The resistance of hydrogenotrophic methanogenic microorganisms to ofloxacin in sludge anaerobic digestion process.

Ofloxacin (OFL) is a commonly used antibiotic that can enter wastewater treatment plants and be adsorbed by the sludge, resulting in a high OFL concentration in sludge and affecting the subsequent sludge anaerobic digestion process. However, the micro mechanisms involved in this process have not been thoroughly studied. Therefore, this study focuses on the effect of OFL on the sludge anaerobic digestion of sludge to provide such support. The experimental results showed that the maximal methane yield decreased from 277.7 to 164.7 mL/g VSS with the OFL concentration increased from 0 to 300 mg/L. Additionally, OFL hindered the intermediate biochemical processes of hydrolysis, acidogenesis, acetogenesis, and acetoclastic methanogenesis. However, it promoted hydrogenotrophic methanogenesis process, using H2 as substrate, with the concentration of 300 mg/L OFL was 5.54 fold methane production of that in the control. Further investigation revealed that the negative effect of OFL was likely due to the induction of reactive oxygen species, which led to a decrease in cell activity and interference with the activity of key enzymes. Microbiological analysis revealed that OFL reduced the relative abundance of hydrolysis and acidogenesis bacteria, and Methanosaeta archaea, while increasing the relative abundance of hydrogenotrophic methanogenesis microorganism from 36.54% to 51.48% as the OFL concentration increase from 0 to 300 mg/L.

Performance and mechanisms of citric acid improving biotransformation of waste activated sludge into short-chain fatty acids.

Numerous effective chemical strategies have been explored for short-chain fatty acids (SCFAs) production from waste activated sludge (WAS), but many technologies have been questioned due to the chemical residues. This study proposed a citric acid (CA) treatment strategy for improving SCFAs production from WAS. The optimum SCFAs yield reached 384.4 mg COD/g VSS with 0.08 g CA/g TSS addition. Meanwhile, CA biodegradation occurred and its contribution to the yield of total SCFAs, especially acetic acid, cannot be ignored. Intensive exploration indicated the sludge decomposition, the biodegradability of fermentation substrates, as well as the abundance of fermenting microorganisms were definitely enhanced in the existence of CA. The optimization of SCFAs production techniques based on this study deserved further study. This study comprehensively revealed the performance and mechanisms of CA enhancing biotransformation of WAS into SCFAs and the findings promotes the research of carbon resource recovery from sludge.

Enhancing methane production from anaerobic digestion of waste activated sludge with addition of sodium lauroyl sarcosinate.

In this study, sodium lauroyl sarcosinate (SLS) was used to promote anaerobic digestion of waste activated sludge for producing methane. It was found maximum cumulative methane production increased from 98.1 ± 3.1 to 166.0 ± 4.3 mL/g Volatile Suspended Solids (VSS) with dosage increasing from 0 (control) to 40 mg SLS/g TSS. But the addition of SLS (>10 mg SLS/g Total Suspended Solids (TSS)) resulted in prolonged lag phase time. Microbiological analysis showed that Syntrophobacter and Syntrophomonas both got enriched in reactors fed with SLS. Furthermore, hydrogenotrophic methanogens genus got more enrichment in contrast to acetoclastic methanogens. Mechanism analysis indicated that addition SLS could decrease surface tension, and promote release of organic matters as well as improve activities of hydrolytic enzymes. Besides, SLS could be nearly degraded completely within 3 days, and its degradation intermediates could be further transformed into methane gradually, thus enhancing methane production eventually.

Tonalide facilitates methane production from anaerobic digestion of waste activated sludge.

