ICSBE 2020

Table of Contents

1. Water Treatment and Pollution Control

   1. Frontmatter

   2. A Model for Management of Sivalakulama Tank Cascade System

      K. A. C. K. H. Gunasekara, K. D. W. Nandalal, U. S. Imbulana

      Abstract

      From ancient times Sri Lanka was considered as a water rich country. But recently people, specially living in dry zone, are facing many issues without having adequate amount of water resources for their daily use. Many water management practices consider availability of water resources and demand for water only without taking interactions between them. For management of a tank cascade system it is important to incorporate dynamic interactions among different sectors that comprise a water resource system, such as, physical components (tanks, canals, etc.), economical aspect, agricultural sector, etc. A model was developed for the optimal management of Sivalakulama cascade system, which comprises of 20 tanks and situated in Galenbindunuwewa DS division in Anuradhapura district. The study was limited to a sub-system of the Sivalakulama tank cascade system comprising 10 tanks, which are connected in series and parallel. The model is based on System Dynamics Modeling approach, which enables incorporation of different sectors such as physical aspects, economic sector and agriculture sector. The model was calibrated using observed water levels in three tanks in the sub system. The model showed the reliability of each tank in the system in supplying the Yala and Maha irrigation requirements and the possibility to study the impact of having other field crops requiring less water.

   3. Study of Coagulant Dosage Variation According to the Design G Value of Coagulation and Flocculation Processes in a Water Treatment Plant

      R. M. M. C. Dassanayake, N. S. Jayasinghe, A. P. K. Wickramage, K. B. K. D. K. Kandeyaya, W. B. M. L. I. Weerasekara, S. K. Weragoda

      Abstract

      There are several treatment processes in conventional water treatment plants (WTP). The coagulation and flocculation processes (CFP) are conducted to remove the turbidity of raw water (RW). CFP has become critical in the water treatment process due to impacts from overdosing and underdosing of coagulant on the public health and treatment efficiency. Most of the WTPs in Sri Lanka perform the jar test considering only the RW pH and turbidity in order to determine the optimum coagulant dose. However, there is no concern over the velocity gradient (G) value in WTP design when conducting the jar test. Therefore, this study was conducted to compare the optimum coagulant doses obtained from a general jar test method (M1) and a WTP design G value considered method (M2) for the same RW sample. The rapid mixing, slow mixing speeds, and settling times for M1; 2 min in 150 rpm, 20 min in 30 rpm, and 30 min respectively. The rapid mixing, slow mixing speeds, and settling times for M2; 3 min in 71 rpm, 30 min in 40 rpm, and 30 min respectively. Two trials were carried out for each method using Poly aluminium chloride as the coagulant (PAC). The optimum coagulant dose of M1 is 0.62 mg/L in trial one and 3.95 mg/L in trial two. The optimum coagulant dose of M2 is 0.70 mg/L in trial one and 4.05 mg/L in trial two. Hence the optimum coagulant dose of M1 is greater than that of M2. Therefore, it is recommended to consider the design G value of the WTP to obtain a more accurate optimum coagulant dose.

   4. Clarification Efficiency of Plate Settlers Analyzed by CFD Modelling

      W. M. L. K. Abeyratne, S. B. Weerakoon, N. G. P. B. Neluwala

      Abstract

      Sedimentation is a crucial process of water treatment facilities, where the gravity settling of suspended solids occur. The sedimentation tanks in conventional water treatment plants occupy a large area and consume up to 30% of the total construction cost. The use of plate settlers is an economical technology which increase the efficiency and capacity of sedimentation tanks. This study investigated the effectiveness of plate settlers compared to the plain settlers using the rectangular tanks in a water treatment plant. The ANSYS CRX 17.2 software was used as the CFD tool for meshing and calculating the results. Four cases including a plain settler and three plate settlers with plates installed at 3, 1 and 0.5 m spacing were analyzed in this study for the comparison of performances. The length, thickness and inclination angle of plates were kept constant. Installing plates reduced the large vortex zones and created a more up-flow distribution of streamlines allowing particles to settle easily compared to the plain settling tank. The efficiency of sedimentation was improved by increasing the number of plates in plate settlers. This is due to the increasing effective settling area of tanks. The inclined plates had different effects on the suspended solid removal efficiency in solids with different diameters, which might be difficult to characterize by experimental studies. The sedimentation efficiency of the particles with larger diameters have higher efficiency than the small diameter particles. The Computational Fluid Dynamics modelling can be used to accurately predict the suspended particle removal efficiency in plain settling and plate settling tanks, and therefore can be used to optimize their design.

