Large Amounts Of Suspended Solids Research Articles

Experimental study on the effect of tight gas fracturing flowback fluid composition on the performance of modified polyacrylamide viscosity reducing and slippery water system

AbstractTight gas belongs to unconventional gas reservoirs, and to obtain high gas production, it needs to be fractured and reformed. After the construction is completed, a large amount of flowback fluid is produced. In order to reduce the cost of flowback fluid treatment and avoid environmental pollution, a slippery water system with flowback fluid is usually used on the site of hydraulic fracturing. Almost all flowback fluids contain high‐order cations such as calcium ions, magnesium ions, iron ions, and a large amount of suspended solids. Some flowback fluids contain incomplete gel‐breaking micelles and unseparated condensate oil. The performance of the viscosity‐reducing and slippery water system with flowback fluid as the base fluid is poor, usually manifested as low viscosity of the slippery water, low friction reduction rate, and high formation damage. To study the effect of tight gas fracturing flowback fluid on the performance of modified polyacrylamide viscosity‐reducing and slippery water system, this paper found through cryo‐electron microscopy scanning experiments that the flowback fluid made the modified polyacrylamide molecular chain unable to form a complex network structure and showed the phenomenon of reduced strength and aggregation. The effects of mineralization degree, calcium and magnesium ions, divalent and trivalent iron ions, suspended solids, pH value, and oil content on the viscosity, friction reduction performance, and rock damage of the viscosity‐reducing and slippery water system were analyzed experimentally. It was found that the viscosity of the viscosity‐reducing and slippery water system was mainly affected by divalent iron ions, calcium and magnesium ions and other divalent cations; the friction reduction rate was mainly affected by the content of suspended solids and oil content; and the rock damage was mainly affected by the pH value and the content of suspended solids. Based on this, recommended parameters for reusing tight gas fracturing flowback fluid are given to guide the smooth progress of hydraulic fracturing construction on‐site.

Effects of an Episodic Storm-Induced Flooding Event on the Biogeochemistry of a Shallow, Highly Turbid, Semi-Enclosed Embayment (Laizhou Bay, Bohai Sea)

Episodic storm-induced flooding is becoming more frequent with a warming climate, which may alter the biogeochemical properties and conditions of estuaries. However, the effects of such extreme events on semi-enclosed bay ecosystems have not been fully investigated because of the difficulty in collecting in situ samples. To address this issue, a comparative study was carried out to understand the biogeochemical changes in Laizhou Bay, a shallow, highly turbid, semi-enclosed bay, by coupling satellite data and surface water samplings collected during an episodic flooding event (August 2018) and during a non-flooding period (August 2017). The results showed that the 2018 Shouguang flood delivered large amounts of suspended solids, phosphorus, and organic matter-enriched terrigenous materials into Laizhou Bay and enhanced the offshore expansion of the low-salinity seawater plume and associated nutrient fronts. Water total suspended solid (TSS) particle and chlorophyll a (Chl-a) concentrations increased by 23.79 g/m3 and 0.63 mg/m3, respectively, on average in the freshwater mixing water plume around the Mi River. Episodic flooding is a crucial driver which temporally dominates the spatial patterns of water biogeochemistry. These results are essential to anticipate the ecosystem response of estuarine regions to the high episodic freshwater flow associated with the increasing storms.

Hybrid process of electrocoagulation and electrooxidation system for wastewater treatment: A review

Water is one of the most essential natural resources required for all living things. Globally, due to various factors, the volume of wastewater generated and contaminant loads are increasing. Therefore, currently, there is high interest and concern in developing more effective wastewater treatment technologies. Particularly, the emerging electrochemical methods, mainly electrocoagulation (EC), electrooxidation (EO), and the hybrid of both EC and EO, have recently attracted attention as a potential method for treating wastewater due to its wide application and environmental compatibility. In the EC process, different metal hydroxide species are formed. The metal hydroxides (coagulant) aggregate the dispersed particles in the solution, which forms bigger flocs and then is removed by sedimentation. In most cases, EC is not able to reduce the stable persistent organic compounds to below the allowable discharge limits. Also, the EO process is an emerging process where contaminants are removed by oxidizing directly at the surface of the electrode or indirectly by generating oxidants in the solution. However, the main drawback of the EO method is that it is not applicable or requires a long operation time for treating water and wastewater with large amounts of suspended solids. Thus, to use the EO treatment system, the suspended solids of the wastewater have to be removed first by using other techniques. This can be achieved by a hybrid process of EC and EO. Besides, the hybrid process can enhance the removal of COD, TOC, NH 4 + -N, nitrates, phenol, which is not effectively achieved by using only EC or EO. Therefore, in this particular review, special emphasis was given to a hybrid of EC and EO processes, in addition to assessing electrocoagulation and electrooxidation as exceptional electrochemical methods. Even though several studies have covered EC, EO, and a hybrid process of EC and EO systems separately, to our best knowledge, there is an extremely limited number of review papers that have been done on the hybrid process of EC and EO. Therefore, this manuscript aims to review the potential of a hybrid of the EC and EO processes for treating wastewater generated from various sources.

