Technical Report: Waste Water Treatment via Bioremediation

Abstract

Bioremediation technology has proved to be suitable in treating wastewater from various sources ranging from municipal wastewater to industrial effluents. Wastewater compositions in these sources may vary as well. Bioremediation inculcates the use of different types of microorganisms for bio-treatment of wastewater from different sources. The wastewater from the municipal sector requires less treatment than industrial effluents. Most industrial effluents are considered highly toxic, and some industrial effluents require more conditioning steps than others. Bioremediation of wastewater may have some shortcomings, such as climate dependency, but it is widely used all over the world due to its cost-effectiveness.

This report studies the performance of three microorganisms in wastewater treatment.

1. Introduction

Wastewater treatment is a growing concern worldwide. With the current increasing population rate, the scarcity of fresh water reserves will become inevitable unless adequate techniques are in place to recycle wastewater (El Kharraz, El-Sadek, Ghaffour, & Mino, 2012). In developed countries, one of the main reasons for widespread diseases is untreated wastewater (Zhu, 2011).

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Research shows that wastewater produced in developed countries has the highest percentage of treatment, followed by developing countries. However, developing countries treat less than 50% of sewage water, and underdeveloped countries treat the least amount of wastewater compared to other countries (Sato, Qadir, Yamamoto, Endo, & Zahoor, 2013).

There are several ways of treating wastewater, but most of these methods have limitations, such as high operational costs, the creation of a large amount of waste as a byproduct, and low treatment capacity (Amin & Azhar, 2013). This technical report focuses on the biotreatment processes, especially bioremediation, to remove toxic inorganic/organic impurities as well as heavy metals in wastewater.

This report highlights the types of contaminants found in wastewater generated from different sources, compares their percentages, and discusses the process by which different types of microorganisms can be used to remove these impurities.

2. Results and Discussion

2.1 Composition of Impurities in Wastewater

The water discharged as a waste stream, whether from domestic, industrial, or agricultural use, contains varying levels and compositions of contamination. However, the three basic types of contamination generally found in wastewater are organic substances, inorganic substances such as heavy metals (Pb, Cr, Cd, etc.), and pathogenic microorganisms (Coelho et al., 2015).

Sewage Sludge

According to research, wastewater generated from domestic use generally contains three classes of organic impurities: fiber, proteins, and sugars, which are commonly found in human feces. The highest concentration of organic matter is fiber at 20.64%, followed by protein at 12.38%, and sugars at 10.65% (Huang, Li, & Gu, 2010). In addition to organic matter, sewage sludge also contains some harmful heavy metals whose toxicity depends on the level of exposure. According to results from a sequential extraction by the Community Bureau of Reference (BCR), who conducted studies on samples from a local municipal and industrial wastewater treatment plant, the concentrations of heavy metals varied significantly. Cu and Zn were present in the highest concentrations, followed by Pb, Cr, and Ni, with Cd present in the least amount (Wang, Hu, Chen, & Wu, 2005).

Industrial Effluent

Several industries regularly discharge polluted water, with those generating the highest volumes of toxic wastewater including mining, textile, paper, pharmaceutical, and leather industries. The color of the effluent determines the level of pollution present in the water, with black color indicating high pollution levels. Therefore, the color of wastewater can provide insights into the number of treatment steps required (Amin, Naik, Azhar, & Nayak, 2013).

The highest percentage of heavy metal detected in the industrial effluent was Chromium.

2.2 Process

Bioremediation is a naturally occurring process by which microorganisms immobilize waste organic and some inorganic materials and agglomerate them in aqueous solutions. The major classes of microorganisms capable of bioremediation include bacteria, algae, fungi, and yeast (Coelho et al., 2015). These microorganisms can either be indigenous to the contaminated area or introduced into the wastewater after isolation in laboratory cultures (Okonko & Shittu, 2007).

Bioremediation has limitations in treating wastewater. Microorganisms are not capable of removing all types of heavy metals; for instance, Cadmium is not easily removable. Additionally, microorganisms require specific environmental conditions for efficient performance and rapid growth, which can pose challenges in regulating these conditions (Amin et al., 2013).

1.3 Microorganisms Used in Bioremediation

Bacteria

Recent research has focused extensively on the use of bacteria in bioremediation of wastewater. Bacterial treatment can be conducted in two ways: anaerobic (without oxygen) and aerobic (with oxygen). For aerobic treatment, the reaction can be represented as:

O₂ + Wastewater + Bacteria → Treated Water + New Bacteria

Bacteria, in most cases, cannot completely eliminate specific heavy metals from water, but they can modify the chemical properties of these heavy metals by altering the physical structure of their atoms. This modification reduces the toxicity of the element. Examples of bacteria with this capability include Bacillus sp. JDM-2-1 and Staphylococcus capitis (Zahoor & Rehman, 2009).

