Treatment of 3,4,5-trimethoxybenzaldehyde and Di-bromo-aldehyde manufacturing wastewater by the coupled Fenton pretreatment and UASB reactor with emphasis on optimization and chemicals analysis

Removal of 17α-ethinylestradiol and caffeine from wastewater by UASB-Fenton coupled system

In aquatic systems, some substances considered as endocrine disruptors have been detected, which can be due to their incomplete elimination in wastewater treatment plants (WWTPs) and inadequate disposal of pharmaceuticals. Among these contaminants are 17α-ethinylestradiol (EE2) and caffeine (CAF). Moreover, it has been reported that this kind of contaminants may provoke different adverse effects in many aquatic organisms. Because of that, in the present study, up-flow anaerobic sludge blanket reactors (UASB) coupled with the Fenton process was evaluated for EE2 and CAF removal spiked in wastewater samples. First, the best reaction conditions were established in each process. For UASB reactor, two hydraulic retention times (HRT 8 and 24 h) were evaluated, achieving the highest chemical organic demand (COD) removal (70 %) and drug elimination (84 %-86 %) with HRT 24 h. Subsequently, Fenton process was conducted at pH 3 with different levels of Fe²⁺ (0.05-0.5 mmol/L) and molar ratios Fe²⁺:H₂O₂ (1:1-1:10). Better results were obtained with 0.5 mmol Fe²⁺/L, and 1:10 ratio molar Fe²⁺:H₂O₂. Finally, UASB-Fenton coupled system allowed 80 % of COD decrease, almost complete removal of drugs and the toxicity of samples on Vibrio fischeri was reduced from 73 % to 30 %, demonstrating that this coupled system is a promising and efficient system for pharmaceutical compounds removal from wastewater.

Anaerobic treatment of glutamate-rich wastewater in a continuous UASB reactor: Effect of hydraulic retention time and methanogenic degradation pathway

To investigate the anaerobic treatment efficiency and degradation pathways of glutamate-rich wastewater under various hydraulic retention times (HRTs), a lab-scale upflow anaerobic sludge blanket (UASB) reactor was operated continuously for 180 days. Results showed that high chemical oxygen demand (COD) removal efficiencies of 95.5%-96.5% were achieved at HRTs of 4.5 h-6 h with a maximum methane yield of 0.31 L-CH₄/g-COD. When the HRT was shortened to less than 3 h, the removal performance of the reactor declined. There also was an excessive accumulation of volatile fatty acids, which implies that an appropriately small HRT is applicable to the UASB reactor treating glutamate-rich wastewater. Methanogenic degradation of glutamate in the UASB reactor depended on the HRT applied, and the typical methane-producing capability of the sludge at an HRT of 3 h, in descending order, was acetate > glutamate > butyrate > H₂/CO₂ > valerate > propionate. Clostridium and Methanosaeta were predominant in the glutamate-degrading sludge. At least three degradation pathways most likely existed in the UASB reactor, and the pathway via 3-methlaspartate by Clostridium pascui was expected to be dominant.

Performance and microbial community variations of a upflow anaerobic sludge blanket (UASB) reactor for treating monosodium glutamate wastewater: Effects of organic loading rate

To investigate the effect of the organic loading rate (OLR) on anaerobic treatment of monosodium glutamate (MSG) wastewater, a lab-scale up-flow anaerobic blanket (UASB) reactor was continuously operated over a 222-day period. The overall performances of COD removal and methane recovery initially exhibited an increase and subsequently decreased when the OLR was increased from 1 g-COD/L/d to 24 g-COD/L/d. At the optimal OLR of 8 g-COD/L/d, superior performance was obtained with a maximum COD removal efficiency of 97%, a methane production rate of 2.3 L/L/d, and specific methanogenic activity of 86 mg-CH₄/g-VSS/d (feeding on glutamate), with superior characteristics of sludge in VSS concentration, average diameter of granules, and settling velocity. According to the results of the specific methanogenic activity, the methanogenic pathway was more inclined to pass through acetate than through hydrogen. Methanosarcina instead of Methanosaeta, with Methanobacterium and greatly increased Firmicutes, dominated in the UASB reactor after long term operation. These results support that the OLR had a substantial effect on both the treatment and energy recovery efficiency of MSG wastewater as well as on microbial community variations in the UASB reactor.