   5. Removal of Fluoride in Water and Wastewater Using Electrodialysis/Electrodialysis Reverse Process: A Review

      T. P. Malalagama, T. Binghui, K. B. S. N. Jinadasa, D. R. Samaraweera, F. Yang

      Abstract

      Fluoride enriched water has a profound effect on human health. Therefore, maximum allowable fluoride concentration in drinking water is limited to 1.5 mg/L in World Health Organization (WHO) standards. Not only drinking water, but also several types of wastewater are contaminated with fluoride. Therefore, untreated fluoride enriched wastewater can be created serious issues on environmental health and aquatic lives. Many methods have been used to remove excessive fluoride present in water and wastewater such as Adsorption, ion exchange, chemical precipitation, electrodialysis, electrocoagulation, reverse osmosis, nanofiltration etc. Many organizations and industries focused on their interest on electrodialysis process to remove excessive fluoride in water due to simplicity and low operational cost of the process. Whilst there are a number of reviews that have attempted to optimize ED performance for fluoride removal from water/wastewater, ED technology still has limitations involving scaling, membrane fouling, and permselectivity. In this paper, an extensive review of current studies on the process, principles, and setups of ED technology on fluoride removal is given to deliver a comprehensive collection of all the main findings published so far. Finally economic feasibility also described.

   6. Development of an Adsorbent Material for Removing Natural Organic Materials from Water

      H. K. T. M. Herath, M. K. D. D. S. Meegoda, K. G. N. Nanayakkara

      Abstract

      Humic acid (HA) is the most prevailing component of Humic substances in total organic carbon (TOC) which is the main fraction of natural organic matter (NOM) in water sources. Studies in many regions of Sri Lanka showed that the TOC levels are higher than the desirable level of 2 mg/l. Even though the presence of NOM higher than the tolerable level may affect the quality of water, there is no treatment procedure carried out other than the conventional treatment process. Due to the low efficiency of conventional treatment processes in removing NOM, adsorption is proposed as a cost-effective, efficient, and simple technique that overcomes the drawbacks of other techniques. Chitosan is an excellent natural, biodegradable, and abundant adsorbent material. In this research, raw chitosan beads and chitosan/hydroxyapatite (Hap) composite beads made with chitosan powder, eggshells, and poly-ethylene–glycol (PEG), were used to investigate and compare the removal efficiencies of the adsorbent and performance in removing HA. A zero-point charge (pH_zpc) study was conducted to characterize the adsorbent materials. Further, the behaviour of the materials with humic acid at neutral pH was investigated using the effect of the contact time, the adsorbent dosage on the removal efficiencies of raw and modified chitosan adsorbents. Moreover, Kinetic studies and isotherm studies were conducted for adsorbents by using a synthetic wastewater sample at neutral pH. A removal efficiency of 74, 60%, and removal capacity of 1.37 mg/g, 1.11 mg/g was achieved for raw and modified chitosan materials, respectively.

   7. Synthesis of Zeolites from Rice Husk Ash for Removal of Dyes in Wastewater

      M. C. Welagedara, D. G. G. P. Karunarathne, A. Manipura

      Abstract

      Rice husk is an agricultural waste which contains high amount of silica. This silica can be extracted from rice husk by burning at higher temperatures. Therefore, rice husk ash (RHA) can be used as the silica source when synthesizing zeolites. Zeolites are three-dimensional microporous aluminosilicate which are widely used in industrial applications. In this study, potential of using zeolites synthesized from RHA for the adsorption of dye in polluted water was tested. RHA was obtained by burning rice husk at 700 °C and zeolites were synthesized by using RHA and sodium aluminate in alkali media. Synthesized zeolites were yielded as 75.4% (w/w) and classified as Zeolite A (LTA) based on the XRD analysis. Adsorption capacity and adsorption rate of synthesized zeolites were tested for Methylene Blue (MB) solution through equilibrium and kinetic studies. The adsorption of MB onto RHA was also studied for comparison. Langmuir model and Pseudo second order kinetic model were well fitted with the experimental data with higher coefficient of determination. The monolayer adsorption capacities of the synthesized zeolites and RHA were 16.89 mg/g, 17.42 mg/g and 12.19 mg/g respectively. Synthesized zeolites show higher adsorption capacity than the RHA revealing that Zeolite A synthesized using RHA can use to adsorb dye in polluted water. This study also can be extended to obtain the best zeolite which has a greater adsorption capacity by adjusting synthesis conditions.

