F. Dilek Sanin

Alkaline solubilization and microwave irradiation as a combined sludge disintegration and minimization method.

Commonly used pretreatment method of alkaline solubilization (using NaOH) and a relatively new technology of microwave (MW) irradiation (160 degrees C) were combined as a pretreatment method of waste activated sludge (WAS) in this study. First alkaline and MW pretreatment methods were examined separately, then their combination for different conditions was investigated in terms of their effect on COD solubilization, turbidity and capillary suction time (CST). For combined pretreatments, soluble COD to total COD ratio (SCOD/TCOD) of WAS increased from 0.005 (control) to 0.18, 0.27, 0.34 and 0.37 for combined methods of MW and pH-10, 11, 12 and 12.5, respectively. Deteriorated dewaterability due to alkaline pretreatment was also improved due to the incorporation of MW irradiation. Further, with small scale batch anaerobic reactors, pH-10, pH-12, MW (alone), MW+pH-10 and MW+pH-12 pretreated WAS samples were anaerobically digested. Highest total gas and methane productions were achieved with MW+pH-12 pretreatment with 16.3% and 18.9% improvements over control reactor, respectively. Finally the performance of MW+pH-12 pretreatment was examined with 2L anaerobic semi-continuous reactors for 92 days and compared to that of the control reactors. These reactors were operated at an SRT of 15 days. After steady state, 43.5% and 55% improvements were obtained in respective daily total gas and methane productions. TS, VS and TCOD reductions were improved by 24.9%, 35.4% and 30.3%, respectively based on a relative calculation with respect to control reactors. This way combined alkaline-microwave treatment proved to be an effective sludge minimization method. Pretreated digested sludge had 22% improved dewaterability than unpretreated digested sludge. Higher SCOD and NH(3)-N concentrations were measured in the pretreated digested sludge supernatant; however, PO(4)-P concentration did not increase much.

Effect of starvation on the adhesive properties of xenobiotic degrading bacteria

The purpose of this study was to observe the effects of different starvation conditions on the surface characteristics and adhesive properties of bacteria. Three pure culture xenobiotic degrading bacteria were used in this study: Pseudomonas sp. strain A, Pseudomonas sp. strain D and Rhodococcus corallinus strain 11. These microorganisms were selected for to their ability to degrade cyanuric acid, which is a derivative of s-Triazine, a common herbicide. These microorganisms were separately starved for carbon (glucose) and nitrogen (cyanuric acid) and their physiological responses to starvation were measured. Results indicated that there was a remarkable shrinkage in size of Pseudomonas strain A starved for carbon for 16 days. The surface properties of these three microorganisms changed significantly on starvation. Surface hydrophobicities for all the microorganisms stayed more or less constant during carbon starvation conditions, whereas, there was a significant decrease in hydrophobicity when all three cultures were starved for nitrogen. In parallel to these findings, it was observed that when the hydrophobicity of the cultures decreased, the attachment capabilities of these microorganisms decreased. This is believed to be due to the production of highly hydrated extracellular polysaccharides when carbon is present in the medium. Results of this study have important implications on the transport and attachment of microorganisms during soil remediation processes.

Ultrasonic pretreatment and subsequent anaerobic digestion under different operational conditions

In this study ultrasonic pretreatment was investigated in order to improve anaerobic digestion. First, the most effective sonication time was selected during the preliminary studies conducted on waste activated sludge samples. Then the optimal time selected was confirmed running batch anaerobic reactors. In the last part of the experiments, the effect of sonication was investigated for different operational conditions of semi-continuous digesters. Preliminary studies showed 15 min of sonication increased 50 mg/L initial soluble COD concentration up to a value of 2500 mg/L. Batch anaerobic digester results indicated that the increased soluble substrate improved anaerobic biodegradability concurrently, again with the maximal improvement observed for 15 min of sonication. Results from semi-continuous reactors indicated that at SRT of 15 days and OLR of 0.5 kg/m(3) d, ultrasonic pretreatment improved the daily biogas production, methane production and volatile solids reduction significantly when compared to control system. During the operation of reactors at 7.5 days of SRT, pretreatment helped to keep the reactors working. A simple economical analysis of the system was performed using the data obtained during the laboratory study.

