Metabolic uncoupler, 3,3′,4′,5-tetrachlorosalicylanilide addition for sludge reduction and fouling control in a gravity-driven membrane bioreactor

• Effects of metabolic uncoupler TCS on the performances of GDMBR were evaluated. • Sludge EPS reduced and transformed into dissolved SMP when TCS was added. • Appropriate TCS increased the permeability and reduced cake layer fouling. • High dosage aggravated fouling due to compact cake layer with low bio-activity. The gravity-driven membrane bioreactor (MBR)system is promising for decentralized sewage treatment because of its low energy consumption and maintenance requirements. However, the growing sludge not only increases membrane fouling, but also augments operational complexities (sludge discharge). We added the metabolic uncoupler 3,3′,4′,5-tetrachlorosalicylanilide (TCS) to the system to deal with the mentioned issues. Based on the results, TCS addition effectively decreased sludge ATP and sludge yield (reduced by 50%). Extracellular polymeric substances (EPS; proteins and polysaccharides) decreased with the addition of TCS and were transformed into dissolved soluble microbial products (SMPs) in the bulk solution, leading to the break of sludge flocs into small fragments. Permeability was increased by more than two times, reaching 60–70 L/m²/h bar when 10–30 mg/L TCS were added, because of the reduced suspended sludge and the formation of a thin cake layer with low EPS levels. Resistance analyses confirmed that appropriate dosages of TCS primarily decreased the cake layer and hydraulically reversible resistances. Permeability decreased at high dosage (50 mg/L) due to the release of excess sludge fragments and SMP into the supernatant, with a thin but more compact fouling layer with low bioactivity developing on the membrane surface, causing higher cake layer and pore blocking resistances. Our study provides a fundamental understanding of how a metabolic uncoupler affects the sludge and bio-fouling layers at different dosages, with practical relevance for in situ sludge reduction and membrane fouling alleviation in MBR systems.     

A “Seawater-in-Sludge” approach for capacitive biochar production via the alkaline and alkaline earth metals activation

• Capacitive biochar was produced from sewage sludge. • Seawater was proved to be an alternative activation agent. • Minerals vaporization increased the surface area of biochar. • Molten salts acted as natural templates for the development of porous structure. Sewage sludge is a potential precursor for biochar production, but its effective utilization involves costly activation steps. To modify biochar properties while ensuring cost-effectiveness, we examined the feasibility of using seawater as an agent to activate biochar produced from sewage sludge. In our proof-of-concept study, seawater was proven to be an effective activation agent for biochar production, achieving a surface area of 480.3 m²/g with hierarchical porosity distribution. Benefited from our design, the catalytic effect of seawater increased not only the surface area but also the graphitization degree of biochar when comparing the pyrolysis of sewage sludge without seawater. This leads to seawater activated biochar electrodes with lower resistance, higher capacitance of 113.9 F/g comparing with control groups without seawater. Leveraging the global increase in the salinity of groundwater, especially in coastal areas, these findings provide an opportunity for recovering a valuable carbon resource from sludge.     

Co-application of energy uncoupling and ultrafiltration in sludge treatment: Evaluations of sludge reduction,supernatant recovery and membrane fouling control

• Effects of metabolic uncouplers addition on sludge reduction were carried out. • TCS addition effectively inhibited ATP synthesis and reduced sludge yield. • The effluent quality such as TOC and ammonia deteriorated but not significantly. • Suitable dosage retarded biofouling during sludge water recovery by UF membrane. Energy uncoupling is often used for sludge reduction because it is easy to operate and does not require a significant amount of extra equipments (i.e. no additional tank required). However, over time the supernatant extracted using this method can deteriorate, ultimately requiring further treatment. The purpose of this study was to determine the effect of using a low-pressure ultrafiltration membrane process for sludge water recovery after the sludge had undergone an energy uncoupling treatment (using 3,3′,4′,5-tetrachlorosalicylanilide (TCS)). Energy uncoupling was found to break apart sludge floc by reducing extracellular polymeric substances (EPS) and adenosine triphosphate (ATP) content. Analysis of supernatant indicated that when energy uncoupling and membrane filtration were co-applied and the TCS dosage was below 30 mg/L, there was no significant deterioration in organic component removal. However, ammonia and phosphate concentrations were found to increase as the concentration of TCS added increased. Additionally, due to low sludge concentrations and EPS contents, addition of 30–60 mg/L TCS during sludge reduction increased the permeate flux (two times higher than the control) and decreased the hydraulic reversible and cake layer resistances. In contrast, high dosage of TCS aggravated membrane fouling by forming compact fouling layers. In general, this study found that the co-application of energy uncoupling and membrane filtration processes represents an effective alternative method for simultaneous sludge reduction and sludge supernatant recovery.     

