Surface Water Turbidity Research Articles

Statistical Model and Estimation of Inland Riverine Turbidity with Landsat 8 OLI Images: A Case Study

Abstract The Landsat 8 Operational Land Imager (OLI) was investigated for its performance in monitoring dynamic riverine surface water turbidity. China's Hanjiang River, the largest tributary of th...

Removal of Water Turbidity Using Different Coagulants

Free Water turbid with high quality of potable water supply is the most important environmental issue. Surface water is usually rich in turbidity. Turbidity imparts a great problem in water treatment. In this present work, the performance and effectiveness of four different inorganic coagulant salts including alum, copper sulphate, ferric sulphate, and ferrous sulfate in water turbidity removal were investigated. No coagulant aids are used in the current study. Desired turbid samples with 100NTU (turbidity of surface water does not exceed 100NTU in no rain condition) are prepared in laboratory, mixing kaolin powder with tap water. The optimum conditions for maximum suspended solid removal are examined. A set of jar test experiments are conducted to find the optimum pH and coagulant dosage to reach appropriate operational conditions. The samples in jar apparatus underwent rapid mixing with speed of 100rpm for 1min. in order to attain uniform concentration of coagulants in water. Slow mixing with speed of 25rpm for 25 min. is used to give the colloidal particles favor to approach from each other to make flocs, and then allow the samples in the beakers to settle for 25 minutes to precipitate the agglomerates by gravity and sludge formation at the bottom of beakers. Results demonstrated that turbidity removal is dependent on pH and coagulant dosage. The highest turbidity removal efficiency was within % 97.9 for Alum when pH value is 6.5, %90.8 for copper sulphate when pH is 7, % 87 for ferric sulphate when pH is 4, and %72 for ferrous sulphate when pH is 4. Results indicated that alum has the best potential ability of water turbidity removal compared with other used coagulants.

Removal of Natural Organic Matter (NOM), Turbidity, and Color of Surface Water by Integration of Enhanced Coagulation Process and Direct Filtration

This work assesses the efficiency of integrated enhanced coagulation and direct filtration processes for the removal of color, turbidity, and natural organic matter (NOM) from surface water. The processes were conducted in a simulated pilot. The operating conditions of the treatment process, including pH, FeCl3 dose, and influent flow, were investigated. Following that, its efficiency was evaluated by measuring specific water quality parameters in the output stream including NOM, turbidity, and color. The results showed that under optimum conditions (pH, FeCl3 dose, and influent flow of 6.2, 95 L/h, and 40 mg/l, respectively), the color and turbidity were removed 96% and 95% respectively. According to factors analysis by the Taguchi method, the influence of these factors on the removal of pollutants decreased as follows: pH → FeCl3 dose → influent flow. The results revealed that the integrated enhanced coagulation process and direct filtration can improve the efficiency of colors, turbidity, and NOM removal in water treatment plants.

지형 기울기에 의한 항공 수심 라이다 수심 측정 오차 보정

Light detection and ranging (LiDAR) is one of the most efficient technologies to obtain the topographic and bathymetric map of coastal zones, superior to other technologies, such as sound navigation and ranging (SONAR) and synthetic aperture radar (SAR). However, the measurement results using LiDAR are vulnerable to environmental factors. To achieve a correspondence between the acquired LiDAR data and reality, error sources must be considered, such as the water surface slope, water turbidity, and seafloor slope. Based on the knowledge of those factors’ effects, error corrections can be applied. We concentrated on the effect of the seafloor slope on LiDAR waveforms while restricting other error sources. A simulation regarding in-water beam scattering was conducted, followed by an investigation of the correlation between the seafloor slope and peak timing of return waveforms. As a result, an equation was derived to correct the depth error caused by the seafloor slope.

