Open Veterinary Journal, (2023), Vol. 13(11): 1458–1464

Original Research

10.5455/OVJ.2023.v13.i11.9

Enhancing the composting process by using lactic acid bacilli for the hygienic disposal of dead fish

Abed Ahmad Erdeni¹, Dhyaa Mohammad Taher Jwher²*, Muntaha Ghazi Hassan² and Dhamyaa Khalaf Al-Doory¹

¹Department of Biology, College of Education for Girls, University of Tikrit, Tikrit, Iraq

²Department of Veterinary Public Health, College of Veterinary Medicine, University of Mosul, Mosul, Iraq

*Corresponding Author: Dhyaa Mohammad Taher Jwher. Department of Veterinary Public Health, College of Veterinary Medicine, University of Mosul, Mosul, Iraq. Email: diaataher [at] uomosul.edu.iq

Submitted: 30/08/2023 Accepted: 29/10/2023 Published: 30/11/2023

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Abstract

Background: Fish producers in Iraq currently facing large and growing problems, represented by the difficulty of getting rid of large numbers of dead fish as a result of mass phenomenon mortality since 2018. As their treatment and disposal have become very cumbersome and costly, and leaving it to wild animals and natural forces is unacceptable, so most of them resort to the composting method because it is a simple, easy, and inexpensive process and benefits outputs, but it takes a long time.

Aim: The study aimed to compare two different composting methods for the disposal of dead fish, one of them includes the use of lactic acid bacilli (LAB) to improve composting efficiency.

Methods: Sawdust, hay, one-inch perforated plastic tubes, plastic covers, and dead fish were used to make four equal composting piles, two of them were treated with LAB, and others were left to compost naturally, the composted content was daily tested physically for color, odors, pH estimation, and LAB count.

Results: The results showed that there are significant differences between normal-composed and LAB-treated groups in duration and efficiency, the total threshold limits of temperature, pH, and LAB count were 60°C ± 8°C, 6.7 ± 0.04, and 10.8 × 10⁶ ± 1.96 CFU/g, respectively, in normal composting groups, while they were 70°C ± 2.8°C, 4.26 ± 0.01, and 23.2 × 10⁶ ± 1.34 CFU/g, respectively, with total decomposition and disintegration of fish carcasses through 31 days in effective microorganisms treated groups.

Conclusion: We concluded that the use of LAB in composted materials led to a quick and efficient composting process in terms of heat, pH, LAB count, total disintegration speed, and the ability of biosafety.

Keywords: Composting, Dead fish, Lactic acid bacilli, Hygienic disposal, Preserving environment.

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Introduction

Fish and fisheries in general are considered one of the most important sources of food and an important element in achieving the concept of food security, as well as being a main source of national income and one of the supporting ways to local and national economy in large number of countries (Bergmann et al., 2020; Petriki et al., 2021).

Therefore, any factor that negatively affects or threatens it in any way will represent a very dangerous matter, given the extent of the damage and the severe negative repercussions on the environment and public health, on this basis, the phenomenon of mass mortality of fish is considered one of the devastating phenomena for fisheries and all sectors benefiting from it (Walli, 2019; Ababneh et al., 2020; Ayilara et al., 2020).

Regardless of the location or nature of the area affected by fish mortality, the damage resulting from this death could extend to the sectors of public health, the economy, and the environment, especially with the recurrence of deaths and the extension of damage to organisms other than fish (Alosairi et al., 2021). The possibility of mortality cannot be controlled or predicted; however, the negative environmental, economic, and health impacts resulting from it can be minimized, by taking the necessary health treatments that reduce the degree of pollution by stopping its sources (Kalogianni et al., 2017; Karaouzas et al., 2018).

One of the most important methods used in the treatment of dead animals is the composting method, which is a biological reduction process under aerobic conditions, in which organic materials such as dead animals are transformed into soil-like substances in multiple stages, and each stage includes different types of microorganisms and different intermediate products, or its define a biological process similar to a slow cooking process that controls the decomposition of the dead animal’s carcasses and converts the organic materials into other materials, where microorganisms play an important role in this process, through its ability to use nitrogen, fats, and carbon contained in animal carcasses and decompose them at a temperature of 60°C–65°C (Karaouzas et al., 2018; Soe et al., 2022). In the composting process, microorganisms break down organic matter and produce carbon dioxide, water, heat, humus, and a stable organic product. Under ideal conditions, the composting process continues through three phases: mesophilic, or moderate-temperature phase, lasting 2–3 weeks, thermophilic phase, or high-temperature phase, lasting several days to several weeks, and finally the cooling and maturation phase, which lasts for several months (Langston et al., 1997; Allen and Mark, 2003; Kalbasi et al., 2005; Soe et al., 2022).

