Treatment Of Synthetic Wastewater Research Articles

Artificial intelligence-driven control for enhancing carbon dioxide-based wastewater pH regulation in tubular reactor

Alkaline wastewater treatment using carbon dioxide can reduce chemical costs and provide a safer alternative to traditional methods. However, complex gas-liquid reactions and narrow operating pH ranges present challenges. This research develops an artificial intelligence-driven control system for treating alkaline wastewater using carbon dioxide in a bench-scale tubular reactor. The proposed control system employs an inverse neural network to regulate the carbon dioxide gas based on the desired setpoint, along with a Smith predictor and a linear controller to compensate for natural delays, model mismatches, and pH disturbances. The inverse neural controller was trained using experimental data from a bench-scale reactor pH treatment of synthetic alkaline wastewater and verified on real influent from an electroplating wastewater treatment plant. The results show that the proposed method efficiently enforces the desired reactor outlet pH setpoint with up to 51.36% faster settling time than a proportional-integral controller while improving pH-adjusting efficiency by 72.24%.

A comparative study on UASB MF-OMBR and AnMF-OMBR treating slaughterhouse wastewater: Process performance, struvite precipitation, and economic evaluation

Up-flow anaerobic sludge blanket microfiltration osmotic membrane bioreactor (UASB MF-OMBR) is a cutting-edge technology derived from the anaerobic osmotic membrane bioreactor (AnOMBR). This study investigated long-term performance of an UASB MF-OMBR and an anaerobic microfiltration osmotic membrane bioreactor (AnMF-OMBR) comparatively focusing on process performance, membrane fouling, microbial community shift, struvite precipitation, and economic evaluation for the treatment of synthetic and real slaughterhouse wastewater (SSW and RSW). The UASB MF-OMBR achieved higher process performance regarding chemical oxygen demand (COD) removal (70 ± 1 %), methane yield (0.24 ± 0.03 L CH4 g−1 CODremoved) and NH4+-N rejection (85 ± 3 %). On the other hand, high COD and PO43−-P rejections were observed in both systems (>92 % and ∼98 %, respectively). The impact of the salinity build-up in the UASB MF-OMBR was the lower due to the bioreactor configuration. In addition, compared to the AnMF-OMBR, the better water fluxes were obtained in the UASB MF-OMBR, which can be attributed to the less membrane fouling. The results of precipitation modelling and Mg2+ measurement in the sludge of both bioreactors demonstrated that the struvite precipitation occurred during the forward osmosis (FO) operation was more often and in higher amounts in the AnMF-OMBR. The economic evaluation indicated that the specific produced permeate cost (SPC) with revenue was slightly lower for the UASB MF-OMBR than that of the AnMF-OMBR.

Comparative Study on Removal of Acid Violet 90 dye by using Catalytic Ozonation Processes with n.CeO2, n.ZnO and n.CeO2/n.ZnO Nanocatalysts and Kinetic Examination

The textile industry uses high amounts of water and dyestuffs, and accordingly, wastewater containing significant amounts of dyestuffs is produced, which have to be treated before being discharged to the environment. The aim of this study is the treatment of synthetic wastewater containing 50 mg/L Acid Violet 90 dyestuff with catalytic ozonation process have been investigated by using n.CeO2, n.ZnO and n.CeO2/n.ZnO (1:1, m:m) nanocatalysts. The process optimization has been performed with the pH, ozone dose, catalyst dose and reaction time parameters. While the optimum conditions have been determined as pH 3, 600 mg/L ozone dose, 10 min reaction time, for all three catalysts, catalyst doses have differed as 50 mg/L for n. CeO2, 30 mg/L for n.ZnO and n.CeO2/n.ZnO. The removal efficiencies of AV 90 have been achieved as 97.04, 96.2 and 95.7% for n.CeO2, n.ZnO and n.CeO2/n.ZnO catalysts, respectively. Kinetic analyses showed that color removal of AV 90 dyestuff followed First order kinetics with R2 values of 0.9987 (n.CeO2), 0.9912 (n.ZnO) and 0.9923 (n.CeO2/n.ZnO) and reaction rate constant values have been calculated as 0,3435 (n.CeO2), 0,3551(n.ZnO) and 0,3226 (n.CeO2/n.ZnO) min−1.

