The objective of this study is to clarify the effects of coexistent substances in landfill leachate in the following processes: the adsorption of 2,4-dichlorophenol (2,4-DCP) from landfill leachate using different adsorbents, the extraction of 2,4-DCP from adsorbents using acetic acid, and the decomposition of 2,4-DCP by ozonation in acetic acid. The adsorption capacities of all adsorbents for 2,4-DCP in landfill leachate were almost the same as that of 2,4-DCP dissolved in distilled water. The adsorption capacities of granular activated carbon (GAC) and SP207 (bromine-bonded styrene-divinyl benzene-type adsorbent) immersed in landfill leachate for 6 months (immersed adsorbents) were almost the same as those of the new GAC and SP207. On the other hand, the amount of adsorbed 2,4-DCP on immersed SP850 (styrene-divinyl benzene-type adsorbent) at an equilibrium concentration of 1 μg·l^-1 2,4-DCP was only 74% of the new SP850. After several adsorption-extraction processes, the adsorption capacities for 2,4-DCP of all immersed adsorbents became constant and 2,4-DCP adsorbed on immersed adsorbents was completely extracted by acetic acid. This suggests that immersed adsorbents regenerated by acetic acid can be used repeatedly. The decomposition rate of 2,4-DCP by ozone in acetic acid after the submersion of immersed GAC was higher than that in the new acetic acid. Organic compounds and Fe³⁺ present in landfill leachate enhanced the decomposition rate of 2,4-DCP by ozonation in acetic acid.

View full abstract

Molecular approaches were applied to study the identification and enumeration of denitrifying bacteria in a fluidized bed reactor (FBR). The FBR was continuously operated as a unit for the removal of nitrogen from domestic sewage treatment plant effluents, with a supplementary supply of methanol as a carbon source. By denaturing gradient gel electrophoresis (DGGE) and sequence analysis of 16S ribosomal DNA, it was revealed that the Thauera group was dominant among the denitrifying bacteria in the biofilms obtained from the FBR. The oligonucleotide probe THA155 for fluorescence in situ hybridization (FISH) was newly designed for specifically targeting the Thauera group. THA155 was able to detect Thauera cells from the biofilm sludge, but only 0.9-5.7 percent of DAPI-stained total cells was hybridized. The real-time polymerase chain reaction (PCR) targeting of the gene sequences of nitrite reductase gene, a key enzyme of denitrification processes, was performed to quantify denitrifying bacteria cells including the Thauera group. An excellent correlation was found between the number of nirS genes in the biofilm sludge and the activity of denitrifiers in the FBR. Therefore, the quantification of the nirS gene by real-time PCR can be an appropriate tool for monitoring denitrifying bacteria in nitrogen removal reactors.

View full abstract

In this study, the fate and behavior of typical endocrine disrupters in wastewater treatment plants of two different treatment processes were investigated for more than one year. All the investigated endocrine disrupters were effectively removed by the wastewater treatment processes. It was considered that the majority of the removal was accomplished by the biological treatment processes. The removal efficiencies of estrone (E1) and 17β-estradiol (E2) in the oxidation ditch process were higher than those in the conventional activated sludge process. The removal efficiency of E1 was lower than those of E2 and E3. In particular, in the conventional activated sludge process, E1 concentrations in effluents were higher than those in influents in many cases. It seems that the cleavage of conjugated estrogen is responsible for the increase in E1 concentration. On the other hand, estrogen-like activity was also effectively removed in the wastewater treatment processes. The estrogen-like activity in effluents was mainly derived from E1 and E2, and the contribution of E1 was particularly high. These results suggest that E1 is very important for the effective removal of estrogenic potency in effluents.

View full abstract

A transport-degradation model for trichloroethylene (TCE) with a modified competitve inhibition Monod kinetics, product toxicity and TCE sorption in soil was developed for the simulation of TCE removal from soil columns. The simulation results were compared with the experimental data. They show quantitatively good agreements with experimental data of TCE removal and carbon source degradation in the soil column amended with methane or aromatic compounds. Parameter sensitivity analysis of the model also shows that the TCE removal rate is highly sensitive to changes in yield coefficient, carbon source concentration, TCE concentration, and transformation capacity. However, it is relatively nonsensitive to changes in the maximum rate of TCE transformation and the half-velocity constant. This model could be an effective tool for predicting the treatability of a biostimulation approach to an aquifer contaminated with TCE.

View full abstract

To determine the level of estrogenic substances in an aquatic environment, four types of in vitro assay, namely, E-Screen, Ishikawa cell-ALP, YES and ELISA, and chemical analysis using GC/MS were carried out. Water samples were collected from coastal areas and rivers in Japan. Estrogenic substances were extracted by solid-phase extraction using a Sep-pak C18 cartridge. Higher levels of estrogenic substances were observed at sites close to sewage treatment plants as measured by in vitro assays. The 17β-estradiol equivalent concentration (E2 equiv.) determined by E-screen tended to be higher than those of the other assays, whereas YES showed a lower sensitivity than E-screen and Ishikawa cell ALP. According to the chemical analysis, the levels of estrone (E1) were higher than those of 17β-estradiol (E2). Although 17α-ethynylestradiol, nonylphenol, octylphenol and bisphenol A were detected in a few samples, their levels were low. E1 and E2 contributed to most parts of E2 equiv. in the water samples.

View full abstract

Nutrient recovery from fish culture water using a seaweed biofilter was investigated. The green alga Ulva onoi was selected for use as a seaweed biomass. The load capacity of ulva per day derived from nitrate (NO₃-N) uptake was 0.9mg-N·g-wet^-1·d^-1. A closed recirculating aquaculture system consisting of a fish tank, an intensive aeration unit, a nitrification unit and a seaweed biofilter tank was constructed. The required amount of seaweed biomass as determined from feed quantity and load capacity was provided into the seaweed biofilter tank, and fish (Oreochromis mossambicus) were cultured in the system. NO₃-N was fixed in the seaweed biomass throughout the experimental period, and did not accumulate in the culture water. The concentrations of ammonium and nitrite were maintained at very low levels of less than 0.15mg-N·l^-1. In addition, the survival rate of the cultured fish was 100%, and the ulva in the seaweed biofilter grew well throughout the experimental period. Each process proceeded smoothly, and the aquaculture system was property maintained. As a result of the nitrogen mass balance in the culture, approximately 70% of all the nitrogen excreted by the fish was fixed by the ulva. For an aquaculture system, a seaweed biofilter is a useful water treatment device for achieving both nutrient removal and seaweed production with low maintenance.

View full abstract