Tonalide (AHTN), a typical polycyclic musk and an emerging pollutant, was found to be enriched in waste activated sludge (WAS). However, the research of its effect on WAS anaerobic digestion was seldom available. This research therefore investigated the effect of AHTN on WAS anaerobic digestion and the underlying mechanism through batch experiments using either real WAS or synthetic wastewaters as the digestion substrates. The results indicated that when the concentration of AHTN increased from 0 to 1000 mg/kg TSS in WAS, the methane production increased linearly from 125.0 ± 2.2 to 162.9 ± 1.6 mL/g VSS, while the AHTN concentration further increased to 2000 mg/kg TSS, the methane production decreased to 146.2 ± 2.1 mL/g VSS. At the same time AHTN can facilitate the utility of volatile fatty acid (VFAs), especially acetate and propionate. It was further found that the degradation efficiency of AHTN in anaerobic digestion was 42.7%. The mechanism investigation demonstrated that AHTN can promote the solubilization, homoacetogenesis, acetogenesis and methanogenesis processes, leading to an increase in methane production. Further analysis revealed that methanogenic archaea mainly belonged to the genera of Methanosaeta and Metheanobacterium, and their relative abundance increased accordingly with the addition of AHTN.

Norfloxacin-induced effect on enhanced biological phosphorus removal from wastewater after long-term exposure.

In this study, long-term experiments were performed under synthetic wastewater conditions to evaluated the potential impacts of norfloxacin (NOR) (10, 100 and 500 µg/L) on enhanced biological phosphorus removal (EBPR). Experimental result showed that long-term exposure to 10 µg/L NOR induced negligible effects on phosphorus removal. The presence of 100 µg/L NOR slightly decreased phosphorus removal efficiency to 94.41 ± 1.59 %. However, when NOR level further increased to 500 µg/L, phosphorus removal efficiency was significantly decreased from 97.96 ± 0.8 5% (control) to 82.33 ± 3.07 %. The mechanism study revealed that the presence of 500 µg/L NOR inhibited anaerobic phosphorus release and acetate uptake as well as aerobic phosphorus uptake during long-term exposure. It was also found that 500 µg/L NOR exposure suppressed the activity of key enzymes related to phosphorus removal but promoted the transformations of intracellular polyhydroxyalkanoate and glycogen. Microbial analysis revealed that that the presence of 500 µg/L NOR reduced the abundances of polyphosphate accumulating organisms but increased glycogen accumulating organisms, as compared the control.

Effect of citric acid on extracellular polymeric substances disruption and cell lysis in the waste activated sludge by pH regulation.

This paper investigated the effects of citric acid (CA) on extracellular polymer destruction and cell lysis in sludge at different initial pH by measuring capillary suction time (CST), extracellular polymeric substances (EPS) and intracellular bound water. The results indicated that under CA concentration at 0.05 g/g suspended solids (SS) and initial pH 4, the CST value decreased from 175.5 s to 112.3 s, slime extracellular polymeric substances (S-EPS) and loosely bound EPS (LB-EPS) content respectively to increase from 4.92 to 41.43, 2.27 to 5.49 mg/g volatile suspended solids (Vss), while tightly bound EPS (TB-EPS) content to decrease from 12.35 to 5.01 mg/g (Vss), which suggested CA could disrupt outer EPS effectively. Intracellular bound water content decreased from 1.23 g/g to 0.41 g/g dry solid (DS). As a result, CA could release intracellular bound water effectively, thereby improving sludge dewatering degree.

Heterogeneous activation of persulfate by Ag doped BiFeO3 composites for tetracycline degradation.

Persulfate (PS) activation have been extensively considered as a promising technology for removing recalcitrant pollutants, due to their production of radicals with superior oxidation reactivity. However, a catalyst with high reactive and convenient recovery for PS activation still remains to be developed. In this work, the silver-doped bismuth ferrite (Agx-BiFeO3, x = 0.1, 0.2, 0.3 and 0.4) catalysts with variable Ag content were synthesized via a facile sol-gel method and applied as heterogeneous catalyst in PS activation for tetracycline (TC) degradation. Ag0.4-BiFeO3 presented the best catalytic activity compared with other Ag doped BiFeO3 composites, 91% TC could be efficiently removed within 60 min under optimized conditions and the reaction rate constant was 0.0338 min-1. On the basis of the characterization analysis and catalytic test results, Ag could be the effective active site in PS activation and had a significant effect on PS activation. Moreover, the initial pH has negligible effect on the catalytic performance, indicating that Ag0.4-BiFeO3/PS system could work in a wide pH range. The results of electron spin-resonance spectroscopy and radical quenching tests suggested that both SO4- and OH radicals were involved in the Ag0.4-BiFeO3/PS system. The possible mechanism of Ag0.4-BiFeO3 activating PS and the major degradation pathway of TC degradation were proposed. At last, the reusability experiment results proved that Ag0.4-BiFeO3 catalyst still has a high catalytic performance after 4 times used.