Speciation Change of Flocs During Electrocoagulation for Wet Flue Gas Desulfurization Wastewater

Wastewater produced from wet flue gas desulfurization (WFGD) process contains large amounts of suspended solids (SS), heavy metals and salinity. Compared to traditional chemical coagulation, electrocoagulation (EC) technology is a novel technology to remove these pollutants with lower O&M costs and simplified facilities. In order to achieve better EC effects, the speciation change of flocs generated from two kinds of sacrificed electrodes (e.g., Al and Fe) is investigated in various operation parameters. The results show that iron anode performed better compared to aluminium anode. At 20V of voltage and 6cm of electrode gap, the percentage of polymeric species of iron flocs can reach more than 50%. The significant domination of polymeric species under the optimal conditions during electrocoagution is responsible for the turbidity removal.

Energy consumption, operating cost and treatment of tea effluent using electrocoagulation

The effluents from tea processing plants are characterized by a strong colour and high turbidity due to the presence of large amounts of suspended solids, dissolved organic matter and inorganic wastes which include detergents, grease/waste oil from machine parts. These altogether poses an environmental and legal challenge calling for appropriate means of treatment. In this regard the study was designed to evaluate energy consumption, operating cost in treatment of tea effluent using electrocoagulation method at optimum conditions of electrode distance 6 mm, electrolysis time 18 min, Current intensity 250 mA The study adopted an experimental research design. From the study findings Energy consumption was found to be 0.0018Kwh/m3 at an operating cost of US$ 0.004179032 /m^3at laboratory scale. The findings further showed that at industrial scale design parameters such as Diameter, height, electrode spacing, retention time, current intensity and reactor volume were 100 cm, 150 cm, 60 mm, 59.94 minutes, 25 Amps and 1.2 m3 respectively which equally reduces COD and Colour removal at 99.43 % and 98.62 with energy consumption of 4.8Kwh/m3 at an operating cost US$ 0.744. In conclusion EC provides the most feasible alternative for treatment of tea effluent with a view of COD reduction and colour removal.

Clarification and solvent extraction studies of a high talc containing copper aqueous solution

Effects of different flocculants on the clarification of a copper aqueous solution destined for solvent extraction were investigated. The test work was conducted on the pregnant leaching solution (PLS) of a high talc containing copper ore that had a high propensity of bearing a large amount of suspended solids. The clarification test work was conducted using three commercial high molecular anionic polyacrylamide polymer flocculants: rheomax® DR 1050, brontë 103, and senfloc® 2660. Solvent extraction tests were done using 30% (v/v) LIX 984N at pH 1.8. The parameters of clarification and solvent extraction were the flocculant dosage (0, 58.14, 116.28, 232.56 and 348.84g/t) and the ratio O/A (1/5, 1/2, 2/3, 1/1, 3/2, 2/1, and 5/1), respectively. The analysis results of the PLS showed it contained 2000ppm of solids in suspension. The optimal conditions for clarification and solvent extraction were a dosage of 116.28g/t and an O/A of 1.5, respectively. Under optimal conditions, the residual total suspended solids (TSS) in the clarified solutions were 1196ppm, 954ppm, and 928ppm; the phases disengagement time (PDT) for organic continuous dispersion were 70s, 80s and 60s; the percent TSS entrained in the organic phase were 26.76%, 28.93% and 25.32%; copper recoveries were 97.63%, 98.98% and 95.13%, with rheomax® DR 1050, brontë 103 and senfloc® 2660, respectively.

