Compliance of the macrophyte quality index (MaQI) with the WFD (2000/60/EC) and ecological status assessment in transitional areas: The Venice lagoon as study case

Currently, traditional high turbidity water treatment technologies (coagulation–sedimentation–filtration) face issues such as non-compliant effluent quality, sediment compaction, and poor sludge discharge. Meanwhile, membrane filtration technology suffers from severe membrane fouling in high turbidity water treatment. Therefore, the development of green and low-carbon high turbidity water treatment technologies is urgently needed. This study employs microfiltration to directly filter high turbidity water, investigating turbidity, filtration methods, and transmembrane pressure difference to elucidate the mechanisms of mitigating membrane fouling in high turbidity water treatment. The results indicate that both excessively high and low influent turbidity are detrimental to high turbidity water treatment. Low turbidity fails to effectively protect the membrane, exacerbating membrane fouling, while high turbidity leads to excessive cake layer thickness, reducing membrane flux. Therefore, the optimal treatment turbidity must be determined based on the specifications of the experimental setup. In this study, the optimal treatment turbidity is 900 NTU. Under constant pressure conditions, cross-flow filtration effectively controls the thickness of the filter cake layer, mitigates membrane fouling, and maintains a high membrane flux. When the influent turbidity is 900 NTU, the membrane flux recovery rate and filtration flux are 80.14% and 0.9077 m h−1, respectively, with irreversible membrane fouling being only 0.97 × 1010 m−1. At a constant influent turbidity, higher transmembrane pressure difference increases the filtration flux but exacerbates membrane fouling. When the pressure increases from 6.67 kPa to 33.33 kPa, irreversible membrane fouling increases by 27.97%, while the filtration flux increases by 116.91%. At a pressure of 13.33 kPa, although the filtration flux is 56.83% of that at 33.33 kPa, the irreversible membrane fouling is only 62.25%. Therefore, this study identifies 13.33 kPa as the optimal transmembrane pressure difference. The Hermia model revealed that transmembrane pressure difference was the primary factor aggravating membrane fouling. Finally, through dosing FeCl3 as a coagulant for cake layer regulation, the cake layer structure formed at 15 mg per L dosage showed optimal pollutant interception and removal efficiency: humic acid (HA) removal efficiency reached 75.86% in actual water sources with 79.06% flux recovery rate; simulated feed water achieved 77.44% HA removal with 84.31% flux recovery rate. This study aims to provide reference for microfiltration processes in direct treatment of high-turbidity water.

ABSTRACTPrevious studies have demonstrated that the Geostationary Ocean Colour Imager (GOCI) could retrieve sea surface currents accurately in low-moderate turbid coastal waters, based on maximum cross-correlation (MCC) technique. However, its performance in highly turbid waters remains unclear. In this study, the MCC method is used to derive hourly sea surface currents in Hangzhou Bay (HZB) with highly turbid waters from the GOCI data, and its performance is examined by in situ measurements and model simulations. The results show that the GOCI-derived sea surface currents can catch tidal phase variations well, yet the performance of the derived velocity is not as good as the previous studies in low-moderate turbid waters. The reason may be due to the rapid deposition and resuspension processes of suspended particulate matter in high turbidity waters, which contaminate the MCC pattern tracking. The GOCI-derived deposition and resuspension rates can reach up to about 190 and 270 mg l–1 h–1 in HZB, respectively, which demonstrates that the potential of geostationary ocean colour imagery in deriving the suspended particle deposition and resuspension rates.

Objectives: This study was aimed at determining the optimum coagulation dosage in a high turbid kaolin water sample using streaming current detection (SCD) as an alternative to the jar test. Methods: SCD is able to optimize coagulant dosing by titration of negatively charged particles. Kaolin particles were used to mimic highly turbid water ranging from 50 to 600 NTU, and polyaluminum chloride (PAC, 17%) was applied as a titrant and coagulant. The coagulation consisted of rapid stirring (5 min at 140 rpm), reduced stirring (20 min at 70 rpm), and settling (60 min). To confirm the coagulation effect, a jar test was also compared with the SCD titration results. Results: SCD titration of kaolin water samples showed that the dose of PAC increased as the pH rose. However, supernatant turbidity less than 1 NTU after coagulation was not achieved for high turbid water by SCD titration. Instead, a conversion factor was used to calculate the optimum PAC dosage for high turbid water by correlating a jar test result with that from an SCD titration. Using this approach, we were able to successfully achieve less than 1 NTU in treated water. Conclusions: For high turbid water influent in a water treatment plant, particularly during summer, the application of SCD control by applying a conversion factor can be more useful than a jar test due to the rapid calculation of coagulation dosage. Also, the interpolation of converted PAC dose could successfully achieve turbidity in the treated water of less than 1 NTU. This result indicates that an SCD system can be effectively used in a water treatment plant even for high turbid water during the rainy season.

