Browsing by Author "Sewwandi, B. G. N."

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Assessing the relationship between water quality parameters and toxic cyanobacterial abundance in a hospital wastewater treatment plant
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Bandara, W. M. J. Y.; Sewwandi, B. G. N.
Cyanobacteria are a group of prokaryotes that thrive in various aquatic environments under favourable conditions such as high levels of nutrients, optimal water temperature, and light. The presence of cyanobacteria in wastewater treatment plants (WWTPs) is concerning, as certain species can produce toxins, posing significant health and environmental problems. Understanding the conditions that promote the growth of cyanobacteria in WWTPs is crucial for developing strategies to prevent or minimise their proliferation. Therefore, this study assesses cyanobacterial abundance with different water quality parameters at a WWTP in Matara District, Sri Lanka, which treats hospital wastewater generated from both black water and grey water. The aim of the study was to identify both toxic and non-toxic cyanobacteria, quantify their abundance, and analyse the relationship between toxic cyanobacterial abundance and various water quality parameters. Wastewater samples were collected from three sampling sites (Site 1- the sedimentation tank; Site 2 - post-chlorination tank; and Site 3 - the discharge field) in the WWTP for five months. Water temperature, pH, dissolved oxygen, total dissolved solids, salinity, electrical conductivity, total suspended solids, nitrate, and phosphate were analysed using standard protocols. Cyanobacteria cells were collected using a plankton net, identified with identification keys, and enumerated using the Sedgewick-Rafter counting method. Water quality parameters and cyanobacterial abundance were measured in triplicate at each sampling site. The relationship between the abundance of cyanobacterial species and water quality parameters was determined using Pearson’s correlation test in Minitab 19.0. Five toxin-producing cyanobacterial species (Oscillatoria sp., Phormidium sp., Limnothrix sp., Pseudanabaena sp., and Cylindrospermopsis sp.) and one non-toxic species (Spirulina sp.) were identified, with Phormidium sp. as the most abundant. The identified species showed varying correlations with water quality parameters. The abundance of Oscillatoria sp., Phormidium sp., Limnothrix sp., and Pseudanabaena sp. showed a strong positive correlation with total dissolved solids, electrical conductivity, and phosphate, indicating they thrive in nutrient-rich environments with abundant dissolved salts and phosphate. Phormidium sp. also showed a positive correlation with dissolved oxygen and nitrate, while Cylindrospermopsis sp. did not show any significant correlation with any parameter, indicating its growth was influenced by other factors. No cyanobacterial species showed a significant correlation with total suspended solids. Limnothrix sp. abundance correlated positively with water temperature, whereas Oscillatoria sp. and Phormidium sp. showed a negative correlation with water temperature. This study highlights that the WWTP is a potential source of toxic cyanobacteria, with water quality parameters such as water temperature, electrical conductivity, total dissolved solids, and phosphate significantly influencing their growth. Hence, it is crucial to monitor and manage these water quality parameters to control the harmful cyanobacterial proliferation in WWTPs. Future research should include additional water quality parameters to gain a more comprehensive understanding of the factors affecting cyanobacterial growth in WWTPs.
Drinking water treatment plant sludge as a potential adsorbent for the removal of Cadmium in wastewater
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Rajakaruna, R. M. A. S. D.; Sewwandi, B. G. N.
Water pollution by heavy metals is a critical environmental issue that causes the deterioration of both human and ecosystem health. Cadmium (Cd2+) is a heavy metal that is non-biodegradable and bioaccumulated through food chains. It also acts as a severe human carcinogen. Adsorption is an effective wastewater treatment method for removing heavy metals from wastewater which is limited due to the high cost of conventional adsorbents. In Sri Lanka, drinking water treatment plant sludge is being produced in large quantities and disposed on landfills without proper usage and exacerbating solid waste problems. The present study investigated the potential of using drinking water treatment plant sludge for the removal of Cd2+ by adsorption from wastewater. The effect of pH, initial Cd2+ concentration, and contact time on adsorption of Cd2+ onto drinking water treatment plant sludge was examined. Adsorption isotherm studies and kinetic studies were carried out to describe the adsorption mechanism of Cd2+ onto drinking water treatment plant sludge. The Langmuir and Freundlich isotherm models were used for isotherm studies. The pseudo first-order and pseudo second-order models were used in kinetic studies. The experiments on effect of pH on adsorption of Cd2+ in the range of pH 3 - 8 showed that adsorption is maximum when medium is basic (pH 7-8). The experiments on effect of initial Cd2+ concentration on adsorption showed that with the increase in initial Cd2+ concentration (2.5 – 100 mg L-1), the adsorption capacity of drinking water treatment plant sludge increased reaching to a maximum adsorption capacity of 14.6 mg g-1. Cd2+ was well fitted to the Langmuir isotherm model indicating monolayer adsorption on a homogeneous adsorbent surface with identical active sites. The experiments on effect of contact time on adsorption showed that adsorption of Cd2+ onto drinking water treatment plant sludge increased with the increase in contact time and then reached the equilibrium within 4 hours of contact time. The kinetic studies showed that adsorption of Cd2+ onto drinking water treatment plant sludge was well described by both pseudo first-order model (R2= 0.9633) and pseudo second-order model (R2=0.9334) indicating that both chemical and physical adsorption contribute to the adsorption of Cd2+ onto drinking water treatment plant sludge. Therefore, this study proves that drinking water treatment plant sludge is an effective, low-cost adsorbent for removing Cd2+ in wastewater. Therefore, future studies are required to be conducted on the field scale application of drinking water treatment plant sludge which will be beneficial for cost-effective wastewater treatment, especially in developing countries.