Removal of Levafix Red from Aqueous Solution with Treated Jute Stick and its Relevance to Pharmaceutical Field

The adsorption of levafix red (LR) dye from waste water via batch adsorption onto treated jute stick powder was investigated. Studies concerning the factors influencing the adsorption such as adsorbent dosage, pH, contact time and temperature were systematically investigated and discussed. The results revealed that the maximum removal of levafix red was ~91% from water. The kinetics data were analyzed using pseudo-first order and pseudo-second order models. It was best described by the pseudo-second order model. The adsorption equilibrium follows Langmuir isotherm. This result indicates that treated jute stick powder could be employed as low-cost alternatives to commercial activated carbon for the removal of levafix red (LR) from waste water. Rapid industrialization in Bangladesh has resulted in increased water pollution that has higher dye level. Waste water from dyeing and finishing factories is a significant source of environmental pollution. The waste water is typically characterized by high levels of COD (chemical oxygen demand) concentration, high concentration of coloring material, large amount of suspended solids, highly fluctuating pH and high temperature. Dyes may therefore present an ecotoxic hazard and introduces the potential danger of bioaccumulation that may eventually affect man by transport through the food chain. As pharmaceutical industries use lots of water and intake of this type of water might have adverse effects on human health. Therefore, water purification is extremely essential for human and animal health and dye free water may be farther purified for its proper use.Bangladesh Pharmaceutical Journal 19(1): 75-84, 2016

Diatomeas (Bacillariophyceae) en humedales de altura de la Provincia de Catamarca (Argentina). III

En el marco de la investigación de humedales de alta montaña que realizamos desde 1998, hemos estudiado ya 24 cuerpos de agua de esta provincia. Con el objetivo de ampliar los conocimientos de la flora diatomológica en ambientes de alta montaña, en esta oportunidad analizamos otros 12 humedales ubicados entre los 25°34’05’’-27°39’23’’ S, a más de 3000 m snm. Encontramos diatomeas en todas las muestras, excepto en la de la laguna Azul, que es casi blanca por la gran cantidad de sólidos en suspensión. En relación a la salinidad, las aguas fueron desde dulces hasta hipersalinas, con predominio de los iones sodio y cloruro. Identificamos, excluyendo las Fragilariaceae, 42 géneros con 123 taxones infragenéricos, 29 de los cuales son nuevos registros para la provincia de Catamarca, 4 para Argentina y proponemos una nueva especie (Anomoeoneis punae sp nov.). La mayoría de las especies pertenecen a los géneros Navicula (17), Nitzschia (13), Halamphora (12), Surirella (8) y Anomoeoneis (7). No se encontraron especies comunes a todas las muestras y sólo seis tuvieron una frecuencia de ocurrencia mayor al 50 %. Se obtuvieron altos porcentajes (54 %) de especies raras, halladas solo en una o dos de las muestras.

A vertical flow constructed wetland for the treatment of winery process water and domestic sewage in Ontario, Canada: Six years of performance data

Wine production is a growing industry in the Canadian province of Ontario. Due to the high organic loads and large amount of suspended solids found in winery process water it is important for wineries to adopt sustainable water management practices. Constructed wetlands (CW) have been shown to be a viable option in the warmer climates of the Mediterranean and the western USA but little research has examined their feasibility in the cold climate of Ontario. The purpose of this paper was to assess six years of performance data from a vertical flow CW treating winery process water and domestic sewage at a winery in the Niagara region of Ontario with an average hydraulic loading rate (HLR) of 22.3mmd−1 and an average chemical oxygen demand (COD) surface loading rate (SLR) of 34.0gm2d−1. The CW has four cells, each 101m2, and was designed to treat 16,620Lday−1 of wastewater consisting of winery process water and domestic sewage. The performance data were separated by season to determine the effect of temperature on treatment performance during the colder months. There was little variation in seasonal performance and the average treatment efficiencies over the six-year period were: 99% for COD, 99% for carbonaceous COD, 98% for total suspended solids, 83% for total phosphorous, 94% for total Kjeldahl nitrogen, and 85% ammonium. Effluent nitrate, total coliforms, and Escherichia coli concentrations were also monitored and consistently met the regulatory standards for discharge to a subsurface leaching bed. The CW system proved to be an option for treating winery wastewater.

