Low Total Suspended Solids Research Articles

Relationship between seepage water volume and total suspended solids of landslide dam failure caused by seepage: an experimental investigation

BackgroundLandslide dams inevitably demonstrate the potential for catastrophic failure with high-risk damage to life and property at the downstream site. Hence, knowledge of the internal stability of dam materials is a key to predicting the seepage failure of landslide dams. In this study, experiments were conducted to examine the relationship between seepage volume and total suspended solids (TSS) of seepage water based on hydro mechanical constrains. Understanding the relationship between the seepage volume and TSS with hydro-mechanical constraints supports the prediction of the seepage failure of landslide dams at the field level.ResultExperiments were conducted with a mixed sample of silica sands. Seepage water was collected from a flume tank with the facility to measure the hydraulic gradient, vertical displacement, and seepage water volume. Grain size affected the life span of the dam. The seepage volume increased with the increase in the percentage of silica sand S4, whereas TSS increased with the increase in the percentage of silica sand S8. With the increase in the dam height, the dam life decreases for low coeficient of uniformity of the grain size distribution. With the increase in the reservoir size, TSS decreased, and the total seepage volume increased.ConclusionDam failure depends on the particle size, dam geometry, inflow rates, reservoir size, hydraulic gradient, and seepage water volume, and TSS of seepage water. The results indicated that with the increase in fine particles, the life span decreases, and TSS increases. With the increase in the flow rate, the dam life span decreases, and the TSS and seepage volume rate increase.The dam height leads to an increase seepage volume with low TSS, where the life span of the dam also depends on the particle size distribution With the increase in the reservoir size, the seepage water volume decreases with low TSS.

The Effects of Natural Suspended Solids on Copper Toxicity to the Cardinal Tetra in Amazonian River Waters.

The aim of the present study was to characterize the effects of particles on metal aquatic toxicity in a tropical system. To this end, we investigated the effects of natural suspended solids on copper (Cu) geochemistry and acute toxicity to the cardinal tetra (Paracheirodon axelrodi), in 2 Amazonian rivers with different total suspended solids (TSS) levels: the Rio Negro (low TSS ~ 8 mg L-1 ) and the Rio Solimões (high TSS ~ 70 mg L-1 ). The effect of particles on Cu aqueous geochemistry was assessed by measuring total, dissolved, and free ionic Cu concentrations in filtered (<0.45 μm) and unfiltered waters. Furthermore, acute Cu toxicity to fish was assessed in both filtered and unfiltered waters, by measuring physiological net fluxes of Na+ , Cl- , K+ , and total ammonia (in both river waters) and 96-h fish mortality (in Rio Solimões only). The particles in the Rio Negro were not abundant enough to play a significant role in our study. On the other hand, the Rio Solimões particles bound approximately 70% of total aqueous Cu in our tests. In agreement with bioavailability-based models, this decrease in dissolved (and free ionic) Cu concentration decreased Cu lethality in the 96-h toxicity tests. In the physiological measurements, the best evidence of particle protection was the total alleviation of Cu-induced Cl- losses. These flux tests also suggested that the particles themselves may negatively affect Na+ balance in the fish. Overall, the present study supports the use of bioavailability concepts to account for the role of natural suspended solids on metal biological effects in the Amazon River basin. Environ Toxicol Chem 2019;38:2708-2718. © 2019 SETAC.

Comparison of unused water and year-old used water for production of channel catfish in the biofloc technology system

Since excreted feed nitrogen is bio-transformed efficiently in a fully functional mixotrophic biofloc technology production system, re-using this biofloc water over multiple production cycles should be beneficial. The present study, conducted in an outdoor biofloc technology production system, evaluated impacts on fish production characteristics and mineral status, common microbial off-flavors, and water quality dynamics for channel catfish (Ictalurus punctatus) reared in one-year-old waters with low or high total suspended solids used previously for two consecutive catfish biofloc studies or in unused (new) water. Total suspended solids were maintained at 300 to 400 mg/L in the unused and low total suspended solids used water treatments and allowed to accumulate in the high total suspended solids used water treatment. Tanks (18.6 m2, 15.7 m3) were stocked with fingerlings (47.5 ± 0.8 g/fish) at 13.5 fish/m2 (16 fish/m3) and grown for 181 days. Channel catfish production characteristics did not differ significantly among treatments. Overall, gross fish yield averaged 10.2 kg/m3 and fish averaged 642 g/fish. Nitrate accumulation rate was affected by total suspended solids concentration with a significant reduction observed at the highest discharge of solids from the system, suggesting wash-out of nitrifiers. Treatment effects on water quality dynamics, macro- and trace-mineral status of water, feed, and fish, 2-methylisoborneol and geosmin off-flavors and associated phytoplankton populations also are discussed. Results of this study suggest that one-year-old biofloc water can be used without adverse impact for a second year of channel catfish production in the biofloc system.