The effects of thiosulfinates on methane production from anaerobic co-digestion of waste activated sludge and food waste and mitigate method.

Thiosulfinates, a natural antibiotic, existed in all parts of Allium, therefore might be accumulated in large amounts in food waste (FW). FW was often added into waste activated sludge (WAS) anaerobic digestion process as a kind of supplement for nutrition balance. However, the impact of thiosulfinates on methane production and the possible approach to mitigate its inhibition on the co-digestion process could be available in few literatures. This work was carried out in a series of batch experiment at pH 7.0 ±â€¯0.2 and 35 ±â€¯1.0 ℃ to promote the further understanding of this process. The experimental results showed that the methane accumulation decreased from 270.6 ±â€¯13.4 to 16.7 ±â€¯7.0 mL/g VSS (volatile suspended solids) when the initial concentration of thiosulfinates increased from 0 to 2.5 µg/g VSS. The activities of functional enzymes (F420 and CoM) were inhibited by 99.06% and 99.82% compared with control group when reactor contained 2.5 µg/g VSS thiosulfinates. Furthermore, different temperature, pH, and combination pretreat were applied to impair the inhibition of thiosulfinate. Compared with no pretreatment group, methane yield was increased by 2.26, 32.18 and 42.2-fold, respectively which group was under pretreatment method of heat (100 ℃), alkali (pH 9) and combination.

The inhibitory effect of thiosulfinate on volatile fatty acid and hydrogen production from anaerobic co-fermentation of food waste and waste activated sludge.

Thiosulfinate, a nature antibiotic, existed in all parts of Allium thereby accumulating in kitchen waste vastly. However, few literatures were available related to its influence on volatile fatty acids (VFA) and hydrogen production when kitchen waste digestion technology was applied. This study aimed to explore the inhibitory effect and the relevant mechanism. Experimental results showed that the hydrogen accumulation decreased from 23.2 ± 0.8 to 8.2 ± 0.1 mL/g VSS (volatile suspended solid) and maximal total VFA yield decreased from 765.7 ± 21.2 to 376.4 ± 21.7 mg COD (chemical oxygen demand)/g VSS when the dosage of thiosulfinate increased from 0 to 12.5 µg/g VSS. The mechanism study indicated, compared with control group, that the butyric acid decreased from 59% to 20.1% of total VFA yield when reactor in present of 12.5 µg/g VSS thiosulfinate. Moreover, the relative activities of functional enzymes were inhibited 73.4% (butyryl-CoA) and 72.7% (NADH), respectively.

Influence of low voltage electric field stimulation on hydrogen generation from anaerobic digestion of waste activated sludge.

Low voltage electric field is an important stimulation condition for biochemical metabolic of microorganism. But few literatures were available related to the effect of low voltage electric field on hydrogen production from anaerobic digestion of waste activated sludge (WAS). This study aims to explore such influencing thus carried a series experiments under 35 ± 1 °C and pH 7.0 ± 0.2. The experimental results showed that the hydrogen production increased from 28.1 to 32.5 mL/g VSS with electric field strengthening from 0 to 40 V/m. The mechanism explorations revealed that the yield of volatile fatty acids (VFAs) yield could reach 1.16-fold of control group when the highest-level electric field (40 V/m) forced in the anaerobic fermentation system with dextran as model substrate. Further analysis of relative activities of functional enzymes, such as NADH, acetate kinase, butyrate kinase and OAATC, showed that it was promoted by electric field stimulation as 2.09, 1.52, 1.28 and 1.16-fold of the control test, respectively. Meanwhile, the conductivity of fermentation liquor in presence of low voltage electric field stimulation increased 83% compared with the control group. This work verified the promotion of low voltage electric field stimulation on hydrogen production from anaerobic digestion of WAS and might provide a new sight for the green energy generation.