Nanofiltration treatment of tomato paste processing wastewater: process modeling and optimization using response surface methodology

Tomato wastewater is characterized by a large amount of suspended solids, red color, and bad smell. In this paper, the effect of transmembrane pressure (10, 15, 20 bar), pH (4, 5, 6), and temperature (30, 40, 50°C) on the permeate flux, total hydraulic resistance, and chemical oxygen demand (COD) rejection of tomato wastewater during nanofiltration treatment was investigated. The flux was found to be approximately constant during long-period operation. The flux was reduced as the pH declined, while it was increased as the temperature and transmembrane pressure increased. The hydraulic resistance (at pH 5 & TMP 1.5 MPa) increased from 5.79 × 1013 to 7.25 × 1013 1/m when the temperature increased from 30 to 50°C. The COD rejection was ranged from 75.65 to 85.35%, in which the highest value was obtained at pH 6, TMP 2.0 MPa, and 30°C. The response surface methodology results demonstrated that the quadratic, the two-factor interaction (2.Fi), and the linear polynomial models are highly significant for modeling the flux (R2 = 0.98), hydraulic resistance (R2 = 0.96), and COD rejection (R2 = 0.90), respectively. Numerical optimization determined the optimum conditions based on the highest flux and rejection and the lowest fouling with transmembrane pressure of 20 bars, temperature of 30°C, and pH of 6, respectively.

Properties of Heat Treatment Alkaline Pulping Black Liquor with Aluminum Chloride

The black liquor contains a large amount of suspended solids, organic pollutants and toxic substances, the black liquor discharged directly into water bodies will lead to serious pollution. So we regards the alkaline pulping black liquor as a research object, using autoclave to heat the mixture of aluminum chloride and soda black liquor lignin. By changing the heating temperature and the pH before the heat treatment, we analyze the lignin and carbohydrates in the cooking liquid to study cleavage situation and the corresponding structural changes. The results show that the lignin content accompanied the increase in temperature, organic matter content decreased and part of the decomposition of organic matter. Without adjusting pH, the lignin content is small and ash (inorganic) content is higher.

Recent results to the evaluation of the long-term effects of metal pollution in Tisza river

In January and March 2000 two tailings dam failures occurred in the upper Tisza catchment area near Baia Mare and Baia Borsa (Romania). These resulted metal pollution of the Lápos-Szamos-Tisza and Visó-Tisza river systems. The mining accidents were followed by a flood event. Many studies reported that elevated Cu, Zn, Pb and Cd concentrations were observable in water, sediment and in soils of flooded areas as well. Mine wastewater contained large amounts of suspended solids with high metal concentrations. The aims of this study were the determination of Lakanen-Erviö extractable, easily available metal contents of the soil samples collected in 2011 from Tivadar floodplain, a pasture near Vásárosnamény, a pasture near Rakamaz and Tiszacsege floodplain along the Tisza, and the comparison of these data and the results of an earlier study in 2000.According to our results the soil profiles of Vásárosnamény, Rakamaz and Tiszacsege is considered to be polluted by Zn, Pb and Cd. Low metal concentrations were found in the soil samples originated from Tivadar floodplain that was not affected by the first tailings pond failure. According to the statistical analyses of these data it can be established that during the 11-year period the easily available Cd, Cu, Zn and Pb contents of the pasture near Vásárosnamény increased significantly. This may caused by the periodical flood events or the mobilization of the pollutants. Further investigations (solid state partitioning of metals by sequential extraction) are required to find an explanation of this increase.

Pilot‐scale treatment of waste‐water from carbon production by a combined physical–chemical process

AbstractBACKGROUND: Due to its strong colour, high concentrations of fluorides and chemical oxygen demand (CODCr) and large amount of suspended solids (SS), the waste‐water from carbon production (WCP) seriously affects the stability of the circulating system of Guizhou Branch, Aluminium Corporation of China. In this paper, the performance of a pilot‐scale (24 m3 d−1) combined treatment plant, consisting of chemical precipitation, coagulation, and Fenton oxidation, for the treatment of WCP was investigated.RESULTS: Lime precipitation and hydrated ferrous sulphate (HFS) coagulation, with polyacrylamide (PAM) as a coagulation aid, proved to be effective in the removal of colour (>70%), suspended solids (SS) (>90%) and fluoride (>80%) from the WCP. Subsequent Fenton oxidation combined with coagulation as a final treatment efficiently removed SS, F−, CODCr, dissolved organic carbon (DOC) and colour. The average total removal efficiencies of these parameters in the pilot‐scale combined technology were as follows: SS = 98.8%, F− = 95.7%, CODCr = 94.8%, DOC = 91.8% and colour = 98.3%, giving an average effluent quality: colour 24 (multiple), CODCr 168 mg L−1, DOC 80 mg L−1, F− 38 mg L−1 and SS 44 mg L−1, consistent with the reusable water limits for the process.CONCLUSIONS: The current experimental results and the economic evaluation suggest that the combined process could be advantageous and feasible for the treatment of WCP. Copyright © 2009 Society of Chemical Industry