Simultaneous organic wastewater treatment and bioelectricity production in a dual chamber microbial fuel cell with Scenedesmus obliquus biocathode

Algal biocathode MFCs (ABMs) are recently being heavily studied due to their advantage over abiotic cathode MFCs (ACMs) as dissolved oxygen (DO) generated by algal growth in the cathodic chamber is directly utilized in cathodic oxidant reduction. In this work growth of pure algae species Scenedesmus obliquus used in the cathode chamber has been studied under a photoperiod of 24 h illumination to supplement oxygen for continual MFC operation without any external supply of air or carbon dioxide and treatment of synthetic wastewater having chemical oxygen demand (COD) equivalent to medium strength domestic wastewater (5.35 g/L COD). Results of ABM showed the highest continuous current density generation of 23.93 mA/m2 and the highest continuous volumetric power density generation of 13.24 mW/m3 were around 120 h with COD removal efficiency of 92.52 % and coulombic efficiency (CE) of 41.88 %. Initial ohmic (Roh) and charge transfer (Rct) resistance values of ABM were found to be 8.3 Ω and Rct of 22.5 Ω which after 216 h of algal growth got reduced to 1 Ω and 15.1 Ω respectively. 16S microbiome profiling of the mixed microbial sludge inoculum used in the anodic chamber showed dominance of Xanthomonadaceae stenotrophomonas (9.7 %), Chitinophaga flexibacter (8.65 %), Sphingomonadaceae sphingomonas (6.82 %), Sphingobacterium multivorum (6.55 %), Dyadobacter fermentans (6.05 %), and Alcaligenaceae achromobacter (5.51 %). Elemental investigation of the bioanode’s and biocathode’s surface carried out using EDS analysis also shows that oxygen was generated in the cathodic chamber by pure Scenedesmus obliquus species.

Treatability of BPA Containing Wastewater by Catalytic and Photocatalytic Ozone Processes Using n.TiO2

In this study, the treatment of synthetic wastewater containing 10 mg/L Bisphenol A (BPA) has been investigated by the catalytic and photocatalytic ozonation process. n.TiO2 nanocatalysts have been used in catalytic (COP) and photocatalytic (PCOP) ozonation processes. Optimum parameters have been determined as pH 6.32, 1200 mg/L ozone dose, 50 mg/L n.TiO2 catalyst dose and 12.5 min reaction time for COP. Optimum parameters have been found as pH 6.32, 1200 mg/L ozone dose, 50 mg/L n.TiO2 catalyst dose, 18 Watt UV light intensity, and 10 min reaction time for PCOP. The removal efficiencies of BPA have been obtained as 95.51% and 98.09% for COP and PCOP, respectively. Kinetic analyses showed that BPA removal has been carried out Pseudo second order kinetics with R2 values of 99.1 for both processes.

Effect of Operating Parameters on Photocatalytic Treatment of Synthetic Wastewater Using CaTiO3

Photocatalysis is thought to be a long-term, environmentally friendly, economically feasible, and promising technique for treating wastewater. The development of semiconductor nanoparticles has generated a great deal of interest in the treatment of wastewater. To break down complex contaminants found in wastewater into simpler compounds, including H2O and CO2, several UV/visible light excitable nanomaterials have been explored as photocatalysts. Their effectiveness can be managed by adjusting several reaction-related parameters like the intensity of light, irradiance time, pH, catalyst dose, temperature, doping, etc. The performance of the photocatalyst in the photodegradation of contaminants is greatly affected by these parameters. The main goal of this study is to find the best operational parameters and their impact on the photocatalytic treatment of synthetic waste-water using calcium titanate (CaTiO3) nanoparticles. For this purpose, sol-gel synthesized CaTiO3 with a band gap of 3.57 eV was used. The size of the synthesized nanoparticles is smaller than 47.62 nm. The results of photocatalytic treatment of synthetic wastewater demonstrate that CaTiO3 exhibits its best photocatalytic performance at 33 W UV light, pH 6.0, and 3.33 g L-1 CaTiO3 dose with 8 hours of irradiation time. With chemical oxygen demand (COD) concentrations varying from 700 to 40000 mg L-1 at the initial stages, the percentage of COD removal under these conditions was 100% to 77%.

