Optimizing nutrient removal of moving bed biofilm reactor process using response surface methodology

Characteristic and mechanism of biological nitrogen and phosphorus removal facilitated by biogenic manganese oxides (BioMnOx) at various concentrations of Mn(II)

Biogenic manganese oxides (BioMnOx) have attracted considerable attention as active oxidants, adsorbents, and catalysts. However, characteristics and mechanisms of nitrification-denitrification in biological redox reactions mediated by different concentrations of BioMnOx are still unclear. Fate of nutrients (e.g., NH4+-N, TP, NO3--N) and COD were investigated through different concentrations of BioMnOx produced by Mn(II) in the moving bed biofilm reactor (MBBR). 34% and 89.2%, 37.8% and 89.8%, 57.3% and 88.9%, and 62.1% and 90.4% of TN and COD by MBBR were synchronously removed in four phases, respectively. The result suggested that Mn(II) significantly improved the performance of simultaneous nitrification and denitrification (SND) and TP removal based on manganese (Mn) redox cycling. Characteristics of glutathione peroxidase (GSH-Px), reactive oxygen species (ROS), and electron transfer system activity (ETSA) were discussed, demonstrating that ROS accumulation reduced the ETSA and GSH-Px activities when Mn(II) concentration increased. Extracellular polymeric substance (EPS) function and metabolic pathway of Mn(II) were explored. Furthermore, effect of cellular components on denitrification was evaluated including BioMnOx performances, indicating that Mn(II) promoted the non-enzymatic action of cell fragments. Finally, mechanism of nitrification and denitrification, denitrifying phosphorus and Mn removal was further elucidated through X-ray photoelectron spectroscopy (XPS), high throughput sequencing, and fourier transform infrared reflection (FTIR). This results can bringing new vision for controlling nutrient pollution in redox process of Mn(II).

Performance evaluation of a new sponge-based moving bed biofilm reactor for the removal of pharmaceutical pollutants from real wastewater

Pharmaceutical pollutants, a group of emerging contaminants, have attracted outstanding attention in recent years, and their removal from aquatic environments has been addressed. In the current study, a new sponge-based moving bed biofilm reactor (MBBR) was developed to remove chemical oxygen demand (COD) and the pharmaceutical compound Ibuprofen (IBU). A 30-L pilot scale MBBR was constructed, which was continuously fed from the effluent of the first clarifier of the Southern Tehran wastewater treatment plant. The controlled operational parameters were pH in the natural range, Dissolved Oxygen of 1.5-2 mg/L, average suspended mixed liquor suspended solids (MLSS), and mixed liquor volatile suspended solids (MLVSS) of 1.68 ± 0.1 g/L and 1.48 ± 0.1 g/L, respectively. The effect of hydraulic retention time (HRT) (5 h, 10 h, 15 h), filling ratio (10%, 20%, 30%), and initial IBU concentration (2 mg/L, 5 mg/L, 10 mg/L) on removal efficiencies was assessed. The findings of this study revealed a COD removal efficiency ranging from 48.9 to 96.7%, with the best removal efficiency observed at an HRT of 10 h, a filling ratio of 20%, and an initial IBU concentration of 2 mg/L. Simultaneously, the IBU removal rate ranged from 25 to 92.7%, with the highest removal efficiency observed under the same HRT and filling ratio, albeit with an initial IBU concentration of 5 mg/L. An extension of HRT from 5 to 10 h significantly improved both COD and IBU removal. However, further extension from 10 to 15 h slightly enhanced the removal efficiency of COD and IBU, and even in some cases, removal efficiency decreased. Based on the obtained results, 20% of the filling ratio was chosen as the optimum state. Increasing the initial concentration of IBU from 2 to 5 mg/L generally improved COD and IBU removal, whereas an increase from 5 to 10 mg/L caused a decline in COD and IBU removal. This study also optimized the reactor's efficiency for COD and IBU removal by using response surface methodology (RSM) with independent variables of HRT, filling ratio, and initial IBU concentration. In this regard, the quadratic model was found to be significant. Utilizing the central composite design (CCD), the optimal operating parameters at an HRT of 10 h, a filling ratio of 21%, and an initial IBU concentration of 3 mg/L were pinpointed, achieving the highest COD and IBU removal efficiencies. The present study demonstrated that sponge-based MBBR stands out as a promising technology for COD and IBU removal.

Response of antibiotic resistance genes expression and distribution on extracellular polymeric substances and microbial community in membrane biofilm during greywater treatment

This study evaluated how organic loading affects antibiotic resistance genes (ARGs) expression and distribution in the membrane biofilm. Organic surface loading rate of 4.65 g chemical oxygen demand (COD)/m2·d achieved the maximum biofilm thickness, concentration and linear alkylbenzene sulfonate (LAS) removal ratio of 136.9 ± 4.7 μm, 5.4 ± 0.1 g VSS/m2 and 99.4 %, respectively. Extracellular polymeric substances (EPS), EPS-attached LAS, and ARGs gradually increased in the membrane air inlet, middle and air outlet. AGRs and Intl1 were abundant in biofilm. LAS promoted EPS secretion, biofilm growth and ARGs proliferation. EPS, protein and carbohydrate were significantly correlated with most of biofilm ARGs, but not corrected with liquid-based ARGs. Microbial community structure impacted ARGs proliferation and transfer in the system. The findings indicated that EPS and microbial community play a crucial role in ARGs proliferation, spread and distribution, which lay the foundation for front-end control of ARGs during biofilm-based wastewater treatment.

