Sludge Liquor Research Articles

Enrichment of nutrients from anaerobically digested centrate minimizing microplastics content using a combination of membrane processes

Centrifuge effluent, or centrate, is a liquid stream generated in the sludge line of wastewater treatment plants in the sludge dewatering process. Nutrients are solubilized in the anaerobic digestion of the sludge, mainly in the form of ammonium-nitrogen and phosphates. Thus, when the dewatering of the digested sludge is performed (usually by centrifugation), a sludge liquor stream enriched in nutrients is generated. However, it also contains microparticles, including microplastics, since most of the microparticles from the wastewater are transferred to the sludge treatment line in wastewater treatment plants. In this work, microplastics in centrate have been analyzed (counted and identified), and membrane technologies (ultrafiltration and forward osmosis) have been applied to concentrate nutrients and to obtain a microplastic-free stream for further nutrient recovery. Two alternative configurations have been compared, changing the application order of these processes. The results showed that obtaining a stream with a concentration higher than 6000 mg/L of ammonium has been possible by using ammonium sulfate (150 g/L) as a draw solution in the forward osmosis process. On the other hand, as a consequence of the ultrafiltration application, microparticles were concentrated in the reject stream up to 800 microparticles/L. At the same time, the permeate presents a lower concentration of microplastics without reducing the concentration of the nutrients. In this way, this pioneering study enables the production of a nutrient-enriched stream with reduced microplastic concentrations, that could be applied to the agricultural soil as biofertilizer.

Biofilm colonization and succession in a full-scale partial nitritation-anammox moving bed biofilm reactor

BackgroundPartial nitritation-anammox (PNA) is a biological nitrogen removal process commonly used in wastewater treatment plants for the treatment of warm and nitrogen-rich sludge liquor from anaerobic digestion, often referred to as sidestream wastewater. In these systems, biofilms are frequently used to retain biomass with aerobic ammonia-oxidizing bacteria (AOB) and anammox bacteria, which together convert ammonium to nitrogen gas. Little is known about how these biofilm communities develop, and whether knowledge about the assembly of biofilms in natural communities can be applied to PNA biofilms.ResultsWe followed the start-up of a full-scale PNA moving bed biofilm reactor for 175 days using shotgun metagenomics. Environmental filtering likely restricted initial biofilm colonization, resulting in low phylogenetic diversity, with the initial microbial community comprised mainly of Proteobacteria. Facilitative priority effects allowed further biofilm colonization, with the growth of initial aerobic colonizers promoting the arrival and growth of anaerobic taxa like methanogens and anammox bacteria. Among the early colonizers were known ‘oligotrophic’ ammonia oxidizers including comammox Nitrospira and Nitrosomonas cluster 6a AOB. Increasing the nitrogen load in the bioreactor allowed colonization by ‘copiotrophic’ Nitrosomonas cluster 7 AOB and resulted in the exclusion of the initial ammonia- and nitrite oxidizers.ConclusionsWe show that complex dynamic processes occur in PNA microbial communities before a stable bioreactor process is achieved. The results of this study not only contribute to our knowledge about biofilm assembly and PNA bioreactor start-up but could also help guide strategies for the successful implementation of PNA bioreactors.8NUh31NTQCwxAXZWHM2SHSVideo

Low-temperature thermal hydrolysis for enhancing sludge anaerobic digestion and antibiotic resistance management: Significance of digester solids retention time

Recently, there has been a growing inclination towards utilizing primary sludge (PS) fermentation prior to anaerobic digestion (AD) in water resource recovery facilities (WRRFs), where sludge liquor containing volatile fatty acids is used for biological nutrient removal. Nevertheless, using a low-temperature thermal hydrolysis process (THP) to improve AD in WRRFs adopting PS fermentation remains an area that has received limited research attention. Here, we studied the impact of THP (90 °C, 90 min) on anaerobic co-digestion of thickened waste activated sludge (TWAS) and fermented primary sludge (FPS) under varying solids retention times (SRTs) in semi-continuous mode. The study involved two THP schemes: scheme 1, where THP was done for both TWAS and FPS, and scheme 2, where THP was applied to TWAS only. The results demonstrated that reducing SRT from 20 to 15 and 10 d leads to decreased methane yield in both schemes. However, THP significantly enhances methane production, showing improvements of up to 37.9 % (scheme 1) and 31.2 % (scheme 2) under a 15-d SRT. Furthermore, while decreasing SRT increased the proliferation of antibiotic resistance genes (ARGs), thermal hydrolysis could effectively reduce most ARGs, indicating its potential to mitigate antibiotic resistance in the AD process. Overall, these results provide useful perceptions regarding the potential adoption of low-temperature THP in WRRFs with PS fermentation.

