Enhancement of anaerobic waste activated sludge digestion by microwave pretreatment

Improvement of biodegradability of waste activated sludge (WAS) depends on enhanced disintegration of the floc structure of sludge and increasing the accessibility to both intracellular (within the microbial cell) and extracellular (within the polymeric network) materials before WAS is sent to anaerobic digesters. This study proposes microwave (MW) technology as a new and an alternative pretreatment method to disintegrate the floc structure of secondary sludge, to enhance the hydrolysis and to improve the anaerobic digestion of WAS in comparison to existing pretreatment methods such as, chemical, mechanical and conventional heating (CH) techniques. In the first stage of the study, the effects of MW pretreatment on disintegration and hydrolysis of WAS by soluble chemical oxygen demand (COD), soluble protein, soluble sugar and nucleic acid leakage detection experiments were investigated. The effects of three variables [MW temperature (T), MW intensity (I), WAS concentration (C)] and the effects of four variables [T, I, C and volume percentage of WAS pretreated (PT)] were investigated on WAS solubilization and biogas production in two multilevel factorial statistical designs containing 24 solubilization runs and 54 mesophilic batch reactors, respectively. In a low temperature range (50-96°C) using a household type (1250 W, 2450 MHz) MW oven, pretreated WAS samples resulted in 3.6 +/- 0.6 and 3.2 +/- 0.1 fold increases in soluble COD/total COD ratios at high [5.4% total solid (TS), w/w] and low (1.4% TS, w/w) sludge concentrations, respectively. WAS, pretreated to 96°C, produced the greatest improvement in biogas production with 15 +/- 0.5 and 20 +/- 0.3% increases over the controls (unpretreated) after 19 d of digestion at low and high WAS concentrations. In the second stage of the study, two different pretreatment temperatures (50 and 96°C) were further tested in a total of 10 semi-continuous digesters at sludge retention times (SRTs) of 5, 10 and 20 d. Digesters using CH WAS were also run to investigate thermal and athermal effects of MW pretreatment. In general, incremental increases in total solid (TS), volatile solids (VS) and total COD removal efficiency of pretreated digesters compared to controls dramatically increased as SRT was gradually shortened from 20 to 10 to 5 d. WAS pretreated to 96°C by MW and CH achieved 29 and 32% higher TS and 23 and 26% higher VS removal efficiencies compared to controls at SRT of 5 d, while similar reactors at SRT of 20 d had only 16% higher TS and 11 and 12% higher VS removals than those of controls, respectively. Ultrafiltration (UF) was also used to characterize the soluble molecular weight (Mw) distributions of control, CH and MW irradiated WAS at 96°C. Soluble CODs of CH and MW irradiated WAS were 361 +/- 45 and 143 +/- 34% higher and resulted in 475 +/- 3 and 211 +/- 2% higher cumulative biogas productions relative to the control at the end of 23 days of mesophilic batch anaerobic digestion, respectively. Depending on the Mw fraction, the range of substrate volumetric utilization rate increases from anaerobic digesters was between 94-184% for the CH and 26-113% for the MW compared to the control for the first 9 days of the digestion. Digesters treating high Mw materials (Mw > 300 kDa) resulted in smaller first-order biodegradation rate constants, k, indicating that microorganisms require a longer time to utilize high Mw fractions which are most likely the cell wall fragments and exopolymers. MW studies under the boiling point (100°C at 1 atm) have promised a significant potential to disintegrate the floc structure and to enhance the hydrolysis and biodegradability of WAS in full-scale digesters

Comparative Analysis of Bacterial and Archaeal Community Structure in Microwave Pretreated Thermophilic and Mesophilic Anaerobic Digesters Utilizing Mixed Sludge under Organic Overloading

The effects of microwave (MW) pretreatment were investigated by six anaerobic digesters operated under thermophilic and mesophilic conditions at high organic loading rates (4.9–5.7 g volatile solids/L/d). The experiments and analyses were mainly designed to reveal the impact of MW pretreatment and digester temperatures on the process stability and microbial community structure by correlating the composition of microbial populations with volatile fatty acid (VFA) concentrations. A slight shift from biogas production (with a reasonable methane content) to VFA accumulation was observed in the thermophilic digesters, especially in the MW-irradiated reactors. Microbial population structure was assessed using a high-throughput sequencing of 16S rRNA gene on the MiSeq platform. Microbial community structure was slightly affected by different MW pretreatment conditions, while substantially affected by the digester temperature. The phylum Bacteroidetes proliferated in the MW-irradiated mesophilic digesters by resisting high-temperature MW (at 160 °C). Hydrogenotrophic methanogenesis (mostly the genus of Methanothermobacter) was found to be a key route of methane production in the thermophilic digesters, whereas aceticlastic methanogenesis (mostly the genus of Methanosaeta) was the main pathway in the mesophilic digesters.Applied Science, Faculty ofOther UBCNon UBCEngineering, School of (Okanagan)ReviewedFacult