Pristine conditions in transitional water ecosystems are characterized by the dominance of aquatic angiosperms. Aquatic plants consolidate bottoms, prevent erosion, support benthic and fish communities as nursery and food areas, and favour the bird presence. Hence, they may contribute to the achievement of a good ecological status as required by the WFD (2000/60/EC). Their reduction or disappearance is a symptom of environmental deterioration. Over the past few decades, the aquatic angiosperms have shown a significant decrease on a worldwide scale and in some areas of Venice Lagoon (Adriatic Sea), particularly in the central and Northern basins, as a consequence of anthropogenic activities. At present, most of the anthropogenic pressures which caused their decline or disappearance in Venice Lagoon have significantly decreased creating the ecological conditions for a new colonization. In this context, the project SeResto (LIFE12 NAT/IT/000331), funded by the European Commission, aims at restoring the angiosperm meadows in the Northern basin of Venice Lagoon where the natural seed spreading is hampered by the presence of island, tidal marsh barriers and long residence times. The project has two main strengths: i) the widespread transplantations of small angiosperm sods and manual dispersion of rhizomes and seeds and based on a low costs and low impact on donor sites approach, ii) the participation of fishermen and hunters daily living the lagoon for recreational purposes. Thirty-five sites have been selected and in each one 9 sod-bearing plants (diameter: 30 cm), supplied by fish farms where angiosperm meadows are almost natural, have been transplanted. In addition, the plant spreading is enhanced by the dissemination of hundreds of rhizomes, 1500 at minimum in each area during the project period (52 months). In 8 sites, out of the 35, biological and chemico-physical conditions are being monitored monthly during the first and last year and quarterly in the intermediate period. Ecological indices, based on the study of macrophytes, macrobenthic fauna and fish fauna (Biological Quality Elements), as required by the WFD 2000/60/EC, will allow to assess changes in the Ecological Status of the study sites. Preliminary results are encouraging in great part of the selected areas although some difficulties have been recorded in areas with high water turbidity and the presence of thionitrophilous macroalgae, especially Ulvaceae, favoured by the unexpected weather conditions of summer 2014. Information on the restoration effectiveness and the relationship between the angiosperm presence/growth and the environmental conditions can be employed for interventions in other lagoon areas and can be exported in other similar transitional environments.

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

The objective of this study is to assess the risk of insufficient water supply posed by high-turbidity water. Several phenomena can pose risks to the sufficiency of a water supply; this study concerns risks to water treatment plants from particular properties of rainfall and raw water turbidity. High-turbidity water can impede water treatment plant operations; rainfall properties can influence the degree of soil erosion. Thus, water turbidity relates to rainfall characteristics. Exceedance probabilities are presented for different rainfall intensities and turbidities of water. When the turbidity of raw water is higher than 5,000NTU, it can cause operational problems for a water treatment plant. Calculations show that the turbidity of raw water at the Ban-Sin water treatment plant will be higher than 5,000NTU if the rainfall intensity is larger than 165mm/day. The exceedance probability of high turbidity (turbidity >5,000NTU) in the Ban-Sin water treatment plant is larger than 10%. When any water treatment plant cannot work regularly, its ability to supply water to its customers is at risk.

