Lower Filtration Rate Research Articles

Cryptosporidium Oocysts Removal by Upflow Direct Filtration: Pilot Scale Assessment

Studies on the removal of Cryptosporidium oocysts by direct filtration suggested that high removal efficiencies (>3.0 log) can be achieved, but the vast majority of the studies focused on the assessment of downflow direct filtration. However, in comparison with downflow direct filtration, filters in upflow direct filtration systems use lower filtration rates, deeper stratified bed, and water flows from coarse to fine sand grain, which may improve the removal of oocysts. In this context, we evaluated the removal of Cryptosporidium oocysts using upflow direct filtration, on a pilot scale, to treat Paranoá Lake water (Brazil) seeded with Cryptosporidium oocysts. The experiments were conducted with raw water with low turbidity (3.2–5.7 NTU) and induced higher turbidity (28–30 NTU). Non-parametric statistical analysis was used to verify correlations between the filtered water values and removal of oocysts, particles, and turbidity. In general, no correlation was observed between the parameters analyzed, nor between their removals. The exception was the correlation between residual values of Cryptosporidium oocysts and particles of 2 to 7 µm during ripening, an aspect that needs further evaluation. Under stable operation, average removal of Cryptosporidium oocysts by upflow direct filtration was >3.87 log. During ripening, removal of oocysts was around 1 log lower.

Strength-enhanced nanocomposite foamed gel as a temporary wellbore plugging fluid: formulation design and working performance

When working over wells with low-pressure reservoirs, loss of workover fluids into the reservoirs has been a problem that must be resolved. To resolve this problem, on the basis of theoretical knowledge and application characteristics of foamed gels, we developed a strong, stable, nanocomposite foamed gel as a temporary plug. The gel has high stability and low density and exhibits low fluid loss compared with traditional workover fluids. The foamed gel comprises 0.5%wt to 0.7%wt partially hydrolyzed polyacrylamide, 1.4%wt foaming agent, 0.25%wt nanosilica, 0.03%wt to 0.05%wt metallic-ion crosslinking agent, and 0.02%wt deoxidant. The temporary plugging simulation experiment shows that, for the core with low permeability, pressure drawdown across cores under a 15 MPa positive pressure differential was less than 1.2 MPa in 60 min and the rate of filtration of fluid through the cores was almost zero. The result shows that the nanocomposite foam gel has a certain capacity for compression and a low filtration rate and can effectively plug reservoir rocks temporarily. Therefore, the prosed foamed gel offers good application prospects in preventing loss of workover fluids in low-pressure reservoirs.

Control and management scheme of air flows in inner space of steel silo during grain storage

The design of steel silo does not provide for constant monitoring of the air amount circulating inside the silo. Silos are not equipped with measuring equipment to control air flow. The height of the grain layer near the vertical wall corresponded to 15 meters and 20 meters at the same pressure of 3000 Pa in the lower part of the layer. At a higher layer height, the lower filtration rates and lower air flow are performed. Near the silo wall, the air rate depends on the height of the layer and is the same for silos of different diameters at the same pressure in the lower part. The silo with a large diameter has a greater variation in the values of the filtration rates along the surface of the grain mass. A typical technological scheme for storing grain in large-capacity steel silo was proposed and tested, taking into account the control and management system for air flows in the inner space of the grain mass.

The determination of hydraulic resistance during laminar filtration through layers of sorbents and ion-exchange granules in environmental mass exchange equipment

The paper presents main calculation dependencies, their advantages and disadvantages for calculating the hydraulic resistance of granular and porous layers in the area of low filtration rates. Approaches are given to account for the influence of porosity and size of particles (sorbent granules) that differ in the values of constants and different ways to account for the influence of particle shape on the hydraulic resistance of the granular layer.