Natural gas processing wastewater management

The aim of this research is to focus on adequate treatment technology for handling wastewater discharged from natural gas processing industries. An Egyptian natural gas company located at Alexandria was selected for the study. The study represents a useful reference for treatment of such kind of wastewater. Dark Fenton, biological treatment and the combination of them were carried out. The wastewater produced by subject industries has high concentration of chemical oxygen demand, (COD=52665 mg/L), low biological oxygen demand (BOD=8350 mg/L) and low total suspended solids (TSS=370 mg/L). The value of BOD/COD was low (0.16) which indicates that this wastewater inhibits the metabolic activity of bacterial seed because of their refractory properties causing biodegradability to be difficult. Fenton oxidation treatment raise the BOD/COD to more than 0.36. Biological treatment using both aerobic and anaerobic bioreactors for the treatment of mixture of Fenton pretreated gas processing wastewater and sewage gave satisfactory results. The subsequent anaerobic treatment using UASB reactor at optimum HRT [18h] qualifies the produced wastewater for discharge into the sewerage system. The additional aerobic treatment using the continuous-flow activated sludge at 12h HRT qualifies the treated wastewater for discharge into the sea.

Energy generation in the treatment of effluent from washing of municipal solid waste collection trucks

The washing of vehicles used to collect Municipal Solid Waste (MSW) requires 400–500 L of water for each vehicle, producing effluent with characteristics similar to the leachate from young sanitary landfills. The treatment process commonly used for this type of effluent is coagulation/flocculation. In this study, effluents from three sites were submitted to physicochemical treatment alone or combined with anaerobic biological treatment. Physicochemical treatment has better results with effluents with high total suspended solids (TSS) content. For effluents with low TSS concentrations, this treatment has high turbidity removal but low chemical oxygen demand (COD) removal. The anaerobic biodegradability and the methane generation potential from raw effluents or after physicochemical treatment were evaluated with and without nutritional supplementation. The effluent after physicochemical treatment does not require nutritional supplementation, obtaining 92% COD removal (final COD of 168 mg/L) and specific methane production of 150.6 mL methane (STP)/g CODremoved. A comparison of operational cost between the physicochemical and anaerobic biological processes for treating 20 m3/day of effluent showed that the latter, in addition to presenting low cost, can generate up to 13.5 kWh/day for the MSW collecting company.

Microwave enhanced advanced oxidation treatment of sewage sludge from the membrane-enhanced biological phosphorus removal process

This study investigated the effectiveness of bench and pilot-scale microwave enhanced advanced oxidation process (MW-AOP) for treatment of sewage sludge in neutral, acidic (pH 4) and alkaline (pH 9) conditions. The MW-AOP treatments were very effective: total suspended solids reduction and chemical oxygen demand solubilization were better in the sets at pH 9 than at pH 4. Alkaline conditions would be more favorable for the subsequent anaerobic digestion for biogas production. Release of orthophosphate, particle size distribution, dewatering properties and settling of the sets at pH 4 were better than at pH 9. The supernatants obtained from the sets at pH 4 had a high orthophosphate concentration and a low total suspended solids content, which were more suitable for struvite (a fertilizer) recovery process. Energy consumption was lower for the pH adjusted treatment sets compared to those of MW only and MW-AOP at neutral conditions; energy for the pH adjusted sets varied between 0.32 and 0.41 kWh/L of sludge treated. The results indicated that the MW-AOP could reduce the volume of sludge for disposal, and produce a high quality treated effluent suitable for further resource and energy recovery. Depending on the needs of each wastewater treatment plant’s treatment priority, the experimental conditions applied in the process can be adjusted accordingly.