Enzyme-accelerated CO2 capture and storage (CCS) using paper and pulp residues as co-sequestrating agents.

In the present work, four CaCO3-rich solid residues from the pulp and paper industry (lime mud, green liquor sludge, electrostatic precipitator dust, and lime dregs) were assessed for their potential as co-sequestrating agents in carbon capture. Carbonic anhydrase (CA) was added to promote both CO2 hydration and residue mineral dissolution, offering an enhancement in CO2-capture yield under atmospheric (up to 4-fold) and industrial-gas mimic conditions (up to 2.2-fold). Geological CO2 storage using olivine as a reference material was employed in two stages: one involving mineral dissolution, with leaching of Mg2+ and SiO2 from olivine; and the second involving mineral carbonation, converting Mg2+ and bicarbonate to MgCO3 as a permanent storage form of CO2. The results showed an enhanced carbonation yield up to 6.9%, when CA was added in the prior CO2-capture step. The proposed route underlines the importance of the valorization of industrial residues toward achieving neutral, or even negative emissions in the case of bioenergy-based plants, without the need for energy-intensive compression and long-distance transport of the captured CO2. This is a proof of concept for an integrated strategy in which a biocatalyst is applied as a CO2-capture promoter while CO2 storage can be done near industrial sites with adequate geological characteristics.

Application of an electrochemical filter-press flowcell in an electrocoagulation-MBR system: Efficient membrane fouling mitigation

In this study, we present efficient fouling mitigation of a pre-pilot Membrane Bio Reactor (MBR) for the treatment of synthetic wastewater through real integration with the Electrochemical Coagulation (EC) process by the application of a satellite filter-press electrochemical flowcell at the recirculation line of permeate produced by submerged hollow fiber membrane module. Flowcell was equipped with an aluminum anode and a steel cathode. Results indicated that the application of 5 volts was the optimum level for an EC-MBR for the removal of COD and fouling mitigation. 5 V-EC led to ca. 80 ± 3% COD removal, while MBR and 5 V-EC-MBR achieved almost 63 ± 4 and > 99% COD removal after 6 hr HRT, respectively. Moreover, the optimum 5 V-EC-MBR extended the membrane operational time by ca. 35 days in comparison with MBR. The formation of large microorganism flocs/more porous sludge cake layer along with the entrapment of Extracellular Polymeric Substances (EPS), were found as major mechanisms influencing the fouling mitigation. Dynamic Light Scattering (DLS) resulted in mean particle size (MPS)/zeta potential (ZP) values of − 5 ± 2.3/89 and − 60 ± 3/12 µm/mV for mixed liquor sludge flocs of 5 V-EC-MBR and MBR respectively, while colloidal re-stabilization (change in the sign of ZP and reduced MPS) was observed when applying larger voltages than 5 V. The presence and the reduction of EPS were verified using Fourier Transform InfraRed (FTIR) and fluorescence Emission Excitation Matrix (EEM). The results of this study pave the way for future techno-economic evaluations of continuous pilot EC-MBR equipped with multiple electrochemical flowcells for the treatment of real wastewater.

Digesters as heat storage: Effects of the digester temperature on the process stability, sludge liquor quality, and the dewaterability.

