Treatment Of High-strength Wastewater Research Articles

Unraveling the intricate fouling behaviors of landfill leachate components during membrane distillation concentration toward zero liquid discharge

Membrane distillation (MD) holds promise for cost-effectively concentrating wastewater toward zero liquid discharge (ZLD), while membrane fouling problems still hinder its practical application, especially for high-strength wastewater containing complex constituents. This study investigated the effects of different foulant components in actual landfill leachate (LFL) on MD deep concentration performances. The fouling behaviors of LFL components were revealed by comprehensively characterizing and analyzing the physicochemical properties of the fouling layers and membrane-foulant interactions. Results illustrated that suspended solids (SS) and macromolecular organics (MO) played significant yet distinct roles in fouling layer formation. SS (>0.45 μm, ∼24 % TOC) possessed strong adhesion energies with membrane surfaces and constructed the main skeleton of the fouling layer at the preliminary concentration stage; while MO (>20 kDa, 0.36 % TOC) deposition resulted in a densely packed fouling layer, influencing the salt crystallization potential and interfering with water and ammonia transport. In contrast, the low-molecular organics with the highest content (<20 kDa, ∼75 % TOC) were mainly electron-donor monopolar substances weakly adsorbed on the nonpolar membrane surface. Removing SS and MO from LFL notably prevented fouling layer formation and maintained high membrane efficacies (water flux decline mitigated from ∼50 % to ∼15 % and ammonia rejection increased from 71 % to 88 %), even as water recovery increased to 95 %. The findings of this work imply conventional anti-fouling strategies (e.g., complete removal or degradation of organic components) may have gone beyond what is necessary, and will inspire the development of simpler and greener methods to maintain membrane efficacy during high-strength wastewater treatment toward ZLD.

Influence of aeration modes and DO on simultaneous nitrification and denitrification in treatment of hypersaline high-strength nitrogen wastewater using sequencing batch biofilm reactor (SBBR)

Sequencing batch biofilm reactor (SBBR) has the potential to treat hypersaline high-strength nitrogen wastewater by simultaneous nitrification-denitrification (SND). Dissolved oxygen (DO) and aeration modes are major factors affecting pollutant removal. Low DO (0.35–3.5 mg/L) and alternative anoxic/aerobic (A/O) mode are commonly used for municipal wastewater treatment, however, the appropriate DO concentration and operation mode are still unknown under hypersaline environment because of the restricted oxygen transfer in denser extracellular polymeric substances (EPS) barrier and the decreased carbon source consumption during the anoxic phase. Herein, two SBBRs (R1, fully aerobic mode; R2, A/O mode) were used for the treatment of hypersaline high-strength nitrogen wastewater (200 mg/L NH4+-N, COD/N of 3 and 3% salinity). The results showed that the relatively low DO (2 mg/L) could not realize effective nitrification, while high DO (4.5 mg/L) evidently increased nitrification efficiency by enhancing oxygen transfer in denser biofilm that was stimulated by high salinity. A stable SND was reached 16 days faster with a ∼10% increase of TN removal under A/O mode. Mechanism analysis found that denser biofilm with coccus and bacillus were present in A/O mode instead of filamentous microorganisms, with the secretion of more EPS. Corynebacterium and Halomonas were the dominant genera in both SBBRs, and HN-AD process might assist partial nitrification-denitrification (PND) for highly efficient TN removal in biofilm systems. By using the appropriate operation mode and parameters, the average NH4+-N and TN removal efficiency could respectively reach 100% and 70.8% under the NLR of 0.2 kg N·m−3·d−1 (COD/N of 3), which was the highest among the published works using SND-based SBBRs in treatment of saline high-strength ammonia nitrogen (low COD/N) wastewater. This study provided new insights in biofilm under hypersaline stress and provided a solution for the treatment of hypersaline high-strength nitrogen (low COD/N) water.

