Sheng-Jie You

Sludge cycling between aerobic, anoxic and anaerobic regimes to reduce sludge production during wastewater treatment: Performance, mechanisms, and implications

Alternate cycling of sludge in aerobic, anoxic, and anaerobic regimes is a promising strategy that can reduce the sludge yield of conventional activated sludge (CAS) by up to 50% with potentially lower capital and operating cost than physical- and/or chemical-based sludge minimisation techniques. The mechanisms responsible for reducing sludge yield include alterations to cellular metabolism and feeding behaviour (metabolic uncoupling, feasting/fasting, and endogenous decay), biological floc destruction, and predation on bacteria by higher organisms. Though discrepancies across various studies are recognisable, it is apparent that sludge retention time, oxygen-reduction potential of the anaerobic tank, temperature, sludge return ratio and loading mode are relevant to sludge minimisation by sludge cycling approaches. The impact of sludge minimisation on CAS operation (e.g., organics and nutrient removal efficiency and sludge settleability) is highlighted, and key areas requiring further research are also identified.

Evaluation of the antifouling and photocatalytic properties of poly(vinylidene fluoride) plasma-grafted poly(acrylic acid) membrane with self-assembled TiO2.

Immobilization of TiO(2) is a promising approach that produces antifouling and photocatalytic membranes that could help advance wastewater treatment and re-use processes. In this study, poly(acrylic acid) (PAA) was plasma-grafted on commercial poly(vinylidene fluoride) (PVDF) to introduce functional groups on the membrane surface that can support the nanoparticles. It was found that plasma treatment at 100 W for 120 s followed by liquid grafting with 70% aqueous AA at 60°C for 2h maximized the number of TiO(2) binding sites. Membrane hydrophilicity was tremendously enhanced by the self-assembly of TiO(2), following a direct proportionality to TiO(2) loading. The membrane with 0.5% TiO(2) loading maintained the highest pure water flux and the best protein antifouling property. UV irradiation triggered the photodegradation of strongly bound foulants, but at least 1.5% TiO(2) and 30 min cumulative irradiation were necessary to completely recover the membranes original performance. The TiO(2)-modified membranes removed 30-42% of 50mg/l aqueous Reactive Black 5 (RB5) dye. The fabricated membranes demonstrate huge potential for use in membrane reactors with high hydrophilicity, fouling mitigation, and photocatalytic capability.

Activated carbons from golden shower upon different chemical activation methods: Synthesis and characterizations

Activated carbons (ACs) were synthesized from golden shower (GS) through chemical activation. Two synthesis processes were used: one-stage and two-stage processes. In the one-stage process, GS that was impregnated with K2CO3 was directly pyrolyzed (GSAC), and the two-stage process consisted of (1) pyrolytic or hydrolytic carbonization to produce biochar or hydrochar and (2) subsequent chemical activation was defined as GSBAC and GSHAC, respectively. The activated carbon’s characteristics—thermal stability and textural, physicochemical, structural, and crystal properties—were thoroughly investigated. Results demonstrated that the characteristics of activated carbons strongly depend on the method used for their synthesis. The Brunauer–Emmett–Teller surface area followed the order GSAC (1413 m2/g) > GSHAC (1238 m2/g) > GSBAC (812 m2/g). The existence of acidic groups was determined through Fourier transform infrared spectroscopy and Boehm titration. The excellent adsorptive capacities of the activated carbons were confirmed from the iodine number (1568–2695 mg/g) and methylene number (143–233 mg/g).

Improving the removal of anions by coagulation and dissolved air flotation in wastewater reclamation

This study investigated the feasibility of improving the removal of anions from a secondary effluent by coagulation/flocculation (Coag/Floc) and dissolved air flotation (DAF) using a pilot-scale wastewater reclamation plant in a high-tech industrial park. The pilot plant was equipped with units of Coag/Floc, DAF, activated carbon beds (AC), micro-filtration modules (MF) and a reverse-osmosis membrane (RO). It was operated in-situ continuously for around one year to evaluate the performance of anion removal in two processes - the AC-RO process and the DAF-AC-RO process. Long-term experimental results indicated that combining Coag/Floc, DAF and AC units increased the potential of pretreatment to remove anions. The removal efficiencies in Coag/Floc-DAF units were in the order phosphate > fluoride > chloride > sulfate > silicate. The charged complex of PACl flocs revealed a higher affinity for adsorption onto phosphate and fluoride than on chloride, sulfate and silicate. Comparison of the performance of Coag/Floc-DAF-AC units in the DAF-AC-RO process with that of a single AC unit in the AC-RO process demonstrated that adding Coag/Floc-DAF units increased the removal efficiencies of phosphate, fluoride and silicate by approximately 70.0 %, 42.7 % and 70.1 %, respectively. Most of the phosphate and fluoride were removed in Coag/Floc-DAF units, while most of the silicate escaped from the Coag/Floc-DAF units, and was adsorbed and/or trapped in the AC unit. The quality of reclaimed water in the DAF-AC-RO process complied with the requirements of high-tech industries in cleaning processes. Combined units of Coag/Floc-DAF-AC were therefore recommended for use in pretreatment in wastewater reclamation in high-tech industrial parks.