Variation of the digester temperature during the year enables the operation of digesters as seasonal heat storage contributing to a holistic heat management at water resource recovery facilities. Full- and lab-scale process data were conducted to examine the effect of the digester temperature on process stability, sludge liquor quality, and dewaterability. Both full- and lab-scale digesters show a stable anaerobic degradation process with a hydraulic retention time of more than 20 days and organic load rates up to 2.2-kg COD/(m3 ·day) at temperatures between 33 and 53°C. The concentrations of soluble COD and ammonium-nitrogen in the sludge liquor digested at 53°C are 2.6 to 5.8 times and 1.3 times higher, respectively, than in the sludge liquor digested at 37°C. Dewatering tests show an enhancement of the dewaterability but a clear increase in the polymer demand at increased digester temperature. PRACTITIONER POINTS: Digesters can operate as seasonal heat storage within mesophilic and thermophilic temperatures Stable anaerobic degradation process for HRT above 20 days Maintenance of process stability as well as quantity and quality of biogas Increase of soluble COD in sludge liquor at higher temperatures Better dewaterability but higher demand for polymers with increasing temperature.

Enhancement of nutrient removal in an activated sludge process using aerobic granular sludge augmentation strategy with ammonium-based aeration control

To enhance nutrient removal from low-strength municipal wastewater in a continuous-flow activated sludge (CFAS) process using aerobic granular sludge (AGS) augmentation strategy, a pilot-scale demonstration was configured with a mainstream reactor (anaerobic/aerobic process) and a sidestream sequencing batch reactor for AGS production. The aeration of the mainstream reactor was controlled based on dissolved oxygen (DO) and ammonium concentrations during Phases I and II–III, respectively. During Phase III, an anoxic zone was created in the mainstream aerobic tank. Throughout the demonstration period, excellent sludge settleability in the mainstream reactor (SVI30 ≤ 80 mL g−1) under long sludge retention time conditions (≥12 d) allowed the maintenance of a high mixed liquor suspended solids concentration (≥3000 mg L−1). The total nitrogen (TN) removal ratio improved significantly during Phases II and III (49.3 ± 4.1% and 50.1 ± 10.2%, respectively) compared to Phase I (43.2 ± 5.5%). Low DO concentration (< 0.5 mg L−1) by the ammonium-based aeration tended to increase the simultaneous nitrification and denitrification efficiency (> 40%), enhancing TN removal (> 50%). The reduction of DO and nitrate concentrations in the returning sludge liquor can stabilize phosphorus removal (approximately 80% of the 25th percentile). In addition, the aeration efficiency during Phase III decreased by 26–29% compared to Phase I. These results suggest that the introduction of ammonium-based aeration control to the CFAS using the AGS augmentation strategy could contribute to superior sewerage treatment, including nutrient removal and a low carbon footprint.

Co-electron donors driven medium-chain fatty acids production: Roles of electron donors, reaction kinetics and metabolic pathways

Energy conversion of waste activated sludge alkaline fermentation liquor (WASAFL) to medium-chain fatty acids (MCFAs) is promising for sludge treatment and carbon recovery. However, the single electron donor (ED) fermentation for MCFAs production has irreparable defects. To resolve the respective shortcomings of single electron donor (ED) and improve the MCFAs production efficiency from WASAFL, a novel biotechnical process utilizing ethanol and lactate as co-EDs within different combination ratios were investigated. The results verified that MCFAs production was highest with ethanol to lactate ratio of 1:3 (6988.54 ± 208.18 mg COD/L), being 1.46 and 1.87 times of that with ethanol and lactate as single ED. The kinetic analysis results confirmed that ethanol to lactate ratio of 1:3 resulted in the highest MCFAs yield and formation rate. The microbial taxa results uncovered that the relative abundance of Sphaerochaeta and Haloimpatiens showed positive correlation with MCFAs production. The metabolic pathway analysis indicated that the ethanol oxidization, lactate oxidization, acrylate pathway, reverse β oxidization and fatty acid biosynthesis pathway might take place in the WASAFL fermentation system, contributing to the WASAFL-to-MCFAs conversion.