Treatment of high-strength wastewater with coupled flocculation and membrane filtration prior to ammoniacal nitrogen enrichment by osmotically assisted reverse osmosis

Membrane scaling poses significant challenges in membrane processes involving high-strength feed streams. In this work, a treatment of high-strength NH4-N-containing wastewater comprising the flocculation of Ca and Si and membrane filtration is introduced. The pretreated wastewater underwent further dewatering and enrichment through a hybrid osmotically assisted reverse osmosis and reverse osmosis (OARO-RO) process. During the treatment, the molar ratio of the acid flocculant FeCl3 to Si was adjusted, as well as the molar ratio of the alkaline flocculant Na2CO3 to Ca. Furthermore, the molar ratio of FeCl3 and Na2CO3, as well as the order of flocculant addition, was optimized in terms of Si and Ca removal and treated water pH necessary for NH4-N recovery. Membrane filtration was afterwards conducted to remove the floc from the treated wastewater prior to the OARO-RO operation. The optimized pretreatment process resulted in removal of approximately 70 % Si and 60 % Ca content in the wastewater. OARO-RO was operated using pretreated wastewater to demonstrate the effectiveness of the coupled flocculation and filtration pretreatment in enrichment of highly concentrated feed streams. Two scenarios of OARO-RO operation were performed by manipulating the operational parameters. Successful continuous operation of the OARO-RO system was observed despite the operational conditions and the wastewater was enriched more than 11 times, without operation interruption and occurrence of scaling, resulting in an enriched wastewater containing around 50,000 ppm T-N. Therefore, coupled flocculation and membrane filtration treatment process is effective to mitigate membrane scaling when concentrating highly concentrated feed streams.

Eliminating adverse effects of fouling layer using composite membranes with dense surface layers for sustainable membrane distillation of high-strength wastewater

This study explored composite membranes (CMs) with dense and water-permeable surface layers for the deep-concentration of high-strength wastewater using membrane distillation (MD). Compared to conventional microporous MD membranes, coating a dense PVA surface layer avoided the detrimental effects of landfill leachate (LFL) foulants (e.g., membrane pore blockage and deformation) during MD concentration. The hydrophilicity and water/salt separation capability of surface layers enhanced the dispersion of water diffusion on membrane surfaces and altered the solute distribution on membrane cross-sections, resulting in inorganic crystallization mitigation and transforming the fouling layer structure to a more porous and water-permeable state. This ensured the membrane efficiency was little affected by membrane fouling even as LFL was highly concentrated (water flux decline: PVDF ∼49 % vs. CM ∼14 % as concentration factor increased to 20). The resistance of foulant intrusion and in-pore deposition, which easily occurred on microporous membranes, and the decrease in membrane-foulant interactions by the surface layer endowed the CM with a high foulant-release capability (clean efficiency: ∼97 %). The surface layer also exhibited an ammonia/water sieving effect which enhanced volatile ammonia rejection (∼1.6 times). This work provides insight into the construction of high-sustainable MD membranes for high-strength wastewater treatment, promoting the practical implementation of MD.

Anaerobic membrane bioreactor coupled with polyaluminum chloride for high-strength phenolic wastewater treatment: Robust performance and potential mechanisms

Anaerobic digestion of phenolic wastewater by anaerobic membrane bioreactor (AnMBR) has revealed increasing attractiveness, but the application of AnMBRs for treating high-strength phenolic wastewater faces challenges related to elevated phenol stress and membrane fouling. In this study, the coupling of AnMBR and polyaluminum chloride (PAC) was developed for efficient treatment of high-strength phenolic wastewater. The system achieved robust removal efficiencies of phenol (99%) and quinoline (98%) at a gradual increase of phenol concentration from 1000 to 5000 mg/L and a constant quinoline concentration of 100 mg/L. The dosing of PAC could effectively control the membrane fouling rate with the transmembrane pressure (TMP) increasing rate as low as 0.17 kPa/d. The robust performances were mainly attributed to the favorable retention of functional microbes through membrane interception, while pulse cross flow buffered against phenol stress and facilitated cake layer removal. Meanwhile, the enriched core functional microbes, such as Syntrophorhabdus, Syntrophus, Mesotoga and Methanolinea, played a crucial role in further reduction of phenol stress. Notably, the significant presence of biomacromolecule degrader, such as Levilinea, contributed to membrane fouling mitigation through extracellular polymer degradation. Moreover, the enlargement of particle size distribution (PSD) by PAC was expected to mitigate membrane fouling. This study provided a promising avenue for sustainable treatment of high-strength phenolic wastewater.

