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Chapter 5 DSS Testing and Sensitivity Analyses Equation Chapter (Next) Section 1 5.1 Introduction The methodologies for evaluation and optimisation of integrated water reuse systems were implemented into a user-friendly hydroinformatics tool. Full features of the developed DSS tool for Water Treatment for Reuse with Network Distribution (WTRNet) are described in Appendix B, which also serves as the software users’ manual. WTRNet was first utilised to test the concepts embodied in the DSS and conduct the sensitivity analyses of some of the parameters using smaller test cases, prior to applying it on a larger-scale case study. The results of these efforts are presented in this Chapter. The purpose of DSS testing was to examine how the developed methodologies achieved their intended purpose, and to develop any necessary modifications, while the sensitivity analyses focused on some of the parameters and weights used as default. For both activities to take place, test case studies were needed that had features appropriate for the kind of analyses that were to be performed. Two separate test cases were developed, which are described in the remainder of this section. Two sections that follow discuss the results of testing and sensitivity analyses, respectively, and an overall summary with conclusions reached from these activities conclude this Chapter. 5.1.1 London Test Case The first test case was developed primarily for the purpose of testing of the sequential approach for distribution system sizing. Therefore, large scale wastewater treatment plants combined with distributed potential end-users requiring seasonally varying demand were sought. After conducting various searches for appropriate area that could be used to develop a hypothetical water reuse scheme, a sewage treatment plant located in London Borough of Hounslow and several golf courses in the general vicinity were identified as fitting the desired criteria. The Mogden Sewage Treatment Works (STW) occupies almost 50ha of land, and it is one of the largest wastewater treatment plants in Europe and second largest plant run by 125 Chapter 5 - DSS Testing and Sensitivity Analyses Thames Water (Koodie and Kirkaldy 2000). It treats effluent from areas North and West of London inhabited by 1.8 million people. First built in 1936, the Mogden STW treats an average flow of 500,000 m³/day, which is just over one half of its rated capacity of 810,000 m³/day. The plant has two parallel treatment trains which include initial screening and de-gritting of raw sewage, primary clarifiers and activated sludge process, in addition to having large volume retention tanks used for wet weather flows exceeding the plant capacity. The importance of its performance is heightened by the fact that its effluent constitutes a major portion of River Thames dry weather flows that pass through central London. Figure 5.1 Mogden STW Serviced Area (Thames Water 2006) The test case considers several golf courses located in the general vicinity of Mogden STW as potential end-users of reclaimed water. Their monthly irrigation demands, summarised in Table 5.1, were estimated based on assumed irrigation areas and average weather conditions for London and represent a small fraction of flows that are treated at Mogden STW. 126 Chapter 5 - DSS Testing and Sensitivity Analyses Table 5.1 Estimated Demands of Potential End-users in London Test Case End-user Monthly Demand (m³) Total Royal Month Wyke Demand Airlinks Mid Richmond Fulwell Green (m³) Surrey Jan 82 46 118 61 113 420 Feb 530 297 766 396 736 2,725 Mar 634 355 915 473 880 3,257 Apr 890 498 1,286 665 1,236 4,575 May 1,168 654 1,687 872 1,622 6,002 Jun 1,400 784 2,022 1,045 1,945 7,197 Jul 1,760 986 2,542 1,314 2,445 9,047 Aug 1,463 819 2,113 1,092 2,032 7,520 Sep 836 468 1,208 624 1,161 4,298 Oct 266 149 384 199 370 1,368 Nov 145 81 209 108 201 743 Dec 7 4 10 5 9 34 5.1.2 Kyjov Test Case The second test case was developed as part of author’s involvement on the AQUAREC project, and was actually the case study used in that project to demonstrate the developed DSS methodology and the WTRNet tool. The test case involved studying industrial water reuse options in the city of Kyjov, located in the South Moravia area of the Czech Republic. The input requirements for the DSS tool were drawn by the author, who also guided the assembling of information by others (Janosova 2005; Kubik 2005) and developed the WTRNet model of the test case. The industrial zone of Kyjov is approximately 5 ha in size, within which the majority of businesses are in the metal and glass industries. The wastewater treatment plant (WWTP) in Kyjov, which is in the immediate vicinity of the industrial zone, is sized for approximately 26,000 population equivalents (PE), and currently receives an average flow of 9,500 m³/d. The WWTP is a mechanical-biological treatment plant with aerobic stabilisation of sludge. Collected sewage is pre-treated using a bar screen, mechanical fine screen and a grit chamber. Another operational complex forms a biological treatment stage, which includes a circulating activation tank, secondary settling tanks, and a pumping station for re-circulated and excess sludge. 