Browsing by Author "Ranasinghe, CJ"

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item: Thesis-Full-text
Analysis of root causes of the excessive chlorine demand in water treatment
Ranasinghe, CJ; Ratnayake, N
To make water suitable for human consumption, water from most sources must first be treated, and the source water that can be used as raw water for public water supplies should conform to quality standards stipulated in the Sri Lanka Standard SLS722. However, sometimes, National Water Supply and Drainage Board (NWSDB) water treatment plants do not receive raw water according to SLS722 due to contamination. In some cases, existing treatment facilities is not enough to face emergency situations, even though the average quality conforms to the SLS 722. In such situations, the operation of treatment plants becomes a challenge, as it is the responsibility of the NWSDB to provide safe drinking water to the consumers, which means that disinfection, has to be carried out even though the chlorine demand may become very high due to excessive amounts of contaminants during such events. The purpose of this research was to analyze the root causes of the excessive chlorine demand in water treatment and recommend an appropriate system capable of removing dissolved iron, ammonia and manganese from the raw water, avoiding the use of chemical treatment if possible, and prepare an emergency plan to face the situation at the Biyagama Water treatment Plant. According to the past water quality data at BWTP colour, turbidity, BOD, faecal coliform, free ammonia content, nitrate, sulfate etc. of raw water were rapidly varying with the occurrence of extreme events such as sudden rainfall followed by prolonged dry season, a few days after flood events etc. In addition, it was found that foul odour is present in the raw water which has been abstracted from the river during the drought season and right after flooding events, etc. In spite of these variations in raw water quality, the treated water quality is achieved through the treatment process without any failure. However, during the drought season and right after flooding event, Chlorine demand at Biyagama Water Treatment Plant was increased and intermediate chlorination was implemented to maintain the optimum Rcl level recently. Hence,aim of this study is to analyze the root causes for the excessive chlorine demand in raw water,investigate adverse effects of treated water due to high chlorine dosages, and prepare an emergency plan to face the situation and suggest the appropriate long term solution to avoid high chlorine demand on treating water without chemicals at the Biyagama Water treatment Plant.Presence of Fe, Mn and TOC in the raw water is known to cause for high chlorine demand at the Biyagama water Treatment Plant. These high chlorine demands have been attributed to the presence and oxidation of Fe, Mn, and TOC by chlorination.In order to find the root causes for the high chlorine demand in the BWTP, it is necessary to first investigate the mechanisms that cause the problem in this particular situation. As such, a comprehensive water quality study was carried out in 19/10/2016 to 21/10/2016, 7/10/2016 to 11/10/2016 and 4/6/2016 to 9/6/2017 by the Biyagama Water Treatment Plant laboratory,Central Laboratory and Bureau Veritase laboratory samples from the intake (raw water),Treated water tank (treated Water), Pattiwila canal and suspected points of connected Marshy area, along the Kelani River up to 5km upstream of Kelani River and along the gahawatta Ela up to BOI waste water treatment plant out let.This study revealed, that the chlorine demand was increased when Fe, Mn or TOC were present alone or together and DO level was less than 5mg/l in raw water at BWTP due to oxidation of Fe, TOC and Mn by chlorination. BWTP is used pre chlorine to alter taste and odor producing compounds, to suppress growth of organisms in the treatment plant, to remove Fe2+,manganese, and to reduce the interference of organic compounds in the coagulation process.However, according to literature, pre chlorination can affect the undesirable THM content of the finished water.According to the WSP at BWTP, there should be an emergency response plan to risk mitigation due to emergency cases. Hence, it is proposed to use the emergency response plan for any similar incident happened in future.However, in the long-term, it is recommended to install tailor made bubble aerator to Biyagama Water treatment Plant to use when the DO content is less than 5.0mg/l in raw water, after pilot scale studies, to include aeration and activated carbon dossing facility to upcoming Kelani Right Bank Project Stage II, to implement the proper catchment management plan to Pattiwila and Mabima Catchment areas to avoid the Mn and Fe contamination, to implement continuous monitoring system to monitor the Fe and Manganese in the raw water at BWTP and to maintain a residual chlorine level of 0.1 to 0.2 mg/l throughout the distribution system in all the time. This may require installing booster chlorination equipment at appropriate locations.
item: Thesis-Abstract
Cost effectiveness of non revenue water reduction in greater Kandy area
Ranasinghe, CJ; Halwathura, R
Proportion of Non-Revenue Water (NRW) measured as a percentage of the total water distributed to consumers varies from 10% to 55% in most of the existing piped water supply schemes. Loss of revenue due to NRW is enormous. Analyses of losses to the utility in the above aspect and comparative studies on the cost of improving existing systems verses cost of construction of new systems may be useful for planners as well as for network system designers. It will also be helpful in reducing the substantial investment to build new water supply project to cater to the increasing demand. However, the time has come for planning, design and construction of systems with minimum operation and maintenance burden using the world's best available practices and also to have programmers for controlling water losses in existing systems. This enable to save the limited water resource, to have the maximum benefit from the money spent mostly out of foreign loans and to expand the pipe borne water supply facility to more than 50% of the population who are deprived of the facility. To analyze the financial viability of Construct ion of new water supply system Vs rehabilitation/augmentation of existing system, this research was conducted. This study is focused to select the most cost effective option in meeting increasing demand for drinking water by cost saving of reduction of NRW compared to investment in development of new scheme in Kandy Area. To attain this purpose, Harispaththuwa ,Akurana,and Ampitiya Schemes were considered to calculate the Cost of Rehablitation . Construction cost of Ulapane scheme was taken as the construction of new water supply scheme. Internal rate of return was calculated for both projects and compared each other. According to, the comparison Rehabilitation/augmentation of existing system was financially viable but NRW saving from rehabilitation is not sufficient to cater to the projected current and future demand
item: Conference-Full-text
Design of power weeder for low land paddy cultivation
(2013-11-15) Ratnaweera, AC; Rajapakse, NN; Ranasinghe, CJ; Thennakoon, TMS; Kumara, RS; Balasooriya, CP; Bandara, MA
Lack of man power has been identified as one of the major problems for the sustainability of the Sri Lankan paddy industry. Hence transplanters and seeders were well developed as a step for mechanization. However, weeding method is still not well developed up to mechanization. Therefore, our main objective is to design and fabrication of a power weeder. Weeding ability will be optimized by weeding three rows simultaneously. The machine is designed to use in the fields, cultivated by using mechanized seeder or mechanized transplanter introduced by Farm Machinery Research Centre (FMRC), Sri Lanka. The double-action weeding drums will be driven by a small 1.3 kW gasoline engine, that can enable removal of weeds, while facilitating the forward motion of the machine. In addition, the conical shaped weeding drums will be designed to loose-up soil without harming the paddy. Totally six drums will be used, in such a way that rear three drums have high angular velocity with respect to the front drums. A novel maneuvering method for row changing when the machine is in paddy fields also introduced in the design. More than 5-fold improvement of weeding efficiency in terms of weeding time is expected in this design. Further, a significant improvement of weeding quality is also expected in this design.