Testing of Commercial Defoamant to Control Anaerobic Digester ...

Filamentous Microorganisms How do they end up in Anaerobic Digesters? Surface wasting and WAS from Aeration Basinsis sent to solids handling How do they produce foam in AnaerobicDigesters? Filamentous bacteria attach themselves onto thebiogas bubbles produced during anaerobicdigestion processes They prosper in anaerobic digesters due to theirability to metabolize hydrocarbons (abundant indigesters)

Operational ProblemsExcess froth in anaerobic digesters can result in operationalproblems: An inverse solids profile insufficient stabilization Reduced digestion capacity andperformance Damage to digester equipment Health and safety issues Significant clean-up costs

Chemical DefoamantsDefoamants alter the physio-chemical properties of foamby reducing the surface tension of the foam This action dissipates the foam on the gas bubbles that arestabilized by filamentous microorganismsCommercial defoamants can be very effective atreducing foam in activated-sludge aeration tanks:Prior to Defoamant Addition During Defoamant Addition Day After Defoamant Addition

Application Guidelines (general)Digester Dosage is typically 5 ppm (based on Digester Volume) Higher initial dose to get concentration up in digester. Recommended continuous feeding during periods of problematicfoaming Feed Point: Recirculation loop (optimal), also Sump wells (post-clarification) Digester sampling ports Sludge feed Need to ensure adequate mixingAeration Tank Ideal if defoamant can be sprayedon to surface of foam (i.e. ESDs)

Surface Tension TestingThe ability of a liquid to froth isrelated to its surface tensionSurface tension measurementstaken on FC Rel defoamant withDI water, MLSS, and digestedsludge using a CSC DuNouoyTensiometerCSC DuNouoy Precision Tensiometer

Surface Tension TestingFC Rel defoamant reduces frothing potential by reducing surface tension Lowering the surface tension helps dissipate gas bubbles which are stabilizedby filamentous growthDigested Sludgehas lower surfacetension than ASdue to thepresence ofbiosurfactants,produced inanaerobicdigestionFC Rel Defoamant

Toxicity Testing Methanogenic bacteria, key to stabilizing digestersludge, are very sensitive to inhibitory substances Ensure defoamant used is non-toxic to themethanogen population Two toxicity tests performed Anaerobic Toxicity Assay Microtox ® Toxicity Test

Anaerobic Toxicity Assay (ATA)ATA tests were performedin serum bottlescontaining digestedsludgeDosed with essentialnutrients, acetatepropionate(substrate),and varyingconcentrations ofdefoamantInhibition of methanogenicbacteria measuredthrough total gasproductionGas Volume Measured ByDisplacement or PressureTransducerMethane ContentMeasured via GCNutrient SolutionWith rbCOD added(ATA test only)Anaerobic SludgeSample (Inoculum)Butyl Rubber septa withaluminum crimp top sealHead SpaceFroth ControlAddititveTypical Serum Bottle Assay (250 ml working Volume)

ATA on FC Rel ® DefoamantFC Rel Defoamant Concentrations: 0-500 mg/LTotal GasProductionFC Rel defoamant was not found to be toxicGas Production RatesSerum bottle with highest dose performed best in terms of total gasproduced and gas production rate

Microtox Toxicity TestThe Microtox test measures the light-output ofbioluminescent organisms, vibrio fischeri, when exposedto a potentially inhibitory substance to quantify toxicity Vibrio-fischeri produce light as a by-product of cellularrespirationThe Microtox machine compares the light output of anon-toxic control to the light output of the bioluminescentbacteria exposed to a potentially toxic substance(defoamant)

Microtox Test on FC Rel DefoamantEC 50 (effective concentration where there is a 50% loss of light output) of the Vibriofischeri bacteria is above what typical dosing concentrations of theFC Rel defoamant would be

ATA and MicroTox ResultsFC Rel Defoamant showed no inhibitory or toxic impactat doses

Frothing Potential TestsA visual inspection of the effectiveness of FC Rel defoamantdetermined using a froth potential test Determined dosingFroth Potential Testing: Graduated cylinders with fine bubble diffusers connected to air flowregulators Froth samples (activated sludge or anaerobic digester sludge) Samples tested with various doses of defoamant Height of froth recorded initially, after 30-min of aeration, and after 1-min of settlingFoaming potential determined based on ratio of foam producedto the initial liquid height