Microbial response and spatial profiling of nitrite-producing denitrification granular sludge in-situ exposed to high nitrite stress

Nitrite-producing denitrification granular sludge (NPG) is emerging as a novel approach to employing anammox for cost-efficient nitrogen removal from high-strength nitrate-containing wastewater. However, the underlying impact of increasing stress of nitrite (NO2–-N) accumulation on microbial metabolism and cooperation of denitrifying bacteria and heterotrophs in NPG was still not clear. This study first demonstrated a high-rate NPG system with elevating nitrate (NO3–-N) from 52.4 mg/L to 613.2 mg/L. During this operation, a rapid increase in granular size from 322.8 µm to 1124.0 µm was observed with a relatively stable nitrate-to-nitrite transformation ratio (NTR) as high as 83.0 %, and effluent NO2–-N of increasing from 16.5 mg/L to 331.9 mg/L. Such an increasing NO2–-N stress improved the capability of the TCA cycle with rising intermediates of amino acid metabolism. This further stimulated the production of exocellular organic matter that replenished as electron donors and promoted the growth of granular size. The homogeneously spatial distribution of key bacteria (Thauera) surrounding the NPG with a calcium-dominated inorganic core inside was revealed to play a key role in enhanced substrate transfer capability. Genes nar and nap encoding NO3–-N reductase dominated by key species belonging to Thauera showed much higher abundance than that encoding NO2–-N reductase, which was the key reason for relatively stable NO2–-N accumulation. It illustrated the excellent persistence of NPG to high NO2–-N stress with special structure of functional bacteria inside granules, providing a great potential for the treatment of high-strength nitrate-containing wastewater.

Metabolomic insight into regulatory mechanism of heterotrophic bacteria nitrification-aerobic denitrification bacteria to high-strength ammonium wastewater treatment

This work aimed to elucidate the metabolic mechanism of heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria influenced by varying concentrations of ammonium nitrogen (NH4+-N) in high-strength synthetic wastewater treatment. The results showed that the removal rates of NH4+-N and total nitrogen, along with enzymatic activities related to nitrification and denitrification, increased with rising NH4+-N concentrations (N500:500 mg/L, N1000:1000 mg/L and N2000:2000 mg/L). The relative abundances of HN-AD bacteria were 50 %, 62 % and 82 % in the three groups. In the N2000 group, the cAMP signaling pathway, glycerophospholipid metabolites, purines and pyrimidines related to DNA/RNA synthesis, electron donor NAD+-related energy, the tricarboxylic acid (TCA) cycle and glutamate metabolism were upregulated. Therefore, influent NH4+-N at 2000 mg/L promoted glutamate metabolism to accelerate the TCA cycle, and enhanced cellular energy and advanced denitrification activity of bacteria for HN-AD. This mechanism, in turn, enhanced microbial growth and the carbon and nitrogen metabolism of bacteria for HN-AD.