Water tracks in the lower Lena River basin

In the permafrost regions, where water filtration zone is limited by the shallow active layer, the surface flow forms a network of hollows, called «water tracks», oriented along the slope gradient. Water tracks are clearly distinguished on satellite images, but poorly defined in the field. The pattern of the water tracks network depends on geomorphological position, permafrost and geological conditions and dominant cryogenic processes. Surface flow could occur in the water tracks during the snowmelt and heavy rains, when the soil is entirely frozen or fully saturated by water. In dry periods, the water tracks form retention zones due to low filtration rates and significant capacity of thawed soil beneath the troughs. Our study of water tracks in the north-western Yakutia showed the changes of their morphology from upstream towards downstream. The water levels in the water tracks have a pronounced diurnal course in reverse phase to the water temperature variation. They are related to diurnal ground thawing dynamics. Hydrology of water tracks depends on the peat thickness, active layer properties and lithology. Water tracks formed by rubble rocks respond to a storm event with rapidly increasing water level. The deeper thawing layer, the smoother water levels rise and decrease.

Performance of pilot Horizontal Roughing Filter as polishing stage of waste stabilization ponds in developing regions and modelling verification

Roughing Filters are natural systems widely used as an efficient, cost-effective and simple treatment method, especially in low income regions. In this study, an experimental Horizontal Roughing Filter (HRF) with two design modifications, i.e., varying (3 and 4) number of compartments and gravel media sizes, was operated and monitored for 2 years under three filtration rates (0.5, 1.0 and 2.0 m/h) as polishing stage of a Waste Stabilization Ponds facility. The proposed modification of the WHO-approved HRF with 3 instead of 4 compartments and with modified gravel sizes showed an improved performance in terms of turbidity, TSS, BOD5, COD and chlorophyll-a reduction, complying with the local standards for irrigation reuse, while lower filtration rates were found to further enhance the efficiency. The experimental results were successfully modelled with the Subwet software, which proved to be a reliable tool for performance verification and HRF design. This study demonstrated that the combined system of Waste Stabilization Ponds and Roughing Filters can be an attractive and effective treatment scheme based only on ecological processes, providing a high treated effluent quality with limited costs and simple operation and maintenance.

Low preoperative glomerular filtration rate is associated with an increased risk of postoperative delirium in elderly patients: a secondary analysis of a randomized controlled study

Objective To evaluate the association between preoperative estimated glomerular filtration rate and the risk of postoperative delirium in elderly patients. Methods The current study was a secondary analysis based on data from a randomized controlled study where 700 elderly patients were admitted to the intensive care unit (ICU) after noncardiac surgery. The preoperative estimated glomerular filtration rate (eGFR) was calculated using the Chronic Kidney Disease Epidemiology Collaboration equation. Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) was used to evaluate the occurrence of delirium twice a day in the first 7 d after surgery. Univariate Logistic regression analyses were performed to identify potential factors associated with the development of postoperative delirium, and factors with P<0.05 were included in a multivariate Logistic regression model to analyze the risk adjusted association between preoperative eGFR and postoperative delirium. Results The median of preoperative eGFR of all enrolled 700 patients was 72.0 ml·min-1·1.73m-2. The incidence of postoperative delirium was higher in patients with low preoperative eGFR (<72.0 ml·min-1·1.73m-2) than those with high preoperative eGFR (≥72.0 ml·min-1·1.73m-2) (19.1% vs. 12.6%, P=0.017). After correction for confounding factors, higher preoperative eGFR was associated with a lower risk of postoperative delirium (OR=0.990, 95%CI 0.980-1.000, P=0.041), a preoperative eGFR <72.0 ml·min-1·1.73 m-2 was an independent risk factor of postoperative delirium (OR=1.796, 95%CI 1.157-2.789, P=0.009). Conclusions For elderly patients admitted to ICU after noncardiac surgery, a low preoperative eGFR is associated with an increased risk of postoperative delirium. Key words: Aged; Non-cardiac surgery; Glomerular filtration rate; Postoperative delirium

Pilot study of a horizontal roughing filtration system treating greywater generated from a peri-urban community in Durban, South Africa