Bioaerosolization behavior along sewage sludge biostabilization

• Aerosolization behavior during a lab-scale sludge biostabilization was determined. • Many pathogenic species were identified to be preferentially aerosolized. • Bioaerosol concentration along the biostabilization ranged from 160 to 1440 cell/m³. • Sludge aerosolization behavior was different with that of other biowaste. Biostabilization is a cost-effective method for the beneficial utilization of sewage sludge. However, during the operation of sludge biostabilization, some microbial species could be released into the atmospheric environment from the solid-phase of sludge easily and present a high risk to human health. This study aimed to evaluate the risk of bioaerosol during sludge biostabilization. We found a total of nine bacterial phyla, one archaeal phylum, and two fungal phyla in the bioaerosol samples. Among them, Proteobacteria, Actinobacteria, Bacteroidetes, and Ascomycota were the dominant phyla. In addition, the bioaerosolization indexes (BI) of prokaryotic phyla and fungal phyla ranged 0–45 and 0–487, respectively. Massilia, Pseudarthrobacter, Pseudomonas, Tremellales spp., and Fusarium were the preferentially aerosolized microbial genera with maximum bioaerosolization indexes of 19962, 10360, 1802, 3055, and 7398. The bioaerosol concentration during the biostabilization ranged from 160 to 1440 cell/m³, and we identified species such as Stenotrophomonas rhizophila and Fusarium graminerum with high bioaerosolization indexes that could be threats to human health. Euryachaeota, which belongs to archaeal phyla, had the highest biostabilization index in our study. We also found that Pseudarthrobacter was the easiest to aerosolize during the sludge biostabilization process.     

Feasibility assessment of up-flow anaerobic sludge blanket treatment of sulfamethoxazole pharmaceutical wastewater

The UASB system successfully treated sulfamethoxazole pharmaceutical wastewater. High concentration sulfate of this wastewater was the main refractory factor. UASB recovery performance after a few days of inflow arrest was studied. The optimal UASB operating conditions for practical application were determined. Treatment of sulfamethoxazole pharmaceutical wastewater is a big challenge. In this study, a series of anaerobic evaluation tests on pharmaceutical wastewater from different operating units was conducted to evaluate the feasibility of using anaerobic digestion, and the results indicated that the key refractory factor for anaerobic treatment of this wastewater was the high sulfate concentration. A laboratory-scale up-flow anaerobic sludge blanket (UASB) reactor was operated for 195 days to investigate the effects of the influent chemical oxygen demand (COD), organic loading rate (OLR), and COD/SO₄^2? ratio on the biodegradation of sulfamethoxazole in pharmaceutical wastewater and the process performance. The electron flow indicated that methanogenesis was still the dominant reaction although sulfidogenesis was enhanced with a stepwise decrease in the influent COD/SO₄^2? ratio. For the treated sulfamethoxazole pharmaceutical wastewater, a COD of 4983 mg/L (diluted by 50%), OLR of 2.5 kg COD/(m³·d), and COD/SO₄^2? ratio of more than 5 were suitable for practical applications. The recovery performance indicated that the system could resume operation quickly even if production was halted for a few days.     