Lebegtetett hordalékmérési módszerek összehasonlító vizsgálata balatoni részvízgyűjtőkön

The present study investigated the quantity of total suspended solids (TSS) in three small catchments and compared the data to turbidity measurements. The TSS data were based on filtration, drying and weight measurements, while the turbidity measurements were retrieved using a handheld device with a turbidity sensor. Water was collected daily at the catchment outlets from November 1, 2016 to May 31, 2017, representing the winter and spring seasons. The lowest quantity of TSS was detected at the catchment outlet of the Esztergályi Stream; however, there were two lakes close to the monitoring point where soil particles may have settled, possibly explaining the low TSS values. The Csorsza and Tetves streams had similar TSS values during winter, but in the spring samples the TSS values were approximately three times higher in the Csorsza Stream than in the Tetves Stream. The relationship between water discharge and TSS values was also investigated for the Tetves Stream, but no significant correlations were observed between them. The results suggested that the labour-intensive TSS measurements (e.g. filtration, soil weight measurements) could be replaced to a good approximation using the handheld device. The spatial heterogeneity within and between the catchments influences the amount of suspended sediment and hence the measurement accuracy. Therefore, the use of the handheld device should also be complemented with other methods, such as the filtration used in the present study, to attain more precise values.

Near‐Channel Versus Watershed Controls on Sediment Rating Curves

AbstractPredicting riverine suspended sediment flux is a fundamental problem in geomorphology, with important implications for water quality, land and water resource management, and aquatic ecosystem health. To advance understanding, we evaluated environmental and landscape factors that influence sediment rating curves (SRCs). We generated SRCs with recent total suspended solids (TSSs) and discharge data from 45 gages on 36 rivers throughout the state of Minnesota, USA. Watersheds range from 32 to 14,600 km2 and represent distinct settings regarding topography, land cover, and geologic history. Rivers exhibited three distinct SRC shapes: simple power functions, threshold power functions, and peaked or negative‐slope functions. We computed SRC exponents and coefficients (describing the steepness of the relation and the TSS concentration at median flows, respectively). In addition to quantifying watershed topography, climate/hydrology, geology, soil type, and land cover, we used lidar topography to characterize the near‐channel environment upstream of gages. We used random forest models to analyze relations between SRC parameters and attributes of the watershed and the near‐channel environment. The models correctly classify 78% of SRC shapes and explain 37%–60% of variance in SRC parameters. We find that SRC steepness (exponent) is strongly related to near‐channel morphological characteristics including near‐channel relief, channel gradient, and presence of lakes along the local channel network, but not to land use. In contrast, land use influences TSS concentrations at moderate and low flow. These findings suggest that the near‐channel environment controls changes in TSS as flows increase, whereas land use drives median and low flow TSS conditions.

Suspended solid concentration reduces feeding in freshwater mussels

We examined the effect of TSS concentration on the clearance rates (CR) of newly transformed juvenile and adult Lampsilis fasciola, L. siliquoidea, Ligumia nasuta, and Villosa iris, as increased total suspended solids (TSS) are thought to interfere with feeding processes. Mussel CR were measured in aerated (or swirled for juveniles) chambers at TSS concentrations up to 15mgL−1 for laboratory-transformed juveniles, and up to 100mgL−1 for adult mussels. The CR of one-week old animals increased with TSS concentration, likely due to ontological differences in feeding (pedal vs. suspension feeding) and gill development, but CR decreased monotonically with TSS concentration in older animals (two-, three- and four-week old juveniles). The CR of adult mussels were significantly lower at TSS concentrations ≥8mgL−1, which represented a threshold in CR. Although this threshold occurred at similar concentrations across the four species, the decline in CR was largest in L. fasciola (46% compared to no-TSS control), and smallest in V. iris (21%). Differences among species are likely related to differences in the TSS and substrate found in their source rivers given that greater decline occurred for species in rivers with relatively lower TSS. The decrease in CR as TSS increased is consistent across marine and freshwater bivalves, at both juvenile and adult stages. The decrease in feeding was five times greater in juvenile compared to adult bivalves, which indicates how the vulnerability to environmental stressors differ across life stages. These results demonstrate that TSS reduces suspension feeding rates in freshwater unionids, therefore TSS should be managed to ensure their survival.

Microwave enhanced oxidation treatment of organic fertilizers.

