Waste Activated Sludge Stripping to Recover Internal Phosphorus Laboratory Scale Test Methods

Transcription

1 1723 S Kings Ave Kings Executive Park, Brandon, FL Waste Activated Sludge Stripping to Recover Internal Phosphorus Laboratory Scale Test Methods Introduction The Waste Activated Sludge Stripping to Recover Internal Phosphorus (WASSTRIP ) process extracts phosphate from waste activated sludge (WAS) prior to thickening and digestion by holding it under anaerobic conditions. WAS from enhanced biological phosphorus removal (EBPR) processes readily releases stored phosphate under anaerobic conditions. The hydraulic retention time of the WASSTRIP process depends on the phosphorus content of the WAS and the availability of volatile fatty acids (s). s accelerate release, reducing process HRT. WAS thickening after WASSTRIP separates released phosphate from thickened WAS. Thickening liquor (e.g. GBT filtrate, DAF subnatant etc.) is treated in the Pearl process, where the phosphate is transformed into Crystal Green fertilizer. TWAS is fed on to digestion. EBPR selects for phosphorus accumulating organisms (PAOs), which store cations such as potassium (K + ) and magnesium (Mg 2+ ) as a counter ion when they store phosphate (PO4 3- ). In WASSTRIP the PAOs release these cations in proportion to phosphate release. Magnesium is typically the rate limiting precipitant for struvite (MgNH3PO4.6H2O) formation in anaerobic digestion. Its removal in WASSTRIP therefore controls struvite formation in the digester and downstream. Potassium impacts digested sludge dewatering performance at plants practicing EBPR by unfavorably changing the ratio of monovalent to divalent cations in digested sludge. Its removal in WASSTRIP therefore improves dewaterability. Outline This document describes three test methods to assess the WASSTRIP process: 1. Test One is a quick method that provides a preliminary indication of process viability with minimal technician time and laboratory analysis 2. Test Two assesses endogenous phosphate release from WAS over time, indicating process HRT, with pre-thickening of WAS 3. Test Three assesses phosphate release from WAS with external carbon source addition over time, indicating process HRT, with pre-thickened WAS Tests Two and Three are sufficiently comprehensive to inform full scale system design, to indicate process performance and to evaluate implications for related processes (e.g. thickening, Pearl etc.). Representative WAS samples should be used for all tests. Factors that affect phosphate concentration and/or release, such as chemically enhanced primary Page 1 of 6

2 Page 2 of 6 treatment, should be considered when sampling. Ostara can provide site specific sampling advice if required. Materials: Fresh WAS samples Vinegar (~5% acetic acid v/v) for use as source 15 to 20 L bucket for storing WAS samples Large stir plate and magnetic stirrer or spoon for stirring bucket contents Beaker for collecting subsamples from bucket Lab centrifuge with centrifuge tubes (optional but makes filtration much easier) Filtration apparatus with glass fiber and 0.45 um cellulose acetate filter papers Sample bottles for storing filtered samples. Personal protective equipment suitable for working with wastewater, as per local regulations. As a minimum, gloves, protective eye wear, lab coat or coveralls and closed toed shoes are recommended. Test One Simple Phosphate Release Test Method: 1. Collect a 10 liter WAS sample Record sampling date and time. 2. Collect an unfiltered sample for analysis of total phosphorus (TP) and total Mg. 3. Store sample in a covered bucket in a location where the temperature is as close as possible to WAS temperature in the operating plant. 4. Gently stir bucket approximately every four to six hours during the day. 5. After 24 hours collect a sample, filter to 0.45 microns (due to high solids content allowing the sample to settle for minutes and filtering the decant will reduce the effort required to filter) and analyze for orthophosphate (PO4-P) and soluble Mg. Report starting TP and total Mg and ending PO4-P and soluble Mg to Ostara.

3 Page 3 of 6 Test Two Endogenous Phosphate Release Test with pre-thickened WAS This method is developed to determine the rate and extent to which phosphorus release will occur in the WASSTRIP tank, incorporating high rate gravity thickening of WAS in the process. The WAS is first gravity thickened for a 1 hour period, after which the clear decant is discarded and the remaining thickened WAS is allowed to ferment over a 48 hour period. Method: 1. Collect a l WAS sample in a bucket (record actual volume), and allow to settle for 1 hour. Record sampling date and time. 2. After 1 hr settling, decant and discard clarified liquor, and retain thickened WAS in the bucket. Typically this will result in discarding about 2/3 of the WAS sample volume and retaining 1/3 of the volume of the original sample. 3. Mix bucket thoroughly and collect an unfiltered sample for analysis of total suspended solids (TSS) total phosphorus (TP), total magnesium (Mg), total potassium (K) and capillary suction time (CST) 4. Store sample in a covered bucket at as close as possible to normal process temperature 5. Collect subsamples at the time intervals indicated in Table 1 below. Mix the bucket contents thoroughly but without aerating the sample before collecting samples. This could be done by placing the bucket on a stir plate with a magnetic stirrer on low speed to prevent vortexing, or by using a spoon/spatula to gently mix the contents each time a sample is collected. Table 1: Sampling and Analysis Schedule Sample Time* (hours) Analytes (soluble) CST Testing 0 Mg, NH4-N, PO4-P, ph, X 4 PO4-P 8 PO4-P 24 Mg, NH4-N, PO4-P, ph, 32 PO4-P 48 Mg, NH4-N, PO4-P, ph, X *Important Note: Sampling times have been selected for convenience and a normal/long work day for a technician completing the test, and can be adjusted if necessary to suit staff scheduling. The suggested sample times aim to identify the time at which luxury uptake phosphate release is completed, which is typically roughly 24 hours. Completion of luxury uptake phosphate release is indicated by a marked slow-down in the increase of PO4-P. It can be necessary to repeat the testing