Abstract There is a growing pressure on the available freshwater resources in South Africa and many other countries around the world. This has led to a large scale of interest in the application of water reclamation and reuse of wastewater as alternative water supply sources. This is becoming critical to sustain development and economic growth in the southern Africa region. This study investigated the performance of a horizontal roughing filtration system treating greywater generated from a peri-urban settlement in Durban, South Africa. The horizontal roughing filtration system consists of three compartments containing different sizes of gravels that serve as the filter media. The horizontal roughing filter was operated at a filtration rate of 0.3 m/hr for 90 days. The results indicated that at this low filtration rate, effective reduction in turbidity, conductivity, chemical oxygen demand and total solids can be achieved. Overall average removal efficiencies of 90% turbidity, 70% chemical oxygen demand, 86% conductivity, and 84% total solids were obtained for the entire duration of operation of the horizontal roughing filtration system. Thus, it was concluded that the horizontal roughing filtration system is suitable for the treatment of greywater for non-potable reuse applications although further investigation needs to be conducted for the microbial removal during the treatment.

Validity of Existing Rain Water Harvesting Dams within Part of Western Desert, Iraq

The study area is located within the western part of Iraq between Latitude (32°45'0'' - 34°0'0'') North and longitude (39°30'0'' - 40°45'0'') East within Anbar Governorate. It covers an area of 4767.423 Km2 with elevation ranges from 360 to 840 m. The general slope decreases from southwest to northeast. Five old dams identified in the study area. The results of SWAT model showed high curve number (70 - 85) indicating low filtration and runoff rate (1.2 - 8.2) mm for the period (1994-2014). These dams have catchment areas ranged between (118.03 - 673.41) km2. They were to be used for agricultural purposes. The results according to the Food, Agriculture Organization (FAO) standards for their distance from agricultural areas using a GIS showed that all are not suitable except dam number (1). The distance to roads showed that dams (1, 4) are highly suitable, (2, 3) are low suitable and dam (5) is not suitable. The average annual quantity of rain water that can be harvested from the 5 dams is about 12.9 million cubic meters.

Erythrocyte fouling on micro-engineered membranes.

Crossflow microfiltration of plasma from blood through microsieves in a microchannel is potentially useful in many biomedical applications, including clinically as a wearable water removal device under development by the authors. We report experiments that correlate filtration rates, transmembrane pressures (TMP) and shear rates during filtration through a microscopically high channel bounded by a low intrinsic resistance photolithographically-produced porous semiconductor membrane. These experiments allowed observation of erythrocyte behavior at the filtering surface and showed how their unique deformability properties dominated filtration resistance. At low filtration rates (corresponding to low TMP), they rolled along the filter surface, but at higher filtration rates (corresponding to higher TMP), they anchored themselves to the filter membrane, forming a self-assembled, incomplete monolayer. The incompleteness of the layer was an essential feature of the monolayer's ability to support sustainable filtration. Maximum steady-state filtration flux was a function of wall shear rate, as predicted by conventional crossflow filtration theory, but, contrary to theories based on convective diffusion, showed weak dependence of filtration on erythrocyte concentration. Post-filtration scanning electron micrographs revealed significant capture and deformation of erythrocytes in all filter pores in the range 0.25 to 2 μm diameter. We report filtration rates through these filters and describe a largely unrecognized mechanism that allows stable filtration in the presence of substantial cell layers.

