Combined thermo-chemo-sonic disintegration of waste activated sludge for biogas production

Investigation of thermal alkaline pretreatment of primary and waste activated sludge on the energy efficiency of sludge digestion

Because of the naturally limited anaerobic degradability and limited biogas yield of raw sludge (RS), this study aims to increase the biogas production of primary sludge (PS) and waste activated sludge (WAS) by the integration of thermal alkaline process (TAP). PH 11 is confirmed to be the most suitable pH value for the TAP of both sludges. Moreover, with the pretreatment at pH 11 and 160 °C (6 bar) for 30 min, the investigated PSs and WASs achieved an increased biogas production of up to 81 % and 72 %, respectively. The improved net electricity production of WASs after TAP varied between 15-43 % compared to conventional WAS digestion. However, the TAP of PS at pH 11 enhanced the biogas production by 1-81 %, which did not constantly contribute to an improved net electricity production.

Optimizing alkali-pretreatment dosage for waste-activated sludge disintegration and enhanced biogas production yield

The rapid transition towards modernization and industrialization led to an increase in urban population, resulting in paramount challenge to municipal sewage sludge management. Anaerobic digestion (AD) serves as a promising venue for energy recovery from waste-activated sludge (WAS). Addressing the challenge of breaking down floc structures and microbial cells is crucial for releasing extracellular polymeric substances and cytoplasmic macromolecules to facilitate hydrolysis and fermentation process. The present study aims to introduce a combined process of alkaline/acid pre-treatments and AD to enhance sludge digestion and biogas production. The study investigates the influence of alkali pretreatment at ambient temperature using four alkali reagents (NaOH, Ca(OH)2, Mg(OH)2, and KOH). The primary goal is to provide insights into the intricate interplay of alkali dosages (0.04-0.12 g/gTS) on key physic-chemical parameters crucial for optimizing the pre-treatment dosage. Under the optimized alkaline/acid pre-treatment condition, the TSS reduction of 18%-30% was achieved. An increase in sCOD concentration (24%-50%) signifies the enhanced hydrolysis and solubilization rate of organic substrate in WAS. Finally, the biomethane potential test (BMPT) was performed for pre-treated WAS samples. The maximum methane (CH4) yield was observed in combination A1 (244 mL/g) and D1 (253 mL/g), demonstrating the pivotal role of alkali optimization in enhancing AD efficiency. This study serves as a valuable resource to policymakers, researchers, and technocrats in addressing challenges associated to sludge management.

Combined sodium citrate and ultrasonic pretreatment of waste activated sludge for cost effective production of biogas

This study aimed to pretreat the waste activated sludge (WAS) by ultrasonication in an energy efficient way by combining sodium citrate with ultrasonic pretreatment at 0.03 g/g suspended solids (SS) of dosage. The ultrasonic pretreatment was done at various (20-200 W) power levels, sludge concentration (7 to 30 g/L), sodium citrate dosages (0.01 to 0.2 g/g SS). An elevated COD solubilization of 26.07 ± 0.6 % was achieved by combined pretreatment at a treatment time of 10 min, ultrasonic power level of 160 W when compared to individual ultrasonic pretreatment (18.6 ± 0.5 %). A higher biomethane yield of 0.26 ± 0.009 L/g COD was achieved in sodium citrate combined ultrasonic pretreatment (SCUP) than ultrasonic pretreatment (UP) 0.145 ± 0.006 L/g COD. Almost 50% of the energy can be saved through SCUP when compared to UP. Future study evaluating SCUP in continuous mode anaerobic digestion is vital.

Untangling the effect of solids content on thermal-alkali pre-treatment and anaerobic digestion of sludge

Total solids (TS) content is critical for thermal hydrolysis and anaerobic digestion (AD) performance, but its role in thermal-alkaline pre-treatment (TAP) is unclear. Therefore, this study aimed to reveal the key role of TS content in TAP and AD of waste activated sludge. The results showed that the optimum TS content of TAP (at 90 °C for 1 h, pH = 10) was 8 %. Sludge disintegration and methane production increased from 19.7 ± 2.2 % to 34.3 ± 2.9 % and from 167.4 ± 4.2 to 246.0 ± 6.2 mL/g volatile solids, respectively, when TS content were increased from 2 % to 8 %. A high TS content will likely promote sludge disintegration since it will reduce heat loss and improve heating efficiency. Additionally, increasing TS content from 2 % to 10 % minimized the production of intracellular reactive oxygen species by 30.4 ± 0.7 % and increased cell viability by 11.5 ± 2.6 %. In contrast, excessive TS content (i.e., ≥10 %) deteriorated the fluidity of sludge, which prevents it from disintegration. Once TS reached 10 %, the accumulation of ammonia nitrogen and volatile fatty acids reached 812.7 ± 27.4 and 1932.0 ± 5.3 mg/L, respectively, which reduced the activity of acidulase and coenzyme F420 and shifted the archaeal community from acetylotrophic to hydrogenotrophic methanogens. This article provides new insights into the TS content in TAP and AD technology.

Amelioration of Biogas Production from Waste-Activated Sludge through Surfactant-Coupled Mechanical Disintegration

The current study intended to improve the disintegration potential of paper mill sludge through alkyl polyglycoside-coupled disperser disintegration. The sludge biomass was fed to the disperser disintegration and a maximum solubilization of 6% was attained at the specific energy input of 4729.24 kJ/kg TS. Solubilization was further enhanced by coupling the optimum disperser condition with varying dosage of alkyl polyglycoside. The maximum solubilization of 11% and suspended solid (SS) reduction of 8.42% were achieved at the disperser rpm, time, and surfactant dosage of 12,000, 30 min, and 12 μL. The alkyl polyglycoside-coupled disperser disintegration showed a higher biogas production of 125.1 mL/gCOD, compared to the disperser-alone disintegration (70.1 mL/gCOD) and control (36.1 mL/gCOD).