Calcareous nannofossil assemblage turnover in response to the Early Bajocian (Middle Jurassic) palaeoenvironmental changes in the Subbetic Basin

The calcareous nannofossil assemblages from three Lower Bajocian pelagic successions from the Subbetic Basin, well dated by ammonites, have been investigated. Biostratigraphically, they encompass the NJT9 to NJT10a nannofossil Tethyan zones. PCA factor analysis, performed on percentage abundances of selected taxa, suggests that the main factors controlling the Early Bajocian nannofossil assemblages of the Subbetic Basin were trophic level (nutrient availability) and nutricline depth. A gradual eutrophication is recorded in the calcareous nannofossil assemblages through an increase in the percentage abundance of Watznaueria spp., especially in the taxa best adapted to unstable and more eutrophic conditions (W. britannica gr. and W. manivitiae gr.). This eutrophication is concomitant with a trend of increasing carbonate δ13C values over the Early Bajocian, and a rise in biogenic silica production and deposits in the study sections and other basins of the Western Tethys. Around the middle part of the Laeviuscula Subzone, a decrease in the absolute and relative abundance of the deep-dwelling taxa (especially Crepidolithus crassus) suggests a deterioration of the environmental conditions in the lower photic zone. This has been interpreted as caused by a nutricline shallowing and/or greater turbidity that could be related, in turn, to surface-water stratification. Two different episodes have been differentiated in relation to nutricline dynamics: 1) from the latest Aalenian to earliest Early Bajocian, a weak and/or deep nutricline with nutrients rather uniformly spread throughout the photic zone, and concomitant with mesotrophic conditions and increasing productivity is suggested; 2) a shallowing of the nutricline and/or increase in surface-water turbidity, concomitant with more eutrophic conditions is suggested for the latest Early Bajocian. The observed decrease in the deep-dwelling taxa supports the hypothesis of a climatically driven fertilization of the surface waters instead of fertilization by upwelling for the Early Bajocian eutrophication episode.

Long-term analysis of turbidity patterns in Danube Delta coastal area based on MODIS satellite data

Abstract The monitoring of coastal areas is becoming an urgent necessity in the context of increased pressure over these ecosystems due to climate change and human activities. Long term evaluation of specific parameters regarding water quality can now be achieved, thanks to the increased number of archived Earth Observation satellite data, now covering decades. Within this study, 12 years of MODIS information were used to compute surface water turbidity products that were further temporal binned into composite datasets (e.g. monthly, annual). A regional algorithm, based on local in situ measurements, was used in order to inverse remote sensing reflectance values into turbidity units. The interpretation of the final maps revealed important characteristics of the processes that play a major role in the regional turbidity dynamics. Observations were made regarding the relation between surface water turbidity and Danube River's discharge rates, winds, currents and also the bottom sedimentary characteristics of the shelf area. We discuss how different regions are affected by various external factors, depending on their geographical location, and we reinforce the idea that the river solid input is not the only parameter controlling water clarity in the Danube Delta coastal area, resuspension processes playing also an important role.

Spatial patterns of littoral zooplankton assemblages along a salinity gradient in a brackish sea: A functional diversity perspective

The distribution patterns and diversity of littoral zooplankton are both key baseline information for understanding the functioning of coastal ecosystems, and for identifying the mechanisms by which the impacts of recently increased eutrophication are transferred through littoral food webs. In this study, zooplankton community structure and diversity along a shallow coastal area of the northern Baltic Sea were determined in terms of horizontal environmental gradients. Spatial heterogeneity of the zooplankton community was examined along the gradient. Altogether 31 sites in shallow sandy bays on the coast of southwest Finland were sampled in the summer periods of 2009 and 2010 for zooplankton and environmental variables (surface water temperature, salinity, turbidity, wave exposure, macrophyte coverage, chlorophyll a and nutrients). Zooplankton diversity was measured as both taxonomic as well as functional diversity, using trait-based classification of planktonic crustaceans. Salinity, and to a lesser extent turbidity and temperature, were found to be the main predictors of the spatial patterns and functional diversity of the zooplankton community. Occurrence of cyclopoid copepods, as well as abundances of the calanoid copepod genus Acartia and the rotifer genus Keratella were found to be key factors in differentiating sites along the gradient. As far as we know, this is the first extensive study of functional diversity in Baltic Sea coastal zooplankton communities.

