Alumina is typically produced from bauxite ore using the Bayer process, in which the ore is mixed with alkaline liquor under elevated temperatures. Australian bauxite ore contains a wide range of ...organics, which detrimentally affect the Bayer process. Therefore, the removal of organic compounds from the alkaline Bayer process liquor is critical in maintaining process efficiency and alumina quality. Oxalate (C2O42−) is a key organic impurity in the Bayer process liquors that requires removal as it increases in concentration in the processing circuit as the Bayer liquor is continually recycled. Compared to conventional physiochemical or physical methods (e.g., chemical precipitation, wet-oxidation, liquor burning), microbial bioreactor treatment processes have the potential to be more economical and environmentally sustainable for oxalate removal. Some Australian alumina refineries have implemented full-scale bioreactors such as moving bed biofilm reactors (MBBRs) and aerobic suspended growth bioreactors (ASGB). While these bioreactors are robust and effective in removing oxalate, they have some limitations, such as the need for pre-acidification of influent and the loss of ammonia (nutrient) through volatilization. Therefore, this study aimed to provide an overview of the fundamentals and recent advances in biotechnical processes for the treatment of alkaline oxalate-containing liquor. Laboratory-scale studies on promising new biotreatment concepts, such as the use of bioelectrochemical systems to facilitate concurrent oxalate degradation and caustics recovery, as well as the utilization of nitrogen-fixing microorganisms to obviate the requirement for external nutrient dosage, are discussed. Perspectives for further research on oxalate-containing waste streams are also proposed.
•Oxalate and other organics accumulate in highly alkaline and saline Bayer liquors.•Biodegradation shows promise for destructing problematic organics.•Various bioreactors, microbes and pathways can be used for oxalate degradation.•Bioelectrochemical systems (BES) enable organics destruction and caustic recovery.•BES reduce ammonia losses and emissions compared to aerobic bioreactors.
The production of excess sludge by the activated sludge system of wastewater treatment plants is a problem. In this study, the EPS characteristics on production and degradation were investigated in ...the real-scale food processing wastewater treatment system (i.e., a micro-aerobic reactor coupled with a membrane bioreactor (MAR-MBR)) with a treatment capacity of 150 t d−1, which could cater for the low production of excess sludge (i.e., 9 t·a−1; 76% moisture content). The total organic carbon concentrations in the different EPS fractions were in the following order: soluble EPS (S-EPS) < loosely bound EPS (LB-EPS) < tightly bound EPS (TB-EPS). Although the components (e.g., protein and humic acid-like substances) of each EPS fraction changed significantly throughout the MAR-MBR process owing to the low production of excess sludge, the degrees of change in S-EPS, LB-EPS, and TB-EPS were significantly different from the corresponding change in their relative molecular weights. Furthermore, the microbial community composition was beneficial for the release and degradation of EPS, and the regulation of gene functions via the MAR-MBR enhanced this process.
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•Excess sludge was minimized in micro aerobic reactor coupled with membrane bioreactor.•The order and degree of change in three fractions of EPS were significantly different.•Aerobic and facultative bacteria converted EPS.•Regulation of gene functions made EPS conversion easily during MAR-MBR process.
Micro-aerobic reactors (MARs) play an important role in simultaneous nitrification, denitrification, and organics removal but are affected by the C/N ratio. In this study, high C/N ratio ...food-processing wastewater was treated using two-step MARs. The average removal efficiencies of total nitrogen and chemical oxygen demand during the MAR process were 84.21% and 95.43%, respectively. The efficiency of simultaneous nitrification and denitrification was 88.87% and 17.26% in MAR-1 and MAR-2, respectively; simultaneously, organic matter was efficiently degraded. Protein-like materials were biodegraded preferentially, and the degree of change in fulvic-like substances was the greatest during the MAR processes. This was attributed to the spatial distribution of the dissolved oxygen concentration in a single MAR, which may influence the microbial community composition (e.g., that of Nitrospira) and the regulation of gene functions.
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•Simultaneous nitrification, denitrification, and organics removal were realized in micro-aerobic reactors (MARs).•Oxygen distribution exhibited significant spatial differences in MARs.•High efficiency of simultaneous nitrification and denitrification found in MARs.•Fulvic-like and humic-like matters were efficiently degraded in MARs.•Dominant microbial abundance (i.e., Nitrospira and Competibacter) positively changed in a MAR.
