Colonization of biofilm in wastewater treatment: A review

Performance evaluation of species varied fixed bed biofilm reactor for wastewater treatment of Dhobi Khola outfall, Setopul, Kathmandu, Nepal

The sustainability of wastewater treatment plants poses significant challenges for developing countries, necessitating substantial investment for operation and maintenance. Biofilm reactors seeded with specific species of microorganisms were investigated under controlled environmental conditions. However, the performance evaluation of such reactors under natural conditions remains largely underexplored. This study investigated wastewater treatment capabilities of bench-scale fixed bed biofilm reactors, employing various species (Wastewater Microbes, Pseudomonas, Algae, and a co-culture of Algae and Pseudomonas). The reactors (Treatments and Control) were filled with 28 mm nominal-size local aggregates as packing media, operated under different contact times, and subjected to varying concentrations of heavy metals (Zn, Cd). To assess the reactor performances, the Bland-Altman Plot and Chemical Oxygen Demand (COD) removal kinetics were evaluated. The results revealed that the reactor initiated with a co-culture exhibited the optimal COD removal efficiency, reaching 84 ± 1 %. The reactor initially seeded with wastewater microbes exhibited the highest heavy metal elimination, achieving 94 ± 1 % and 88 ± 1 % removal for Zn and Cd respectively. The wastewater-seeded reactor demonstrated the zero-order COD removal kinetic coefficient (k) of 46.41 mg/L/h at an average influent COD concentration of 558 mg/L at 10 h contact time. While Pseudomonas-seeded reactor demonstrated k = 0.73 mg/L/h at 20 h contact time with 69 mg/L influent COD and heavy metal concentrations Zn = 26 mg/L and Cd = 3.57 mg/L. The findings of this study suggest that variations in environmental conditions, contact time, and heavy metal concentration have minimal impact on the pollutant removal efficacy of the reactors, and provide robust evidence for their viability as a sustainable alternative in municipal wastewater treatment. The study also identifies the possibility of treating specific wastewater characteristics by altering the dominant species in the reactors, paving the way for further research on the efficacy of other microbial genomes in fixed bed biofilm reactors.

Role of microalgae-bacterial consortium in wastewater treatment: A review

In the global effort to reduce CO2 emissions, the concurrent enhancement of pollutant degradation and reductions in fossil fuel consumption are pivotal aspects of microalgae-mediated wastewater treatment. Clarifying the degradation mechanisms of bacteria and microalgae during pollutant treatment, as well as regulatory biolipid production, could enhance process sustainability. The synergistic and inhibitory relationships between microalgae and bacteria are introduced in this paper. The different stimulators that can regulate microalgal biolipid accumulation are also reviewed. Wastewater treatment technologies that utilize microalgae and bacteria in laboratories and open ponds are described to outline their application in treating heavy metal-containing wastewater, animal husbandry wastewater, pharmaceutical wastewater, and textile dye wastewater. Finally, the major requirements to scale up the cascade utilization of biomass and energy recovery are summarized to improve the development of biological wastewater treatment.

Determinants of microbial colonization on microplastics through wastewater treatment processes: The role of polymer type and sequential treatment

This study examines the microbial colonization characteristics of microplastics (MPs) in wastewater treatment plants (WWTPs), focusing on polymer types (High-Density Polyethylene (HDPE) and Polyethylene Terephthalate (PET)) and various stages of wastewater treatments. Through individual and sequential deployment approaches, the research aimed to identify the determinants of bacterial colonization on MPs, whether they were introduced at each stage of treatment individually or in sequence from primary to tertiary stages. The study revealed that the stage of wastewater treatment profoundly influenced bacterial colonization on the polymer types MPs, with bacterial attachment being largely niche-specific. HDPE showed increased sensitivity to wastewater composition, leading to selective biofilm formation. For instance, in HDPE, Firmicutes accounted for 25.1 ± 0.04 % during primary treatment, while Alphaproteobacteria increased significantly in the tertiary treatment to 19.8 ± 0.1 %. Conversely, PET exhibited a stochastic pattern of bacterial colonization due to differences in surface hydrophilicity. Additionally, in sequential deployments, a notable shift towards stochastic bacterial attachment on MPs, particularly with HDPE was observed. The Shannon diversity values for MP biofilms were consistently higher than those for wastewater across all stages, with PET showing an increase in diversity in sequential deployments (Shannon diversity: 5.01 ± 0.03 for tertiary stage). These findings highlight the critical role of MPs as carriers of diverse bacteria, emphasizing the necessity for strategies to mitigate their impact in WWTPs. This study presents a significant advancement in our understanding of the interactions between MPs and microbial populations in WWTP environments.