Phenol and its components are common pollutants found in wastewaters from various industries such as coal thermal power plants, petroleum, and fertilizer industries. Bacteria like Acinetobacter sp., Bacillus sp., and Pseudomonas sp. can synthesize biofilms on the surface of the medium, making them ideal for treating wastewater containing phenol and phenol-based impurities. This technology is suitable for large-scale treatment, as these bacteria can also reduce the Chemical Oxygen Demand (COD) (Poi, Aburto-Medina, Mok, Ball, & Shahsavari, 2017).

Encapsulating bacteria is another efficient method for removing heavy metals. Electrospun cyclodextrin fibers (CD-F) trap bacteria in a fibrous bio-composite form. This method is more effective than using single bacterial cells because CD-F allows bacteria to grow more efficiently in the presence of additional nutrient sources (San Keskin, Celebioglu, Sarioglu, Uyar, & Tekinay, 2018).

Modern methods of preparing bacterial mediums involve combining nanoparticle technology and microbes for bioremediation in FeO₃ Biochar Composite, yielding better results, especially for photosynthetic bacteria (He et al., 2017).

Fungi

Wastewater treatment using fungi can be approached in two ways: inoculating fungi during supplementation to the contaminated water and preparing fungal biomass before introducing it to the contaminated site. The choice of method depends on the specific process and may vary from one industry to another. For example, in the de-colorization of textile effluent, the inoculation approach has been found to produce better results than using fungal biomass (El-Rahim & Moawad, 2010).

Fungal biomasses are generally highly effective in removing heavy metals during bioremediation (Bishnoi, 2005). Mixed cultures of different fungi can also be prepared and introduced to wastewater for bioremediation. Often, microorganisms are extracted from the waste sludge itself and used in treatment. For instance, in a tannery industry's wastewater treatment facility, ascomycetous fungi like Penicillium commune, Paecilomyces lilacinus, and Fusarium equiseti have been reused. These fungi, when stirred in a bioreactor and supported in a nylon mesh for immobilization, produced the following results:

However, this treatment duration lasted for 5 days, which may be considered a lengthy process, making it less viable in some applications.

Algae - Phycoremediation

Microalgae, a type of algae that utilizes inorganic nitrogen and phosphorous as nutrients for growth, can play a crucial role in reducing eutrophication in water bodies, thus mitigating oxygen depletion. They are also capable of removing heavy metals and some toxic organic compounds (Abdel-Raouf, Al-Homaidan, & Ibraheem, 2012; Lim, Chu, & Phang, 2010; Mouchet, 1986).

Microalgae such as S. quadricauda can potentially be used to reduce Biochemical Oxygen Demand (BOD) and phosphate, while C. vulgaris exhibits a higher capacity for removing nitrate and COD from wastewater (Kshirsagar, 2013). Some microalgae, like Chlorella minutissima, produce significant amounts of manure suitable for fertilizers and biomass as by-products. They also perform better in water biotreatment compared to algal biomasses, as shown in the table below:

One critical limitation of phycoremediation using microalgae is their prototrophic nature, and their contaminant removal performance depends on light intensity. Thus, their efficiency is highly weather-dependent, requiring a continuous supply of sunlight to perform effectively (Raeesossadati, Ahmadzadeh, McHenry, & Moheimani, 2014).

3. Conclusions

This report has focused on three classes of microorganisms, namely bacteria, fungi, and algae, which can be effectively employed in the bioremediation of wastewater. Each of these microorganisms offers unique advantages and can play a significant role in treating different types of wastewater contaminants.

Bacteria: Bacteria have proven to be effective in modifying metals to less harmful chemical structures. They are particularly well-suited for treating wastewater from petroleum and coal industries. Innovative techniques such as encapsulation and hybrid methods, which incorporate nano-particle technology and Biochar composites, can be employed to enhance their adsorption capacity.

Fungi: Fungi have demonstrated excellent performance in removing a high percentage of impurities from wastewater, especially in the leather industry. However, it is important to note that the bioremediation process using fungi can take a longer time. Two distinct methods of using fungi in bioremediation include inoculation during co-supplementation and the preparation of fungal biomass.

Algae - Phycoremediation: Microalgae show great potential in wastewater treatment due to their ability to utilize nitrogen and phosphorous as nutrients. They are highly effective in Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) removal. Additionally, microalgae produce valuable by-products, including fertilizer and biomass that can be converted into biofuels.

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