The size distribution of airborne bacteria and human pathogenic bacteria in a commercial composting plant

•Bacterial concentrations from eight stages were 10⁴–10⁵copies/m³. •Diameter influenced clustering of bacterial and HPB lineages. •Dg of 8 HPB ranged from 2.42 to 5.09 μm in composting areas. •Dg of 8 HPB ranged from 3.70 to 8.96 μm in packaging areas. •HPB had high concentrations and small sizes in composting areas. Composting plants are regarded as one of the important sources of environmental bioaerosols. However, limitations in the size distribution of airborne bacteria have prevented our comprehensive understanding of their risk to human health and their dispersal behavior. In this study, different sizes of airborne bacteria were collected using an eight-stage impactor from a full-scale composting facility. Size-related abundance and communities of airborne bacteria as well as human pathogenic bacteria (HPB) were investigated using 16S rRNA gene sequencing coupled with droplet digital PCR. Our results indicate that the bacterial concentrations from the eight stages were approximately 10⁴–10⁵copies/m³. Although no statistical correlation was detected between the particle size and the Shannon index, the influence of size on bacterial lineages was observed in both composting and packaging areas. For airborne bacteria from different stages, the dominant phyla were Firmicutes, Proteobacteria, and Actinobacteria, and the dominant genera was Bacillus. Seven out of eight HPB with a small geometric mean aerodynamic diameter had a high concentration in composting areas. Based on diameters of 2.42 to 5.09 μm, most HPB in the composting areas were expected to be deposited on the bronchus and secondary bronchus. However, in the packaging areas, the deposition of HPB (diameters 3.70 to 8.96 μm) occurred in the upper part of the respiratory tract. Our results on the size distribution, abundance, and diversity of these bacteria offer important information for the systematic evaluation of bacterial pathogenicity and the potential health impacts on workers in composting plants and the surrounding residents.     

Anaerobic biodegradation of trimethoprim with sulfate as an electron acceptor

Anaerobic biodegradation of trimethoprim (TMP) coupled with sulfate reduction. Demethylation of TMP is the first step in the acclimated microbial consortia. The potential degraders and fermenters were enriched in the acclimated consortia. Activated sludge and river sediment had similar core microbiomes. Trimethoprim (TMP) is an antibiotic frequently detected in various environments. Microorganisms are the main drivers of emerging antibiotic contaminant degradation in the environment. However, the feasibility and stability of the anaerobic biodegradation of TMP with sulfate as an electron acceptor remain poorly understood. Here, TMP-degrading microbial consortia were successfully enriched from municipal activated sludge (AS) and river sediment (RS) as the initial inoculums. The acclimated consortia were capable of transforming TMP through demethylation, and the hydroxyl-substituted demethylated product (4-desmethyl-TMP) was further degraded. The biodegradation of TMP followed a 3-parameter sigmoid kinetic model. The potential degraders (Acetobacterium, Desulfovibrio, Desulfobulbus, and unidentified Peptococcaceae) and fermenters (Lentimicrobium and Petrimonas) were significantly enriched in the acclimated consortia. The AS- and RS-acclimated TMP-degrading consortia had similar core microbiomes. The anaerobic biodegradation of TMP could be coupled with sulfate respiration, which gives new insights into the antibiotic fate in real environments and provides a new route for the bioremediation of antibiotic-contaminated environments.     

New method for efficient control of hydrogen sulfide and methane in gravity sewers: Combination of NaOH and nitrite

• The combination of NaOH and nitrite was used to control harmful gas in sewers. • Hydrogen sulfide and methane in airspace were reduced by 96.01% and 91.49%. • Changes in sewage quality and greenhouse effect by chemical dosing were negligible. • The strong destructive effects on biofilm slowed down the recovery of harmful gases. • The cost of the method was only 3.92 × 10⁻³ $/m³. An innovative treatment method by the combination of NaOH and nitrite is proposed for controlling hydrogen sulfide and methane in gravity sewers and overcome the drawbacks of the conventional single chemical treatment. Four reactors simulating gravity sewers were set up to assess the effectiveness of the proposed method. Findings demonstrated hydrogen sulfide and methane reductions of about 96.01% and 91.49%, respectively, by the combined addition of NaOH and nitrite. The consumption of NaNO₂ decreased by 42.90%, and the consumption rate of NaOH also showed a downward trend. Compared with a single application of NaNO₂, the C/N ratio of wastewater was increased to about 0.61 mg COD/mg N. The greenhouse effect of intermediate N₂O and residual methane was about 48.80 gCO₂/m³, which is far lower than that of methane without control (260 gCO₂/m³). Biofilm was destroyed to prevent it from entering the sewage by the chemical additives, which reduced the biomass and inhibited the recovery of biofilm activity to prolong the control time. The sulfide production rate and sulfate reduction rate were reduced by 92.32% and 85.28%, respectively. Compared with conventional control methods, the cost of this new method was only 3.92 × 10⁻³ $/m³, which is potentially a cost-effective strategy for sulfide and methane control in gravity sewers.     