DISPOSAL OF WATER FILTERING DOWNLOADING FROM CALCIUM CARBONATE

The article presents the results of the study of the efficiency of removal of iron ions from aqueous solutions by filtration through a filter with loading from the particles of calcium carbonate. It is established that as a result of such an operation, the characteristics of the water significantly change. Thus, when filtering distilled water, there is an increase in pH from the initial 6.3 to 8.8 - 10.0 after passing through calcium carbonate. Moreover, the lower the rate of filtration, the greater the growth of pH. The rigidity of distilled water at low filtration rates increases from 0.1 mg-ekv/dm3 to 0.9 mg-ekv/dm3, but with an increase in filtration rate to 2 m/h, it decreases to 0.5 mg‑ekv/dm3. Water from the Kiev water supply system also significantly changes its parameters. As in the previous case, the hydrogen index rises from the initial 7.0 to 8.6 - 10.1. With regard to stiffness, it is worth noting that with increasing filtration rate it begins to increase, which can be associated with a decrease in pH. When filtering through loading of sewage with different pH values it is observed their neutralization and transfer of pH to the alkaline area. This fact essentially affects the conditions for the removal of heavy metals and does not allow the use of this method for the treatment of drinking water. It should also be noted that with a hydrogen index below 4.0 there is an intense decomposition of calcium carbonate with carbon dioxide emissions and the destruction of loading. This can be considered as one of the negative effects of using the method. Water filtration through loading from the particles of calcium carbonate is accompanied by an increase in the alkalinity of treated water. Thus, at a filtration rate of 0.6 m / h, the alkalinity of distilled water increases from 0.7 to 1.0 mmol/dm3, and the alkalinity of the tap water is from 0.8 to 2.0 mmol/dm3. Such changes are not always acceptable, especially in the case of re-use of treated water. The degree of water purification from Fe2+ and Fe3+ ions depends to a large extent on both the initial content and the rate of filtration. Thus, at initial concentrations of ions in a solution of 24 mg/dm3, 12 mg/dm3 and 6 mg/dm3, their concentration after passing the solution through a column at a rate of 0.2-0.3 m/h was 0.65 mg/dm3, respectively, 0.55 mg/dm3 and 0.5 mg/dm3. Moreover, in all three cases, the purification of Fe2+ and Fe3+ ions is more effective at lower filtration rates. Repeated flow of treated water through the same filter with the same speed reduces the content of iron ions to trace concentrations.Key words: non-ironification, calcium carbonate, filtration, water treatment, iron ions.

Development of Novel and Cost Effective Techniques for Purification of Commercial Grade Phosphoric Acid for Fertilizers, Food and Pharmaceutical Industries

AbstractCultivation of 1.5 millions Faddens is one of the major projects for securing food supply to the ever increasing population; therefore, expansion of the fertilizer industry becomes a must.Phosphate ores from New Valley and Nile Valley are chemically processed by sulphuric acid to produce phosphoric acid intermediate by the dihydrate process. Two plants are already inoperation at “Abu Zabaal” and “Fayoum” and another two plants are under establishment, onealong the Red Sea Coast at El-Sokhna and the other at the “New Valley”. Two major problems are facing the industry, namely, the low filtration rate of the acid from solid gypsum and the second is the high level of impurities which decreases the P2O5 water solubility of the produced fertilizers. The filtration rate has been doubled by utilization of surface active agents(Surfactants) to modify the gypsum crystals. On the other hand, novel technique is being developed to decrease the impurities especially iron from 4% to < 1% leading to increasing the P2O5 water solubility of the produced fertilizer. Further decrease of Fe content of the fertilizer grade acid to < 0.1% is achieved through application of a novel membrane technology. The purified acid could be used for food and pharmaceutical industries, thus the economics of the acid production units greatly improve. The paper reviewed the results obtained so far which will improve significantly the value added products. The effects of the different parameters such as oxalic acid dose, temperature and concentration of phosphoric acid on Fe2O3 removal efficiencyhave been studied. Increasing the oxalic acid dose up to 7.5 g/100g of 28% P2O5 (80oC, 100 rpm) raised the removal efficiency of Fe2O3 to 90.8%. Increasing the dose of oxalic acid to 10 g/100g led to slight increase in the removal efficiency of Fe2O3 to 91.6%.

Investigation of sub-acute levels of zinc oxide nanoparticles on the filtration rate of Mytilaster lineatus and Dressina polymorpha in the short term