Optimization of moving bed biofilm reactors for the treatment of municipal wastewater

The properties of biocarriers significantly influence the performance of a moving bed-biofilm reactor (MBBR). This study aimed to assess the impact of media type, filling ratio, and hydraulic retention time (HRT) on biofilm formation and MBBR performance in both batch and continuous setups using real municipal wastewater. Two different media, high-density polyethylene (HDPE) and polypropylene (PPE), with varying surface area and properties were used. Biofilm growth and MBBR performance were monitored and optimized using response surface methodology. The effect of different media was investigated for three filling ratios of 20%, 40% and 60% and HRT of 4, 6 and 8 h. Results depicted a better biofilm growth on HDPE media in comparison to PPE carriers due to difference in media structure and surface properties. At all the conditions tested, HDPE media showed comparatively better performance for the removal of organic matter and nutrients than PPE media. The maximum organic matter removal efficiency was found as 77% and 75% at an HRT of 6 h and filling ratio of 40% for HDPE and PPE media, respectively. The ammonia removal was also found better for HDPE media due to its geometry and structure favoring the anoxic conditions with maximum removal of 89% achieved at 6-h HRT and 40% filling ratio. Overall, the system with HDPE media indicated more stability in terms of reactor performance than PPE carriers with variations in the operating conditions.

Thickness of hydrogel for nitrifying biomass entrapment determines the free ammonia susceptibility differently in batch and continuous modes

Hydrogels immobilizing nitrifying bacteria with different thicknesses of 0.55 and 1.13 cm (HG-0.55 and HG-1.13, respectively) were produced. It was recognized that the thickness of media is a crucial parameter that affects both the stability and efficiency of wastewater treatment. Batch mode experiments were conducted to quantify specific oxygen uptake rate (SOUR) values at various total ammonium nitrogen (TAN) concentrations and pH levels. In the batch test, HG-0.55 exhibited 2.4 times higher nitrifying activity than HG-1.13, with corresponding SOUR values of 0.00768 and 0.00317 mg-O2/L mL-PVA min, respectively. However, HG-0.55 was more susceptible to free ammonia (FA) toxicity than HG-1.13, resulting in a reduction of 80% and 50% in SOUR values for HG-0.55 and -1.13, respectively, upon increasing the FA concentration from 15.73 to 118.12 mg-FA/L. Continuous mode experiments were conducted to assess the partial nitritation (PN) efficiency in practical applications, where continuous wastewater inflow maintains low FA toxicity through high ammonia-oxidizing rates. With step-wise TAN concentration increases, HG-0.55 experienced a gentler increase in FA concentration compared to HG-1.13. At a nitrogen loading rate of 0.78-0.95 kg-N/m3 day, the FA increase rate for HG-0.55 was 0.0179 kg-FA/m3 day, while that of HG-1.13 was 0.0516 kg-FA/m3 day. In the batch mode, where wastewater is introduced all at once, the high accumulation of FA posed a disadvantage for the FA-susceptible HG-0.55, which made it unsuitable for application. However, in the continuous mode, the thinner HG-0.55, with its larger surface area and high ammonia oxidation activity, proved to be suitable and demonstrated its effectiveness. This study provides valuable insights and a framework for the utilization strategy of immobilized gels in addressing the toxic effects of FA in practical processes.

The effect of biocarriers on the nitrification and microbial community in moving bed biofilm reactor for anaerobic digestion effluent treatment

The performance of a moving bed biofilm reactor (MBBR) depends largely on the type of biofilm carrier used. However, how different carriers affect the nitrification process, particularly when treating anaerobic digestion effluents, is not completely understood. This study aimed to evaluate the nitrification performance of two distinct biocarriers in MBBRs over a 140-d operation period, with a gradually decreasing hydraulic retention time (HRT) from 20 to 10 d. Reactor 1 (R1) was filled with fiber balls, whereas a Mutag Biochip was used for reactor 2 (R2). At an HRT of 20 d, the ammonia removal efficiency of both reactors was >95%. However, as the HRT was reduced, the ammonia removal efficiency of R1 gradually declined, ultimately dropping to 65% at a 10-d HRT. In contrast, the ammonia removal efficiency of R2 consistently exceeding 99% throughout the long-term operation. R1 exhibited partial nitrification, whereas R2 exhibited complete nitrification. Analysis of microbial communities showed that the abundance and diversity of bacterial communities, particularly nitrifying bacteria such as Hyphomicrobium sp. And Nitrosomonas sp., in R2 was higher than that in R1. In conclusion, the choice of biocarrier significantly impact the abundance and diversity of microbial communities in MBBR systems. Therefore, these factors should be closely monitored to ensure the efficient treatment of high-strength ammonia wastewater.