Coupling membrane electro-bioreactor with anammox process to treat wastewater at low temperatures

Membrane bioreactors (MBRs)have been extensively applied to municipal wastewater treatment. Nevertheless, MBRs cannot eliminate nutrients to an adequate level without extra operation units and intensive chemical supplies. Furthermore, low temperatures destroy the performance of the MBR process. In this work, a pioneering anammox membrane electro-bioreactor (MEBR/anammox) system was designed and operated at a constant flow rate of 7L/d with continuous monitoring of sludge liquor temperature (8–22 °C). The MEBR/anammox worked with a sludge retention time (SRT) of 20 days and a hydraulic retention time (HRT) of 24 h. It was found that temperature variations did not significantly influence the effluents quality in terms of nutrients and COD. At lower operating temperatures, the effluent concentrations of NH4-N, TN, PO4-P, and COD in the MEBR-anammox were 0.77 mg/L, 6.42 mg/L, 0.80 mg/L, and 24.95 mg/L, respectively. The corresponding removal efficiencies were 94.46%, 88.62%, 95.60%, and 90.76%, respectively. Taken together, the implementation of a low/periodic direct current (DC) of 14.85 A/m2 and anammox process inside the MBR, achieving a MEBR/anammox, was found to enhance the efficacy of the treatment system, improve sludge properties and increase membrane fouling control in low-temperature milieus compared to traditional MBR. The MEBR/anammox system, introduced in this work, establishes an innovative wastewater technology that minimizes the footprint, capital and operating expenditures of the plant. In addition, this system could open new prospects for the treatment of municipal sewage in cold regions.

Deammonification Potential of Pig Slurries and Vapor Condensates from Sewage Sludge Drying-Substrate Quality and Inhibition.

Deammonification is a well-established process for sludge liquor treatment and promising for wastewaters with high nitrogen loads because of its low energy demand compared to nitrification/denitrification. Two wastewaters with high NH4-N concentrations and a rising significance in Germany-pig slurry (12 samples) and condensates from sewage sludge drying (6 samples)-were studied for their deammonification potential. Furthermore, a comprehensive quality assessment is presented. Both wastewaters show a wide range in terms of CODt, CODs, TN and NH4-N, whereby condensates show a greater variability with no direct relation to dryer type or temperature. In the slurries, CODt shows a relative standard deviation of 106% (mean 21.1 g/L) and NH4-N of 33% (mean 2.29 g/L), while in condensates it reaches 148% for CODt (mean 2.0 g/L) and 122% for NH4-N (mean 0.7 g/L). No inhibition of ammonium-oxidizing-bacteria was detected in the slurries, while two out of five condensates showed an inhibition of >40%, one of >10% and two showed no inhibition at all. Since the inhibition could be avoided by mixing, deammonification can be recommended for condensate treatment. For slurry treatment, the importance of employing some form of solid-liquid-separation as a pretreatment was noted due to the associated COD.

Complex Agent for Phosphate Sequestration from Digested Sludge Liquor: Performances and Economic Cost Analysis

Phosphorus (P) management in the “water-energy-resource-nexus” in wastewater treatment plants (WWTPs) remains a longstanding challenge. P adsorption from the P-enriched digested sludge liquor (DSL) is a comparatively more practical and economically viable approach for P recovery in WWTPs. However, high concentrations of impurities in DSL might pose a negative and interferential effect on P adsorption, hindering the application of sorbents or precipitation methods. Given such a situation, highly efficient and cost-effective sorbent towards P reclamation from DSL is highly needed. Therefore, this study aims to develop a novel complex agent containing aluminum coagulant and superparamagnetic nano-sorbent (SNS) that can be used in magnetic seeding coagulation for P recovery. The complex agents with different PACl: SNS ratios showed varied turbidity removal rates and P recovery efficiencies and the optimal ratio was 15 mg PACl: 15 g SNS. PAC and SNS showed significant interaction because PAC could enhance P adsorption by shielding the interferential effect of colloidal impurities. In addition, the complex is highly regenerative, with turbidity and P removal rate stably maintained at 70–80% after 10 adsorption/regeneration cycles. The cost–benefit analysis of the dosing complex agent showed a dosing cost of 0.154 EUR/m3, admittedly much higher than the conventional magnetic seeding coagulation, which could probably be covered by the profit if the expensive and rare P product is reclaimed. This work indicated that the complex agent was superior due to its high adsorption capacity, easy separation, and repeated dosing, and therefore had the potential for P recovery from DSL.

