Influent Substrate Concentration Research Articles

Enhancing nitrogen removal in constructed wetlands: The role of influent substrate concentrations in integrated vertical-flow systems

Recent advancements in constructed wetlands (CWs) have highlighted the imperative of enhancing nitrogen (N) removal efficiency. However, the variability in influent substrate concentrations presents a challenge in optimizing N removal strategies due to its impact on removal efficiency and mechanisms. Here we show the interplay between influent substrate concentration and N removal processes within integrated vertical-flow constructed wetlands (IVFCWs), using wastewaters enriched with NO3−-N and NH4+-N at varying carbon to nitrogen (C/N) ratios (1, 3, and 6). In the NO3−-N enriched systems, a positive correlation was observed between the C/N ratio and total nitrogen (TN) removal efficiency, which markedly increased from 13.46 ± 2.23% to 87.00 ± 2.37% as the C/N ratio escalated from 1 to 6. Conversely, in NH4+-N enriched systems, TN removal efficiencies in the A-6 setup (33.69 ± 4.83%) were marginally 1.25 to 1.29 times higher than those in A-3 and A-1 systems, attributed to constraints in dissolved oxygen (DO) levels and alkalinity. Microbial community analysis and metabolic pathway assessment revealed that anaerobic denitrification, microbial N assimilation, and dissimilatory nitrate reduction to ammonium (DNRA) predominated in NO3−-N systems with higher C/N ratios (C/N ≥ 3). In contrast, aerobic denitrification and microbial N assimilation were the primary pathways in NH4+-N systems and low C/N NO3−-N systems. A mass balance approach indicated denitrification and microbial N assimilation contributed 4.12–47.12% and 8.51–38.96% in NO3−-N systems, respectively, and 0.55–17.35% and 7.83–33.55% in NH4+-N systems to TN removal. To enhance N removal, strategies for NO3−-N dominated systems should address carbon source limitations and electron competition between denitrification and DNRA processes, while NH4+-N dominated systems require optimization of carbon utilization pathways, and ensuring adequate DO and alkalinity supply.

A comprehensive root cause analysis of anammox bioreactor performance decline

The cultivation of anaerobic ammonia oxidizing bacteria (anammox) has gained enormous awareness over the last few decades. Although numerous studies focus massively on successfully growing these anammox to different enrichment environments, in reality, the failure rates are somewhat comparable to the reported success rates. This study combines a variety of measurement techniques to observe and monitor the sequence of a bioreactor performance decline following elevated influent substrate concentration. After attaining stable substrate removal throughout a nitrogen loading rate (NLR) range of 0.691 to 1.669 kg-N·m−3·d−1, the performance of the lab-scale anammox-sequencing batch reactor (SBR) abruptly broke down as the NLR reached 2.01 kg-N·m−3·d−1. The gathered information showed that the increased NLR firstly caused a significant and unfavorable change in the free ammonia (FA) and free nitrous acid (FNA) concentration in the bioreactor. A subsequent drop in N2 production and a decline from a peak high of 0.381 to a low of 0.012 kg-N·kg-VSS−3·d−1 of the specific nitrogen removal rate (SNRR) led to an 82% absurd decline in microbial cellular energy production. Prior to these anammox switching to survival mode and secreting larger quantities (32% higher) of extracellular polymeric substances (EPS), the activity of syntrophic decomposers increased substantially leading to the internal production of excess CO2 in the bioreactor and thereby diverging the bioreactor pH to lower levels. The purposes of this study are to understand the reason an anammox process shows different signals during a decline phase and to enable immediate response to performance deterioration.