Effects of continuous flow centrifugation on measurements of trace elements in river water: intrinsic contamination and particle fragmentation

AbstractContinuous flow centrifugation (CFC) is a well‐established technique used in natural surface water studies to collect large amounts of suspended solids, thus allowing a broad spectrum of measurements. However, a potential contamination or changes in the particle size distribution during the centrifugation may restrain the use of CFC effluents for element analysis in the colloidal and dissolved fractions. In this paper we evaluate the possibility of using the effluent of a Westfalia centrifuge (type KA2‐06‐075, 9700 rpm) for such analysis. This evaluation is based on two laboratory experiments with deionized and tap water and two field experiments in rivers. Elemental concentration changes across the CFC were assessed from the CFC influent and effluent after a filtration at 0·45 µm. Significant increases were found, mainly in the field experiments at a high suspended solids level and a slightly acid pH. A hypothesis was made on the origin of these increases as a superposition of a centrifuge intrinsic contamination and a particle fragmentation effect. A numerical model based on elemental concentration measurements (inductively coupled plasma mass spectrometry) gave a particle fragmentation level of 0·55% (mass percentage of particles broken up into smaller fragments during centrifugation). In another experiment, a direct particle counting (single particle counter) shows an excess of particles smaller than 500 nm in the CFC effluent, corresponding to a fragmentation level of 0·11%. In consequence, the use of CFC effluent for element analysis is possible in low‐turbidity river or lake waters, but should be carefully considered in waters with high suspended matter contents. Copyright © 2006 John Wiley & Sons, Ltd.

Effect of urban emissions on the horizontal distribution of metal concentration in sediments in the vicinity of Asian large cities

Metal contents of sediments in Manila Bay - Laguna Lake watershed in the Philippines were measured and detailed horizontal distribution was obtained. The distribution of zinc and lead concentration in Manila Bay clearly shows the effect of anthropogenic contamination and it was explained by the diffusion of lead and zinc rich anthropogenic particles discharged from Pasig River. The sediments in Laguna Lake were mostly natural particulate matters from surrounding mountains and they contained 20 mgPb/kg and 100 mgZn/kg, while the sediment taken at the heavily polluted branches of the Pasig River contained as high as 88 mgPb/kg and 310 mgZn/kg. The lead and zinc concentrations in the sediments of Manila Bay - Laguna Lake watershed were compared with those in the mouth of the Tama River, Tokyo, where the faster deposition of coarser natural origin particles and slower deposition of lead and zinc rich anthropogenic particles determined the sediment concentration. The comparison was also made with Hanoi City, Vietnam. In spite of the difference in time when leaded gasoline was prohibited, the difference in the lead concentrations of roadside deposits and sediments was not obvious in the vicinity of these three target cities. This is probably due to dilution by a large amount of suspended solids conveyed by the Pasig River in the case of the Philippines. Storm water runoff containing roadside deposits and discharge of untreated wastewater were identified as factors increasing zinc and lead concentrations of sediments in receiving waters based on the measurements on roadside deposits and the estimation of the contribution of untreated wastewater.