The removal efficiency of nine pharmaceutical compounds from primary sludge was evaluated in two different operating conditions: (i) in conventional Mesophilic Anaerobic Digestion (MAD) alone and ...(ii) in a co-treatment process combining Mesophilic Anaerobic Digestion and a Thermophilic Aerobic Reactor (MAD-TAR). The pilot scale reactors were fed with primary sludge obtained after decantation of urban wastewater. Concerning the biodegradation of organic matter, thermophilic aeration increased solubilization and hydrolysis yields of digestion, resulting in a further 26% supplementary removal of chemical oxygen demand (COD) in MAD-TAR process compared to the conventional mesophilic anaerobic digestion. The highest removal rate of target micropollutants were observed for caffeine (CAF) and sulfamethoxazole (SMX) (>89%) with no substantial differences between both processes. Furthermore, MAD-TAR process showed a significant increase of removal efficiency for oxazepam (OXA) (73%), propranolol (PRO) (61%) and ofloxacine (OFL) (41%) and a slight increase for diclofenac (DIC) (4%) and 2 hydroxy-ibuprofen (2OH-IBP) (5%). However, ibuprofen (IBP) and carbamazepine (CBZ) were not degraded during both processes. Anaerobic digestion affected the liquid-solid partition of most target compounds. Sorbed fraction of pharmaceutical compounds on the sludge tend to decrease after digestion, this tendency being more pronounced in the case of the MAD-TAR process due to much lower concentration of solids.
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•A hybrid digester was implemented to evaluate pharmaceutical compounds removal.•MAD-TAR allowed a better removal of VSS (76%) compared to MAD (47%).•Removal higher than 90% was found for CAF and SMX whatever the process.•Moderate (DIC, 2OH-IBP) to high (OXA, PRO, OFL) removal was observed in MAD-TAR.•Biodegradable compounds removal was correlated with their fraction in liquid phase.
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•Baffled anaerobic–aerobic bioreactors were used to treat low-strength DWW.•More functional microorganisms were entrapped by introducing MBF carriers.•HN-AD species growth was ...facilitated by influx of low C/N ratio digestate.•Nitrogen metabolic pathways were interpreted based on metagenomics.
In this study, baffled anaerobic–aerobic reactors (AOBRs) with modified basalt fiber (MBF) carriers and felt were used to treat domestic wastewater (DWW). The influent was first treated in anaerobic compartments, with the NH4+-N containing digestate refluxed into aerobic compartment for nitrification. The nitrified liquid was channeled to the anaerobic compartments for further denitrification. Under optimal conditions, AOBR with MBF carriers could remove 91% chemical oxygen demand (COD) and 81% total nitrogen (TN), with biomass production increased by 7.6%, 4.5% and 8.7% in three successive anaerobic compartments compared to the control. Biological viability analysis showed that live cells outnumbered dead cells in bio-nests. Metagenomics analysis showed that multiple metabolic pathways accounted for nitrogen conversion in anaerobic and aerobic compartments. More importantly, low COD/TN ratio digestate facilitated heterotrophic nitrification-aerobic denitrification (HN-AD) species growth in aerobic compartment. This study provides a promising strategy to source treatment of DWW from urban communities.
Living machine (LM) system is widely exploited as an ecological restoration technology in decentralized wastewater treatment. This is the first study reporting the influence of regular addition of ...mixed ore powder (maifanite, zeolite, oyster shell, and montmorillonite) on an open aerobic reactor of LM system for black water treatment. The maximum removal efficiency of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) achieved 50.74%, 25.18%, and 17.19%, respectively, after the mixed ore addition. Furthermore, the numbers and species of algae, zooplankton, and other aquatic animals considerably changed with the mixed ore addition. Compared with those in control system, the maximum increase of the relative abundances of Acinetobacter, Chryseobacterium, C39, Pseudomonas, Flavobacterium, Novosphingobium, Rhodoluna, Mycobacterium, and Malikia in the experimental system reached 28.82%, 18.00%, 12.39%, 15.12%, 13.67%, 6.65%, 11.78%, 7.83%, and 10.50%, respectively. Presence of Rhodoluna suggests that addition of the mixed ore powder may be benignant and beneficial for formation of a healthy ecological environment during black water treatment with LM system.
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•It is the first time to report the influence of addition of ore on Living Machine.•The maximum increase of COD, TN, and TP removal achieved 10.42%, 3.04%, and 7.23%.•The numbers and species of algae and aquatic animals were significantly changed.•The relative abundances of the major bacterial groups were obviously increased.