   8. A Comparison Study of Removing Rhodamine B from Wastewater by Nitric Acid Functionalized Rice Husk, Coconut Husk and Synthetic Porous Carbon

      Charitha Thambiliyagodage, Sulakshini Ranchagoda, Shanitha Mirihana

      Abstract

      The present comparison study describes the effectiveness of different carbon based adsorbents for the successful removal of Rhodamine B (RhB) from wastewater. Selected adsorbents are rice husk (RH) and coconut husk (CH) as the agricultural waste products and porous carbon synthesized by resorcinol formaldehyde polymerization via sol gel method (SC). Such porous materials were functionalized using nitric acid. Morphology of the materials were examined by the Scanning electron microscope (SEM) and the surface functionalities were determined by FT-IR spectroscopy. Adsorption of all functionalized and raw porous materials was determined by varying parameters such as pH of the medium, adsorbent dosage, dye concentration and contact time. Generally, all the selected adsorbents were capable of removing RhB and functionalized adsorbents were much effective than the untreated adsorbents. Among all the adsorbents selected for the comparison, functionalized rice husk (FRH) showed highest activity compared to other adsorbents as it consists of both carbon and silica, while others have only carbon. Interestingly adsorbents prepared by natural waste materials were more effective than the synthetic carbon suggesting that these tested materials could be used in novel water purification systems to decontaminate waste and drinking water.

   9. Modified Sawdust in Adsorption of Heavy Metals from Textile Effluent

      W. A. G. T. N. Gunawardhana, W. S. M. S. K. Wijerathna, W. C. T. K. Gunawardana, K. Kawamoto

      Abstract

      Cr(III) adsorption from textile industrial effluent was studied with the aim of contributing towards achieving targets of SDG 6 (Sustainable Development Goals). Highly toxic effluent discharge from textile industries cause the majority of the pollution of waterways which is due to the unaffordability of the existing effluent treatment techniques. Proven efficiency of modified sawdust to adsorb heavy metals could be a sustainable solution as an abundantly available industrial byproduct of sawdust. Biochar derived from sawdust by pyrolizing at 400 °C was further modified using 0.1M KOH or 0.1M H₂O₂ solutions separately. Batch experiments conducted using synthetic Cr(III) aqueous solution in neutral pH condition indicated an equilibrium contact time of 1 h with optimum initial Cr(III) concentration of 5 mg/L with 1 and 2 g of adsorbent dosages for KOH and H₂O₂ modified biochars respectively under single solute system. Further competitive Cr(III) adsorption with the presence of Cu(II) and Zn(II) were examined through batch studies. Results indicated that Cr(III) adsorption was favored in pH base range when examined under multi-metal system along with Cu(II) and Zn(II). Adsorption capacities were increased with the physical and chemical modifications. The physical characterization carried out using Specific Surface Area (SSA) analysis showed a 97.9% increase of SSA when raw sawdust was modified into biochar. KOH and H₂O₂ modifications had further increased the SSA of biochar by 37.8% and 51.5% respectively. X-ray Powder Diffraction (XRD) analysis confirmed the removal of impurities in adsorbents after physical and chemical modifications while the Point of Zero Charge (pH_pzc) analysis established the favorability of using a neutral pH in the solution media. Heavy metal removal percentages were observed as 97.5 and 94.1% for KOH modified biochar and H₂O₂ modified biochar under optimum conditions. Findings suggest that the higher SSA and stability of the added functional groups lead the KOH modification to sawdust derived biochar to be an efficient, environmental friendly adsorbent which could be used in treatment of heavy metals in industrial effluent. Further chemical characterizations using SEM and FTIR analyses could be recommended to evaluate the surface properties of the adsorbents.

   10. Assessment of Land Use/Land Cover (LULC) Changes and Urban Growth Dynamics Using Remote Sensing in Dhaka City, Bangladesh

       Md. Sajib Hossain, Mafizur Rahman

       Abstract

       Dhaka, the capital city of Bangladesh is considered one of the main economic drivers of the country that contributes a significant amount to the nation’s economy. Consequently, the city failed to cope with the increasing demand for accommodation, industrial and infrastructure development, which caused rapid and haphazard development in and around the city. As land is considered a finite resource, the proper use of it should not be underestimated. As a result, understanding the growth pattern of urban areas is of immense importance in urban planning. By applying remote sensing techniques, a series of spatiotemporal changes can be observed to identify possible ecologically sensitive areas. The study identified the spatiotemporal LULC pattern and measured the built-up dynamics and the growth intensity index of Dhaka and its nearby areas within 5 km using remote sensing techniques. The supervised classification technique was applied to classify the images into six different classes namely built-up, sandfill/barren land, water-body, vegetation, wetland and agricultural land. The study suggests that over the study period the built-up and sandfill/barren land have increased by 67% and 679%. As a result of vast demand for accommodation, primarily lowlands and agricultural land around the city are sand-filled to facilitate building new satellite towns like Purbachal, Uttara 3rd phase, Jhilmil and Jalshiri. In terms of the degree of dynamism and annual intensity index, peripheral cities like Kaliganj and Bandar showed the highest degree of change in the study period, which signifies faster urbanization in those areas. This study, therefore, will help us understand the built-up dynamics especially in the peripheral regions of Dhaka city and will also help planners to make better decisions.

