Bingzhi Dong

Formation of chloroform during chlorination of alanine in drinking water

Currently, dissolved nitrogenous organic matters in water, important precursors of disinfection by-products (DBPs), are of significant concern. This study was to explore the formation of chloroform (CF) during chlorination of alanine (Ala), an important nitrogenous organic compound commonly present in water sources. Our results indicated that the CF yield reached a maximum value of 0.143% at the molar ratio of chlorine atom to nitrogen atom (Cl/N)=1.0 over a Cl/N range of 0.2-5.0 (pH=7.0, reaction time=5d, and initial Ala=0.1mM). At an acidic-neutral condition (pH 4-7), the formation of CF was suppressed. However, the highest CF yield (0.227%) occurred at weakly alkaline condition (pH 8.0) (initial Ala=0.1mM, and Cl/N=1.0). The increase of Br(-) in water can increase total trihalomethanes (THMs) and bromo-THMs. However, the bromo-THMs level reached a plateau at Br(-)/Cl>0.04. Finally, based on the computation of frontier electron density and identification and measurement of key intermediates during Ala chlorination, we proposed a formation pathway of CF from Ala chlorination: Ala-->monochloro-N-alanine (MC-N-Ala)-->acetaldehyde (AAld)-->monochloroacetaldehyde acetaldehyde (MCAld)-->dichloroacetaldehyde (DCAld)-->trichloroacetaldehyde (TCAld)-->CF.

Pretreatment and Membrane Hydrophilic Modification to Reduce Membrane Fouling

The application of low pressure membranes (microfiltration/ultrafiltration) has undergone accelerated development for drinking water production. However, the major obstacle encountered in its popularization is membrane fouling caused by natural organic matter (NOM). This paper firstly summarizes the two factors causing the organic membrane fouling, including molecular weight (MW) and hydrophilicity/hydrophobicity of NOM, and then presents a brief introduction of the methods which can prevent membrane fouling such as pretreatment of the feed water (e.g., coagulation, adsorption, and pre-oxidation) and membrane hydrophilic modification (e.g., plasma modification, irradiation grafting modification, surface coating modification, blend modification, etc.). Perspectives of further research are also discussed.

Dewatering of Chlorella pyrenoidosa using diatomite dynamic membrane: Filtration performance, membrane fouling and cake behavior

The diatomite dynamic membrane (DDM) was utilized to dewater Chlorella pyrenoidosa of 2 g dry weight/L under continuous-flow mode, whose ultimate algae concentration ranged from 43 g to 22 g dry weight/L of different culture time. The stable flux of DDM could reach 30 L/m(2) h over a 24 h operation time without backwash. Influences of extracellular organic matters (EOM) on filtration behavior and membrane fouling were studied. The DDM was divided into three sub-layers, the slime layer, the algae layer and the diatomite layer from the outside to the inside of the cake layer based on components and morphologies. It was found that EOM caused membrane fouling by accumulating in the slime and algae layers. The DDM intercepted polysaccharides, protein-like substances, humic-like substances and some low-MW organics. Proteins were indicated the major membrane foulants with increased protein/polysaccharide ratio from the slime layer to the diatomite layer as culture time increased. This method could be applied to subsequent treatment of microalgae coupling technology of wastewater treatment or microalgae harvesting for producing biofuel.

Pretreatment of micro-polluted surface water with a biologically enhanced PAC-diatomite dynamic membrane reactor to produce drinking water

Abstract This study developed a biologically enhanced powder activated carbon (PAC) diatomite dynamic membrane reactor (BPDDMR) to pretreat micro-polluted surface water for drinking water production at lab-scale in continuous mode. In the start-up operation period, the BPDDMR required approximately 26 and 31 d to achieve stable removal efficiency of CODMn and NH3–N, respectively. Turbidity was always below 0.5 NTU throughout the operation experiment in the permeate flux range of 21−54lm−2 h−1. The BPDDMR could effectively remove the hydrophilic portion of dissolved organic materials (DOM) present in the raw water. The temperature affected pollutant removal (especially CODMn), which was mainly ascribed to microbial degradation and was also enhanced by PAC and diatomite adsorption. During the precoating period, the stainless steel support mesh (aperture 74 μm) first intercepted the large PAC (50−100 μm), and then diatomite particles (5−20 μm) were intercepted to form a two-layer structure of the biologicall...

Kinetics and mechanism for methiocarb degradation by chlorine dioxide in aqueous solution

The kinetics and mechanism for methiocarb (MC) degradation by aqueous ClO2 were investigated under simulated water treatment conditions. Experimental results indicate that the reaction between MC and ClO2 was of second-order overall, and the rate constant rapidly increased from 0.56 to 4.5 M(-1) s(-1) as the solution pH increased from 6.0 to 9.1 at 23 degrees C. The activation energy was determined to be 75 kJ mol(-1) in the studied temperature range of 7-35 degrees C. Methiocarb sulfoxide (MCX) and methiocarb sulfone (MCN) were quantified to be the major byproducts from MC degradation. Unlike the sequential formation of sulfoxide and sulfone during the oxidation of many thioethers, the two byproducts were formed simultaneously during MC degradation by ClO2. The solution pH significantly affected the type and quantity of the degradation byproducts. For example, at pH 6.5 MCX and MCN accumulated as the reaction proceeded and finally accounted for 71% and 28% of MC degraded, respectively; while at pH 8.6 three more minor byproducts were identified. Though ClO2 can effectively oxidize MC in water, the significant increase in toxicity raises a potential risk to consumers.