A special denitrifying capsule that was designed according to the theory of maldistribution of DO (dissolved oxygen) for simultaneous nitrification and denitrification (SND) in an aerobic reactor was ...prepared by an encapsulation technique. The morphology of the denitrifying capsule and its SND performance in an aerobic reactor used for treating synthetic low C/N wastewater were systematically investigated. The spherical capsule comprised a porous membrane, denitrifying active sludge and semen litchi powder, which were cohered together by a physical method. Well-shaped pores were distributed in the membrane and the average pore diameter was approximately 0.25 µm. Circular pores were present in the cross section of the membrane, and the thickness of the membrane ranged from 95.0 µm to 120.0 µm. After 7 days of acclimation, the denitrifying capsule showed good SND performance in an aerobic reactor with a DO concentration of 5.09 mg/L. The NH4+-N concentration of 51.09 mg/L was removed completely after 8 h, the effluent dissolved inorganic nitrogen (DIN) concentration decreased to 6.11 mg/L, the SND ratio reached to 91.6% at 6 h, and finally decreased to 2.09 mg/L at 15 h and could also reach 98.91%. The influent of NH4+-N loading had little effect on the nitrogen removal performance. And decreased of air input induced lower hydraulic shearing force compared to reactors with higher DO had a little effect on the diffusion and mass transfer of NO3--N. With this core shell structure denitrifying capsule, it was easy to achieve SND without controlling the DO concentrations at low levels or using intermittent aeration.
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•Denitrifying capsule was designed according to maldistribution of DO theory.•Denitrifying capsule was prepared by a novel encapsulation method.•Simultaneous nitrification and denitrification was facilitated in aerobic reactor.•SND ratio could reach to 99.8% at influent NH4+-N 52.09 mg/L and DO 5.16 mg/L.
The source separation and decentralised treatment technology for domestic wastewater is an important method to improve sewage treatment rates and water reuse. The Living Machine (LM) system is a ...widely applied decentralised domestic wastewater treatment technology. In order to enhance the black water (toilet water) treatment performance, an underwater lamp was placed in the open aerobic reactor of the LM system, and treatment efficiency and micro-ecosystem changes with different light intensities were studied in this research. Compared to the control reactor (C), removal efficiencies of ammonia, total nitrogen (TN), and total phosphorus (TP) were increased from 22.07%, 16.03%, and 13.81% to 42.20%, 22.82%, and 17.20%, respectively, in the underwater light reactor (L) with an average intensity of 2083.00 LX, and COD removal was not obviously effected. The species and numbers of algae and the species of zooplankton and other aquatic animals were increased sharply in L, but their number did not fit a linear relation with light intensity. The bacteria group was prominently changed in L, whereas Malikia_spinosa, Emticicia_sediminis, and Rhodocyclaceae_bacterium_MORI13 were increased, and Rhodocyclaceae_bacterium_ICHIDE18 was obviously decreased. Although underwater illumination enhanced the wastewater reactor performance of the LM open aerobic reactor, further research is needed to learn more about the process optimization and relative mechanism.
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•N and P removal and DO level increased by installing underwater lamp.•Algae and aquatic animal's species richness increased by underwater illumination.•Microbial communities prominently changed in underwater illuminated reactors.
Anaerobic digestion has become a possible approach for treating organic fraction of urban solid waste. However, the treatment of the digestate is still a matter for technological development. In this ...work a single anaerobic–aerobic fixed-bed reactor subjected to recirculation was used to treat the effluent from an anaerobic digester fed with organic food waste. The reactor was operated for 100 days, with hydraulic retention time of 24 h. The organic loading rate applied was 1 kg COD m
−3
d
−1
. The efficiency in removing nitrogen, organic matter, and phosphorus were 73%, 83%, and 23%, respectively. This reactor configuration proved to be quite promising to promote simultaneous removal of carbon, nitrogen, and phosphorus from effluents with high nitrogen and organic matter contents.
Phosphates enter the surface waters from agricultural sources has been regarded as an important cause of eutrophication. Excess of phosphate concentration can cause severe health problems such as ...kidney damage and osteoporosis. The adsorption is one of the most popular removal methods used for treating wastewaters containing agricultural nutrients. The challenge is the time that phosphorous concentration is very high in agricultural related industries and is higher than the adsorption capacity of the system. This research investigated the treatment of agricultural wastewater by developing and adding two novel media (ALLODUST, ALLOCHAR) to a Single Batch Aerobic Reactor (SiBAR). ALLODUST and ALLOCHAR consisted of allophanic soil mineral material sourced from either a Horotiu soil (Allophanic soil) or a Craigieburn soil (Allophanic Brown soil). Central Composite Design (CCD) and Response Surface Methodology (RSM) were hired to design the experiment and model the nature of the response surface of the novel media in the experimental design and to analyze the optimum operational conditions. The SiBAR design was optimized for three ranges of P contamination: 1-50 mg L-1 (low range); 51-175 (mid-range); and 176-300 (high range). The ALLODUST novel media demonstrated a higher P adsorption capacity compared to the ALLOCHAR media and Allophane compound itself. The ALLODUST adsorbent dosage of 3 g L-1 was the optimum: being able to remove 100% of P up to 50 mg L-1 in 30 minutes with the lowest aeration rate (1.5 L min-1) and remove 76% of P up to 300 mg L- 1 in 450 minutes with the highest aeration rate (7.5 L min-1).