Qadermarzi A, Pouladi M, Rezamand A, Hoseinifar SH, Hedayati AA. 2018. Investigation of sub-acute levels of zinc oxide nanoparticles on the filtration rate of Mytilaster lineatus and Dressina polymorpha in the short term. Nusantara Bioscience 10: 53-57. The filtration rate is one of the physiological indices in the bivalves which indicate the degree of efficacy of the filtration function in the exposure to contaminants. In this study, changes in the filtration rate of freshwater bivalves (D. polymorpha and M. lineatus) were investigated after exposure periods of 5 and 10 days with nanoparticles. Bivalves were transferred from the natural environment to the laboratory. The distribution of nanoparticles was measured by differential light scattering (DLS). Bivalves were exposed to 2.5, 25 and 50 ppm nanoparticles for ten days in water reservoirs. The filtration rates were significantly different in the treatments compared to the control samples, with the highest filtration rate was observed in the control group. On the fifth day, the highest filtration rate was obtained in the first treatment of M. lineatus and the lowest filtration rate was obtained in the third treatment of D. polymorphia. The highest filtration rates were observed in the first and second treatments and the lowest filtration rate was observed in the third treatment. Also, there was no significant difference in the filtration rate of M. lineatus in the 1st treatment with control (P&gt; 0.05) on the 5th day, but filtration rate was significantly (P &lt;0.05) less than other concentrations and control group in the third treatment. On the other hand, the filtration rates on the 10th day showed similar differences compared to the 5th day. It could be concluded that the changes infiltration rate are an appropriate indicator for the measurement of contamination in nanoparticles.

Estimating current and long-term risks of coronary artery in silico by fractional flow reserve, wall shear stress and low-density lipoprotein filtration rate

Background. Hemodynamic changes and consequent low-density lipoprotein (LDL) filtration play an important role in the atherosclerotic plaque development of coronary arteries. In this pilot controlled case study, we aimed to investigate the correlation between parameters derived from computational fluid dynamics (CFD) simulation and risks (both current and long-term) of coronary atherosclerosis. Methods. We reconstructed geometric models from the baseline computed tomography (CT) angiography of two subjects, one patient and one healthy control, and performed CFD simulations. We estimated the current risk of ischemia by fractional flow reserve (FFR). We estimated the potential risk of plaque development by wall shear stress (WSS) and LDL filtration rate with follow-up clinical imaging validation. We investigated the effects of simulation methods (transient/static) and rheological models (Newtonian/Carreau–Yasuda) by comparing the corresponding results (FFR, WSS and LDL filtration rate) in the patient’s left anterior descending coronary artery. Results. In baseline CFD simulation, FFR indicated mild current ischemic risk of the patient, in accordance with existing angina pectoris. Baseline WSS and LDL filtration rate results were related with in vivo plaque development. The plaque-growth locations in follow-up CT angiogram coincided with areas of low WSS and high LDL filtration rate in the baseline simulation. The LDL filtration rate delineated more specific risky areas than WSS. Between transient and static results, the difference of FFR was less than 5% in the whole model. As to WSS and LDL filtration rate the transient/static difference was within 20% in most areas, but rose up to 50% for WSS and even higher for LDL filtration rate, in areas with low WSS and high LDL filtration rate. As to rheological effects, Newtonian/Carreau–Yasuda difference was negligible for FFR throughout the model, within 30% for WSS and LDL filtration rate in major areas, and 50% or higher in certain segments where low WSS and high LDL filtration rate existed. Conclusion. CFD results appeared to be related with in vivo development of coronary atherosclerosis. Simulated FFR and its threshold value 0.8 demonstrated the ischemic risk. Both WSS and LDL filtration rate could indicate areas of plaque growth.

Sources of paralytic shellfish toxin accumulation variability in the Pacific oyster Crassostrea gigas

This study was designed to assess the contribution of feeding behavior to inter-individual variability of paralytic shellfish toxin (PST) accumulation in the Pacific oyster Crassostrea gigas. For this purpose 42 oysters were exposed for 2 days to non-toxic algae and then for 2 other days to the PST producer Alexandrium minutum. Individual clearance rate (CR) of oysters was continuously monitored over the 4 days using an ecophysiological measurement system. Comparison of CR values when exposed to toxic and non toxic algae allowed to estimate a clearance rate inhibition index (CRII). Toxin concentration of oysters was quantified at the end of the experiment. These data allowed to estimate the toxin accumulation efficiency (TAE) as the ratio of toxin accumulated on toxin consumed. Changes of clearance rate during the experiment indicated that all individuals stopped feeding immediately after being exposed to A. minutum for at least 7 h. This fast response likely corresponded to a behavioral mechanism of avoidance rather to a toxin-induced response. Individuals also showed high inter-variability in their recovery of filtration after this period. Most of the inter-individual variability (78%) in PST accumulation in C. gigas could be explained by the consumption of A. minutum cells, thus emphasizing the importance of the feeding behavior in accumulation. Based on the toxin concentration in their tissues, oysters were clustered in 3 groups showing contrasted patterns of PST accumulation: the high accumulation group was characterized by high feeding rates both on non-toxic and toxic diet and subsequently a low CRII and high TAE. Inversely, the low accumulation group was characterized by low filtration rates, high CRII and low TAE. Both filtration capacity and sensitivity of oysters to toxins may account for the differences in their accumulation. The contribution of TAE in PST accumulation is discussed and might result from differences in assimilation and detoxification abilities among individuals.

