Modelling of self-sustainable microbial fuel cell type oil sensors based on restricted oxygen transfer and two-population competition.

Oil leaks during oil industrial chain pose threats to the ecosystem. The microbial fuel cell-type oil sensor has been developed for early warning of such issues. Oil contacting with the sensor restricts oxygen availability and triggers correlative signal anomaly which serves as indicative of the oil presence. To extend its application for the real world, modelling of the sensor is required to pre-describe the signal behavior under unknown conditions. Therefore, by integrating Butler-Volmer, restricted oxygen transfer (ROT) and Monod equations, a dynamic ROT-MFC model with sufficient substrate precondition was developed. The ROT-MFC model was trained on the experimental single-oil-shock test (R 2 = 0.996) and validated by the experimental sequential-shocktest (R 2 = 0.998). Numerical analysis of the trained ROT-MFC model indicates that the single-shock detection has higher sensitivity (≥40.6 mV/detection) and the sequential-shocks detection spends a shorter response time (≤2.2 h). Besides, the sequential-shocks detection with proper strategy is more applicable due to flexible options on detection limit and working range. The model was further evolved into the TPC-ROT-MFC model by introducing a two-population competition (TPC) theory to describe performance under limited substrate conditions. Results indicate a critical substrate concentration range (42.1 to 62.8 mg-COD/L) for dividing baseline steadiness, and that the impact of substrate concentration on anodic charge transfer coefficient soars when the substrate concentration lessens furtherly. This sensor model is relatively easy to implement and may enhance practical use for design and operation.

On-line monitoring of minor oil spills in natural waters using sediment microbial fuel cell sensors equipped with vertical floating cathodes.

Oil spills near natural water bodies pose considerable threats to aquatic ecosystem and drinking water system. Various detection techniques have been developed to identify the oil pollution in natural waters. These techniques mainly focus on large and major oil spills involving significant changes in environmental characteristics. However, monitoring of minor oil spills (from seepage and dripping) in waters remains a bottleneck, allowing inconspicuous and persistent oil contamination. To overcome this drawback, a sediment microbial fuel cell (SMFC) sensor equipped with a vertical floating cathode is developed for on-line and in-situ monitoring of minor oil spills in natural waters. The vertical floating cathode was intended for recognizing oil on water surface. Oil on the cathode will trigger current drop. Two kinds of natural sediments were adopted in two sensors (SMFC1 from a lake and SMFC2 from an urban stream) for comparison. Both showed linear relationship between net steady-state current decrease and oil dose (30.78 and 27.29 µA/mL of sensitivity, respectively). The current change process was fitted well to a pseudo-first order kinetic equation. A one-point/two-point dynamic identification methods were derived from the kinetic equation. Therefore, the detection time was shortened from 10 h to 10/30 min. The triggered current decrease was mainly attributed to the increase in internal resistance related to charge and mass transfer. Despite the power loss after oil contamination, results implied SMFC sensor could still achieve self-sustainability. This study shows that the SMFC sensor with vertical floating cathodes is applicable to monitoring the unnoticeable minor oil pollutions in natural waters.

Characteristics of rural domestic wastewater with source separation.

Rural domestic wastewater (RDW), one of the non-point pollution sources, has become a significant object related to sanitation improvement and water pollution control in Taihu Lake Basin, China. Current research on RDW characteristics and management with source separation is limited. In this study, a source-separated investigation into the characteristics of RDW was conducted, and the management suggestions were proposed. The results showed that the average RDW production coefficient was 94.1 ± 31.6 (range: 71.8-143.0) liters per capita (person) per day. Household-level wastewater generation peaked two or three times daily, and the synchronous fluctuation could cause hydraulic loading shocks to treatment facilities. The population equivalents of chemical oxygen demand, ammonium nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP) in RDW were 78.7, 3.7, 4.12, and 0.8 g/(cap·d), respectively. Blackwater from water closet source accounted for 30.4% of the total wastewater amount, contributing 93.0%, 81.7%, and 67.3% to loads of NH4+-N, TN, and TP, respectively. Graywater from the other sources with low nutrient-related pollutant concentrations and loads, accounting for 69.6% of the total wastewater amount, was a considerable alternative water resource. The quantitative and qualitative characteristics indicated that GW and BW had the potential of being reused in relation to water and nutrients, respectively.