Effect of clarithromycin on the production of volatile fatty acids from waste activated sludge anaerobic fermentation.

This study investigated the effect of Clarithromycin (CLA) on volatile fatty acids (VFAs) production during waste activated sludge (WAS) anaerobic fermentation for the first time. Experimental results showed that when CLA concentration in WAS increased from 0 to 1000 mg/kg TSS, the maximum yield of VFAs increased from 27.7 to 35.7 mg COD/g VSS (without pH pretreatment) and from 59.3 to 65.6 mg COD/g VSS (initial pH 9 pretreatment), respectively. Mechanism exploration revealed that CLA facilitated the disruption of extracellular polymeric substances, thus promoting WAS solubilization. CLA inhibited all the other anaerobic fermentation processes. However, its inhibition to acetogenesis and methanogenesis was severer than that to hydrolysis and acidogenesis, resulting in the decrease in VFAs consumption. Microbial analysis showed that CLA slightly increased the abundance of microorganisms responsible for hydrolysis and acidogenesis whereas decreased the proportion of VFAs-consuming microorganisms.

Sulfate radical-mediated degradation of phenol and methylene blue by manganese oxide octahedral molecular sieve (OMS-2) activation of peroxymonosulfate.

Activation of peroxymonosulfate (PMS) has been concentrated on degrading refractory organic pollutants owing to the generation of sulfate radical ([Formula: see text]) with high standard redox potential. In this study, manganese oxide octahedral molecular sieve (OMS-2) with cryptomelane type was synthesized by a new hydrothermal method to activate PMS for the degradation of phenol and methylene blue (MB) in water. The as-prepared composites were fully characterized, and the effects of PMS dosage, OMS-2 dosage, initial pollutant concentration, pH, and chloride on the degradation of phenol were elaborately investigated. Moreover, the phenol degradation was evaluated through the variations of total organic carbon (TOC) and three-dimensional excitation emission matrix (3D-EEM), and reaction intermediates were also investigated. Both electron spin resonance (ESR) spectra and comparative experiments suggested [Formula: see text] and hydroxyl radical (HO•) took part in the phenol degradation and [Formula: see text] was more significant than HO•. The fine degradation efficiency of phenol in different water source, as well as the stability after continuous use, indicated the possible application of PMS/OMS-2 in real wastewater treatment.

Heterogeneous activation of peroxymonosulfate using Mn-Fe layered double hydroxide: Performance and mechanism for organic pollutant degradation.

On account of high oxidation ability of sulfate radical-based advanced oxidation processes (AOPs), the eco-friendly catalysts for peroxymonosulfate (PMS) activation have received considerable attentions. Previous studies mainly focused on Cobalt-based catalyst due to its high activation efficiency, such as Co3O4/MnO2 and FeCo-layered double hydroxide (LDH), whereas Cobalt-based catalyst usually has serious risk to environment. To avoid this risk, MnFe-LDH was primarily synthesized in this research by simple co-precipitation and subsequently utilized as an effective catalyst for peroxymonosulfate (PMS) activation to degrade organic pollutants. The experimental results demonstrated that MnFe-LDH with a lower dosage (0.20 g/L) could efficiently activate PMS to achieve 97.56% removal of target organic pollutants Acid Orange 7 (AO7). The AO7 degradation process followed the pseudo-first-order kinetic well with an activation energy of 21.32 kJ/mol. The intrinsic influencing mechanism was also investigated. The quenching experiment and electron spin resonance (ESR) indicated that sulfate and hydroxyl radicals were produced by the effective activation of PMS by MnFe-LDH, resulting in a high rate of decolorization. The possible AO7 removal pathway in the constructed MnFe-LDH/PMS system was presented on the basis of UV-vis spectrum analysis and GC-MS, which suggested that the AO7 degradation was firstly initiated by breaking azo linkages, then generated phenyl and naphthalene intermediates and finally presented as ring-opening products. This effective MnFe-LDH/PMS system showed great application potential in the purification of wastewater contaminated by refractory organic pollutants.

