Ruihua Dai

Effects of amino acids on microcystin production of the Microcystis aeruginosa

A Microcystis aeruginosa which produced high content of microcystin-LR (MC-LR) but no microcystin-RR (MC-RR) was isolated from Dianchi Lake in China. In the molecular structure of MC-LR, glutamic acid, aspartic acid, leucine, alanine and arginine are the constitutional components which are abundant in natural water. In this paper, effects of six amino acids at their natural concentrations on the growth of the M. aeruginosa and the microcystin (MC) production were studied in batch culture. M. aeruginosa could assimilate alanine, leucine and arginine as sole nitrogen sources for growth and MC production. However, glutamic acid, aspartic acid and lysine could not be assimilated quickly, although they could pass the cell membrane and enter into the cell rapidly. Our experiment demonstrated that the possible reason of such phenomenon was that different amino acids had different effects on the process of metabolism through the free dissolved amino acids within the cells.

Influence of soluble microbial products (SMP) on wastewater disinfection byproducts: trihalomethanes and haloacetic acid species from the chlorination of SMP

IntroductionEffluent organic matter from biological wastewater treatment plants is composed of degradation products and soluble microbial products (SMP). Protein, polysaccharide, humic acid, and DNA were major biomolecules of SMP. Little is known about the effects of SMP as microbially derived precursors on disinfection byproduct formation and speciation in biologically treated wastewater. In addition, there has never been any attempt to directly chlorinate the major biomolecules of SMP.Materials and methodsIn this study, model compounds (bovine serum albumin, starch, DNA, and humic acid) and SMP collected from a sequencing batch reactor (SBR) were chlorinated to verify the trihalomethane and haloacetic acid species that were produced from them.Results and discussionThe results showed that chloroform, dichlorobromomethane, dichloroacetic acid, and trichloroacetic acid were generated from the chlorination of SMP in the SBR, and there was a close relationship between the species predicted from the model chemical compounds and those obtained from the SMP.

Relationship of energy charge and toxin content of Microcystis aeruginosa in nitrogen-limited or phosphorous-limited cultures.

Effects of nitrogen-limitation and phosphorus-limitation on microcystin (MC) content and energy charge (EC) of the Microcystis aeruginosa were investigated in batch cultures and semi-continuous cultures. In batch cultures, nitrogen-limitation retarded the MC synthesis and phosphorus-limitation had little effects on MC production. The EC remained constant in nitrogen-limited cultures, while it decreased largely when phosphorus was extinct in phosphorus-limited culture. In the semi-continuous cultures, MC production in nitrogen- and phosphorus-limited cultures increased with the increase of dilution rate; however, MC content in phosphorus-limited cultures was more than that in nitrogen-limited cultures. The EC in nitrogen-limited cultures remained constant and in phosphorus-limited cultures increased with the increase of dilution rate. In phosphorus-limited semi-continuous cultures, a direct relationship between EC and MC content was demonstrated. No correlation was observed in nitrogen-limited semi-continuous cultures. Based on the above analysis, a mechanism of nitrogen and phosphorus effect on the MC synthesis was suggested, that the MC synthesis was determined by the combination of necessary enzymes and precursors and EC.

The effect of continuous Zn (II) exposure on the organic degradation capability and soluble microbial products (SMP) of activated sludge.

This study describes the change of organic degradation capability and soluble microbial products (SMP) generated in activated sludge under continuous exposure to Zn (II) in a sequencing batch reactor (SBR). In 338 days of operation, the added Zn (II) concentrations were gradually increased from 50 to 100, 200, 400 to 600 and 800 mg/L. Results showed that after adaptation, the activated sludge could endure 400mg/L Zn (II) without showing evident reduction in organic degradation ability (92±1% of chemical oxygen demand (COD) removal in stable state). However, when 600 and 800 mg/L Zn (II) were applied, the effluent water quality significantly deteriorated. Meanwhile, under increasing Zn (II) concentrations, the SMP content in the activated sludge, together with its main biochemical constituents, first increased slightly below 400mg/L of Zn (II), then rose sharply under 600 and 800 mg/L Zn (II). Furthermore, a close correlation was found between SMP content and effluent soluble COD in both the Experimental Reactor and Control Reactor. In addition, the Zn (II) concentrations in the effluent and SMP extraction liquid were further analyzed and discussed to reveal the role that SMP constituents played in defense and resistance to the toxicity of Zn (II).

Effects of Ni2+ on the characteristics of bulking activated sludge.

This study investigated effects of the continuous addition of a high-concentration of Ni(2+) on the characteristics of bulking activated sludge as well as on the variety and recovery of their ability removing organic pollutants and ammonia in a sequencing batch reactor (SBR). To the knowledge of the authors, this is the first study to examine the changes in quantity and composition of the extracellular polymeric substances (EPS) in bulking activated sludge before and after the addition of a high-concentration of Ni(2+). The correlation between these changes and the sludge characteristics was also investigated. The results showed that after a 40-day acclimation to the addition of 60 mg/L Ni(2+), the ability to remove organic pollutants was recovered; but the ability to remove ammonia was not. The addition of Ni(2+) made a great change in the quantity and composition of the EPS in bulking sludge, including both exterior soluble EPS (EPS(S)) and interior bound EPS (EPS(b)), showing a slight increase followed by a large decrease before reaching a steady state. The difference between the change in the amounts of EPS(S) and EPS(b) was not significant. However, among the component fractions, the change in protein content was obvious than that of polysaccharide and humic acid.

Investigation of a sewage-integrated technology combining an expanded granular sludge bed (EGSB) and an electrochemical reactor in a pilot-scale plant.