Froth PotentialsStable and Unstable FrothStable froth is a better indicator froth severity Unstable froth produced during aeration may dissipate once aerationhas halted‘non-frothing’ to ‘severe frothing’ based on qualitative analysis oftest resultFroth Severity Rating SystemFroth Rating Stable Froth Unstable FrothNon-Frothing 0-0.1 0-1.0Mild Frothing 0.1-0.3 1.0-2.0Frothing 0.3-0.5 2.0-3.0Severe Frothing > 0.5 > 3.0

Defoamant TestingTest SetupDefoamant Test

Foaming Potential TestsFC Rel Defoamant on Froth from Activated Sludge &Digesters:Control 5 mg/L 15 mg/L 35 mg/L 50 mg/L Control 5 mg/L 15 mg/L 35 mg/L 50 mg/LActivated Sludge Sample during AerationDigested Sludge sample during aeration

Dosing TestsFC Rel Defoamant Dosing Determination on AnaerobicDigester SludgeTesting showed FC Rel defoamant is most effective atreducing digester foam at a concentration of 5 - 10 mg/L

Full-Scale TestingRoutine monitoring of Froth Potentials provided insightinto upcoming digester frothing eventsNon-Frothing

Full-Scale Testing – Round 1 August 2011 – Routine sampling showedincreased foaming potential in digesters at theHunts Point WWTP

Testing Schedule – Round 1 August 2011 testing Initial defoamant dose added to Digester 2(Experimental Digester) Digester 3 used as a control Target dose of 15 mg/L Samples taken each morning and afternoon forfoaming potential testing Defoamant dosed on days 1, 4, and 8

Testing Setup

Results – Stable Froth

Results – Round 1Prior to defoamant addition, both Digesters exhibitedsevere froth ratios Very similar values for bothAfter defoamant addition, Dig 2 stable froth ratiosignificantly lower than Dig 3 Dig 2 stable froth ratio still in ‘frothing’ to ‘severe frothing’ range Addition of defoamant prevented further increase (observed in Dig3)Dig 2 consistently lower in both stable and unstablefrothing potential Use of defoamant in Dig 2 resulted in a reduction in frothingpotential.

Full-Scale Testing – Round 2 December 2011 – Routine sampling showedincreased foaming potential in digesters at theHunts Point WWTP

Full-Scale Testing – Round 2 Initial foaming potentialPreliminary Stable Froth Potential Results from 12-6-2011

Testing Schedule – Round 2 December 2011 testing Initial defoamant dose added to Digester 2(Experimental Digester) Digester 3 used as a control Target dose of 15 mg/L Samples taken each morning and afternoon forfoaming potential testing Holiday weekend necessitated a break in the testingmid-way through Defoamant dosed on days 1, 3, 5 and 6

HP Full-Scale Defoamant Addition

Results – Round 2 Second defoamant test did not show degree ofimpact seen in previous test Dose and timing were not as consistent due toholiday and back-order of defoamant Performed new defoamant dose test onfoaming sludge

Defoamant Dose Test

Results – Round 2 Results indicate that dose was not have beenhigh enough for sustained reduction of froth Initial dose of 15 mg/L was targeted Higher dose (> 20 mg/L) and more consistentdosing needed Recommendations Pre-test for dose optimization More frequent additions (daily)

Conclusions and Recommendations Defoamant is not toxic to anaerobic digestionprocess Defoamant is effective at reducing frothingpotential of digested sludge when applied at thecorrect dose Continuous addition of the defoamant, startingwhen frothing conditions are first noted, isrecommended to maximize the effectiveness ofthe defoamant addition A pre-test to confirm the dose required isrecommended prior to testing

AcknowledgementsVera Gouchev and David Wankmuller,Manhattan College GRAsSarah Dailey, Hazen and Sawyer EngineersAllen Deur and Keith Beckmann, NYCDEPResearch conducted through NYCDEP AppliedNitrogen Research Program (PO-88)This work is part of the WERF funded DigesterFoaming Research Project which is cosponsoredby Hazen and Sawyer Engineers andBaxter and Woodman, with Dr. Krishna Pagillafrom IIT serving as Primary Investigator.