Experiments were conducted to determine the performance of larval walleye (Stizostedion vitreum) reared in clear, 0.2 nephelometric turbidity units (NTU), and turbid water, 20 or 50 NTU, on formulated feed. Larvae were cultured for 21, 28, or 30 days posthatch in four trials with 3 or 4 replicate tanks per treatment (clear and turbid) in each trial. Duration of each trial was dependent on the arrival of newly hatched larvae for subsequent trials. The desired turbidity levels were obtained by pumping a solution of clay to the culture tanks every 20 (trial 1) or 30 min (trials 2, 3 and 4). Other than turbidity, all environmental conditions (dissolved oxygen, alkalinity, pH, total ammonia, un‐ionized ammonia, nitrate, nitrite, chloride, and hardness) and rearing techniques were similar between treatments. Larvae were stocked at 20/L and fed formulated feed (Fry Feed Kyowa B‐400 and B‐700) every 3 to 7 min, 24 hours per day. Significant differences in feed acceptance and total length between larvae in the clear and turbid water were observed as early as 7d posthatch. Larvae in turbid water began eating the formulated diet one to two days before those in clear water. In all trials, survival, final length, and final weight of larvae reared in water of high turbidity were significantly greater than for larvae reared in clear water. Mean survival (±SE) for all four trials was 27.7 ± 5.6% in high turbidity water and 5.9 ± 1.3% in clear water. At the end of the trials, mean total length of the larvae reared in turbid water was at least 3.2mm (15%) greater than that in the clear water. Mean final weight of the larvae from turbid water was 2.25 times greater than larvae from clear water over the four trials. In two of the four trials, gas bladder inflation (GBI) of larvae reared in high turbidity was significantly greater than for fish reared in clear water, but the difference in GBI was not significant in the other two trials. In this study, performance of larval walleye was greatly enhanced by water with a turbidity of at least IS NTU.

The present study deals with the suitability of the coagulation-flocculation process using Moringa oleifera seed as an environment-friendly natural coagulant and antimicrobial agent for clarification of turbid water. It has higher efficiency up to 99.99% for higher turbid water. But for low turbid water the removal efficiency is comparatively less. Almost all the industrial effluents are of high turbidity and the drinking water sources are of low or medium turbidity levels. The available literature recommended extraction of active components of MO seed powder by oil extraction, salt extraction, micro filtration and ultra filtration techniques for improving the removal efficiency in low turbid water. The performance of crude extract prepared by salt extraction of MO powder after oil extraction improves the removal efficiency due to the isolation of active components. The crude extract of MO treated water after coagulation and flocculation directly passed through rapid sand filters without sedimentation results greater turbidity removal efficiency up to 99% for low turbid water. In the case of medium or high turbid water necessary sedimentation/floatation steps will reduce the filter clogging. This technology is helpful for treating contaminated turbid water with low cost, lesser time and easiness. Also unskilled persons can operate this system effectively.

The global methane (CH4) emission of lakes is estimated at between 6 and 16% of total natural CH4 emissions. However, these values have a high uncertainty due to the wide variety of lakes with important differences in their morphological, biological, and physicochemical parameters and the relatively scarse data from southern mid-latitude lakes. For these reasons, we studied CH4 fluxes and CH4 dissolved in water in a typical shallow lake in the Pampean Wetland, Argentina, during four periods of consecutive years (April 2011-March 2015) preceded by different rainfall conditions. Other water physicochemical parameters were measured and meteorological data were reported. We identified three different states of the lake throughout the study as the result of the irregular alternation between high and low rainfall periods, with similar water temperature values but with important variations in dissolved oxygen, chemical oxygen demand, water turbidity, electric conductivity, and water level. As a consequence, marked seasonal and interannual variations occurred in CH4 dissolved in water and CH4 fluxes from the lake. These temporal variations were best reflected by water temperature and depth of the Secchi disk, as a water turbidity estimation, which had a significant double correlation with CH4 dissolved in water. The mean CH4 fluxes values were 0.22 and 4.09mg/m2/h for periods with low and high water turbidity, respectively. This work suggests that water temperature and turbidity measurements could serve as indicator parameters of the state of the lake and, therefore, of its behavior as either a CH4 source or sink.

Effects of pre-chlorination on ultrafiltration process in directly treating seasonal high-turbidity surface water: Membrane fouling control and shock load resisting

This paper presents the use of Artificial neural networks (ANN) as a viable means of predicting water turbidity. This was based on the experimental data collected from a physical settling basin model, which was set up at the Civil Engineering Department in Jomo Kenyatta University of Agriculture and Technology. High turbid water has contributed to low water application efficiencies in Kiriku-Kiende project. Lack of adequate detention time for sediment settlement in the basin has resulted to sediment being released in to irrigation network. To have an optimal settling basin design, then prediction of hourly water turbidity is paramount. The turbidity of the water at the inlet and outlet of the settling basin in Kiriku-Kiende irrigation project in Embu Sub-County was determined. Samples collected were analyzed and more data collected from the physical model. Two variables (flow rate and settling Time) were used in this analysis as input variables and water turbidity as output variable. Four hundred ANN models were developed out of which four best models were used to identify the most effective model. Sensitivity analysis (SA) was carried out by using leave one out approach to assess the effect of the parameters of ANN on the prediction of turbidity of raw water in a water-settling basin. The ANNs developed were successfully trained and tested using the experimental data sets and the performance of ANNs models were determined using various statistical measures. Results show that using the five statistical measures, the ANN-PN204 with a nomenclature of 1-9-1 gave the best prediction for water turbidity. This demonstrates that ANN is capable of modeling hourly turbidity levels with good accuracy when proper variables, their previous time step on sediment settling and their discharges are used as inputs of networks.