Effect of surfactant assisted ultrasonic pretreatment on production of volatile fatty acids from mixed food waste

In this study, the potential effect of surfactant assisted ultrasonic pretreatment on mixed food waste was investigated. Surfactants, such as Rhamnolipid, Sodium dodecyl sulfate; Glucopon and Triton X 100 were evaluated in this work. Among them, the maximum solubilization of chemical oxygen demand of 45.5 % and the highest release of soluble COD of 31 g/L were observed for ultrasonication assisted by Triton X 100 at a dose of 0.01 g/g TS in 30 min. The presence of a surfactant also reduced 27.5 % of energy demand when compared to ultrasonic pretreatment alone. Compared to the non-pretreated samples after anaerobic digestion, ultrasonication assisted by Triton X 100 led to 95 % increase of volatile fatty acid titers and 83 % increase of carbon conversion efficiency. Thus, sonication with the addition of Triton X 100 was proven to be highly effective toward increasing digestibility of and yield of volatile fatty acid from mixed food waste.

A novel conversion of marine macroalgal biomass to biofuel (biohydrogen) via calcium hypochlorite induced dispersion

Environmental pollution due to the consumption of non-renewable energy lead the search for alternative eco-friendly renewable fuel. The study details the biohydrogen production efficiency by potential macroalgal (Ulva reticulata) biomass improved by a disperser combined with calcium hypochlorite pretreatment technology. Calcium hypochlorite was added to decrease the surface energy of the medium induced by sole disperser pretreatment. Optimum condition for algal disperser treatment was 10,000 rpm with 30 min as dispersion time. The specific energy spent for the disintegration of the macroalgal biomass was 1231.58 kJ/kg TS. COD solubilization rate of 11.79% was attained with mechanical pretreatment whereas increased to 20.23% with combined pretreatment. Combination of disperser with calcium hypochlorite significantly reduced the specific energy input spent to 500 kJ/kg TS. The amount of organic materials such as carbohydrates, proteins and lipids released were 680 mg/L, 283 mg/L and 136 mg/L respectively. Thus, the combinative pretreatment with disperser rotor speed (10,000 rpm) for pretreatment time (12 min) and calcium hypochlorite dosage (0.1 g/g) derived as optimum condition for effective solubilization of macroalgal biomass. Biohydrogen production potential was maximum in the macroalgae pretreated with both disperser and calcium hypochlorite recorded highest yield (54.6 mL H₂/g COD) compared to the macroalgae pretreated with disperser alone (31.7 mL H₂/g COD) and untreated macroalgae (11.5 mL H₂/g COD).

Thermo-chemo-sonic pretreatment of lignocellulosic waste: Evaluating anaerobic biodegradability and environmental impacts

In the present study, yard waste was pretreated by thermo-chemo-sonic pretreatment prior to anaerobic digestion to improve its anaerobic biodegradability. First, the pretreatment conditions were optimized using Box-Behnken design based response surface methodology for the maximum organic matter solubilisation. Then, the possible mechanism of delignification by thermo-chemo-sonic pretreatment was discussed. Moreover, the anaerobic digestion performance of untreated yard waste (UYW) and pretreated yard waste (PYW) was compared. The optimum pretreatment condition based on the increase in soluble COD and volatile solids (VS) was: 2997 kJ/kgTS ultrasonic energy, 74 °C, and 10.1 pH. The highest methane yield of 374 ± 28 mL/gVS_added for the PYW at the optimum condition was achieved, which was 37.5 % higher than the UYW (272 ± 16 mL/gVS_added). Finally, the environmental impacts associated with anaerobic digestion of both UYW and PYW were compared. The life cycle assessment confirmed a positive environmental impact of pretreatment.

Biohydrogen production from waste activated sludge through thermochemical mechanical pretreatment

Generation of excess sludge in large quantities from wastewater treatment plant face huge problem in terms of handling and management, whereas it possess higher organic and inorganic constituents and thus it can be used as a feedstock for the generation of biofuel with proper disintegration techniques.In this regard, an effort has been made in this study to combine thermo-chemo-disperser pretreatment for the disintegration of paper mill waste activated sludge for the production of biohydrogen in an energy efficient way. These combinations of thermo-chemo-disperser (TCD) tend to be effective in disintegration and possess 24.3% COD solubilization and higher suspended solid reduction of 18.8% at the specific energy usage of 2081.82 kJ/kg TS. The pretreatment with TCD technique shows the biohydrogen production of 120.2 mLH₂/gCOD as compared to thermochemically pretreated alone (73.6 mLH₂/gCOD) sample. Thus, the combined process was considered to be potentially effective in sludge disintegration.

Impact of novel deflocculant ZnO/Chitosan nanocomposite film in disperser pretreatment enhancing energy efficient anaerobic digestion: Parameter assessment and cost exploration

This paper proposed to interpret the novel method of extracellular polymeric substance (EPS) removal in advance to sludge disintegration to enrich bioenergy generation. The sludge has been subjected to deflocculation using Zinc oxide/Chitosan nanocomposite film (ZCNF) and achieved 98.97% of solubilization which enhance the solubilization of organics. The obtained result revealed that higher solubilization efficiency of 23.3% was attained at an optimal specific energy of 2186 kJ/kg TS and disintegration duration of 30 min. The deflocculated sludge showed 8.2% higher solubilization than the flocculated sludge emancipates organics in the form of 1.64 g/L of SCOD thereby enhancing the methane generation. The deflocculated sludge produces methane of 230 mL/g COD attained overall solid reduction of 55.5% however, flocculated and control sludge produces only 182.25 mL/g COD and 142.8 mL/g COD of methane. Based on the energy, mass and cost analysis, the deflocculated sludge saved 94.1% of energy than the control and obtained the net cost of 5.59 $/t which is comparatively higher than the flocculated and control sludge.