   11. Development of a Combined Electrocoagulation and Electrochemical Oxidation Reactor for Treating Service Station Effluent

       B. U. Kaushalya, R. Inthushan, M. A. C. R. Mallikaarachchi, K. G. N. Nanayakkara

       Abstract

       Effluents generated from service stations contain several categories of pollutants such as detergents, oil and grease, organic materials, and heavy metals. Most of the literature suggests the electrochemical methods as effective and sustainable methods to treat such wastewater. This research focuses on removing total suspended solids (TSS), oil and grease (O&G), and chemical oxygen demand (COD) from both synthetic and actual service station wastewater samples by using an electrochemical cell carrying a novel anode. An aluminium anode was used to support electrocoagulation (EC), while a copper-plated graphite anode was used to support electrochemical oxidation (EO). Two separate batch reactors were tested initially for individual EC and EO efficiencies of treating the targeted pollutants for 40 min of reaction time under a current density of 30 mA/cm². The EO efficiencies of removing TSS, O&G, and COD were increased by 21%, 56.3%, and 29.2%, respectively, from the modification of graphite by copper-plating. The efficiency study of the combined reactor with both EC and EO anodes was carried out under two approaches, i.e., the constant current study and constant time study, in order to investigate the optimum operating conditions. TSS, O&G, and COD removal efficiencies of 100%, 100%, and 99.4% were achieved respectively under a reaction time of 60 min at a constant current density of 20 mA/cm² for synthetic wastewater. The efficiency study of the electrochemical cell carried out under the optimum operating conditions for actual service station effluent resulted in TSS and O&G removal of 100% and COD removal of > 99%. Therefore, the developed combined reactor carrying novel electrodes can be suggested as an efficient treatment method for the treatment of service station effluent.

   12. Variation of Copper Adsorption with Initial pH and Pyrolysis Temperature by Saw Dust and Paddy Husk Biochar Made in an Industrial Type Pyrolizer

       H. M. P. Wijeyawardana, Biplob Pramanik, A. K. Karunarathna, Chamila Gunasekara, David Law, K. G. N. Nanayakkara

       Abstract

       Copper (II) ions (Cu²⁺) are one of the widely spread heavy metals in the environment causing ecological and human health risk. Among the conventional methods of Cu²⁺ removal, adsorption is observed as the most favorable. Biochar, a product of pyrolysis, has a relatively structured carbon matrix with high degree of porosity and extensive surface area, like activated carbon suggesting its suitability to be used as an adsorbent material. In this study, biochar was synthesized using an industrial type pyrolyzer and low-cost agricultural waste materials; saw dust and paddy husk as feedstocks. Six sets of biochar were made adhering to three temperature ranges: 350–450, 450–550 and 550–650 °C with a resident time of 30 min. Further, the effect of solution pH on the adsorption of Cu was tested. All the biochar materials exhibit similar trend of maximizing adsorptive removal at pH = 6. At lower pH values the surface charge of the biochar materials is positive creating unfavorable grounds for Cu²⁺ removal. As pH increases above 6.5, Cu²⁺ precipitates as Cu(OH)₂ lowering the amount of soluble Cu²⁺ in the solution. Thus, the negative adsorptive removal efficiencies can be observed at the pH values above 6. The trend followed the shape of a maximum graph for almost all biochar materials where the removal maximizes at 450–550 °C pyrolysis temperature as lower temperatures favor more functional groups while the higher temperatures favor the development of higher specific surface area. At most pH values, the saw dust biochar shows higher removal percentage compared to the paddy husk biochar. Hence, a positive indication of Cu removal is present at lower pH values. The kinetics follow the pseudo-second order model suggesting that chemisorption is dominant. However, isotherms of adsorption, surface characterization of the materials, tests for leaching of adsorbed pollutants must be performed before field applications are done with the developed biochar materials.