Spatial and temporal variations in high turbidity surface water off the Thule region, northwestern Greenland

Glacial meltwater discharge from the Greenland ice sheet and ice caps forms high turbidity water in the proglacial ocean off the Greenland coast. Although the timing and magnitude of high turbidity water export affect the coastal marine environment, for example, through impacts on biological productivity, little is known about the characteristics of this high turbidity water. In this paper, we therefore report on the spatial and temporal variations in high turbidity water off the Thule region in northwestern Greenland, based on remote sensing reflectance data at a wavelength of 555 nm (Rrs555). The high turbidity area, identified on the basis of high reflectivity (Rrs555 ≥ 0.0070 sr−1), was generally distributed near the coast, where many outlet glaciers terminate in the ocean and on land. The extent of the high turbidity area exhibited substantial seasonal and interannual variability, and its annual maximum extent was significantly correlated with summer air temperature. Assuming a linear relationship between the high turbidity area and summer temperature, annual maximum extent increases under the influence of increasing glacial meltwater discharge, as can be inferred from present and predicted future warming trends.

Surface water quality monitoring of an agricultural watershed for nonpoint source pollution control

Water pollution is a major environmental problem in the United States. To improve the surface water quality of the 2,493 ha (6,160 ac) Coulee Baton watershed in Louisiana, a collaborative nonpoint source pollution control study was initiated in 2004. Conservation measures and best management practices (BMPs) including cross-fencing of pasturelands (726.9 m [2,385 ft]), irrigation land leveling (12.9 ha [32 ac]), grade stabilization structures (two), irrigation water pipeline (975.4 m [3,200 ft]), and a livestock well covering a total of 92.7 ha (229 ac) of agricultural land, and repair or replacement of 80 septic systems in the watershed were voluntarily implemented by landowners and homeowners. Water samples were collected from seven monitoring sites for 66 rain events from September 24, 2009, to August 9, 2011. Laboratory determinations of water samples included total suspended solids (TSS), total dissolved solids (TDS), total solids (TS), five-day biological oxygen demand (BOD5), nitrate/nitrite-nitrogen (NO3/NO2-N), soluble reactive phosphate (SRP), total phosphorus (TP), total Kjeldahl N (TKN), chloride (Cl), fluoride (Fl), sulfate (SO4), and fecal coliform counts. Surface water temperature, dissolved oxygen (DO), turbidity, conductivity, and pH were determined in the field using YSI Sonde (YSI Incorporated, Yellow Springs, Ohio). For the watershed, DO, BOD5, and TS concentrations and fecal coliform count ranged, respectively, between 1.2 and 14.1 mg L−1 (ppm), 2 and 40.1 mg L−1, 35 and 5,719 mg L−1, and 400 × 106 and 17 × 106 most probable number (MPN) per 100 mL. The months of March, April, June, and September showed, on average, higher concentrations of TS and TDS, fecal coliform count, NO3/NO2-N, and SRP and TP, respectively. As compared to the ongoing BMPs, the post-BMPs, TSS, NO3/NO2-N, SRP, and BOD5 concentrations, on average, were lower by 56.2%, 23.1%, 82.5%, and 27.4%, respectively. Developed land use types and the failed septic systems were identified as major sources of fecal coliform pollution. These results suggest comprehensive strategies are necessary for effective nonpoint source pollution control in agricultural watersheds.

Severe Weather Effects on Water Quality in Central Arizona

Extreme weather events affect surface water supplies. Water quality measurements in Central Arizona were used to quantify changes in dissolved organic carbon (DOC) and turbidity following dust storms, floods, and drought‐associated wildfires. This article describes specific extreme events, quantifies changes in DOC and turbidity, and discusses the effects of water quality changes on treatment processes and public perceptions of water quality. Study findings show a co‐occurrence of some dust storm events (high particulate matter) and increased surface water turbidity, attenuation of high DOC loads following upper watershed storm events, significant increases in total organic carbon and turbidity following severe flooding in 2005, and differing effects of upland and lowland wildfires on water quality. Finally, a means to mitigate these effects on both perceived and actual water quality by integrating information from radar systems, stream gauge readings, and online water quality analyzers is suggested.

