Treatment of oily bilge waste water using marine fungi

1 Introduction

Motorized transportation of raw materials and products is increasing continuously. In the twenty-first century, 80% of the world’s trade has been delivered by ships meaning over ten billion tons of cargo transported across the world’s seas (Walker et al., 2019). It has been forecasted that global shipping traffic will increase more than tenfold by 2050 (Sardain et al., 2019). Along with the increasing traffic, oil pollution in the seas is a growing environmental concern. Motorized vessels release oily bilge water to the sea. Although these waters are dilute, they are toxic to sea organisms (Afshar et al., 2019).

Ships generate bilge water that is a byproduct of various ship operations like condensation, oil leakage, and wastewater from various onboard activities. Bilge water contains fats, oils, greases, inorganic compounds, and highly toxic polycyclic aromatic hydrocarbons (PAHs) (Wei et al., 2021). Bilge water pollutants are toxic to aquatic flora, fauna, and microbes (Afshar et al., 2019; Tiselius and Magnusson, 2017). The organization of the International Convention for the Prevention of Pollution from Ships (MARPOL) has set regulations for the discharge of oil residues into the marine environment. The oil concentration of the effluent without dilution must not exceed 15 mg/L. The limit set by MARPOL has not succeeded to limit pollution enough. In many cases, the treatment of oily waste is not efficient enough compared to the MARPOL requirements and more efficient onboard treatment techniques must be developed. Due to the enormously increasing maritime traffic also smaller discharges such as oily bilge waters from vessels must be cleaned throughout the world.

Numerous techniques have been developed to treat industrial oily wastewater as reviewed recently (Adetunji and Olaniran, 2021). Chemical and physical techniques such as chemical- and electrocoagulation, carbon adsorption, membrane filtration, and gravity separation are commonly used. Biological treatments use microorganisms that can degrade crude oil using it for their growth (Tahri et al., 2013). Bacteria are thought to be the most efficient degraders of crude oil and they are known to convert toxic substances into non-toxic forms (Xu et al., 2018). Crude oil is also known to be degraded by certain fungal species (Al-Hawash et al., 2018). While most oily waste treatments use bacteria, also fungi may have certain benefits that are increasingly studied. It is important to select natural species that are adapted to local conditions. Indigenous fungi, for instance in coastal mangrove habitats, was shown to degrade oil on site (Ameen et al., 2015; 2016; 2022). Thus, indigenous microbes have the potential to be utilized to treat oily waste water and oily port soils. Microbial degradation is an economic and simple method to treat bilge water, and importantly, the treated water could be further utilized in irrigation if shown to be non-phytotoxic. This aspect is extremely important in an arid area such as the Arabian Peninsula. In the Arabian Peninsula where farming is based on artificial irrigation, the utilization of treated waste water would be of great value. Our study aims to find efficient fungal species to treat bilge water that can be used for irrigation in farming after the treatment.

2 Materials and methods

3 Results

3.2

3.2 Seed germination

The seeds did not germinate (0%) in raw bilge wastewater of which crude oil concentration was 320 mg/L (Fig. 1). Germination was 81% and 74% in tap water and distilled water, respectively. The highest germination was observed after the F. magnifereae treatment, when 90% of the seeds germinated (Fig. 2). The germination after the Acremonium sp. treatment was 82%, and after Ceratocystis sp. 78%. Seed germination and crude oil concentration correlated strongly (r = 0.90, n = 15). The significant regression model explained 81% of the variation, and thus, showed high dependence between the variables (Table 3). The equation was as follows. Seed germination = −2.5 × Crude oil concentration + 183. The equation indicated a significant, strong, and relatively sharp decrease in germination when the crude oil concentration increased.

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Fig. 1

Seed germination in A) bilge water; B) tap water, C) distilled water, and D) bilge wastewater after the treatment with the fungi F. magnifereae.

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Fig. 2

Relation of seed germination and crude oil concentration after the treatments with five different fungi. The line refers to the linear regression equation.

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Table 3 ANOVA-table of the regression analysis between seed germination (%) and crude oil concentration (mg/L) after the treatments with different fungi.

ANOVA
	df	SS	F	P
Regression	1	8720	57.3	4.04E-06
Residual	13	1975
Total	14	10,696

4 Discussion

The treatment of oily bilge wastewater must be developed to be more efficient due to the increasing oil pollution caused by the increasing motorized traffic in all seas. Around the Arabian Peninsula, many busy ports with high traffic pollute coastal waters. The seas around the Arabian Peninsula suffer from oil accidents and also from oil pollution originating from ordinary operating ships (Suneel et al., 2019). Local solutions to treat bilge waters onboard the vessels and near the ports with indigenous microbes are needed.

Economic and local solutions to treat bilge wastewater are offered by microorganisms such as fungi. Previously, sixty different fungal isolates from 13 genera were isolated from crude oil-contaminated fields in Iran (Dawoodi et al., 2016). This shows that the potential to find local fungi to be utilized in bilge wastewater treatment is high. Efficient oil degraders were found also in India; the marine fungi Fusarium sp. and Acremonium sp. (Barnes et al., 2018). In our experiment, the same genera were the most efficient degraders. F. magnifereae reduced the crude oil concentration of bilge water to ca. one-tenth of the original concentration (320 mg/L) in bilge water. Other bilge wastewater properties (turbidity, biological and chemical oxygen demand) were also reduced to ca. one-tenth of the original values. These values confirm that the oil has been degraded to one-tenth of the original concentration. In our experiment, the crude oil concentration was originally 320 mg/L. It appeared that the concentration was suitable to be degraded efficiently. Namely, the results showed that the higher the oil concentration the lower is the degradation of oil; higher than 320 mg/L would have been degraded inefficiently. When the concentration was as high as 500 mg/L, the degradation efficiency was half of the lowest tested 100 mg/L concentration. This was shown by the ZOI for our best species F. magnifereae. ZOI was 55 mm in the lowest concentration and 25 mm in the highest concentration. The two other efficient species, Acremonium sp. and Ceratocystis sp., showed the same trend, the degradation decreased to half when the oil concentration increased from 100 to 500 mg/L.