Treatment of high-strength saline bilge wastewater by four pilot-scale aerobic moving bed biofilm reactors and comparison of the microbial communities

Four Pilot-scale Moving Bed Biofilm Reactors (MBBRs) were operated for the treatment of real, saline, bilge wastewater. The MBBRs were connected in pairs to create two system configurations with different filling ratios (20%, 40%) and were operated in parallel. The inflow organic loading rate (OLR) varied from 3.6 ± 0.2 to 7.8 ± 0.6 g COD L-1 d-1, salinity was >15 ppt and three hydraulic residence times (HRTs) were tested 48, 30 and 24 h. In both systems, the first-stage bioreactors (R1 and R3) eliminated the higher part of the organic load (57%-65%). The second-stage bioreactors (R2 and R4) removed an additional fraction (18%-31%) of the organic load received by the effluent of R1 and R3, respectively. The microbial communities of the influent wastewater, suspended, and attached biomass were determined using 16S rRNA gene amplicon sequencing analysis. The evolution of the microbial communities was investigated and compared over the different operational phases. The microbial communities of the biofilm presented higher diversity and greater stability in composition over time, while the suspended biomass exhibited intense and rapid changes in the dominance of genera. Proteobacteria, Bacteroidetes and Firmicutes were highly present in the biofilm. The genera Celeribacter, Novispirillum, Roseovarius (class: Alphaproteobacteria) and Formosa (class: Flavobacteriia) were highly present during all operational phases. Principal Component Analysis (PCA) was used to identify similarities between samples, exhibiting high relation of samples according to the series of the bioreactor (1st, 2nd).

Mathematical modelling and comparative analysis of treatment technologies for upgrading wastewater treatment plants: A case study of biofilm reactors in El-Gouna, Egypt

In recent years, Moving Bed Biofilm Reactors (MBBRs) have been preferred to conventional processes with suspended biomass. The main reason for this preference is that it can achieve better removal efficiencies than conventional systems with smaller footprints. However, unlocking the full potential of MBBRs in large-scale WWTPs remains challenging in real life. In this study, the performance of three different treatment technologies, Extended Aeration Activated Sludge (EAAS), Hybrid Fixed Bed Biofilm Reactor (HFBBR), and Hybrid Moving Bed Biofilm Reactor (HMBBR), was investigated over a year in a WWTP located in El-Gouna, Egypt. The COD removal efficiencies of the three systems were comparable, with the EAAS achieving 93.5%, HFBBR 94%, and HMBRR 95%. Nevertheless, the NH4 removal efficiency of the EAAS was slightly lower (97.5%) than that of the HFBBR and the HMBBR, that achieved a removal efficiency of 98%. BioWin Software was able to mimic the real case of the WWTP of El-Gouna and critically defined all plant limitations and operational data. Different simulations were modeled to test the hydraulic and organic loading capacities of the three systems under different scenarios and operating conditions. The HMBBR system failed to withstand the increase in organic load because of the biomass sloughing effect and subsequently high TSS loads in the settlers. Biomass sloughing overloaded the settlers and lead to biomass loss in the effluent. As the settleability of the HMBBR sludge was significantly lower than for the HFBBR the TSS loss in the effluent happened that much earlier that the moving carrier application had an adverse effect contradicting with the primary purpose of adding media carriers. Model simulations and data analysis findings were used to recommend the most suitable configuration for upgrading an existing system using the attached growth technique with all kinetic parameters and operational conditions. The recommended configuration focuses mainly on the separation of plastic media in a compartment with a very low hydraulic retention time to absorb the incoming shock load.

