Guidance Manua pdf
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- Bu səhifədəki naviqasiya:
- 4.3 MONITORING IN PRESSURIZED WATER DISTRIBUTION SYSTEMS
- 4.4 PREDICTION OF TO PROBLEMS 4.4.1 Rationale for Prediction
- 4.4.2 Reservoirs
- Lake Pleasant 0 10 20 30 40 50 Aug-99
- Feb-01 Apr-01 Jun-01 Aug-01 Oct-01 Dec-01 Feb-02 Apr-02
22 geosmin. The presence of certain culprit algae may not necessarily mean that MIB and/or geosmin is being produced. Several of the MIB producers appear to be able to turn on/off production in the laboratory. Production of T&O compounds should be verified by GC/MS analysis.
MIB and geosmin. Analyze by FPA, or preferably by GC/MS. Rapid turnaround is paramount for making decisions on water supply management, canal treatment, or in- plant process options. Analytical results reported within 72 hours of sampling is a reasonable goal.
Flavor Profile Analysis (FPA) panels should be trained by experts and chlorine should be quenched with hydrogen peroxide in order to specifically detect MIB or geosmin.
MIB and geosmin can be measured using Solid-Phase Microextraction/Gas Chromatography/Mass Spectroscopy (SPME-GC/MS) (Watson et al., 2000; Lloyd et al., 1998). Details of the method used in the recent study are given in Appendix C.
Algae do not pass through sand filtration systems at the WTPs nor grow in the absence of light, and therefore typically are not present in pressurized pipe water distribution systems carrying finished drinking water from the WTPs. However, fungi, bacteria (e.g., actinomycetes) and other organisms can grow in water distribution systems and also impart earthy, musty, moldy odors to water. Therefore, customer complaints about tap water may be caused from either: (1) T&O compounds in finished water leaving the WTP or (2) T&O compounds produced within the pressurized water distribution system. If a water utility suspects the latter due to numerous complaints from a localized region of the water distribution system, then samples from the distribution system should be collected. Preferred sampling would include a responsive program where samples from the service tap and customer faucet are collected and analyzed for chlorine residual (field) and MIB/geosmin (lab). Many complaints are actually from chlorine residual. If a routine monitoring program is desired, then points within the water distribution system should represent points of historic microbial concern (e.g., high plate counts, low chlorine residuals). 4.4 PREDICTION OF T&O PROBLEMS 4.4.1 Rationale for Prediction
The ability to predict the occurrence of T&O episodes is important for water resources planning and for water treatment plant staff for three reasons:
1. Some T&O episodes may be prevented. For example, canal treatments can be used to prevent the growth of T&O culprit algae. To utilize canal treatments effectively, it is desirable to know where and when T&O episodes are likely to
23 occur, because it is too expensive to treat the entire canal throughout the T&O season.
2. Some T&O episodes may be avoided. In many cases, it may not be possible to prevent the production of T&O compounds upstream, but water resources managers could manage the water supply system to prevent poor-tasting water from reaching consumers. This can be done through reservoir management, blending of source waters, or source switching (reducing production at a WTP receiving poor-tasting water while simultaneously increasing production at a WTP receiving better quality water). These management procedures will be discussed later.
3.
Water treatment plants can remove T&O compounds, but need advance warning to do this effectively. T&O compounds can generally be reduced below threshold levels using powdered activated carbon (PAC) within the WTPs. However, treatment plant operators need to know when T&O episodes will occur so that they can order PAC and prepare their WTPs for an episode.
MIB was produced in all three of the water storage reservoirs above the canal distribution system (Section 2). Prediction of when MIB is likely to be released from each reservoir, and its impact on Phoenix’s water supply, is now possible.
As noted above, MIB is produced by certain blue-green algae, which grow primarily either in shallow near shore areas or suspended in the epilimnion. MIB concentrations in the epilimnia of all three reservoirs commonly exceed 20 ng/L during the summer stratification period. Concentrations of MIB in the outlets from the reservoirs during summer stratification are nearly always much lower than found in the epilimnion, because water is released from the hypolimnion. Figures 4-2 through 4-4 show MIB concentrations in the reservoirs and their outlets.
Figure 4-2. MIB in the epilminion, hypolimnion, and outflow from Lake Pleasant. Yüklə 0,58 Mb. Dostları ilə paylaş:
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