Real-time in situ auto-correction of K+ interference for continuous and long-term NH4+ monitoring in wastewater using solid-state ion selective membrane (S-ISM) sensor assembly.

Potassium ions (K+) present in wastewater has caused severe interference for NH4+ monitoring, over-estimation of NH4+ concentration and ultimately leads to extra energy consumption. Past effort for enhancing the selectivity of NH4+ over K+ were oftentimes complex, costly, or compromised the selectivity and accuracy of the NH4+ ion selective membrane (ISM) sensors. This study targeted this imminent challenge by developing an integrated NH4+/K+ auto-correction solid-state ISM (S-ISM) sensor assembly combined with a data-driven model to monitor [NH4+] under different [NH4+] and [K+] concentrations. The results showed that the interference of K+ was substantially alleviated for NH4+ measurement. The accuracy was enhanced by over 70% when examined using real wastewater and energy consumption was expected to reduce by 26% for a wastewater treatment plant, especially for wastewater with high [K+]. Furthermore, the uniquely structured S-ISMs were made by embedding the ionophores in a robust polyvinyl chloride (PVC) matrix containing plasticizers and a layer of carbon nanotubes (CNT) as ion-to-electron transducer, which maintained the selectivity and accuracy of the S-ISM sensor for 4 weeks in wastewater. NH4+/K+ sensor assembly integrated with data-driven correction models poses great potential in high-efficiency and energy-saving wastewater treatment and water reuse processes.

Towards high resolution monitoring of water flow velocity using flat flexible thin mm-sized resistance-typed sensor film (MRSF).

Novel flexible thin mm-sized resistance-typed sensor film (MRSF) fabricated using ink-jet printing technology (IPT) was developed in this study to monitor water flow rate in pipelines in real time in situ mode. The mechanism of MRSF is that the mm-sized interdigitated electrodes made by printing silver nanoparticles on an elastic polyimide film bend under different flow rates, leading to variation of the resistance of the sensor at different degrees of curvature. Continuous flow tests showed that MRSF possessed a high accuracy (0.2 m/s) and excellent sensitivity (0.1447/ms-1). A model of sensor resistance and flow velocity was established to unfold the correlation between the fundamentals of fluid mechanics and the mechanic flexibility of sensor materials. An analytical model yielded a high coefficient of determination (R2 > 0.93) for the relationship between the resistance increment of the MRSF and the square of the flow velocity at the velocity range of 0.25-2 m/s. Furthermore, a temperature-correction model was developed to quantify the effect of water temperature on the sensor resistance readings. MRSF exhibited a low temperature coefficient of resistance (TCR, 0.001) at the water temperature range of 20-60 °C. Computational fluid dynamics (CFD) simulations using the finite element method were conducted and confirmed both the underlying load assumptions and the deformation characteristics of the sensor film under various flow and material conditions. High-resolution monitoring of water flow rate using MRSF technology was expected to save at least 50% energy consumption for a given unit, especially under flow fluctuation. MRSF possesses a great potential to perform real-time in situ monitoring at high accuracy with ultralow cost, thus enabling the feedback control at high spatiotemporal resolution to reduce the overall energy consumption in water and wastewater systems.

Nitrogen and phosphorus removal processes under different aeration strengths in the principal-type tank of alternate multiple tanks system and process control.