A Review on the Fate of Legacy and Alternative Antimicrobials and Their Metabolites during Wastewater and Sludge Treatment

Antimicrobial compounds are used in a broad range of personal care, consumer and healthcare products and are frequently encountered in modern life. The use of these compounds is being reexamined as their safety, effectiveness and necessity are increasingly being questioned by regulators and consumers alike. Wastewater often contains significant amounts of these chemicals, much of which ends up being released into the environment as existing wastewater and sludge treatment processes are simply not designed to treat many of these contaminants. Furthermore, many biotic and abiotic processes during wastewater treatment can generate significant quantities of potentially toxic and persistent antimicrobial metabolites and byproducts, many of which may be even more concerning than their parent antimicrobials. This review article explores the occurrence and fate of two of the most common legacy antimicrobials, triclosan and triclocarban, their metabolites/byproducts during wastewater and sludge treatment and their potential impacts on the environment. This article also explores the fate and transformation of emerging alternative antimicrobials and addresses some of the growing concerns regarding these compounds. This is becoming increasingly important as consumers and regulators alike shift away from legacy antimicrobials to alternative chemicals which may have similar environmental and human health concerns.Applied Science, Faculty ofNon UBCEngineering, School of (Okanagan)ReviewedFacult

Incorporating hydrothermal liquefaction into wastewater treatment – Part I: Process optimization for energy recovery and evaluation of product distribution

International audienceThe treatment of significant amounts of municipal sewage sludge requires novel and efficient technologies. This study evaluated hydrothermal liquefaction as a means to sustainably convert sludge waste into a renewable energy source – biocrude, which can mitigate both environmental and energy-related challenges. Response surface methodology was employed to investigate the effects of reaction temperature (290–360 °C) and residence time (0–30 min) on product yield and biocrude quality. Both the highest and the lowest reaction temperature or residence time had negative effects on biocrude yield and energy recovery (ER), while high reaction severities improved biocrude quality. Under optimized conditions (332 °C for 16.9 min), biocrude yield (48.9%, dry ash-free) and ER (70.8%) were maximized. Biocrude composition followed the order of N-heterocycles > O-heterocycles > hydrocarbons, while nitrogenous compounds reduced, and hydrocarbons increased with reaction temperature. More distillable fractions in biocrude were also produced at higher reaction severities. The possible reaction pathways of biocrude formation were discussed and updated to include catalytic effects on inherent metals and Brønsted (acidic and basic) sites. The high content of O (7.8–13.1%), N (4.4–4.9%), and TAN (48.6–63.6 mg KOH/g) suggested the necessity of biocrude upgrading. Separating and recycling trace metals (e.g., 497–656 mg/kg Fe) from biocrude are necessary to relieve upgrading challenges. C, N, and P were mostly distributed into HTL biocrude, aqueous, and hydrochar, respectively, allowing their recovery. Most metals were concentrated in hydrochar. The results contribute to the advancement of the state of the art in biorefinery, which will guide the design of full-scale HTL sludge treatment systems combining resource recover

Occurrence of the Persistent Antimicrobial Triclosan in Microwave Pretreated and Anaerobically Digested Municipal Sludges under Various Process Conditions

Treatment of emerging contaminants, such as antimicrobials, has become a priority topic for environmental protection. As a persistent, toxic, and bioaccumulative antimicrobial, the accumulation of triclosan (TCS) in wastewater sludge is creating a potential risk to human and ecosystem health via the agricultural use of biosolids. The impact of microwave (MW) pretreatment on TCS levels in municipal sludge is unknown. This study, for the first time, evaluated how MW pretreatment (80 and 160 °C) itself and together with anaerobic digestion (AD) under various sludge retention times (SRTs: 20, 12, and 6 days) and temperatures (35 and 55 °C) can affect the levels of TCS in municipal sludge. TCS and its potential transformation products were analyzed with ultra-high-performance liquid chromatography and tandem mass spectrometry. Significantly higher TCS concentrations were detected in sludge sampled from the plant in colder compared to those in warmer temperatures. MW temperature did not have a discernible impact on TCS reduction from undigested sludge. However, AD studies indicated that compared to controls (no pretreatment), MW irradiation could make TCS more amenable to biodegradation (up to 46%), especially at the elevated pretreatment and digester temperatures. At different SRTs studied, TCS levels in the thermophilic digesters were considerably lower than that of in the mesophilic digesters.Applied Science, Faculty ofNon UBCEngineering, School of (Okanagan)ReviewedFacult

