This study examined the characteristics of M. aeruginosa (UTEX 2061) dominance under the existence of a competitor, Cyclotella sp. (CCAP 1070/4), at high N:P ratio through a series of culture experiments, and revealed the effects of initial cell density of Cyclotella sp. on the dominance of M. aeruginosa as well. At N:P ratio of 140 (P = 0.1 mg/L), M. aeruginosa could defeat Cyclotella sp., even though the initial cell density for M. aeruginosa was less than that for Cyclotella sp. Although it is generally accepted that the low N:P ratio favors the dominance of cyanobacteria, the results obtained in this study clearly indicate that the growth of M. aeruginosa would not depend on the low N:P ratio, and that M. aeruginosa could potentially dominate over other algal species in high N:P ratio. At N:P ratio of 1400 (P = 0.01 mg/L), M. aeruginosa could become a superior competitor when the same initial cell density of 5,000 cells/mL for M. aeruginosa and Cyclotella sp. was employed. The condition of higher initial cell density for Cyclotella sp. than that for M. aeruginosa was also examined. This experimental situation led to the dominance of Cyclotella sp. when a share of phosphorus concentration, Ps, was lower than the half saturation constant for M. aeruginosa.
The spatial variability of the food availability in different depositional environments (Nanakita estuary, Japan) was investigated using fatty acid biomarkers. The main objective of the present study was to determine the food availability for Nuttallia olivacea and Hediste spp. in connection with the depositional environment of organic matter (OM). Sandy sediment was mainly occupied by diatoms, bacteria and marine organic matter. Meanwhile, muddy sediment is dominated by diatoms, bacteria and terrestrial organic matter. The main food sources and food availability for N. olivacea were mostly dominated by diatoms, bacteria and dinoflagellates in connection with the depositional environment. Meanwhile, the food utilization characteristics of Hediste spp. may be attributable to the lower food selectivity due to their deposit feeding. From these results, the food availability for N. olivacea was more influenced by the depositional environment in estuarine tidal flat than Hediste spp.
In this study, we investigated the effect of silt and clay in the sediment on the settlement of Ruditapes philippinarum larvae. Mountain, river and sea sands of which silt and clay (< 0.075 mm) content was adjusted using silt and clay originating from these sands or dredged sediment (DS) were examined for settlement of R. philippinarum larvae. The addition of DS and Otagawa river sand-originated silt and clay did not accelerate the larval settlement, whereas the mountain and Jigozen sea sands-originated silt and clay promoted larval settlement at 5%. The negative impact of Otagawa river sand-originated silt and clay might be due to its high leachability of Mn, while the accelerated larval settlement by Jigozen sea sands-originated silt and clay could be attributed to its organic contents. The provided results indicate that a suitable ratio of the fine particles to coarse particles exists for the acceleration of the larval settlement, though the effect might be dependent on their chemical properties.
Huge quantities of untreated domestic and industrial wastes are being released everyday in Sitalakhya River, flowing along the eastern side of Dhaka City. The water quality of this river is deteriorating rapidly, especially during the dry season at certain reaches of the river. A one-dimensional quasi-steady state water quality model has been developed and calibrated using primary field data. A number of load reduction scenarios have been developed to assess their impacts on the river water quality. The model results indicate that Sitalakhya River water quality near intake point of Saidabad water treatment plant may not improve appreciably through reduction of waste load from a single major point source and even if all the wastewater entering into the river system are treated according to the present national effluent standard, the water quality improvement is not significant during the dry season. A revision of the national standards for disposal of effluents seems necessary.
In this study, the formation characteristics of aerobic granular sludge (AGS) mainly composed of nitrifying bacteria (referred to as nitrifying granules) in a continuous stirred-tank reactor (CSTR) were investigated at several surface loading rates (equal to the liquid linear velocity at the sludge settling zone). The surface loading rate strongly affected the selection of larger granular sludge similarly to the sludge settling time in a sequencing batch reactor. By setting an appropriate surface loading rate (1.4 m3/m2/d), small particles were effectively washed out, and larger granular sludge selectively remained in the reactor. As a result, nitrifying granules were effectively formed even with keeping an identical flow condition from the startup. To the best of our knowledge, this is the first study that has succeeded in forming nitrifying granules with keeping an identical flow condition from the startup using a continuous-flow reactor. These findings will contribute to the dissemination of AGS technology because information on the formation of AGS in a continuous-flow reactor is limited.
Oseltamivir and zanamivir are the two most prescribed antiviral drugs against influenza in Japan. Oseltamivir and its metabolite are frequently detected in surface water bodies in Japan during the last few years particularly in seasonal influenza period posing a potential threat of emergence of drug-resistant genes in human pathogens. Despite the second largest use of zanamivir as an antiviral drug in Japan, its presence and fate in environmental waters is unknown until now. Accurate assessment on the presence and fates of these drugs in environmental waters is the very first step in countering the potential negative impact on human health. We have recently developed a novel solid-phase extraction (SPE) method for simultaneous recovery of oseltamivir and zanamivir in environmental waters. These antiviral drugs were quantified in Neya River water and a nearby conventional sewage treatment plant (STP) during the 2010/2011 seasonal influenza using the SPE method in this investigation. Oseltamivir and zanamivir concentrations in the river water and STP water samples are discussed and compared with those of the 2009/2010 pandemic influenza in this article. This successful simultaneous quantitation of zanamivir in wastewater and river water with high recovery ratios paves the way for its monitoring in environmental waters.
Behaviour of somatic and F-specific coliphages, as model viruses, in a full-scale slow sand filtration (SSF) treatment plant of Japan was investigated through enumeration with the conventional plaque-forming unit (PFU) and the real-time reverse transcription polymerase chain reaction (RRT-PCR). The results showed that in the effluent of SSF, concentration of coliphages decreased while Qβ phage, as a part of F-specific coliphages, was still detected by the RRT-PCR method. The detection of Qβ may indicate that F-specific RNA phages in the water were mainly derived from human faeces. Moreover, the practice of partial regeneration of the filters did not obviously affect the whole performance of the sand filters in removing coliphages and indicator bacteria (E.coli, total coliforms, general bacteria and heterotrophic bacteria). Furthermore, strong correlations were not obtained among all model viruses and indicator bacteria in the SSF effluent as well as the general water quality indices (turbidity, DOC and UV260). However, a relatively strong correlation was found existent between the indicator bacteria and particle numbers.