Different types of microorganisms predominate during the different phases of composting, the initial decay is caused by moderate temperature or mesophilic microorganisms that quickly break down soluble materials and decompose easily and produce heat, this causes an increased temperature of composted material rapidly when the temperature rises above 40°C, it will reduce the ability of mesophilic microorganisms to compete and be replaced by high-temperature thermophilic microorganisms that start at a temperature of 50°C and above when the heat reaches more than 60°C, that leading to accelerating the breakdown of protein, fats and complex carbohydrates such as cellulose, hemicellulose, and large structural molecules that are rich in energy, finally the temperature of the mixture begins to decrease gradually and the moderate heat mesophilic microorganisms start working again for processing of maturation of remaining organic matter (Saqib et al., 2004; Li et al., 2018). There are many microorganisms observed during the different stages of the composting process that have been proven to have a significant role in the success of the process, including lactic acid bacteria and bacterial within the dead body, fungi, protozoa, and rotifers (MAF, 1996; Kalbasi et al., 2005; Carter et al., 2007; Soe et al., 2022). The composting process depends on several physiochemical factors, temperature and acidity which play roles as the keys to the success of the composting process, as well as moisture content, particle size, aeration, nutrients, and system composition, factors needed by different microorganisms to ensure fast and optimal process (Eldridge and Collins, 1996; Ellis, 2001; Kalbasi et al., 2005). The advantages of the composting method are that it has a low cost and is biologically safe due to the fact that dead carcasses are not transferred to another place and the final product is useful for amending the soil (Kalbasi et al., 2006).

Effective microorganisms (EMs) are live microorganism (probiotic) that were developed in Japan 30 years ago and is now a Global technology with an enormous following around the world, its composed of a diverse group of bacteria, yeasts, and fungi (more than 80 strains) which has been thoroughly tested and proven safe for humans, animals, and environment. recently introduced into many fields and field applications and proved its effective in disposal of poultry carcasses (Tabbaa and Taher, 2009; Taher and Tabbaa, 2012), enhancing poultry health and its productivity (Jwher et al., 2013), improving the productivity and environmental performance of fish (Jwher and Al-Sarhan, 2022), as well as its effectiveness in animal production and preserving environment (Ezzulddin and Jwher, 2022).

From the above, the study aimed to compare two different composting methods for the disposal of dead fish, one of them includes the use of EM to reach the optimal solutions in terms of composting speed, disintegration, total decomposition, and biosafety efficiency to achieve the best use of these methods for effective environmental treatment.

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Materials and Methods

According to Kalbasi et al. (2006), sawdust, hay, 2-m-long one-inch diameter perforated plastic tubes, plastic covers, water, and dead fish carcasses were used to make four equal composting units. Two of these composted units were treated with lactic acid bacilli (LAB) represented by the EM substance (Taher and Tabbaa, 2012).

Effective microorganisms

EM are a live microorganism (probiotic). Natural bio-product of the (EM.1/EM Agriton^®/Turkey), a joint Turkish-Japanese production under the supervision of EMRO institute/Japan, which contains the active organisms, composed of five groups of micro-organisms: LAB, Lacticaseibacillus casei, Lacticaseibacillus plantarum, and Streptococcus lactis; Photosynthetic Bacteria: Rhodobacter sphaeroides and Rhodobacter palustris; yeast: saccharomyces cerevisiae, Pichia Jadinii, and Candida utilis torula; Actinomycestes spp.: Streptomyces albus and Streptomyces griseus; and Fermenting Fungi: Mucor hiemalis and Aspergillus oryzae, which has been carefully examined and assured secure for humans and animals; they are the basis for all multi-Kraft products, which are created by composting (Balogun et al., 2016).

Composted units

Four equal composting units were created on open, raised land near a fish farm. Each unit with dimensions: 2 m long and 1.5 m wide. Each composted unit was formed from several alternating layers of sawdust with a thickness of 20 cm at the bottom, followed by a 10 cm thick layer of hay, followed by a layer of dead fish 15 cm in thickness. One-inch green plastic tubes 2 m in length, were perforated from all sides with 3 mm diameter along the tubes and in all directions, and passed in width through the dead fish layer (10 tubes per composting unit, with a distance of 20 cm between them) to provide ventilation, then followed by a layer of hay 10 cm thick. Finally, a layer of sawdust 20 cm thick according to Tabbaa and Taher (2009) and Taher and Tabbaa (2012), as shown in Figure 1.

Fig. 1. Components and installation of composting unit.