The role of in situ Fenton coagulation on the removal of benzoic acid

Fenton (Fe²⁺ + H₂O₂) reagents acting to remove organic pollutants possess dual functions, including the oxidation by hydroxyl radicals and the coagulation of Fe(III). Previous papers have extensively studied the oxidation reactions by hydroxyl radicals, however, the coagulation role of Fenton for benzoic acid (BA) removal is not clear. Comparing three coagulation systems, it was found that Fenton coagulation possesses a significant advantage for the removal of BA. Through Fenton conditional experiments, results showed that with the increase of H₂O₂ dosage, not only was the Fenton oxidation effect improved, but the Fenton coagulation effect was also significantly enhanced. Interestingly, the flocs produced by in situ Fenton possess a better coagulation effect than an aged Fenton system when processing BA. To further explain these results, Zeta potential, Transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray absorption fine structure (EXAFS) and Brunner-Emmet-Teller (BET) measurements were used for characterization, and we found that the flocs produced by Fenton possessed a smaller particle size, lower polymerization states and a larger specific surface area and pore volume, which exposed more active sites to create a better coagulation effect. Additionally, through Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and Gas chromatography-mass spectrometer (GC-MS), we found that in situ Fenton oxidation and coagulation have synergistic effects, and the carboxyl-containing intermediates produced by the Fenton oxidation of BA can be combined with hydroxyl active sites of the flocs produced by in situ Fenton, resulting in a better removal effect. Finally, Fenton oxidation increases oxygen/carbon (O/C) to promote Fenton coagulation, and in situ Fenton more fully utilizes the active sites on the flocs' surface.

Effect of cephalexin after heterogeneous Fenton-like pretreatment on the performance of anaerobic granular sludge and activated sludge

Effects of Fe₃O₄ NPs heterogeneous Fenton-like pretreatment on the physicochemical properties and microbial community structure of anaerobic granular sludge (AGS) and activated sludge (AS) with cephalexin were investigated. Results showed that the average removal rate of chemical oxygen demand (COD) by the AGS was 80.9%, 85.9%, 90.3% and 91.6%, respectively, at cephalexin without pretreatment, pretreatment with 20% (H₂O₂), 40% (H₂O₂) and 60% (H₂O₂). Compared to the reactor without pretreatment, the COD removal rate increased by 24.14% with 60% (H₂O₂) pretreatment for the AS. Dehydrogenase levels in the AS were 313.05, 351.12, 434.81 and 480.77 mg TF (g·h)^-1, which increased with higher concentrations of the pretreatment. Three-dimensional fluorescence (EEM) spectra analysis showed that the absorption peak intensities of humic acid in soluble microbial products (SMP) decreased in the AGS with increasing pretreatment. In the AGS, the dominant bacterial populations were Levilinea, Litorilinea and Clostridium sensu stricto. Clostridium sensu stricto accounting for 4.35% without pretreatment, while it was as high as 17% when it was pretreated with 60% (H₂O₂). The increase in the proportion of Clostridium sensu stricto was beneficial to the removal of organic pollutants. The pretreatment was also beneficial to the growth of acetic acid producing Methanothrix. For the AS, Gemmobacter were the dominant species, which increased from 6.56% to 32.61% after increasing the pretreatment to 40% (H₂O₂). Furthermore, the microbial capacities of amino acid metabolism and carbohydrate metabolism were enhanced by addition of pretreatment.