Enhanced hydrogen production in microbial electrolysis through strategies of carbon recovery from alkaline/thermal treated sludge

• High hydrogen yield is recovered from thermal-alkaline pretreated sludge. • Separating SFL by centrifugation is better than filtration for hydrogen recovery. • The cascaded bioconversion of complex substrates in MECs are studied. • Energy and electron efficiency related to substrate conversion are evaluated. The aim of this study was to investigate the biohydrogen production from thermal (T), alkaline (A) or thermal-alkaline (TA) pretreated sludge fermentation liquid (SFL) in a microbial electrolysis cells (MECs) without buffer addition. Highest hydrogen yield of 36.87±4.36 mgH₂/gVSS (0.026 m³/kg COD) was achieved in TA pretreated SFL separated by centrifugation, which was 5.12, 2.35 and 43.25 times higher than that of individual alkaline, thermal pretreatment and raw sludge, respectively. Separating SFL from sludge by centrifugation eliminated the negative effects of particulate matters, was more conducive for hydrogen production than filtration. The accumulated short chain fatty acid (SCFAs) after pretreatments were the main substrates for MEC hydrogen production. The maximum utilization ratio of acetic acid, propionic acid and n-butyric acid was 93.69%, 90.72% and 91.85%, respectively. These results revealed that pretreated WAS was highly efficient to stimulate the accumulation of SCFAs. And the characteristics and cascade bioconversion of complex substrates were the main factor that determined the energy efficiency and hydrogen conversion rate of MECs.     

Effects of hydraulic retention time on net present value and performance in a membrane bioreactor treating antibiotic production wastewater

• The membrane bioreactor cost decreased by 38.2% by decreasing HRT from 72 h to 36 h. • Capital and operation costs contributed 62.1% and 37.9% to decreased costs. • The membrane bioreactor is 32.6% cheaper than the oxidation ditch for treatment. • The effluent COD also improved from 709.93±62.75 mg/L to 280±17.32 mg/L. • Further treatment also benefited from lower pretreatment investment. A cost sensitivity analysis was performed for an industrial membrane bioreactor to quantify the effects of hydraulic retention times and related operational parameters on cost. Different hydraulic retention times (72–24 h) were subjected to a flat-sheet membrane bioreactor updated from an existing 72 h oxidation ditch treating antibiotic production wastewater. Field experimental data from the membrane bioreactor, both full-scale (500 m³/d) and pilot (1.0 m³/d), were used to calculate the net present value (NPV), incorporating both capital expenditure (CAPEX) and operating expenditure. The results showed that the tank cost was estimated above membrane cost in the membrane bioreactor. The decreased hydraulic retention time from 72 to 36 h reduced the NPV by 38.2%, where capital expenditure contributed 24.2% more than operational expenditure. Tank construction cost was decisive in determining the net present value contributed 62.1% to the capital expenditure. The membrane bioreactor has the advantage of a longer lifespan flat-sheet membrane, while flux decline was tolerable. The antibiotics decreased to 1.87±0.33 mg/L in the MBR effluent. The upgrade to the membrane bioreactor also benefited further treatments by 10.1%–44.7% lower direct investment.     