Potential of High Spatial and Temporal Ocean Color Satellite Data to Study the Dynamics of Suspended Particles in a Micro-Tidal River Plume

Ocean color satellite sensors are powerful tools to study and monitor the dynamics of suspended particulate matter (SPM) discharged by rivers in coastal waters. In this study, we test the capabilities of Landsat-8/Operational Land Imager (OLI), AQUA&TERRA/Moderate Resolution Imaging Spectroradiometer (MODIS) and MSG-3/Spinning Enhanced Visible and Infrared Imager (SEVIRI) sensors in terms of spectral, spatial and temporal resolutions to (i) estimate the seawater reflectance signal and then SPM concentrations and (ii) monitor the dynamics of SPM in the Rhône River plume characterized by moderately turbid surface waters in a micro-tidal sea. Consistent remote-sensing reflectance (Rrs) values are retrieved in the red spectral bands of these four satellite sensors (median relative difference less than ~16% in turbid waters). By applying a regional algorithm developed from in situ data, these Rrs are used to estimate SPM concentrations in the Rhône river plume. The spatial resolution of OLI provides a detailed mapping of the SPM concentration from the downstream part of the river itself to the plume offshore limits with well defined small-scale turbidity features. Despite the low temporal resolution of OLI, this should allow to better understand the transport of terrestrial particles from rivers to the coastal ocean. These details are partly lost using MODIS coarser resolutions data but SPM concentration estimations are consistent, with an accuracy of about 1 to 3 g·m−3 in the river mouth and plume for spatial resolutions from 250 m to 1 km. The MODIS temporal resolution (2 images per day) allows to capture the daily to monthly dynamics of the river plume. However, despite its micro-tidal environment, the Rhône River plume shows significant short-term (hourly) variations, mainly controlled by wind and regional circulation, that MODIS temporal resolution failed to capture. On the contrary, the high temporal resolution of SEVIRI makes it a powerful tool to study this hourly river plume dynamics. However, its coarse resolution prevents the monitoring of SPM concentration variations in the river mouth where SPM concentration variability can reach 20 g·m−3 inside the SEVIRI pixel. Its spatial resolution is nevertheless sufficient to reproduce the plume shape and retrieve SPM concentrations in a valid range, taking into account an underestimation of about 15%–20% based on comparisons with other sensors and in situ data. Finally, the capabilities, advantages and limits of these satellite sensors are discussed in the light of the spatial and temporal resolution improvements provided by the new and future generation of ocean color sensors onboard the Sentinel-2, Sentinel-3 and Meteosat Third Generation (MTG) satellite platforms.

The Efficacy of the Seeds of Adansonia digitata L. as a Biocoagulant and Disinfectant in Water Purification

Context: Water is an essential commodity for the sustenance of life, yet its availability is drastically reducing due to pollution. The conventional methods used for the treatment of water is relatively expensive and not readily available and hence the need for alternative sustainable means of water treatment. Aim: The aim of the study was to evaluate the efficacy of Adansonia digitata L. seeds as a biocoagulant and disinfectant in the purification of water. Materials and Methods: Dried fruits of A. digitata were collected from the Department of Biological Sciences, Ahmadu Bello University, Zaria. The seeds were excised, washed, sun-dried, powdered and defatted using n-hexane. Synthetic turbid water used for the biocoagulant study was prepared using beneficiated kaolin while that used for disinfection studies was prepared using Escherichia coli isolate. Surface water was also used for the study and was obtained from the Kubanni Reservoir, Ahmadu Bello University, Zaria. The experimental design was complete randomized design (CRD). Experiments were performed in triplicates using 0 mg/L (control), 50 mg/L, 100 mg/L, 150 mg/L and 200 mg/L of A. digitata seed extract. Statistical Analysis: One-way analysis of variance (ANOVA) was used to compare the means of the various parameters measured. Duncan Multiple Range Test (DMRT) was used in separating means where significant. The level of significance was taken at P < 0.05. Results: Results revealed that as a biocoagulant, an optimum dose of 150 mg/L was able to reduce turbidity of synthetic water significantly (P < 0.05) by 96.7% while there was no significant reduction in the turbidity of surface water. As a disinfectant, a dose of 200 mg/L was able to significantly reduce (P < 0.05) the concentration of E. coli of synthetic water from 1.65 × 104 cfu/mL to 5.00 × 102 cfu/mL (97.0%) and that of surface water from 4.27 × 102 cfu/mL to 6.67 × 101 cfu/mL (84.4%). Conclusion: From the investigations done, A. digitata seeds possess biocoagulant and disinfectant potentials, which may be harnessed for water purification.