Response of biofilm-based systems for antibiotics removal from wastewater: Resource efficiency and process resiliency

Biofilm-based systems have efficient stability to cope-up influent shock loading with protective and abundant microbial assemblage, which are extensively exploited for biodegradation of recalcitrant antibiotics from wastewater. The system performance is subject to biofilm types, chemical composition, growth and thickness maintenance. The present study elaborates discussion on different type of biofilms and their formation mechanism involving extracellular polymeric substances secreted by microbes when exposed to antibiotics-laden wastewater. The biofilm models applied for estimation/prediction of biofilm-based systems performance are explored to classify the application feasibility. Further, the critical review of antibiotics removal efficiency, design and operation of different biofilm-based systems (e.g. rotating biological contactor, membrane biofilm bioreactor etc.) is performed. Extending the information on effect of various process parameters (e.g. hydraulic retention time, pH, biocarrier filling ratio etc.), the microbial community dynamics responsible of antibiotics biodegradation in biofilms, the technological problems, related prospective and key future research directions are demonstrated. The biofilm-based system with biocarriers filling ratio of ∼50-70% and predominantly enriched with bacterial species of phylum Proteobacteria protected under biofilm thickness of ∼1600 μm is effectively utilized for antibiotic biodegradation (>90%) when operated at DO concentration ≥3 mg/L. The C/N ratio ≥1 is best suitable condition to eliminate antibiotic pollution from biofilm-based systems. Considering the significance of biofilm-based systems, this review study could be beneficial for the researchers targeting to develop sustainable biofilm-based technologies with feasible regulatory strategies for treatment of mixed antibiotics-laden real wastewater.

Regulating mechanism of denitrifier Comamonas sp. YSF15 in response to carbon deficiency: Based on carbon/nitrogen functions and bioaggregation

There is an urgent demand to investigate mechanisms for the improvement of denitrification in carbon-deficient environment, which will effectively reduce the eutrophication in water bodies polluted by nitrate. In this study, denitrifying bacterium Comamonas sp. YSF15 was used to explore the differences in different carbon source concentrations, with the complete genome, metabolomics, and other detecting methods. Results showed that strain YSF15 was able to achieve efficient denitrification, with complete pathways for denitrification and central carbon metabolism. The carbon deficiency prompted the bacteria to use extracellular amino acid-like metabolites initially, to alleviate inhibition and maintain bioactivity, which also facilitated glycogen storage. The biogenic inhibitors (tautomycin, navitoclax, and glufosinate) at extremely low level potentially favored the competitiveness and intraspecific utilization of extracellular polysaccharides (PS). Optimal solutions for bioaggregation in carbon-deficient condition are achieved by regulating the hydrophobicity, and hydrogen bond in extracellular metabolites. The strategy contributes to the maintenance of bioactivity and adaptation to carbon deficiency. Overall, this study provides a new perspective on understanding the denitrification strategies in carbon-deficient environment, and helps to improve the nitrate removal in low-carbon wastewater treatment.

Illuminating plant-microbe interaction: How photoperiod affects rhizosphere and pollutant removal in constructed wetland?

Rhizosphere is a crucial area in comprehending the interaction between plants and microorganisms in constructed wetlands (CWs). However, influence of photoperiod, a key factor that regulates photosynthesis and rhizosphere microbial activity, remains largely unknown. This study investigated the effect of photoperiod (9, 12, 15 h/day) on pollutant removal and underlying mechanisms. Results showed that 15-hour photoperiod treatment exhibited the highest removal efficiencies for COD (87.26%), TN (63.32%), and NO3--N (97.79%). This treatment enhanced photosynthetic pigmentation and root activity, which increased transport of oxygen and soluble organic carbon to rhizosphere, thus promoting microbial nitrification and denitrification. Microbial community analysis revealed a more stable co-occurrence network due to increased complexity and aggregation in the 15-hour photoperiod treatment. Phaselicystis was identified as a key connector, which was responsible for transferring necessary carbon sources, ATP, and electron donors that supported and optimized nitrogen metabolism in the CWs. Structural equation model analysis emphasized the importance of plant-microbe interactions in pollutant removal through increased substance, information, and energy exchange. These findings offer valuable insights for CWs design and operation in various latitudes and rural areas for small-scale decentralized systems.