Strategy for rapid recovery of simultaneous sulfide and nitrite removal under high substrate inhibition

The paper deals with the strategy for a quick recovery of reactor treating sulfide and nitrite simultaneously under inhibition caused by high substrate concentration. For influent sulfide concentration of 360 mg S/L, respective sulfide and nitrite removal percentages dropped to 74.19% and 14.33% due to inhibition caused by high sulfide and nitrite concentrations. It was found that reduction in the influent substrate concentration (300 mg S/L) could not revive the nitrite removal performance in 4 days’ operation, which still showed a declining tendency from 47.16% to 18.52%. Regulating the influent pH around 6.70 ± 0.10, it only took 4 days to recover the performance for 300 mg S/L. Furthermore, at influent sulfide concentration increased to 360 mg S/L, respective sulfide and nitrite removal percentages were 99.76 ± 0.27% and 100.00%. The strategy of regulating influent pH could recover the process performance in a short term, which would provide great convenience for subsequent process research.

Variations of Net C/N Ratio with the Coulombic Efficiency in Dual-cathode MFC for the Simultaneous Removal of Organics and Nitrogen

The objective of this study was to suggest a method of determining the appropriate C/N ratio in a dual-cathode MFC that allowed to remove nitrogen and organics simultaneously with a single external resistance. The electrochemical characteristics and removal performances of MFC was analyzed based on the initial dose of organic matter and nitrogen. While ammonia was consistently removed regardless of the initial COD concentration, the amount of nitrate removal decreased as the C/N ratio decrease. Also, the coulombic efficiency (CE) decreased as the initial COD concentration increased. The C/N ratios based on the influent substrate concentration was revealed of 1.8~8.5 that had wider range than that of 3.36~7.57 which was calculated from substrate concentration removed during the reaction. The calculated C/N ratio considering the CE was a relatively consistent 3.16. The net C/N ratio was similar to the stoichiometric value of 2.86 g NO3- N/g COD, showing that the electrons transferred to the cathode were mostly used for denitrification. Electrons produced from the oxidation of organic matter for denitrification in the MFC exhibited greater loss at the anode compared to the cathode. Consequently, the amount of COD required for denitrification can be determined by considering the CE to the net C/N ratio.

MODEL ESTIMASI BIOKINETIKA UNTUK PROSES POST-DENITRIFIKASI AIR LIMBAH DOMESTIK PADA UNIT ANAEROBIC BAFFLED REACTOR

This study developed a combination of Continuous Stirred Tank Reactor (CSTR) for the acid fermentation and the Anaerobic Baffled Reactor (ABR) post-denitrification through high nitrite injection. Volatile Fatty Acids (VFAs) as a substrate for the post-denitrification process were optimally produced in the acid fermentation process. The aim of this study was to obtain the estimation of biokinetic values to predict the effluent wastewater quality in ABR post-denitrification process under unsteady state. The reactor was operated for HRT 7 days at temperature 25-28 ˚C and pH 6-7,2. The influent and effluent substrate concentration were monitored continuously for 160 days. Post-denitrification biokinetic from the Contois equation resulted in the value of hydrolysis rate (Kh) of 0.077 day-1, the substrate transport rate (k) of 4.364×10-6 Lmg-1day-1, maximum specific growth rate (μmax) of 0.559 day-1, half saturation constant (KS) of 0.209 mgL-1, microbial decay coefficient (b) of 0.0145 days-1; yield coefficient (Y) of 0.084 g-VSSg-COD-1. The validation of biokinetic parameters based on statistical analysis showed fairly precise results following the trend of experimental data to determine the substrate concentration in the effluent unit. Therefore, the biokinetic values can be applied in the design of ABR post-denitrification using primary sludge incorporation with high strength nitrate.Keywords: Anaerobic baffled reactor, biokinetics, Contois, hydrolysis, post-denitrification.