Treatment performance of multistage active biological process (MSABP) reactor for saline sauerkraut wastewater: acclimatization, optimization and improvement

The wastewater with a high concentration of organics and salt is a major contaminant in the production of sauerkraut. In this study, a multistage active biological process (MSABP) system was constructed to treat sauerkraut wastewater. The key process parameters of the MSABP system were analyzed and optimized by response surface methodology. The optimization results indicated that the most optimal removal efficiencies and removal loading rates of chemical oxygen demand (COD) and NH₄⁺-N were 87.9%, 95.5%, 2.11 kg·m^-3·d^-1 and 0.12 kg·m^-3·d^-1, respectively, with hydraulic retention time (HRT) of 2.5 d and pH of 7.3. Meanwhile, this system could also be improved for the further treatment of COD and total nitrogen by effluent recycle and ozone oxidation. The COD and total nitrogen removal efficiencies of the modified MSABP system were 99.9% and 60.2%, respectively. In addition, the modified system could also reduce the potential harm from high concentrations of NO₂^--N.

Elucidating the performance of integrated anoxic/oxic moving bed biofilm reactor: Assessment of organics and nutrients removal and optimization using feed forward back propagation neural network

A lab-scale integrated anoxic and oxic (A/O) moving bed biofilm reactor (MBBR) was investigated for the removal of organics and nutrients by varying chemical oxygen demand (COD) to NH₄-N ratio (C/N ratio: 3.5, 6.75, and 10), hydraulic retention time (HRT: 6 h, 15 h, and 24 h), and recirculation ratio (R: 1, 2, and 3). The use of activated carbon coated carriers prepared from waste polyethylene material and polyurethane sponges attached to a cylindrical frame in the integrated A/O MBBR increased the attached growth biomass significantly. >95 % of COD removal was observed under the C/N ratio of 10 at an HRT of 24 h. While the low C/N ratio favored the removal of NH₄-N (∼98 %) and PO₄^3--P (∼90 %) with an optimal R of 1.75. Using the experimental dataset, to predict and forecast the performance of integrated A/O MBBR, a feed-forward-backpropagation-neural-network model was developed.

An alternative approach towards nitrification and bioremediation of wastewater from aquaponics using biofilm-based bioreactors: A review

Aquaponics combines the advantages of aquaculture and hydroponics as it suits the urban environment where a lack of agricultural land and water resources is observed. It is an ecologically sound system that completely reuses its system waste as plant fertilizer. It offers sustainable water savings, making it a supreme technology for food production. The two major processes that hold the system together are nitrification and denitrification. The remains of fish in form of ammonia reach the bio filters where it is converted into nitrite and further into nitrate in presence of nitrifying and denitrifying bacteria. Nitrate eventually is taken up by the plants. However, even after the uptake from the flow stream, the effluent contains remaining ammonium and nitrates, which cannot be directly released into the environment. In this review it is suggested how integrating the biofilm-based bioreactors in addition to aquaculture and hydroponics eliminates the possibility of remains of total ammonia nitrogen [TAN] contents, leading to bioremediation of effluent water from the system. Effluent water after releasing from a bioreactor can be reused in an aquaculture system, conditions provided in these bioreactors promote the growth of required bacteria and encourages the mutual development of plants and fishes and eventually leading to bioremediation of wastewater from aquaponics.

Treatment capacity of a novel flexible fibre biofilm bioreactor treating high-strength milk processing wastewater

This study was focused on the capacity investigation of a novel multistage flexible fibre biofilm reactor (MS-FFBR) to treat milk processing wastewater (MPW) with high organic loading (OLR). The MS-FFBR performance was evaluated at four intermediate stages separately, and also the final effluent quality of the overall system with an influent chemical oxygen demand (COD_in) ranged from 1500 ± 20 to 6000 ± 50 mg/L and hydraulic retention times (HRTs) of 8, 12, and 16 h. By comparting the bioreactors into the four stages effectively enhanced the bioreactor's performance. The maximum TCOD removal efficiency was achieved at the first stage, which was about 89 ± 20, 82 ± 20, and 78 ± 20% at HRTs of 16, 12, 8 h, and low COD_in of 1600 ± 20, 1590 ± 20, and 1673 ± 20 mg/L, respectively. However, the first stage had less contribution to TCOD removal at high COD_in concentrations, reported to be about 42 ± 4%, 46 ± 4%, and 25 ± 4% at COD_in of 5960 ± 40, 5830 ± 40, and 5870 ± 40 mg/L, respectively. Furthermore, the MS-FFBR was effective in removing total suspended solids (TSS) and turbidity. The bioreactor has reduced the effluent turbidity to 9.0 ± 0.2, 20.0 ± 0.6, and 16.1 ± 0.5 NTU at low COD_in concentrations of 1600 ± 20, 1590 ± 20, and 1670 ± 20 mg/L and HRTs of 16, 12, and 8 h, respectively. The bioreactor revealed a high COD removal rate increased from 2.3 ± 0.1 to 12.2 ± 0.4 kg TCOD/m³d by increasing the OLR from 2.4 ± 0.1 to 17.6 ± 0.4 kg TCOD/m³d, confirming high reactor capacity for treatment of high-strength wastewater. Kinetic studies confirmed that the biomass yield was low at various HRTs ranging from 0.1 to 0.2 gVSS/gCOD.