Phagocytosis of microbial symbionts balances the carbon and nitrogen budget for the deep‐water boreal sponge Geodia barretti

AbstractGeodia barretti is a massive nearly spherical sponge that forms dense assemblages on the continental shelf of the North Atlantic and the Norwegian Sea. We studied the metabolism of individual sponges collected using a remotely operated vehicle and maintained in large tanks with high volumes of unfiltered water brought from 160 m depth. We used direct methods (In‐Ex) to measure excurrent flow rates, oxygen removed, and carbon and nutrient flux through the sponges. G. barretti had very low specific filtration (0.26 mL min−1 mL−1 sponge tissue) and low respiration (5.34 ± 0.98 nmol O2 min−1 mL−1 sponge tissue; 8.44 ± 1.51 μmol O2 h−1 g C−1) rates in comparison to other sponges. A net release of nitrogen was detected as . Bacteria were removed from the water filtered with up to 99% efficiency, yet comprised only 5% of the sponges′ total carbon budget; the remainder consisted of dissolved organic carbon and detritus. High bacterial removal was aided by the presence of a tight gasket of cells that surrounds the collar of each choanocyte filter. A test for potential bypass canals showed removal of fluorescent microspheres until they were excreted 5–12 h after feeding. Electron micrographs showed active uptake of Escherichia coli “fed” to the sponge as well as phagocytosis of symbiont microbes by sponge cells in the mesohyl. These data provide the first comprehensive study of metabolism in a deep‐water high microbial abundance sponge.

Efficiency and Mechanism of Purifying High Iron-Manganese from Ground Water in the Cold Villages and Towns Based on The Coupling of Rice Husk and Iron-Manganese Oxidizing Bacteria

Aiming at the special geo-climatic conditions and typical problems constraining the development of villages and towns, making villages and towns have the following characteristics:green and low-carbon, energy saving and environmental friendly, the coupling process of adsorption by carbonized rice husk particles and biological oxidation using Bacillus megaterium bacteria was developed for purifying high iron-manganese from groundwater in the cold villages and towns. The quick start-up method of biological filter at low temperature was studied. Based on the contact oxidation and biological method, iron removal efficiency and reaction rate in different filtration layers under different filtration conditions were comparatively analyzed, and iron removal mechanism of biological filter was determined. Filter materials and the solid samples in backwash water at different stages were characterized and the manganese removal mechanism of biological filter was analyzed through SEM, FTIR, XPS, Raman spectra and EPR. The results showed that the active biological membrane reached mature and stable only after 15 d with the operation mode of bacteria liquid cycle and low filtration rate in the filter column. The effluent concentration met the requirements of drinking water quality (GB 5749-2006) in the stable operation process. Fe, Mn and bacteria were lower than 0.3 mg·L-1, 0.1 mg·L-1, 100 CFU·mL-1, respectively. Iron removal mechanism relied mainly on the physical and chemical effects, supplemented by biological function. During the biofilm culturing stage and initial stable operation stage of filter column, manganese removal relied mainly on the biological effect. The physical chemistry was preferred at later stable operation stage. The study provides technical support for the applications of treating collectively Fe2+ and Mn2+ in groundwater.