Effects of air blower and pump failures on the performance of A2O processes for wastewater treatment

The unexpected failure of equipment such as pumps and fans in wastewater treatment plants can reduce wastewater treatment efficiency, leading to direct leakage of untreated wastewater into the environment. It is hence important to predict the possible consequences of equipment failure to minimize the leakage of harmful substances. This study examines the impacts of equipment shutdown on the performance and recovery time of a laboratory-scale anaerobic/anoxic/aerobic system with regard to reactor conditions and water quality. Two days after the air blowers are stopped, the concentrations of the soluble chemical oxygen demand, NH4–N, and PO4–P in the effluent of the settling tank increase to 122 mg/L, 23.8 mg/L, and 46.6 mg/L, respectively. These concentrations return to their initial values after 12, 24, and 48 h of restarting the air blowers. The concentrations of PO4–P and NO3–N in the effluent increase to 58 mg/L and 20 mg/L, respectively, about 24 h after stopping the return activated sludge and mixed liquor recirculation pumps, owing to the release of phosphates in the settling tank and inhibition of denitrification.

Enhanced Methane Production from Sludge Anaerobic Digestion with the Addition of Potassium Permanganate.

This work aims to reveal the effect of potassium permanganate (KMnO4) on the sludge anaerobic digestion process, as well as the relevant mechanisms. Experimental data showed that the biomethane production was gradually increased from 159.3 ± 3.0 to 211.5 ± 5.1 mL/g VSS (volatile suspended solids) when the KMnO4 content was increased from 0 to 0.08 g/g VSS, with an increasing rate of 32.8%. A further increase in the KMnO4 dosage however resulted in the decline of the methane yield. First-order kinetic model analysis indicated that higher methane production potentials and hydrolysis rates were achieved in KMnO4-added reactors than in the control. Mechanism analysis demonstrated that KMnO4 not only efficiently disintegrated the sludge flocs, which resulted in the increased contents of dissolved organics, but also enhanced the proportion of biodegradable substances in the sludge liquor. Meanwhile, the biodegradabilities of recalcitrant humus and lignocellulose substances were found to be promoted by KMnO4 treatment as higher methane yields were attained from KMnO4-treated model substrates. 16S rRNA analysis illustrated that the functional microbes participated in anaerobic digestion were largely enriched in the KMnO4-pretreated digestor. Furthermore, efficient inactivation of the fecal coliform was achieved by KMnO4 pretreatment.

Characterization and Removal of Microplastics in Landfill Leachate Treatment Plants in Istanbul, Turkey

This study was carried out to determine the abundance, size, and type of microplastics (MPs) in landfill leachate of Kömürcüoda and Odayeri sanitary landfills in Istanbul. Within this framework, membrane bioreactor (MBR)-ultrafiltration (UF) and nanofiltration (NF) samples were collected to determine the concentration of microplastics in both landfill leachate treatment plants (LLTPs). The highest suspected microplastic concentrations were determined to be 196, 147, and 183 particles/L in the mixed liquor sludge from a membrane bioreactor (MBR) in Kömürcüoda LLTP and aerobic and anoxic basins in Odayeri LLTPs. The main particle color detected in Kömürcüoda LLTP was transparent, followed by black, whereas transparent and blue were dominant in the Odayeri LLTP. In the effluents of UF and NF units of Kömürcüoda LLTP, the microplastic concentrations were 7.24 particle/L and 2 particle/L. The results show that UF and NF efficiently removed microplastics at 99%. In the effluent of the UF unit in Odayeri LLTP, approximately 96% microplastic removal was achieved. According to these results, the most common microplastic type in all units was fiber and the principal sizes were between 500 and 999 and 1000 and 1999 µm at all sampling points.

