Modern Biotechnological Methods in Wastewater Treatment: A Review Chimica Techno Acta REVIEW published by Ural Federal University 2022, vol. 9(2), No. 202292S3 eISSN 2411-1414; chimicatechnoacta.ru DOI: 10.15826/chimtech.2022.9.2.S3 1 of 6 Modern biotechnological methods in wastewater treatment: a review C.L. Beya ab*, O.N. Kanwugu a , M.N. Ivantsova a a: Institute of Chemical Engineering, Ural Federal University, Ekaterinburg 620002, Russia b: Polytechnic Faculty, Department of Industrial Chemistry, University of Lubumbashi, Lubumbashi 7110501, DR Congo * Corresponding author: borhomelwamba@gmail.com This paper belongs to the MOSM2021 Special Issue. © 2021, the Authors. This article is published open access under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract Given that water is the main solvent in living organisms as well as in domestic and industrial activities, it must be treated as carefully as possible after multiple uses to get a harmless water quality. To re- move the undesirable materials (e.g. organic matters, surfactants, petroleum products, unwanted metals, dyes, et.), the physicochemi- cal water treatment process is used as the common method. This method of wastewater treatment uses flocculation – coagulation technique, which consists of mixing coagulant matters with water to collect, in solid clusters, the materials in suspension by gravity. Re- cently, environmental scientists have suggested biotechnology meth- ods as the main alternatives in the treatment of wastewater, as they offer more benefits to the water quality and human health than chemical methods. This paper describes and assesses some modern biotechnology methods used in wastewater treatment. Keywords wastewater and biological treatment bioadsorption membrane biofilm reactor BES Received: 02.11.21 Revised: 08.04.22 Accepted: 09.04.22 Available online: 16.04.22 1. Introduction Water is source of all life and a vital resource for all man- kind in the sense that each human consists averagely of 65– 70% water. For the environment water remains the object par excellence, without which no life is possible [1]. After being used water is said to be waste due to the presence of some pollutants, which affect its quality. These pollutants include heat, sediments, inorganic chemicals, organic com- pounds, radioactive substances, and dead organic matter; it should be noted that most of the pollution from our wastewater is organic [2]. Rivers can absorb and degrade these organic pollutants to a certain extent by the self- purification process. Even though nature is capable of self- cleansing, the amount of organic matter we produce far exceeds the self-purification capacity of the watercourse [3]. According to WHO, approximately 30% of all diseases and 40% of deaths throughout the world are due to polluted water [4]. It is, thus, essential to develop technologies ca- pable of treating wastewater to allow its reuse without damaging the ecosystem. Biotechnology finds a wide range of applications in many fields, such as the environmental decontamination, the food industry, and the mining sector [5]. As a modern technology and in comparison to the conventional physi- cochemical method, which uses mainly chemicals to treat wastewater, biotechnology methods consist of using mi- croorganisms such as algae, fungi, bacteria or their parts, which interact with and remove unwanted matters within wastewater [6–7]. A successful use of biotechnology in the wastewater treatment, however, needs to properly inte- grate microorganisms with the modern bioreactors. This is because microbial communities require certain conditions to live (under aerobic or anaerobic conditions) and then to oxidize or incorporate organic matters in wastewater into cells that can be eliminated by a removal process or sedi- mentation [8]. The bioadsorption, the membrane biofilm reactor, mi- crobial fuel cells and the biofilters are modern technolo- gies allowing treating the wastewater using biotechnology methods. Indeed, biotechnological treatment is extensive- ly used for the removal as well as stabilization of biode- gradable matters in wastewater [6–7]. Scientists and envi- ronment engineers have realized that major issues for re- claiming water quality are concerned either with oxidized contaminants, or with those that do not share electrons, but receive them [6]. Biotechnological processes for wastewater treatment are more suitable to achieve this goal than electrochemical treatment. In general, the wastewater treatment process relies on the combination http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2022.9.2.S3 https://orcid.org/0000-0003-3887-1058 https://orcid.org/0000-0002-2389-0523 mailto:borhomelwamba@gmail.com http://creativecommons.org/licenses/by/4.0/ https://crossmark.crossref.org/dialog/?doi=https://doi.org/10.15826/chimtech.2022.9.2.S3&domain=pdf&date_stamp=2022-4-16 Chimica Techno Acta 2022, vol. 9(2), No. 202292S3 REVIEW 2 of 6 of separate treatment processes, which allow the genera- tion of an effluent of specified characteristics from a wastewater of a known rate and composition [9]. This paper is intended to give a brief description of modern wastewater treatment technologies using biotech- nological processes and some of their applications. 