Gravity filtration performances of the bio-diatomite dynamic membrane reactor for slightly polluted surface water purification.

A bio-diatomite dynamic membrane (BDDM) reactor for surface water treatment under a water head of 30, 40, 50, 60 and 70 cm, respectively, was investigated, which was very effective for pollutants removal. The water head exerted strong influences on filtration flux of BDDM during the precoating process, as well as on the formation of BDDM and turbidity variations. A high filtration flux (approximately 200-300 L/m2 h) could be achieved in the long filtration times of BDDM with a stable effluent turbidity of approximately 0.11-0.25 NTU. The BDDM could remove particles larger than 25 μm completely. The adopted sintered diatomite mainly consisted of macro pores, which were beneficial for improving the filtration flux of BDDM. During the backwash stage, the BDDM could be removed completely by the air backwash.

Growth effects on mixed culture of Dunaliella salina and Phaeodactylum tricornutum under different inoculation densities and nitrogen concentrations

Leptin is a 16 kDa protein synthesized by white adipose tissue and involved in regulation of feed intake, energy balance, fertility and immune function. In order to evaluate the leptin gene receptor polymorphism, we used a restriction fragment length polymorphism (RFLP) method. Blood samples were collected from 100 randomly chosen Mazandaran native fowls. Genomic DNA was extracted using modified salting-out method and amplified polymerase chain reaction technique. Exon and intron 9-11 of the fowl leptin gene receptor was amplified to produce a 382 bp fragment. The PCR products were electrophoresed on 1% agarose gel and stained by etidium bromide. Then, amplicons with Tsp509I were digested and revealed two alleles, A and B. Data were analysed using PopGene 32 package. In this population, AA, AB, BB genotype have been identified with the 69.14, 30.16 and 0.7% frequencies. A and B alleles frequencies were 0.84 and 0.16, respectively. χ 2 test did not show Hardy–Weinberg equilibrium in this population (p<0.05). Further association analysis is required to clarify the effects of these marker genotypes on production traits in this breeder flock. Key words: Leptin gene receptor, polymerase chain reaction-restriction fragment length polymorphism (PCRRFLP),polymorphism, breeder hen.

Comparative Evaluation of Aluminum Sulfate and Ferric Sulfate-Induced Coagulations as Pretreatment of Microfiltration for Treatment of Surface Water

Two coagulants, aluminum sulfate and ferric chloride, were tested to reduce natural organic matter (NOM) as a pretreatment prior to polyvinylidene fluoride (PVDF) microfiltration (MF) membranes for potable water treatment. The results showed that the two coagulants exhibited different treatment performance in NOM removal. Molecular weight (MW) distributions of NOM in the tested surface raw water were concentrated at 3–5 kDa and approximately 0.2 kDa. Regardless of the coagulant species and dosages, the removal of 0.2 kDa NOM molecules was limited. In contrast, NOM at 3–5 kDa were readily removed with increasing coagulant dosages. In particular, aluminum sulfate favorably removed NOM near 5 kDa, whereas ferric chloride tended to reduce 3 kDa organic substances. Although aluminum sulfate and ferric chloride could improve the flux of the ensuing MF treatment, the optimal coagulant dosages to achieve effective pretreatment were different: 2–30 mg/L for aluminum sulfate and >15 mg/L for ferric chloride. The scanning electron microscope (SEM) image of the membrane-filtered coagulated raw water showed that coagulation efficiency dramatically affected membrane flux and that good coagulation properties can reduce membrane fouling.

Effect of PACs pretreatment on UF performance for NOM removal

AbstractThis paper investigated the effect of various powdered activated carbon (PAC) pretreatment on ultrafiltration (UF) performance for the removal of natural organic matters (NOM) from Taihu Lake. The hydrophilicity/hydrophobicity and molecular weight (MW) distribution of NOM were analyzed to understand the correlation between PAC adsorption and NOM characteristics. Experimental results demonstrated that PAC addition into raw water could enhance NOM removal efficiency of UF, whereas PAC-NOM particles could increase the trans-membrane pressure slightly. PAC was able to adsorb organics with small MW while UF alone could retain large MW. Fractionation results showed that UF could retain strongly hydrophobic acids (SHA) and neutral hydrophilic compounds (NEU), both of which could also be removed by PAC absorption. Fluorescence excitation–emission matrix spectra showed that PAC pretreatment could decrease extracellular protein-like organics and soluble microbial products significantly from the raw water.

Effect of dissolved organic matter on arsenic removal by nanofiltration

Abstract Arsenic is known as a carcinogen that causes skin cancer and various internal cancers. The arsenic contamination in water forced the water and health authorities to introduce stringent standards for arsenic control level in drinking water. Nanofiltration presents a promising method to remove arsenic, by the effect of both size exclusion and electric repulse, which is reliable, easy to produce, obtain, operate, and maintain. In this work, the influences of dissolved organic matter (DOM) on arsenic removal by nanofiltration process were investigated through a series of laboratory bench-level experiments. The existing of humic acid (HA), which was used as substitute of DOM, increased the arsenic removal due to the formation of humic/arsenic complexes. With the presence of high concentration of HA (10 mg total organic carbon [TOC]/L), the removal efficiency of arsenic was almost 100%, which was higher compared with the result (80%) obtained at low concentration of HA (2 mg TOC/L). The membrane flux f...