Studies on evaluation of surfactant coupled sonication pretreatment on Ulva fasciata (marine macroalgae) for enhanced biohydrogen production

Biohydrogen production from marine macroalgal biomass by advanced pre-treatment strategies is considered a clean energy technology. The present study focuses on investigating the effects of sonication pre-treatment (SP) and saponin coupled sonic pre-treatment (SSP) on Ulva fasciata for enhancing the production of biohydrogen. The SP and SSP were optimized to improve the hydrolysis process during digestion. The optimized time and sonication power were found respectively as 30 min and 200 W. A high concentration of biopolymer release was noticed in SSP than SP at optimized conditions. The surfactant dosage in SSP was optimized at 0.0036 g/g TS. The effect of SSP process was assessed by estimation of COD (Chemical Oxygen Demand) and SCOD (Soluble Chemical Oxygen Demand) release. The study revealed that, at a specific energy of 36,000 KJ/Kg TS, the SCOD release was higher in SSP (1900 mg/L) than SP (1050 mg/L). The SSP process could improve the COD solubilization to 15 % more than the SP. Carbohydrate and protein release are also more in SSP than SP. The use of biosurfactants significantly reduced the energy utilization in the hydrolysis process. The SSP pre-treated Ulva fasciata biomass has yielded a higher biohydrogen of 91.7 mL/g COD which is higher compared to SP (40.5 mL/g COD) and Control (9 mL/g COD).

Recent advances on food waste pretreatment technology via microalgae for source of polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polyester which are biosynthesized from the intracellular cells of microalgae through the cultivation of organic food waste medium. Before cultivation process, food waste must undergo several pre-treatment techniques such as chemical, biological, physical or mechanical in order to solubilize complex food waste matter into simpler micro- and macronutrients in which allow bio-valorisation of microalgae and food waste compound during the cultivation process. This work reviews four microalgae genera namely Chlamydomonas, Chlorella, Spirulina, and Botryococcus, are selected as suitable species due to rapid growth rate, minimal nutrient requirement, greater adaptability and flexibility prior to lower the overall production cost and maximized the production of PHAs. This study also focuses on the different mode of cultivation for the accumulation of PHAs followed by cell wall destabilization, extraction, and purification. Nonetheless, this review provides future insights into enhancing the productivity of bioplastic derived from microalgae towards low-cost, large-scale, and higher productivity of PHAs.

Effect of Different Pretreatments on Sludge Solubilization and Estimation of Bioenergy Potential

Most of the conventional treatments of waste-activated sludge (WAS) are devoted to their minimization and destruction. On the other hand, the biomass contained in WAS can be utilized as a valuable source of renewable carbon. In this study, the influence of different pretreatments (ultrasonication, chemical, thermal, and combined pretreatments) was explored for sludge solubilization. Effects of the pretreatments were investigated as a function of the solubilization of total solids (TS), volatile solids (VS), and chemical oxygen demand (COD). Concentrations of soluble carbohydrates and total nitrogen were also measured. The most effective pretreatment to hydrolyze sludge was found to be the combined alkali–thermal (pH 12, 75 °C) pretreatment method, leading to TS and vs. solubilization of 9.6% and 17.2%, respectively. Soluble COD, carbohydrates, total nitrogen, and proteins estimated in the liquid phase were 5235 mg/L, 732 mg/L, 430 mg/L, and 2688 mg/L, respectively. Thus, the alkali–thermal method could be used for efficient valorization of WAS. Moreover, the solid fraction from all pretreated samples was further subjected to thermogravimetric analysis to estimate its potential for bioenergy from its higher heating value (HHV), which was found to be in the range of 10–11.82 MJ/kg. This study can provide better insight into the efficient valorization of liquid and solid phases of sludge after pretreatment.

Enhanced biogas production from anaerobic digestion of wastewater from the fruit juice industry by sonolysis: experiments and modelling

The aim of this study is to investigate the use of ultrasound pretreatment as potential technique to solubilize organic matter and fermentation of fruit juice effluents in anaerobic batch reactor. The efficacy of ultrasound pretreatment has been assessed at low frequency of 20 kHz and at different sonication times (20, 40 and 60 min). Compared with control, the amount of biogas produced increased by 47, 57 and 60% for sonication times of 20, 40 and 60 min, respectively. Methane content of the produced biogas was about 59% in the control and 64% in the case of effluent subjected to ultrasonication for 60 min. After 20 days of anaerobic digestion of the fruit juice effluents, the efficiency of chemical oxygen demand (COD) increased by 9, 31 and 35% with respect to control for sonication times of 20, 40 and 60 min, respectively, corresponding to total sugars uptake efficiency of about 35, 51 and 54%, respectively. The modified Gompertz equation was used to describe the cumulative biogas production. A good agreement was found between simulated and experimental data.