The four composted units were divided into two groups: two of them were left to composted naturally, and the remaining two units were treated (sprayed dead fish layer) with EM after diluting by 10% with distilled water, then enveloped by a plastic cover to keep it from heat loss, rain, and prevent attract flies, rodents, or dogs.

The air temperature and compost unit’s components were also fixed at the beginning of the experiment on the 20th of February 2023.

Daily follow-up of the experiment

The experiment was conducted on the 20th of February 2023 and lasted a period of 65 days, during which daily regular observation of the composting stages was registered including temperature and pH by using a Professional Portable pH Meter-HI98163/Hanna Instruments® USA (designed to measure temperature and value of pH together), and LAB Count.

After 3 weeks the composted units were flipping to increase porosity, and then supervision of the experiment for both methods was continued until the end.

LAB count

To perform LAB count, 50 g of fermented materials were collected from various places and randomly from each pile of the experiment groups, were placed in sterile containers and transported directly to the scientific research laboratory in the College of Education for Girls at Tikrit University to conduct bacteriological tests on them.

MRS agar (Newgen^®/USA) was used for the LAB count present in the composted piles of each group. Serial dilutions were made in deciliters and cultured on plates. The culture was incubated under anaerobic conditions at 37°C for 48 hours. Bacterial counts were achieved according to Kangawa et al. (2018).

The LAB count was performed after the first week of starting the experiment and returned every 4 days until the maturation phase was completed.

statistics analysis

The T-test was used to measure the differences between experimental groups’ means at a significant level of p < 0.05 (Petrie and Watson, 2013).

Ethical approval

Not needed for this study.

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Results

The results of our experiments showed that there are clear differences in the course of the composting process for both methods (normal composting and EM treated) in terms of time, fermentation speed, and process efficiency. The composting process by LAB (EM) was more raped, with higher temperature, and more stabilized in the second phase of composting where it reached 70°C ± 2.4°C compared to the normal composting groups, which amounted to 60°C ± 4°C.

Fig. 2. Temperature track rate for the normal group and the LAB-treated group during the experimental period.

Table 1. Comparison of the temperature, pH, and LAB count (Mean ± SE) in normal and LAB-treated groups during the experimental period.

Fig. 3. pH track rate of the normal group and the LAB-treated group during the experimental period.

Fig. 4. The tracking rate of LAB count (CFU/g) in the normal and LAB-treated groups during the experimental period (×106).

Figure 2 and Table 1 show that there is a significant difference in average temperatures between the two groups of all experimental periods, the temperature of the normal group ranged between 20°C ±2°C to 60°C ± 4°C, an average of 43.87°C ± 1.52°C and it took more than 60 days to complete the process, while the temperature in the LAB (EM) treated group ranged between 20°C ± 1.2°C to 70°C ± 2.4°C, an average of 51.95°C ± 1.54°C and it took 37 days to complete process and we got complete digestion of fish carcasses through 31 days.

The results also showed significant differences in pH in the different composting phases in both groups, where the pH of the normal group ranged between 7.48 ± 0.05 to 6.5 ± 0.06, an average of 6.85 ± 0.88 peaked at day 26, whereas, the pH of the LAB (EM) treated group ranged from 6.93 ± 0.03 to 4.26 ± 0.01, an average of 5.76 ± 0.13 and its drop peak was on day 20, as shown in Figure 3 and Table 1.

The results also revealed a significant and clear difference in the number of LAB count between the two experimental groups, as it ranged from 8.1 ± 0.15 × 10⁶ CFU/g to 11 ± 2.97 × 10⁶ CFU/g at average of 9.21 ± 1.85 × 10⁶ CFU/g for the normal group, and 11.2 ± 1.16 ×10⁶ CFU/g to 24.3 ± 0.78 × 10⁶ CFU/g at average of 18.18 ± 1.64 × 10⁶ CFU/g for the LAB (EM) treated group. As described in Figure 4 and Table 1.

In addition, very clear differences were recorded during the experiment for both groups in terms of the time taken for the different phases of the composting process and threshold limits for each of the temperature, pH, and numbers of LAB, as shown in Table 2.

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Discussion

From an ecological point of view, composting is a dynamic process due to the combined activity of a wide range of microorganisms, including bacteria, actinomycosis, and fungi, which are linked to successive environmental conditions through a symbiotic relationship with each other (Moreno et al., 2013).

The composting process is determined by the various physical and chemical factors that are related to each other and that alternate with different environmental conditions, including the availability of nutrients, temperature, amount of oxygen, pH, particle size, humidity, and so on; therefore, it is necessary to try to modify these data and control it well, so that the microorganisms can find the best conditions to perform their biological activities in the best way, where LAB play a major role in all stages of the composting process through events related to the biotransformation of organic components, being a more effective bacterium due to its versatility in metabolism; therefore, understanding the role played by microorganisms will have an impact on the composting process and improve its efficiency (Brown et al., 2008; Ayilara et al., 2020).