Effect of the Influent Substrate Concentration on Nitrogen Removal from Summer to Winter in Field Pilot-Scale Multistage Constructed Wetland–Pond Systems for Treating Low-C/N River Water

The quality of micropolluted water is unstable and its substrate concentration fluctuates greatly. The goal is to predict the concentration effect on the treatment of nitrogen in a river with an actual low C/N ratio for the proposed full-scale Xiaoyi River estuary wetland, so that the wetland project can operate stably and perform the water purification function effectively in the long term. Two pilot-scale multistage constructed wetland–pond (MCWP) systems (S1 and S2, respectively) based on actual engineering with the same “front ecological oxidation ponds, two-stage horizontal subsurface flow constructed wetlands and surface flow constructed wetlands (SFCWs) as the core and postsubmerged plant ponds” as the planned process were constructed to investigate the effect of different influent permanganate indexes (CODMn) and total nitrogen (TN) contents on nitrogen removal from micropolluted river water with a fixed C/N ratio from summer to winter in the field. The results indicate that the TN removal rate in the S1 and S2 systems was significant (19.56% and 34.84%, respectively). During the process of treating this micropolluted water with a fixed C/N ratio, the influent of S2 with a higher CODMn concentration was conducive to the removal of TN. The TN removal rate in S2 was significantly affected by the daily highest temperature. There was significant nitrogen removal efficiency in the SFCWs. The C/N ratio was a major determinant influencing the nitrogen removal rate in the SFCWs. The organic matter release phenomenon in SFCWs with high-density planting played an essential role in alleviating the lack of carbon sources in the influent. This research strongly supports the rule that there is seasonal nitrogen removal in the MCWPs under different influent substrate concentrations, which is of guiding significance for practical engineering.

Controlling filamentous sludge bulking by regulating oxygen supply in the start of BISURE system

BISURE (BIological SUlfide REmoval) systems are efficient biological systems for sulfide removal and elemental sulfur recovery. However, they often suffer from disturbance caused by filamentous sludge bulking during startup, which are inoculated with activated sludge. In this study, BISURE startup by increasing the influent substrate concentration (IC-mode) and speeding up the influent flow rate (IF-mode) were investigated to understand and avoid the disturbance. The results showed that the BISURE system could be successfully started up in both the IC mode and IF mode, but both modes could trigger filamentous sludge bulking by Thiothrix (a filamentous sulfur-oxidizing bacteria, F-SOB). “CSO going first, PSO following up” was an effective approach to control the filamentous sludge bulking during startup. The procedure mechanism of oxygen effect was revealed: the growth of zoogloeal SOB (Z-SOB) with its larger surface-to-volume ratio (SVR) was first promoted to achieve a “proportion advantage” over F-SOB in the bacterial community; the external location of Z-SOB was then fixed to achieve the “location advantage” over F-SOB in the sludge floc; finally, prior uptake of DO by Z-SOB was ensured to achieve a “sequence advantage” over F-SOB in the substrate utilization. After elimination of filamentous sludge bulking, the dominant SOB in the bacterial community in IC-mode were Thiobacillus, accounting for more than 90% of the population; while dominant SOB in IF-mode were Thiobacillus and Annwoodia, which together accounted for more than 60% of bacteria. These findings are helpful in characterizing biological desulfurization and going forward, should be important in further developing BISURE systems.

Modelisation and Optimization of a Microbial Desalination Cell System

In this work, we used a hybrid system composed of a Microbial Desalination Cell (MDC). This system allows, at the same time, the treatment of wastewater and the production of electrical energy for the desalination of saltwater. MDC is a cleaning technology used to purify wastewater. This process has been driven by converting organic compounds contained in wastewater into electrical energy through biological, chemical, and electrochemical processes. The produced electrical energy was used to desalinate the saline water. The objective of this work is the desalination or pre-desalination of seawater. For this, we have established a theoretical model consisting of differential equations describing the behavior of this system. Subsequently, we developed a program on MAT-LAB software to simulate and optimized the operation of this system and to promote the production of electrical energy in order to improve the desalination efficiency of the MDC. The theoretical result shows that the electrical current production is maximal when the methanogenic growth rate equal to zero, increases with the increasing of influent substrate concentration and the efficiency of desalination increased with flow rate of saline water.

