Accomplishments. 1 Nevada Renewable Energy Consortium Quarterly Progress Report

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1 Subtask.4.: Chemically promoted mechanical dewatering of wastewater sludge FINAL REPORT for work completed January, 200 December 3, 200. (PI: Charles Cornella, UNR) More than 6,000 wastewater treatment plants in the US produce more than 40 million tons of sludge as a byproduct, every year. Waste disposal is expensive, and costs about $ billion per year. Finding cost-effective means of dewatering and drying the sludge is seen as a important strategy for reducing those costs, and is the goal of this work. Enhancing the effectiveness of dewatering is key to the success of our strategy. Our approach is chemical pre-treatment to decrease the water-sludge energy interactions chemically, to enhance the efficiency of typical mechanical dewatering methods. With a belt filter press, WWTPs are able to dewater sludge to about 70% moisture, or to about 80% for digested sludge. Clearly, the attraction between water and biomass substrate is quite strong. It is reasonable to expect that the presence of disrupting molecules might significantly affect the chemical activity of the water. In previous measurements at UNR, we have seen that warm acetone has such an effect, and recent work performed by others demonstrates the effectiveness of alkalinity in promoting dewaterability. The means to test the effect on dewaterability is straightforward. Small samples of very wet sludge are placed in a centrifuge for controlled period of time, which results in a clear liquid and a compressed sludge. The volume of water separated determines the extent of dewatering. The effects of various additives on sludge dewaterability will be measured by mixing the additive prior to centrifuging. This work is being performed primarily at UNR, with assistance from DRI. The major goal of this project is to expand upon previous work related to sludge drying, and extend this work in several new directions. Individual objectives within the project include the following: Develop a test protocol for sludge dewaterability Determine the dewatering characteristics of rehydrated dried sludge Test candidate additives for enhanced dewatering Accomplishments Task.4..: Develop test protocol To initiate our project, we developed a formal working arrangement between UNR and the Truckee Meadows Water Reclamation Facility (TMWRF). This Interlocal agreement was signed by city councils from both Reno and Sparks Nevada, as of January 0, 200. The agreement granted students from UNR access to the facility in order to procure samples of sludge, and further to conduct on-site demonstration of a sludge dryer built under a separate contract. All the tests done as part of this project were done on digested sludge procured from TMWRF, with an average moisture content of 86%. Test protocols were developed for measuring moisture content of sludge, and for testing the effectiveness of additives to promote mechanical dewatering of sludge.. Measuring moisture content. The moisture content of the sludge samples is determined by how much mass is lost from a sludge sample after being dried in an oven. A sample is placed in a drying oven at 05 C for 24 hour. The difference between the mass of the wet sludge and dried sludge determines the moisture content of the sludge. Comparisons between moisture contents Nevada Renewable Energy Consortium Quarterly Progress Report

2 of untreated and treated centrifuged sludge demonstrate the degree of dewatering achieved by mechanical dewatering and the extent that chemical treatments of sludge enhance that process. 2. Enhanced dewatering. Approximately 20g of sludge, or about four to six scoops with a metal scoopula, is placed into a 000mL flask for chemical addition. About 00mL of a solution containing a specific additive is mixed in with the sludge so that the sludge has a homogenous quality similar to mud; the solution may be stirred with the scoopula until this consistency is reached. The sludge solution is allowed to sit for 3 hours under a fume hood. Multiple solutions of sludge may be prepared at one time using this procedure. During this period of 3 hours, untreated sludge samples, to be used for comparison with the chemically treated samples, are assembled. A tin foil cup is labeled using a marker, and its mass is recorded using an analytical balance. The scoopula is cleaned and is used to place a sample of untreated sludge in the tin foil cup. The mass is measured once again, and then, the sample is placed into the drying oven located in LME 222. Three.5mL microcentrifuge tubes are labeled, 2, and 3 and their masses are recorded. A metal spatula can be used to place sludge into the centrifuge tubes, but in lieu of a spatula, the metal scoopula and a -200µL pipet tip can be used to pack sludge. The centrifuge tubes should be filled to 80% of capacity for each of the three labeled tubes, and the masses of the sludge filled tubes are measured. The untreated samples in the centrifuge tubes are centrifuged for 0 minutes and the liquid water that has accumulated at the top is decanted using a µl micropipette. The centrifuge tube samples masses are measured and recorded. The tubes are then opened and hung off the side of a porcelain crucible. After the 3 hours have expired, the procedure for filling the centrifuge tubes and centrifugation are repeated for the chemically treated sludge. These sludge filled tubes are hung alongside the untreated sludge tubes (all centrifuge tubes should be labeled appropriately) and are placed into the drying oven overnight. The microcentrifuge is turned on, and the lid is lifted after hearing the click that signals that the centrifuge has been unlocked. The sludge filled centrifuge tubes are placed into centrifuge and are spaced appropriately so that the centrifuge is balanced. Water-filled tubes may be used if there are an odd number of sludge filled tubes. The centrifuge is then started by setting the dial to 0 minutes. If the centrifuge does not start right away, gently move the lid, and it should initiate centrifugation. After it has finished, the centrifuge will unlock, and the samples may be taken out. DRI has completed mineral analysis on a sludge sample and an ash sample provided by UNR. A sample of dried wastewater sludge was analyzed. A second sample consisting of ash remaining after complete oxidation of all organic matter in a sludge sample was also analyzed. Metals content of 5 metals were measured by XRF. The significant results are shown in the table below. The total metals content of the ash is reported to be 62.9%, and the total metals content of dried sludge is 2.5%. Metal Sludge Ash Dry Sludge Phosphorous concentration (% mass) Calcium concentration (% mass) Iron concentration (% mass) Silicon concentration (% mass) Nevada Renewable Energy Consortium Quarterly Progress Report