Nanoparticles Synergistic Effect with Various Substrate Pretreatment and their Comparison on Biogas Production from Algae Waste

Algae waste is one of the potential substrates for biogas and biohydrogen production and can comprehend multiple benefits of waste treatment and resource utilization. In view of the key bottlenecks such as low substrate degradation rate and poor productivity of algae waste production process, this study analyzes the combined effect of two metallic and metallic oxide nanoparticles with different substrate pretreatment methods (autoclave, ultrasonic, and microwave methods) to investigate the effect of anaerobic digestion of green algae (Enteromorpha). The results showed that out of the three pretreatment methods, microwave pretreatment and nanoparticles' synergistic effect significantly increases biogas production. The microbial community composition at the phylum level was analyzed. It was observed that the Firmicutes were most abundant across all samples. The relative abundance of Firmicutes for control, Ni NPs + MW, Co NPs + MW, and Fe3O4 NPs + MW groups were 51.78, 70.37, 75.77, and 83.93%,      respectively. The second most abundant was of Bacteroidetes that also contributes to hydrogen production. This relatively high abundance of Firmicutes and Bacteroidetes promises its potential applications in a hydrogen production facility. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

A review on energy and cost effective phase separated pretreatment of biosolids

Extracellular Polymeric Substances (EPS) existent in anaerobic sludge proves to be a barrier for sludge liquefaction and biomass lysis efficiency. Hence EPS deaggregation heightens the surface area for the subsequent pretreatment thereby uplifting the sludge disintegration and biomethanation rate. This review documents the role of EPS and its components which inhibits sludge hydrolysis and also the various phase separated pretreatment methods available with its disintegration mechanism to enhance the biomass lysis and methane production rate. It also illustrates the effects of phase separated pretreatment on the sludge disintegration rate which embodies two phases-floc disruption and cell lysis accompanied by their computation through biomethane potential assay and fermentation analysis comprehensively. Additionally, energy balance study and cost analysis requisite for successful implementation of a proposed phase separated pretreatment on a pilot scale level and their challenges are also reviewed. Overall this paper documents the potency of phase separated pretreatment for full scale approach.

Potential of biogas production from manure of dairy cattle fed on natural soil supplement rich in iron under batch and semi-continuous anaerobic digestion

This study provides a novel method for improving the anaerobic digestion (AD) of Holstein dairy manure (HDM) by the direct addition of Mineraso (MnS), a natural soil-derived supplement, to the feed of Holstein dairy cattle (HDC). MnS is chiefly composed of approximately 69.08% Fe₃O₄ and was supplemented at rates of 0 (F1), 25 (F2), and 50 (F3) g/head of HDC/d for two months. The HDM was then examined for non-absorbed iron prior to the batch and semi-continuous bench AD experiments. The results revealed that MnS enhanced CH₄ generation in F2 and F3 by 25% and 42%, respectively, in the batch experiments compared to that of F1. Additionally, the gas yield improved in F2 and F3 by 45% and 66%, respectively, over the control after 7 d in the bench experiments. Therefore, supplementing animals with MnS represents a sustainable and economic approach to enhancing CH₄ yields.

Immobilized ZnO nano film impelled bacterial disintegration of dairy sludge to enrich anaerobic digestion for profitable bioenergy production: Energetic and economic analysis

Proper treatment and disposal of sludge is a substantial task around the biosphere. To address this issue, sludge deflocculation using photocatalyst was opted to enhance bacterial disintegration which in turn accelerate sludge digestion anaerobically. During this investigation, Direct current (DC) sputtering together with annealing process was used to immobilize Zinc oxide (ZnO). This immobilized ZnO removes the extracellular components at 15 min. The deflocculation mediated bacterial pretreatment induced 22.9% of soluble organics solubilization which auguments the biodegradability to 0.195 g COD/g COD during anaerobic digestion. The quantity of methane generated by deflocculated sludge was 39.2% higher than sludge with bacterial disintegration only with maximum methane yield of 437.14 mL/g COD. Hence, the outcome of the proposed work confirmed that the method is scalable with a net profit of 27 USD with the maximum methane generation of 413.1 kWh. Additionally, this method reduced 57% of dry sludge (solid).

Cost effective biomethanation via surfactant coupled ultrasonic liquefaction of mixed microalgal biomass harvested from open raceway pond

The present study aimed to enhance the biomethanation potential of mixed microalgae via cost effective surfactant coupled ultrasonic homogenization (SCUH). Mixed microalgae biomass was harvested using a coagulant (Alum) from a raceway pond. The harvested algal biomass was subjected to ultrasonic homogenization (UH) by varying the power from 100 to 180 W. A maximal soluble organic release of 2131 mg/L was achieved at an ultrasonic input energy (UIE) of 25200 kJ/kg TS. In order to enhance soluble organic release and to reduce energy spent, the optimized condition of ultrasonic pretreatment was coupled with varying sodium dodecyl sulphate (SDS) dosage. A higher solubilization of 30.5% was achieved at a UIE of 4200 kJ/kg SS with surfactant dosage of 0.02 g SDS/g SS for SCUH. SCUH showed higher methane production of 358 mL/g COD when compared to UH (185.9 mL/g COD), SCUH was economically feasible than UH.

Application of chemo thermal coupled sonic homogenization of marine macroalgal biomass for energy efficient volatile fatty acid recovery

The present study aimed to employ energy efficient chemo thermal coupled sonic homogenization (CTSH) to obtain VFA from marine macroalgal hydrolysate, (Ulva fasciata). At first, chemo thermal homogenization (CTH) was applied on macroalgal biomass by adjusting the temperature, pH and treatment time from 60 to 90 ℃, 4-7 and 0-60 min, respectively. A higher organic matter solubilisation of 11.81% was obtained at an optimum pH of 6 at a temperature of 80 ℃ with 40 min of homogenization time. The results of CTSH implied that a higher organic matter solubilization of 26.4% was achieved by combined CTSH (sonic power & treatment time - 140 W & 14 min treatment time). CTSH considerably doubles the liquefaction in comparison with CTH. Based on OMS grouping, achieving 25% was sufficient for VFA production (2172.09 mg/L) and considered as economically feasible with net cost of 97.17 USD/ton of macroalgae.