Ethnomedicinal Knowledge on Water Purification in Selected Rural Areas of Ethiopia

Plants have been used for water purification dating back to perhaps 2000 BC as noted in Egyptian inscriptions. Plant coagulants have the potential to serve as alternative water treatment agents especially in rural areas. Hence this study aimed to examine four promising plants and their uses as local coagulants for purification of turbid water in order to tackle rural quality water problems. Semi-structured interviews, focus group discussions, market surveys, and observation were used to gather information from three rural areas. Jar test experiments were carried out for treatment of high (209 NTU), medium (63 NTU), and low level (26 NTU) turbidity with the flocculent dosages of 0.03 g/L of powdered plant material. The four plant species used for treatment of turbid water were Maerua subcordata (Gilg) DeWolf, Moringa stenopetala (Baker f.) Cufod., Sansevieria ehrenbergii Schweinf. ex Baker, and Sansevieria forskaliana (Schult. & Schult.f.) Hepper & J.R.I.Wood. The finding shows that societies in each study area still depend on plant species for purification of turbid surface water. Coagulation tests revealed that tubers of M. subcordata and seeds of M. stenopetala were able to remove turbidity up to 97% at high turbidity levels and performance was better than leaves of S. ehrenbergii and S. forskaliana. Complementing traditional water treatment knowledge with coagulation tests and purification of the specific protein coagulant could help to identify appropriate solutions for rural people with difficulty preparing purified water.

Salinization of coastal freshwater wetlands; effects of constant versus fluctuating salinity on sediment biogeochemistry

Globally, coastal lowlands are becoming more saline by the combined effects of sea level rise, land subsidence and altered hydrological and climatic conditions. Although salinization is known to have a great influence on biogeochemical processes, literature shows contrasting effects that challenge the prediction of future effects. In addition, the effects of fluctuating salinity levels, a more realistic scenario than constant levels, on nutrient cycling in coastal wetland sediments have hardly been examined. A better understanding is therefore crucial for the prediction of future effects and the definition of effective management. To test the effects of constantly brackish water (50 mmol Cl l−1, 3.2 psu) or fluctuating salinity (5–50 mmol Cl l−1), versus constantly low salinity (5 mmol Cl l−1, 0.32 psu) on nutrient biogeochemistry, we conducted a controlled laboratory experiment with either peat or clay sediments from coastal wetlands. Increased salinity showed to have a fast and large effect. Sediment cation exchange appeared to be the key process explaining both a decrease in phosphorus availability (through calcium mobilization) and an increase in nitrogen availability, their extent being strongly dependent on sediment type. Supply of brackish water decreased surface water turbidity and inhibited sediment methane production but did not affect CO2 production. Constant and fluctuating salinity levels showed similar longer term effects on nutrient and carbon cycling. The contrasting effects of salinization found for nitrogen and phosphorus, and its effects on water turbidity indicate major ecological consequences for coastal wetlands and have important implications for water management and nature restoration.

