In closed aquatic environments like ponds or lakes, water bloom caused by eutrophication has severely damaged aquatic ecosystems. Some previous studies suggested that submerged macrophytes contribute to the development of aquatic ecosystems and water purification. Although water purification and lake ecosystem restoration using submerged macrophytes have been greatly studied, their specific mechanisms remain unclear. We evaluated the effect of a submerged macrophyte Potamogeton pusillus on water quality and plankton community using mesocosms with and without the macrophytes. The concentrations of chlorophyll-a, total nitrogen and phosphorus, particulate nitrogen and phosphorus in the mesocosm with P. pusillus were lower than those without P. pusillus as long as the macrophytes thrived. The cell concentration of cyanobacteria was significantly decreased in the presence of P. pusillus, while differences for chlorophytes and diatoms remained minimal. The number of large-sized cladocerans (> 0.1 mm of body length), known as heavy grazers of phytoplankton, was markedly higher in the mesocosm with P. pusillus. Our results suggested that P. pusillus is potentially useful for water purification and aquatic ecosystem restoration.

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Suspended organic sludge from freshwater and biofloc Nile tilapia systems were examined for the presence of denitrifying and dissimilatory nitrate reduction to ammonium (DNRA) activities under nitrate and sulfide stimulation. Initial nitrate concentrations at 25 and 100 mg NO₃^--N/L were added to the freshwater sludge and biofloc samples to simulate low and high nitrate levels that are normally found in aquaculture systems. The results showed that freshwater sludge and biofloc both had denitrifying activity immediately after nitrate addition. However, ammonium accumulated in the biofloc reactors but not in the freshwater reactors, indicating the activity of DNRA in the high C/N biofloc particles. The influence of sulfide on nitrate reduction was also studied by adding different concentrations of sulfide along with 100 mg NO₃^--N/L. The results showed that elevated sulfide concentrations partially inhibited denitrification in the freshwater sludge and caused nitrite and ammonium accumulation, in which ammonium formation was probably responsible by DNRA activity. In sulfide-added biofloc reactors, ammonium accumulated at the same level as found in the biofloc reactors without sulfide. Therefore, DNRA bacteria residing in the biofloc aquaculture system were more likely to be heterotrophs that did not use sulfide as their electron donor.

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Organically enriched sediment has been found in water environments. The tsunami originating from the Great East Japan Earthquake in 2011 deposited large amount of sediment, thus providing evidence about its huge accumulation in coastal marine areas possibly due to human activities such as fish culture and marine product processing of industries. Here, degradation potential of organically enriched sediment deposited on a coastal site at Higashi-Matsushima, Miyagi, Japan was investigated under both sulfate- and iron-reducing conditions. Sediment slurry was prepared by mixing the sediment with artificial seawater. The effects of supplementation with sulfate and lepidocrocite (a crystalline Fe[III] oxide) on the structure and activity of the slurry microorganisms were examined by the combined physicochemical analyses and 16S rRNA deep sequencing. The sediment slurry was incubated for 5 days, during which the concentrations of TOC, sulfate, and ferrous iron remained at constant levels and the TG-DTA patterns did not change. The composition of dominant members of the microbial communities was stable, although the rare microbial populations slightly changed. The result in this study revealed that the organically enriched sediment was resistant to biodegradation under the sulfate- and iron-reducing conditions.

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We propose that rapid algal bioassay using delayed fluorescence (DF) may be useful to apply to the whole effluent toxicity test. In this report, we compared the conventional algal growth inhibition test and the rapid algal bioassay using DF to detect the toxicity of industrial effluents. We used the industrial effluents from eight factories in Toyama Prefecture. Delayed fluorescence is a special type of luminescence; it detects the growth of only those cells that have photosynthetic capability. Therefore, DF can detect algal growth inhibition in a shorter time than the 72 h conventional test, as cells that have lost photosynthetic capability can be detected. The DF test in 6 h and 24 h exposure found algal inhibition from six out of eight effluent samples, and found chronic toxicity unit over 10 from four out of eight effluent samples, the same as the conventional 72 h growth test. These observations suggest that the rapid bioassay using DF is potentially applicable to the selected industrial effluents.

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Emissions of greenhouse gases were evaluated using a lab-scale continuous activated sludge reactor for the purpose of power saving at on-site domestic wastewater treatment facility. In addition, the behavior of N₂O production was investigated to figure out the factors reducing N₂O production. The experiments were performed under three power saving conditions. The relation between N₂O production and ammonia, nitrite, nitrate, and dissolved oxygen concentrations was clarified. As a result, it was found that suitable control of ammonia oxidization is an important factor to reduce N₂O production. Higher emission of greenhouse gases was observed in long-term power saving condition compared with the other conditions because of high N₂O emission. The emissions of greenhouse gases were almost the same for conventional condition and short-term power saving condition. However, in light of power shortages, short-term power saving condition has an advantage over conventional condition.

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The removal of household pollutants of recent concern such as selected pharmaceuticals and personal care products (PPCPs), linear alkylbenzene sulfonate (LAS), and nutrients by solidified coal ash and water lettuce (Pistia stratiotes) was evaluated to possibly enhance conventional sewage treatment system and/or implement in developing countries as a cost-effective method. Porous concrete blocks were manufactured with cement and solidified coal ash, and riverine biofilm was collected by submerging into an urban creek. Relatively fast removal was found for an anionic surfactant LAS and total phosphorus (T-P) while the removal of total nitrogen (T-N) and total organic carbon (TOC) was moderate in both batch and continuous systems. Among the selected PPCPs, more than 98% of triclosan and acetaminophen was removed with the combination of the activated sludge and water lettuce treatment in 120 h of sequential batch experiments.

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Bioethanol is an important renewable resource that facilitates the sustainable development of society. In Miyako Island, Okinawa Prefecture, bioethanol is produced from sugarcane molasses, but molasses-based distillery wastewater is a highly polluted and dark brown-colored effluent that can cause serious problems in wastewater treatment. In a trial of seven adsorbents to investigate the separation of the colorants from wastewater, Diaion HP20 was selected as the most suitable adsorbent. Adsorbing and desorbing operations using column chromatography with HP20 recovered 74.5% of the colorants from wastewater (33.7 and 40.8% for 20 and 50% ethanol-eluted fractions, respectively). The isolated colorants as well as the wastewater itself exhibited scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH), and contained polyphenols. The distillery wastewater contained 11.3 g-tocopherol equivalent/L of DPPH radical-scavenging constituents and 7.66 g-catechin equivalent/L of polyphenol constituents.

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