The selective removal of low-concentration heavy metal ions from heavy-metal-contaminated water was investigated using the activity or sulfate-reducing bacteria (SRB) immobilized on a fibrous slag (FS), which was employed as a both biocarrier and a fine particle collector medium. An upflow-type bioreactor composed of an FS-packed column, where SRB were immobilized at a lower part, was used. In this process, sulfate ions in the liquid are biologically reduced to sulfide ions, which react with metal ionic species to produce ultrafine metal sulfide particles. Subsequently, formed particles adhere onto the FS surface in the upper part of the reactor, thereby accumulating heavy metal ions as their sulfide precipitates. Five different organic compounds were evaluated, and as a result, lactic acid was found to serve as the most suitable electron donor for SRB in this system. In the continuous treatment of water contaminated with several heavy metal ions (Cd²⁺, Cu²⁺, Ni²⁺, Zn²⁺, and Mn²⁺), almost complete removal was attained over an 80-day operation period, except for Mn²⁺ having a relatively high solubility product constant. Heavy metal sulfide precipitates gradually accumulated on an FS bed. These experimental results indicate that the proposed bioreactor, which is the sulfate-reducing bioreactor with a fibrous slag carrier (SRB-FS), enables the efficient recovery of heavy metal ions from heavy-metal-contaminated water.

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The retention of 10 pharmaceuticals by 5 types of nanofiltration membranes was examined experimentally. The retention of acidic pharmaceuticals was dependent on the pH of the solution, while that of neutral pharmaceuticals was not affected by pH. The retention was low in the case of lower pH where the acidic pharmaceuticals were neutral solutes, while the retention was high at higher pH where they were negative ions. The retention was a function of the size of solutes in the low pH region where the sieving effect was dominant rather than the electrochemical effect. The retention by a tight membrane was high regardless of the solute size of the pharmaceuticals and of solution pH.

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In this study, the influence of the food-to-microorganism ratio (F/M) and permeate flux on membrane fouling was investigated using pilot-scale membrane bioreactors (MBRs) fed with actual municipal wastewater. Membrane fouling rate was affected by both F/M and permeate flux. It was shown that the influence of permeate flux on the membrane fouling rate was more significant than that of F/M. Batch filtration experiments were conducted to evaluate the degree of irreversible fouling caused by different fractions (suspended solids, colloids, soluble matter) in the mixed liquor of MBRs. From the results of the batch experiments, it was revealed that (a) irreversible fouling was caused mainly by the soluble fraction, and (b) irreversible fouling became significant when the MBR operated with a high F/M and a short solid retention time. There was a relationship between the fouling rate and the concentration of dissolved organic carbon (DOC) particles in the mixed liquor, whose size was between 0.2 μm and 0.5 μm. The concentration of organic matter with an apparent molecular weight of around 1MDa was also correlated with the fouling rate. These two constituents in the mixed liquor suspension seemed to affect membrane fouling.

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In this paper, we describe the issues regarding nonylpheol formation in the activated sludge process. In this research, a lad-scale experiment simulating a conventional activated sludge process was conducted for 160 days where hydraulic retention time was set at I day, solid retention time varied from 10 to 15 days and the dissolved oxygen (DO) level in the aeration section was controlled below 0.5mg·l^-1. Nonylphenol ethoxylates (NPnEOs) (n=3 to 14) solution (200mg·l^-1) were fed as a single organic substance. NPnEOs were degraded in the aeration section, but a large amount of NPnEOs (n=1-4) and NP accumulated in the activated sludge. However, nonylphenol formation was not observed in the batch biodegradation experiments under either saturated DO conditions or anaerobic conditions. It indicates that the reduction rate of short-chain NPnEOs and the formation rate of NP were strongly dependent upon the DO condition.