Attaining superior nitrogen removal from integrated mature landfill leachate and kitchen waste digestion liquid via a two-stage partial nitrification/anammox (PN/A) process

The advanced nitrogen removal of mature landfill leachate (MLL) with low carbon to nitrogen ratio (C/N) is a topic worthy of further research. A two-stage partial nitrification/anammox (PN/A) system for integrated MLL and kitchen waste digestion liquid (KWDL) treatment was established in this study. The nitrogen removal efficiency (NRE) of this process was 98.1 ± 1.3 %, with an effluent TIN concentration of 15.2 ± 1.8 mg/L. In the partial nitrification-sequencing batch reactor (PN-SBR), aerobic hydraulic retention time (HRT) accounted for just 36.4 % of the whole process with dissolved oxygen (DO) < 0.3 mg/L, which significantly reduced energy consumption. Furthermore, the introduction of KWDL heightened anoxic denitrification and aerobic simultaneous nitrification and denitrification (SND) processes, contributing to 74.2 ± 4.3 % and 25.8 ± 4.3 % of the total NRE, respectively. This greatly strengthened the nitrogen removal capacity of PN-SBR. Batch tests indicated that the capacity of KWDL as a carbon source to drive the process of partial denitrification coupled with anammox (PDA) was equal to that of sodium acetate. Adding KWDL in the later phase of each cycle in the anammox-sequencing batch reactor (A-SBR) facilitated achieving stable PDA and advanced nitrogen removal. The nitrate accumulation problem in the traditional two-stage PN/A process has been resolved without the addition of carbon sources. Nitrosomonas (3.7 %→7.9 %), Thauera (0.04 %→40.7 %) and a salt-tolerant AnAOB microbe, unclassified_f_Brocadiaceae (0 %→5.3 %) were dominant in the combined system. This study revealed a pioneering avenue for efficient high-strength wastewater treatment.

Eco-friendly cultivation of microalgae using a horizontal twin layer system for treatment of real solid waste leachate

Solid waste leachate (SWL) requires dilution with water to offset the negative effects of high nutrient concentration and organic compounds for its microalgae-based treatment. Among attached cultivation systems, twin layer is a technology in which limited information is available on treatment of high strength wastewater using microalgae. Moreover, widespread application of twin layer technology is limited due to cost of substrate and source layer used. In the present study, potential of Scenedesmus sp. for the treatment of SWL was assessed on horizontal twin layer system (HTLS). Novel and cost-effective substrate layers were tested as attachment material. Wetland treated municipal wastewater (WMW) was used to prepare SWL dilutions viz, 5%, 10%, 15%, 20% and 25% SWL. Recycled printing paper showed maximum biomass productivity of 5.19 g m−2 d−1. Among all the SWL dilutions, Scenedesmus sp. achieved maximum growth of 103.05 g m−2 in 5% SWL which was 16% higher than WMW alone. The maximum removal rate of NH4+ –N, TKN, and PO43− P was obtained in 20% SWL which was 1371, 1588 and 153 mg m−2 d−1 respectively. Varying concentrations of nutrients in different SWL dilutions significantly affected lipid biosynthesis, with enhanced productivity of 2.28 g m−2 d−1 achieved in 5% SWL compared to 0.97 g m−2 d−1 in 20% SWL. Hence, it can be concluded that 5% SWL dilution was good for biomass and lipid production, while the highest nutrient removal rates were obtained at 20% SWL mainly attributed to biotic and abiotic processes. Based on these results HTLS can be a promising technology for pilot scale to explore industrialized application of wastewater treatment and algal production.

Optimization of COD and TDS removal from high-strength hospital wastewater by electrocoagulation using aluminium and iron electrodes: Insights from central composite design

Simple and eco-friendly, electrocoagulation process is used. It eliminates intractable hospital wastewater pollutants like TDS and COD. The treatment of high-strength hospital wastewater (HWW) using electrocoagulation (EC) using aluminium (Al), iron (Fe), and hybrid (Al and Fe) electrodes was investigated in this study. The effects of two factors, reaction time (20–90 min) and voltage (15–25 V) on COD and TDS treatment efficiencies were examined. The determination of optimal conditions was conducted through the utilization of the central composite design (CCD). The optimization results for both TDS and COD were as follows: Fe-Fe performed best at 15 V for 57 min (57% and 60%), Al-Al at 16 V for 51 min (65% and 59%), and Al-Fe at 20 V for 51 min (59% and 61%). Based on energy consumption, the optimal electrode pattern was the Al-Al experimental set, with 3.17 kWh/kg COD and 8.31 kWh/kg TDS.