Microbial Biofilms: Applications, Clinical Consequences, and Alternative Therapies

Biofilms are complex communities of microorganisms that grow on surfaces and are embedded in a matrix of extracellular polymeric substances. These are prevalent in various natural and man-made environments, ranging from industrial settings to medical devices, where they can have both positive and negative impacts. This review explores the diverse applications of microbial biofilms, their clinical consequences, and alternative therapies targeting these resilient structures. We have discussed beneficial applications of microbial biofilms, including their role in wastewater treatment, bioremediation, food industries, agriculture, and biotechnology. Additionally, we have highlighted the mechanisms of biofilm formation and clinical consequences of biofilms in the context of human health. We have also focused on the association of biofilms with antibiotic resistance, chronic infections, and medical device-related infections. To overcome these challenges, alternative therapeutic strategies are explored. The review examines the potential of various antimicrobial agents, such as antimicrobial peptides, quorum-sensing inhibitors, phytoextracts, and nanoparticles, in targeting biofilms. Furthermore, we highlight the future directions for research in this area and the potential of phytotherapy for the prevention and treatment of biofilm-related infections in clinical settings.

Microalgae-based constructed wetland system enhances nitrogen removal and reduce carbon emissions: Performance and mechanisms

Combination of constructed wetlands (CWs) and microalgae-based technologies has been proved as effective wastewater treatment option; however, little attention was paid to investigate the optimal combination ways. This study showed that the integrated system (IS) connecting microalgal pond with CWs exhibited improved pollutant-removal efficiencies and preferred carbon reduction effects compared to other alternatives such as coupled system or independent CWs. Microbial analysis demonstrated that core microorganisms (e.g., Acinetobacter and Thermomonas) of the IS were mostly associated with carbon, nitrogen, and energy metabolism. Based on co-occurrence networks, microbial quantity with denitrification function in the IS accounted for 71.01 % of the microorganism related to nitrogen metabolism, which was higher than that of 48.84 % in the independent CWs, indicating that the presence of microalgae in IS played important role in promoting biological denitrification. These findings provide insights into the microbial mechanism and highlights the complementary effects between microalgae and CWs.

Biomass production of Chlorella pyrenoidosa by filled sphere carrier reactor: Performance and mechanism

Microalgae-based Carbon Capture, Utilization and Storage is vital for mitigating global climate change. A filled sphere carrier reactor was developed to achieve high biomass production and carbon sequestration rate of Chlorella pyrenoidosa. By introducing air (0.04% CO₂) into the reactor, the dry biomass production achieved 8.26 g/L with the optimized parameters of polyester carrier, 80% packing density, 5-fold concentrated nutrient combining 0.2 mol/L phosphate buffer. At simulated flue gas CO₂ concentration of 7%, the dry biomass yield and carbon sequestration rate reached up to 9.98 g/L and 18.32 g/L/d in one day, which were as high as 249.5 and 79.65 times comparing with those of suspension culture at day 1, respectively. The mechanism was mainly attributed to the obvious intensification of electron transfer rate and remarkable increase of RuBisCO enzyme activity in the photosynthetic chloroplast matrix. This work provided a novel approach for potential microalgae-based carbon capture and storage.