Quantitative analysis of methane and glycolate production from microalgae using undiluted wastewater obtained from chicken-manure biogas digester

Microalgal biomass is often used as a raw material in methane production. Some microalgae possess a complex cell-wall structure which has a low degradability of microorganisms in anaerobic digestion. However, some microalgae produce glycolate, which is excreted outside the cell and can be used to produce methane under anaerobic condition. This research aims to investigate microalgal cultivation using wastewater to reduce nutrients and efficiently create glycolate. Two strains of microalgae (Acutodesmus sp. AARL G023, Chlorella sp. AARL G049) and two microalgal consortia were cultivated at dilutions of 0.5-fold (W50), 0.75-fold (W75) and undiluted wastewater (W100). The results showed that the microalgal consortium with undiluted wastewater (WCW100) consisted of Leptolyngbya sp. (30.4%), Chlorella sp. (16.1%) and Chlamydomonas sp. (52.2%), revealed the highest biomass productivity at 64.38 ± 14.54 mg·L^-1·d^-1 and the highest glycolate productivity at 5.12 ± 0.48 mmol·L^-1·d^-1. The cultivation of microalgae effectively reduced ammonium‑nitrogen (NH₄⁺-N) and soluble reactive phosphorus (SRP) levels in the wastewater at 43.5 ± 1.3% and 49.6 ± 6.9%. Furthermore, WCW100 showed the highest biogas productivity at 1.44 ± 0.07 mL·g^-1·d^-1 and the highest methane content at 58.3 ± 6.0% v/v. This study indicates that there is a definite potential of using undiluted wastewater for microalgal biomass production and glycolate production that can reduce the wastewater volume and be applied as a raw material for methane production.

Biorefinery of spent coffee grounds waste: Viable pathway towards circular bioeconomy

The circular bioeconomy plan is an innovative research based scheme intended for augmenting the complete utilization and management of bio-based resources in a sustainable biorefinery route. Spent coffee grounds based biorefinery is the emerging aspect promoting circular bioeconomy. The sustainable circular bioeconomy by utilizing SCG is achieved by cascade approaches and the inclusion of many biorefinery approaches to obtain many bio-products. The maximum energy recovery can be obtained by process integration. The economic analysis of the biofuel production from SCG is dependent on the cost of raw material, transportation, the need of labor and energy, oil extraction operations and biofuel production. The inclusion of new products from already established product can minimize the investment cost when related to the production cost. A positive net present value can be achieved via SCG biorefinery which indicates the profitability of the process.

Prospects for biogas production and H2S control from the anaerobic digestion of cattle manure: The influence of microscale waste iron powder and iron oxide nanoparticles

Improving the quality and quantity of biogas usually requires pre-treatment to maximize methane yields and/or post-treatment to remove H₂S, which involves considerable energy consumption and higher costs. Therefore, this study proposes a cost-effective method for the enhanced anaerobic digestion (AD) of dairy manure (DM) without pre/post-treatment by directly adding waste iron powder (WIP) and iron oxide nanoparticles (INPs) to batch digesters. The results showed that the addition of iron in the form of microscale WIP (generated from the laser cutting of iron and steel) at concentrations of 100 mg/L, 500 mg/L, and 1000 mg/L improved methane yields by 36.99%, 39.36%, and 56.89%, respectively. In comparison, the equivalent dosages of INPs improved yields by 19.74%, 18.14%, and 21.11%, respectively. Additionally, the highest WIP dose (1000 mg/L) achieved the maximum improvement in the rate of hydrolysis (k), which was 1.25 times higher than in control reactions, and a maximum biomethane production rate (R_max) of 0.045 L/gVS/d according to kinetic analysis models (i.e., first-order and the Gompertz kinetic models). The rate of H₂S production was also significantly reduced (by 45.20%, 58.16%, and 77.24%) using the three WIP concentrations in comparison with INPs (which achieved reductions of 33.59%, 46.30%, and 53.52%, respectively). Therefore, the direct mixing of WIP with cattle manure is proposed as a practical and economical means of addressing complex and high-cost pre- and post-treatments that are otherwise required in the digestion process.

Lysis characteristics and mechanism of excess sludge degraded by ozone and ultrasonic treatment

As a byproduct of activated sludge process, excess sludge has become one of the current problems in the field of environmental protection for its yield huge、high moisture content and easy to pollution. In this study, the joint technology combining ozone with ultrasonic was applied in treatment of excess sludge by strong ozone oxidation and prominent ultrasonic cavitation. The effect on lysis excess sludge cells was explored comprehensively. The lysis mechanism of excess sludge cells degraded by ozone + ultrasonic was revealed by analysis of three-dimensional spectral fluorometer, optical microscope and scanning electron microscopy (SEM). The results showed that the MLSS was 22.92% lower than the untreated sludge, the SCOD and [Formula: see text] -N content in the supernatant of the sludge was 1792 and 105.77 mg/L, which was 96.49% and 17.67% higher than the untreated. The supernatant of treated excess sludge contained macromolecular organic matters composed of proteins, polysaccharides, humic acids, and fulvic acids, etc. The whole process of lysis cells of excess sludge degraded by ozone + ultrasonic could be inferred that the microbial particles of excess sludge were exposed after EPS destructed, and then the cell walls of these exposed microbial particles were broken so that a great number of intracellular materials were released. Furthermore, these intracellular material composed of macromolecular organic matters were degraded into small molecule organic matters, H₂O, CO₂, etc. Finally, the excess sludge was treated gradually by ozone + ultrasonic.