3 Metal Sludge Ash Dry Sludge Aluminum concentration (% mass) Titanium concentration (% mass) Potassium concentration (% mass) Sulfur concentration (% mass) Zinc concentration (% mass) Strontium concentration (% mass) Barium concentration (% mass) Copper concentration (% mass) Manganese concentration (% mass) Zirconium concentration (% mass) Chlorine concentration (% mass) Vanadium concentration (% mass) Chromium concentration (% mass) Lead concentration (% mass) Nickel concentration (% mass) Antimony concentration (% mass) Rubidium concentration (% mass) Yttrium concentration (% mass) Palladium concentration (% mass) Thallium concentration (% mass) Content of metals in the sludge is similar to typical values reported in literature. More than 99% of the metals detected consist of metals, including phosphorous, calcium, iron, silicon, aluminum, titanium, potassium, sulfur, zinc, strontium, and barium. Task.4..2: Compare dewaterability of rehydrated dried sludge with that of fresh sludge TSludge with high moisture content, such as that procured from TMWRF, becomes biologically active after a period of days, and produces strong odors. Furthermore, it is possible that the dewaterability of the activated sludge is affected by the presence of a large amount of living bacteria. Therefore, storage of sludge on campus might be facilitated greatly if it could be dried, with the plan to rehydrate sludge to produce a sludge with moisture content identical to that originally collected. If the rehydrated sludge has dewatering characteristics similar to the sludge before drying, then lab procedures are greatly simplified. After several tests of drying and rehydrating, we concluded that the dewaterability of rehydrated sludge is affected by drying. Apparently, drying causes irreparable damage to cells that makeup the sludge. Thus, all tests of sludge dewatering for task 3 were done with sludge collected on the same day as the evaluation. Task.4..3: Evaluate additives for enhanced dewatering Using the protocols described above, each of the following additives were evaluated for potential to improve sludge dewaterability. Hot organic solvents- By displacing water in the biomass of sludge, it is possible that water soluble organics might be effective in promoting dewatering. Subsequent recovery of the solvent is required, but if the solvent is selected with a low boiling point, then recovery need not be expensive. We discovered that hot acetone does in fact improve 3 Nevada Renewable Energy Consortium Quarterly Progress Report

4 dewaterability of sludge, from 86% down to about 82%. That increase was perceived as too small to pursue further. Sodium hydroxide- We hypothesized that osmotic and Ionic forces would cause dewatering through enhanced lysing. However, a saturated solution of NaOH promoted no additional dewatering. Glycerol- We evaluated glycerol for the potential to enhance dewaterability. Instead, glycerol greatly decreases dewaterability, forming a stable emulsion with the sludge. It apparently has the same density as the dried biomass (.2 g/cm 3 ). Sodium Dodecyl Sulfate (SDS)- SDS is used to solubilize phospholipid cell membranes. We hoped that breaking down cell membranes would allow bound water to escape the biomass during centrifugation, but this turned out not to be the case. Instead, sludge treated with SDS showed greater resistance to dewatering than untreated sludge. Sodium Chloride- By creating osmotic pressure within cell membranes, we expect lysing to occur when sludge is treated with NaCl. 0.25M, 0.5M and M NaCl solutions decreased moisture content of sludge by an average of 3.9%, 4.0%, and 4.9%, respectively. Although these reduced moistures are beneficial, we expect that added materials costs to result from use of salt, due to its corrosivity. Therefore, these modest gains in improved dewaterability were deemed insufficient, and is not further pursued. Industrial enzymes- Two brands of meat tenderizers containing salt, sugar, food starch, and enzymes were first tested. In 0: (water:tenderizer) solutions, the meat tenderizer containing the enzyme bromelain decreased MC by 5.6%, and the meat tenderizer containing the enzyme papain decreased MC by 8.0%. Protease DS and Cellulase DS from Amano Enzymes Inc. were later tested but had little to no effect on sludge dewatering at both optimal and nonoptimal conditions.cost Status Cost Status Schedule Status The progress to-date on each project task is consistent with the original schedule. The entire schedule is shown below. Project Schedule Months from Contract Initiation Activity Task : Develop test protocol Task 2: Compare dewaterability of rehydrated dried sludge with that of fresh sludge Task 3: Evaluate additives for enhanced dewatering Task 4: Project management and reporting Deliverables* Q Q Q D F *Deliverables: Q = Quarterly report; D = Draft Report; F = Final Report Changes in Approach or Aims None 4 Nevada Renewable Energy Consortium Quarterly Progress Report

5 Actual or Anticipated Problems No significant problems were encountered during this reporting period. Absence or Changes in Key Personnel One graduate student working on the project left the university suddenly in May of 200. We compensated by hiring two undergraduates, but we were always playing catch-up after that. Products and Technology Transfer None 5 Nevada Renewable Energy Consortium Quarterly Progress Report