Taste & Odor Problems in Drinking Water

1. Taste & Odor Problems in Drinking Water NMED Drinking Water Bureau

2. Overview • There are several possible causes of taste and odor problems in drinking water, the most common include: • Chlorine • Iron and Manganese • H2S in source water • Stale water • Algae • Many T&O compounds have very low thresholds Drinking Water Bureau

3. Overview • Most T&O compounds are not a health concern, but some can be. • T&O problems may create the perception that water is not safe to drink. • It’s important to not only address the T&O problems, but also to have a public relations strategy. Drinking Water Bureau

4. Overview Drinking Water Bureau

5. Chlorine Zone 1: Chlorine consumed by reducing compounds (e.g. H2S) Zone 2: Formation of chloramines and chlorinated organics. Chlorine odor. Zone 3: Chloramines and organics partly destroyed. Zone 4: Residual formed. Too much residual → chlorine taste & odor Drinking Water Bureau

6. Iron & Manganese • Water with dissolved iron (Fe) or manganese (Mn) may appear clear at first, but may form red or black particles as it oxidizes. • Fe and Mn can exist in suspended or colloidal form which will give water a tint. • Fe can form reddish-brown stains. Mn can cause brownish-black stains. • Fe and Mn can build up in pipelines and tanks. • Secondary standards Fe, Mn: .3mg/l, .05 mg/l, Drinking Water Bureau

7. Iron & Manganese Removal of Fe and Mn: • Test to identify types and concentrations of Fe/Mn • Oxidation/filtration is most common approach for dissolved Fe/Mn. • Cl is a common oxidant, but could cause DBPs • Other oxidants, e.g. Potassium permanganate (KMnO4), can be temperamental • Ion exchange can be used for low concentrations of Fe/Mn (~5 mg/l combined) Drinking Water Bureau

8. H2S • Hydrogen Sulfide (H2S) in drinking water generally does not pose a health risk at low concentrations. • Often occurs naturally, but can be caused sulfur-reducing bacteria in wells. • Taste and odor threshold is ~ 100 ppb Drinking Water Bureau

9. H2S • Shock chlorination can kill sulfur-reducing bacteria in wells. • There are a variety of ways H2S can be removed from water, depending in part on concentration: • Aeration • Manganese Greensand • Oxidation (e.g. chlorination) Drinking Water Bureau

10. Water Age • There is a correlation between water age and deteriorated water quality. • Water age is a function of demand, system design and system operation. Drinking Water Bureau

11. Water Age • Water quality can change over time: • Lower chlorine residual • Increased bacterial growth (biofilms) • Changes in temperature, pH, dissolved O2 • Precipitation of minerals • Increased disinfection byproducts • Taste & odor problems Drinking Water Bureau

12. Water Age • Considerations for reducing water age problems: • Eliminate dead ends • Have a flushing program • Don’t over design your system • Tank management • Replace deteriorated pipe Drinking Water Bureau

13. Algae • Algae is a large diverse group of photosynthetic organisms. • It is possible to have several types of algae growing together. • Algae requires light and nutrients to grow in water. Many prefer warmer water. Drinking Water Bureau

14. Algae • Many species of algae produce volatile organic compounds (VOCs) that can result in taste and/or odor in water. • Tastes and odors can include fruity, musty, fishy, grassy, banana, glue, acrid. • Some VOCs are produced and excreted during growth, others released when cell dies or is damaged. Drinking Water Bureau

15. Algae Cyanobacteria • AKA blue-green algae. • Actually a bacteria. • Several cyanobacteria produce cyanotoxins. • Microcystin is the most common cyanotoxin. • World Health Organization provisional guideline for Microcystin is 1 μg/l (1 ppb) in drinking water. Drinking Water Bureau

16. Algae • Cyanobacteria • Many cyanobacteria produce taste and odor compounds. • Most common T&O compounds are Geosmin and 2-methylisoborneol (MIB) → musty T&O • MIB and Geosmin are not toxic, but some cyanobacteria produce these and toxins. Some produce toxins, but no T&O compounds. Drinking Water Bureau

17. Algae • Cyanobacteria • Geosmin • odor threshold is ~5 ng/l (parts per trillion or ppt) • taste threshold is ~16 ppt • MIB • odor threshold is ~15 ppt • taste threshold is ~18 ppt Drinking Water Bureau

18. Algae There are several other problematic groups of algae including: • Chrysophyta – can form blooms and give off a strong fishy odor • Chlorophyta – AKA “Green Algae”. Can form blooms and add a lot of organics to the water. Taste and odor generally grassy, but can be fishy. Drinking Water Bureau

19. Algae Growth Conditions leading to algae growth: • Algae are naturally occurring. • Algal blooms usually result from excess nutrients, primarily phosphorous (possibly nitrogen). • Nutrient sources include farm and range runoff, wastewater. Drinking Water Bureau

20. Algae Growth Conditions leading to algae growth: • Blooms usually occur in summer • Cyanobacteria generally like calm water so they can position themselves in the optimal location in the water column. Drinking Water Bureau

21. Algae Growth Treatment plant issues • If clarifiers are not enclosed, algae growth can occur within the clarifiers • Excess algae can clog filters • Pretreatment with an oxidant will kill the algae and release T&O compounds. • The algae and T&O compounds can increase DBP production. Drinking Water Bureau

22. Algae Monitoring • Monitoring Program may include: • Algae species • T&O compounds • Toxic compounds • Nutrients • Take a progressive approach to identify problematic portions of system, causes, species, compounds. Drinking Water Bureau

23. Algae Monitoring • To collect planktonic (free floating) algae for ID, need to find right location, depth and time. • Higher concentrations of algae may be below surface so may need ability to sample at depth. • Use Secchi disk to determine photic depth. Drinking Water Bureau

24. Algae Monitoring Monitoring program will alert the system to when algae concentrations increase. Water systems should know if there are cyanotoxins in the water in addition to T&O compounds. Only a few labs ID algae and test for MIB, Geosmin or cyanotoxins. Drinking Water Bureau

25. Algae Control • Goal is to limit algae growth • Prevent excess nutrients in watershed, i.e. source water protection • Artificial mixing in reservoirs to prevent cyanobacteria growth. • Kill algae with an algaecide such as copper sulfate. Drinking Water Bureau

26. Algae Control Source Water Protection • Try to reduce nutrient input • Requires working with agricultural and wastewater sources upstream and limiting erosion. • Difficult to do if watershed is large and/or lots of inputs. Drinking Water Bureau

27. Algae Control • Could cause other algae to increase • Could increase turbidity • Could cause other chemical changes Artificial Mixing • Disrupts Cyanobacteria depth control • May deceases light penetration Drinking Water Bureau

28. Algae Control Algaecide • Copper Sulfate (CuSO4) is most common • Cost ~ $10/acre per application • Very short lived. Reacts with minerals and precipitates. May require multiple applications. • Toxic to fish. • Killing algae will release internal T&O/toxic compounds. CuSO4 should only be used to prevent algae blooms. Drinking Water Bureau

29. Climate • Warmer temps could make other T&O problems worse such as chlorine or stale water. Climate in New Mexico is predicted to get warmer with lower spring runoff. These conditions will favor the development of algae blooms. Drinking Water Bureau

30. Public Notification • When there is a taste or odor problem, some members of the public will assume the water is unsafe. • Be proactive. Let them know • What the problem is • Cause of the problem • Health implications • Duration • What the system is doing about it Drinking Water Bureau