Biofouling Control by Facultative Quorum Quenching Bacteria in Anaerobic Membrane Bioreactors for High-Strength Wastewater Treatment

Biofouling Control by Facultative Quorum Quenching Bacteria in Anaerobic Membrane Bioreactors for High-Strength Wastewater Treatment

Micronano-bubble ozonation as an efficient pretreatment technology for raw oxytetracycline production wastewater discharged to biological treatment

Efficient high-strength antibiotic production wastewater treatment is a significant challenge that restricts sustainable pharmaceutical industry development. A novel ozone micronano-bubble (MNB) treatment system has been firstly developed to enhance oxytetracycline (OTC) degradation primarily by ozone and singlet oxygen. For practical applications employing pretreatment combined with biological treatment for raw OTC production wastewater, it is necessary to clarify the treatment performance (including the removal of parent OTC, toxicity, and organic fraction), and the potential impact on following bioprocesses. In this study, three pretreatment technologies (i.e., MNB ozonation, conventional ozonation, and thermal hydrolysis) were developed to treat real raw OTC production wastewater and were comprehensively compared. Conventional ozonation requires treatment time of over 14 h for complete removal of OTC and toxicity. Under the high-temperature operating condition (85°C), thermal hydrolysis achieves the shortest treatment time (3 h) for complete OTC removal from production wastewater without toxic substance generation. Nevertheless, the hydrolysis products and high-concentration dissolved organic matter (DOM) cannot undergo further transformation. Despite the formation of some toxic oxygen-rich transformation products, these products can be rapidly degraded to innoxious substances with lower molecular weights within 8 h via MNB ozonation. In addition, MNB ozonation can promote a 30.0% organic fraction transformation to produce more methane (584.0 mL) during the anaerobic inhibition tests than thermal hydrolysis (356.0 mL). Consequently, MNB ozonation technology is more conducive to combination with biological post-treatment. This study demonstrates the promising application potential of MNB ozonation as an efficient pretreatment technology for OTC production wastewater, and provides comprehensive insight into different pretreatment technologies to obtain an optimal treatment strategy for practical applications.

Treatability of high-strength real sheep slaughterhouse wastewater using struvite precipitation coupled Fenton's oxidation: The MAPFOX process

