Effect of Initial pH Adjustment on Hydrolysis and Acidification of Sludge by Ultrasonic Pretreatment

Nanoscale zero-valent iron (nZVI) has attracted considerable attention for its potential to sequestrate and immobilize heavy metals such as Cr(VI) from an aqueous solution. However, nZVI can be easily oxidized and agglomerate, which strongly affects the removal efficiency. In this study, graphene-based nZVI (nZVI/rGO) composites coupled with ultrasonic (US) pretreatment were studied to solve the above problems and conduct the experiments of Cr(VI) removal from an aqueous solution. SEM-EDS, BET, XRD, and XPS were performed to analyze the morphology and structures of the composites. The findings showed that the removal efficiency of Cr(VI) in 30 min was increased from 45.84% on nZVI to 78.01% on nZVI/rGO and the removal process performed coupled with ultrasonic pretreatment could greatly shorten the reaction time to 15 min. Influencing factors such as the initial pH, temperature, initial Cr(VI) concentration, and co-existing anions were studied. The results showed that the initial pH was a principal factor. The presence of HPO42−, NO3−, and Cl− had a strong inhibitory effect on this process, while the presence of SO42− promoted the reactivity of nZVI/rGO. Combined with the above results, the process of Cr(VI) removal in US-nZVI/rGO system consisted of two phases: (1) The initial stage is dominated by solution reaction. Cr(VI) was reduced in the solution by Fe2+ caused by ultrasonic cavitation. (2) In the following processes, adsorption, reduction, and coprecipitation coexisted. The addition of rGO enhanced electron transportability weakened the influence of passivation layers and improved the dispersion of nZVI particles. Ultrasonic cavitation caused pores and corrosion at the passivation layers and fresh Fe0 core was exposed, which improved the reactivity of the composites.

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Silica Removal from a Paper Mill Effluent by Adsorption on Pseudoboehmite and γ-Al2O3

Water ◽

10.3390/w13152031 ◽

2021 ◽

Vol 13 (15) ◽

pp. 2031

Author(s):

Ruben Miranda ◽

Isabel Latour ◽

Angeles Blanco

Keyword(s):

Paper Mill ◽

Ph Adjustment ◽

Paper Mill Effluent ◽

Kinetics Studies ◽

Silica Removal ◽

Industrial Water Use ◽

Optimum Ph ◽

Initial Ph ◽

Equilibrium And Kinetics ◽

Kinetics Of

Effluent reuse is a common practice for sustainable industrial water use. Salt removal is usually carried out by a combination of membrane processes with a final reverse osmosis (RO). However, the presence of silica limits the RO efficiency due to its high scaling potential and the difficulty of cleaning the fouled membranes. Silica adsorption has many advantages compared to coagulation and precipitation at high pHs: pH adjustment is not necessary, the conductivity of treated waters is not increased, and there is no sludge generation. Therefore, this study investigates the feasibility of using pseudoboehmite and its calcination product (γ-Al2O3) for silica adsorption from a paper mill effluent. The effect of sorbent dosage, pH, and temperature, including both equilibrium and kinetics studies, were studied. γ-Al2O3 was clearly more efficient than pseudoboehmite, with optimal dosages around 2.5–5 g/L vs. 7.5–15 g/L. The optimum pH is around 8.5–10, which fits well with the initial pH of the effluent. The kinetics of silica adsorption is fast, especially at high dosages and temperatures: 80–90% of the removable silica is removed in 1 h. At these conditions, silica removal is around 75–85% (<50 mg/L SiO2 in the treated water).