Experimental evaluation of ripening behavior: Down-Flow vs. Up-Flow rapid sand filters

Filter ripening is progressive development of media charge and build-up of collector efficiency, during starting phase of granular filtration. In the present work, a comparative study of ripening behavior was carried out by conducting simultaneous laboratory filtration experiments on Down-Flow (DF) and Up-Flow (UF) sand filters. The artificial influent was used for filtration studies. It was prepared to replicate pretreated low turbidity surface water. The Filter Ripening Sequence (FRS) curve for the UF filter was observed to be significantly distinct. It was corroborated that the ripening depends on filtration rate (v) for the both filters. Enhancement in the ripening performance of the both filters was witnessed for the influents with less negative zeta potential of influent particles (ζp). Further, the technique of Extended Terminal Sub-fluidized Wash (ETSW) with cationic polymer in wash water was also tested to improve ripening process. It was found effective in reducing initial degradation of effluent for the both filters. However, the ETSW with polymer modified wash water resulted in considerable increase in head loss during ripening for the DF filter. Particularly, the incremental increase in head loss subsequent to polymer modified ETSW was less for the UF filter.

Hydrodynamic and Sediment Modelling within a Macro Tidal Estuary: Port Curtis Estuary, Australia

An understanding of sediment transport processes and resultant concentration dynamics in estuaries is of great importance to engineering design awareness and the management of these environments. Predictive modelling approaches provide an opportunity to investigate and address potential system responses to nominated events, changes, or conditions of interest, often on high temporal and spatial resolution scales. In this study, a three-dimensional hydrodynamic model and wave model were validated and applied to generate forcing conditions for input into a sediment transport model for the period 7 May 2010–30 October 2010 within a macro tidal estuary, Port Curtis estuary (Australia). The hydrodynamic model was verified against surface and near-bottom current measurements. The model accurately reproduced the variations of surface and near-bottom currents at both a mid-estuary and upper-estuary location. Sediment transport model predictions were performed under varying meteorological conditions and tidal forcing over a 180-day period and were validated against turbidity data collected at six stations within Port Curtis estuary. The sediment transport model was able to predict both the magnitudes of the turbidity levels and the modulation induced by the neap and spring tides and wind-wave variations. The model-predicted (converted) turbidity levels compared favourably with the measured surface water turbidity levels at all six stations. The study results have useful practical application for Port Curtis estuary, including providing predictive capabilities to support the selection of locations for monitoring/compliance sites.

Impact of Upflow Gravel Filtration on the Clogging Potential in Microirrigation

AbstractThis paper evaluates the effect of six water treatment combinations for the treatment of turbid surface water on four types of emitters by looking at clogging potential and distribution uni...

Strength properties of composite clay balls containing additives from industry wastes as new filter media in water treatment

Pebble matrix filtration (PMF) is a water treatment technology that can remove suspended solids in highly turbid surface water during heavy storms. PMF typically uses sand and natural pebbles as filter media. Hand-made clay pebbles (balls) can be used as alternatives to natural pebbles in PMF treatment plants, where natural pebbles are not readily available. Since the high turbidity is a seasonal problem that occurs during heavy rains, the use of newly developed composite clay balls instead of pure clay balls have the advantage of removing other pollutants such as natural organic matter (NOM) during other times. Only the strength properties of composite clay balls are described here as the pollutant removal is beyond the scope of this paper. These new composite clay balls must be able to withstand dead and live loads under dry and saturated conditions in a filter assembly. Absence of a standard ball preparation process and expected strength properties of composite clay balls were the main reasons behind the present study. Five different raw materials from industry wastes: Red Mud (RM), Water Treatment Alum Sludge (S), Shredded Paper (SP), Saw Dust (SD), and Sugar Mulch (SM) were added to common clay brick mix (BM) in different proportions. In an effort to minimize costs, in this study clay balls were fired to <TEX>$1100^{\circ}C$</TEX> at a local brick factory together with their bricks. A comprehensive experimental program was performed to evaluate crushing strength of composite hand-made clay balls, using uniaxial compression test to establish the best material combination on the basis of strength properties for designing sustainable filter media for water treatment plants. Performance at both construction and operating stages were considered by analyzing both strength properties under fully dry conditions and strength degradation after saturation in a water bath. The BM-75% as the main component produced optimum combination in terms of workability and strength. With the material combination of BM-75% and additives-25%, the use of Red Mud and water treatment sludge as additives produced the highest and lowest strength of composite clay balls, with a failure load of 5.4 kN and 1.4 kN respectively. However, this lower value of 1.4 kN is much higher than the effective load on each clay ball of 0.04 kN in a typical filter assembly (safety factor of 35), therefore, can still be used as a suitable filter material for enhanced pollutant removal.

