Preparation of composite adsorbents of activated carbon supported MgO/MnO2 and adsorption of Rhodamine B.

Activated carbon (AC) was modified by MgO and MnO2 through an impregnation-precipitation-calcination procedure. The batch experiments of adsorption of Rhodamine B (RB) by a modified adsorption material, an MgO-MnO2-AC composite, were carried out and the characteristics of the composite adsorbent were evaluated. The results showed that manganese/magnesium loading changed the surface area, pore volume and increased the number of active adsorption sites of AC. The highest Brunauer-Emmett-Teller (BET) surface area (1,036.18 m2·g-1) was obtained for MgO-MnO2-AC compared with AC. The content of AC loaded with magnesium and manganese was 34.24 and 5.51 mg·g-1 respectively. The adsorption of RB on MgO-MnO2-AC was significantly improved. The maximum adsorption capacity of RB on MgO-MnO2-AC was 16.19 mg·g-1 at 25 °C under the RB concentration of 50 mg·L-1. The adsorption of RB by AC and MgO-MnO2-AC increased with the initial concentration of RB. The adsorption of RB increased first and then decreased when pH was between 3 and 11. The results indicated that the pseudo-second-order kinetic equation and Langmuir equation can be used to describe the adsorption of RB on MgO-MnO2-AC.

Effect of kaolin on floc properties for reactive orange removal in continuous coagulation process.

Magnesium hydroxide was used as a coagulant for treating reactive orange wastewater in a real continuous process. Effects of kaolin on coagulation performance and floc properties were investigated with controlled experiments through floc size distribution, zeta potential, scanning electron microscopy and Fourier transform infrared spectroscopy. Kaolin had significant influence on magnesium hydroxide-reactive orange floc formation and growth. The results showed that average floc size reached 16.31, 12.88 and 20.50 µm, respectively, in the rapid mixer, flocculation basin and sedimentation tank when kaolin concentration was 10 mg/L and reactive orange initial concentration was 0.25 g/L. The floc size tended to increase with the increase of kaolin suspension to 10 mg/L. All of the flocs under investigation showed that floc breakage led to decreased average floc size and remained stable in the flocculation basin. Reactive orange and kaolin could be removed effectively in the continuous coagulation process. Reactive orange was adsorbed in the surface of magnesium hydroxide through charge neutralization and adsorption.

Adsorption behavior and mechanism of cu(II) by sodium alginate/carboxymethylcellulose/magnesium hydroxide (SC-MH) hydrogel.

In the present work, an environmentally-friendly, reusable hydrogel ball characterized by its great adsorption capacity to Cu(II) was synthesized. The preparation of this hydrogel drew on sodium alginate (SA) and carboxymethyl cellulose (CMC) as primary composition elements. The endeavor brought novelty by ingeniously infusing it with slurry magnesium hydroxide (MH). The factors (pH, SC-MH amount, initial concentration, adsorption time) that are critical to adsorption were also investigated. FTIR, SEM-EDS and XPS were used to reveal the adsorption mechanism of Cu on SC-MH. The results show that the surface of SC-MH is rough, and there are a large number of gully-like structures conducive to adsorption, which are rich in hydroxyl and carboxyl groups. Under the optimum conditions, the maximum adsorption capacity reached 215.68 mg/g. Based on its high R2 value (0.999), the Langmuir model is determined to be the most appropriate for describing the adsorption behavior, indicating monolayer homogeneous adsorption. The kinetic data align well with the pseudo-second-order kinetic model. Furthermore, thermodynamic analysis reveals the adsorption process to be spontaneous and endothermic, as demonstrated by a negative ΔG and positive ΔH (38.8859 KJ/mol). The mechanism involves electrostatic attraction, chelation, Mg(OH)2 adsorption and ion exchange.

Recovery of ammonia nitrogen from simulated reject water by bipolar membrane electrodialysis.