PERFORMANCE AND MICROBIAL DIVERSITY OF A MEMBRANE BIOREACTOR TREATING REAL TEXTILE DYEING WASTEWATER

The textile industry is one of the major industries of Taiwan but unfortunately it produces toxic and low biodegradable wastewater. To remedy this problem, this study compared the performance of the membrane bioreactor (MBR) and sequencing batch reactor (SBR) processes for treating real textile dyeing wastewater. The microbial diversity of the MBR process was also identified by a combination of culturing methods and molecular biotechnology. The removal efficiencies of the MBR process for color, COD, BOD, and SS were 54, 79, 99, and 100%, respectively, all higher than the corresponding parameters for the SBR process: i.e., 51, 70, 96, and 60%. All the above four parameters for the MBR effluent meet the criteria of the Taiwan EPA, while on the other hand, for the SBR process, only color and COD meet the Taiwan EPA effluent criteria. Furthermore, the genus Microbacterium, in particular Microbacterium aurum, was the most predominant population, accounting for 70.6% of the total isolates, and might be responsible for the degradation of the dyeing wastewater. Another two textile dyeing degradation bacteria, Paenibacillus azoreducens and Bacillus sp., were also observed as predominant bacteria in MBR sludge.

Phosphorus Removal Characteristics of a Combined As-Biofilm Process Cultured by Different COD/TP Ratios

The COD/TP ratio of influent is an important parameter for the phosphorus removal in a biological nutrient removal (BNR) process. In this study, we investigated the phosphorus removal and denitrification characteristics of a combined activated sludge-biofilm process, as cultured by different influent COD/TP ratios ranged from 12 to 120. Experimental results indicated that, when COD/TP ratios exceeded 30, the removal efficiencies of COD, TN and TP were 98%, 76% and 100%, respectively. However, when the COD/TP ratios were less than 30, the COD removal efficiency still surpassed 98%, but the TP removal efficiency decreased to 41% and 31.8% when COD/TP ratios were 20 and 12. Moreover, the weight percentage of phosphorus in the sludge attained a stable value when the COD/TP ratios were below 30. The maximum weight percentage of phosphorus in the sludge was found to be about 6% and, under this condition, the critical COD/TP ratio of influent was 30 of the process under a sludge retention time of 12 days. Although the amount of accumulated PHAs per mg phosphate released (γPHA/PO4) remained stable between a COD/TP ratio of 30 to 120, it increased with a decreased of the COD/TP ratio when the COD/TP ratio was less than 30.

Incorporation of zinc for fabrication of low-cost spinel-based composite ceramic membrane support to achieve its stabilization.

In order to reduce environment risk of zinc, a spinel-based porous membrane support was prepared by the high-temperature reaction of zinc and bauxite mineral. The phase evolution process, shrinkage, porosity, mechanical property, pore size distribution, gas permeation flux and microstructure were systematically studied. The XRD results, based on a Zn/Al stoichiometric composition of 1/2, show a formation of ZnAl2O4 structure starting from 1000°C and then accomplished at 1300°C. For spinel-based composite membrane, shrinkage and porosity are mainly influenced by a combination of an expansion induced by ZnAl2O4 formation and a general densification due to amorphous liquid SiO2. The highest porosity, as high as 44%, is observed in ZnAl4 membrane support among all the investigated compositions. Compared with pure bauxite (Al), ZnAl4 composite membrane support is reinforced by ZnAl2O4 phase and inter-locked mullite crystals, which is proved by the empirical strength-porosity relationships. Also, an increase in average pore diameter and gas flux can be observed in ZnAl4. A prolonged leaching experiment reveals the zinc can be successfully incorporated into ceramic membrane support via formation of ZnAl2O4, which has substantially better resistance toward acidic attack.