Effects of Temperature and Substrate Concentration on N2O Release of ANAMMOX Process

The greenhouse gas N2O is released during the biological nitrogen removal process. ANAMMOX (anaerobic ammonium oxidation) is regarded as a promising nitrogen removal process for treating municipal wastewater, and the N2O emission patterns and mechanisms need further investigation. In this study, batch tests were performed to study the release of N2O at different temperatures and substrate concentrations, and the microbial mechanisms of N2O emission were discussed. The results showed that the increase of the influent substrate concentration of the ANAMMOX process promoted the release of N2O. At 35℃, when the influent nitrite increased from 40 mg·L-1 to 60 mg·L-1, 120 mg·L-1, the maximum accumulated concentration of N2O increased from 0.5 mg·L-1 to 1.5 mg·L-1 and 2.4 mg·L-1, accounting for 0.85%, 1.43%, and 1.11% of the total nitrogen removal, respectively. Lowering temperature had an obvious inhibitory effect on ANAMMOX activity. The specific ANAMMOX activity at 15℃ was only 6% of that at 30℃. Furthermore, the intracellular ATP concentration was reduced. At 15℃, the intracellular ATP concentration was 4% of that at 30℃. The decrease in temperature led to a decrease in the release of N2O in the ANAMMOX process. When the temperature decreased, the denitrification rate would decrease, leading to a lower N2O production rate and lower N2O accumulation. 16S rRNA amplicon sequencing showed that ANAMMOX bacteria Candidatus Brocadia and Ca. Jettenia were enriched, accounting for 6.9%-13.8% and 1.4%-2.6% of microbial community, respectively. Abundant heterotrophic bacteria were also found in the microbial community. The accumulation of N2O in the ANAMMOX process was mainly attributed to denitrifying bacteria producing and consuming N2O. This study provides support for controlling N2O emission during the ANAMMOX process for treating municipal wastewater.

The reaction of wastewater treatment and power generation of single chamber microbial fuel cell against substrate concentration and anode distributions.

This study demonstrated the effectiveness of single chamber up-flow membrane-less microbial fuel cell (UFML-MFC) in wastewater treatment concurrently with bioelectricity generation. The objectives of this study were to examine the effect of influent substrate concentration (0.405g/L, 0.810g/L, 1.215g/L, 1.620g/L), anode distributions (11cm, 17cm, 23cm )and surface morphologies for biofilm formation on the performance of wastewater treatment and power generation. The optimum performance was obtained with substrate concentration of 0.810g/L. The COD removal efficiency, output voltage, internal resistance, power density and current density obtained were 84.64%, 610mV, 200Ω, 162.59mW/m2 and 468.74mA/m2,respectively. The Coulombic Efficiency (CE), Normalized Energy Recovery (NERS and NERv) were 1.03%, 789.38 kWh/kg COD and 22.56 kWh/m3,respectively. The results also indicate that the output voltage and power generation obtained in a continuous up-flow MFC were higher with A3 (23cm), which is of larger electrodes spacing followed by A2 (17cm) and A1 (11cm) caused by the enrichment of anaerobic microbial population at A1.

Performance of a high-rate anammox reactor under high hydraulic loadings: Physicochemical properties, microbial structure and process kinetics

In this study, a lab-scale upflow anaerobic sludge blanket (UASB) reactor was applied to studying the high-rate nitrogen removal of granule-based anammox process. The nitrogen removal rate (NRR) finally improved to 15.77 kg/m3/d by shortening hydraulic retention time (HRT) to 1.06 h. Well-shaped red anammox granules were extensively enriched inside the reactor. The results of nitrogen removal kinetics indicated that the present bioreactor has great nitrogen removal potential, because the maximum rate of substrate utilization (Umax) predicted by Stover-Kincannon model is suggested as 55.68 kg/(m3·d). Analysis of the microbial community showed that the anammox genus Candidatus Kuenenia dominated the bacterial communities. The relative abundance of Candidatus Kuenenia rose from 12.29% to 36.95% after progressively shorter HRT and higher influent substrate concentrations, illustrating the stability of nitrogen removal performance and biomass enrichment offered by the UASB in carrying out high-rate anammox process.

