Jing Kang

Influence of humic acid on the removal of arsenate and arsenic by ferric chloride: effects of pH, As/Fe ratio, initial As concentration, and co-existing solutes

The influence of humic acid (HA) on the removal of arsenic by FeCl3 was systematically studied in this paper. Jar tests were performed to investigate the influence on arsenic during FeCl3 coagulation of the pH adjusting method, the initial As/Fe ratio, the equilibrium As concentration, and co-occurring anions and cations. Compared with results in HA-free systems, the removal trends of arsenic in HA solutions were quite different. It was found that As(V) removal was higher at low equilibrium concentration, yet the opposite was true for As(III) removal. The presence of HA influenced the effective number of active sites for arsenic removal by FeCl3 flocculation. In addition, in the presence of HA, the impacts of co-existing solutions on arsenic removal were also different from that of an HA-free system. This study examined the influence of co-occurring anions, such as phosphate, sulfate, and silicate on arsenic removal, depending on their ability to compete for sorption sites and to hinder or facilitate the aggregation of ferric hydroxide flocs. The presence of Ca2+ or Cd2+ significantly increased arsenic removal at higher pH. Low concentrations of dissolved HA and high concentrations of colloid affected the adsorption of arsenic onto iron oxide. The influence of HA on the adsorption of arsenic onto iron oxide primarily depended on the relative content of the dissolved and mineral combination states of HA and the interface combination forms.

Leaching mechanisms of constituents from fly ash under the influence of humic acid

As a low-cost material for adsorption, FA is one of the most efficient adsorbents of HA. However, the leaching of elements from FA is problematic during utilization in water treatment. In this investigation, the potential leaching behaviors of Calcium, Arsenic, Born, Chromium, and other elements from FA in HA solution were studied via batch test. The data show that HA had an effect on the leaching of each element of FA, depending on the pH, the initial concentration of HA and the addition of calcium oxide (CaO). The Langmuir isotherm could better fit the equilibrium data in different initial concentrations of HA from 10 to 100mg/L. Because of the interaction between HA and the FA leaching elements, multi-layer adsorption occurred when the initial concentration of HA was more than 100mg/L. The pH and free CaO content played major roles in HA adsorption and FA leaching. Using SEM and XRD to characterize the solid of FA being mixed with CaO treated in solution, the results demonstrated that the reaction between FA and CaO could generate crystal minerals, such as portlandite, gismondine, ettringite (AFt) and calcite, which effectively restrained the leaching of elements, reduced secondary pollution.

Response surface methodology investigation into optimization of the removal condition and mechanism of Cr(VI) by Na2SO3/CaO

The removal of Cr(Ⅵ) by chemical reduction-precipitation is widely applied in wastewater treatment plants. Nevertheless, the formation of Cr(OH)3 with gel properties has weak settlement performance, making it necessary to add a coagulant aid to reduce the settling time and improve the settling effect. In this investigation, a high concentration of Cr(Ⅵ) was removed using Na2SO3 as a reducing agent and CaO as a coagulant. An improved reduction and precipitation experiment was modeled by applying a three-factor central composite experimental design (CCD). To reveal as many mechanisms as possible for CrT removal, other verification experiments were performed. The CrT removal efficiency decreased, which can be explained by the following three reasons: dissolution of Cr(Ⅲ), competition for adsorption between Ca2+ and Cr(Ⅲ) at different coagulation times, and formation of a solubility complex with Cr(Ⅲ) due to the surplus SO32- in solution. The increasing CrT removal efficiency can be explained by the following two reasons: dissolved Ca2+ from CaO can neutralize CrO2- that is produced by the dissolution of Cr(OH)3 in alkaline solution and can broaden the optimal final pH range of coagulation. Ca2+ could also strengthen the CrT removal through adsorption bridging and co-precipitation with CaO as the core of flocs.

Heterogeneous Catalytic Ozonation of Sulfamethoxazole in Aqueous Solution over Composite Iron–Manganese Silicate Oxide

ABSTRACT Composite iron–manganese silicate oxide (FMSO) was synthesized and used as a heterogeneous catalyst for the ozonation of sulfamethoxazole. Results showed that FMSO/O3 process significantly increased the TOC removal efficiency from 27% (sole ozonation) to 79.8%. Generated intermediates exhibited much higher adsorption affinity on FMSO than sulfamethoxazole. Presence of FMSO could accelerate the mass transfer of ozone, adsorb a certain amount of ozone on its surface, and subsequently decompose ozone into hydroxyl radical. Neutral charge surface of FMSO was more favorable to interact with the ozone molecules. FMSO maintained a good catalytic activity after several repeated use and revealed low metal ion leaching during ozonation.

Influence of potassium permanganate pre-oxidation on the interaction of humic acid with cadmium/arsenic

Permanganate pre-oxidation could enhance coagulation in water treatment of surface water in the presence of humic acid (HA). The pre-oxidation process affects the characteristics of HA and the species of Cd/As, thereby influencing the diverse associations of HA with trace elements. In the present study, KMnO4 pre-oxidation was found to enhance the coagulation of arsenic in HA aqueous solution by iron chloride, but the opposite result was observed for cadmium removal. This finding may be attributed to the fact that KMnO4 could oxidise the organics, thereby allowing them to be easily adsorbed by the hydrolysis products of the coagulant. KMnO4 may also have influenced the removal of arsenic and cadmium in the process of coagulation. Another reason may be that the manganese dioxide (MnO2) formed in situ could adsorb arsenic and cadmium successively. KMnO4 pre-oxidation was employed in this paper and the changes between the unoxidised and potassium permanganate pre-oxidised systems were investigated. These changes included the interactions of HA with Cd/As ions, the zeta potential value and the spectral analysis, such as specific binding sites on HA and quantifying binding parameters.