The role of immobilized quorum sensing strain in promoting biofilm formation of Moving Bed Biofilm Reactor during long-term stable operation

Quorum sensing (QS) signaling plays a significant role in the natural regulation of biofilm formation. Multiple species QS systems in wastewater treatment processes have received significant attention in recent years and this study presents a long-term analysis of QS signaling, bacterial structures and extracellular polymeric substance (EPS) during biofilm formation, detachment and reformation processes. Six types of Acyl homoserine lactones (AHLs) were found to be closely related to different phases of biofilm development, with both QS and quorum quenching (QQ) strains being identified as drivers of various biofilm phases and 10 strains presenting a close relationship with AHLs (p < 0.05). Meanwhile, QS strain Sphingomonas rubra was immobilized and added into reactor systems, resulting in significant increase in AHL content, EPS production, and adhesion strength of biofilm (p < 0.05), which might promote biofilm formation processes during long-term stable operation. This study provides a potentially simple and economical way to improve activity and stability of MBBR in complex wastewater systems.

Investigating the long and short-term effect of free ammonia and free nitrous acid levels on nitritation biomass of a sequencing batch reactor treating thermally pre-treated sludge reject water

This work examined the short and long-term effects of different free ammonia (FA) and free nitrous acid (FNA) levels on (i) acclimatized biomass treating sludge reject water via nitrite in a sequencing batch reactor (SBR) and (ii) non-aclimatized biomass treating municipal wastewater via nitrate in the activated sludge process. In the acclimatized biomass, the threshold for the transition from nitrification to nitritation was the FA increase to 10-20 mgNH₃-N/L while the SBR unit showed no inhibition on the ammonia uptake rate (AUR) at FA levels up to 65 mgNH₃-N/L. Short-term exposure of the acclimatized biomass on FNA showed that AUR inhibition could be more than 50 % for FNA concentration >10 μgHNO₂-N/L. The FNA inhibition results were simulated using non-competitive inhibition kinetics that showed that the inhibition constant corresponding to the FNA concentration that inhibits the process by 50 % (i.e. K_iFNA) was much higher in the acclimatized biomass.

Metagenomic insights into microbial nitrogen metabolism in two-stage anoxic/oxic-moving bed biofilm reactor system with multiple chambers for municipal wastewater treatment

To explore the microbial nitrogen metabolism of a two-stage anoxic/oxic (A/O)-moving bed biofilm reactor (MBBR), biofilms of the system's chambers were analyzed using metagenomic sequencing. Significant differences in microbial populations were found among the pre-anoxic, oxic and post-anoxic MBBRs (P < 0.01). Nitrospira and Nitrosomonas had positive correlations with ammonia nitrogen (NH₄⁺-N) removal, and were also predominant in oxic MBBRs. These organisms were the hosts of functional genes for nitrification. The denitrifying genera were predominant in anoxic MBBRs, including Thiobacillus and Sulfurisoma in pre-anoxic MBBRs and Dechloromonas and Thauera in post-anoxic MBBRs. The four genera had positive correlations with total nitrate and nitrite nitrogen (NO_X^--N) removal and were the hosts of functional genes for denitrification. Specific functional biofilms with different microbial nitrogen metabolisms were formed in each chamber of this system. This work provides a microbial theoretical support for the two-stage A/O-MBBR system.

Performance and bacterial community analysis of a two-stage A/O-MBBR system with multiple chambers for biological nitrogen removal

A two-stage anoxic/oxic (A/O)-moving bed biofilm reactor (MBBR) system with multiple chambers was established for municipal wastewater treatment. At the total hydraulic retention time (HRT) of 11.2 h and nitrate recycling ratio of 1, the removal efficiencies reached 83.8%, 82.5%, and 77.8% for soluble chemical oxygen demand (SCOD), 98.0%, 97.5%, and 94.9% for ammonia nitrogen (NH₄⁺-N), and 91.8%, 92.0%, and 87.7% for total inorganic nitrogen (TIN) in summer, autumn and winter, respectively. Biofilms with functional bacterial populations were formed in the pre-anoxic reactors, the pre-oxic reactors, the post-anoxic reactors and the post-oxic reactors of the two-stage A/O-MBBR system. The highest nitrification potential was found in the last oxic reactor of the first A/O-MBBR subsystem with the highest relative abundances of the functional genes including [EC:1.14.99.39] and [EC:1.7.2.6]). The highest denitrification potential was found in the post-anoxic reactors with the highest relative abundances of the functional genes including [EC:1.7.2.1], [EC:1.7.2.5] and [EC:1.7.2.4]. This work constructed an efficient municipal biological nitrogen removal technology to achieve high effluent nitrogen standards in winter, and investigated its working mechanism to provide a basis for its design and optimization.