Economic evaluation of submerged anaerobic hybrid membrane bioreactor operating at mesophilic temperature.

A laboratory-scale mesophilic submerged anaerobic hybrid membrane bioreactor (An-HMBR) was operated for 270days for the treatment of high-strength synthetic wastewater at different hydraulic retention times (HRTs) (3days, 2days, 1day, and 0.5days). Chemical oxygen demand (COD) removal efficiency of 92% was obtained with methane yield rate of 0.18 LCH4/g CODremoval at 1-day HRT. The results of lab scale reactor at 1-day HRT were utilized for upscaling and cost analysis. Cost analysis revealed that the total capital cost comprised tank system (48%), membrane cost (32%), screen and PUF sponge (5% each), PLCs (4%), liquid pumps (3%), and others (2%). The operational cost comprised chemical cost (46%), pumping energy (42%), and sludge disposal (12%). The results revealed that the tank and heating costs accounted for the largest fraction of the total life cycle cost for full-scale An-HMBR. The heating cost can be compensated by gas recovery. Sensitivity analysis revealed that the interest rates, influent flow, and membrane flux were the most crucial parameters which affected the total cost of An-HMBR.

Simultaneous biological nutrients removal from wastewater with high ammonium and phosphorus loading using aerobic granular sludge

In this study, two SBRs were inoculated with biomass from a flocculant biological nutrient removal facility and operated for the biological treatment of synthetic wastewater to explore the impact of low influent COD/TN/TP ratio on the start-up, performance, and development of stable, matured AGS. AGS maturation and simultaneous nutrient removals were investigated for 422 days under applying limited DO (1.5–2.0 mg L−1); after that, an optimization period was performed till day 558 to study the influence of applying high DO levels (5.0–8.5 mg L−1). Initial observations at day 118 indicated high settling velocities for granules with a size ≥1.5 mm, with 90 % COD removal achieved since day 35, while exhibiting moderate levels of ammonium (68–71 %) and phosphorus removal (42–44 %). By day 422, the maturation of granules continued, reaching sizes exceeding 3 mm, with a 70 % increase in biomass growth (14.3 g L−1). P-release and P-uptake rates of 52 and 12 mg-P/g-MLVSS·h, respectively, resulted in reduced effluent PO4−3-P (1.5 ± 0.2 mg-P L−1). TN removal performance reached 82 % (NH4-N removal of 88 %), and SND of 99 % was achieved by matured granules maintaining effluent nitrite/nitrate concentrations ≤0.5 ± 0.3 mg-N L−1 (days 330–422). The optimization period was conducted by enhancing biomass mixing conditions and increasing DO, resulting in improved nitrification, with oxidation rate reaching 19.2 mg-NH4/g-MLVSS·h at DO 6 mg L−1. However, DO > 6.5 mg L−1 adversely affected EPS secretion, and granules exhibited poor settleability.

Model-based development of cell voltage control system for modified bio-electro-Fenton process

A modified bio-electro-Fenton (M−BEF) process with a cell voltage control system that improves the efficiency of organic removal and energy savings is demonstrated. The M−BEF process can accomplish bioelectricity generation, H2O2 production, and the Fenton reaction in a continuous-flow reactor. During synthetic wastewater treatment containing biodegradable (glucose) and recalcitrant (biphenyl) organic matter, the effluent chemical oxygen demand (COD) concentration was maintained between 2 and 6 mg L-1. To investigate the impact of different operating schemes on energy usage, model-based design (MBD) modeling and simulations were performed, which showed that COD removal efficiency without an external voltage supply was unstable at < 70 %. The automatic cell voltage control system saved 90 % of the power compared to the continuous cell voltage supply system. Further testing on more environmental samples and pollutants will enable real-time optimization of supplied power and wastewater treatment using the cell voltage control system.

