to plants is significantly influenced by the number of heavy metals in the soil solution.
Table 3
Table 3
Heavy Metal analysis in plant body after 30 days 1st stage cutting.
Vermicompost | Sample | Cr (mg/kg) | Pb (mg/kg) | Cu (mg/kg) | Fe (mg/kg) | Ni (mg/kg) |
Soil (S) | Leaves | 0.033 | 0.411 | 0.039 | 2.528 | 0.358 |
Stem | 0.046 | 0.456 | 0.063 | 2.871 | 0.412 |
Root | 0.046 | 0.456 | 0.029 | 2.802 | 0.401 |
Treated Shaving dust (TSD) | Leaves | 0.067 | 0.064 | 0.078 | 2.201 | 0.507 |
Stem | 0.110 | 0.181 | 0.058 | 1.829 | 0.508 |
Root | 0.260 | 0.335 | 0.065 | 1.850 | 0.510 |
Cow dung (CD) | Leaves | 0.035 | 0.322 | 0.047 | 2.517 | 0.417 |
Stem | 0.045 | 0.318 | 0.091 | 2.850 | 0.588 |
Root | 0.041 | 0.382 | 0.095 | 2.701 | 0.501 |
Fleshing (F) | Leaves | 0.024 | 0.337 | 0.106 | 2.498 | 0.439 |
Stem | 0.036 | 0.327 | 0.168 | 2.504 | 0.494 |
Root | 0.049 | 0.401 | 0.170 | 2.302 | 0.321 |
WHO-FAO Standard | | 1.3 | 2.0 | 10.0 | 20.0 | 10.0 |
The plants which were grown using vermicompost prepared from tannery wastage can also bio-accumulate heavy metals from used soil or fertilizers which can be bio-transferred to animals or humans. Therefore, the samples were analyzed separately for their root, stem and leave using AAS after 30 days (1st stage cutting) and 45 days (2nd stage cutting) respectively. The concentration of heavy metals reduced significantly in the second stage than in the first stage. The concentrations of heavy metals in soil, fertilizer, and plant body are also compared with WHO standards are shown in Table 3.
The permissible limit of chromium for soil and plants is 1.30 mg/kg recommended by WHO [24]. The intake of chromium from soil or fertilizer to the plant body proved negligible. In the root, stem, or leaves of the plant Napier grass, the concentration of chromium was found far below the permissible limit and ranges from 0.26 mg/kg to 0.011 mg/kg. The intake rate decreases with the lifetime of the compost.
The permissible limit of lead for soil and plants is 1.7 mg/kg recommended by WHO [24]. In the composts and soil, the concentration of lead was below the permissible limit which ranges from 0.452 mg/kg to 0.367 mg/kg. In the leaves, roots, and stems of Napier grass, the concentration of lead was recorded far below the permissible limit for shaving dust, fleshing waste, and cow dung compost as well as for soil. The concentration ranges from 0.456 mg/kg to 0.051 mg/kg.
The permissible limit of copper for soil and plants is 10 mg/kg or 0.72 mg/L recommended by WHO. The concentration of copper was found below the limit in the soil and composts which were between 0.385 mg/kg and 0.147 mg/kg. The accumulation of copper in the body of Napier grass was negligible and ranged between 0.039 mg/kg and 0.168 mg/kg.
The permissible limit of nickel sets by WHO is 10 mg/kg for soil and plants. In the composts and soil concentration was below the limit and ranges from 0.707 mg/kg to 0.516 mg/kg. In the plant's body parts, the concentration was found between 0.508 mg/kg to 0.358 mg/kg.
The standard limit of iron for soil is 20 mg/kg and for plants, 4mg/kg is recommended by WHO. In the composts and soil, the concentration is found below the permissible limit. The uptake of iron from soil to the plant bodies was small and ranges below the permissible limit according to WHO.
Heavy metals over their standard values are hazardous to human, plant, and animal life, hence this issue needs to be addressed. To evaluate the quantities of heavy metals in used soil, fertilizer, and grown plants, a study was conducted.
The amount of industrial solid waste is increasing and is a significant contributor to the global waste issue. Waste management and waste treatment techniques are crucial for this reason. Hazardous waste is handled more precisely than other types of waste because it could seriously harm the environment. The majority of hazardous waste is managed following national legislative regulations, just like municipal waste. For issues like operating permits for the handling, storing, or disposal of hazardous waste, requirements are established. Waste can be treated or disposed of using a variety of methods, including (i) recycling waste, (ii) treatment, (iii) storage, and (iv) disposal procedures. The vast majority of byproducts from numerous industrial processes that were formerly regarded as waste are now seen as "new raw materials." According to their composition, the solid wastes generated by various sectors are divided into several categories. Even though different treatment techniques are used following legal requirements, disposal costs are still rising. Out of all the possible waste types, fleshing and shaving were chosen for this study which can be further added.