Nanoparticle induced biological disintegration: A new phase separated pretreatment strategy on microalgal biomass for profitable biomethane recovery

This study involves the application of new phase separated biological pretreatment (PSBP) strategy on microalgal biomass using the nickel nanoparticle induced cellulase secreting bacterial disintegration. Particularly, interest was focussed on cell wall weakening (CWW) of microalgae biomass besides the cell disintegration (CD) and release of organics. During CWW, protein, carbohydrate, cellulose, hemicellulose and DNA were used as evaluation indexes. Similarly, during CD, soluble chemical oxygen demand was used as evaluation index to assess the disintegration effect. A higher CWW was achieved at nickel nanoparticle (Np) dosage of 0.004 g/g SS. During CD, a clear demarcation in biomass solubilisation was achieved by PSBP (36%) than the sole biological pretreatment -BP (24%). The biomethanogenesis test results showed that enhanced methane production of 411 mL/g COD was achieved by PSBP than BP. Energy analysis showed that a higher net energy production of 6.467 GJ/d was achieved by PSBP.

Combining Microwave Pretreatment with Iron Oxide Nanoparticles Enhanced Biogas and Hydrogen Yield from Green Algae

The available energy can be effectively upgraded by adopting smart energy conversion measures. The biodegradability of biomass can be improved by employing pretreatment techniques; however, such methods result in reduced energy efficiency. In this study, microwave (MW) irradiation is used for green algae (Enteromorpha) pretreatment in combination with iron oxide nanoparticles (NPs) which act as a heterogeneous catalyst during anaerobic digestion process for biogas enhancement. Batch-wise anaerobic digestion was carried out. The results showed that MW pretreatment and its combination with Fe3O4 NPs produced highest yields of biogas and hydrogen as compared to the individual ones and control. The biogas amount and hydrogen % v/v achieved by MW pretreatment + Fe3O4 NPs group were 328 mL and 51.5%, respectively. The energy analysis indicated that synergistic application of MW pretreatment with Fe3O4 NPs produced added energy while consuming less input energy than MW pretreatment alone. The kinetic parameters of the reaction were scientifically evaluated by using modified Gompertz and Logistic function model for each experimental case. MW pretreatment + Fe3O4 NPs group improved biogas production potential and maximum biogas production rate.

Novel insights into scalability of biosurfactant combined microwave disintegration of sludge at alkali pH for achieving profitable bioenergy recovery and net profit

In the present study, a novel alkali rhamnolipid combined microwave disintegration (ARMD) was employed to achieve net energy production, increased liquefaction and to increase the amenability of sludge towards biomethanation. Additionally, biosurfactant rhamnolipid under alkali conditions enhances the liquefaction at alkali pH of 10 with a maximal liquefaction of 55% with reduced energy consumption (1620 kJ/kg TS) than RMD (45.7% and 3240 kJ/kg TS specific energy) and MD (33.7% and 6480 kJ/kg TS specific energy). A higher biomethane production of 379 mL/g COD was achieved for ARMD when compared to RMD (329 mL/g COD) and MD (239 mL/g COD). The scalable studies imply that the ARMD demands input energy of -282.27 kWh. A net yield of (0.39 USD/ton) was probably achieved via novel ARMD technique indicating its suitability at large scale execution when compared to RMD (net cost -31.34 USD/ton) and MD (-84.23 net cost USD/ton), respectively.

Improved methane production from waste activated sludge by combining free ammonia with heat pretreatment: Performance, mechanisms and applications

Anaerobic digestion of waste activated sludge (WAS) is often limited by low hydrolysis efficiencies and poor methane potentials. This work presents a novel pretreatment technology for WAS anaerobic digestion, i.e., combining free ammonia with heat pretreatment (CFHP). Experimental results showed that compared with control, solo free ammonia (135.4 mg NH₃-N/L) and solo heat (70 °C) pretreatment, the combined free ammonia and heat (135.4 mg NH₃-N/L with 70 °C) obtained 52.2%, 25.5% and 30.2% faster in hydrolysis rate and 25.2%, 17.9% and 16.5% higher in biochemical methane potential, respectively. Mechanism investigations showed that the combined pretreatment not only largely facilitated the disintegration of WAS but also increased the proportion of biodegradable organic matters, thereby providing better contract between biodegradable organics and the anaerobic microbes for methane production. Considering its effectiveness and renewability, the combined pretreatment is an attractive technology for the application in real-world situations.

A critical review on anaerobic digestion of microalgae and macroalgae and co-digestion of biomass for enhanced methane generation

Biogas production using algal resources has been widely studied as a green and alternative renewable technology. This review provides an extended overview of recent advances in biomethane production via direct anaerobic digestion (AD) of microalgae, macroalgae and co-digestion mechanism on biomethane production and future challenges and prospects for its scaled-up applications. The effects of pretreatment in the preparation of algal feedstock for methane generation are discussed briefly. The role of different operational and environmental parameters for instance pH, temperature, nutrients, organic loading rate (OLR) and hydraulic retention time (HRT) on sustainable methane generation are also reviewed. Finally, an outlook on the possible options towards the scale up and enhancement strategies has been provided. This review could encourage further studies in this area, to intend and operate continuous mode by designing stable and reliable bioreactor systems and to analyze the possibilities and potential of co-digestion for the promotion of algal-biomethane technology.

