Analysing the role of Fe (II) on flocculation of sand-clay mixtures under estuarine mixing.

Estuaries are fragile environment that are most affected by climate change. One of the major consequences of climate change on estuarine processes is the enhancement in salt intrusion leading to higher salinity values. This has several implications on the estuarine sediment dynamics. Of the various factors that affect the flocculation of cohesive sediments, salinity and turbulence have been recognized as to have great significance. Many of the estuaries are contaminated with heavy metals, of which, the concentration of Iron (Fe (II)) are generally on the higher range. However, the influence of Fe (II) on the flocculation of cohesive sediments at various estuarine mixing conditions is not well known. The present study investigated the influence of Fe (II) on the flocculation of kaolin at various concentration of Fe (II), salinity and turbulence shear. The results indicated that Fe (II) and salinity have a positive influence on kaolin flocculation. The increase in turbulence shear caused an initial increase and then a decrease in floc size. In case of sand-clay mixtures, that are observed in mixed sediment estuarine environments, a reduction in the floc size was observed, which is attributed to the breakage of flocs induced by the shear of sand. Breakage coefficient, which is a measure of break-up of flocs, is generally adopted as 0.5 assuming binary breakage. The present study revealed that the breakage coefficient can take values from 0 to 1 and is a direct function of Fe (II) and salinity and an inverse function of turbulence and sand concentration. Thus, a new model for breakage coefficient with the influencing parameters has been proposed, which is an improvement of existing model that is expressed in terms of turbulence alone. Sensitivity analysis showed that the proposed model can very well predict the breakage coefficient of Fe (II) - kaolin flocs. Thus, the model can quantify the breakage coefficient of flocs in estuaries contaminated with Fe (II) that is a vital parameter for population balance models.

Analysing the performance of the NARX model for forecasting the water level in the Chikugo River estuary, Japan.

Estuaries are dynamic environments which are driven by various natural processes like river discharge, tides, waves, influx of saline water and sediments, etc. These ecosystems are the most sensitive to sea level rise and fluctuations in river discharge associated with climate change. A direct response of sea level rise and river discharge can be observed in the water level of estuaries. However, existing models have not considered these parameters for forecasting water level. This paper focuses on developing a water level forecast model for the Chikugo River estuary in Japan using Nonlinear Autoregressive with Exogenous inputs (NARX Model). NARX neural network was used to do the one-step-ahead prediction of water level considering the various parameters that can very well be influenced by climate change: previous water level, river discharge, and salinity. Accordingly, three models were developed: (i) Model I considering previous water level; (ii) Model II additionally considering river discharge; and (iii) Model III additionally considering salinity. All the models showed appreciable performance in forecasting the water level. Model III had the best correlation with the water level with a cross-correlation value of 0.6030, while the river discharge had only a cross-correlation of 0.1113 indicating that the Chikugo River estuary is tide-dominated. The model was trained using different combinations of available data - previous water level, river discharge, and salinity. Cross-correlation results showed a better correlation between water level and salinity than various other combinations trained. Therefore, tidal intrusion influences the water level in the estuary, thereby depicting that sea level rise can affect the water level, and its influence can be well predicted by the developed model. The water level significantly affects the flora and fauna and the predictability of future estuarine floods can help in taking necessary mitigation strategies.

Implications of solid waste dumps on the microplastic abundance in groundwater in Kollam, India.

Water pollution caused by microplastics has garnered increasing attention in recent years due to its potential ecological and human health risks. However, there are very limited studies and a general lack of consensus regarding the presence and negative impacts of microplastics in groundwater. Due to their small size, microplastics can easily be transported at surface as well as subsurface levels, potentially reaching the groundwater table and contaminating the groundwater system This contamination is expected to occur more rapidly in landfill areas and other locations where plastic waste is dumped. In this study, we examined well water samples collected from areas near various dumping sites to assess the abundance and characteristics of microplastics. An average of 12 items/L of microplastics were found in groundwater wells near eight dumping sites in Kollam Corporation. The predominant shape of microplastics in the groundwater samples was fibres, followed by flakes, with black being the predominant colour. The areal extent of solid waste dumping was observed to have an influence on the abundance of microplastics. Additionally, the pH of groundwater near heavy dumping sites was found to be in the acidic range, indicating the intrusion of leachate from dumps into groundwater. The study revealed that the leachate from solid waste dumps is the primary source of microplastics in groundwater. Furthermore, a risk assessment of the microplastic pollution was carried out using an index namely Microplastic Pollution Index and the areas of high risks were identified. The locations having heavy solid waste dumping and those near coastal areas were observed to be at high risk, thereby indicating that both the leachate from dumps and sea water intrusion can cause higher microplastic pollution risk in the groundwater system. The findings of this study are expected to support managers in formulating and implementing effective solid waste management plans to mitigate microplastic pollution in the groundwater system.