The physical efficiency of a number of coagulants alum, ferrous sulfate and ferric chloride in addition to coagulation organic aids like poly ethylene glycol (PEG), polyacrylamide (PAM) and non-organic like Bentonite in removing turbidity of raw water in its high and low turbidity 850 NTU, 52 NTU respectively was studied. The optimal dose was determined for each of them that give less turbidity and higher removal percentage. The results declared that alum was the best removal for both high and low turbidity which reach 99.59% and 97.54% respectively. Ferrous sulfate, Ferric chloride, and calcium oxide were the best for removing turbidity of high turbid raw water 98.26, 98.66 and 92.18% respectively. For coagulation aids, the best of them was (PAM) for both raw water turbidity, while (PEG) record good removal percentage for low turbidity that reach 89.81%. Bentonite give lowest removal percentage for low turbidity 31.92%, on contrast with high turbidity 74%. used of Bentonite with alum improved the removal to 88.92%.

Drinking water for residents who live in flood area is the concern of the government and environmental management. Using natural coagulants to transform flood water into potable water in order to reduce the number of chemical coagulants (aluminum salt) that have a negative impact on human health. The results of the flocculation procedure using agricultural residue extracts, dragon fruit branches (DFBE) and avocado seeds (ASE), did not meet the Vietnamese standard for the provision of potable water. Using DFBE and ASE as coagulation aides improves the flocculation efficacy of alum in high turbid water (150 to 175 NTU) and low turbid water (20 to 30 NTU). The ratio of ASE to Alum was determined to be 1/6 for high-turbidity water and 0.2 for low-turbidity water. The ratio of DFBE/Alum was determined to be greater than 1/3 for high turbidity water and less than 0.2 for low turbidity water. This ratio is also evaluated for a portable, simple, and user-friendly water filter that is suitable for flood-prone residents. Combining natural coagulation aides with Alum in water flocculation satisfies the Vietnamese standard with DFBE for sources with high turbidity and ASE for sources with low turbidity. This demonstrates the utility of natural coagulation aids derived from agricultural residues for water purification in flooded areas.

High turbid water in the river has been one of the major concerns to the downstream residence. During heavy local rainfall, high turbid water occurs in many countries located in the Asian monsoon climate region. The Andong and the Imha reservoir, two adjacent multipurpose dams, located in the upstream of the Nakdong River in Korea have suffered from severe turbid water problem. This study applied hydrodynamic water quality model CE-Qual-Riv1 to simulate turbidity propagation in downstream coupled with long-term watershed hydrologic model SWAT to consider contributions of tributaries. The outputs of runoff and suspended sediment in tributaries are incorporated into the input data necessary for the hydrodynamic water quality model. The simulation focused on the joint dam operation to minimize the negative impact of high turbid water in downstream river. Simulated turbidity in downstream shows a good agreement with the observed data, and the approach proposed in this study is applicable for establishing a sound turbid water management in downstream of the reservoir.

We review approaches and tools currently used in Nordic countries (Denmark, Finland, Norway and Sweden) for integrated assessment of 'ecological status' sensu the EU Water Framework Directive as well as assessment of 'eutrophication status' in coastal and marine waters. Integration principles for combining indicators within biological quality elements (BQEs) and combining BQEs into a final-integrated assessment are discussed. Specific focus has been put on combining different types of information into indices, since several methods are currently employed. As a consequence of the variety of methods used, comparisons across both BQEs and water categories (river, lakes and coastal waters) can be difficult. Based on our analyses, we conclude that some principles and methods for integration can be critical and that a harmonised approach should be developed. Further, we conclude that the integration principles applied within BQEs are critical and in need of harmonisation if we want a better understanding of potential transition in ecological status between surface water types, e.g. when riverine water enters a downstream lake or coastal water body.