Performance and hydrodynamic study of a new multi‐stage solar photoreactor with immobilized ZnO for synthetic wastewater treatment

AbstractThis study aims to design a new multi‐stage photoreactor with immobilized ZnO and assess its performance in reducing textile wastewater toxicity using solar energy. The electric conductivity measurement is retained as a detection method to obtain the residence time distribution (RTD) function. The RTD is then used to characterize the hydrodynamic behavior of the photoreactor and to evaluate its deviation from the distribution curves of ideal reactors. Solar experiments are conducted to demonstrate the performance of this multistage reactor towards the degradation of a textile azo dye namely Solophenyl Red 3BL (SR 3BL). The influence of the flow rate and the SR 3BL initial concentration (CO) are considered. The variation of the flow rate slightly influences the SR 3BL photodegradation efficiency and it is inversely proportional to its concentration. The study of the reuse of the immobilized catalyst shows that the degradation efficiency of 98% is reached even after multiple photocatalytic cycles. The figure of merit collector area per order was in the range of 35 to 110 . This result provides useful information for scaling up and estimating energy efficiency of the reactor.

Optimal conditions and nitrogen removal performance of aerobic denitrifier Comamonas sp. pw-6 and its bioaugmented application in synthetic domestic wastewater treatment.

To assess the possibility of using aerobic denitrification (AD) bacteria with high NO2--N accumulation for nitrogen removal in wastewater treatment, conditional optimization, as well as sole and mixed nitrogen source tests involving AD bacterium, Comamonas sp. pw-6 was performed. The results showed that the optimal carbon source, pH, C/N ratio, rotational speed, and salinity for this strain were determined to be succinate, 7, 20, 160 rpm, and 0%, respectively. Further, this strain preferentially utilized NH4+-N, NO3--N, and NO2--N, and when NO3--N was its sole nitrogen source, 92.28% of the NO3--N (150 mg·L-1) was converted to NO2--N. However, when NH4+-N and NO3--N constituted the mixed nitrogen source, NO3--N utilization by this strain was significantly lower (p < 0.05). Therefore, a strategy was proposed to combine pw-6 bacteria with traditional autotrophic nitrification to achieve the application of pw-6 bacteria in NH4+-N-containing wastewater treatment. Bioaugmented application experiments showed significantly higher NH4+-N removal (5.96 ± 0.94 mg·L-1·h-1) and lower NO3--N accumulation (2.52 ± 0.18 mg·L-1·h-1) rates (p < 0.05) than those observed for the control test. Thus, AD bacteria with high NO2--N accumulation can also be used for practical applications, providing a basis for expanding the selection range of AD strains for wastewater treatment.

Effects of Alkaline Cleaning Agents on the Long-Term Performance and Aging of Polyethersulfone Ultrafiltration Membranes Applied for Treatment of Car Wash Wastewater.

The commercial ultrafiltration polyethersulfone (PES) membranes (10 and 100 kDa) blended with polyvinylpyrrolidone (PVP) were applied for the filtration of car wash wastewater. Periodical membrane rinsing with water did not prevent fouling and a decrease in permeate flux was observed. Fouling was reduced by washing the membranes with cleaning agents, which are used in car washes to clean wheels and remove insects. In addition to surfactants, these agents contain NaOH, hence the pH value of cleaning solutions was over 11. Long-term contact with such solutions resulted in the removal of PVP from the membrane matrix and an increase in pore size. The PES membranes were soaked in an alkaline solution (pH = 11.5) for 20 months, after which the 200 kDa dextran rejection decreased from 95% to 80%. To compare with the static degradation conditions, 8 weeks of alkaline agent filtration was realized, after which the dextran (200 kDa) rejection decreased below 50%. This indicated that the cross-flow of alkaline agents can accelerate the removal of components building the membrane matrix. Despite membrane degradation, the separation efficiency (the rejection of chemical oxygen demand-COD, turbidity, and surfactants) during the treatment of synthetic car wash wastewater was similar to that obtained for pristine membranes.

