Cigdem Eskicioglu

Synergetic pretreatment of sewage sludge by microwave irradiation in presence of H2O2 for enhanced anaerobic digestion.

A microwave-enhanced advanced hydrogen peroxide oxidation process (MW/H(2)O(2)-AOP) was studied in order to investigate the synergetic effects of MW irradiation on H(2)O(2) treated waste activated sludges (WAS) in terms of mineralization (permanent stabilization), sludge disintegration/solubilization, and subsequent anaerobic biodegradation as well as dewaterability after digestion. Thickened WAS sample pretreated with 1gH(2)O(2)/g total solids (TS) lost 11-34% of its TS, total chemical oxygen demand (COD) and total biopolymers (humic acids, proteins and sugars) via advanced oxidation. In a temperature range of 60-120 degrees C, elevated MW temperatures (>80 degrees C) further increased the decomposition of H(2)O(2) into OH* radicals and enhanced both oxidation of COD and solubilization of particulate COD (>0.45 micron) of WAS indicating that a synergetic effect was observed when both H(2)O(2) and MW treatments were combined. However, at all temperatures tested, MW/H(2)O(2) treated samples had lower first-order mesophilic (33+/-2 degrees C) biodegradation rate constants and ultimate (after 32 days of digestion) methane yields (mL per gram sample) compared to control and MW irradiated WAS samples, indicating that synergistically (MW/H(2)O(2)-AOP) generated soluble organics were slower to biodegrade or more refractory than those generated during MW irradiation.

Fate of estrogenic hormones in wastewater and sludge treatment: A review of properties and analytical detection techniques in sludge matrix

Estrogenic hormones (estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethinylestradiol (EE2)) are the major contributor to the total estrogenicity in waterways. Presence of these compounds in biosolids is also causing concern in terms of their use as soil amendment. In comparison with wastewater treatment, removal of estrogenic compounds in sewage sludge has received less attention. This paper presents a literature review regarding the source and occurrence of these pollutants in our environment. The removal pathways of estrogenic compounds in engineered systems, such as full-scale wastewater treatment plants (WWTPs), are also discussed. Review of the fate studies revealed that activated sludge system with nutrient removal shows very high (>90%) removal of estrogenic hormones in most of the cases. Although, aerobic digestion showed better attenuation of estrogenic compounds, anaerobic digestion increased the overall estrogenicity of biosolids. Finally, this paper highlights the challenges involved in analytical determination of these compounds in sewage sludge matrix.

Microwave, ultrasonic and chemo-mechanical pretreatments for enhancing methane potential of pulp mill wastewater treatment sludge

Microwave (2450 MHz, 1250 W), ultrasonic (20 kHz, 400 W) and chemo-mechanical (MicroSludge® with 900 mg/L NaOH followed by 83,000 kPa) pretreatments were applied to pulp mill waste sludge to enhance methane production and reduce digester sludge retention time. The effects of four variables (microwave temperature in a range of 50-175°C) and sonication time (15-90 min), sludge type (primary or secondary) and digester temperature (mesophilic and thermophilic) were investigated. Microwave pretreatment proved to be the most effective, increasing specific methane yields of WAS samples by 90% compared to controls after 21 days of mesophilic digestion. Sonication solubilized the sludge samples better, but resulted in soluble non-biodegradable compounds. Based on the laboratory scale data, MicroSludge® was found the least energy intensive pretreatment followed by sonication for 15 min alternative with net energy profits of 1366 and 386 kWh/tonne of total solids (TS), respectively. Pretreatment benefits were smaller for thermophilic digesters.

Effect of microwave irradiation on anaerobic degradability of model kitchen waste.