The alternate multiple tanks (AMT) system was a new highly compact sewage treatment with cost-effective balance and automated management. Dissolved oxygen (DO) and oxidation-reduction potential (ORP) as monitoring indicators are closely linked to contaminants and controlling strategy. Thus, this paper was to investigate the N and P removal mechanisms and the real-time control under different aeration strengths through the principal-type tank. Results showed that N and P removal could reach an optimal balance when the air-water ratio (Rs) was 30 with 540L-air/h and 18L-water/h. Under such a condition, the TP, TN, ammonia and nitrate remained 0.4 mg/L (88.4% of removal efficiency), 5.0 mg/L (84.7%), 0.5 mg/L (98.4%) and 4.0 mg/L, respectively, during the discharge. However, restrained aeration reduced the P release and uptake efficiencies and retarded the ammonia oxidation and nitrification, and excessive aeration broke the balance of P release and uptake, prevented denitrification, and had no more effect on nitrification. Inadequate aeration caused residual DO low and insensitive to controlling critical points, while redundant aeration was of no extra effect compared to moderate aeration. An enhanced practical real-time response was obtained, where characteristic points of TP and nitrogen were sensitive to the DO, ORP and systematic manipulation.

Performance and adsorption mechanism of a magnetic calcium silicate hydrate composite for phosphate removal and recovery.

A novel magnetic calcium silicate hydrate composite (Fe3O4@CSH) was proposed for phosphorus (P) removal and recovery from a synthetic phosphate solution, facilitated by a magnetic separation technique. The Fe3O4@CSH material was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), zeta-potential and magnetic curves. The chemical composition and structure of Fe3O4@CSH and the successful surface loading of hydroxyl functional groups were confirmed. Phosphate adsorption kinetics, isotherm, and thermodynamic experiments showed that adsorption reaches equilibrium at 24 h, with a maximum adsorption capacity of 55.84 mg P/g under optimized experimental conditions. Adsorption kinetics fitted well to the pseudo second-order model, and equilibrium data fit the Freundlich isotherm model. Thermodynamic analysis provided a positive value for ΔH° (129.84 KJ/mol) and confirmed that phosphate adsorption on these materials is endothermic. The P-laden Fe3O4@CSH materials could be rapidly separated from aqueous solution by a magnetic separation technique within 1 min. A removal rate of more than 60% was still obtained after eight adsorption/desorption cycles, demonstrating the excellent reusability of the particles. The results demonstrated that the Fe3O4@CSH materials had high P-adsorption efficiency and were reusable.

Degradation of sulfamethoxazole in bioelectrochemical system with power supplied by constructed wetland-coupled microbial fuel cells.

The removal rate and degradation pathway of Sulfamethoxazole (SMX) in bioelectrochemical system (BES) and the elimination dynamics of SMX in a BES driven by stacked constructed wetland-coupled microbial fuel cells (CW-MFCs) were investigated. The results found that SMX (30mgL-1) was rapidly degraded in the BES, and the SMX removal kinetics was simulated well by a first-order kinetic model (R2>0.93). Low current had no effect on the degradation products but enhanced the SMX removal rate. Biotransformation was the main pathway for the SMX elimination in the BES. The CW-MFCs supplied adequate and stable electricity (0.84-1.01V) to support the BES for rapid SMX degradation without additional energy inputs. The relative abundance of Methanosarcina (18.7%) and VadinCA11 (3.1%) increased with an increase in voltage up to 1.2V. However, the opposite was observed for Methanosaeta and Methanomassiliicoccus. The current in the BES influenced the methanogenic communities.

Efficient model calibration method based on phase experiments for anaerobic-anoxic/nitrifying (A2N) two-sludge process.

A systematic calibration and validation procedure for the complex mechanistic modeling of anaerobic-anoxic/nitrifying (A2N) two-sludge system is needed. An efficient method based on phase experiments, sensitivity analysis, and genetic algorithm is proposed here for model calibration. Phase experiments (anaerobic phosphorus release, aerobic nitrification, and anoxic denitrifying phosphate accumulation) in an A2N sequencing batch reactor (SBR) were performed to reflect the process conditions accurately and improve the model calibration efficiency. The calibrated model was further validated using 30 batch experiments and 3-month dynamic continuous flow (CF) experiments for A2N-SBR and CF-A2N process, respectively. Several statistical criteria were conducted to evaluate the accuracy of model predications, including the average relative deviation (ARD), mean absolute error (MAE), root mean square error (RMSE), and Janus coefficient. Visual comparisons and statistical analyses indicated that the calibrated model could provide accurate predictions for the effluent chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), and total phosphorus (TP), with only one iteration.