Synergistic effect of chitosan-based sludge aggregates CS@NGS inoculum accelerated the start-up of biofilm reactor treating aquaculture effluent: Insights into performance, microbial characteristics, and functional genes

The moving bed bioreactor (MBBR) process has drawn more attention as a promising biological wastewater treatment process. Nevertheless, achieving quick start-up and microbial biofilm formation remains a significant challenge. Consequently, the present study investigated a novel chitosan-based natural sludge (CS@NGS) seeding strategy for the accelerated start-up of MBBR. Three identical bioreactors were employed; the first bioreactor was without sludge seed as the control (BR1), the second was inoculated only with sludge (BR2), and the third was inoculated with CS@NGS according to the proposed seeding method (BR3). All bioreactors were utilised to treat simulated recirculating aquaculture systems (RAS) effluent. Resultantly, the CS@NGS shortened the start-up period from over twenty to seven days due to the enhanced initial microbial adhesion and biofilm formation. Under optimal conditions, the ammonium removal in BR3 approached 100%, which was relatively higher than BR2 (96.35 ± 1.12%) and BR1 (92.56 ± 2.17%). Moreover, a low nitrite accumulation was exhibited in the effluents, approximately ≤0.03 mg L^-1. The process performance correlated positively with core bacteria from the genera Nakamurella, Hyphomicrobium, Nitrospira, Paenarthrobacter, Rhodococcus, and Stenotrophobacter. The quantitative polymerase chain reaction (qPCR) results demonstrated that the CS@NGS enhanced the expressions of amoA, nxrB, nirK, nirS, narG, and napA nitrogen metabolism-related functional genes to varying degrees. The present study findings can assist the rapid start-up of aquaculture biofilters utilised to solve high nitrite and ammonia accumulation in recirculated water from industrial RAS.

Composite hydrolytic acidification - aerobic MBBR process for treating traditional Chinese medicine wastewater

Traditional Chinese medicine (TCM) wastewater is characterized by high organic content, unstable water quality and quantity and low biodegradability. In this paper, the hydrolytic acidification reactor-aerobic moving bed biofilm (MBBR) process was used to degrade TCM wastewater. Besides, a small pilot study was conducted. The appropriate operating parameters: hydraulic retention time (HRT) of the hydrolytic reactor was 16 h, HRT of MBBR was 30 h, dissolved oxygen of MBBR was 6 mg/L, sludge return ratio of MBBR was 100%. The hydrolytic reactor was started for 25 days. MBBR was run in series with the hydrolytic reactor after 24 days of separate operation. The start-up of the composite reactor was completed after another 26 days. The average removal efficiencies of chemical oxygen demand and ammonia nitrogen were 92% and 70%. The hydrolytic reactor was effective in decomposing macromolecules and MBBR had a strong ability to degrade pollutants through the excitation-emission-matrix spectra. The evolution pattern of the dominant bacterial genera and the surface morphology of sludge were studied by scanning electron microscopy and high-throughput sequencing analysis. It could be seen that the surface morphology of the biological filler was suitable for the growth and reproduction of microorganisms.

A review of ammonia removal using a biofilm-based reactor and its challenges

Extensive growth of industries leads to uncontrolled ammonia releases to environment. This can result in significant degradation of the aquatic ecology as well as significant health concerns for humans. Knowing the mechanism of ammonia elimination is the simplest approach to comprehending it. Ammonia has been commonly converted to less hazardous substances either in the form of nitrate or nitrogen gas. Ammonia has been converted into nitrite by ammonia-oxidizing bacteria and further reduced to nitrate by nitrite-oxidizing bacteria in aerobic conditions. Denitrification takes place in an anoxic phase and nitrate is converted into nitrogen gas. It is challenging to remove ammonia by employing technologies that do not incur particularly high costs. Thus, this review paper is focused on biofilm reactors that utilize the nitrification process. Many research publications and patents on biofilm wastewater treatment have been published. However, only a tiny percentage of these projects are for full-scale applications, and the majority of the work was completed within the last few decades. The physicochemical approaches such as ammonia adsorption, coagulation-flocculation, and membrane separation, as well as conventional biological treatments including activated sludge, microalgae, and bacteria biofilm, are briefly addressed in this review paper. The effectiveness of biofilm reactors in removing ammonia was compared, and the microbes that effectively remove ammonia were thoroughly discussed. Overall, biofilm reactors can remove up to 99.7% ammonia from streams with a concentration in range of 16-900 mg/L. As many challenges were identified for ammonia removal using biofilm at a commercial scale, this study offers future perspectives on how to address the most pressing biofilm issues. This review may also improve our understanding of biofilm technologies for the removal of ammonia as well as polishing unit in wastewater treatment plants for the water reuse and recycling, supporting the circular economy concept.

Bioelectrochemical degradation of petroleum hydrocarbons: A critical review and future perspectives

As typical pollutants, petroleum hydrocarbons that are widely present in various environmental media such as soil, water, sediments, and air, seriously endanger living organisms and human health. In the meantime, as a green environmental technology that integrates pollutant removal and resource recovery, bioelectrochemical systems (BESs) have been extensively applied to the removal of petroleum hydrocarbons from the environment. This review introduces working principles of BESs, following which it discusses the different reactor structures, application progresses, and key optimization factors when treating water, sewage sludges, sediments, and soil. Furthermore, bibliometrics was first used in this field to analyze the evolution of knowledge structure and forecast future hot topics. The research focus has shifted from the early generation of bioelectric energy to exploring mechanisms of soil remediation and microbial metabolisms, which will be closely integrated in the future. Finally, the future prospects of this field are proposed. This review focuses on the research status of bioelectrochemical degradation of petroleum hydrocarbons and provides a scientific reference for subsequent research.