Highly efficient removal of hazardous aromatic pollutants by micro-nano spherical carbons synthesized from different chemical activation methods: a comparison study

ABSTRACT Glucose-derived micro-nano spherical activated carbon (GAC) was synthesized through two-stage and three-stage chemical activation processes in different impregnation ratios (K2CO3: precursor). GAC was characterized by nitrogen adsorption/desorption isotherm, point of zero charge, scanning electron microscope, and Fourier transform infrared. The prepared spherical GAC and commercial non-spherical AC were applied to remove a cationic dye (methylene green 5; MG5), an anionic dye (acid red 1; AR1), and phenol. The batch adsorption experiments were conducted to analyse the effects of different operation conditions (i.e. solution pH, contact time, initial adsorbate concentration, temperature, and desorbing agent) on the adsorption process. The adsorption equilibrium was rapidly reached in kinetic experiments with a removal rate of 47–83% (within 1 min). The three-stage process-synthesized GAC exhibited the highest adsorption capacity, with the maximum adsorption capacity reaching at 1365 mg/g for MG5, 562 mg/g for AR1, and 322 mg/g for phenol adsorption. The process of MG5 and AR1 adsorption was endothermic (+ΔH°), while phenol adsorption was exothermic (–ΔH°). The primary adsorption mechanism was pore filling and π-π interactions. The pore of spherical GAC might be easily enlarged than that of non-spherical AC when the temperature of solution increased. Therefore, the spherical activated carbon can server as a green promising and renewable adsorbent for efficiently remove hazardous aromatic pollutants from aquatic environment. GRAPHICAL ABSTRACT

Synthesis of ternary g-C3N4/Bi2MoO6/TiO2 nanotube composite photocatalysts for the decolorization of dyes under visible light and direct sunlight irradiation

Abstract Novel ternary nanocomposite photocatalysts based on g-C3N4/Bi2MoO6/TiO2 nanotube were synthesized using simple solid combustion, hydrothermal and wetness impregnation methods. The structural and morphological properties of the synthesized photocatalysts were systematically characterized using powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy and scanning electron microscopy (SEM). The crystal structure and phase purity of unitary, binary, and ternary photocatalysts were confirmed by XRD analysis. The SEM analysis reveals the tubular morphology of the TiO2 nanotube, and the presence of Ti, C, N, Bi, Mo, O, C, and N in the ternary composites was confirmed by EDX analysis. The photocatalytic decolorization efficiency of the ternary composites was evaluated by monitoring the decolorization of reactive black 5 and methylene blue dyes under visible light and direct sunlight irradiation, and these ternary composites were compared with binary composites and unitary photocatalysts in terms of the decolorization efficiency. After five cycles of adsorption and decolorization reactions, it was confirmed that the ternary composite photocatalysts were highly stable and reusable. From the results, we conclude that ternary composites (g-C3N4/Bi2MoO6/TiO2 nanotube) are efficient photocatalysts for the decolorization of dyes.

Combined photocatalysis and membrane bioreactor for the treatment of feedwater containing thin film transistor-liquid crystal display discharge

The nitrogen content of waste water generated by the thin film transistor-liquid crystal display (TFT-LCD) industry is not satisfactorily removed through the conventional aerobic-activated sludge process. In this study, the performance of three reactors – suspended type TiO2 membrane photoreactor (MPR), anoxic/oxic membrane bioreactor (AOMBR), and their combination (MPR-AOMBR) – was evaluated using feedwater containing TFT-LCD discharge. The parameters that maximized monoethanolamine (MEA) removal in the MPR were continuous ultraviolet (UV) irradiation and pH 11. Among the tested loadings, 0.1 g/l of TiO2 promoted MEA removal but degradation rate may further increase with photocatalyst concentration. The nitrified sludge recycle ratio R of the AOMBR was adjusted to 1.5 to minimize the amount of nitrate in the effluent. The AOMBR greatly decreased chemical oxygen demand and MEA, but removed only 32.7% of tetramethyl ammonium hydroxide (TMAH). The MPR was configured as the pre-treatment unit for AOMBR, and the combined MPR-AOMBR has improved TMAH removal by 80.1%. The MPR bolstered performance by decomposing slowly biodegradable compounds, and had no negative effects on denitrification and carbon removal.