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Supported Nanosizedα-FeOOH Improves Efficiency of Photoelectro-Fenton Process with Reaction-Controlled pH Adjustment for Sustainable Water Treatment

International Journal of Photoenergy ◽

10.1155/2012/689807 ◽

2012 ◽

Vol 2012 ◽

pp. 1-7 ◽

Cited By ~ 3

Author(s):

Chuan Wang ◽

Hong Liu ◽

Zhimin Sun ◽

Jian Huang ◽

Yang Liao

Keyword(s):

Iron Oxide ◽

Water Treatment ◽

Fenton Reaction ◽

Fenton Process ◽

Major Step ◽

Ph Adjustment ◽

Extra Energy ◽

Initial Ph ◽

The Individual ◽

20 Nm

The overall photoelectro-Fenton (PE-Fenton) process for water treatment with neutral initial pH includes three steps of pH reduction, PE-Fenton reaction, and pH elevation. Reaction-controlled pH adjustment (RCpA), which utilizes the intrinsic electrochemical reactions instead of chemical addition, has been employed to lower the pH, maintain the lowered pH for the Fenton reaction, and recover the pH for final effluent discharge. This study demonstrated that the overall efficiency of this sustainable PE-Fenton process was improved by rapidly recycling the iron substance. Nanosized iron oxide was prepared and employed to ensure such rapid recycling. SEM and XRD results showed that the as-prepared iron oxide wasα-FeOOH with 20 nm in size. The experimental results of dimethyl phthalate (DMP) degradation showed that diatomite-supportedα-FeOOH (N-α-FeOOH/diatomite) could efficiently reduce the DMP concentration and total organic carbon. Furthermore, compared with Fe3+, the N-α-FeOOH/diatomite saved 160 min for iron settlement at 20 mg L−1DMP concentration. Also, with the increment in the initial DMP concentration, extra energy consumed by the individual step of PE-Fenton reaction using the N-α-FeOOH/diatomite became negligible compared with that using free iron ions with the increment in the initial DMP concentration. This development is expected to be a major step of the PE-Fenton process with RCpA towards actual water treatment.

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Ozone-based advanced oxidation process as pre-treatment of wastewater from the wood-based industry

Linnaeus Eco-Tech ◽

10.15626/eco-tech.2014.057 ◽

2017 ◽

Author(s):

Alexandre Amaro ◽

Henrik Hanson ◽

Fabio Kaczala ◽

Marcia Marques ◽

William Hogland

Keyword(s):

Wastewater Treatment ◽

Activated Sludge ◽

Wastewater Treatment Plant ◽

Municipal Wastewater ◽

Treatment Plant ◽

Advanced Oxidation ◽

Municipal Wastewater Treatment ◽

Ph Adjustment ◽

Municipal Wastewater Treatment Plant ◽

Initial Ph

Three ozone-based advanced oxidation treatments (O3; O3 with initial pH adjustment and; O3/UV with initial pH adjustment) were compared for the treatment of a recalcitrant wastewater generated during washing/cleaning of surfaces and equipment used in filling and gluing processes (urea-formaldehyde and phenol-formaldehyde resins) in a wood-floor industry in Sweden. The wastewater (initial COD 3,400-4,000 mg/L) was obtained at the outlet of a sedimentation tank, which receive an inflow with an average COD of 45,000 mg/L. The experiments were performed in a semi-batch microbubble column reactor connected to a UV reactor, where 2.5 L samples of wastewater were submitted to the maximum dose of 2 g of O3 per gram of initial COD. For the full-factorial design, the independent variables were O3 concentration (g O3/Nm3); recirculation flow (L/min); and initial pH (pHi). The evaluation of the treatment performance was based on COD and TOC reductions (in %), and the effluent obtained was used in respirometric assays with activated sludge obtained at a municipal wastewater treatment plant to assess biodegradability/inhibitory effects. The results showed that ozonation at the original low pH promoted a reduction of 65% and 31% of COD and TOC respectively, but made the effluent less biodegradable. The highest COD and TOC reductions were achieved when O3 /UV treatment with pHi = 9.3 were applied (93% e 56% reductions for COD and TOC respectively). The results with the respirometry tests suggest that application of O3 only at higher pH values promoted biodegradability enhancement of the effluent, making it treatable by microbiota obtained with activated sludge from a municipal wastewater treatment plant.