Pathogen reduction capabilities of freeze/thaw sludge conditioning

Abstract Freezing and thawing sludge has become an economically feasible technique of sludge conditioning in regions where natural freezing is available. Even though the dramatic effects of freeze/thaw on dewatering have been studied extensively, its effects on the survival of pathogenic microorganisms have not been investigated. If freeze/thaw conditioning can be shown to reduce pathogenic microorganisms, then sludges treated in this fashion can be disposed of on land with less risk of health effects. In this paper, the effects of freezing rate, temperature and time in the frozen state on the removal of pathogens are tested. The response of seven indicators of microbial contamination; fecal coliforms, Salmonella , plaque forming units, fecal streptococci, poliovirus, helminths and protozoa to the freeze/thawing of both aerobically and anaerobically digested sludges is examined. Fecal coliforms, fecal streptococci, and plaque forming units are chosen as the commonly used indicators of bacteria and viruses, respectively in wastewater sludges. Pathogenic bacteria ( Salmonella ), virus (Poliovirus) and parasites ( Ascaris suum and Cryptosporidium parvum ) tested in the second phase are chosen as sample microorganisms in their respective classes. Freeze/thaw sludge conditioning is proven to be an effective means of removing most pathogenic microorganisms. Fecal streptococci are found to be the best indicator of the effectiveness of freeze/thawing on enteric bacteria. Results of this study indicate that freeze/thaw conditioning coupled with sludge digestion can significantly enhance the overall pathogenic microorganism reduction achieved in a wastewater treatment plant. Added effectiveness by freeze/thaw treatment may become critical for a plant in meeting the pathogen reduction requirements by U.S. regulations prior to any practice of land application or land disposal of sludge.

Operational Conditions of Activated Sludge: Influence on Flocculation and Dewaterability

Selected operational conditions of activated sludge are investigated in relation to their effect on flocculation and dewatering. Semi-continuous reactors with 2 -L volume were operated at different mean cell residence times, C/N ratios, and three different influent cations. Results show that MCRT, C/N ratio, and the cation type affect the bioflocculation capacity of activated sludge measured by the quantity of extracellular polymeric substances. As the MCRT value operated in the reactors and the C/N ratio of the influent wastewater increase, total amount of polymers produced increases. High MCRT values and low C/N values cause good dewatering of the sludge. All cations are shown to stimulate the EPS production in a way that the highest total EPS concentrations are observed at the highest cation dosages. The dewaterability of the sludges improves only with increasing calcium and magnesium concentrations and deteriorates with increasing potassium concentration.

The Dewaterability of Disintegrated Sludge Samples Before and After Anaerobic Digestion

Sludge pretreatment systems emerged during the past few decades to reduce the ever-increasing quantities of sludge. A variety of different techniques have been studied for their effectiveness in solubilizing the chemical oxygen demand (COD) and increasing the digestability and decreasing the final quantity of sludge. In this study different pretreatment techniques and their effects on dewaterability were investigated at two stages of treatment. First, dewaterability was measured as capillary suction time (CST) right after the application of pretreatment; second, the dewaterability of pretreated and subsequently digested sludge was measured at the end of the anaerobic digestion period. The pretreatment techniques applied were acid and alkali treatment, ultrasonication, microwave (MW) treatment, and a combination of MW and alkali treatment. For all the methods tested, it was found that CST value deteriorated after pretreatment compared to untreated samples. From all the methods studied, acid treatment influenced the CST the least, whereas alkali treatment influenced it the greatest. Sonication and MW had similar intermediate effects. MW treatment helped improve the high CST values caused by the alkali treatment when the two methods were combined. In the second stage of the study, the pretreated samples were anaerobically digested and the CST values were measured afterwards. This time a completely different line of results was observed; there was almost no difference in CST values following digestion regardless of the method used. This indicated that anaerobic digestion process has such a dominant impact on sludge dewaterability that the significant effects created by different pretreatment techniques prior to digestion were dampened and the CST values were brought down to a narrow range following digestion in which the control and pretreated sludge had almost equal CST values.

Investigation of nonylphenol and nonylphenol ethoxylates in sewage sludge samples from a metropolitan wastewater treatment plant in Turkey