Preparation of sludge-cyanobacteria composite carbon for synergistically enhanced co-removal of Cu(II) and Cr(VI)

Traditional sludge disposal is currently restricted by the risk of secondary pollution. Sludge carbon material has gained widespread attention because of its low cost and environmentally sustainable properties. However, owing to the high ash content and low-energy density of sludge, sludge pyrolysis alone has certain limitations, and the performance of carbon materials needs to be improved. Herein, a sludge-cyanobacteria composite carbon (SCC) was easily synthesized, and the adsorption process of Cu(II) and Cr(VI) by SCC was examined. SCC-700-2-50% exhibited a high S_BET (1047.54 m²/g) and developed pore structure rich in functional groups (such as -NH, -OH, and C-O). The combination of pore structure and functional groups improved the adsorption performance of SCC. The adsorption processes exhibited a synergistic effect in a binary system: the q_m of Cu(II) and Cr(VI) were 386 mg/g and 341 mg/g, respectively, and the selectivity of Cu(II) adsorption by SCC was greater than Cr(VI). The adsorption process, examined by SEM-EDS, FTIR, and XPS analysis, indicated that Cu(II) as a cationic interface strengthens Cr(VI) adsorption through electrostatic interaction, and the anion Cr(VI) created a valid electrostatic shield against the electrostatic repulsion between H⁺ and Cu(II), facilitating Cu(II) adsorption. SCC had great reusability: Cu(II) and Cr(VI) adsorption capacity were 90% and 84%, of the initial adsorption capacity, respectively, after six cycles. This study demonstrates the prospect of SCC as a valid adsorbent for multiple heavy metal contaminations removal.

Core Species Derived from Multispecies Interactions Facilitate the Immobilization of Cadmium

Microbial consortia have opened new avenues for heavy-metal remediation. However, the limited understanding of the overall effect of interspecific interactions on remediation efficacy hinders its application. Here, the effects of multispecies growth and biofilm formation on Cd immobilization were explored from direct and multiple interactions through random combinations of two or three rhizosphere bacteria. In monocultures, Cd stress resulted in an average decrease in planktonic biomass of 26%, but through cooperation, the decrease was attenuated in dual (21%) and triple cultures (13%), possibly involving an increase in surface polysaccharides. More than 65% of the co-cultures exhibited induction of biofilm formation under Cd stress, which further enhanced the role of biofilms in Cd immobilization. Notably, excellent biofilm-forming ability or extensive social induction makes Pseudomonas putida and Brevundimonas diminuta stand out in multispecies biofilm formation and Cd immobilization. These two core species significantly increase the colonization of soil microorganisms on rice roots compared to the control, resulting in a 40% decrease in Cd uptake by rice. Our study enhances the understanding of bacterial interactions under Cd stress and provides a novel strategy for adjusting beneficial soil consortia for heavy-metal remediation.

Biofilm-based technology for industrial wastewater treatment: current technology, applications and future perspectives

The microbial community in biofilm is safeguarded from the action of toxic chemicals, antimicrobial compounds, and harsh/stressful environmental circumstances. Therefore, biofilm-based technology has nowadays become a successful alternative for treating industrial wastewater as compared to suspended growth-based technologies. In biofilm reactors, microbial cells are attached to static or free-moving materials to form a biofilm which facilitates the process of liquid and solid separation in biofilm-mediated operations. This paper aims to review the state-of-the-art of recent research on bacterial biofilm in industrial wastewater treatment including biofilm fundamentals, possible applications and problems, and factors to regulate biofilm formation. We discussed in detail the treatment efficiencies of fluidized bed biofilm reactor (FBBR), trickling filter reactor (TFR), rotating biological contactor (RBC), membrane biofilm reactor (MBfR), and moving bed biofilm reactor (MBBR) for different types of industrial wastewater treatment. Besides, biofilms have many applications in food and agriculture, biofuel and bioenergy production, power generation, and plastic degradation. Furthermore, key factors for regulating biofilm formation were also emphasized. In conclusion, industrial applications make evident that biofilm-based treatment technology is impactful for pollutant removal. Future research to address and improve the limitations of biofilm-based technology in wastewater treatment is also discussed.