Struvite (MAP, magnesium ammonium phosphate hexahydrate, MgNH4PO4.6H2O) precipitation-aided Fenton's OXidation (MAPFOX process) was explored in the treatment of high-strength real sheep slaughterhouse wastewater (RSSW) for the first time under a comprehensive soft-computing-based modeling study. The experimental results showed that under the highest-efficiency conditions (chemical combination of MgCl2.6H2O + NaH2PO4.2H2O, a molar ratio of Mg2+:NH4+-N:PO43–P = 1.2:1:1, a reaction pH of 9.0 ± 0.10, [NH4+-N]0 = 240 ± 20 mg/L, and a reaction time of 15 min), MAP precipitation could effectively remove more than 80 %, 60 %, 55 %, and 70 % of color, total chemical oxygen demand (TCOD), soluble COD (SCOD), and ammonium nitrogen (NH4+-N) from the raw RSSW. The results of the Fenton's oxidation used as the post-treatment unit of the proposed MAPFOX system indicated that the integrated advanced oxidation process (AOP) was able to reduce the residual pollutant levels in the MAP-pretreated RSSW to the relevant discharge standards. Under the subsequent condition of [Fe2+]0 = 90 mmol/L, [H2O2]0 = 180 mmol/L, reaction pH = 3.25, and total reaction time = 60 min, more than 97 % of color, TCOD, SCOD, and NH4+-N could be removed from the RSSW via the Fenton's oxidation after the MAP-based physicochemical treatment. According to SEM micrographs, surface morphology of dehydrated struvite exhibited irregular-shaped and overlapping sharp-edged particles of various sizes with an average size of about 50.9 μm. The Fourier Transform Infrared (FTIR) spectroscopy confirmed the active functional groups and type of bonds for the high-strength RSSW-oriented struvite (heated) within the spectral range of 4000–450 cm−1. Thermogravimetric Analysis (TGA), Derivative Thermogravimetry (DTG), Differential Thermal Analysis (DTA), and Differential Scanning Calorimetry (DSC) of the dehydrated struvite revealed that the weight loss occurred in three temperature zones, the maximum weight loss rate of 0.252 mg/min was recorded at around 224 °C and at time of 20.83 min, and the sample had strong endothermic and medium exothermic peaks at about 241 °C and 679 °C, respectively. The predictive successes of the implemented soft-computing approaches were benchmarked in terms of various statistical goodness-of-fit parameters. The performance assessment indices corroborated the superiority of the support vector machines-Pearson VII universal kernel function (SVM-PUKF)-based model (correlation coefficient (CC) = 0.9999–1.0000), mean absolute error (MAE) = 0.0222–0.0389 %, mean absolute percentage error (MAPE) = 0.0270–0.0506 %, root mean squared error (RMSE) = 0.0258–0.0415 %, coefficient of variation of RMSE (CV(RMSE) = 0.0003–0.0008, Nash–Sutcliffe efficiency (NSE) = 0.9998–1.000, Legates and McCabe's index (LMI) = 0.9894–0.9952) over other data-intelligent models in predicting the pollutant removal efficiencies. The computational results also indicated that the narrowest uncertainty bands (±1.96Se = 0.0537–0.1483 %) and the lowest amounts of expanded uncertainty (U95 = 3.1224–5.3124 %) values for all efficiency sets were achieved for the applied SVM-PUKF-based strategy. This study demonstrated the first-ever and successful application of the proposed MAPFOX process in treatability of the RSSW and capability of the implemented soft-computing strategy in modeling a highly nonlinear treatment system.

Application of Integrated Technologies for the Treatment of High-Strength Industrial Wastewater in Vietnam

Application of Integrated Technologies for the Treatment of High-Strength Industrial Wastewater in Vietnam

Carbon-neutral potential in treatment of N, N-dimethylformamide-containing industrial wastewater: Comparative investigation of energy conservation, carbon reduction and expenditure between UASB and Fenton process

The methanogenic degradation of N, N-dimethylformamide (DMF) is a sustainable and low-carbon technology for the treatment of high-strength industrial wastewater. Compared with the state-of-the-art chemical degradation method like Fenton, the UASB process exhibited its promising superiority in bio-energy recovery, economic profit gaining and carbon emission reduction. The lab-scale UASB obtained high DMF removal efficiency of over 98 % with methane recovered as bio-energy at a limited organic loading rate (OLR) of 4.2 COD kg/m3/d. Compared with the Fenton process, the UASB process is demonstrated more suitable to the carbon-neutral treatment of high-strength DMF-containing wastewater: The Fenton process is suitable to the relative low COD concentration below 1500 mg/L; The UASB was capable of covering all electricity consumption when COD > 3586 mg/L; The UASB also achieved zero CO2 emission when COD > 5720 mg/L; The UASB process obtains net profit when COD > 3616 mg/L. This study provided clear evidence of the promising potential and remarkable feasibility of bio-energy production in carbon-neutral treatment of DMF-containing wastewater.

Toward Integrating EBPR and the Short-Cut Nitrogen Removal Process in a One-Stage System for Treating High-Strength Wastewater.