Effect of preventive measures in the containment of SARS-CoV-2 epidemic: a comparative study.

From the time when the first cases of COVID-19 were reported in Wuhan City, China, in December 2019, strict regulations are being implemented by policy makers to contain the spread of the virus. The measures taken in different countries spanned from complete isolation and lockdown to different degrees of restrictions to people's movement, contact between people, hygiene and sanitation. Accordingly, the success in containing the virus also differed. Italy was one among the worst-affected countries in the world despite the lockdown measures adopted. A combination of lockdown and Level-3 State of Emergency measures were adopted in Portugal and South Africa, which helped to delay and flatten the epidemic curve. The timely application of Level-3 State of Emergency in Mozambique resulted in recording low infection rates. Above all the tripod, orderly movement of people, social distance and hygiene and sanitation is the keystone measure to prevent spread of the virus. However, for successful outcome, the measures have to be tailored to the local context.

Coagulation studies on photodegraded and photocatalytically degraded polystyrene microplastics using polyaluminium chloride.

Microplastics are ubiquitous persistent emerging contaminants, and its presence has been detected even in the most pristine and fragile ecosystems. Advanced oxidation processes are one of the novel degradation technologies used for the elimination of microplastics from the environment. In this study, the effect of ultraviolet C (UV-C, 253.7 nm) and ultraviolet A (UV-A, 365 nm) irradiations on polystyrene (PS) microplastic properties in the presence and absence of titanium dioxide were studied along with their coagulation performances using polyaluminium chloride (PAC). The effects of solar irradiation on the chemical properties of microplastics in aqueous and dry conditions were also investigated. PS microplastics (1.5 g) in three size ranges, 300-150 µm, 150-75 µm, and <75 µm were used during this experiment. After 45 days of irradiation, samples showed discolouration, brittleness, and loss of hydrophobicity. Images obtained from scanning electron microscope revealed smoothening and melting of PS surfaces upon UV exposure. Attenuated total reflectance- Fourier transform infrared spectroscopy and X-ray photon spectroscopy of photoaged samples revealed chemical alterations, bond cleavage and formation of oxygenated functional groups on microplastic surfaces. PAC coagulation of samples before and after UV irradiation showed drastic differences in removal efficiencies, with UV-C irradiated microplastics exhibiting maximum efficiency. Large sized and photocatalytically degraded microplastics showed better removal efficiencies than small sized particles. The 300-150 µm sized PS microplastic, degraded photo catalytically under UV-C irradiation showed approximately 99 % removal efficiency, while PS < 75 µm photodegraded under UV-A irradiation showed only 74.2 % removal efficiency.

A correlation-regression model for the physicochemical parameters of the groundwater in Coimbatore city, India.

The textile hub of Coimbatore city is facing a serious water pollution problem, both for surface water and groundwater. Industrial and domestic waste is continuously discharged into surface water bodies, resulting in the degradation of groundwater quality. In order to assess the quality of groundwater, the Singanallur area was selected for the present study. The quality of groundwater is worse in this area and the physicochemical parameters exceed the permissible limits of the Indian drinking water standards. The water type of the study area was predominantly NaCl and MgCl. A statistical analysis was carried out to understand the linear relation between the best correlated parameters. The relationship for different parameters for the study area was analysed for two seasons, pre-monsoon and post-monsoon, because the water quality varies widely seasonally. The study showed that there is a good and equal correlation between total hardness and calcium, total hardness and magnesium, and calcium and magnesium in both time periods. The relationship can be utilized to determine the value of calcium and magnesium when the value of total hardness is known for the study area. Cluster analysis was performed to obtain a dendrogram for the study area, from which the source of pollution was identified for different regions.