Comprehensive evaluation of a novel pilot-scale UVA-LED photoreactor for water treatment applications: Characterization, catalytic efficiency, energy performance and economic viability

A comprehensive assessment was conducted on a novel pilot plant employing a tubular photo-reactor configuration integrated with UVA-LED technology for advanced municipal wastewater treatment applications. The plant consists of eight UVA-LED strips (150 LEDs/strip, 348–400 nm with peak emission at 370 nm) achieving a maximum irradiance of 28.1 W/m2 at 100 % power of the LED, symmetrically distributed across two borosilicate tubes. The iron concentration (0.025–0.100 mM) and UVA-LED irradiance (1.4–28.1 W/m2) combined effect on the photo-Fenton process efficiency was thoroughly examined in synthetic tap water and synthetic municipal wastewater treatment plant (MWWTP) secondary effluent using sulfamethoxazole as model microcontaminant. In general, an LED intensity threshold from which process efficiency reaches a plateau maximum value was found. The determination of the electrical energy per order (EEO) showed higher energy efficiencies as LED intensity decreases, iron concentration increases, and the water matrix is simpler. The lowest EEO obtained was 0.009 kWh/m3·order for 0.10 mM iron concentration in synthetic MWWTP secondary effluent at 5 % LED intensity. The economic study revealed that the weight of operating costs is more significant than the weight of investment costs, regardless of the selected operating conditions. Working with an iron concentration of 0.10 mM helps reduce the total costs, while operating either under excess LED intensity or insufficient LED intensity negatively impacts the total treatment cost. The lowest treatment cost (0.19 €/m3) was obtained with 0.10 mM iron concentration at only 10 % LED intensity. A comparison with the same process driven by natural solar radiation in a raceway pond reactor demonstrated the feasibility of the novel photo-reactor design in terms of treatment cost.

Machine learning approaches to predict adsorption performance of sugarcane derived-carbon dot −based composite in the removal of dyes

This study presents a sustainable and low-cost approach to uniformly blend nanofillers (TiO2) and CDs) into chitosan polymer matrices, aiming to enhance the adsorption capacity and regeneration efficiency of the composite. The effect of degree of deacetylation on the composite was examined using crosslinkers EDA and ECH, achieving a DD of 78.8 % and demonstrating improved chemical and thermal stability compared to chitosan alone. Furthermore, SEM, TEM, and EDX mapping confirmed successful dispersion of nanofillers within the crosslinked chitosan matrix, with excellent adsorption performance towards cationic and anionic dyes (1666.67 mg/g and 1630 mg/g, respectively). The study also presents a novel approach that employs machine learning techniques to accurately predict optimization results. This study combines experiments and AI techniques using Python and machine learning algorithms on a dataset of over 600 experiments, achieving high forecast accuracy with the Random Forest model, evidenced by an R2 value of 1 and the lowest mean squared error for both dyes. The adsorption process followed Freundlich and the pseudo-second-order model. The statistical physical model explained a mixed orientation of anionic dye molecules and a multi-molecular mechanism of cationic dye molecules over nanocomposite, with FTIR results indicating electrostatic attraction, π-π interaction, and hydrogen bonding as key factors in the adsorption process. The composite material used in the study showed a consistent ability to adsorb dyes over 5 regeneration cycles in the column adsorption study, indicating its reusability. The results of this comprehensive investigation contribute to advancing sustainable wastewater treatment through the development of innovative nanocomposites and the use of sophisticated modelling techniques.