Enhanced biological phosphorus removal (EBPR) is an economical and sustainable process for phosphorus removal from wastewater. Despite the widespread application of EBPR for low-strength domestic wastewater treatment, limited investigations have been conducted to apply EBPR to the high-strength wastewaters, particularly, the integration of EBPR and the short-cut nitrogen removal process in the one-stage system remains challenging. Herein, we reported a novel proof-of-concept demonstration of integrating EBPR and nitritation (oxidation of ammonium to nitrite) in a one-stage sequencing batch reactor to achieve simultaneous high-strength phosphorus and short-cut nitrogen removal. Excellent EBPR performance of effluent 0.8 ± 1.0 mg P/L and >99% removal efficiency was achieved fed with synthetic high-strength phosphorus wastewater. Long-term sludge acclimation proved that the dominant polyphosphate accumulating organisms (PAOs), Candidatus Accumulibacter, could evolve to a specific subtype that can tolerate the nitrite inhibition as revealed by operational taxonomic unit (OTU)-based oligotyping analysis. The EBPR kinetic and stoichiometric evaluations combined with the amplicon sequencing proved that the Candidatus Competibacter, as the dominant glycogen accumulating organisms (GAOs), could well coexist with PAOs (15.3-24.9% and 14.2-33.1%, respectively) and did not deteriorate the EBPR performance. The nitrification activity assessment, amplicon sequencing, and functional-based gene marker quantification verified that the unexpected nitrite accumulation (10.7-21.0 mg N/L) in the high-strength EBPR system was likely caused by the nitritation process, in which the nitrite-oxidizing bacteria (NOB) were successfully out-selected (<0.1% relative abundance). We hypothesized that the introduction of the anaerobic phase with high VFA concentrations could be the potential selection force for achieving nitritation based on the literature review and our preliminary batch tests. This study sheds light on developing a new feasible technical route for integrating EBPR with short-cut nitrogen removal for efficient high-strength wastewater treatment.

Valorization of potato starch wastewater using anaerobic acidification coupled with Chlorella sorokiniana cultivation

Wastewater from the potato processing industry called protamylasse is rich in proteins and carbohydrates that potentially can be valorized through cultivation of microalgae by mixotrophic metabolism. However, the complex organic compounds are a challenge, as algae grow best on simple compounds such as volatile fatty acids (VFA). This study demonstrates a new two-stage system. First, VFA production was achieved by testing mesophilic and thermophilic anaerobic acidification (AA) at a short hydraulic retention time (HRT; 3.3 and 5 days) resulting in the release of ammonium and phosphate. HRT of 5 days and thermophilic conditions was optimal considering the high acetate yield of 0.23 g and 22 ml CH4 per g volatile solids (VS). Then, Chlorella sorokiniana was chosen based on the obtained growth rate, and better adaption in ammonium-rich AA effluent after screening several tested microalgae (Chlorella sorokiniana, Chlorella vulgaris, Scenedesmus obliquus, and Haematococcus pluvialis). It was cultivated for valorization of nutrients and organics and successfully upscaled to 25 L photobioreactor (PBR) scale under both batch and continuous operation with high dosage of 25% (8.2 g L−1 of VS) of AA effluent at an HRT of 5 days in the PBR. Chlorella sorokiniana removed more than 99% of the chemical oxygen demand (COD) and the VFA during continuous flow PBR operation. This approach contributed to the final removal efficiency of 71%, 91%, and 78% for phosphorus, nitrate, and ammonia, respectively, and production of microalgae biomass with more than 73% protein. Thus, a promising process for simultaneous treatment of high strength wastewater for microalgal protein production.

Effect of biocarriers on the nitrification and microbial community in moving bed biofilm reactor for anaerobic digestion effluent treatment

