Enhanced treatment of landfill leachate by biochar-based aerobic denitrifying bacteria functional microbial materials: Preparation and performance.

Objective: In this work, polyvinyl alcohol (PVA) and sodium alginate (SA) were used as entrapped carriers and Artemisia argyi stem biochar (ABC) was used as an absorption carrier to immobilize aerobic denitrifying bacteria screened from landfill leachate, thus a new carbon-based functional microbial material (PVA/SA/ABC@BS) was successfully prepared. Methods: The structure and characteristics of the new material were revealed by using a scanning electron microscope and Fourier transform infrared spectroscopy, and the performance of the material for treating landfill leachate under different working conditions was studied. Results: ABC had abundant pore structures and that the surface contained many oxygen-containing functional groups, carboxyl groups, and amide groups, etc. and it had good absorbing performance and strong acid and alkali buffering capacity, which was beneficial to the adhesion and proliferation of microorganisms. After adding ABC as a composite carrier, the damage rate of immobilized particles was decreased by 1.2%, and the acid stability, alkaline stability, and mass transfer performance were increased by 9.00, 7.00, and 56%, respectively. When the dosage of PVA/SA/ABC@BS was 0.017g/ml, the removal rates of nitrate nitrogen (NO3 --N) and ammonia nitrogen (NH4 +-N) were the highest, which were 98.7 and 59.4%, respectively. When the pH values were 11, 7, 1, and 9, the removal rates of chemical oxygen demand (COD), NO3 --N, nitrite nitrogen (NO2 --N) and NH4 +-N reached the maximum values, which were 14.39, 98.38, 75.87, and 79.31%, respectively. After PVA/SA/ABC@BS was reused in 5 batches, the removal rates of NO3 --N all reached 95.50%. Conclusion: PVA, SA and ABC have excellent reusability for immobilization of microorganisms and degradation of nitrate nitrogen. This study can provide some guidance for the great application potential of immobilized gel spheres in the treatment of high concentration organic wastewater.

Elevated salinity deteriorated enhanced biological phosphorus removal in an aerobic granular sludge sequencing batch reactor performing simultaneous nitrification, denitrification and phosphorus removal.

Hypersaline wastewater may pose threats to biological wastewater treatment processes. An aerobic granular sludge-based sequencing batch reactor (SBR) performing simultaneous nitrification, denitrification and phosphorus removal (SNDPR) was evaluated with increased salinity from 1 to 2 % (w/v). Nitrogen removal performance was unaffected by salinity up to 20 g/L in terms of reliable and efficient nitrification and denitrification. Enhanced biological phosphorus removal (EBPR) process was completely deteriorated at salinity up to 2 %, in contrast to excellent phosphorus removal at 1 %. Profiles of phosphorus over one cycle demonstrated that higher salinity not only inhibited anaerobic phosphorus release but also impeded aerobic/anoxic phosphorus uptake. Illumina MiSeq sequencing revealed multiple halophilic and non-halophilic bacteria within aerobic granules with family Anaerolineaceae being the predominant potential salt adapter. Besides, ammonia oxidizing bacteria (AOB), glycogen accumulating organisms (GAOs) were more tolerant to salt than nitrite oxidizing bacteria (NOB) and phosphorus accumulating organisms (PAOs) and denitrifying PAOs (DNPAOs). These results deciphered the resilience of aerobic granular sludge-based biological nitrogen and phosphorus removal processes to hypersaline stress.

Novel pectin based composite hydrogel derived from grapefruit peel for enhanced Cu(II) removal.

Novel biochar/pectin/alginate hydrogel beads (BPA) derived from grapefruit peel were synthesized and used for Cu(II) removal from aqueous solution. FTIR, SEM-EDS, XRD, TGA and XPS, etc. were applied for characterization analysis. The synergistic reinforcing effect of polymer matrix and biochar fillers improved the adsorptive, mechanical and thermostabilized performance of BPA. Factors like component contents of biochar and pectin, pH, contact time, Cu(II) concentration and coexisting inorganic salts or organic ligands were systematically investigated in batch mode. The adsorption isotherms were fitted well by the Freundlich model and the experimental maximum adsorption capacity of optimized BPA-9 beads (mass ratio of pectin to alginate = 10:1) with 0.25% biochar, was ∼80.6 mg/g at pH 6. Kinetic process was well described by the pseudo-second-order model and film diffusion primarily governed the overall adsorption rate, followed by intraparticle diffusion. Thermodynamics analysis suggested spontaneous feasibility and endothermic nature of adsorption behavior. Moreover, BPA also showed better environmental adaptability in the presence of NaCl, MgCl2, CaCl2, EDTA-2Na and CA as well as good adsorption potential for other heavy metal [e.g. Pb(III)]. Crucially, the BPA beads showed good regeneration ability after five cycles. All these results indicated the potential of BPA for removing heavy metal from water.