Several species and isolates need to be studied locally to find the most efficient indigenous strains. For instance, Cladosporium sp., which was relatively inefficient in our experiment, degraded crude oil efficiently when isolated from the Gulf of Mexico (Al-Hawashet al., 2018). From the Red Sea Coast of Saudi Arabia, the isolates of Cladosporium sphaerospermum degraded diesel fuel efficiently (Ameen et al., 2016). This shows that the molecular identification of the isolates, which we had carried out, is needed in the reports.

Many other efficient fungal isolates have also been presented, Aspergillus oryzae isolated from the Saudi Arabian coast degraded crude oil almost totally (99%) (Amr et al., 2017). Penicillium sp. isolated from an oil field in Iraq was shown to degrade crude oil (Al-Hawash et al., 2018). Several fungi (Alternaria alternata, Aspergillus terreus, Cladosporium sphaerospermum, Eupenicillium hirayamae, and Paecilomyces variotii) isolated from mangrove habitat on the Red Sea coast of Saudi Arabia degraded diesel hydrocarbons (Ameen et al., 2016). In addition to above mentioned, at least the genera Cephalosporium, Rhizopus, Paecilomyces, Torulopsis, Pleurotus, Mucor, Talaromyces, Gliocladium, Rhodotorula, and Geotrichum include oil degraders (Dawoodi et al., 2015; Al-Nasrawi, 2012; AI-Jawhari, 2014; Hanafy et al., 2016; Marchand et al., 2017). Degradation of oil and hydrocarbons derivatives by isolated yeast strains from Ras Tanura in Saudi Arabia were studied by Al-Dhabaan (2022).

The final crude oil concentration of the treated bilge wastewater in our experiment was 34 mg/L, which is still too high compared to the MARPOL regulations for bilge wastewater to be released back into the sea (15 mg/L). Increasing the incubation time from four days would most probably reduce the concentration above the limit and needs further studies.

Petroleum hydrocarbons have been shown to be phytotoxic and inhibit the germination of seeds (Fasih et al., 2021). However, the effect of bilge wastewater on seed germination has been studied scarcely. Seed germination in bilge wastewater has been shown to vary greatly between plant species. Of different crop species studied, Sorghum bicolor seeds were most affected, with less than 30% of the seeds germinating in raw bilge wastewater (Olorunfemi and Idada, 2013). The germination of two Solanum species was inhibited greatly, less than 10% were germinated in bilge water (Olorunfemi et al., 2012). In our experiment, the germination of V. radiata seeds was totally inhibited by bilge wastewater. The difference may be due to the relatively high oil concentrations in our experiment. However, V. radiata as an indicative species can be recommended to be used to test the phytotoxicity of crude oil solutions.

Surprisingly, the germination of seeds was slightly lower in distilled and tap water than in cleaned bilge water. This may be due to the lack of nutrients and other elements in distilled or tap water. Bilge water was shown to contain nitrogen and other elements (Olorunfemi et al., 2012) that possibly improved the germination. The germination below 90% was observed also previously in distilled water (Olorunfemi et al., 2012, Olorunfemi and Idada, 2013).

Regarding cleaned bilge wastewater, we found no studies on phytotoxicity. Phytotoxicity seemed to be reduced only slightly when experimental petroleum refinery wastewater was treated using an electrochemical process; the germination of wheat seeds increased from 17% to 23% (Gousmi et al., 2016). Our microbial treatment increased the germination from 0% to 90%, and thus, was shown to reduce phytotoxicity remarkably. The relation between the crude oil concentration and seed germination was negative and strong. The statistically significant regression analysis indicated the remarkable difference between ca 50 – 65 mg/L concentration and 30–40 mg/L concentration. While the former concentration inhibited the germination remarkably, the latter concentration allowed almost all seeds to germinate. It shows that the oil concentration needs to be reduced to 30 – 40 mg/L to be satisfactory. Our results show that the treatment with F. magnifereae was successful and efficient in reducing phytotoxic compounds. Our F. magnifereae-treatment seemed to remove the phytotoxic compounds present in bilge wastewater. This result is outstanding in the arid Arabian Peninsula where the possibility to utilize treated wastewater will be of great value.

5 Conclusion

Many methods are used to treat and detoxify bilge wastewater. We applied five marine fungi and found that F. magnifereae had a high crude oil reduction ability. F. magnifereae was the most efficient fungus not only to decrease the crude oil concentration but to detoxify bilge water. Bilge water was detoxified as assessed with the seed germination test. The phytotoxicity of untreated bilge wastewater was high and shown to be reduced remarkably by the treatment with the marine fungi F. magnifereae. The result gives promising implications that the cleaned water could be used for irrigation in farming.

Author contributions

All authors participated equally in data analysis, authoring, and revising the article. The final version of the manuscript has been reviewed and approved by all authors.