Influence of amoxicillin after pre-treatment on the extracellular polymeric substances and microbial community of anaerobic granular sludge

A combined process coupling a Fe₃O₄ nanoparticles (Fe₃O₄ NPs) heterogeneous Fenton-like reaction and an anaerobic biological technology was investigated in order to effectively treat amoxicillin-containing wastewater. With the increase in the pretreatment degree, the average COD removal rate correspondingly increased from 84.8% to 92.4% using the anaerobic biological treatment, and the biodegradability and COD removal efficiency was improved by the pretreatment processes. During the process of amoxicillin degradation, hydroxyl free radicals tended to attack the lactamide, amide and pentacyclic rings of amoxicillin. In the excitation-emission matrix (EEM) spectra of soluble microbial products (SMPs), the absorption peak of humic acid gradually decreased with application of the pretreatment. The pretreatment products were more beneficial to the characteristics of anaerobic granular sludge. For the microbial community structure, the proportion of Methanothrix and Clostridia increased with addition the heterogeneous Fenton-like pretreatment, which favored conversion of organic contaminants to volatile fatty acids and biogas.

Performance and microbial shift during acidification of a real pharmaceutical wastewater by using an anaerobic sequencing batch reactor (AnSBR)

In this study, a lab-scale anaerobic sequencing batch reactor (AnSBR) was used for the acidification of a pharmaceutical wastewater sourced from etodolac chemical synthesis tanks. The effects of the organic loading rate (OLR), and etodolac and sulfate concentrations on the acidification rate and microbial community in AnSBR were investigated at 35 °C with a hydraulic retention time (HRT) of 37 h, a pH of 5, and OLRs up to 5.2 kgCOD/m³·day. The AnSBR accomplished a 60% acidification ratio and 50-60% etodolac removal at OLRs up to 2.6 kgCOD/m³·day. However, at OLR = 3.9 kgCOD/m³·day, acidification was not achieved due to sulfite inhibition; pre-ozonation was applied to overcome this sulfite inhibition. Although etodolac and COD removals were improved, the wastewater was not successfully acidified. Real-time polymerase chain reaction (Q-PCR) and fluorescent in situ hybridization (FISH) analyses revealed that acidification was inhibited by the dominance of sulfate reducing bacteria (SRB) over acidification bacteria in the AnSBR. However, increasing the OLR to 5.2 kgCOD/m³·day led to toxicity stress in the SRB due to increased sulfite concentrations. Sulfate load fundamentally affected acidification process and microbial community composition. The presence of etodolac with concentration up to 56 mg/L did not have a significant effect on VFA production and the microbial community.

Effect of heterogeneous Fenton-like pre-treatment on anaerobic granular sludge performance and microbial community for the treatment of traditional Chinese medicine wastewater

The effect of a heterogeneous Fenton-like pre-treatment on the anaerobic processes, characteristics and microbial community of sludge was investigated for traditional Chinese medicine (TCM) wastewater containing rhein. When the concentrations of rhein were 50mg/L and 100mg/L, the toxic effect was physiological toxicity for anaerobic granular sludge. Using a single double circle (DC) reactor for the treatment of TCM wastewater containing rhein at concentrations of 15-20mg/L, the chemical oxygen demand (COD) removal rate was 69%, and coenzyme F420 was nearly undetectable in the 3D-excitation-emission matrix (EEM) spectra of soluble microbial products (SMP). The abundances of Methanoregula, Methanobacterium, Methanosphaerula were only 5.57%, 2.39% and 1.08% in the DC reactor, respectively. TCM wastewater containing rhein could be successfully treated by the combination of the heterogeneous Fenton-like pre-treatment and the DC reactor processes, and the COD removal rate reached 95%. Meanwhile, the abundances of Methanoregula, Methanobacterium, Methanosphaerula increased to 22.5%, 18.5%, and 13.87%, respectively. For the bacterial community, the abundance of Acidobacteria_Gp6 decreased from 6.99% to 1.07%, while the abundances of Acidobacteria_Gp1 and Acidobacteria_Gp2 increased from 1.61% to 6.55% and from 1.28% to 5.87%, respectively.