Treatment of Wastewater Containing a Large Amount of Suspended Solids by a Novel Multi-Staged UASB Reactor

Treatment of artificial wastewater containing a large amount of suspended solids comprised of soybean processing waste and pig fodder was studied using a novel multi-staged upflow anaerobic sludge blanket reactor. The reactor consisted of three compartments, each containing a gas solid separator. The wastewater had chemical oxygen demand of approximately 21600 mg l−1, suspended solids of 12800 mg l−1, and an ammonia concentration of 945 mg l−1. A continuous experiment without effluent circulation showed that the multi-staged reactor was not that effective for the treatment of wastewater containing a large amount of suspended solids. However, operation of the reactor with circulation of effluent enabled the reactor to achieve organic removal of 85% and approximately 70% methane conversion at loading rates of between 4.0 to 5.4 kg-chemical oxygen demand per cubic meter per day, meaning that the reactor was more effective when effluent was circulated. Morphological investigation revealed that the crude fiber in the sludge was partially degraded and that it had many small depressions on its surface. Evolved biogas may have become caught in these depressions of the fibers and caused washout of the sludge.

Natural and anthropogenic variations in a channelized water course in Centre of Portugal

The present study took place in the Mondego River, located in the Centre of Portugal. The lower sector of the river (Lower Mondego) is largely man-made due to regularization and rectification of the channel. The objective was to assess the impacts on the aquatic communities (fishes and benthic invertebrates). Fauna inventories were performed in June and September of 2000 and 2001, together with habitat characterization. Three sampling sites were selected in this segment and compared to a reference site located upstream. It is concluded that the presence of structures such as submerged weirs and riprap, promoted the diversity, due to the physical complexity, which they introduced into the system. The dramatic flood peaks that occurred in the winter of 2000/01 also caused substantial changes in the fluvial dynamics and in the habitats: the large amount of suspended solids transported resulted in a riverbed of unstable fine materials, and in a subsequent biological impoverishment. However, both communities displayed a high resilience to these changes; the inter-annual differences being obscured by the seasonal ones on macroinvertebrate communities.

Complete physico-chemical treatment for coke plant effluents

Naturally found coal is converted to coke which is suitable for metallurgical industries. Large quantities of liquid effluents produced contain a large amount of suspended solids, high COD, BOD, phenols, ammonia and other toxic substances which are causing serious pollution problem in the receiving water to which they are discharged. There are a large number of coke plants in the vicinity of Jharia Coal Field (JCF). Characteristics of the effluents have been evaluated. The present effluent treatment systems were found to be inadequate. Physico-chemical treatment has been considered as a suitable option for the treatment of coke plant effluents. Ammonia removal by synthetic zeolite, activated carbon for the removal of bacteria, viruses, refractory organics, etc. were utilized and the results are discussed. A scheme has been proposed for the complete physico-chemical treatment, which can be suitably adopted for the recycling, reuse and safe disposal of the treated effluent. Various unit process and unit operations involved in the treatment system have been discussed. The process may be useful on industrial scale at various sites.

Chemical removal of biomass from waste air biotrickling filters: screening of chemicals of potential interest

A protocol was developed to rapidly assess the efficiency of chemical washing for the removal of excess biomass from biotrickling filters for waste air treatment. Although the experiment was performed on a small scale, conditions were chosen to simulate application in full-scale biotrickling filters. From 18 treatments with different combinations and concentrations of chemicals, only washing with 0.4% (w/v) NaOH, 0.26 and 1.31% (w/v) NaClO and 11.3% (w/v) H 2O 2 resulted in a biomass removal significantly higher than treatment with pure water with wet biomass removal efficiencies of 50.2, 49.2, 77.0 and 69.0%, respectively. Biomass removal by H 2O 2 and NaClO was accompanied by complete loss of activity of unremoved biomass, whereas after treatment with NaOH low residual biological activity was observed. However, treatment with NaOH resulted in generation of relatively large amounts of suspended solids (22.3% of dry biomass removed) and dissolved carbon (65.3% of C-biomass removed). NaClO was found to be the most promising reagent for biomass control in biotrickling filters because of its ability to remove large amounts of biomass and its low cost.

The effects of watercress growing on chalk headwater streams in dorset and hampshire

Chalk stream headwaters are of high value for water supply, amenity, game fishing and fish farming. The water quality implications of modern watercress growing watercress beds are reflected in increasing concentrations of phosphorus and potassium downstream of the beds. Zinc concentrations in both suspended solids emanating from the beds and in sediments downstraam of the watercress farms reach high levels in some cases. Ranunculus plants downstream of the watercress farms show elevated levels of zinc. Large amounts of suspended solids enter the receiving streams from watercress beds and in many cases the stream bed directly downstream of the farms has a high proportion of fine organic sediments derived from the watercress farms.