Liquid organic fertilizers (LOFs) are relatively easier to degrade than those of solid organic fertilizers, and the nutrients are readily available for plant uptake. Microwave enhanced advanced oxidation treatment (MW/H2 O2 -AOP) was used to convert solid organic fertilizers (insoluble blood meal, bone meal, feather meal, sunflower ash and a mixture) into LOF. After the MW/H2 O2 -AOP treatment, high soluble nitrogen (11-29%), soluble phosphorus (64%) and potassium (92%), as well as low total suspended solids content could be obtained. The resulting LOF would make the nutrients more bioavailable, and would provide some of them for the plant uptake immediately. Temperature and hydrogen peroxide dosage were found to be significant factors affecting nitrogen release from blood meal and feather meal, while temperature and pH were found to be significant factors for solubilizing phosphorus and potassium from bone meal and ash, respectively. The MW/H2 O2 -AOP reduced suspended solids, and released nutrients into solution; therefore, it was an effective treatment method to make LOFs. © 2016 Society of Chemical Industry.

The removal of N and P in aerobic and anoxic-aerobic digestion of waste activated sludge from biological nutrient removal systems

Biological nutrient removal (BNR) activated sludge (AS) systems produce a waste activated sludge (WAS) that is rich in nitrogen (N) and phosphorus (P). When this sludge is thickened to 3-6% total suspended solids (TSS) and digested (aerobic or anaerobic), a high proportion of N and P are released to the bulk liquid resulting in high concentrations of ammonia/nitrate and orthophosphate up to several hundred mg/l (without denitrification or P precipitation). This research investigates P removal by P precipitation in anoxic-aerobic digestion of P-rich BNR system WAS. The experimental setup for this work was a lab-scale membrane UCT BNR system fed real settled sewage with added acetate, orthophosphate, and cations Mg and K to increase biological excess P removal. This WAS was fed to batch aerobic digesters at various TSS concentrations, and to two 20-day retention time continuous anoxic-aerobic digesters (AnAerDig) with aeration cycles of 3-h air on and 3-h air off, one fed concentrated WAS (20 g TSS/l ) and the other fed diluted WAS (3 g TSS/l). Nitrogen removal has been discussed in the previous paper. This paper focuses on the P removal by P precipitation observed in the batch tests and continuous systems. The rate of polyphosphate release (bGP) during batch aerobic digestion at low TSS without P precipitation was found to be 2.5 times faster than the endogenous respiration rate (bG) of phosphorus accumulating organics (PAO), i.e. bGP = 0.1/d. This rate was then applied to the high-TSS aerobic batch tests and continuous anoxic-aerobic digesters to estimate the P precipitation at various TSS concentrations, with and without additional Mg or Ca dosing. Newberyite (MgHPO4-3H2O) and amorphous tricalcium phosphate (ACP or TCP, Ca3(PO4)2-xH2O) are found to be the most common phosphate precipitates.

Effects of feeding a fishmeal-free versus a fishmeal-based diet on post-smolt Atlantic salmon Salmo salar performance, water quality, and waste production in recirculation aquaculture systems

The Atlantic salmon farming industry has progressively decreased the proportion of fishmeal used in commercial diets due to rising costs and sustainability concerns. A variety of alternate proteins have been identified to partially replace fishmeal; however, very little research has described the effect of feeding alternate protein, fishmeal-free diets to Atlantic salmon, particularly post-smolts cultured in recirculation aquaculture systems (RAS). Therefore, a 6-month study was conducted to compare the effects of feeding a fishmeal-free diet (FMF) versus a fishmeal-based diet (FM) on post-smolt Atlantic salmon performance, water quality, and waste production rates in six replicated RAS. Experimental diets were fed to Atlantic salmon (281±5g to begin) in triplicate RAS. Protein ingredients used in the FMF diet included mixed nut meal, poultry meal, wheat flour, and corn protein concentrate; while the FM diet contained menhaden meal, poultry meal, soy protein concentrate, and blood meal proteins. Fish oil derived from whiting fish trimmings was used in the FMF diet to establish a wild fisheries input to farmed fish output ratio of 0:1; while menhaden oil was the primary lipid source for the FM diet. Both diets were formulated with approximately 42% crude protein and 27% crude fat. Each RAS was operated with flushing rates that created an average system hydraulic retention time of 20 days (5% system volume flushed daily) and a mean feed loading rate of 3.2kg feed/m3 of daily make-up water volume. Atlantic salmon growth, survival, and feed conversion ratios (FCR) were unaffected (P>0.05) by diet. At the conclusion of the study, Atlantic salmon fed the FMF and FM diets were 1.716±0.076 and 1.720±0.065kg; cumulative survival was >99% for both; and average FCR was 0.89±0.03 and 0.90±0.02, respectively. The FMF diet resulted in greater total phosphorous (TP), carbonaceous biochemical oxygen (cBOD), and total suspended solids (TSS) mass per kg feed in the effluent (P<0.05). The FMF and FM diets produced 0.009±0.001 v. 0.006±0.001kg TP/kg feed; 0.079±0.005 v. 0.056±0.005kg cBOD/kg feed; and 0.297±0.028 v. 0.221±0.032kg TSS/kg feed, respectively. A significantly higher percentage of TSS was captured by radial flow settlers of RAS receiving the FMF diet compared to capture by settlers associated with the FM diet. Mass balance data, radial settler removal efficiency, and observations of flushed solids suggested that the FMF diet produced fecal matter with better settling characteristics. Lower TSS and true color values (P<0.05), indicative of clearer water, were measured in RAS receiving the FMF diet. Total phosphorous (most of which was dissolved) was 4 times greater in the culture water of RAS that received the FMF diet, e.g., 4.3±0.1mg/L v. 0.9±0.0mg/L for the FM Diet. This was the first research attempt to formulate a fishmeal-free diet for Atlantic salmon with this ingredient profile and one of few studies to demonstrate uncompromised Atlantic salmon performance when feeding a diet without fishmeal.