The effect of clam grazing on phytoplankton spring blooms in the low-salinity zone of the San Francisco Estuary: A modelling approach

Benthic grazing by estuarine bivalves can be an important top-down process impacting pelagic food webs. In the low-salinity zone of the San Francisco Estuary mass balance calculations and models have reported that clams (especially the invasive Potamocorbula amurensis) suppress phytoplankton blooms. However, spring blooms frequently occur. We aimed to understand this clam paradox using a biogeochemical modelling approach to evaluate the effects of clam grazing and excretion on phytoplankton production and nutrient uptake. The conceptual framework combines both the reduction of phytoplankton biomass by grazing and the role of ammonium (from clam excretion, wastewater plant discharge and sediment efflux) in minimizing chlorophyll accumulation, since phytoplankton cannot access nitrate (the major form of available nitrogen) for growth, due to ammonium suppression of nitrate uptake. We constructed the CLAMFLOW model by adding a clam module (with pathways of nitrogen for clam grazing, clam excretion and sediment efflux) to an existing phytoplankton-nitrogen-flow model. Whatever the parameter that was varied in the model (clam abundance, grazing, excretion, sediment efflux or flow) it decreased the peak nitrate uptake by the phytoplankton and shifted the time to reach peak uptake so delaying the likelihood of bloom initiation.Outcomes of the CLAMFLOW model were to demonstrate how clams can indirectly impact phytoplankton growth through excretion of ammonium, and to illustrate how most published laboratory filtration rates are likely too high for application in the field. There are management implications from using too high a clam grazing rate in models that may overestimate their impact on trophic estuarine and wetland productivity. We suggest that improved prediction of bloom occurrences requires the use of lower filtration rates combined with observed clam abundances, and a suitable combination of flow and ammonium source concentrations. This simple modular model (CLAMFLOW) offers portability to other ecosystems and is designed to connect with estuary scale three-dimensional circulation or numerical biogeochemical models. Our model and results are applicable to other situations, including aquaculture development and bivalve restoration efforts, where the biogeochemical effects of bivalves on phytoplankton productivity need to be quantitatively understood.

Reduced growth, body condition and foot length of the bivalve Austrovenus stutchburyi in response to parasite infection

Parasites often have direct impacts on their host physiology or function, which can in turn have indirect effects on interspecific interactions and ecosystem structure. The present study investigates the effect of trematode parasite infection on the ecologically and commercially important venerid clam Austrovenus stutchburyi. Although the indirect impacts of clam infection on the broader benthic community, mediated by impaired burrowing of parasitized clams, have been well documented before, the more direct impacts on the clam itself remain poorly studied. The consequence of parasite infection on clam growth rate, mortality, body condition and foot length was quantified in a three-month laboratory experiment, in which juvenile clams were infected with varying levels of the echinostome trematode Curtuteria australis. Although mortality was unaffected by parasite infection, greater numbers of parasites deleteriously affected the growth rate, body condition and foot length of clams. This may result in delayed maturity and a lower filtration rate for infected individuals, as well as a reduced ability to bury into the sediment. Consequently, increased parasite infection not only has subsequent broader impacts on the surrounding ecological community, but can also affect the clam host directly and lower its value as a harvested species.

The suitability of natural and synthetic filter material for the removal of petroleum products from the aqueous media

Petroleum products that have leaked into the natural environment are very hazardous. They are particularly dangerous for aquatic ecosystems. The major part of oils is carried into natural water bodies together with the surface outwashes from urban areas. One of the most inexpensive and easiest methods of the removal of oil contaminants from runoff is filtering. The authors of this study examined several synthetic substances (Duck and Reo-dry), and several vegetal materials (shredded stems of reeds, bulrush and lesser bulrush) and compared their filtration characteristics with the characteristics of the synthetic substance Fibroil now widely used for filtration. The authors of this study feel that the materials tested are suitable for the petroleum removal filter medium. Industrialists submit specifications of their products that were recorded under ideal conditions, at a low filtration rate. The authors studied filter material of natural origin as well as synthetic ones by simulating actual conditions that originate during heavy rains, i.e. at high filtration rates. In some aspects, low-cost vegetal material for the surface treatment of runoff performed better than the synthetic filters.