Enhancement of volatile fatty acid production and biogas yield from food waste following sonication pretreatment

The positive effect of sonication on volatile fatty acid (VFA) and hydrogen production was investigated by batch experiments. Several sonication densities (2, 1.6, and 1.2 W/mL) and times (5, 10, and 15 min) were tested. The optimal sonication condition was ultrasonic density 2 W/mL and ultrasonic time 15 min (2-U15). The FW particle size larger than 50 μm (d > 50 μm) were more susceptible to the sonication treatment than the smaller particle size (d ≤ 50 μm). The SCOD increased and VS reduction accelerated under sonication treatment. The maximum VFA production and the highest proportion of hydrogen in the biogas increased 65.3% and 59.1%, respectively, under the optimal sonication conditions compared to the unsonicated batch. Moreover, a reduction of over 50% in the time required to reach its maximum production was also observed. Butyric acid fermentation type was obtained whether following sonication treatment or not. The composition of key microbial community differed under the various sonication conditions. The genera Clostridium and Parabacteroides are predominantly responsible for VFA generation and both were found to be abundant under the optimal condition.

Optimizing dewaterability of drinking water treatment sludge by ultrasound treatment: Correlations to sludge physicochemical properties

Sludge dewatering has proven to be an effective method to reduce the volume of sludge. In this study, drinking water treatment sludge (DWTS) was treated by ultra-sonication under variable conditions comparing two sonoreactor types (bath and probe), four frequencies (25, 40, 68, 160 kHz) and four energy density levels (0.03, 1, 3, 5 W/mL). The effects of these conditions were studied using specific resistance to filtration and capillary suction time as measures of dewaterability, and floc size, the Brunauer, Emmett and Teller (BET) specific surface area and Zeta potential to determine treated sludge characteristics. The results indicated that the dewaterability of sonicated sludge improved at relatively low energy densities of 0.03 and 1.0 W/mL, while an optimum for sonication duration (within 10 min) was also identified. Higher frequencies (tested up to 160 kHz) with acoustic energy density of 0.03 W/mL also reduced the dewatering property. At higher energy densities of 3.0 and 5.0 W/mL, dewaterability of sludge deteriorated regardless of ultra-sonication time, with an increase of solubilized organic matter content and severely changed floc characteristics. The deterioration of the dewatering capacity was closely related to the considerably reduced floc sizes, dissolution of proteins and polysaccharides, and to the Zeta potential of sonicated sludge flocs. The dewaterability was not correlated with BET specific surface area. Mechanistic explanations for the observations were discussed by analyzing corrosion patterns of aluminum foil as a measure for cavitation field distribution.

Marsilea spp.-A novel source of lignocellulosic biomass: Effect of solubilized lignin on anaerobic biodegradability and cost of energy products

The present study concerns the liquefying potential of an unusual source of lignocellulosic biomass (Marsilea spp., water clover, an aquatic fern) during combinative pretreatment. The focus was on how the pretreatment affects the biodegradability, methane production, and profitability of thermochemical dispersion disintegration (TCDD) based on liquefaction and soluble lignin. The TCDD process was effective at 12,000 rpm and 11 min under the optimized thermochemical conditions (80 °C and pH 11). The results from biodegradability tests imply that 30% liquefaction was sufficient to achieve enhanced biodegradability of about 0.280 g-COD/g-COD. When biodegradability was >30% inhibition was observed (0.267 and 0.264 g-COD/g-COD at 35-40% liquefaction) due to higher soluble lignin release (4.53-4.95 g/L). Scalable studies revealed that achievement of 30% liquefaction was beneficial in terms of the energy and cost benefit ratios (0.956 and 1.02), when compared to other choices.

Surfactant assisted disperser pretreatment on the liquefaction of Ulva reticulata and evaluation of biodegradability for energy efficient biofuel production through nonlinear regression modelling

The present study aimed to increase the disintegration potential of marine macroalgae, (Ulva reticulata) through chemo mechanical pretreatment (CMP) in an energy efficient manner. By combining surfactant with disperser, the specific energy input was considerably reduced from 437.1 kJ/kg TS to 264.9 kJ/kg TS to achieve 10.7% liquefaction. A disperser rpm (10,000), pretreatment time (30 min) and tween 80 dosage (21.6 mg/L) were considered as an optimum for effective liquefaction of algal biomass. CMP was designated as an appropriate pretreatment resulting in a higher soluble organic release 1250 mg/L, respectively. Anaerobic fermentation results revealed that the volatile fatty acid (VFA) concentration was doubled (782 mg/L) in CMP when compared to mechanical pretreatment (MP) (345 mg/L). CMP pretreated algal biomass was considered as the suitable for biohydrogen production with highest H₂ yield of about 63 mL H₂/g COD than (MP) (45 mL H₂/g COD) and control (10 mL H₂/g COD).