Characteristic and correlation analysis of influent and energy consumption of wastewater treatment plants in Taihu Basin

Poor biodegradability and insufficient carbon source are discovered from influent. Influent indices presented positively normal distribution or skewed distribution. Average energy consumption of WWTPs in Taihu Basin was as high as 0.458 kWh/m³. Energy consumption increases with the increase in influent volume and COD reduction. The total energy consumption decreases with the NH₃-N reduction. The water quality and energy consumption of wastewater treatment plants (WWTPs) in Taihu Basin were evaluated on the basis of the operation data from 204 municipal WWTPs in the basin by using various statistical methods. The influent ammonia nitrogen (NH₃-N) and total nitrogen (TN) of WWTPs in Taihu Basin showed normal distribution, whereas chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), suspended solid (SS), and total phosphorus (TP) showed positively skewed distribution. The influent BOD₅/COD was 0.4%–0.6%, only 39.2% SS/BOD₅ exceeded the standard by 36.3%, the average BOD₅/TN was 3.82, and the probability of influent BOD₅/TP>20 was 82.8%. The average energy consumption of WWTPs in Taihu Basin in 2017 was 0.458 kWh/m³. The specific energy consumption of WWTPs with a daily treatment capacity of more than 5 × 10⁴ m³ in Taihu Basin was stable at 0.33 kWh/m³. A power function relationship was observed between the reduction in COD and NH₃-N and the specific energy consumption of pollutant reduction, and the higher the pollutant reduction is, the lower the specific energy consumption of pollutant reduction presents. In addition, a linear relationship existed between the energy consumption of WWTPs and the specific energy consumption of influent volume and pollutant reduction. Therefore, upgrading and operation with less energy consumption of WWTPs is imperative and the suggestions for Taihu WWTPs based on stringent discharge standard are proposed in detail.     

Trophic mode and organics metabolic characteristic of fungal community in swine manure composting

Fungal trophic modes and substrates utilization ability was observed in composting. Fungi had the higher diversity and more trophic types in thermophilic phase. Fungi had the higher metabolic potential in fresh swine manure and mature production. Redox potential, organics and moisture are main factors impacting fungal community. Composting reduced pathogenic fungi and enrich dung saprotroph fungi in swine manure. The succession of fungal community, trophic mode and metabolic characteristics were evaluated in 60 days composting of swine manure by high-throughput sequencing, FUNGuild and Biolog method, respectively. The result showed that the fungal community diversity reached to the highest level (76 OTUs) in the thermophilic phase of composting, then sustained decline to 15 OTUs after incubation. There were 10 fungal function groups in the raw swine manure. Pathotroph-saprotroph fungi reached to 15.91% on Day-10 but disappeared on Day-60. Dung saprotroph-undefined saprotroph fungi grown from 0.19% to 52.39% during the treatment. The fungal community had more functional groups but the lower substrate degradation rates in the thermophilic phase. The fungal communities on Day-0 and Day-60 had the highest degradation rates of amino acids and polymers, respectively. Redundancy analysis showed that ORP (49.6%), VS/Ash (45.3%) and moisture (39.2%) were the main influence factors on the succession of fungal community in the swine manure composting process.     

Start-up of PN-anammox system under low inoculation quantity and its restoration after low-loading rate shock

• PN-A was start-up under low inoculation amount and a higher NRR was achieved. • PN-anammox system was successfully restored by aggressive sludge discharge. • Increase in granular sludge was the important factor to rapid recovery. • Enrichment of AOB and AnAOB in granular sludge favors the stable operation. Partial nitritation (PN)-anaerobic ammonium oxidation (anammox) is a promising pathway for the biological treatment of wastewater. However, the destruction of the system caused by excessive accumulation of nitrate in long-term operation remains a challenge. In this study, PN-anammox was initialized with low inoculation quantity in an air-lift reactor. The nitrogen removal rate of 0.71 kgN/(m³·d) was obtained, which was far higher than the seed sludge (0.3 kgN/(m³·d)). Thereafter, excess nitrate build-up was observed under low-loading conditions, and recovery strategies for the PN-anammox system were investigated. Experimental results suggest that increasing the nitrogen loading rate as well as the concentration of free ammonium failed to effectively suppress the nitrite oxidation bacteria (NOB) after the PN-anammox system was disrupted. Afterwards, effluent back-flow was added into the reactor to control the up-flow velocity. As a result, an aggressive discharge of sludge that promoted the synergetic growth of functional bacteria was achieved, leading to the successful restoration of the PN-anammox system. The partial nitritation and anammox activity were in balance, and an increase in nitrogen removal rate up to 1.07 kgN/(m³·d) was obtained with a nitrogen removal efficiency of 82.4% after recovery. Besides, the proportion of granular sludge (over 200 mm) increased from 33.67% to 82.82%. Ammonium oxidation bacteria (AOB) along with anammox bacteria were enriched in the granular sludge during the recovery period, which was crucial for the recovery and stable operation of the PN-anammox system.     