Role of biochar addition to improve anaerobic membrane bioreactors to resist oil stress in synthetic food wastewater treatment

This study investigated biochar addition to improve the performance and stability of anaerobic membrane bioreactor (AnMBR) to resist different oil contents in food wastewater treatment. Results show that an increase in oil content in synthetic food wastewater from 2 to 4 g/L of oleate-Na aggravated AnMBR performance in terms of methane (CH4) production and membrane fouling as showed by an obvious increase in transmembrane pressure (TMP). The reduced performance was caused by the accumulation of volatile fatty acids (VFAs) to inhibit the growth and activity of Methanobacterium in response to increased oil content. Nevertheless, biochar addition improved AnMBR resistance to against oil increase. The dominance of Methanobacterium and their potential mutualism with genus T78 were enhanced by biochar to sustain CH4 yield. Moreover, biochar reduced the production of extracellular polymeric substance (EPS) to alleviate membrane fouling.

Impact of Combined Electrolysis and Activated Sludge Process on Municipal Wastewater Treatment

Electrochemical methods for the treatment of municipal and industrial wastewater are used either independently or in conjunction with biological methods for pretreatment or posttreatment of biologically treated wastewater. In our work, the combination of these processes was studied, where pre-electrolysis was used to produce dissolved iron before the activation process. Electrolysis was also directly introduced into the activation using either iron or carbon electrodes. The surface of one iron electrode was 32.2 cm2, voltage at the electrodes was 21 V, and current was 270 mA. The surface of one carbon electrode was 7.54 cm2, current was 82.5 mA, and voltage at the electrodes was 21 V. Laboratory research on synthetic municipal wastewater treatment using a combination of electrolysis and activation processes showed that the use of iron electrodes increases the efficiency of phosphorus removal compared to its precipitation with iron salts. Electrolysis has shown a positive effect on the sedimentation properties of sludge and the destruction of filamentous microorganisms. Even though it negatively affected the respiration rates of activated sludge and the denitrification efficiency, it did not have a negative impact on the nitrification activity of sludge.

Synergistic degradation efficiency of nitrogen, phosphorus and microbial dynamic succession driven by a novel strain Gordonia sp. D4 during synthetic wastewater treatment

Nitrogen (N) and phosphorus (P) coexist in the industrial and domestic wastewater posed a pressing challenge for synergistic removal of N and P by bioenhancement. In this study, a novel denitrifying phosphorus-accumulating organism (DPAO) of Gordonia sp. D4, exhibited peak NO3--N, NO2--N, NH4+-N and TP removal efficiencies of 98.11%, 65.02%, 85.34% and 100%, corresponding to 9.30 mg/(L·h), 6.08 mg/(L·h), 3.63 mg/(L·h) and 0.47 mg/(L·h) removal rates, respectively. Strain D4 contained the nitrogen cycling genes narK, narI, narJ, narH, narG, nirB and nirD, as well as the phosphorus cycling genes ppk1, ppk2 and ppx-gppA, which contributes to its excellent simultaneous removal of N and P. More importantly, the addition of D4 into the sequencing batch reactor (SBR) significantly improved the P, TN and NO3--N removal efficiencies by 18.91%, 7.35%, and 18.55%, respectively. This was closely related to the clear enrichment of Gordonia and its contribution to the increasing abundances of Pararhodobacter, unclassified_f_Cyclobacteriaceae, unclassified_o_Rhodospirillales, Thauera and Candidatus Promineofilum and their associated functional genes that drive P or N removal, thereby enhancing the N and P synergistic degradation efficiency. This study provides a valuable strain resource and process reference for the simultaneously removing N and P from the wastewater.

Improving antifouling performance of FO membrane by surface immobilization of silver nanoparticles based on a tannic acid: diethylenetriamine precursor layer for municipal wastewater treatment.

In this study, a facile method for multifunctional surface modification on forward osmosis (FO) membrane was constructed by surface immobilization of AgNPs based on tannic acid (TA)/diethylenetriamine (DETA) precursor layer. The cellulose triacetate (CTA) FO membranes modified by TA and DETA with different co-deposition time (6 h, 12 h, 24 h) were investigated. Results indicated that the TA/DETA (24)-Ag CTA membrane with a TA/DETA co-deposition time of 24 h was identified to be optimal, which attained more hydrophilic. And it had the bacterial mortality of Escherichia coli and Staphylococcus aureus reaching 98.23% and 99.83% respectively and possessed excellent physical and chemical binding stability. Meanwhile, the coating layer resulted in the antifouling ability without damaging the membrane intrinsic transport characteristics. As for synthetic municipal wastewater treatment, the water flux of CTA FO membrane decreased approximately 49% of the initial flux after running for 14 days. In contrast, the flux decline rate of TA/DETA (24)-Ag CTA membrane was about 37%. Furthermore, less foulant deposition and higher recovery rate of water flux was observed for TA/DETA (24)-Ag CTA membrane, implying that the modified membrane effectively alleviated membrane fouling and processed a lower flux decline during municipal wastewater treatment. It was attributed to the enhanced surface hydrophilicity and antibacterial property of the coating layer, which improved antifouling property.