2. Types of biological wastewater treat- ment systems According to some researches, biological wastewater treatment processes can be summarized in three main systems which include: Bioremediation, Phytoremediation and Mycoremediation [10]. Mycoremediation, thought to be an effective method of combating the ever-growing problem of water pollution, uses fungi's digestive enzymes or their derivatives to break down contaminants like heavy metals, pesticides, and hydrocarbons and remove pollutants from water [11]. Phytoremediation, on the other hand, uses plants and some rhizosphere microorganisms to aid in the recovery of polluted water [12]. The former (microbial bioremediation) relies on aerobic and anaero- bic microbial treatments such as oxidation ponds, aeration and anaerobic lagoons, aerobic and anaerobic bioreactors, activated sludge, percolating or trickling filters, rotating biological contactors, etc. [10]. Besides these, biostimula- tion, which employs a combination of indigenous microor- ganisms and environmental modifications (e.g. additional mineral nutrients for the enhancement of pollutants’ me- tabolism by microbes) and bioaugmentation, where extra cultures of microbes with particular contaminant reducing abilities are added to a polluted area, have enjoyed wide utilization [13]. In addition, bioelectrochemical systems (BES) and bioadsorption can also be classified as modern biotechnological processes of wastewater treatment. In fact, bioelectrochemistry is a mix of biotechnology and electro- chemistry incorporating electrodes within bioreactors where biological and electrochemical processes take place [14], while bioadsorption, which occurs along with biodeg- radation, is a special adsorption process using organic or biological matters as adsorbents in bioreactors [15]. 3. Bioadsorption Bioadsorption is an adsorption process that uses a biological material called bioadsorbent, which typically includes micro- organisms and their components, seaweed, vegetables, indus- trial waste, agricultural waste, and natural waste as adsorp- tive medium [16–17]. This process aims to remove or recover organic and inorganic substances in aqueous solutions. The bioadsorption process occurs by interactions between con- taminants such as metal oxides or metal hydroxides and spe- cific active sites (carboxyl, amino, sulfate groups, among oth- ers), present in the coatings of the biomaterial [16]. In general, the chemical and physical structures of an ad- sorbent determine its adsorption and desorption perfor- mance [18–19]. For instance, the type of adsorption forces and the desorption capability of an adsorbent are influenced by chemical structures such as functional groups. On the oth- er hand, physical structures, i.e. specific surface area and pore size, dictate the accessibility of an adsorbent to dyes [18]. Bioadsorption processes for decontamination of wastewaters can be carried out either continuously, in fixed- bed reactors/columns, or discontinuously, in batch reactors. This method is mostly used in marine oily and dye wastewater treatment. Bioadsorption is mainly applied in dye wastewater treatment due to its technical feasibility, flexibility and operation simplicity (Figure 1) [18–21]. 4. Mechanism of adsorption in dye wastewater treatment The interaction between a cell surface and positive ions of dye is the underlying principle of bioadsorption in living bi- omass. Polysaccharides, proteins, and lipids, which are parts of the cell surface of living biomass, have negative charges, that accumulate sufficient amount of positive ion of dyes pre- sent in wastewater [21–22]. The presence of hydroxyl, nitro, azo groups increase adsorption of dye, while sulfonic acid groups decrease adsorption. Thus, ion-exchange mechanisms account for the efficiency and selectivity of adsorption by microbial biomass [21]. Figure 1 Interaction between microbial biomass and dye. Reproduced with permission [21]; 2019, Elsevier. Chimica Techno Acta 2022, vol. 9(2), No. 202292S3 REVIEW 3 of 6 Major factors affecting industrial-scale treatment of dye wastewater through bioadsorption technology in- clude adsorption and desorption capability as well as reusability of the bioadsorbent, all of which are based on its chemical and physical structures (Figure 2). However, industrial-scale treatment of dye wastewater via bioad- sorption technologies remains stagnant, mainly due to its high costs [18]. 