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.

Planktonic Growth and Biofilm Formation by Providencia rettgeri and Subsequent Effect of Tannic Acid Treatment under Food-Related Environmental Stress Conditions

ABSTRACT

Providencia rettgeri is an opportunistic foodborne pathogen with a strong biofilm-forming ability in low-nutrition environments. However, information regarding the impact of simulated food processing conditions on P. rettgeri planktonic growth and biofilm formation is limited. Using response surface methodology (RSM), the combined effects of temperature (19 to 37°C), pH (5 to 9), and sodium chloride (NaCl) concentration (0.50 to 2.0%, w/v) were applied to construct planktonic growth and biofilm formation models for P. rettgeri. For both RSM models, an increase in NaCl concentration restricted P. rettgeri growth. Planktonic growth and biofilm formation were maximum at 27.83 and 25.41°C, respectively. Tannic acid (TA) is a highly effective antibacterial agent that inhibited planktonic and biofilm P. rettgeri under optimal growth conditions. The viability of P. rettgeri cells was decreased by TA treatment, which caused destruction of the cell membrane and production of endogenous reactive oxygen species. TA significantly inactivated P. rettgeri biofilms, as verified by observation. The obtained models in this study may be useful for describing the impact of temperature, pH, and NaCl concentration on the growth by P. rettgeri in the food processing environment and better understanding the impacts of food-related conditions on bacterial planktonic growth and biofilm formation. These results obtained for P. rettgeri planktonic cells and biofilms can provide a framework for removal strategies for other foodborne pathogens.

HIGHLIGHTS

Response of substrate kinetics and biological mechanisms to various pH constrains for cultured Nitrobacter and Nitrospira in nitrifying bioreactor

Nitrite (NO₂^-) oxidation is an essential step of biological nitrogen cycling in natural ecosystems, and is performed by chemolithoautotrophic nitrite-oxidizing bacteria (NOB). Although Nitrobacter and Nitrospira are regarded as representative NOB in nitrification systems, little attention has focused on kinetic characterisation of the coexistence of Nitrobacter and Nitrospira at various pH values. Here, we evaluate the substrate kinetics, biological mechanism and microbial community dynamics of an enrichment culture including Nitrobacter (17.5 ± 0.9%) and Nitrospira (7.2 ± 0.6%) in response to various pH constrains. Evaluation of the Monod equation at pH 6.0, 6.5, 7.0, 7.5, 8.0 and 8.5 showed that the enrichment had maximum rate (r_max) and maximum substrate affinity (K_S) for NO₂^- oxidation at pH 7.0, which was also supported by the largest absolute abundance of Nitrobacter nxrA (5.26 × 10⁷ copies per g wet sludge) and Nitrospira nxrB (1.975 × 10⁹ copies per g wet sludge) genes. Moreover, the predominant species for the Nitrobacter-like nxrA were N. vulgaris and N. winogradskyi, while for the Nitrospira-like nxrB, the predominant species were N. japonica, N. calida and Ca. N. bockiana. Furthermore, the r_max was strongly and positively correlated with the abundance of the Nitrobacter nxrA or Nitrospira nxrB genes, or N. winogradsk, whereas K_S was positively correlated with the abundance of Nitrobacter nxrA or Nitrospira nxrB genes or Ca. N. bockiana. Overall, this study could improve basis kinetic parameters and biological mechanism of NO₂^- oxidation in WWTPs.

Simultaneous shortcut nitrification and denitrification in a hybrid membrane aerated biofilms reactor (H-MBfR) for nitrogen removal from low COD/N wastewater

The residues of nitrogen contaminants due to insufficient organic carbon sources in sewage has always been the main problem faced by wastewater treatment plants in the process of nitrogen removal. In this study, simultaneous shortcut nitrification and denitrification (SND) was achieved in the hybrid membrane aerated biofilm reactor (H-MBfR) for treating low COD/N ratio (∼x223C 4: 1) wastewater. The effects of the aeration pressure and the influent COD/N ratio in H-MBfR were investigated and further optimized by the response surface methodology (RSM). By controlling the dissolved oxygen to achieve SND, the removal efficiencies of NH₄⁺-N, COD and TN of low COD/N ratio wastewater reached maximum values of 95.52%, 96.61% and 72.23%, respectively. Microbial community analysis showed that the influent COD/N ratio had an obvious influence on the microbial community structure. In particular, ammonia oxidizing bacteria (AOB) and denitrifying bacteria had a good commensalism when the COD/N ratio was 4.3. Compared to control reactor, the analysis of membrane bio-fouling showed that H-MBfR has a lower amount of extracellular polymeric substance (EPS) on membrane and a low concentration of MLSS in bulk liquid, which is helpful for the longer-term operation of H-MBfR.