Ammonia monohydrate (NH3·H2O) is an important chemical widely used in industrial, agricultural, and pharmaceutical fields. Reject water is used as the raw material in self-built bipolar membrane electrodialysis (BMED) to produce NH3·H2O. The effects of electrode materials, membrane stack structure, and operating conditions (current density, initial concentrations of the reject water, and initial volume ratio) on the BMED process were investigated, and the economic costs were analyzed. The results showed that compared with graphite electrodes, ruthenium-iridium-titanium electrodes as electrode plates for BMED could increase current efficiency (25%) and reduce energy consumption (26%). Compared with two-compartment BMED, three-compartment BMED had a higher ammonia nitrogen conversion rate (86.6%) and lower energy consumption (3.5 kW· h/kg). Higher current density (15 mA/cm2) could achieve better current efficiency (79%). The BMED performances were improved when the initial NH4+ concentrations of the reject water increased from 500 mg NH4+/L to 1000 mg NH4+/L, but the performance decreased as the concentration increased from 1000 mg NH4+/L to 1500 mg NH4+/L. High initial volume ratio of the salt compartment and product compartment was beneficial for reducing energy consumption. Under the optimal operating conditions, only 0.13 $/kg reject water was needed to eliminate the environmental impact of reject water accumulation. This work indicates that BMED can not only achieve desalination of reject water, but also generate products that alleviate the operational pressure of factories.

Rapid start-up of an innovative pilot-scale staged PN/A continuous process for enhanced nitrogen removal from mature landfill leachate via robust NOB elimination and efficient biomass retention.

The start-up and stable operation of partial nitritation-anammox (PN/A) treatment of mature landfill leachate (MLL) still face challenges. This study developed an innovative staged pilot-scale PN/A system to enhance nitrogen removal from MLL. The staged process included a PN unit, an anammox upflow enhanced internal circulation biofilm (UEICB) reactor, and a post-biofilm unit. Rapid start-up of the continuous flow PN process (full-concentration MLL) was achieved within 35 days by controlling dissolved oxygen and leveraging free ammonia and free nitrous acid to selectively suppress nitrite-oxidizing bacteria (NOB). The UEICB was equipped with an annular flow agitator combined with the enhanced internal circulation device of the guide tube, which achieved an efficient enrichment of Candidatus Kuenenia in the biofilm (relative abundance of 33.4 %). The nitrogen removal alliance formed by the salt-tolerant anammox bacterium (Candidatus Kuenenia) and denitrifying bacteria (unclassified SBR1031 and Denitratisoma) achieved efficient nitrogen removal of UEICB (total nitrogen removal percentage: 90.8 %) and at the same time effective treatment of the refractory organic matter (ROM). The dual membrane process of UEICB fixed biofilm combined with post-biofilm is effective in sludge retention, and can stably control the effluent suspended solids (SS) at a level of less than 5 mg/L. The post-biofilm unit ensured that effluent total nitrogen (TN) remained below the 40 mg/L discharge standard (98.5 % removal efficiency). Compared with conventional nitrification-denitrification systems, the staged PN/A process substantially reduced oxygen consumption, sludge production, CO2 emissions and carbon consumption by 22.8 %, 67.1 %, 87.1 % and 87.1 %, respectively. The 195-day stable operation marks the effective implementation of the innovative pilot-scale PN/A process in treating actual MLL. This study provides insights into strategies for rapid start-up, robust NOB suppression, and anammox biomass retention to advance the application of PN/A in high-ammonia low-carbon wastewater.

Carbon footprint analysis and comprehensive evaluation of municipal wastewater treatment plants under different typical upgrading and reconstruction modes.

The issue of greenhouse gas (GHG) emissions resulting from the upgrading and reconstruction of municipal wastewater treatment plants (MWWTPs) along with improved water quality is receiving attention and research. There is an urgent need to explore the impact of upgrading and reconstruction on carbon footprint (CF) in order to address concerns that the upgrading and reconstruction will increase GHG emissions while improving water quality. Here we accounted for the CF of five MWWTPs in Zhejiang Province, China, before and after three different upgrading and reconstruction models - "Improving quality and efficiency" ("Mode I"), "Upgrading and renovation" ("Mode U") and "Improving quality and efficiency plus Upgrading and renovation" ("Mode I plus U"). The upgrading and reconstruction was found to not necessarily result in more GHG emissions. In contrast, the "Mode I" had a more significant advantage in terms of CF reduction (1.82-12.6 % reduction in CF). Overall, the ratio of indirect emissions to direct emissions (indirect emissions/direct emissions) and the amount of GHG emitted per unit of pollutant removed (CFCOD、CFTN、CFTP) decreased, while both the carbon and energy neutral rates increased significantly (up to 33.29 % and 79.36 % respectively) after all three upgrading and reconstruction modes. In addition, the wastewater treatment efficiency and capacity are the main factors that affect the level of carbon emission. The results of this study can provide a calculation model that can be used for other similar MWWTPs during the upgrading and reconstruction processes. More importantly, it can provide a new research perspective as well as valuable information to revisit the impact of upgrading and reconstruction in MWWTPs on GHG emissions.

Applying real-time control for achieving nitrogen removal via nitrite in a lab-scale CAST system.