The occurrence of extreme hydrological events in Colombo district and their impacts
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Rathnayake, B. N.; Premarathna, A. D. A. P.; Hewawasam, H.G.T.D.; Magisa, T.; Sewwandi, B. G. N.
Extreme hydrological events in the Colombo district of Sri Lanka were assessed using the Standardized Precipitation Index (SPI) and the Rainfall Anomaly Index (RAI) and possible adaptation measures to reduce the impacts in the affected areas were proposed as objectives in the research. The analysis encompasses rainfall data from 1989 to 2020 and focuses on four meteorological stations within the Colombo district: Colombo, Ratmalana, Angoda, and Homagama. Rainfall data and impact data were obtained from the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) website and the Desinventar website, respectively. RStudio and Microsoft Excel were used for the calculations. The daily rainfall data and the monthly rainfall data were used to calculate the Rainfall Anomaly Index (RAI), and the Standard Precipitation Index (SPI), respectively. The SPI for a three-month period (SPI3) was employed to analyze flood and drought conditions. The RAI serves as a complementary tool to assess wet and dry events. The findings from the SPI analysis indicate several notable periods of extreme wetness, including November and December 1997, March to May 2008, January, February, September, and October 2011, and May, June, and July 2016. These periods pose a high risk of flooding in the Colombo district, potentially leading to significant environmental impacts. The RAI index confirms the occurrence of extremely wet events in October 1997 and May 2016. Furthermore, the research identifies drought periods, particularly in 1992, 1994, 2012, and 2016, using SPI calculations. However, the absence of substantial drought impacts in the Colombo district, which is located within the Wet Zone of Sri Lanka, indicates that the local population may not be severely affected by the dry events. Deaths, injuries, property damages and destructions, and destruction of crops are some of the impacts that people are directly and indirectly affected due to flood. The findings of this research highlight the effectiveness of the SPI and RAI indices in assessing extreme hydrological events. It is fair to conclude that floods have occurred in 1999, 2006, 2008, 2009, 2010, 2011, 2016, and 2019 because impact statistics and identified wet periods from calculations are compatible with each other in those years. It also suggests several measures to reduce damage from flooding, such as improving drainage infrastructure, implementing rainwater harvesting systems, and maintaining clean streets and sidewalks. By understanding the patterns and impacts of extreme wetness and dryness, appropriate adaptation measures can be implemented to mitigate the environmental and societal consequences of climate change in the region.
Sustainable Approaches forWastewater Treatment: An Analysis of Sludge-Based Materials for Heavy Metal Removal from Wastewater by Adsorption
(2023) Rajakaruna, R. M. A. S. Dhananjana; Sewwandi, B. G. N.; Najim, Mohamed M. M.; Baig, Mirza Barjees; Alotaibi, Bader Alhafi; Traore, Abou
A comprehensive study incorporating results from different findings related to heavy metal removals from wastewater using sludge as an absorbent will assist researchers and practitioners in planning wastewater treatment processes. This study aims to provide a comprehensive foundation on the potential of using sludge-based materials to remove heavy metals from wastewater based on recent studies. The physicochemical properties of sludge and the nature of metal ions have significantly contributed to the adsorption of heavy metals into sludge-based materials. Many researchers found the effects of pH, temperature, initial heavy metal concentrations, contact time, and adsorbent dose on the adsorption characteristics of heavy metals into sludge-based materials. Isotherm, kinetic, and thermodynamic studies have explained the mechanism of heavy metal adsorption by sludge-based materials. The effectiveness of regeneration of sludge-based adsorbents has been investigated by some researchers, providing an environmentally friendly solution to remove heavy metals from wastewater. It was found that less attention has been paid to metal recovery and recycling of sludge-based adsorbents, which indicates the need for future studies to enhance the reusability of sludge in wastewater treatment. Moreover, many studies have been conducted as lab-scale experiments on heavy metal adsorption from aqueous solutions using sludge-based adsorbents, leaving a research gap for future studies to focus on the removal of heavy metals from actual wastewater at field scale.