What’s new in Water Treatment? Coagulants and Filter Aids Sticky Particles vs. Sticky Media
Particle Capture Efficiency • Sand filters are inefficient capturers of particles • Particles come into contact with filter media surfaces many times, yet it is common for filters to only remove 90% - 99% of the particles. • Failure to capture more particles is due to ineffective attachment (not limited by transport)
Techniques to Increase Particle Attachment Efficiency • Make the particles stickier • The technique used in conventional water treatment plants • Control coagulant dose and other coagulant aids (cationic polymers) • Make the filter media stickier • potato starch?
Sticky Media Potentially treat filter media at the beginning of each filter run No need to add coagulants to water for low turbidity waters Filter will capture particles much more efficiently Sticky Particles Easier to add coagulant to water than to coat the filter media Sticky Media vs. Sticky Particles
How can we make filter media sticky?Why do slow sand filters work? • Slow sand filters don’t use any coagulants, yet their performance improves with time • Their improved performance is due to natural particulate matter that is captured by the filter • What is it about this particulate matter that makes the filters work better?
Role of Natural Particulates in SSF • Could be removal by straining • But we are removing particles 1 mm in diameter! • To remove such small particles by straining the pores would have to be close to 1 mm and the head loss would be excessive • Removal must be by attachment to the sticky particles!
Research project in CEE 453 in 2000 • Successfully extracted a coagulant from Cayuga Lake Seston using 1.0 N HCl • The CLSE fed filters removed up to 99.9999% of the influent coliforms!!!! • Analysis of the CLSE • Nonvolatile solids were 44% of the TSS • Volatile solids were 56% of the TSS • Aluminum was dominant metal
E. coli removal as a function of time and CLSE application rate Horizontal bars indicate when CLSE feed was operational for each filter.
What do we know about this Polymer? • Soluble at very low (<1) and at very high (>13) pH • Forms flocs readily at neutral pH • Contains protein (amino acids) • In acid solution amino acids are protonated and exist as cations • In basic solution amino acids are deprotonated and exist as anions
Future Work • Identify the amino acids • Develop a better source of the protein coagulant (synthetic, bacteria culture, algae culture?) • Develop application techniques to optimize filter performance • How can we coat all of the media? • Will the media remain sticky through a backwash? • Will it be possible to remove particles from the media with a normal backwash? • What are the best ways to use this new coagulant?
Dissolved Air Flotation • Shown to be more effective at removing Cryptosporidium than conventional sedimentation • DAF clarification performed better than lamella sedimentation and consistently resulted in lower turbidity levels and particle counts. • Journal AWWA - Giardia and Cryptosporidium Removals by Clarification and Filtration Under Challenge Conditions Vol. 92 - No. 12
Gunther F. Craun and Rebecca L. Calderon JOURNAL AWWA September 2001 Vol. 93, No. 9 pp. 64–75 Waterborne disease outbreaks caused by distribution system deficiencies • Distribution system contamination has resulted in a significant number of waterborne disease outbreaks in the United States. A review of the 113 distribution-associated outbreaks reported over the past 30 years finds 498 hospitalizations and nine deaths. Since 1996, distribution system deficiencies have caused 45% of all outbreaks reported in community water systems. Most distribution-associated outbreaks were attributable to chemical and microbial contamination from cross-connections and backsiphonage. • Preventing contamination of the distribution system is key to reducing the risk of waterborne disease outbreaks. Important preventive steps include maintaining adequate water pressure throughout the system; identifying and replacing older, leaking water mains; maintaining a chlorine residual and routinely monitoring the residual; adopting cross-connection control programs; inspecting storage facilities on a routine basis; adequately disinfecting after system repairs; and increasing corrosion control efforts. • An aging water system infrastructure renders the United States even more vulnerable to the risk of waterborne disease outbreaks. More regulations may be required to prevent these outbreaks unless water suppliers take action to reduce distribution system contamination and sufficient funds are allocated for system maintenance, repair, and replacement.