The impact of ultrasonic treatment on activity of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria in activated sludge

Conditions for ultrasonic treatment to achieve partial nitritation are optimized. Ultrasound reduces metabolic activity and releases intracellular metabolites. Mechanical shearing is essential to inhibit nitrite oxidation. The ultrasonic treatment of sludge has been considered as an effective method to facilitate the partial nitritation of municipal sewage. This study aims to reveal the effects of ultrasound on ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). The impact factors including ultrasonic irradiation time and intensity, sludge concentration, thermal effect and released free radicals were studied. The maximized difference between the changes in AOB and NOB activities were obtained with 10 g mixed liquor suspended solids (MLSS)/L, using 0.9 kJ/mL ultrasonic energy density and 12 h interval time. The increased ultrasonic intensity destroyed the floc structure of activated sludge, increased the microbial death, and decreased the cellular ATP level. Further, the mechanism exploration indicated that the mechanical shearing could be a critical factor in achieving the nitritation with inhibitory effect on nitrite oxidation.     

Enhanced methane production during long-term UASB operation at high organic loads as enabled by the immobilized Fungi

• Fungi enable the constant UASB operation even at OLR of 25.0 kg/(m³×d). • The COD removal of 85.9% and methane production of 5.6 m³/(m³×d) are achieved. • Fungi inhibit VFAs accumulation and favor EPS generation and sludge granulation. • Fungi enrich methanogenic archaea and promote methanogenic pathways. Anaerobic digestion is widely applied in organic wastewater treatment coupled with bioenergy production, and how to stabilize its work at the high organic loading rate (OLR) remains a challenge. Herein, we proposed a new strategy to address this issue via involving the synergetic role of the Aspergillus sydowii 8L-9-F02 immobilized beads (AEBs). A long-term (210-day) continuous-mode operation indicated that the upflow anaerobic sludge bed (UASB) reactor (R1, with AEBs added) could achieve the OLR as high as 25.0 kg/(m³×d), whereas the control reactor (R0, with AEBs free) could only tolerate the maximum OLR of 13.3 kg/(m³×d). Remarkably, much higher COD removal (85.9% vs 23.9%) and methane production (5.4 m³/(m³×d) vs 2.2 m³/(m³×d)) were achieved in R1 than R0 at the OLR of 25.0 kg/(m³×d). Such favorable effect results from the facts that fungi inhibit VFAs accumulation, favor the pH stabilization, promote the generation of more extracellular polymeric substance, and enhance the sludge granulation and settleability. Moreover, fungi may enhance the secretion of acetyl-coenzyme A, a key compound in converting organic matters to CO₂. In addition, fungi are favorable to enrich methanogenic archaea even at high OLR, improving the activity of acetate kinase and coenzyme F₄₂₀ for more efficient methanogenic pathway. This work may shed new light on how to achieve higher OLR and methane production in anaerobic digestion of wastewater.     

Distribution and removal of antibiotic resistance genes during anaerobic sludge digestion with alkaline,thermal hydrolysis and ultrasonic pretreatments

Sludge digestion is critical to control the spread of ARGs from wastewater to soil. Fate of ARGs in three pretreatment-AD processes was investigated. UP was more efficient for ARGs removal than AP and THP in pretreatment-AD process. The total ARGs concentration showed significant correlation with 16S rRNA gene. The bacteria carrying ARGs could be mainly affiliated with Proteobacteria. Sewage sludge in the wastewater treatment plants contains considerable amount of antibiotic resistance genes (ARGs). A few studies have reported that anaerobic digestion (AD) could successfully remove some ARGs from sewage sludge, but information on the fate of ARGs in sludge pretreatment-AD process is still very limited. In this study, three sludge pretreatment methods, including alkaline, thermal hydrolysis and ultrasonic pretreatments, were compared to investigate the distribution and removal of ARGs in the sludge pretreatment-AD process. Results showed that the ARGs removal efficiency of AD itself was approximately 50.77%, and if these three sludge pretreatments were applied, the total ARGs removal efficiency of the whole pretreatment-AD process could be improved up to 52.50%–75.07%. The ultrasonic pretreatment was more efficient than alkaline and thermal hydrolysis pretreatments. Although thermal hydrolysis reduced ARGs obviously, the total ARGs rebounded considerably after inoculation and were only removed slightly in the subsequent AD process. Furthermore, it was found that the total ARGs concentration significantly correlated with the amount of 16S rRNA gene during the pretreatment and AD processes, and the bacteria carrying ARGs could be mainly affiliated with Proteobacteria.     