High temperature and pressure microwave (MW) irradiation was investigated as a pre-treatment to enhance anaerobic biodegradability and methane production from a model kitchen waste (KW). Heating rates of 7.8, 3.9 and 1.9 degrees C/min from room temperature to a final pre-treatment temperature of 175 degrees C with 1 min temperature holding time were tested. MW irradiation was successful in solubilization of particulate chemical oxygen demand (COD) resulting in higher soluble COD, protein and sugar concentrations in the supernatant phase (<0.45 microm) as well as in the whole fraction of pretreated KW compared to controls (not pretreated). Anaerobic biodegradability of the supernatant and whole fractions of pretreated KW was assessed by using a batch biochemical methane potential assay (BMP) at 33 degrees C. Although the highest level of solubilization was achieved at a heating rate of 1.9 degrees C/min, improvement in anaerobic biodegradability was observed only at the fastest heating rate of 7.8 degrees C/min for whole waste and for all conditions with the supernatant phase. BMP indicated increased biodegradability of between 5% and 16% for the supernatant fraction relative to controls. For the whole fraction, anaerobic biodegradability improved by 9% at a heating rate of 7.8 degrees C/min.

Performance of anaerobic waste activated sludge digesters after microwave pretreatment.

Effects of microwave pretreatment on waste activated sludge (WAS) in mesophilic semicontinuous digesters with acclimatized inoculum at solids retention times (SRTs) of 5, 10, and 20 days are presented. Batch digesters determined optimum microwave temperature, intensity, WAS concentration, and percentage of WAS pretreated for highest WAS solubilization (soluble to total chemical oxygen demand ratio [SCOD:TCOD]) and biogas production. Pretreatment results indicated the potential to damage floc structure and release 4.2-, 4.5-, and 3.6-fold higher soluble proteins, sugars, and SCOD:TCODs compared with controls, with nucleic acid release. Pretreatment increased dewaterability and bioavailability of WAS with 20% higher biogas production compared with controls in batch digestion. In semicontinuous digesters, relative (to control) improvements in removals dramatically increased, as SRT was shortened from 20 to 10 to 5 days, with 23 and 26% higher volatile solids removals for WAS pretreated to 96 degrees C by microwave and conventional heating at a 5-day SRT.

Anaerobic digestion of whole stillage from dry-grind corn ethanol plant under mesophilic and thermophilic conditions.

Anaerobic digestion of whole stillage from a dry-grind corn-based ethanol plant was evaluated by batch and continuous-flow digesters under thermophilic and mesophilic conditions. At whole corn stillage concentrations of 6348 to 50,786 mg total chemical oxygen demand (TCOD)/L, at standard temperature (0 °C) and pressure (1 atm), preliminary biochemical methane potential assays produced 88±8 L (49±5 L CH4) and 96±19 L (65±14 L CH4) biogas per L stillage from mesophilic and thermophilic digesters, respectively. Continuous-flow studies for the full-strength stillage (TCOD=254 g/L) at organic loadings of 4.25, 6.30 and 9.05 g TCOD/L days indicated unstable performance for the thermophilic digester. Among the sludge retention times (SRTs) of 60, 45 and 30 days tested, the mesophilic digestion was successful only at 60 days-SRT which does not represent a practical operation time for a large scale bioethanol plant. Future laboratory studies will focus on different reactor configurations to reduce the SRT needed in the digesters.

Initial examination of microwave pretreatment on primary, secondary and mixed sludges before and after anaerobic digestion

The effects of microwave pretreatment on disintegration and mesophilic digestion of waste activated sludge (WAS), primary sludge (PS), combined (PS + WAS) sequencing batch reactor (SBR) sludge and anaerobically digested biocake were investigated by both household and bench scale industrial types microwaves at temperatures below and above boiling point. Pretreatment variables, temperature, intensity (cooking rate) and sludge concentration had statistically significant effects on solubilization. The microwave pretreatment also increased the bioavailability of sludge components under batch anaerobic digestion and enhanced the dewaterability of pretreated sludges after digestion. However, the level of improvements in solubilization and biodegradation from different waste sludges were different. While the largest improvement in ultimate biodegradation was observed in WAS, microwave irradiation only affected the rate of biodegradation of pretreated PS samples. Similarly, relatively lower solubilization ratios achieved for combined - SBR sludge was attributed to high sludge age of extended aeration SBR unit. It is possible that initial sludge characteristics may influence final pretreatment outcomes so that general statements of performance cannot always be made.

Mesophilic batch anaerobic co-digestion of fruit-juice industrial waste and municipal waste sludge: process and cost-benefit analysis.