Effects of calcium on the performance, bacterial population and microbial metabolism of a denitrifying phosphorus removal system.

A sequencing batch reactor was operated to study the effects of influent Ca2+ on the efficiency, bacterial population, and microbial metabolism of denitrifying phosphorus removal system. Results showed that high Ca2+ loading (≥80mg/L) significantly inhibited the performance of simultaneous nitrogen and phosphorus removal. The abundance of phosphorus removal-related organisms (Dechloromonas and Candidatus Accumulibacter) decreased with increasing Ca2+ concentration from 20 to 140mg/L, while the abundance of glycogen-accumulating organisms and other bacteria increased. Metabolomic analyses revealed that the metabolic profiles of microbial community were also affected by high influent Ca2+ concentrations. 3-Hydroxybutyrate, acetate, alanine, and glutamate were the main differentiated metabolites in the system. An accumulation of amino acids and a reduction of nucleotides and amines were important response to high Ca2+ loading. Long-term Ca2+ loading had a reversible effect on the denitrifying phosphorus removal system as it could revive after a 50-day recovery process.

Dynamics of antibiotic resistance genes in microbial fuel cell-coupled constructed wetlands treating antibiotic-polluted water.

Microbial fuel cell-coupled constructed wetlands (CW-MFCs) use electrochemical, biological, and ecological functions to treat wastewater. However, few studies have investigated the risks of antibiotic resistance genes (ARGs) when using such systems to remove antibiotics. Therefore, three CW-MFCs were designed to assess the dynamics of ARGs in filler biofilm and effluent over 5000 h of operation. The experimental results indicated that relatively high steady voltages of 605.8 mV, 613.7 mV, and 541.4 mV were obtained at total influent antibiotic concentrations of 400, 1,000, and 1600 µg L-1, respectively. The 16S rRNA gene level in the cathode layer was higher than those in the anode and two middle layers, but the opposite trend was observed for the sul and tet genes. The relative abundance of the three tested sul genes were in the order sulI > sulII > sulIII, and those of the five tet genes were in the order tetA > tetC > tetW > tetO > tetQ. The levels of sul and tet genes in the media biofilm showed an increase over the treatment period. The effluent water had relatively low abundances of sul and tet genes compared with the filler biofilm. No increases were observed for most ARGs over the treatment period, and no significant correlations were observed between the ARGs and 16S rRNA gene copy numbers, except for sulI and tetW in the effluent. However, significant correlations were observed among most of the ARG copy numbers.

Enrichment culture of denitrifying phosphorus removal sludge and its microbial community analysis.

An efficient one-step domestication method with mixed electron acceptors and short-time post-aeration was developed for the enrichment culture of denitrifying phosphorus removal sludge. The acclimation time, performance of nitrogen and phosphorus simultaneous removal and microbial community structure were investigated to reveal the difference among the obtained phosphorus removal sludge using different acclimation ways. Results showed that the proposed method with optimal proportion of nitrite and nitrate could significantly shorten domestication time (28 days) compared with the traditional two-step method (60 days), but exerted nearly no influence on the removal efficiency of nitrogen and phosphorus. High-throughput sequencing revealed that similar microbial community structure of DPAOs sludge was obtained with different acclimation methods. Compared with seed sludge, microbial community shifted obviously, and the dominant microbial population of Dechloromonas-related phosphorus removal bacteria increased significantly. It could be inferred that the appropriate concentration of nitrite was conducive to the rapid enrichment of DPAOs under alternative anaerobic/anoxic operation. Meanwhile, anaerobic/oxic condition was favorable for the enrichment of Candidatus Accumulibacter-related phosphorus removal organisms, and short-time post-aeration in the proposed method could reduce the potential public health hazard.