Microbial community dynamics at high organic loading rates revealed by pyrosequencing during sugar refinery wastewater treatment in a UASB reactor

High strength sugar refinery wastewater was treated in a mesophilic UASB. Pyrosequencing reveals microbial community succession with OLR increase. Diversity of microbial communities in OLR12 is much higher than those in OLR36 and OLR54.0 kgCOD/(kg VSS·d). Fermentative bacteria could deal with increasing OLR through the increase of microbial diversity and quantity. Hydrogen-producing acotogens and methanogens mainly coped with high OLR shocks by increasing the quantity of community The performance and microbial community structure in an upflow anaerobic sludge blanket reactor (UASB) treating sugar refinery wastewater were investigated. The chemical oxygen demand (COD) removal reached above 92.0% at organic loading rates (OLRs) of 12.0–54.0 kgCOD/(m³·d). The volatile fatty acids (VFAs) in effluent were increased to 451.1 mg/L from 147.9 mg/L and the specific methane production rate improved by 1.2–2.2-fold as the OLR increased. The evolution of microbial communities in anaerobic sludge at three different OLRs was investigated using pyrosequencing. Operational taxonomic units (OTUs) at a 3% distance were 353, 337 and 233 for OLR12, OLR36 and OLR54, respectively. When the OLR was increased to 54.0 kgCOD /(m³·d) from 12.0 kgCOD/(m³·d) by stepwise, the microbial community structure were changed significantly. Five genera (Bacteroides, Trichococcus, Chryseobacterium, Longilinea and Aerococcus) were the dominant fermentative bacteria at the OLR 12.0 kgCOD/(m³·d). However, the sample of OLR36 was dominated by Lactococcus, Trichococcus, Anaeroarcus and Veillonella. At the last stage (OLR= 54.0 kgCOD/(m³·d)), the diversity and percentage of fermentative bacteria were markedly increased. Apart from fermentative bacteria, an obvious shift was observed in hydrogen-producing acetogens and non-acetotrophic methanogens as OLR increased. Syntrophobacter, Geobacter and Methanomethylovorans were the dominant hydrogen-producing acetogens and methylotrophic methanogens in the samples of OLR12 and OLR36. When the OLR was increased to 54.0 kgCOD/(m³·d), the main hydrogen-producing acetogens and hydrogenotrophic methanogens were substituted with Desulfovibrio and Methanospirillum. However, the composition of acetotrophic methanogens (Methanosaeta) was relatively stable during the whole operation period of the UASB reactor.     

Characterization of value-added chemicals derived from the thermal hydrolysis and wet oxidation of sewage sludge

• Hydrothermal treatment can greatly improve resource recovery from sewage sludge. • tCOD removal during WO was ~55% compared with ~23% after TH. • TOC solubilization during hydrothermal treatment followed first-order kinetics. • Solids and carbon balance confirmed loss of organics during thermal hydrolysis. • Reaction pathways for thermal hydrolysis and wet oxidation are proposed. We evaluated the effect of hydrothermal pretreatments, i.e., thermal hydrolysis (TH) and wet oxidation (WO) on sewage sludge to promote resource recovery. The hydrothermal processes were performed under mild temperature conditions (140°C–180°C) in a high pressure reactor. The reaction in acidic environment (pH= 3.3) suppressed the formation of the color imparting undesirable Maillard’s compounds. The oxidative conditions resulted in higher volatile suspended solids (VSS) reduction (~90%) and chemical oxygen demand (COD) removal (~55%) whereas TH caused VSS and COD removals of ~65% and ~27%, respectively at a temperature of 180°C. During TH, the concentrations of carbohydrates and proteins in treated sludge were 400–1000 mg/L and 1500–2500 mg/L, respectively. Whereas, WO resulted in solids solubilization followed by oxidative degradation of organics into smaller molecular weight carboxylic acids such as acetic acid (~400–500 mg/L). Based on sludge transformation products generated during the hydrothermal pretreatments, simplified reaction pathways are predicted. Finally, the application of macromolecules (such as proteins), VFAs and nutrients present in the treated sludge are also discussed. The future study should focus on the development of economic recovery methods for various value-added compounds.     