Table 2. Comparison between three phases in duration/day and threshold point of temperature, pH, and LAB count (CFU/g) (Mean ± SE) in normal and LAB-treated groups during the experimental period.

Mahmud et al. (2015). indicated that to achieve the condition of the composting process, the temperature must rise in the first phase, specifically during the first days, to reach 40°C to 45°C to reach their threshold, and then start the second phase of the composting process, which is the high-temperature stage where the temperature reaches 60°C, which is very important in composting success. This was evident in the results of our study by reaching EM groups to the second phase in less time compared to the normal composting groups.

The LAB showed a higher growth pattern than the patterns naturally found in the carcasses of dead fish, where the growth was according to the need for nutrients and their ability to use nitrogen and other nutrients resulting from protein decomposition. nutrients, heat, and deodorization of gases resulting from the composting process, thus preventing the arrival of insects, birds, and disease vectors over dead bodies, and thus reducing the spread of diseases. This matches what the researchers reported (Lopez-González et al., 2015; Mahmud et al., 2015; Villar et al., 2016).

The degrading enzymes produced by the LAB work to break down keratin and other proteins in the scales and skin, which yield carbon, sulfur, and energy, which are used by the bacteria for growth and sustainability (Burtt, 1999).

LAB patterns are present everywhere and they can grow on natural media without any special needs, this feature is used to break down organic matter in large quantities, moreover, LABs are thermophilic microorganisms that prefer high temperatures, this property is also used to control the process of rapid and efficient breakdown of scales, skin, and tissues, as confirmed by researchers (DeRouchey et al., 2005; Taher and Tabbaa, 2012). In addition to the enzymes that break down complex molecules such as keratin, which are among the many enzymes that are widely used in the chemical, medical, and animal feed industries (Ichida et al., 2001).

The addition of LAB (EM) played a role in increasing the numbers of LAB, which was reflected in a faster digestion and disintegration process with higher temperatures compared to normal composting groups.

The temperature in the group that was treated with the LAB reached more than 70°C, which is an ideal and preferred temperature because it leads to accelerates the process of decomposition and disintegration of tissues and the exclusion of other bacterial species that cause decay and killing larvae of flies and other insects that transmit diseases, and this what Yoon et al. (2019) explained.

According to researchers (Tabbaa and Taher, 2009; Taher and Tabbaa, 2012; Mahmud et al., 2015), the pH is very important for the microorganisms in the composting processes in several directions through helping to accelerate the digestion of organic materials and the production of organic acids in the early stages of composting, that lead to encourage the growth of fungi that destroy the remaining complex materials that bacteria cannot break down as they grow and spread with many cells and hairs and attack the dry and acidic organic residues and break down lignin and cellulose. This was evident in the results of the current study by decreasing the pH value of LAB composting, which was like a slow cooking process, compared to the normal composting groups.

This improvement in the composting process is due to the increase in the number of synergistic microorganisms formed in the natural bio-product LAB, which was evident through the ratio of LAB number, which constitutes 80% of the components of the LAB, and had the greatest effect on the course of this process in terms of time, speed of disintegration, decomposition, and maturation.

Therefore, adding LAB-producing enzymes that decompose organic matter is considered a ways to dispose of organic matter and animal carcasses, as the results encourage belief in using LAB to treat other types of waste to preserve the environment from various pollution problems.

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Conclusion

We concluded that the using of LAB(EM) in the composted materials from dead fish carcasses led to a quick and efficient composting process in terms of temperature, pH, LAB count, total disintegration speed, and the ability of biosafety to eliminate pathogens. Because of their significant impact on the composting period and reducing the composting time. The pH of composted materials, where the composting process changed as a result of acid digestion of dead fish, thus disintegration and digestion faster. In our experiment, we obtained a complete digestion and dissolution of the dead fish in 31 days.

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Acknowledgment

The researchers extend their deep thanks and great gratitude to the Deanship of the College of Education for Girls, Tikrit University, and to the Deanship of the College of Veterinary Medicine, University of Mosul, for the unlimited support to complete this work.

Conflict of interest

The authors declare that there is no conflict of interest.

Funding

Self-funding.

Authors contributions

The experiment was designed and the manuscript was written by Abed Erdeni and Dhyaa Jwher. Muntaha Hassan and Dhamyaa Al-Doory participated in the work by monitoring the experiment and analyzing the data.

Data availability

All data supporting the findings of this study are available within the manuscript.

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