A sewage-integrated treatment system (SITS) for the treatment of municipal wastewater, consisting of an expanded granular sludge bed (EGSB) reactor to remove soluble organic matter and an electrochemical (EC) reactor to oxidize the NH(3)-N, was evaluated. The performance of the EGSB reactor was monitored for 12 months in a pilot-scale plant. Iron shavings were added to the EGSB reactor on the sixtieth day to improve the removal efficiency of the chemical oxygen demand (COD), suspended solids (SS) and total phosphorus (TP). After the iron shavings were added, the effluent COD, SS and TP decreased from 104 to 46 mg L(-1), 21 to 8.6 mg L(-1) and 3.62 to 1.36 mg L(-1), respectively. Moreover, in the EC reactor, which was equipped with IrO(2)/Ti anodes, the NH(3)-N and total nitrogen (TN) concentrations decreased from 25 to 12 mg L(-1) and 29 to 15 mg L(-1), respectively. The NH(3)-N was directly oxidized to N(2), resulting in no secondary pollution. The results demonstrated the possibility of removing carbon and nutrients in a SITS with high efficiency. The system runs efficiently and with a flexible operation, making it suitable for low-strength wastewater. The results and parameters presented here can provide references for the practical project.

The effect of Ni(II) on properties of bulking activated sludge and microbial analysis of sludge using 16S rDNA gene.

This study investigated the effect of nickel on properties and microbial community of bulking activated sludge when 60-240 mg/L Ni(II) was dosed continuously in a sequencing batch reactor (SBR) over 350 days. Results showed that 120 mg/L nickel did not significantly inhibited removal of organic pollutant by activated sludge. However, the system was completely upset when 240 mg/L Ni(II) was dosed. Improvement of settling and dewatering ability was also observed with the addition of Ni(II). In addition, investigations by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) of 16S rDNA of bacteria strain demonstrated that Ni(II) significantly affected microbial community of bulking activated sludge, judging from the elimination of original species and emergence of possible new nickel-resistant bacteria. The effect of nickel on shift of microbial community was an important cause resulted in the improvement of sludge properties in this bulking activated sludge system.

Trihalomethanes and haloacetic acid species from the chlorination of algal organic matter and bromide.

Bromide and algal pollution are important factors influencing disinfection byproduct (DBP) formation and speciation in reservoir water in coastal areas. In this study, the chlorination of model algal cellular compounds (bovine serum albumin, fish oil and starch), Microcystis aeruginosa and its extra-cellular organic matter (EOM) were conducted in the absence and presence of bromide. The main aim of the present study is to explore their potential as precursors for trihalomethanes (THMs) and haloacetic acid (HAAs) speciation upon chlorination in the presence of bromide. The results showed that all brominated THMs species were generated, whereas only bromochloroacetic acid (BCAA) or/and dibromoacetic acid (DBAA) was/were produced as for brominated HAAs (Br-HAAs) from the three model compounds in the presence of bromide. The effect of bromide on Br-HAAs speciation upon fish oil chlorination was more evident than with BSA and starch. There was a good correlation between the species predicted from the model compounds and those obtained from specific algal species. Br-HAAs and Br-THMs species from Microcystis aeruginosa cells or EOM were the same as those from bovine serum albumin in the presence of bromide.

Speciation and formation of iodinated trihalomethane from microbially derived organic matter during the biological treatment of micro-polluted source water.

Water sources are micro-polluted by the increasing range of anthropogenic activities around them. Disinfection byproduct (DBP) precursors in water have gradually expanded from humic acid (HA) and fulvic acid to other important sources of potential organic matter. This study aimed to provide further insights into the effects of microbially derived organic matter as precursors on iodinated trihalomethane (I-THM) speciation and formation during the biological treatment of micro-polluted source water. The occurrence of I-THMs in drinking water treated by biological processes was investigated. The results showed for the first time that CHCl2I and CHBrClI are emerging DBPs in China. Biological pre-treatment and biological activated carbon can increase levels of microbes, which could serve as DBP precursors. Chlorination experiments with bovine serum albumin (BSA), starch, HA, deoxyribonucleic acid (DNA), and fish oil, confirmed the close correlation between the I-THM species identified during the treatment processes and those predicted from the model compounds. The effects of iodide and bromide on the I-THM speciation and formation were related to the biochemical composition of microbially derived organic precursors. Lipids produced up to 16.98μgL(-1) of CHCl2I at an initial iodide concentration of 2mgL(-1). HA and starch produced less CHCl2I at 3.88 and 3.54μgL(-1), respectively, followed by BSA (1.50μgL(-1)) and DNA (1.35μgL(-1)). Only fish oil produced I-THMs when iodide and bromide were both present in solution; the four other model compounds formed brominated species.

Effect of urea on growth and microcystins production of Microcystis aeruginosa.

The effects of urea on the growth and toxin content of Microcystis aeruginosa isolated from Dianchi Lake in China were investigated. Experiments were carried out in lab using (15)N isotopic technique to characterize urea-N biosynthesis to microcystins. High urea concentration (3.6 mmol-N L(-1)) would restrict the growth of M.aeruginosa and the production of microcystin-LR, while low urea concentration (0.4-1.4 mmol-N L(-1)) would promote the growth of M.aeruginosa and the production of microcystin-LR. The (15)N labeling experiment further demonstrated that there existed selectivity when M.aeruginosa assimilated urea to form its structure. The majority of M.aeruginosa assimilated 1 urea molecule at first which was biosynthesized into the Ala or Leu residue. On day 18, The m/z=1004 parent ion assimilated 9 (15)N except that the Mdha residue did not assimilate any urea-(15)N. The results give deeper insight to the biosynthesis of urea into microcystins.