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Chlorinated aliphatic compounds such as trichloroethylene are main contaminants of groundwater, and the dechlorination technique using iron powder as metallic reduction agents was investigated as a remediation technology for such contaminations. As for the iron powder obtained from industrial processes or waste, as well as the dechlorination rate constants of chlorinated aliphatics could be obtained through laboratory experiments, as well as the data on specific surface area and iron content. Furthermore, X-ray photoelectron spectroscopy (XPS) was used for measuring the fraction of zero-valent iron, divalent iron, and trivalent iron at the surface of iron powder, and for measuring the distribution of iron species along the depth direction by XPS after each etching time. The rate constant of a pseudo-first-ordered reaction can be ranked using the index of reaction area, which is determined by multiplying specific surface area by the mean zero-valent iron fraction measured by XPS.

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The transcription level of the nitrite reductase gene of denitrifying bacteria in a lab-scale denitrifying reactor was investigated by real-time reverse transcription (RT)-PCR technique as an indicator of in-situ microbial activity. Two types of batch experiment were conducted to clarify the effects of dissolved oxygen (DO) and carbon/nitrogen (C/N) ratio on the relative nirS mRNA level in denitrifying sludge. The reverse transcription of total RNA with the primer, nirS 6R, specific for the nirS gene was suitable for the subsequent quantification of the nirS gene by real-time PCR. The presence of DO and a low C/N ratio in the medium resulted in a rapid decrease in the relative transcription level of nirS mRNA from 10⁵ to 10³ copies·ng^-1 total RNA within four hours of the batch experiments. The relative transcription remained at the same level after nitrate concentration decreased to a level low enough to reduce denitrification rate. Although there was no relationship between the denitrification rate of the reactor and the relative transcription level of nirS mRNA in the batch experiments, a quick response of transcriptional induction of nirS mRNA corresponding to the changes in DO and C/N ratio was detected.

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In this study, we aimed to develop an effective biological nitrogen removal method by applying a membrane bioreactor (MBR). Two different processes, A and B, were investigated using a pilot-scale plant with a capacity of 52 m³·d^-1·Both processes are based on three-stage nitrification-denitrification with a post-denitrification process. In process A, membrane separation was carried out after the post-denitrification tank treatment, whereas in process B, mixed liquid was circulated directly from the post-denitrification tank to the first and third anoxic tanks. Raw wastewater was supplied to both processes. The T-N concentration of raw wastewater was 35 mg·l^-1 on average. It was confirmed that a T-N concentration of less than 3 mg·l^-1 could be achieved in process A with hydraulic retention time (HRT) of 11 hrs. It was also confirmed that a T-N concentration of less than 5 mg·l^-1 could be achieved in process B with HRT of 10 hrs. In process B, effective phosphorus removal by enhanced biological phosphorus removal (EBPR) was observed, because the post-denitrification tank caused material in the first anoxic tank to become anaerobic. It was suggested that ORP control in the use of the denitrification tank is essential to ensure satisfactory denitrification in process A. The excess sludge production per inflow SS was 0.64 kg·kg-SS^-1 with SRT of 20 days. It was confirmed that the proposed biological nitrogen removal processes could achieve a high level of nitrogen removal and reduce excess sludge production, while occupying only half the area of the existing multistage nitrification-denitrification process.

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Three series of laboratory-scale subsurface vertical flow (SSF) wetland systems with and without forage rice (Oryza sativa L.) were designed for evaluating nitrogen removal performance and biomass production. In these systems, artificial nitrogen-contaminated river water and livestock wastewater were supplied at three hydraulic loading rates (HLRs) using two flow types: flooded continuously SSF and non-flooded intermittently SSF. The average removal efficiencies of total nitrogen (T-N) in flooded SSF systems with forage rice varied from 45% to 77%, whereas those of non-flooded SSF systems were lower, ranging from 18% to 44% in river water treatments. On the other hand, the average removal efficiencies of T-N varied from 27% to 36% in livestock wastewater treatments. A variance analysis showed a significant difference in T-N removal efficiency between systems with and without forage rice. The above-ground biomasses of forage rice in both river and livestock water treatment systems ranged from 1.1 to 4.6 kg dry weight m^-2, whereas the amount of nitrogen assimilated by this forage rice ranged from 12.0 to 69.8 gN m^-2. Since forage rice containing nitrogen could be supplied to the livestock industry through whole-crop silage, the results indicate that wetland systems using forage rice are useful for the reduction of nitrogen loading in the environment as well as for increasing feed self-sufficiency rate in Japan.

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