Modelling the influence of total suspended solids on E. coli removal in river water.

Following sewer overflows, fecal indicator bacteria enter surface waters and may experience different lysis or growth processes. A 1D mathematical model was developed to predict total suspended solids (TSS) and Escherichia coli concentrations based on field measurements in a large-scale flume system simulating a combined sewer overflow. The removal mechanisms of natural inactivation, UV inactivation, and sedimentation were modelled. For the sedimentation process, one, two or three particle size classes were incorporated separately into the model. Moreover, the UV sensitivity coefficient α and natural inactivation coefficient kd were both formulated as functions of TSS concentration. It was observed that the E. coli removal was predicted more accurately by incorporating two particle size classes. However, addition of a third particle size class only improved the model slightly. When α and kd were allowed to vary with the TSS concentration, the model was able to predict E. coli fate and transport at different TSS concentrations accurately and flexibly. A sensitivity analysis revealed that the mechanisms of UV and natural inactivation were more influential at low TSS concentrations, whereas the sedimentation process became more important at elevated TSS concentrations.

Modeling changes in hydraulic conductivity due to siltation using soil columns from Alshuwaib dam site, United Arab Emirates

Changes in soil hydraulic conductivity (K) as a function of total suspended solids (TSS) concentration in the infiltrating water were studied in the laboratory using the constant-head technique. Soil samples collected from Alshuwaib dam site in the United Arab Emirates were selected for the study. The soil samples were collected from two distinct layers at the dam site; an upper layer which is composed of silt and clay and a lower layer which is mainly composed of sand. Formation of the upper layer is believed to be due to deposition of TSS originally present in the intercepted stormwater or due to dust deposition at the site. Temporal variations in the saturated K of the soil were studied using water with various TSS concentrations. The infiltrating turbid solution was prepared using tap water mixed with soil samples collected from the upper layer. Results show that presence of TSS in the water introduced into the columns caused a drop in K over time. Changes in K follow a sharp drop shortly after injecting the turbid solution and a slower drop at later times. The sharp initial drop was more pronounced for cases with higher injected TSS concentration. For an experimental time of about 80 h, K dropped an order of magnitude for cases with low influent concentration. Changes in K were simulated using a mechanistically based model that assumes formation of new layers with lower K values as a result of particle entrapment below the soil surface followed by particle deposition on the surface. The developed layers model closely predicts variations of K over time, with no observed particle entrapment, except at low TSS concentration. Meanwhile, predicted deposited masses of TSS are in agreement with those determined after the completion of the experiments. Results presented here could also be useful to managers of surface recharge facilities in the country and elsewhere.

