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The buildup of sediment deposits in reservoirs is a long-standing problem with serious consequences on the reservoirs' functionality and the ecology of their river systems. In the last two decades, hydraulic dredging has been used as a more viable engineering solution to restore reservoirs' sustainability. This study proposes a novel ejector-pump dredging system (EPDS) that solely utilizes hydraulic dredging for removal and transport of the sediments deposited at the reservoir's bed. Unlike conventional dredging methods, air is injected into the header pipeline to create a turbulent three-phase flow regime that enhances the solids suspension and continuous flow in the system. Introducing air effectively reduces the critical value of the deposition velocity of the dredged solids and transports them in a slug flow regime. This technique minimizes the tendency of the sediment to settle, and therefore eliminates system plugging. A laboratory prototype of the proposed system has proven the efficacy of removal and transport of mixed-size sediments up to 150 mm. Field trials have further shown the feasibility of the proposed system. Removal of large sediments with productivity approaching 70 m3/h was made possible using the suction-type EPDS. The hopper-type EPDS enabled carrying the dredged material for up to 1,000 m without resorting to a booster pump. The developed system was successfully used as part of an integrated dredging management program carried out for the Oouchibaru, Saigo, and Yamasubaru dams in the Mimi River basin, Japan. The very low turbidity levels recorded during the sediment dredging and transport operations of EPDS are indicative of the eco-friendly performance of the system. [ABSTRACT FROM AUTHOR]

Polyacrylamide has become an effective tool for reducing construction-related suspended sediment and turbidity, which are considered to have significant adverse impacts on aquatic ecosystems and are a leading cause of the degradation of North American streams and rivers. However, little is known about the effects of polyacrylamide on many freshwater organisms, and prior to the present study, no information existed on the toxicity of polyacrylamide compounds to native freshwater mussels (family Unionidae), one of the most imperiled faunal groups globally. Following standard test guidelines, we exposed juvenile mussels (test duration 96 h) and glochidia larvae (test duration 24 h) to 5 different anionic polyacrylamide compounds and 1 non-ionic compound. Species tested included the yellow lampmussel ( Lampsilis cariosa), an Atlantic Slope species that is listed as endangered in North Carolina; the Appalachian elktoe ( Alasmidonta raveneliana), a federally endangered Interior Basin species; and the washboard ( Megalonaias nervosa), a common Interior Basin species. We found that median lethal concentrations (LC50s) of polyacrylamide ranged from 411.7 to >1000 mg/L for glochidia and from 126.8 to >1000 mg/L for juveniles. All LC50s were orders of magnitude greater (2-3) than concentrations typically recommended for turbidity control (1-5 mg/L), regardless of their molecular weight or charge density. The results demonstrate that the polyacrylamide compounds tested were not acutely toxic to the mussel species and life stages tested, indicating minimal risk of short-term exposure from polyacrylamide applications in the environment. However, other potential uses of polyacrylamide in the environment (e.g., wastewater treatment, paper processing, mining, algae removal) and their chronic or sublethal effects remain uncertain and warrant additional investigation. Environ Toxicol Chem 2017;36:2715-2721. Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America. [ABSTRACT FROM AUTHOR]

The temporal variability of hydrological variables in the Guadalquivir estuary was examined during three years through a real-time remote monitoring network (RTRM). The network was developed with the aim of studying the influence of hydrodynamical and hydrological features within the estuary on the functioning of the pelagic ecosystem. Completing this data-gathering network, monthly cruises were performed in order to measure biogeochemical variables that are indicative of the trophic status of the aquatic environment. The results showed that several sources of physical forcing, such as wind, tide-associated currents and river discharge were responsible for the spatio-temporal patterns of dissolved oxygen, salinity and turbidity in the estuary. The analysis was conducted under tidal and flood regime, which allowed us to identify river discharge as the main forcing agent of the hydrology inside the estuary. In particular, episodes of elevated turbidity detected by the network, together with episodes of low salinity and dissolved oxygen were closely related to the increase in water supply from a dam located upstream. The network installed provided accurate data that can be rapidly used for research or educational applications and by policy-makers or agencies in charge of the management of the coastal area.

The temporal variability of hydrological variables in the Guadalquivir estuary was examined during three years through a real-time remote monitoring network (RTRM). The network was developed with the aim of studying the influence of hydrodynamical and hydrological features within the estuary on the functioning of the pelagic ecosystem. Completing this data-gathering network, monthly cruises were performed in order to measure biogeochemical variables that are indicative of the trophic status of the aquatic environment. The results showed that several sources of physical forcing, such as wind, tide-associated currents and river discharge were responsible for the spatio-temporal patterns of dissolved oxygen, salinity and turbidity in the estuary. The analysis was conducted under tidal and flood regime, which allowed us to identify river discharge as the main forcing agent of the hydrology inside the estuary. In particular, episodes of elevated turbidity detected by the network, together with episodes of low salinity and dissolved oxygen were closely related to the increase in water supply from a dam located upstream. The network installed provided accurate data that can be rapidly used for research or educational applications and by policy-makers or agencies in charge of the management of the coastal area. [ABSTRACT FROM AUTHOR]

An efficient bioreactor, termed a ‘synchronized fresh cell bioreactor’, was developed and consisted of a pH-dependent substrate feed system coupled with cross flow filtration and turbidity control. The effect of high dilution rate and high cell density coupled with high cell viability on the production of l-lactic acid in continuous culture by Lactococcus lactis IO-1 in enzyme-hydrolysed sago starch medium was investigated. For all changes in dilution rate, cells responded in a synchronized way to the addition of glucose by increasing the rate of biomass formation. Consequently, a glucose-free feed solution was required to maintain the cell concentration at a particular pre-set value. This set-up facilitated the maintenance of the cells in a permanent log phase. At a cell concentration of 15 gl−1 and a feed glucose concentration of 53 gl−1, volumetric LA productivities of 8.2, 19.3 and 33.1 gl−1h−1 were obtained at dilution rates of 0.21, 0.50 and 1.1 h−1, respectively. The respective residual glucose concentrations in the spent medium were 1.90, 0.24 and 3.80 gl−1. By increasing the cell density, the volumetric productivity increased proportionally. At high cell density, higher dilution rates resulted in lower lactate concentrations in the culture medium resulting in higher productivity. This reactor facilitated efficient operation with high cell viability by maintaining the cells in continuous growth phase for long-term fermentation. Therefore, the growth rate (μ) was calculated according to the Monod equation. Using this system, high specific productivities can be obtained which guarantees high commercial productivity at economical cost with only a small investment for setting up the sago industry. [Copyright &y& Elsevier]