127 Chapter 5 - DSS Testing and Sensitivity Analyses Six industries were identified as potential end-users of upgraded wastewater from the Kyjov WWTP, whose locations relative to the WWTP are shown in Figure 5.2. Table 5.2 displays the details of these industries, along with their estimated quantity requirements for reclaimed water. The total reclaimed water demand estimated for these users represents less than 10% of the current plant average flow. Nevertheless, an assumption was made that 10% of the effluent from the WWTP would need to receive additional treatment in order to satisfy the requirements of these potential users. MLÉKÁRNA Kyjov a.s. VETROPACK MORAVIA GLASS a.s. ŠROUBÁRNA Kyjov spol. s r.o. ŠEBESTA spol. s r.o. WWTP EK OR s.r.o. BETAS MORAVIA a.s. Figure 5.2 Kyjov Test Case Overview (Geonardo 2005) Table 5.2 Demand of Potential End-users of Reclaimed Water in Kyjov Estimated Water Company Industry Type Demand (m3/d) Manufacturing of packaged Sebesta spol. s r.o. 23 wastewater treatment plants Manufacturing of building and KM Beta a.s. 35 roofing products Sroubarna Kyjov spol. s r.o Manufacturing of fasteners 122 EKOR s.r.o Waste management 9 Mlekarna Kyjov, a.s. Dairy works 74 Vetropack Moravia Glass a.s Glass manufacturer 297 Total Demand 600 128 Chapter 5 - DSS Testing and Sensitivity Analyses 5.2 Testing 5.2.1 Sequential Approach for Distribution System Sizing The testing of the sequential approach used in the DSS for sizing of all distribution system components, conducted using the London test case, was carried out primarily to confirm that the algorithm functions as intended in a variety of situations. An overview of the location of the Mogden STW relative to the end-users considered is shown in Figure 5.3, in which the distribution system components are also indicated. The test case includes three possible storage elements (earthen basins) and three possible pumping locations. The first storage facility is located at the Mogden STW, and its maximum volume was set at 200,000 m³. Central pumping was also assumed at that location. The remaining two possible storage facilities were limited to 100,000 m³ each, and they are located near the Royal Mid Surrey and Wyke Green golf courses. Off-line pumping stations were also placed at both of these locations. Figure 5.3 London Test Case Overview As described in Section 3.4, the application of the sequential approach will vary according to the availability and distribution of available reclaimed water and potential 129 Chapter 5 - DSS Testing and Sensitivity Analyses end-user demands over the course of the year. The approach uses different formulations of the NLP model, and also excludes the NLP altogether in cases of adequate quantity and distribution of demand. With golf course irrigation demands fixed at their estimated values, the testing consisted of changing the volume of available reclaimed water (i.e. the size of the reclamation facility) and analysing the optimisation results related to the distribution system. Unit costs of alternate supplies, which can be used to indicate user preferences for providing reclaimed water to different end-users, were all fixed at a constant value of 0.5 €/m³ throughout the testing. The size of the reclamation facility was varied between 500 m³/day, where storage would be needed but most of demands would remain unsatisfied, and 9,500 m³/day, at which point all maximum monthly demands could be met without the need for storage. Results of the analyses described above are summarised in Figure 5.4. The graph on the left side shows the optimal sizes of storage facilities for different treatment capacities determined using the sequential approach, and the graph on the right side shows the resulting annual shortfalls and spills. The first remark made on the results is that the algorithm correctly increased the overall storage capacity of the system up to the point where only additional treatment capacity could further decrease the shortfalls. Beyond that point, the need for storage facilities diminishes but is still necessary to balance the varying monthly demands with fixed production of reclaimed water, indicating that the general performance of the approach is correct for a wide range of conditions. 2,000 Wyke Green Airlinks Wyke Green 1,800 400 Royal Mid Surrey Royal Mid Surrey Richmond ³ Fulwell Spill ) Mogden STW 1,600 300 1,400 1,200 1,000 200 800 600 Storage Size (x10³ m³ 100 m (x10³ Spill or Shortfall 400 200 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 Supply (x10³ m³/day) Supply (x10³ m³/day) Figure 5.4 Storage and Shortfall Volumes - London Test Case By further examining the displayed results, it appears that Royal Mid Surrey and Richmond golf courses were favoured as their demands were the first to be met.