탁도와 총유기탄소 제거를 위한 최적응집제 및 투여량 선정 연구

본 연구는 급격한 수질변화에 따른 현장 적용에 적합한 응집제를 선정하고, 응집제 별 최적 주입량을 찾기 위해 aluminium sulfate, poly aluminum chloride, poly aluminum silicate chloride를 이용하여 Jar-Test와 Pilot-Test의 검증으로 실험 하였다. 분석 항목은 탁도, TOC, pH로 제거율을 측정하였다. 실험 결과를 바탕으로 PASC의 경우 기존 응집제 인 Alum이나 PAC 보다 최적 주입량 (15 mg/L)이 상대적으로 적었으며, 제거율도 높게 나타남을 확인할 수 있었다. Jar-Test에서는 원수 탁도 3-20 NTU 범위에서 응집제(PASC)의 최적 주입량을 주입하였을 때, 탁도 제거율(80%)과 TOC 제거율(89%)이 가장 높았으며, Pilot-Test에서는 원수 탁도 3.6-27 NTU 범위에서 응집제 최적 주입량을 주입하였을 때 탁도 제거율(82%)과 TOC 제거율(88%)을 확인할 수 있었다. 따라서 본 연구 결과를 바탕으로 응집제의 제거 효과는 원수 탁도와 TOC가 높아질수록 상승하는 경향을 확인할 수 있었다. 【Three coagulants, alum sulfate(alum), poly aluminum chloride(PAC) and poly aluminum silicate chloride (PASC), were used to remove low to high turbidity and TOC in surface and ground blended water. Laboratory experiments and pilot plant experiments were carried out to evaluate the optimal coagulant and its dosage. To determine the optimized coagulant and its dosage, the turbidity, TOC and pH were measured. The experimental results showed the best removal performance using PASC. The optimal dosage of PASC between 3-20 NTU was found to be 15 mg/L in the jar test. In the pilot test, a 15 mg/L PASC dosage was applied and resulted in the efficient removal of turbidity and TOC between 3.6-27 NTU. The removal efficiency of PASC increased with increasing turbidity and TOC.】

Structure and dynamics of the shark assemblage off Recife, Northeastern Brazil.

Understanding the ecological factors that regulate elasmobranch abundance in nearshore waters is essential to effectively manage coastal ecosystems and promote conservation. However, little is known about elasmobranch populations in the western South Atlantic Ocean. An 8-year, standardized longline and drumline survey conducted in nearshore waters off Recife, northeastern Brazil, allowed us to describe the shark assemblage and to monitor abundance dynamics using zero-inflated generalized additive models. This region is mostly used by several carcharhinids and one ginglymostomid, but sphyrnids are also present. Blacknose sharks, Carcharhinus acronotus, were mostly mature individuals and declined in abundance throughout the survey, contrasting with nurse sharks, Ginglymostoma cirratum, which proliferated possibly due to this species being prohibited from all harvest since 2004 in this region. Tiger sharks, Galeocerdo cuvier, were mostly juveniles smaller than 200 cm and seem to use nearshore waters off Recife between January and September. No long-term trend in tiger shark abundance was discernible. Spatial distribution was similar in true coastal species (i.e. blacknose and nurse sharks) whereas tiger sharks were most abundant at the middle continental shelf. The sea surface temperature, tidal amplitude, wind direction, water turbidity, and pluviosity were all selected to predict shark abundance off Recife. Interspecific variability in abundance dynamics across spatiotemporal and environmental gradients suggest that the ecological processes regulating shark abundance are generally independent between species, which could add complexity to multi-species fisheries management frameworks. Yet, further research is warranted to ascertain trends at population levels in the South Atlantic Ocean.