Valorization and optimization of agro-industrial orange waste for the production of enzyme by halophilic Streptomyces sp

This study underlines the biotechnical valorization of the accumulated and unusable remains of agro-industrial orange fruit peel waste to produce α-amylase under submerged conditions by Streptomyces sp. KP314280 (20r). The response surface methodology based on central composite design (RSM-CCD) and artificial neural network coupled with a genetic algorithm (ANN-GA) were used to model and optimize the conditions for the α-amylase production. Four independent variables were evaluated for α-amylase activity including substrate concentration, inoculum size, sodium chloride powder (NaCl), and pH. A ten-fold cross-validation indicated that the ANN has a greater ability than the RSM to predict the α-amylase activity (R²_ANN = 0.884 and R²_RSM = 0.725). The analysis of variance indicated that the aforementioned four factors significantly affected the α-amylase activity. Additionally, the α-amylase production experiments were conducted according to the optimal conditions generated by the GA. The results indicated that the amylase yield increased by 4-fold. Moreover, the α-amylase production (12.19 U/mL) in the optimized medium was compatible with the predicted conditions outlined by the ANN-GA model (12.62 U/mL). As such, the ANN and GA combination is optimizable for α-amylase production and exhibits an accurate prediction which provides an alternative to other biological applications.

Enhancement of mariculture wastewater treatment using moving bed biofilm reactors filled with modified biocarriers: Characterisation, process performance and microbial community evaluation

This research investigated two proposed modified biofilm carriers' performances in treating recirculating aquaculture systems (RAS) wastewater under different salinities (12‰, 26‰, and 35‰) for about 92 days. Three moving bed biofilm reactors (MBBRs; R1, R2, and R3) were filled with unmodified novel sponge biocarriers (SB) served as a control, modified novel SB with ferrous oxalate (C₂FeO₄@SB), and modified novel SB with combined ferrous oxalate and activated carbon (C₂FeO₄-AC@SB), respectively. Under the highest saline condition, a significantly higher ammonia removal efficiency of 98.86 ± 0.7% (p ˃ 0.05) was obtained in R3, whereas R2 and R1 yielded 95.18 ± 2.8% and 91.66 ± 1.5%, respectively. Microbial analysis showed that Vibrio, Ruegeria, Formosa, Thalassospira, and Denitromonas were predominant genera, strictly halophilic heterotrophic nitrifying bacteria involved in nitrogen removal. In conclusion, the synergistic effects of novel sponge, C₂FeO₄ and AC accelerated biofilm formations and stability, subsequently enhanced the removal of ammonia from the mariculture RAS wastewater by the C₂FeO₄-AC@SB carriers in R3.

Understanding the toxicity effect and mineralization efficiency of in-situ electrogenerated chlorine dioxide for the treatment of priority pollutants of coking wastewater

Oxidation of phenol, cyanide and aniline have been analyzed by the enhanced electro-oxidation process in which sodium chlorite was used as an electrolyte and results were validated using statistical tool based on Box-Behnken design. The mineralization efficiency of 78.4%, and 98.18% were predicted at optimized variables condition for phenol, and aniline respectively, whereas complete mineralization has been observed for the cyanide at the optimized conditions, which describes the significance of the design model approach.The process mineralizes the higher phenol concentration revealing a drastic reduction in power consumption in comparison of direct oxidation, i.e., 799.36 kWh/kg to 138.18 kWh/kg for more than 90% mineralization of phenol even at a higher current density of 13.63 mA/cm². The kinetic modelling approach justified that higher current density has also played a role in higher mineralization of pollutants at the specific operating conditions. The by-product formation and toxicity effect on microalgae in wastewater were assessed by the full scan mass spectrometry and microalgae pigment inhibition test after the electro-oxidation of coking wastewater. The pigment growth inhibition rate of Chlorella sp. NCQ and Micractinium sp. NCS2 suggests that sodium chlorite as an electrolyte aid can also effectively used as an oxidizing agent and algal inhibiter in the coking wastewater.

Rapid recruitment of hydrogen-producing biofilms for hydrogen production in a moving bed biofilm reactor by a sequential immobilization and deoxygenization approach

To reduce start-up time and enhance hydrogen production efficiency, a sequential immobilization and deoxygenization (SIDO) strategy for hydrogen production was investigated in continuous-flow moving bed biofilm reactors (MBBRs). The pre-immobilization process accelerated the initial enrichment of hydrogen-producing bacteria (HPB) and promoted the biofilm formation, which contribute to higher hydrogen production efficiency in SIDO-MBBRs compared to a non-immobilized reactor. A similar deoxygenization effect was achieved by inoculation with Pseudomonas aeruginosa compared with N₂ sparging, and the P. aeruginosa pre-immobilized MBBR (Pse-MBBR) showed a higher H₂ yield in the initial stage of operation. Microbial community analysis found a higher abundance of putative HPB in the range of 82.82-96.56%, with the predominant populations in the SIDO-MBBR assigned to genera Clostridium and Enterobacter. The results suggest that the SIDO-MBBR is an effective approach for rapid recruitment of HPB and start-up of fermentative hydrogen production.