The performance of a moving bed biofilm reactor (MBBR) depends largely on the type of biofilm carrier used. However, how different carriers affect the nitrification process, particularly when treating anaerobic digestion effluents, is not completely understood. This study aimed to evaluate the nitrification performance of two distinct biocarriers in MBBRs over a 140-d operation period, with a gradually decreasing hydraulic retention time (HRT) from 20 to 10 d. Reactor 1 (R1) was filled with fiber balls, whereas a Mutag Biochip was used for reactor 2 (R2). At an HRT of 20 d, the ammonia removal efficiency of both reactors was >95%. However, as the HRT was reduced, the ammonia removal efficiency of R1 gradually declined, ultimately dropping to 65% at a 10-d HRT. In contrast, the ammonia removal efficiency of R2 consistently exceeding 99% throughout the long-term operation. R1 exhibited partial nitrification, whereas R2 exhibited complete nitrification. Analysis of microbial communities showed that the abundance and diversity of bacterial communities, particularly nitrifying bacteria such as Hyphomicrobium sp. And Nitrosomonas sp., in R2 was higher than that in R1. In conclusion, the choice of biocarrier significantly impact the abundance and diversity of microbial communities in MBBR systems. Therefore, these factors should be closely monitored to ensure the efficient treatment of high-strength ammonia wastewater.

The elevation of salinity above 1% deteriorated nitrification performance and reshaped nitrifier community of an MBR: An often overlooked factor in the treatment of high-strength ammonium wastewater

The effects of synchronous variations of influent salinity with the elevation of NH4+-N concentration on nitrification performance and microbial community structure of bioreactor are often ignored. In this study, we investigated the dynamic response of nitrifying activated sludge to synchronously increased salinity and ammonia loading rate (ALR) in a nitrification membrane bioreactor (MBR). We found that the increase in influent salinity above 1% (from 0.91 to 1.32%) led to the deterioration of the nitrification performance of the MBR. The combined inhibition effect of salinity (1.32%), free ammonia (FA, an average of 1.37 mg/L), and free nitrous acid (FNA, an average of 0.155 mg/L) on nitrite-oxidizing bacteria (NOB) resulted in long-term (35 days) nitrite accumulation. The further increase of salinity and ALR exhibited little influence on the nitrification performance of MBR after the activated sludge had adapted to high salinity (>1%), effective nitrification performance was achieved at high ALR up to 1.71 kg NH4+-N/m3·d and high salinity (2.13%). The microbial analysis showed that the elevated salinity and accumulation of FNA reshaped the microbial community structure of ammonia-oxidizing bacteria (AOB) and NOB. The dominant species of AOB and NOB shifted from the salinity-resistant species Nitrosomonas aestuarii to the species Nitrosomonas mobilis with dual resistant to salinity and FNA, and from non-salinity-resistant species Candidatus Nitrospira defluvii to salinity-resistant species Nitrobacter winogradskyi and Nitrospira marina, respectively. Therefore, the salinity of 1% may be a critical level for the nitrification performance and the shift in the nitrifier community of activated sludge without salinity acclimation.

New insight into the irreversible membrane fouling in different pore-sized ultrafiltration ceramic membrane bioreactors (UCMBRs) for high-strength textile wastewater treatment

Despite great achievements in ceramic membrane bioreactor applications, membrane fouling, which decreases the permeability and separation performance of bioreactors and is associated with increased operational costs and energy consumption, remains a problem. The aim of this study was to expand our understanding of the fouling behavior in the long-term performance of ultrafiltration ceramic membrane bioreactors (UCMBRs) for high-strength textile wastewater reclamation. Using real textile wastewater effluent, the effects of ultrafiltration (UF) membrane pore sizes, cleaning strategies, and foulant distribution were systematically evaluated over more than three months of continuous operation. The results showed that UCMBR system achieved chemical oxygen demand and total nitrogen removal efficiencies as high as 91–95% and 39–43%, respectively. The high PN concentration can easily increase the viscosity of mixed liquor samples, contributing to a fouling layer on the membrane surface. In addition, the fouling layer formed on the surface of small-pore-sized ceramic UF membranes was not completely reversible but was difficult to eliminate by simple physical cleaning. Soluble extracellular polymeric substances, especially proteins and low molecular weight neutrals, remained, resulting in irreversible fouling on the UF membrane. However, saturated CO2 backwash showed great potential for enhancing the system through efficient fouling control without using environmentally unfriendly cleaning chemicals. The cake-intermediate and complete-standard models were suitable for explaining the fouling mechanism in the large- and small-pore-sized UF membranes, respectively.