The feasibility of anaerobic co-digestion of two juice-based beverage industrial wastes, screen cake (SC) and thickened waste activated sludge (TWAS), along with municipal sludge cake (MC) was investigated. Experiments were conducted in twenty mesophilic batch 160 ml serum bottles with no inhibition occurred. The statistical analysis proved that the substrate type had statistically significant effect on both ultimate biogas and methane yields (P=0.0003<0.05). The maximum and minimum ultimate cumulative methane yields were 890.90 and 308.34 mL/g-VSremoved from the digesters containing only TWAS and SC as substrate. First-order reaction model well described VS utilization in all digesters. The first 2-day and 10-day specific biodegradation rate constants were statistically higher in the digesters containing SC (P=0.004<0.05) and MC (P=0.0005<0.05), respectively. The cost-benefit analysis showed that the capital, operating and total costs can be decreased by 21.5%, 29.8% and 27.6%, respectively using a co-digester rather than two separate digesters.

Conductive heating and microwave hydrolysis under identical heating profiles for advanced anaerobic digestion of municipal sludge

Microwave (2.45 GHz, 1200 W) and conventional heating (custom pressure vessel) pretreatments were applied to dewatered municipal waste sludge (18% total solids) using identical heating profiles that span a wide range of temperatures (80-160 °C). Fourteen lab-scale semi-continuous digesters were set up to optimize the energy (methane) output and sludge retention time (SRT) requirements of untreated (control) and thermally pretreated anaerobic digesters operated under mesophilic and thermophilic temperatures. Both pretreatment methods indicated that in the pretreatment range of 80-160 °C, temperature was a statistically significant factor (p-value < 0.05) for increasing solubilization of chemical oxygen demand and biopolymers (proteins, sugars, humic acids) of the waste sludge. However, the type of pretreatment method, i.e. microwave versus conventional heating, had no statistically significant effect (p-value >0.05) on sludge solubilization. With the exception of the control digesters at a 5-d SRT, all control and pretreated digesters achieved steady state at all three SRTs, corresponding to volumetric organic loading rates of 1.74-6.96 g chemical oxygen demand/L/d. At an SRT of 5 d, both mesophilic and thermophilic controls stopped producing biogas after 20 d of operation with total volatile fatty acids concentrations exceeding 1818 mg/L at pH <5.64 for mesophilic and 2853 mg/L at pH <7.02 for thermophilic controls, while the pretreated digesters continued producing biogas. Furthermore, relative (to control) organic removal efficiencies dramatically increased as SRT was shortened from 20 to 10 and then 5 d, indicating that the control digesters were challenged as the organic loading rate was increased. Energy analysis showed that, at an elevated temperature of 160 °C, the amount of methane recovered was not enough to compensate for the energy input. Among the digesters with positive net energy productions, control and pretreated digesters at 80 °C were more favorable at an SRT of 10 d.

Effect of low temperature microwave pretreatment on characteristics and mesophilic digestion of primary sludge

The main obstacles existing in the biodegradation of primary sludge are particle de‐amalgamation and the degradation‐resisting structure of large‐size particulate. Microwave irradiation solubilizes primary sludge by interaction of the electromagnetic field with polar particles in the sludge, which leads to a temperature increase in the irradiated sample. The influence of microwave irradiation on the characteristics and biochemical methane potential of microwave‐pretreated primary sludge was studied in terms of microwave intensity (40 and 80% of total microwave power), sludge solid concentration (1 to 4% total solids, w/v) and pretreatment temperature achieved (35 to 90 °C). Microwave irradiation was found to increase the concentration of soluble chemical oxygen demand in the sludge. The ratio of soluble to total chemical oxygen demand increased from 2.5 to between 6 and 7% for primary sludge with 4% total solids concentration at a pretreatment temperature of 90 °C. In biochemical methane potential tests, biogas production rate increased with both pretreatment temperature and sludge total solids concentrations. For primary sludge with 4% total solids concentration pretreated to 90 °C, biogas production rate increased by 37% or resulted in a 28% reduction in required digestion time to achieve 85% of the ultimate biogas production. A first‐order reaction model showed a constant increase in the biogas production rate coefficient with the increase in microwave pretreatment temperature. Microwave intensity in the range of pretreatment temperatures studied (35 to 90 °C) presented no obvious impact on primary sludge solubilization or anaerobic digestion in terms of ultimate biodegradation efficiency.