Enhanced simultaneous nitrification, denitrification and phosphorus removal through mixed carbon source by aerobic granular sludge.

Aerobic granular sludge-based simultaneous nitrification, denitrification and phosphorus removal (SNDPR) systems were configured for the treatment of low-strength municipal wastewater. Granular characteristics, process performance, and the corresponding microbial ecology dynamics were comprehensively explored with sodium acetate and succinate as mixed carbon source. Results revealed that aerobic granules kept structural and functional resilience, while mixed carbon source largely altered and balanced the growth and competition of phosphorus/glycogen accumulating organisms (PAOs/GAOs). Appropriate ratio of mixed carbon source was vital for superb physiochemical behaviors and reliable removal performance by aerobic granules. Therefore, the aerobic granular SNDPR system could achieve deep-level nutrients removal through enhancing the anaerobic carbon uptake rate and strengthening the carbon usage efficiency. The present work could add some guiding sight into the application of aerobic granular SNDPR system for wastewater treatment.

A comprehensive comparison between non-bulking and bulking aerobic granular sludge in microbial communities.

Filamentous sludge bulking poses great threats to operational stability of aerobic granular sludge. Exploration of the microbial community aids knowledge of the causative factors to sludge bulking and guides directions for corresponding actions for prevention and controlling. Detailed changes of bacterial community within the non-bulking and bulking were performed and compared with a non-specific method through 1‰ (v/v) hydrogen peroxide (H2O2) addition. Results revealed that non-bulking/bulking granules maintained effective carbon and nitrogen removal, while bulking completely deteriorated enhanced biological phosphorus removal (EBPR). Excess extracellular polymeric substances (EPS) especially polysaccharide (PS) were directly linked with sludge bulking and abundant PS contributed to subsequent granular re-stability. Filamentous bulking dramatically altered the bacterial populations and 1‰ H2O2 effectively controlled bulking by eliminating causative filaments Singulisphaera and Thiothrix. Together, this study provides new insights into the non-bulking/bulking granules and could direct the prevention and control of filamentous bulking in aerobic granules.

Highly efficient removal of Cr(VI) and Cu(II) by biochar derived from Artemisia argyi stem.

In this work, a novel biochar was prepared from the Artemisia argyi stem at 300 °C (AS300), 450 °C (AS450), and 600 °C (AS600). The structural properties of these biochars were characterized with various tools. The sorption kinetic processes of Cr(VI) and Cu(II) onto these biochars were better described by the pseudo-second order. The sorption isotherm processes of Cr(VI) onto these biochars were better described by the Freundlich model while the adsorption processes of Cu(II) were consistent with the Langmuir model. Batch sorption experiments showed that AS600 had the maximum adsorption capacity to Cr(VI) and Cu(II) with 161.92 and 155.96 mg/g, respectively. AS600 was selected for the follow-up batch and dynamic adsorption experiments. Results showed that AS600 had larger adsorption capacity for Cr(VI) at lower pH while the larger adsorption capacity for Cu(II) was found at higher pH. The effect of ionic strength on the adsorption of Cu(II) by AS600 was greater than that on the adsorption of Cr(VI). Dynamic adsorption experiments showed that Cu(II) had a higher affinity for the adsorption sites on the AS600 compared with Cr(VI). The adsorption mechanisms mainly involved electrostatic attraction, ion exchange, pore filling, and chemical bonding effect. Graphical abstract.

Hybrid functionalized chitosan-Al2O3@SiO2 composite for enhanced Cr(VI) adsorption.

In this study, we prepared a novel hybrid functionalized chitosan-Al2O3@SiO2 composite (FCAS) for removing hexavalent chromium [Cr(VI)] from aqueous system. Spectroscopic studies like Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and energy dispersive spectroscope (EDS) were characterized. The effects such as dosage of adsorbent, pH, contact time and initial Cr(VI) concentration were evaluated. It has been illustrated that a wide acidic condition in the pH range of 2-6 was conducive to Cr(VI) adsorption and only 10 min was required to reach about 80% adsorption. Also, the adsorption properties of prepared adsorbent such as kinetics, thermodynamics and isotherms were comprehensively studied. Additionally, the adsorption capacity barely declined even after five cycles. Studies found that FCAS with characteristics of high performance of adsorption rate and capacity and better reusability would be a potential adsorbent for wastewater treatment.