5. The membrane biofilm reactors Treatment of wastewater with biofilm technology was inspired by the industrial operation of trickling filters in the early 1880 [23]. The biofilm method is a type of bio- logical sewage treatment technology similar tothe activat- ed sludge method in the sense that the treatment process- es of activated sludge and aerobic biofilm reactors are less dependent on temperature, although temperature plays a decisive role in most wastewater treatment processes [24]. In fact, biofilm is formed by growing and breeding microorganisms on filter material or carrier. Recently, new membrane reactors, including the micro porous membrane bioreactor (MBR), moving bed biofilm reactor (MBBR), sequential batch biofilm reactor (SBBR), and the up flow anaerobic sludge bed-anaerobic biological filter (UASB-BF) have been made [23–25]. Biofilm processes in relation to wastewater treatment are divided into two groups: the moving-medium and the mixed-medium sys- tems. In the former, the biofilm media are static in the reactors and the biological reactions take place in the bio- film developed on the static media (trickling filters and biological aerated filters), while the biofilm media are kept constantly in motion in the moving-medium sys- tems. Hydraulic, mechanical, or air forces (moving-bed biofilm reactors, vertically moving biofilm reactors, flu- idized bed biofilm reactor, and rotating biological contac- tors) are employed to move the biofilm media in the moving-medium systems [23]. The use of biofilm systems in wastewater treatment is rapidly increasing because of its alluring approach of pollutant removal from wastewater, which is both cost-effective and environ- mentally sound [26]. The biofilm structures can be smooth or rough, fluffy or dense, as well as flat or fila- mentous; the structure is influenced by both the chemical composition of the surrounding medium and the hydro- dynamics of the system [27]. 6. Biofilm formation and mechanism Usually, 3 steps are involved in the biofilm formation, namely, the biofilm attachment, growth, and detachment. Surface, nutrients, and water are the minimum require- ments for its formation (Figure 4) [26]. Once the sewage gets in contacts with the biofilm, or- ganic pollutants in the wastewater are taken in as nutri- ents by the microorganisms on the biofilm, resulting in the purification of the sewage wastewater [29]. Biofilms are hugely complex; they have a difficult structure for quantification and are heterogeneous consor- tia of cells which are significantly influenced by the envi- ronmental and mechanical conditions to which they are subjected. During the quantification, different parame- ters must be taken into account, including specific sur- face area, porosity, thickness, surface area coverage, thickness variability, fractal dimension, density, and pore radius [27]. Table 1 presents the advantages and disadvantages of some of the membrane biofilm reactors used in wastewater treatment. 7. Bioelectrochemical systems The bioelectrochemical systems (BES), as noted earlier, combine two sciences in industrial wastewater treatment. This technology uses the integration of electrodes within the biological reactors to regain resources present in the wastewater and takes advantage of a solid electron accep- tor or donor interactivity with microorganisms to achieve bioenergy recovery from organic substances [14, 31]. Figure 2 Dye wastewater treatment. Reproduced with permission [18]; 2019, Elsevier. Chimica Techno Acta 2022, vol. 9(2), No. 202292S3 REVIEW 4 of 6 Figure 3 A biofilm reactor model used in wastewater treatment. Reproduced with permission [28]; 2015, Elsevier. 8. Processes within the bioelectrochemical reactors The BES catalyze distinct oxidation and reduction reac- tions by using microorganisms attached to electrodes (an- ode and cathode) with the aim of recovering resources contained in the wastewater. Bacteria in wastewater de- grade organic matter and release electrons and protons, which are collected at the anode and cathode, respectively, while CO2 is released [32]. The anode (negative or reduc- ing electrode) transfers electrons to the external circuit but oxidizes during the electrochemical reaction, whereas the cathode (positive or oxidizing electrode) gains elec- trons from the external circuit but is reduced during the electrochemical reaction, necessitating additional contam- inant treatment [33]. Thus, electrons that result from oxidation are trans- mitted to the anode and are important to electrical energy generation [14]. Three features are mainly focal while us- ing BES technology in the wastewater treatment: trapping electrical power from organic pollutants in microbial fuel cells, collecting additional products like CH2, H2 and high standard water in microbial electrosynthesis cells, and eliminating contaminants such as perchlorate, heavy metal etc. [31]. 