A novel cementitious microfiltration membrane: mechanisms of pore formation and properties for water permeation

This study involved the fabrication of a novel low-cost microfiltration membrane using quartz and cement. The entire fabrication process was conducted at room temperature, rather than utilizing high-temperature sintering, as is generally done during the fabrication of traditional inorganic membranes. The mean pore size of the membrane ranged from 0.4 to 2.4 μm depending on the quartz-to-cement ratio (q/c) used. Two types of pores (I and II) were formed in the membrane. The formation of type I pores was mainly attributed to the stacking of cement particles. The formation of type II pores, which were less prevalent than type I pores, was attributed to the division of bigger pores by the thin needle-like ettringite. The sizes of the type I and type II pores varied significantly, depending on the used q/c. Moreover, investigation of the membrane properties showed that as the q/c used increased, increases were obtained for both the membrane porosity (from 18.4% to 31.4%) and water flux (from 0.16 to 13.26 m3 m−2 h−1 bar−1), whereas the bending strength decreased (from 9.75 to 3.54 MPa). Additionally, element dissolution experiments demonstrated that the membrane was suitable for use for water treatment.

Investigation on the Kinetics of Heterogeneous Catalytic Ozone Decomposition in Aqueous Solution over Composite Iron-Manganese Silicate Oxide

ABSTRACT The kinetics of heterogeneous catalytic ozone decomposition in aqueous solution over composite iron-manganese silicate oxide (FMSO) was investigated. Results showed that the presence of FMSO significantly accelerated the ozone decomposition rate from 0.022 (without FMSO) to 0.101 min−1. The effects of inorganic anions and solution pH indicated that surface hydroxyl groups on FMSO were the active sites for catalyzing ozone decomposition and neutral charge surface seemed to show the highest catalytic performance. Tert-butanol inhibition experiments demonstrated that FMSO effectively accelerated the transformation rate of ozone into hydroxyl radicals. The contribution of hydroxyl radicals on ozone decomposition with and without FMSO was subsequently determined.

Impact of carbon to nitrogen ratio on the performance of aerobic granular reactor and microbial population dynamics during aerobic sludge granulation

Carbon to nitrogen (C/N) ratio is one of the most important factor affecting aerobic granular sludge (AGS) growth and pollutant removal in aerobic granular sludge sequencing batch reactor (AGSBR). For stability of sludge granulation process, AGSs were domesticated in five sequence batch reactors (SBRs) with different C/N ratios (6, 7, 8, 9, and 10), which the ammonia nitrogen concentration of influent was 165 mg/L. The effects of C/N ratio on morphology and property of AGS were studied. The results showed that stable AGS was yielded with good settleability, high pollutant removal efficiency and rich microbial diversity when C/N ratio was 8. AGS yielded had stable structure due to higher protein in extracellular polymeric substances (EPS). High throughput 16S rDNA gene analysis revealed the microbial community diversity increased in AGS under the C/N ratio. The dominant microbes changed at the phylum, class and family three levels with the increasing operation time.

Removal of tetracycline by aerobic granular sludge and its bacterial community dynamics in SBR

In this study, the removal efficiency and mechanism of tetracycline by aerobic granular sludge (AGS) in SBR were investigated. The removal of tetracycline present in livestock and poultry wastewater and the effect on conventional pollutants, such chemical oxygen demand, and nitrogen and phosphorous removal performance have been assessed demonstrating that AGS was able to remove tetracycline by adsorption and biodegradation processes. The removal rate of tetracycline was more than 90%, and conventional pollutants were also efficiently removed. The high-throughput sequencing technology was applied to decipher the species succession and community structure of tetracycline-resistance granular sludge. The Chryseobacterium, Actinotignum, Lactococcus, Shinella and Clavibacter were gradually dominant and considered as the functional bacteria for the removal of tetracycline. The numbers of functional genes including amino acid, carbohydrate and inorganic ion transport and metabolism, as well as energy production and conversion, and secondary metabolites biosynthesis, were also increased. These functional genes played an important role in the biodegradation of tetracycline.

The key role of inoculated sludge in fast start-up of sequencing batch reactor for the domestication of aerobic granular sludge

Two types of inoculated sludges, granular sludge that had been stored at -20°C and activated sludge, were investigated for the domestication of aerobic granular sludges (AGSs) in sequencing batch reactors (SBRs). The results showed that using the stored granular sludge as inoculation sludge could effectively shorten the domestication time of AGS and yielded mature granular sludge after 22 days of operation. The AGS domesticated by stored granular sludge had better biomass and sedimentation properties; its MLSS and SVI reached 8.55 g/L and 35.27 mL/g, respectively. The removal efficiencies for chemical oxygen demand (COD), ammonium nitrogen (NH4+-N) and total phosphorus (TP) reached 90.76%, 97.39% and 96.40%, respectively. By contrast, 54 days were needed to obtain mature granules using activated sludge. The microbial community structure was probed by using scanning electron microscopy (SEM) and high-throughput sequencing. The results showed that the diversity of the microbial community in mature granules was reduced when stored granular sludge rather than activated sludge was employed as inoculation sludge, and the dominant microbes were changed. The dominant species in mature granules domesticated using stored granular sludge were Zoogloea, Acidovorax and Tolumonas at the genus classification level, while the dominant species were Zoogloea and TM7-genera in granules developed from activated sludge.