In this study, a bench-scale Cyclic Activated Sludge Technology (CAST) reactor (72?L), fed with domestic sewage, was operated in alternating anoxi-aerobic operation mode to investigate the feasibility of achieving short-cut nitrification and denitrification with a real-time control strategy. An online system for controlling the length of the aeration and stirring phases was implemented, based on pH and oxidation-reduction potential signals, to switch between aerobic and anoxic sequences. Results show that the real-time control strategy was successful in achieving a stable nitrogen removal performance. Furthermore, short-cut nitrification can be achieved by controlling aeration length under the modified real-time control strategy. Gradually reducing the energy supply for nitrite-oxidizing bacteria caused the limitation of their growth and, finally, their elimination. When short-cut nitrification was obtained, the nitrite pathway became the primary way for nitrogen removal, and aeration duration was reduced by 28.4%.

Comparison between thermophilic and mesophilic anaerobic digestion of waste activated sludge by combined NaOH-microwave pretreatment.

The purpose of this study was to investigate the performance of the thermophilic and mesophilic anaerobic digestion process (TADP, MADP) fed with NaOH-microwave pretreated waste activated sludge. The experiment was conducted in anaerobic CSTR reactors. During this experiment, the reactors were stable in operation and were not inhibited by ammonia. The methane production and reduction of organic matters from MADP were less than those from TADP. The dewatering performance of mesophilic sludge was better than that of the thermophilic sludge. The experimental results showed that the continuous TADP and MADP were effective, when the reactors were fed with the waste activated sludge pretreated by NaOH-microwave. MADP was more suitable to combine the NaOH-MW pretreatment process than TADP.

Enhancement of thermophilic anaerobic digestion of thickened waste activated sludge by combined microwave and alkaline pretreatment.

Abstract Pretreatment of thickened waste activated sludge (TWAS) by combined microwave and alkaline pretreatment (MAP) was studied to improve thermophilic anaerobic digestion efficiency. Uniform design was applied to determine the combination of target temperature (11 degrees-210 degrees C), microwave holding time (1-51 min), and NaOH dose (0-2.5 g NaOH/g suspended solids (SS)) in terms of their effect on volatile suspended solids (VSS) solubilization. Maximum solubilization ratio (85.1%) of VSS was observed at 210 degrees C with 0.2 g-NaOH/g-SS and 35 min holding time. The effects of 12 different pretreatment methods were investigated in 28 thermophilic batch reactors by monitoring cumulative methane production (CMP). Improvements in methane production in the TWAS were directly related to the microwave and alkaline pretreatment of the sludge. The highest CMP was a 27% improvement over the control. In spite of the increase in soluble chemical oxygen demand concentration and the decrease in dewaterability of digested sludge, a semi-continuous thermophilic reactor fed with pretreated TWAS without neutralization (at 170 degrees C with 1 min holding time and 0.05 g NaOH/g SS) was stable and functioned well, with volatile solid (VS) and total chemical oxygen demand (TCOD) reductions of 28% and 18%, respectively, which were higher than those of the control system. Additionally, methane yields (L@STP/g-CODadded, at standard temperature and pressure (STP) conditions of 0 degree C and 101.325 kPa) and (L@STP/g VSadded) increased by 17% and 13%, respectively, compared to the control reactor.

Startup and performance of a novel single-stage partial nitritation/anammox system for reject water treatment.

A novel internal circulation contact oxidation membrane bioreactor (ICCOMBR) was constructed to investigate a three steps startup strategy of single-stage partial nitritation-anammox (SPNA) system. A stable nitrite accumulation rate (NAR) of 86.60% was achieved with NH4+-N over 250 mg/L in nitritation process. The partial nitritation process could be effectively achieved by reducing the aeration rate (AR) by about 50% in the nitritation process, with an effluent NO2--N/NH4+-N ratio of 1.15 ± 0.04. The SPNA system was started up in 27 days following the inoculated anammox granular sludge. A total nitrogen removal efficiencies of 82% was achieved at a NLR of 0.60 gN/L/d and dissolved oxygen (DO) concentration below 0.55 mg/L. Anammox function genus (Ca.Kuenenia and Ca. Anammoximicrobium) abundance accounted for 20.77% in the biofilm, which is approximately equal to 22.2% in the suspended sludge. Nitrosomon as the dominant AOB genera, was detected in the biofilm (6.5%) and suspended sludge (13.3%).

Impact of the acetate/oleic acid ratio on the performance, quorum sensing, and microbial community of sequencing batch reactor system.