The removal of N and P in aerobic and anoxic-aerobic digestion of waste activated sludge from biological nutrient removal systems

Biological nutrient removal (BNR) activated sludge (AS) systems produce a waste activated sludge (WAS) that is rich in nitrogen (N) and phosphorus (P). When this sludge is thickened to 3–6% total suspended solids (TSS) and digested (aerobic or anaerobic), a high proportion of N and P are released to the bulk liquid resulting in high concentrations of ammonia/nitrate and orthophosphate up to several hundred mg/ℓ (without denitrification or P precipitation). This research investigates P removal by P precipitation in anoxic-aerobic digestion of P-rich BNR system WAS. The experimental setup for this work was a lab-scale membrane UCT BNR system fed real settled sewage with added acetate, orthophosphate, and cations Mg and K to increase biological excess P removal. This WAS was fed to batch aerobic digesters at various TSS concentrations, and to two 20-day retention time continuous anoxic-aerobic digesters (AnAerDig) with aeration cycles of 3-h air on and 3-h air off, one fed concentrated WAS (20 g TSS/ℓ ) and the other fed diluted WAS (3 g TSS/ℓ). Nitrogen removal has been discussed in the previous paper. This paper focuses on the P removal by P precipitation observed in the batch tests and continuous systems. The rate of polyphosphate release (bGP) during batch aerobic digestion at low TSS without P precipitation was found to be 2.5 times faster than the endogenous respiration rate (bG) of phosphorus accumulating organics (PAO), i.e. bGP = 0.1/d. This rate was then applied to the high-TSS aerobic batch tests and continuous anoxic-aerobic digesters to estimate the P precipitation at various TSS concentrations, with and without additional Mg or Ca dosing. Newberyite (MgHPO4·3H2O) and amorphous tricalcium phosphate (ACP or TCP, Ca3(PO4)2·xH2O) are found to be the most common phosphate precipitates.Keywords: biological excess phosphorus removal, waste activated sludge, anoxic-aerobic digestion, phosphaterelease, mineral precipitation

Performance evaluation and a sizing method for hydrodynamic separators treating urban stormwater runoff.

This study reports on 6 years of performance monitoring of stormwater hydrodynamic separators in Korean urban catchments. One hundred and thirty-seven storm events were monitored in four hydrodynamic separators of two different types from 2006 to 2012. Mean values of the event average removal efficiencies of total suspended solids (TSS) for the four hydrodynamic separators were 43.69, 8.54, 42.84, and 14.35% with corresponding mean values of the event average surface overflow rates of 28.62, 40.07, 16.02, and 38.81 m/h, respectively. The low TSS removal efficiency was due to the high instantaneous surface overflow rates frequently occurring throughout a storm event and the abundance of fine particle fractions in the inflow (median particle diameter <75 μm). The Weibull function was used to simulate particle size distribution (PSD) in the runoff and the simulated PSD functions were further applied to the discrete settling theory to develop curves of TSS removal efficiency, as a function of surface overflow rate and median particle size of the inflow. The developed curves should be useful in determining the design peak flow rate and the size of a hydrodynamic separator for a stated goal of TSS removal efficiency.

The susceptibility of cladocerans in North Andean Patagonian lakes to volcanic ashes

Summary Explosive volcanic eruptions are one of the few natural phenomena that can produce global catastrophic effects. On 4 June 2011, an eruption in the Puyehue volcanic complex (40°35′S, 72°06′W, Chile) discharged massive amounts of ash and pumice into the surrounding landscape in Argentina (North Andean Patagonia). The ejected material affected nearby aquatic environments, producing an increase in total suspended solids. We combined field data and laboratory experiment data to determine the effect of the volcanic ashes suspended in the water column on cladoceran populations. During the summer of 2011–2012 (6 months after the eruption), zooplankton populations in these lakes decreased, mainly due to the disappearance of cladocerans. This decrease in zooplankton was not caused by food shortage; chlorophyll a concentrations in the lakes were higher than in previous years or in the following season, and no change in phytoplankton size was observed. By the following summer (2013), 18 months after the eruption, a recovery of cladoceran populations was observed, with a concomitant decrease in total suspended solids. We performed a life‐table experiment, examining Daphnia commutata survival and fecundity at a series of ash concentrations. Ash concentrations of 2, 3, 5 and 8 mg L−1 negatively affected survival and fecundity. Populations exposed to 8 mg L−1 of ash cannot persist; these organisms fail to produce offspring because they die before reaching reproductive age. We conclude that the disappearance of cladocerans was due to the presence of ash. As the sedimentation process occurs, ash concentrations decrease, favouring population recovery, as observed the following summer. When the lakes recovered their original transparency with low total suspended solids values, the cladoceran populations also returned to their historical abundances. Previous data on other explosive volcanic eruptions and the present data indicate that immediately after ash fall, the zooplankton suffer reduced abundance, particularly of non‐selective filter feeders such as daphnids. However, recovery of zooplankton population growth can be expected within a few years.