Insight into the response of anammox granule rheological intensity and size evolution to decreasing temperature and influent substrate concentration

Anammox granules are advantageous because of their relatively higher nitrogen removal rate (NRR) and biomass retention capacity in ammonia-containing wastewater treatment. However, little attention has been paid to granule rheological intensity and size evolution, especially under low temperature and substrate concentration conditions. In this study, the size evolution and variations in rheological properties associated with biochemical characteristics of anammox granules were investigated at decreasing temperatures (35 → 13 °C) and influent substrate concentrations (300 → 50 mg NH4+-N L−1). Both the specific anammox activities (SAA) and yield stress (τc) (or storage modulus (G′)), which reflected granules' intensity, decreased with decreasing temperature and influent substrate concentration. An exponential correlation was found between SAA and τc (or G′). Granule size strongly decreased at low temperature (13 °C) and influent substrate concentration (50 mg NH4+-N L−1), despite slight variations in τc (or G′). A threshold τc (or G′) that is closely related to the hydrodynamic shear force in the reactor may exist for the anammox granules. Once the τc (or G′) of the anammox granules was lower than this threshold value (τc∗ = 10.13–15.63 kPa), granules that could not endure hydrodynamic shear forces would disintegrate and their size would decrease substantially. Candidatus Kuenenia was the dominant genus in the expanded granular sludge bed reactor, reaching a minimum abundance of 14.6% at 16 °C because of the low-temperature shock, but increasing in abundance to 57.0% at 13 °C, indicating it has a competitive advantage at low temperatures. This contributed to achieving a high reactor nitrogen loading rate (>1.0 kg N m−3 d−1) even at 13 °C or with 50 mg NH4+-N L−1 influent. Overall, the results of this study will facilitate management of anammox bioreactors that run at various temperatures and influent substrate concentrations by clarifying the correlation between rheological intensity and anammox granule sludge activity and identifying the τc (or G’) threshold.

Nonlinear adaptive control of microbial fuel cell with two species in a single chamber

Microbial fuel cells are emerging devices with an ability to harvest electrical energy from wastewater. We develop an integrated control-oriented model with uncertain parameters and a nonlinear adaptive control scheme that can estimate parameters on-line so as to provide robustness against parametric uncertainties with influent substrate concentration as an input variable for a single chamber unit with two bacterial species. In presence of parametric uncertainties, the closed-loop characteristics of the substrate concentration and influent substrate concentration are analyzed through lyapunov stability analysis and validated through appropriate simulation work. The results indicate that the suggested adaptive compensation scheme provides satisfactory performance in presence of parametric uncertainties.

Production of biohydrogen from waste wheat in continuously operated UPBR: The effect of influent substrate concentration

Utilization of waste materials is one of the most economical approaches to biohydrogen production. Continuous generation of biohydrogen in a bioreactor makes the process more economical with respect to the conventional physical and chemical method. The two main parameters that affect the biohydrogen production in a continuously operated bioreactor are hydraulic retention time (HRT) and influent substrate concentrations. The effect of influent substrate concentration on biohydrogen generation in an up-flow packed bed reactor (UPBR) at HRT = 3 h was investigated in this study. The substrate was waste wheat which was acid hydrolyzed in H2SO4 by adjusting the pH value to pH = 2, under high temperature as T = 90 °C in an autoclave to obtain fermentable sugar solution. A natural and porous support particle namely, aquarium biological sponge (ABS) was the microbial immobilization surface in the reactor. Total and hydrogen gas volumes, hydrogen percentage, influent and effluent substrate concentrations, VFA concentrations were monitored. The influent substrate concentration (TSo) was varied between TSo = 10 g/L and TSo = 35 g/L. The process performance was evaluated as biohydrogen volume, percentages, rate and yield under varying operating conditions. The production volume (4275 ml/day) and the rate (3.05 L H2/L day) were maximum at influent sugar concentration of TSo = 25 g/L, but the yield reached to its maximum value as Y = 1.22 mol H2/mol glucose at TSo = 19 g/L. Substrate limitation and inhibitions were observed at influent concentrations of TSo = 10 g/L and TSo = 35 g/L, respectively. The results indicated that ABS could be suggested as a microbial support particle for hydrogen generation in immobilized systems.