Succession dynamics of microbial communities responding to the exogenous microalgae ZM-5 and analysis of the environmental sustainability of a constructed wetland system

Constructed wetlands (CWs) are economical and effective swine tailwater treatment systems. However, nitrogen removal in CWs is limited by the lack of carbon source for denitrification. In this study, we studied the feasibility of dosing the microalgae ZM-5 to improve the nitrogen removal ability in CWs. Compared to the control CW, a 20 % higher removal capacity of COD and TN was observed for the coupled system (EG). The microalgae ZM-5 could interact with denitrifying bacteria to compensate for the deficiency of denitrifying stage in CWs. HT-qPCR chip analysis also provided evidence that denitrification genes significantly increased (p < 0.05). According to the life cycle assessment (LCA), ultrasonic extraction had the best environmental sustainability among four lipid extraction processes. As an improvement strategy, clean energy could be utilized to optimize the electricity source to reduce environmental load (45 %-60 %). These findings offer new insights into the feasibility of EG for environmentally sustainable wastewater treatment.

Characterization of Biofilm Microbiome Formation Developed on Novel 3D-Printed Zeolite Biocarriers during Aerobic and Anaerobic Digestion Processes

Background: Aerobic or anaerobic digestion is involved in treating agricultural and municipal waste, and the addition of biocarriers has been proven to improve them further. We synthesized novel biocarriers utilizing zeolites and different inorganic binders and compared their efficiency with commercially available biocarriers in aerobic and anaerobic digestion systems. Methods: We examined BMP and several physicochemical parameters to characterize the efficiency of novel biocarriers on both systems. We also determined the SMP and EPS content of synthesized biofilm and measured the adherence and size of the forming biofilm. Finally, we characterized the samples by 16S rRNA sequencing to determine the crucial microbial communities involved. Results: Evaluating BMP results, ZSM-5 zeolite with bentonite binder emerged, whereas ZSM-5 zeolite with halloysite nanotubes binder stood out in the wastewater treatment experiment. Twice the relative frequencies of archaea were found on novel biocarriers after being placed in AD batch reactors, and >50% frequencies of Proteobacteria after being placed in WWT reactors, compared to commercial ones. Conclusions: The newly synthesized biocarriers were not only equally efficient with the commercially available ones, but some were even superior as they greatly enhanced aerobic or anaerobic digestion and showed strong biofilm formation and unique microbiome signatures.

Hydrophilic spongy biochar crosslinked with starch and polyvinyl alcohol biocarrier for nitrate, phosphorus, and cadmium removal in low carbon wastewater: Enhanced performance mechanism and detoxification

This study aims to develop a functional biocarrier with hydrophilic spongy biochar crosslinked with starch and polyvinyl alcohol (WSB/starch-PVA) for simultaneous removal of NO₃^--N, total phosphorus (TP) and Cd²⁺ in low carbon wastewater. Results showed that the WSB/starch-PVA bioreactor achieved the maximum NO₃^--N removal efficiency in subphase 1.2 with 98.07 % (3.64 mg L^-1h^-1) versus control (75.30 %, 2.81 mg L^-1h^-1), and removed 54.84 % and 73.97 % of TP and Cd²⁺. Material characterization suggested that functional groups (related to C, N and O) on biocarrier and biofilm, and biogenic co-precipitation facilitated TP and Cd²⁺ removal. The WSB made the biocarrier pores larger and regular, and decreased fluorescent soluble microbial products. The predicted metagenome further suggested that central citrate cycle, oxidative phosphorylation of bio-community, and NO₃^--N removal were enhanced. Functions for microbial induced co-precipitation, Cd²⁺ transport/efflux, antioxidants, and enhanced biofilm formation favored the NO₃^--N/TP removal and Cd²⁺ detoxification.

Functionalization of Multi-Walled Carbon Nanotubes Changes Their Antibiofilm and Probiofilm Effects on Environmental Bacteria