4 Page 4 of 6 with different sample times based on earlier test results to home in on when completion of luxury uptake phosphate release occurs. This time establishes process HRT required. 6. Centrifuge each sample for 7 minutes at 4000 RPM, and collect the centrate from the centrifuge tubes for filtration and analysis. If a centrifuge is not available gravity settling and decanting or direct filtration can be used to collect filtered samples. 7. Filter (to 0.45 microns) and refrigerated centrate samples immediately upon collection to separate the filtrate from the fermenting biomass. 8. Analyze the samples for the all the parameters listed in Table 1 using standard laboratory procedures. 9. If possible carry out PO4-P analysis immediately after collecting samples (e.g. using Hach apparatus or similar). This allows the testing to be stopped when luxury uptake phosphorus release has ceased, or extended if release is continuing at the end of the planned test period. 10. Samples collected for CST should be whole unfiltered samples drawn from the bucket after mixing. Reporting 1. Report data in the following table format: Sampling time TP TMg TSS PO4-P NH4-N Sol Mg CST (sec) ph Test Three Carbon Supplemented Phosphate Release Test with pre-thickened WAS This method is developed to demonstrate the rate of P release when supplemented by an external carbon source. Primary sludge, fermenter decant or acetic acid/acetate can be used as a carbon source in normal operation, however for initial testing using vinegar (5% acetic acid) is usually easier. Carry out the test as outlined below, keeping in mind that Steps 3-5 should be performed as rapidly as possible (i.e. in less than 30 minutes if possible) to avoid sample degradation before the first sample is drawn. Preparing sampling and filtering equipment

5 Page 5 of 6 in advance of the test will be important to be able to accomplish this. A test run the day before the actual test is planned may be helpful to ensure all needed equipment is available and functioning as expected. 1. Collect a l WAS sample in a bucket (record actual volume), and allow to settle for 1 hour. Record sampling date and time. It is recommended that the sample be collected in the morning (or beginning of shift) to allow for the test to be monitored more intensely over the first 8 hours. 2. After 1 hr settling, decant and discard clarified liquor, and retain thickened WAS in the bucket. Typically this will result in discarding about ½ to 2/3 of the WAS sample volume and retaining ½ to 1/3 of the volume of the original sample. 3. Collect an unfiltered sample of the thickened WAS for analysis of total suspended solids (TSS) total phosphorus (TP), total Mg and CST. 4. Mix thickened WAS and Vinegar ( source) in the bucket mg per mg VSS (or 0.02 mg /mg TSS) in the WAS sample is typically sufficient, so for a 1.5% TSS sludge with ~66% VSS:TSS ratio, ~300 as acetic acid would be needed, or 6 ml of vinegar (5% acetic acid) per L of thickened WAS sample. This dosage may need to be optimized based on actual P release performance. Please consult Ostara to determine dose. 5. Collect initial (time = 0) sample immediately upon mixing to establish baseline concentrations. 6. Keep in a covered bucket in a location as close to normal process water temperature as practical. 7. Collect subsamples at the time intervals indicated in Table 2 below. Mix the bucket contents thoroughly but without aerating the sample before collecting samples. This could be done by placing the bucket on a stir plate with a magnetic stirrer on low speed to prevent vortexing, or by using a spoon/spatula to gently mix the contents. Table 2: Sampling and Analysis Schedule Sample Time* (hours) Analytes (soluble) CST Testing 0 Mg, NH4-N, PO4-P,, ph X 0.5 PO4-P 1 PO4-P 1.5 PO4-P 2 Mg, NH4-N, PO4-P,, ph 3 PO4-P 4 Mg, NH4-N, PO4-P,, ph 8 PO4-P 24 Mg, NH4-N, PO4-P,, ph X *Note: Sampling times have been selected for convenience to fit within an 8 hour work day (start and end of each day) in order to get as much time coverage as possible. Alternative sampling times more convenient to the person carrying out the test would be acceptable as long as there are a similar number of data points spread throughout the period.

6 Page 6 of 6 8. Centrifuge each sample for 7 minutes at 4000 RPM, and collect the centrate from the centrifuge tubes for filtration and analysis immediately upon sample collection. Centrifugation is primarily to minimize filtration effort in the following step and can be replaced with direct filtration if practical. 9. Filter (glass microfiber followed by 0.45 um cellulose acetate) and refrigerate centrate samples as soon as practical to separated the liquor from the biomass and stop the release process. 10. Analyze the samples for the analytes listed in Table 1 using standard laboratory procedures. If possible carry out PO4-P analysis immediately after collecting samples (using Hach apparatus or similar). Experiment can be stopped when phosphorus release has ceased, and should be extended if the phosphorus release is observed to be incomplete at the end of the planned test period. 11. Samples collected for CST (Capillary suction time) should be whole unfiltered samples drawn from the bucket after mixing. Reporting 2. Report data in the following table format: Sample Time TP Mg total TSS PO4-P NH4- N Mg sol CST (sec) ph Contact Details For any questions or clarifications, please contact: Ahren Britton Ostara USA LLC. Phone: abritton@ostara.com