Performance of novel sponge biocarrier in MBBR treating recirculating aquaculture systems wastewater: Microbial community and kinetic study

In this study, a novel sponge biocarriers (SB) in moving bed bioreactor (MBBR) treating recirculating aquaculture systems wastewater was evaluated for the first time. Two lab-scale MBBRs were operated simultaneously for 116 days under various hydraulic retention times (HRTs). The reactors R1 and R2 were filled with K5 plastic carriers and SB, respectively. From the results, at an optimum HRT of 6 h, ammonia removal efficiency and nitrification rate were 86.67 ± 2.4% and 1.43 mg/L.h for the R1 and, 91.65 ± 1.3% and 1.52 mg/L.h for the R2, respectively. The microbial community analysis showed that the predominant genera in the nitrifying community were Nitrosomonas (AOB) and Nitrospira (NOB) in co-existence with heterotrophic genera Hyphomicrobium, Mesorhizobium, Zhizhongheella, and Klebsiella spp. Modified Stover-Kincannon model examined the ammonia removal kinetics, and the values of kinetic parameters obtained were U_max: 0.909 and 1.111 g/L.d and K_B: 0.929 and, 1.108 g/L.d for the R1 and R2, respectively. The correlation coefficients (R²) of the MBBRs were higher than 0.98, indicating that the model adequately described the experimental data. Overall, MBBR, filled with the proposed novel SB operated at 6 h HRT, can achieve the highest nitrification performance and increase the diversity of the functional microbial communities.

Prediction the performance of multistage moving bed biological process using artificial neural network (ANN)

Complexity, uncertainty, and high dynamic nature of nutrient removal through biological processes (BPs) makes it difficult to model and control these processes, forcing designers to rely on approximations, probabilities, and assumptions. To cope with this difficult task and perform an effective and well-controlled BP operation, an artificial neural network (ANN) algorithm was developed to simulate, model, and control a three-stage (anaerobic/anoxic and MBBR) enhanced nutrient removal biological process (ENR-BP) challenging real wastewater. The effect of surface area loading rate (SALR), organic matters (OMs), nutrients (N & P), feed flow rate (Q_feed), hydraulic retention time (HRT), and internal recycle flow (IRF) on the performance of the ENR-BP to fulfil rigorous discharge limitations were evaluated. Experimental data was used to develop the appropriate architecture for the AAN using iterative steps of training and testing. Significant removals of chemical oxygen demand (COD) (89.2 to 98.3%), NH₄⁺ (88.5 to 98.9%), and total phosphorus (TP) (77.9 to 99.9%) were achieved at a total HRT of 13.3 h (HRT_Z-1 = 3 h, HRT_Z-2 = 6 h and HRT_Z-3 = 5.3 h) and an IRF value of 1.75. The ENR-BP treatment mechanism relies on the use of OMs as a source of energy for phosphorus bio-uptake and the simultaneous nitrification and denitrification (SND) of nitrogen compounds. The removal efficiencies in the proposed ENR-BP were four fold higher than the suspended growth process and in the same order of magnitude of 5-stage Bardenpho-MBBR. The developed ANN-based model provides an efficient and robust tool for predicting and forecasting the performance of the ENR-BP.

Study on optimization and performance of biological enhanced activated sludge process for pharmaceutical wastewater treatment

Simulated pharmaceutical wastewater was treated by moving bed biofilm reactor (MBBR) and total reflux sludge reactor process (STR) system. By cultivating specific bacterial groups, optimizing reactor process parameters, and comparatively analyzing the pollutant removal efficiency under stable operating conditions of the system, the treatment efficiency of the two systems under the combined impact load of organic pollutants on the target pollutants indole and naphthalene was studied. The optimal operation parameters of reactors: hydraulic retention time (HRT) was 8 h, aeration was 0.12 m³/h. The effect was better in 25 ± 1 °C than that in 20 ± 2 °C. During stable operation, the average removal rate of chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N) of the MBBR system was significantly higher than that of STR, and the two kinds of target pollutants concentration in water was lower than the detection limit. In the combined impact test of organic pollutants, the dominant bacterial group obtained by domestication had a high degradation ability, so the combined impact of indole and naphthalene had little effect on the two reactors. But in the fourth stage, the residual naphthalene concentration in the STR system effluent exceeded the target value. Therefore, the MBBR process has a stronger treatment effect on pharmaceutical wastewater than the STR system during the stable period and the impact load stage.

Performance of HABR + MSABP system for the treatment of dairy wastewater and analyses of microbial community structure and low excess sludge production

The potential of the system, a hybrid anaerobic baffled reactor (HABR) coupled with a multi-stage active biological process (MSABP) reactor, for simulated dairy wastewater at various temperature, hydraulic retention time (HRT), and pH was investigated. Percentage removals of chemical oxygen demand (COD) and NH₄⁺ were optimized using response surface methodology. Under optimized conditions (temperature, 33 °C; HRT, 24 h; pH, 7.35), the removal efficiencies of COD and NH₄⁺ were 99.89% and 97.83%, respectively. Miseq sequencing analysis exhibited that the anaerobic segment of the system was dominated by fermentation and acetogenic bacteria, and in the aerobic segment, microorganisms involved in the nitrogen cycle were significantly enriched. Meanwhile, it could be found that the excess sludge production of the process was much lower than that of other bio-processes. The average excess sludge production rate was 0.025-0.05 g SS/g COD removed under different organic loadings.