Releasing multi-walled carbon nanotubes (MWCNTs) into ecosystems affects the biofilm formation and metabolic activity of bacteria in aquatic and soil environments. Pristine (pMWCNTs), oleophilic (oMWCNTs), hydrophilic (hMWCNTs), and carboxylated (cMWCNTs) carbon nanotubes were used to investigate their effects on bacterial biofilm. A pronounced probiofilm effect of modified MWCNTs was observed on the Gram-negative bacteria of Pseudomonas fluorescens C2, Acinetobacter guillouiae 11 h, and Alcaligenes faecalis 2. None of the studied nanomaterials resulted in the complete inhibition of biofilm formation. The complete eradication of biofilms exposed to MWCNTs was not observed. The functionalization of carbon nanotubes was shown to change their probiofilm and antibiofilm effects. Gram-negative bacteria were the most susceptible to destruction, and among the modified MWCNTs, oMWCNTs had the greatest effect on biofilm destruction. The number of living cells in the biofilms was assessed by the reduction of XTT, and metabolic activity was assessed by the reduction of resazurin to fluorescent resorufin. The biofilms formed in the presence of MWCNTs reduced tetrozolium to formazan more actively than the control biofilms. When mature biofilms were exposed to MWCNTs, dehydrogenase activity decreased in Rhodococcus erythropolis 4-1, A. guillouiae 11 h, and A. faecalis 2 in the presence of pMWCNTs and hMWCNTs, as well as in A. guillouiae 11 h exposed to cMWCNTs. When mature biofilms were exposed to pMWCNTs, hMWCNTs, and cMWCNTs, the metabolism of cells decreased in most strains, and oMWCNTs did not have a pronounced inhibitory effect. The antibiofilm and probiofilm effects of MWCNTs were strain-dependent.

Advances on Bacterial and Fungal Biofilms for the Production of Added-Value Compounds

Simple Summary

The production of bio-based materials, including organic acids, antibiotics, enzymes, ethanol, and hydrogen, is generally done by the cultivation of suspended cells rather than using immobilized cells. However, several studies suggest the application of productive biofilms as a reliable alternative for biocatalysis, with many advantages over suspended-growth systems. This review gives an overview of the breakthrough in the application of biofilm platforms for the sustainable production of valuable compounds, with particular insight into the latest advances in the production of recombinant proteins. Productive biofilms are shown to improve production rates and product yields, demonstrating great potential for industrial applications.

Abstract

In recent years, abundant research has been performed on biofilms for the production of compounds with biotechnological and industrial relevance. The use of biofilm platforms has been seen as a compelling approach to producing fine and bulk chemicals such as organic acids, alcohols, and solvents. However, the production of recombinant proteins using this system is still scarce. Biofilm reactors are known to have higher biomass density, operational stability, and potential for long-term operation than suspended cell reactors. In addition, there is an increasing demand to harness industrial and agricultural wastes and biorefinery residues to improve process sustainability and reduce production costs. The synthesis of recombinant proteins and other high-value compounds is mainly achieved using suspended cultures of bacteria, yeasts, and fungi. This review discusses the use of biofilm reactors for the production of recombinant proteins and other added-value compounds using bacteria and fungi.

Exploiting Biofilm Characteristics to Enhance Biological Nutrient Removal in Wastewater Treatment Plants

Biological treatments are integral processes in wastewater treatment plants (WWTPs). They can be carried out using sludge or biofilm processes. Although the sludge process is effective for biological wastewater systems, it has some drawbacks that make it undesirable. Hence, biofilm processes have gained popularity, since they address the drawbacks of sludge treatments, such as the high rates of sludge production. Although biofilms have been reported to be essential for wastewater, few studies have reviewed the different ways in which the biofilm properties can be explored, especially for the benefit of wastewater treatment. Thus, this review explores the properties of biofilms that can be exploited to enhance biological wastewater systems. In this review, it is revealed that various biofilm properties, such as the extracellular polymeric substances (EPS), quorum sensing (Qs), and acylated homoserine lactones (AHLs), can be enhanced as a sustainable and cost-effective strategy to enhance the biofilm. Moreover, the exploitation of other biofilm properties such as the SOS, which is only reported in the medical field, with no literature reporting it in the context of wastewater treatment, is also recommended to improve the biofilm technology for wastewater treatment processes. Additionally, this review further elaborates on ways that these properties can be exploited to advance biofilm wastewater treatment systems. A special emphasis is placed on exploiting these properties in simultaneous nitrification and denitrification and biological phosphorus removal processes, which have been reported to be the most sensitive processes in biological wastewater treatment.