Nao Ishikawa

Biological oxidation of arsenite in synthetic groundwater using immobilised bacteria.

Biological oxidation of arsenite (As(III)) in synthetic groundwater was examined by using arsenite oxidising bacteria (AOB) isolated from an activated sludge. The phylogenetic analysis indicated that the isolated AOB was closely related to Ensifer adhaerens. Batch experiments showed that for an As(III) oxidation with the isolated AOB the optimum ratio of nitrogen source (NH₄-N) concentration to As(III) concentration was 0.5 (52 mg/L-110 mg/L) and the isolated AOB preferred pH values ranging from 6 to 8, and water temperatures greater than 20 °C. Further continuous experiments were conducted using a bioreactor with immobilised AOB. With an initial As(III) concentration of 1 mg/L at a hydraulic retention time (HRT) of 1 h, an As(III) oxidation rate was around 1 × 10⁻⁹ μg/cell/min and an As(III) oxidation efficiency of 92% was achieved. Although the maximum oxidation rate measured at an HRT of 0.5 h was 2.1 × 10⁻⁹ μg/cell/min, the oxidation efficiency decreased to 87%. These results advocate that a biological process involving immobilised AOB may be useful as an economical and environmentally friendly pre-treatment step for As removal from groundwater.

Separation of metals and phosphorus from incinerated sewage sludge ash.

Microbial acidification of incinerated sewage sludge ash and dissolution of metals from the acidified ash were investigated using a semi-batch reactor at different solid retention times (SRTs). The average pH values ranged from 0.91 to 1.2 at SRTs longer than 10 days, whereas the reduction of SRT to 4 days resulted in an increase in the pH value to about 2. The dissolution efficiencies of Al, As, Cd, Cu and Mn were greater than 60% at a SRT of 4 days. Moreover, the effect of pH on precipitation of metals and P (dissolution of 80%) in the filtrate removed from the acidified sewage ash suspension, and the separation of phosphorus and the other metals in the filtrate using ethylenediaminetetraacetic acid (EDTA) or ferric ion, were examined. Although neutralisation of the filtrate to a pH of 5 simultaneously precipitated 100% of Al and 80% of P recovered from the acidified sewage ash, the addition of EDTA decreased their precipitation to 70 and 50%, respectively, at the same pH value, which would promote precipitation of P as calcium phosphate. Furthermore, neutralising to a pH of 2.5 after the addition of ferric ion precipitated P separately from Al and heavy metals.

Accelerated anaerobic release of K, Mg and P from surplus activated sludge for element recovery and struvite formation inhibition

Accelerated release of potassium (K), magnesium (Mg) and phosphorus (P) from surplus activated sludge (SAS) was investigated to develop a new system for the recovery of the elements. Anaerobic cultivation of SAS during 24 h released 78% of K and about 50% of Mg and P from SAS more effectively compared to aerobic cultivation (K: 40%, Mg: 15%, P: 15%). Furthermore, the addition of sodium acetate as an organic carbon source remarkably accelerated the release of K, Mg and P from SAS under anaerobic condition. However, no increase in the maximum release efficiencies was observed. The elements released from SAS could be transferred to separate liquid with the existing mechanical thickener and be recovered as MgKPO4 by some additional process. Furthermore, the removal of the elements from SAS would inhibit the formation of struvite causing the blockage of sludge transport pipe after anaerobic digestion process of thickened sludge.

Determination of tylosin excretion from sheep to assess tylosin spread to agricultural fields by manure application

Antibiotics administered to livestock are partly excreted with urine and feces. As livestock excrement is used as manure on agricultural fields, soil may be contaminated by excreted antibiotics, potentially resulting in the development of antibiotic-resistant bacteria. Therefore, it is necessary to determine the amount of antibiotic administered to livestock that could spread to agricultural fields through manure application. This study reveals the excretion ratio of tylosin from sheep. After developing an analysis procedure for tylosin in urine and feces from sheep, a tylosin excretion study was performed with two sheep. Tylosin was excreted in urine and feces for four days, after which its concentrations dropped below the limits of quantification (urine: 0.5μg/kg, feces: 2.4μg/kg). The total excretion ratio was 11% on average. The results of our study can provide useful knowledge for treating excrement in order to prevent the spread of antibiotics to agricultural fields through manure application.

Effect of pH and Chemical Composition of Solution on Sorption and Retention of Cesium by Feldspar, Illite, and Zeolite as Cesium Sorbent From Landfill Leachate

ABSTRACT This study investigated cesium (Cs) sorption and retention by 4 types of minerals, which were considered as candidate sorbents to prevent radiocesium leaching from landfill sites containing radiocesium wastes. Feldspar, 2 types of illite, and natural zeolite were examined for sorption of stable Cs under deionized water or landfill leachate conditions. In the pH range of 6 to 11, feldspar had a large effect on Cs sorption, but the other minerals did not. The sorption isotherms were obtained using 2 types of Cs solutions, which were fit to the Freundlich model. The difference of Freundlich exponent between the 2 types of Cs solutions was attributed to the sorption mechanisms of the minerals. These minerals had two or more types of sorption sites for cations; however, one specific type of site had a potentially higher selectivity for Cs in the leachate. Additionally, extraction test results showed that retention capacity for Cs in the leachate decreased in the following order: natural zeolite > illite Y > illite W > feldspar. Although illite W and illite Y were identified as the same mineral by XRD analysis, they had different retention capacities described as radiocesium interception potential, which is an index of the number of specific sites for Cs.