Mechanisms governing the dissolution of phosphorus and iron in sewage sludge by the bioacidification process and its correlation with iron phosphate speciation

In the last two decades, phosphorus (P) recovery from sewage sludge liquors gained much interest for its high-quality product potential. However, the consistently reported constraints are the low phosphorus availability and the technical-economical difficulties to increase it through chemical acidification. This article discusses the mechanisms of phosphorus dissolution by the biological acidification process (Biological acidification or acidic fermentation) as an alternative to chemical acidification. In addition, we investigate the potential correlation between the phosphorus dissolution and iron phosphate speciation of several types of sludge from different sewage treatment plants and P removal technologies. The results show that the percentage of P dissolution by bioacidification is always higher than the P dissolution by chemical acidification at equal pH for all types of sludge except for the settled primary sludge. The highest P dissolution was recorded for the sludge from the Enhanced Biological P Removal process assisted with Chemical P Removal process (EBPR-CPR) with around 65% of P dissolution. Three mechanisms were identified as contributing to the increased P dissolution by bioacidification: P release by the Polyphosphate Accumulating Organisms (PAO), P dissolution by pH decrease, and P dissolution by a biological activity at acidic pH (3.7–4) that includes iron reduction and aluminum dissolution. The principal component analysis and Pearson's correlation indicate that P dissolution by bioacidification is negatively correlated with the P-bound to ferric iron, hence positively correlated with the P-bound to ferrous iron, which characterizes the sludge from the EBPR-CPR process. This study suggests that the choice of the P removal technology significantly influences the P recovery from sewage sludge liquors.

Recovery of biomethane from a submerged anaerobic membrane bioreactor treating domestic wastewater blended with semi-solid organic wastes discharged from residential establishments

Recent research studies on the innovative concept of submerged anaerobic membrane bioreactor (SAnMBR) technology have demonstrated superior treatment and operational performance for treating a broad range of waste streams discharged from various industries. This study aimed to investigate the treatment and recovery of biomethane (bio-CH4) performance of ceramic ultrafiltration (UF) coupled with ”co-digestion based SAnMBR”, which was not previously studied by others, for treating an organic fraction of food waste (OFFW) blended with domestic wastewater (DWW) at surge organic loading rates (OLRs) disposed at modern high-rise establishments and similar residential clusters. The SAnMBR was operated in five phases (Phase 1–5), with different organic loading rates (OLRs) varying from 0.49 to 22.57 kg-COD/m3/d. All bio-CH4, mixed liquor sludge, and treated permeate samples were analyzed using standard methods. The key parameters representing the cumulative bio-CH4 yield during each phase were estimated using sigmoidal models, and the simulated results were validated using ANOVA. It was found that the SAnMBR produced high-quality, low-turbid reclaimed water showing an increasing trend in yield of bio-CH4 with an increase of OLR. It was also observed that the SAnMBR demonstrated stable and superior treatment performance at shock-loads of organics. The maximum bio-CH4 yield recorded during the study was 73.06 ± 6.48%. The findings of this study confirmed the suitability of applying this novel concept of ”co-digestion-based SAnMBR” towards sustainable and efficient waste management in modern-high rise establishments.

Industrial Waste Pretreatment Approach for 3D Printing of Sustainable Building Materials

The large volume of industrial by-products and wastes from the construction, timber and paper industries has become a serious challenge worldwide. Recycling these industrial wastes as functional materials in the construction industry is an efficient approach for sustainable development. This study presents a pretreatment approach for recycling construction and demolition waste (CDW) and industrial side-streams (such as green liquor sludge, fiber waste, flotation sand and fly ash) in order to produce a geopolymer for the 3D printing of construction materials. A treatment approach was developed for screening the residues from CDW with a maximum size of 16 mm and for a combined line treatment for industrial side streams. The treatment processes utilized suitable and economical separation techniques for the recycling of waste materials. The crushing of the screened residues resulted in a homogeneous material size that facilitates the separation of mixed wastes and simplifies the classification of materials. The combined plant enabled the cost-effective treatment of various industrial wastes in a single process unit. The results show that the economic and environmental impact of the chosen techniques, in terms of their energy consumption, is highly dependent on the treatment line, separation technique and quantity of the individual waste that is processed. These recycled industrial wastes can be used as sustainable materials for the production of geopolymer concrete, contributing to the sustainability of the construction industry.