This study comprehensively investigated the impact of acetate/oleic acid ratios (80%/20%, 60%/40%, 40%/60%, and 20%/80%) on sequencing batch reactor (SBR) with respect to the variations in performance, quorum sensing (QS), and microbial community. Results showed that NH+4-N removal was not affected by the acetate/oleic acid ratios, while the COD, total nitrogen (TN), and PO3-4-P removal was considerably affected. The increasing oleic acid ratios led to severe sludge bulking, which was significantly positively correlated with proteins/polysaccharides (p < 0.001). The correlation of QS with the performance and sludge properties was also observed. High-throughput sequencing demonstrated that microbial compositions considerably shifted with varying acetate/oleic acid ratios. Moreover, the potential correlation of bacterial genera with the SBR performance and QS was proposed. This study elucidated the effect of acetate/oleic acid ratios on SBR from microbial viewpoint, which provided insights into fully understanding the essential roles of carbon source on wastewater treatment.

Thermophilic anaerobic digestion reduces ARGs in excess sludge even under high oxytetracycline concentrations.

The feasibility of thermophilic anaerobic digestion (AD) for the attenuation of antibiotic resistance genes (ARGs) in biomass wastes under high antibiotic concentrations remains unclear. In this study, a thermophilic completely stirred digester (55 °C) was fed with municipal excess sludge spiked with increasing concentrations of oxytetracycline (OTC) (0-1000 mg/L) over a period of 280 days. Results showed that thermophilic AD could maintain stable methane production (338.40 ±â€¯26.26 mL/d/gVS) even at an OTC dose of 1000 mg/L with the sludge phase OTC concentration reaching around 24,000 mg/kg. More important, the abundance of resistome detected by high-throughput quantitative PCR in the substrate was reduced (p < 0.01) by 55.54%-86.27% by thermophilic AD over the whole period. Partial canonical correspondence and network analyses showed that the reduction of ARGs was achieved mainly through two ways: eliminating the original hosts of ARGs in the substrate (from 41.74% ±â€¯2.60% in the substrate to 12.08% ±â€¯1.02% in digested sludge), and blocking the horizontal proliferation of ARGs in the digested sludge by reducing the abundance of mobile genetic elements and restricting their horizontal exchange within a small number of thermophilic genera. This study showed that thermophilic AD is feasible for the attenuation of ARGs in biomass even containing high level of OTC.

Insights into the effects of carbon source on sequencing batch reactors: Performance, quorum sensing and microbial community.

Effects of carbon source on the performance, quorum sensing (QS) and microbial communities in the sequencing batch reactors were investigated in this work. Among the chosen carbon source, sodium acetate (R1), glucose (R2), starch (R3) and Tween 80 (R4), sodium acetate was the best carbon source for nutrient removal, while starch was favorable for inducing the sludge bulking, and Tween 80 was beneficial to the production of extracellular polymeric substances (EPS) and proliferation of Microthrix parvicella. Additionally, the R2 value of linear correlation between sludge settleability and particle size in four reactors followed an order of R1 > R2 > R3 > R4. Moreover, Person correlation analysis showed that various significant correlations were observed in reactors fed with different carbon sources and the QS mainly mediated the production and component of EPS. High-throughput sequencing analysis revealed that the carbon source affected microbial communities and the Canonical correspondence analysis results indicated that QS related to microbial communities. It was inferred that the interactions between microbial communities and QS affected system performance.

Rapid establishment of thermophilic anaerobic microbial community during the one-step startup of thermophilic anaerobic digestion from a mesophilic digester.

The purpose of this study was to explore how fast the thermophilic anaerobic microbial community could be established during the one-step startup of thermophilic anaerobic digestion from a mesophilic digester. Stable thermophilic anaerobic digestion was achieved within 20 days from a mesophilic digester treating sewage sludge by adopting the one-step startup strategy. The succession of archaeal and bacterial populations over a period of 60 days after the temperature increment was followed by using 454-pyrosequencing and quantitative PCR. After the increase of temperature, thermophilic methanogenic community was established within 11 days, which was characterized by the fast colonization of Methanosarcina thermophila and two hydrogenotrophic methanogens (Methanothermobacter spp. and Methanoculleus spp.). At the same time, the bacterial community was dominated by Fervidobacterium, whose relative abundance rapidly increased from 0 to 28.52 % in 18 days, followed by other potential thermophilic genera, such as Clostridium, Coprothermobacter, Anaerobaculum and EM3. The above result demonstrated that the one-step startup strategy could allow the rapid establishment of the thermophilic anaerobic microbial community.