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Effect of pre-sonication on removal of organic matters resulting from chlorinated humic acids

Water Science & Technology ◽

10.2166/wst.1998.0259 ◽

1998 ◽

Vol 38 (6) ◽

pp. 253-260 ◽

Cited By ~ 6

Author(s):

Ying-Shih Ma ◽

Jih-Gaw Lin

Keyword(s):

Ionic Strength ◽

Humic Acids ◽

Wastewater Sludge ◽

Experimental Results ◽

Ultrasonic Pretreatment ◽

Pretreatment Method ◽

Total Organic Carbon Removal ◽

Ultrasonic Process ◽

Initial Ph ◽

By Products

Humic acids are amorphous organic macromolecules that are responsible for the color of natural water. They play an important role in the formation of disinfection by-products, the stabilization of wastewater sludge, and the treatment of wastewater. An ultrasonic process is applied as a pretreatment method for the purpose of reducing the risk of chlorinated by-products. Experimental results indicate that the initial pH, ionic strength, and chlorine demand affect the amount of total organic carbon removal and Cl2 consumption significantly. The formation of chlorinated by-products depends on both the initial pH and ionic strength. Experimental results also propose a good agreement that the humic acid can be removed efficiently by ultrasonic pretreatment under aerobic conditions. In this study, when the ultrasound/O2 process is used as a pretreatment method, the biodegradability which is defined as the formation of BOD5 increases with sonication time.

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Effect of pH control strategies and substrate concentration on the hydrogen yield from fermentative hydrogen production in large laboratory-scale

Water Science & Technology ◽

10.2166/wst.2012.777 ◽

2012 ◽

Vol 65 (2) ◽

pp. 262-269 ◽

Cited By ~ 2

Author(s):

I. Mariakakis ◽

J. Krampe ◽

H. Steinmetz

Keyword(s):

Hydrogen Production ◽

Control Strategies ◽

Sucrose Concentration ◽

Ph Control ◽

Laboratory Scale ◽

Hydrogen Yield ◽

Batch Experiments ◽

Ph Adjustment ◽

Fermentative Hydrogen Production ◽

Initial Ph

A series of batch experiments investigating two different pH control strategies, initial pH adjustment and continuous pH control, have been carried out in large laboratory-scale reactors with working volumes of 30 L. In both cases, pH was varied between 5 and 7.5. Sucrose concentrations were also varied starting from 0 up to 30 g/L. Higher hydrogen production yields can be achieved by batch experiments through continuous pH control than by simple initial pH adjustment. In the case of continuous pH control, maximization of hydrogen yield was acquired for slightly acidic pH of 6.5. Continuous pH control in the neutral pH range of 7.0 and in pH lower than 6.5, induced a reduction in the hydrogen production yield. Sucrose can be completely degraded only for a pH higher than 6. Lower pH values seem to inhibit the hydrogen-producing bacteria. Under the conditions of continuous pH adjustment at pH 6.5 and a sucrose concentration of 25 g/L the maximum hydrogen yield of 1.79 mol H2/mol hexose was obtained. These conditions could be applied for the batch start-up of large fermentors.

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Effective removal of lead (II) ions by dead calcareous skeletons: sorption performance and influencing factors

Water Science & Technology ◽

10.2166/wst.2016.368 ◽

2016 ◽

Vol 74 (7) ◽

pp. 1577-1584 ◽

Cited By ~ 3

Author(s):

Ai Phing Lim ◽

Zufarzaana Zulkeflee ◽

Ahmad Zaharin Aris

Keyword(s):

Removal Efficiency ◽

Contact Time ◽

Low Cost ◽

High Concentration ◽

Initial Concentration ◽

Ph Adjustment ◽

Equilibrium Time ◽

Factors Influencing ◽

Effective Removal ◽

Initial Ph

Dead calcareous skeletons (CSs) as low-cost adsorbents were studied to remove lead ions (Pb (II)) in an aqueous solution. Factors influencing the efficiency of CSs were evaluated by adsorbent size, contact time, initial concentration, dosage concentration and pH. The optimum CS size for removal of Pb (II) was 710 μm at an equilibrium time of 720 min. The best dosage of CS was 10 g/L for a 99% removal efficiency without pH adjustment. Pb (II) ions were effectively removed in the initial pH of the metal solution. CS was able to remove a high concentration (100 mg/L) of Pb (II) at a removal efficiency of 99.92% and at an adsorption capacity of 13.06 mg/g. Our results demonstrated the potential of CS as a metal adsorbent in the aqueous phase with a high-removal efficiency and distinct physical characteristics.

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