9. Assessment of BES in wastewater treatment The bioelectrochemical systems allow the improvement of the current processes performance and are the potential alternative energy storage systems. These systems are particularly able to carry out the electromethanogenesis process, which consists in the conversion of CO2 (carbon dioxide) to methane (Figure 5). In addition, the BES present advantage in terms of: • stabilizing the biological process, increasing both quality and quantity of biogas produced; • reducing the high costs of wastewater treatment re- sulting from conventional water purification technologies; • reusing the products obtained during the process, as other sorts of sources of energy. Table 1 Comparison among Bioreactors: merits and limitations. Adapted from [30]. Bioreactor Merits Limitations Moving bed biofilm reactor (slurry reac- tor) Heterogeneous version of stirred tank. High cell concentration in biofilm promotes rate of bio- conversion. Capacity wise inferior to column reactors. Biofilm could get dis- turbed due to high rate of agitation. Fluidized bed biofilm reactor Operates at high capaci- ties, provides high de- gree of bioconversion. Once fully fluidized, pressured drop across the bed remains con- stant and does not in- crease with increase in feed flow rate. Degree of bioconversion in- creases with increase in feed flow rate due to bed expansion. Entrainment loss of particle-biofilm aggregates possi- ble. Operating cost higher than trickle bed (packed bed). Semifluidized bed biofilm reactor Higher degree of bio- conversion (than fluid- ized beds) at higher capacities and low reac- tor volume require- ment. Degree of biocon- version increases with increase in feed flow rate, even if reactor volume is kept constant. Higher operating cost than fluidized beds. Continuous, circulating mode of operation not possible. Inverse fluid- ized biofilm reactor Low operating cost due to down flow mode of operation. Larger size particles could be used. Reasonably large degree of bioconversion. Lower capacity than fluidized /semi-fluidized bed. Larger reac- tor volume re- quirement. Figure 4 Biofilm life cycle. Reproduced from [26]; 2019, Intechopen. Chimica Techno Acta 2022, vol. 9(2), No. 202292S3 REVIEW 5 of 6 It should be noted that actually the BES technology is still experimental and has not yet been proven in terms of its technical and economic viability on industrial scale [31]. 10. Conclusions and recommendations The big problem in the wastewater treatment is to oxidize all soluble and insoluble organic compounds present. The use of microorganisms in sewage treatment through modern biological methods has shown to be more effi- cient at achieving this goal. Compared to chemicals, mi- croorganisms offer several benefits such as being envi- ronmentally friendly, cost-effective, and abundant in na- ture. Although their use in bioreactors seems perfect, choosing the right microorganism remains difficult and tricky since it depends on areas of its use. In the pa- permaking and dying industry wastewater, which are the examples of alkaline wastewater, a detachment of a bio- film may happen, which could lead to a collapse of bio- logical wastewater treatment systems. It would, thus, be much better and useful to make bioflocculant-producing strains that can form biofilm in alkaline conditions. Nev- ertheless, it is still difficult to define a universal method that could be used for the elimination of all contaminants from wastewater. One of the major reasons is because, practically, only few industries have been successful in removing the production of all wastewater requiring dis- posal unit after treatment even if the theory of zero dis- charge is still popularly adopted. Therefore, water treatment with both biotechnological and traditional methods must be monitored continuously to ensure that the desired water quality is always achieved. Supplementary materials No supplementary materials are available. Funding This research had no external funding. Acknowledgments None. Author contributions Conceptualization: C.L.B., O.N.K., M.N.I. Data curation: M.N.I. Formal Analysis: C.L.B., O.N.K., M.N.I. Funding acquisition: C.L.B., O.N.K., M.N.I. Investigation: C.L.B. Methodology: C.L.B., O.N.K., M.N.I. Project administration: O.N.K., M.N.I. Resources: C.L.B., O.N.K., M.N.I. Software: C.L.B., O.N.K., M.N.I. Supervision: M.N.I. Validation: C.L.B., O.N.K., M.N.I. Visualization: C.L.B. Writing – original draft: C.L.B. Writing – review & editing: O.N.K., M.N.I. Conflict of interest The authors declare no conflict of interest. Figure 5 BES scheme. Reproduced from [34]; 2019, infoANALÍTICA. Chimica Techno Acta 2022, vol. 9(2), No. 202292S3 REVIEW 6 of 6 Additional information Authors’ IDs: Beya, Charles L.: ; Kanwugu, Osman N., Scopus ID 57195573903; Ivantsova, Maria N., Scopus ID 6507519617. Websites of Ural Federal University: https://urfu.ru/en; University of Lubumbashi: https://www.unilu.ac.cd. 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