   13. Three-Dimensional Modelling of Flow in a Vertical Slot Fishway

       H. M. P. M. Hitihamu, D. M. Pananwala, S. B. Weerakoon

       Abstract

       The flow characteristics of fishways constructed to facilitate fish migration bypassing barriers in rivers, depend on the fishway geometry and the layout. Hence, the selection of the baffles and pools arrangement within the channel is essential for an optimum design of a fishway. In this study, the suitability of flow characteristics of vertical slot fishway (VSF) with selected geometric design was assessed by both experimental study and numerical modelling. Three—dimensional computational fluid dynamic model was developed by using ANSYS CFX 17.2 software. Model validation was done based on the water depth and velocity measurements obtained from laboratory experiments. Suitability of flow characteristics were assessed for increasing slopes by developing CFD models for 7, 9, 11 and 13% slope cases. It was found that the maximum values of velocity, turbulent kinetic energy and energy dissipation rate in the fishway occur at the slots and they increase with the increasing slope. The low velocity pool volumes corresponding to each slope were computed to assess the adequacy of the resting zones for fish. The study concludes that the pool length of the VSF could be 43% larger than the recommended values with the fishway slope up to 13%, while ensuring favourable flow conditions for fish passage to economize the VSF design.

   14. Two—Dimensional Modelling of Flow in Rantambe Reservoir for Sediment Management

       W. M. D. M. Wasala, R. M. C. B. Rathnasiri, S. B. Weerakoon

       Abstract

       Sediment accumulation in reservoirs reduces reservoir capacities and expected benefits from reservoir projects. This is especially prominent in small reservoirs built across rivers carrying high sediment loads. Rantambe reservoir built across the Mahaweli river just downstream of the Randenigala reservoir is one of the reservoirs severely affected by sedimentation. The original capacity of the reservoir was 11.5 MCM in 1990 and in 2014 the capacity was 6.14 MCM. Randenigala reservoir releases and the flow of the Uma-Oya tributary are the main sources of the Rantambe reservoir, and the Uma-Oya tributary carries large sediment load to the reservoir annually. Flushing of sediment is carried out using the two bottom outlets each with an area of 9.7 m² during the flood season, though it is not adequate to restore the reservoir capacity. This study focuses on investigating the potential of reducing the sediment entering into the reservoir from the Uma-Oya during the flood season using a sediment bypass tunnel which originates from a low weir built across the Uma-Oya. A two-dimensional hydrodynamic model was set up, flow patterns and bed shear stress were analyzed. For calibration of the model, simulated velocities were compared with the measured velocities. The model was validated with Manning’s roughness coefficient of 0.03. The model was then applied introducing a low weir and a bypass tunnel. The bed shear and velocities increase in Uma-Oya, and the flow is directed towards to the tunnel. There is a 18% increment in the area of high bed shear stress to erode the deposited sediments compared to the condition under current practice of flushing under same conditions. This proposed sediment bypass tunnel is an effective technique to control the sediment management of the Rantambe reservoir.

   15. Investigation on the Performance of Multi-stacked Floating Wetlands for Leachate Treatment in a Controlled Environment

       M. A. I. A. Moragoda, K. D. A. N. Kumarage, G. M. P. R. Weerakoon, M. I. M. Mowjood

       Abstract

       Leachate releasing from solid waste dump sites or sanitary landfills, is rich in organic pollutants and heavy metals, contributes heavily in contamination of water bodies. Therefore, it is necessary to treat the landfill leachate appropriately up to the effluent standards, before releasing them in to the environment. Constructed wetlands have been identified as an appropriate technology for wastewater treatment in tropical developing countries. However, despite many advantages the large land area requirement and the impacts of outdoor environmental conditions have been identified as major limitations for application of this technology at many places. Therefore, this study has been focused on reducing the land area requirement by designing a multi-stacked floating wetland system. The experimental set-up had three multi-stacked wetland systems, each containing 3 units of 32 cm × 52 cm × 28 cm (length:width:height) in size stacked one over the other and planted with Eichhornia crassipes (common water hyacinth). Two of them were placed inside a greenhouse, while the remaining system was kept outside the greenhouse in open environment. One of the system kept inside the greenhouse was set with a supplementary lighting arrangement. All three units were fed with synthetic leachate to achieve a 60 cm/day hydraulic loading rate (HLR). Results showed that the wetland system kept inside the greenhouse with supplementary lighting had a significant positive impact in removing BOD₅, COD, TOC, Pb, Cu and Zn with average removal efficiencies of 77.4%, 79.1%, 97.9%, 89%, 89.3% and 87.7%, respectively.