Geochemical techniques to discover open cave passage in karst spring systems

Dissolved O2 (DO) and pH data provide a novel, inexpensive field method to detect open cave passages in karst spring systems that can be complemented by laboratory measurements of major elements and nutrients, total suspended solids (TSS), Escherichia coli (E. coli) levels, and stable isotopes. Karst springs in east-central Missouri that have no known air-filled passages (“phreatic” springs) typically have low DO and pH values (<80% saturation and <7.7, respectively), which are characteristic of groundwaters that do not communicate with the atmosphere. In contrast, springs draining vadose cave passages have higher DO and pH values (>60% saturation and >7.7, respectively) that resemble surface waters due to the equilibration of DO with the overlying cave atmosphere and the simultaneous degassing of dissolved CO2. Traverses down phreatic spring branches show exchange with the atmosphere causes an increase in DO only a short distance downstream of the spring orifice, while the pH concurrently increases due to the degassing of CO2. Further downstream both parameters tend to level off reflecting a general approach to equilibrium under surface conditions, though this process is more rapid for DO than for pH. In contrast, the DO and pH along cave spring branches change little from values at the cave entrance. Additionally, (1) degassing processes affect the saturation state of calcite, with cave springs being the most saturated with respect to calcite, (2) phreatic springs typically have lower TSS and E. coli levels than open cave springs due to slower and less variable flow delivery, longer residence times, and less turbulent flow, and (3) phreatic springs tend to plot on the global meteoric water line (MWL), while waters from open cave systems tend to be enriched in 18O and D and can plot below the line due to evaporation and exchange of the water with the overlying cave atmosphere.

Evaluating the efficiency of different microfiltration and ultrafiltration membranes used as pretreatment for Red Sea water reverse osmosis desalination

Conventional processes are widely used as pretreatment for reverse osmosis (RO) desalination technology since its development. However, these processes require a large footprint and have some limitation issues such as difficulty to maintain a consistent silt density index, coagulation control at low total suspended solids, and management of higher waste sludge. Recently, there has been a rapid growth in the use of low-pressure membranes as pretreatment for RO systems replacing the conventional processes. However, despite the numerous advantages of using this integrated membrane system mainly providing good and stable water quality to RO membranes, many issues have to be addressed. The primary limitation is membrane fouling which reduces the permeate flux; therefore, higher pumping intensity is required to maintain a consistent volume of product. This paper aims to optimize the permeation flux and cleaning frequency by providing high permeate quality. Different low-pressure polyethersulfone membranes with different pore sizes ranging from 0.1μm to 50 kDa were tested. Eight different filtration configurations have been applied including the variation of coagulant doses aiming to control membrane fouling. Results showed that all the configurations with/without coagulation, provided permeate with excellent water quality which improves the stability of RO performance. However, more stable fluxes with less-energy consumption were achieved by using the 0.1μm and 100 kDa membranes with 1 mg/L FeCl3 coagulation. The use of UF membranes, having tight pores, without coagulation also proved to be an excellent option for Red Sea water RO pretreatment.

Characterization of the potential impact of retention tank emptying on wastewater primary treatment: a new element for CSO management

Theoretical studies have shown that discharges from retention tanks could have a negative impact on the WWTP's (Wastewater Treatment Plant) effluent. Characterization of such discharges is necessary to better understand these impacts. This study aims at: (1) characterizing water quality during emptying of a tank; and (2) characterizing the temporal variation of settling velocities of the waters released to the WWTP. Two full-scale sampling campaigns (18 rain events) have been realized in Quebec City and laboratory analyses have shown a wide variability of total suspended solids (TSS) and Chemical Oxygen Demand (COD) concentrations in the water released from the tank. Suspended solids seem to settle quickly because they are only found in large amounts during the first 15 min of pumping to the WWTP. These solids are hypothesized to come from the pumping in which solids remained after a previous event. When these solids are evacuated, low TSS containing waters are pumped from the retention tank. A second concentration peak occurs at the end of the emptying period when the tank is cleaned with wash water. Finally, settling velocity studies allowed characterizing combined sewer wastewaters by separating three main fractions of pollutants which correspond to the beginning, middle and end of emptying. In most cases, it is noticed that particle settling velocities increase as the pollutant load increases.