Enhanced methane production from waste activated sludge by combining calcium peroxide with ultrasonic: Performance, mechanism, and implication.

This study reported a novel and high-efficient pretreatment method for anaerobic digestion, i.e., combining calcium peroxide (CaO2) with ultrasonic (US), by which not only the methane production was remarkably improved but also the removal of refractory organic contaminants was enhanced. Experimental results showed the optimum condition for methane production was achieved at 0.1 g CaO2/g VSS combined with US (1 W/ml, 10 min). Under this condition, the maximal methane yield of 211.90 ±â€¯2.6 L CH4/kg VSS was obtained after 36 d of anaerobic digestion, which was respectively 1.36-fold, 1.19-fold and 1.26-fold of that from the control, solo US (1 W/ml, 10 min) and solo CaO2 (0.1 g/g VSS). Mechanism investigations revealed that CaO2 + US not only improved the disintegration of waste activated sludge (WAS) but also increased the proportion of biodegradable organic matters. Moreover, the total frequency of recalcitrant contaminants contained in WAS decreased significantly when CaO2 + US was applied.

Enhanced volatile fatty acids production from waste activated sludge anaerobic fermentation by adding tofu residue.

In this study, an economical and eco-friendly strategy (i.e., adding tofu residue (TR) into waste activated sludge (WAS)) to enhance volatile fatty acid (VFA) production was reported. Experimental results indicated that the maximal VFA yield at T/W ratio (TR/WAS, the ratio of the volatile suspended solids (VSS)) of 0.64 on 5 d was 240.8 mg COD/g VSS, which was 10.2 and 1.1-fold of that in sole WAS and sole TR, respectively. The feasible fermentation time was shortened by 2 days, as compared with sole WAS or sole TR. Mechanism investigation showed that the addition of TR promoted solubilization, hydrolysis, and acidogenesis processes. The synergistic effect of microorganisms contained in TR and WAS may be responsible for the enhancement of lignocellulose hydrolysis and VFA generation. Appropriate amounts of mineral elements in TR benefited solubilization, the soluble iron and calcium in TR could contribute to the phosphorus removal in fermentation liquor.

Hydrated lanthanum oxide-modified diatomite as highly efficient adsorbent for low-concentration phosphate removal from secondary effluents.

The requirement to the phosphorus (P) emission from wastewater treatment plants (WWTPs) is becoming increasingly strict, which makes an advanced treatment for the low-concentration phosphate removal from secondary effluents indispensable. In present work, hydrated lanthanum (La) oxide-modified diatomite composites (La-diatomite) were fabricated by a facile method and employed as the highly efficient adsorbent for the low-concentration phosphate removal from simulating secondary effluents. Comparative experiments indicated that the La-diatomite treated by 0.1 mol/L LaCl3 exhibited the highest La availability (P/La molar ratio of 2.30) and performed good selectivity to phosphate adsorption even with the coexistence of competing anions and humic acid. The maximum P adsorption capacity reached to 58.7 mg P/g and the 96% P was removed quickly within 30 min at initial phosphate concentration 2 mg P/L. Insignificant La leaching was observed during the process due to the La stabilization by macroporous diatomite. Eight cycles of adsorption-desorption experiments revealed that the excellent repeated use property of La-diatomite. At the column test, La-diatomite showed superior treatment capacities of 3455 kg water/kg La-diatomite for simulated secondary effluents. The La-diatomite maintained high and stable adsorption effectiveness in wide pH range, which should be attributed to the synergistic effect of electrostatic interactions, ligand exchange and Lewis acid-based interaction. This work might provide a candidate for low-concentration phosphate removal from secondary effluent to alleviate the eutrophication.

Thermal Effects.

This review focuses on the research literatures published in 2016 relating to thermal effects in water pollution control. This review is divided into five sections: biological nitrogen removal, organic pollutant degradation, resource recovery, pretreatment and anaerobic digestion, microbial community.