Application of fluidized bed homogeneous crystallization for simultaneous recovery of Fe(II) and Cu(II) as particles from wastewater

The mixture of copper and iron often results in materials with favorable properties. The material production processes involving these metals including electroplating produce hazardous wastewater. In this study, the Fluidized Bed Homogeneous Crystallization (FBHC) process was applied to treat iron and copper-containing wastewater. The initial iron copper particles were successfully recovered from synthetic wastewater with [Fe]0:[Cu]0 of 2:1, the total metal concentration of 3 mM, at effluent pH = 7.75 ± 0.75, with the upflow velocity (U) of 1.76 m/h. The agglomerates hardening process is a crucial step for initial particle synthesis. The SEM analysis reveals the spherical particle's densified crust and porous core. The particle formation mechanism which includes the formation of the nucleus, attachment of precipitate flakes, and densification of particles was proposed after microscopic observation. The initial particles synthesized were used to initiate the treatment of synthetic wastewater at the operating condition pH = 7.75 ± 0.5, [Fe]0:[Cu]0 of 2:1, the total metal concentration of 3 mM, [CO32−]0:[M]0 = 1.2:1, and U of 28.66 m/h which results in the total metal removal of 99% and crystallization ratio of 90% and 88% for iron and copper respectively. The conditions were then applied to treat electroplating wastewater and resulted in the total metal removal of 99% for both iron and copper and a crystallization ratio of 83% and 79% for iron and copper, respectively. The treatment provided advantages in terms of treating larger amounts of sludge while eliminating the need to provide seed thus yielding a higher purity of product.

Upcycling nitrogen and curbing greenhouse gas emissions from wastewater through H2-driven assimilatory mixotrophic metabolism

Biological nitrogen assimilation is an emerging technique for the removal and upcycling of nitrogen from wastewater in the form of microbial protein (MP). For this purpose, a mixed hydrogen-oxidizing bacteria (HOB) culture capable of growing mixotrophically was evaluated for the treatment of synthetic and real wastewater under different carbon-to-nitrogen (C/N) ratios. The same mixed HOB culture was grown under heterotrophic conditions to compare treatment and process performances in terms of ammonium nitrogen (N-NH4+) removal and assimilation, chemical oxygen demand (COD) removal, CO2 release, biomass concentration, yield and protein content. Under mixotrophic conditions, the highest biomass concentration was 342.5 mg VSS∙L−1, doubling that obtained under heterotrophic conditions (161.2 mg VSS∙L−1). Discharge limits for both COD and total N were met under mixotrophic conditions, with nitrogen removal and assimilation into protein-rich biomass achieving up to 99 %. On the contrary, under heterotrophic conditions, the high content of residual nitrogen as nitrite (up to 26 mg∙L−1 of N-NO2−) did not allow to meet discharge limits for total N. The mixed HOB culture gave promising results in terms of biomass yield (0.32 g VSS·g CODH2+acetate−1) and protein content (up to 56 % of VSS) when grown mixotrophically. Under heterotrophic conditions, instead, the biomass yield (0.25 g VSS·g CODacetate−1) and protein content (35 %) were substantially lower. This study suggests that the H2-driven assimilatory mixotrophic metabolism can be successfully applied for wastewater treatment to produce effluents that meet discharge limits while mitigating greenhouse gas emissions (CO2 and N2O) and upcycling nitrogen into MP.