Pilot tests of a cubic-lattice-based rotating biological contactor were implemented to remove organic matter from wastewater from a milk factory and a hospital in Vietnam. In the milk factory wastewater, the biochemical oxygen demand (BOD) removal ratio was stable between 60% and 90% (average 75%) using this method, with a BOD surface load of 0.002-0.020 kg•m−2•day−1. The average nutrient ratio of the raw wastewater was 0.13 of total nitrogen and 0.015 of total phosphorus compared with 1.0 of BOD. The BOD of treated water was less than 50 mg•L−1, achieving category B of the industrial wastewater standard of Vietnam (QCVN 40:2011). For the hospital wastewater, the BOD removal ratio was stable between 60% and 90% (average 78%), with a BOD surface load of 0.005-0.022 kg•m−2•day−1. The average nutrient ratio of the raw wastewater was 0.25 of total nitrogen and 0.018 of total phosphorus compared with 1.0 of BOD. The BOD of treated water was less than 50 mg•L−1, satisfying category B of the medical wastewater standard of Vietnam (QCVN 28:2010/BTNMT). The electric power consumption was 0.73 KWh•m-3 of wastewater. The sludge conversion ratio from BOD was 0.51 kg TSS•kg BOD−1 based on the excess sludge and suspended solids in raw wastewater and treated water.

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The purpose of our study is to develop a treatment procedure for humic substances (HS hereafter) and phosphate ion in wastewater and environmental water by percolation of the water through a constructed soil layer at the hydraulic loading of a few metres per day. In the present work, batch sorption tests were conducted for more than 80 samples of soil, sludge, mineral and organic materials in order to find good sorbents for fulvic acid (FA hereafter) and phosphate ion. The results showed that the sorption of FA was high for some charcoal, and apatite and goethite minerals. Comparatively high sorption of FA was found for some Andosols and volcanic ash soil. Significant sorption of phosphate ion, on the other hand, was found for various types of soil, sludge from water treatment plants and some waste materials. The linear isotherm was obtained for the sorption of FA to a charcoal, apatite and goethite minerals, and Andosols.

In this study, we investigated the behavior of estrogens in the rhizosphere of white clover (Trifolium repens, clover hereafter) with two different pot tests, using soil and agar as growth media. In a pot test using agar spiked with estrogen, the estrogen concentration in the agar with clover decreased to non-detectable levels within one month, while in the agar without clover, 60% of initially added estrogen remained after one month. The half-lives of estrone (E1) and 17beta -estradiol (E2) in the agar with clover were 2.4-3.8 and 13.2 d, respectively. The dissipation of E1 followed first-order rate law, while that of E2 fitted a zero-order reaction, indicating that they had different mechanisms of dissipation from agar. In the soil pot test, the behavior of E1 and E2 was not influenced by clover. An initial rapid decrease in the amount of estrogen extracted by methanol/acetic acid was followed by persistence for 1-3 months, regardless of presence of clover. Moreover, in three weeks E1 and E2 were only partly degraded by microbes extracted from the soil used in the pot test. In this study, abiotic degradation of estrogens and sorption of estrogen to soil, rather than the effects of soil microbes and clover, contributed to the initial rapid dissipation of estrogens in the soil. However, the results of the agar pot test suggested that vegetation such as clover may significantly contribute to removal of estrogens when estrogens in aqueous phase are discharged with surface runoff and preferential flow after heavy rain in agricultural fields, or when present in soils with low estrogen sorptivity.

Bacterial diversity of the microbial consortia in a biological filtration pilot plant for the simultaneous removal of arsenic (As), iron (Fe) and manganese (Mn) from groundwater was analyzed. PCR-based denaturing gradient gel electrophoresis (DGGE) of bacterial 16S ribosomal RNA (rRNA) genes represented at least 6 dominant signals and many weak signals. Phylogenetic analysis using the nucleotide sequences of the 16S rRNA gene clone library constructed from the pilot plant sample showed the presence of the bacteria closely related to Gallionella and Leptothrix, which are supposed to be involved in the production of Fe and Mn oxides utilized for adsorbents of As in this system. On the other hand, aoxB gene was not detected, suggesting that arsenite-oxidizing bacterium would not be involved in the As removal of the pilot plant. These results indicated that the simultaneous removal of As, Fe and Mn from groundwater was conducted by the physicochemical sorption of As by the biogenic Fe and Mn oxides produced by the bacteria closely related to Gallionella and Leptothrix included in the microbial consortia of the pilot plant.