Insight into the sludge reduction performances by hydrodynamic cavitation

Insight into the sludge reduction performances by hydrodynamic cavitation (HC) were investigated. Mixed liquor suspended sludge (MLSS) and mixed liquor volatile suspended solids (MLVSS) decreased first and then increased as the increase of HC time from 0 to 240 min, and the lowest MLSS was 756.86 mg/L at 120 min. HC treatment promoted the increase in the solute chemical oxygen demand (sCOD) concentration and disintegration degree (DDsCOD) of sludge, and the values of sCOD and DDsCOD at 240 min were 319.66 mg/L and 22.98 %, respectively. The particle sizes at the 10th percentile (d(0.1)), the 50th percentile (d(0.5)) and the 90th percentile (d(0.9)) in particle size distributions decreased from 8.97, 21.10 and 49.10 μm to 0.04, 4.45 and 26.90 μm, respectively. The protein concentration in tightly bound extracellular polymers (TB-EPS) reduced with the increasing HC time from 0 to 240 min, while that in loosely bound EPS (LB-EPS) decreased firstly (during 0–120 min) and then gradually increased (during 120–240 min). As the increase of HC time, tryptophan protein in LB-EPS at 120 min and tyrosine protein in TB-EPS at 240 min disappeared in 3D excitation–emission matrix spectra.

Production of volatile fatty acids concomitant with phosphorus removal and lignin recovery by co-fermentation of waste activated sludge and black liquor

Waste activated sludge (WAS) and black liquor (BL) are the stubborn solid waste and wastewater in the industry that need high investment and operational costs for treatment. In this study, co-fermentation of WAS and BL was performed following a novel process for the production of volatile fatty acids (VFAs) concomitant with phosphorus removal and lignin recovery. BL offers alkaline liquor for WAS pretreatment, and the organic carbon in BL can be used for fermentation. The results showed that the semi-continuous fermentation test at pH 10 and the addition of 800 mg/L of Mg2+ were the optimal conditions for the production of VFAs (approximately 15,000 mg/L) and P removal (≈94%). Additionally, Mg2+ was suited to remove P due to the weak adsorption of Mg2+ by BL under alkaline conditions. Moreover, the composition of VFAs was affected by the pH, for example, high ratios of acetate and propionate were obtained under conditions of high and low pH, respectively. The dominant functional bacteria of Alkalibacterium, Propionibacterium, Proteiniphilum, and Tessaracoccus were found through the analysis of microbial diversity to be responsible for the production of VFAs. The bioconversion of small molecular lignin was also demonstrated through the characterization analyses. Co-fermentation was suggested as an economic and eco-friendly strategy for the treatment and resource utilization of WAS and BL via the overall assessment of the technical process.

The effect of aeration mode on the operational effectiveness and membrane bioreactors for greywater treatment and membrane fouling

This study aims to investigated the effect of aeration mode on membrane bioreactors (MBRs) using a self-designed integrated hollow fiber MBR and flat sheet organic MBR for rural greywater treatment. The pollutant removal efficiency, characteristics of activated sludge and mixed liquor, and mechanisms of membrane fouling were systematically analyzed under intermittent aeration and continuous modes. The results indicate that the permeability of MBRs in intermittent aeration mode is higher than that in the continuous aeration mode when operating at the same aeration rate. Due to the higher extracellular polymeric substance (EPS) and soluble microbial product (SMP) concentrations. The removal rates of TN and TP by both MBRs at the intermittent aeration mode were higher than those in the continuous aeration mode due to the difference in the aeration environment. Compared to the flat-sheet organic membrane, the hollow-fiber membrane surface was more likely to form biofilms, which cause biological fouling.The relative abundance of Thermomonas showed a positive correlation with the EPS concentration, indicating that Thermomonas participates in EPS synthesis. This study provides a theoretical basis for evaluating the influence of aeration modes on MBRs,and would be a useful guide for the better control of membrane fouling and treatment of rural greywater.