Recovery and reuse of floc sludge for high-performance capacitors

• The feasibility of facile fabrication of capacitor from floc sludge is discussed. • The porous carbon composites are obtained by acidification and KOH activation. • The as-prepared 3D structure has large surface area and optimal pore size. • Admirable specific capacitance and outstanding cycling stability are obtained. In this paper, floc sludge was transformed into porous carbon matrix composites by acidification and KOH activation at high temperature and used as an electrode material for application in capacitors. The effects of different treatment processes on the electrochemical properties of sludge materials were compared. The results of electrochemical tests showed that the sludge electrode exhibited excellent energy storage performance after HNO₃ acidification and KOH activation with a mass ratio of 3:1 (KOH/C). The specific capacitance of the sludge electrode reached 287 F/g at a current density of 1 A/g. In addition, the sludge electrode material showed excellent cycle stability (specific capacity retained at 93.4% after 5000 cycles at 5 A/g). Based on XRD, FTIR, SEM, TEM, and BET surface analysis, the morphology of sludge electrode materials can be effectively regulated by chemical pretreatment. The best-performing material showed a 3D porous morphology with a large specific surface area (2588 m²/g) and optimal pore size distribution, improving ion channels and charge conductivity. According to the life cycle assessment of floc sludge utilization, it reduced the resource consumption and toxicity risk by more than 90% compared with ordinary sludge disposal processes. This work provided a cost-effective and eco-friendly sludge reuse method and demonstrated the application potential of sludge-based materials in high-performance supercapacitors.     

Forward osmosis coupled with lime-soda ash softening for volume minimization of reverse osmosis concentrate and CaCO3 recovery: A case study on the coal chemical industry

• Forward osmosis (FO) coupled with chemical softening for CCI ROC minimization • Effective removal of scale precursor ions by lime-soda ash softening • Enhanced water recovery from 54% to 86% by mitigation of FO membrane scaling • High-purity CaCO₃ was recovered from the softening sludge • Membrane cleaning efficiency of 88.5% was obtained by EDTA for softened ROC Reverse osmosis (RO) is frequently used for water reclamation from treated wastewater or desalination plants. The RO concentrate (ROC) produced from the coal chemical industry (CCI) generally contains refractory organic pollutants and extremely high-concentration inorganic salts with a dissolved solids content of more than 20 g/L contributed by inorganic ions, such as Na⁺, Ca²⁺, Mg²⁺, Cl⁻, and SO₄²⁻. To address this issue, in this study, we focused on coupling forward osmosis (FO) with chemical softening (FO-CS) for the volume minimization of CCI ROC and the recovery of valuable resources in the form of CaCO₃. In the case of the real raw CCI ROC, softening treatment by lime-soda ash was shown to effectively remove Ca²⁺/Ba²⁺ (>98.5%) and Mg²⁺/Sr²⁺/Si (>80%), as well as significantly mitigate membrane scaling during FO. The softened ROC and raw ROC corresponded to a maximum water recovery of 86% and 54%, respectively. During cyclic FO tests (4 × 10 h), a 27% decline in the water flux was observed for raw ROC, whereas only 4% was observed for softened ROC. The cleaning efficiency using EDTA was also found to be considerably higher for softened ROC (88.5%) than that for raw ROC (49.0%). In addition, CaCO₃ (92.2% purity) was recovered from the softening sludge with an average yield of 5.6 kg/m³ treated ROC. This study provides a proof-of-concept demonstration of the FO-CS coupling process for ROC volume minimization and valuable resources recovery, which makes the treatment of CCI ROC more efficient and more economical.