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

International audienceA 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

Enhancement of lignocellulosic biomass anaerobic digestion by optimized mild alkaline hydrogen peroxide pretreatment for biorefinery applications

Lignocellulosic energy crops are promising feedstocks for producing renewable fuels, such as methane, that can replace diminishing fossil fuels. However, there is a major handicap in using lignocellulosic sources to produce biofuels, which is their low biodegradability. In this study, the application and the optimization of a lignocellulose pretreatment process, named alkaline hydrogen peroxide, was investigated for the enhancement of methane production from the energy crop switchgrass. Four independent process variables, solid content (3-7%), reaction temperature (50-100 degrees C), H2O2 concentration (1-3%), and reaction time (6-24 h), and three response variables, soluble reducing sugar, soluble chemical oxygen demand, and biochemical methane potential were used in process optimization and modeling. The optimization was performed by two different approaches as maximum methane production and cost minimization. The optimum conditions for the highest methane production were found as 6.65 wt% solid content, 50.6 degrees C reaction temperature, 2.94 wt% H2O2 concentration, and 16.05 h reaction time. The conditions providing the lowest cost were 6.43 wt% solid content, 50 degrees C reaction temperature, 1.83 wt% H2O2 concentration, and 6.78 h reaction time. For maximum methane production and cost minimization, specific methane yields of 338.52 mL CH4/g VS and 291.34 mL CH4/g VS were predicted with 62.4 % and 39.8 % enhancements compared to untreated switchgrass, respectively. Finally, it was found that the predicted methane production for the maximum methane production represents 77 % of the theoretical methane yield and 82.22 % energy recovery.Project Management Unit of Akdeniz University from Turkey [FYL-2015-711]This research has been financed (Grant no: FYL-2015-711) by the Project Management Unit of Akdeniz University from Turkey. The authors would like to express their gratitude to Prof. Dr. Suleyman Soylu from Selcuk University and Prof. Dr. Osman Yaldiz from Akdeniz University for supplying switchgrass samples

Carbon molecular sieve production from defatted spent coffee ground using ZnCl2 and benzene for gas purification

The aim of the current study is to manufacture molecular sieve from the defatted spent coffee ground. The defatted spent coffee ground for the specified particle size (100 mu m) was chemically activated with different agents (ZnCl2, H3PO4, KOH) and then carbonized at different temperatures (400-900 degrees C). A thorough characterization of the produced activated carbon was performed and activated carbons with the highest BET surface area were subsequently used to produce carbon molecular sieve. The surface modification was performed with benzene vapor at different temperatures (600-900 degrees C) and different combustion times (30-90 min.). In addition to the BET analysis, SEM, TGA and FT-IR analysis were also undertaken. The results obtained through characterizations showed that the pore diameters of carbon molecular sieve produced from defatted spent coffee ground varied from 2 to 4 angstrom. To conclude, the results suggest that the fabricated carbon molecular sieve can be used for the removal of impurities such as CH4, CO2, NOx and other impurities in natural and biogas considering the porosity of the sieves

Biogas Production from Organic Waste: Recent Progress and Perspectives

Anaerobic digestion (AD) from organic waste has gained worldwide attention in reducing greenhouse gas emissions, lowering fossil fuel combustion, and facilitating a sustainable renewable energy supply. Biogas mainly consists of methane (CH4) (50–75%), carbon dioxide (CO2) (25–50%), hydrogen sulphides (H2S), hydrogen (H2), ammonia (NH3) (1–2%) and traces of other gases such as oxygen (O2) and nitrogen (N2). Methane can replace fossil fuels in various applications such as heat and power generation and the transportation sector. The degradation of organic waste through an AD process o?ers many advantages, such as the decrease of pathogens and prevention of odour release. The digestate from anaerobic fermentation is a valuable fertilizer, however, the amount of organic materials currently available for biogas production is still limited. New substrates, as well as more e?ective conversion technologies, are needed to grow this industry globally. This paper reviewed the latest trends and progress in biogas production technologies including potential feedstock. Recycling of waste has recently become an important topic and has been explored in this paper.The Unit of Scientifc Research Project Coordination (Bilimsel Araştırma Projeleri Koordinatörlüğü, BAP) of Erciyes Univerity, Kayseri, Turkey for the fnancial support under the University Project: FOA-2018-8183 (Priority Research Project) (Öncelikli Araştırma Proje). This work was also supported in part by grants from the Korea Ministry of Environment, as a “Global Top Project” (Project No.: 2016002210003)