Nonylphenol ethoxylates (NPEOs) have drawn significant attention within the last decade for both scientific and legislative reasons. In Turkey, the Regulation Regarding the Use of Domestic and Urban Sludges on Land states a limit value for the sum of nonylphenol (NP), nonylphenol monoethoxylate (NP1EO) and nonylphenol diethoxylate (NP2EO) as NPE (NPE=NP+NP1EO+NP2EO). Unfortunately a standard method for the determination of these chemicals has not been yet set by the authorities and no data exists about the concentrations of NP and NPEOs in sewage sludge in Turkey. The aim of this study is to propose simple and easily applicable extraction and measurement techniques for 4-n-nonylphenol (4-n-NP), NP, NP1EO and NP2EO in sewage sludge samples and investigate the year round concentrations in a Metropolitan Wastewater Treatment Plant (WWTP) in Turkey. Different extraction techniques and GC/MS methods for sewage sludge were tested. The best extraction method for these compounds was found to be ultrasonication (5 min) using acetone as the solvent with acceptable recovery of analytes suggested by USEPA and other studies. The optimized extraction method showed good repeatability with relative standard deviations (RSDs) less than 6%. The recovery of analytes were within acceptable limits suggested by USEPA and other studies. The limits of detection (LODs) were 6 µg kg(-1) for NP and NP1EO, 12 µg kg(-1) for NP2EO and 0.03 µg kg(-1) for 4-n-NP. The developed method was applied to sewage sludge samples obtained from the Central WWTP in Ankara, Turkey. The sum NPE (NP+NP1EO+NP2EO) was found to be in between 5.5 µg kg(-1) and 19.5 µg kg(-1), values which are in compliance with Turkish and European regulations.

Evaluation of solar sludge drying alternatives by costs and area requirements

Thermal drying is a common method to reach above 90% dry solids content (DS) in sludge. However, thermal drying requires high amount of energy and can be expensive. A greenhouse solar dryer (GSD) can be a cost-effective substitute if the drying performance, which is typically 70% DS, can be increased by additional heat. In this study feasibility of GSD supported with solar panels is evaluated as an alternative to thermal dryers to reach 90% DS. Evaluations are based on capital and O&M costs as well as area requirements for 37 wastewater treatment plants (WWTPs) with various sludge production rates. Costs for the supported GSD system are compared to that of conventional and co-generation thermal dryers. To calculate the optimal costs associated with the drying system, an optimization model was developed in which area limitation was a constraint. Results showed that total cost was minimum when the DS in the GSD (DS(m,i)) was equal to the maximum attainable value (70% DS). On average, 58% of the total cost and 38% of total required area were associated with the GSD. Variations in costs for 37 WWTPs were due to differences in initial DS (DS(i,i)) and sludge production rates, indicating the importance of dewatering to lower drying costs. For large plants, GSD supported with solar panels provided savings in total costs especially in long term when compared to conventional and co-generation thermal dryers.

Effect of digester f/m ratio on gas production and sludge minimization of ultrasonically treated sludge.

Sludge pretreatment by mechanical, chemical or thermal methods before anaerobic digestion has been applied to increase the digestability of excess sludge. Pretreatment processes rely on their ability to disrupt cell membranes and to release organic materials from the cells into the aqueous phase. Pretreatment by mechanical disintegration has grown rapidly in recent years in parallel with the advances in technology. Ultrasonic sludge disintegration -one of the most commonly used mechanical pretreatment methods- enables the occurrence of cavitation bubbles for the break-up of microorganism cells to extract intracellular materials. The purpose of this study was to conduct disintegration experiments to optimize sonication parameters and to operate subsequent batch anaerobic digesters to examine the effect of food to microorganism ratio (F/M) in sonicated and unsonicated samples. Results showed that high sonication powers and longer treatment times were effective in sludge disintegration in terms of soluble chemical oxygen demand release. Sonicated sludge digested in batch reactors with higher initial F/M ratio caused higher methane generations, higher sludge reductions and had better dewatering characteristics.

Potential risk reduction of Aroclor 1254 by microbial dechlorination in anaerobic Grasse River sediment microcosms

Aroclor 1254 was the second most produced commercial PCB mixture and is found in soils, sediments and sewage throughout the globe. This commercial PCB mixture is considered particularly toxic because of the relatively high concentrations of congeners with dioxin-like properties. The potential for risk reduction by microbial reductive dechlorination of Aroclor 1254 (A1254) was investigated in sediment microcosms from Grasse River (GR), Massena, NY. The specificity of A1254 dechlorination was doubly- and singly-flanked chlorines in meta positions and to a less extent doubly-flanked para chlorines of 2345-substituted chlorobiphenyl rings. The average dechlorination rate of A1254 was 0.0153 Cl-/biphenyl/day, and dechlorination rates of single congeners ranged between 0.001 and 0.0074 Cl-/biphenyl/day. Potential risk associated with A1254 based on the toxic equivalency factors of the dioxin-like congeners was reduced by 83%. Additional potential risk associated with bioaccumulation in fish was reduced by 35% based on biota-sediment accumulation factor estimates for all detected congeners. Finally, the dechlorination end-products were tri- and tetra-chlorobiphenyls with unflanked chlorines, all of which are susceptible to further degradation by aerobic microorganisms. The combined results indicate that microbial reductive dechlorination has the potential for reducing risk associated with toxicity and bioaccumulation in fish in sites contaminated with A1254.