Fermentative Hydrogen Production and Bacterial Community Analysis of Immobilized Sewage Sludge

A novel anaerobic batch fermentation seeded with immobilized sludge was developed for enhanced fermentative hydrogen production using pretreated sweet sorghum substrate as carbon source. Municipal sewage sludge was immobilized to produce hydrogen gas under anaerobic conditions. Cell immobilization was essentially achieved by gel entrapment approach. Hydrogen production was more efficient with the immobilized-cell system than with the free sludge. When the heat treated and acclimatized sludge's were immobilized, the cumulative hydrogen production enhanced. The batch fermentation was operated at a hydraulic retention time (HRT) of 24 h and an influent substrate concentration of 10–40 g/L. With highest concentration of substrate, the acclimatized sludge produced 15.98 mL of H2/g of substrate. In all the treatments, maximum hydrogen yield was obtained at the substrate concentration of 40 g/L, inoculum volume of 10 g/L, at room temperature and HRT of 24 h. The immobilized beads retained 60% of their activity up to three cycles. The best fermentative hydrogen production performance was eventually dominated by presumably enhanced hydrogen-producing bacterial species identified as Escherichia coli.

Biofilter scaling procedures for organics removal: A potential alternative to piloting

To provide information for the design and improvement of full-scale biofilters, pilot-scale biofiltration studies are the current industry standard because they utilize the same filter media size and loading rate as the full-scale biofilters. In the current study, bench-scale biofilters were designed according to a biofilter scaling model from the literature, and the ability of the bench-scale biofilters to accurately represent the organics removal of pilot-scale biofilters was tested. To ensure similarity in effluent water quality between bench- and pilot- or full-scale biofilters at the same influent substrate concentration, the tested model requires that either mass transport resistance or biofilm shear loss takes primacy over the other. The potential primacy of mass transport resistance or biofilm shear loss was evaluated via water quality testing (dissolved organic carbon, specific ultraviolet absorbance, liquid chromatography – organic carbon detection, trihalomethane formation potential, and haloacetic acid formation potential). The biofilters also were characterized for adenosine triphosphate (ATP) content, enzyme activity, extracellular polymeric substances, and microbial community structure. The results of this study indicate that biofilm shear loss takes primacy over mass transport resistance for bench-scale biofilter design in this system; thus, bench-scale biofilters designed in this manner accurately represent organics removal in pilot-scale biofilters. Applying this scaling procedure can reduce filter media requirements from many kilograms to just a few grams and daily water requirements from thousands of liters to less than 10 L. This scaling procedure will allow future researchers to test alternative treatment designs and operating conditions without the need for expensive pilot-scale studies.

A comprehensive insight into the functional bacteria and genes and their roles in simultaneous denitrification and anammox system at varying substrate loadings.

Simultaneous denitrification and anammox process are newly developed wastewater treatment processes with high-nitrogen removal efficiency, but little information is available regarding its optimal operational conditions and molecular mechanisms. In this study, a lab-scale up-flow anaerobic sludge blanket bioreactor fed with nitrate and ammonia was continuously operated for 180days to establish the simultaneous denitrification and anammox system, so as to investigate the changing patterns of nitrogen removal efficiency and functional bacteria and genes at varying substrate loadings. Results showed that the optimal removal efficiency of total nitrogen (TN) reached 92.47%, corresponding to TN loading removal rate of 0.9kg-Nm-3day-1 that was achieved at low influent substrate concentrations and short hydraulic retention time (HRT) (4h). High-throughput sequencing of 16S rRNA gene amplicons revealed that the predominant denitrifying and anammox bacteria in the coupling system were Thauera (relative abundance of 25.30%) and Candidatus Brocadia (relative abundance of 6.85%), respectively. Quantitative real-time PCR showed that the anammox genes (hzsA, hzsB, and hzo) and denitrifying genes (narG, napA, and nirS) demonstrated high abundance in the optimized bioreactor. Batch experiments were also conducted to determine the temporal difference in the expression of the anammox and denitrifying genes. NarG was found to play a crucial role in nitrate reduction to produce nitrite for anammox bacteria, while nirS was identified as the key genes for nitrite reduction to produce nitric oxide, which acted as an important role in both denitrification and anammox reaction.

Modeling Power Generation and Energy Efficiencies in Air-Cathode Microbial Fuel Cells Based on Freter Equations

The model proposed in this study was based on the assumption that the biomass attached to the anode served as biocatalysts for microbial fuel cell (MFC) exoelectrogenesis, and this catalytic effect was quantified by the exchange current density of anode. By modifying the Freter model and combining it with the Butler–Volmer equation, this model could adequately describe the processes of electricity generation, substrate utilization, and the suspended and attached biomass concentrations, at both batch and continuous operating modes. MFC performance is affected by the operating variables such as initial substrate concentration, external resistor, influent substrate concentration, and dilution rate, and these variables were revealed to have complex interactions by data simulation. The external power generation and energy efficiency were considered as indices for MFC performance. The simulated results explained that an intermediate initial substrate concentration (about 100 mg/L under this reactor configuration) needed to be chosen to achieve maximum overall energy efficiency from substrate in the batch mode. An external resistor with the value approximately that of the internal resistance, boosted the power generation, and a resistor with several times of that of the internal resistance achieved better overall energy efficiency. At continuous mode, dilution rate significantly impacted the steady-state substrate concentration level (thus substrate removal efficiency and rate), and attached biomass could be fully developed when the influent substrate concentration was equal to or higher than 100 mg/L at any dilution rate of the tested range. Overall, this relatively simple model provided a convenient way for evaluating and optimizing the performance of MFC reactors by regulating operating parameters.

Unknown Inputs Nonlinear Observer for an Activated Sludge Process

This paper deals with the jointly estimation problem of unknown inputs and nonmeasured states of one altering aerated activated sludge process (ASP). In order to provide accurate and economic concentration measures during aerobic and anoxic phases, a cascade high gain observer (HGO) approach is developed. Only two concentrations are available; the other process’s states are assumed unavailable. The observer converges asymptotically and it leads to a good estimation of the unavailable states which are the ammonia and substrate concentration, as well as a quite reconstruction of the unknown inputs, which are the influent ammonia and the influent substrate concentrations. To highlight the efficiency of the proposed HGO with this MIMO system’s dynamics, simulation results are validated with experimental data.

Experimental validation of online monitoring and optimization strategies applied to a biohydrogen production dark fermenter

This work presents the proposal and experimental validation of an online optimization strategy for maximizing the hydrogen production rate (HPR) in an anaerobic bioreactor through the dark fermentation of glucose. The proposal comprises a heuristic optimization strategy, a coupled nonlinear observer, and a PI controller to track the desired maximum HPR. The optimization is achieved by solving online a nonlinear programming problem which considers the relation between the HPR and the organic loading rate (OLR), such that the latter is manipulated to maximize the former. Since the OLR requires online knowledge of the unmeasured influent substrate concentration, the nonlinear observer is used to estimate it using measurements of the hydrogen flow rate at the output of the bioreactor. This observer comprises the coupled operation of a robust Luenberger observer and a super-twisting observer. The proposal was designed and tested experimentally in a continuous stirred tank laboratory bioreactor fed with glucose, and the results are very promising.