Lignocellulosic Biomass Transformations via Greener Oxidative Pretreatment Processes: Access to Energy and Value-Added Chemicals

Anthropogenic climate change, principally induced by the large volume of carbon dioxide emission from the global economy driven by fossil fuels, has been observed and scientifically proven as a major threat to civilization. Meanwhile, fossil fuel depletion has been identified as a future challenge. Lignocellulosic biomass in the form of organic residues appears to be the most promising option as renewable feedstock for the generation of energy and platform chemicals. As of today, relatively little bioenergy comes from lignocellulosic biomass as compared to feedstock such as starch and sugarcane, primarily due to high cost of production involving pretreatment steps required to fragment biomass components via disruption of the natural recalcitrant structure of these rigid polymers; low efficiency of enzymatic hydrolysis of refractory feedstock presents a major challenge. The valorization of lignin and cellulose into energy products or chemical products is contingent on the effectiveness of selective depolymerization of the pretreatment regime which typically involve harsh pyrolytic and solvothermal processes assisted by corrosive acids or alkaline reagents. These unselective methods decompose lignin into many products that may not be energetically or chemically valuable, or even biologically inhibitory. Exploring milder, selective and greener processes, therefore, has become a critical subject of study for the valorization of these materials in the last decade. Efficient alternative activation processes such as microwave- and ultrasound irradiation are being explored as replacements for pyrolysis and hydrothermolysis, while milder options such as advanced oxidative and catalytic processes should be considered as choices to harsher acid and alkaline processes. Herein, we critically abridge the research on chemical oxidative techniques for the pretreatment of lignocellulosics with the explicit aim to rationalize the objectives of the biomass pretreatment step and the problems associated with the conventional processes. The mechanisms of reaction pathways, selectivity and efficiency of end-products obtained using greener processes such as ozonolysis, photocatalysis, oxidative catalysis, electrochemical oxidation, and Fenton or Fenton-like reactions, as applied to depolymerization of lignocellulosic biomass are summarized with deliberation on future prospects of biorefineries with greener pretreatment processes in the context of the life cycle assessment.

Effects of alkali types on waste activated sludge (WAS) fermentation and microbial communities

The effects of two alkali agents, NaOH and Ca(OH)₂, on enhancing waste activated sludge (WAS) fermentation and short chain fatty acids (SCFAs) accumulation were studied in semi-continuous stirred tank reactors (semi-CSTR) at different sludge retention time (SRT) (2-10 d). The optimum SRT for SCFAs accumulation of NaOH and Ca(OH)₂ adding system was 8 d and 10 d, respectively. Results showed that the average organics yields including soluble chemical oxygen demand (SCOD), protein, and carbohydrate in the NaOH system were as almost twice as that in the Ca(OH)₂ system. For Ca(OH)₂ system, sludge hydrolysis and protein acidification efficiencies were negatively affected by Ca²⁺ precipitation, which was revealed by the decrease of Ca²⁺ concentration, the rise of zeta potential and better sludge dewaterability in Ca(OH)₂ system. In addition, Firmicutes, Proteobacteria and Actinobacteria were the main microbial functional groups in both types of alkali systems. NaOH system obtained higher microbial quantities which led to better acidification. For application, however, Ca(OH)₂ was more economically feasible owning to its lower price and better dewaterability of residual sludge.

Biological disintegration of microalgae for biomethane recovery-prediction of biodegradability and computation of energy balance

The present study investigates the synergistic effect of combined bacterial disintegration on mixed microalgal biomass for energy efficient biomethane generation. The rate of microalgal biomass lysis, enhanced biodegradability, and methane generation were used as indices to assess efficiency of the disintegration. A maximal dissolvable organics release and algal biomass lysis rate of about 1100, 950 and 800mg/L and 26, 23 and 18% was achieved in PA+C (protease, amylase+cellulase secreting bacteria), C (cellulase alone) and PA (protease, amylase) microalgal disintegration. During anaerobic fermentation, a greater production of volatile fatty acids (1000mg/L) was noted in PA+C bacterial disintegration of microalgal biomass. PA+C bacterial disintegration improve the amenability of microalgal biomass to biomethanation process with higher biodegradability of about 0.27gCOD/gCOD, respectively. The energy balance analysis of this combined bacterial disintegration of microalgal biomass provides surplus positive net energy (1.14GJ/d) by compensating the input energy requirements.

Dispersion induced ozone pretreatment of waste activated biosolids: Arriving biomethanation modelling parameters, energetic and cost assessment

In this study, the phase separated effect of dispersion induced ozone pretreatment (DOP) was investigated. Solid reduction, biomass lysis and biomethane production were used as essential parameters to assess the potential of DOP over ozone pretreatment (OP). A higher suspended solid reduction of about 25.2% was achieved in DOP than OP 18%. The ozone dosage of 0.014gO₃/g SS supported a maximal biomass lysis of about 32.8% when the biosolids were subjected to prior dispersion at 30s and 3000rpm. However, the same ozone dosage without phase separation achieved 9.6% biomass lysis. The second exponential model results of the biomethane assay showed that DOP enhanced the accessibility of disintegrated biosolids for methane production and induced about 1150mL/g VS of methane production. The energy analysis reveals that DOP provides significant amount of positive net energy (152.65kWh/ton) when compared to OP (-12.42kWh/ton).

The fate of trace organic contaminants in sewage sludge during recuperative thickening anaerobic digestion

The aim of this work was to study the fate of trace organic contaminants (TrOCs) in sewage sludge during recuperative thickening anaerobic digestion. Sludge shearing at 3142s^-1 for 5minutes improved biogas production. By contrast, shearing at ≥6283s^-1 for 5minutes caused a notable reduction in biogas production and the removal of volatile solids. Results reported here showed the prevalent occurrence of 17 TrOCs in sewage sludge and highlights the importance of assessing TrOC removal via mass balance calculation by taking into account partitioning between the aqueous and solid phase as well as biodegradation. Hydrophilic and readily-biodegradable TrOCs (caffeine, trimethoprim, and paracetamol) were well removed and were not affected by shearing. TrOCs such as carbamazepine, gemfibrozil, and diuron showed biodegradation only at high shearing. It is possible that shearing can facilitate the circulation of TrOCs between aqueous and solid phases, thus, enhancing the biodegradation of some TrOCs.

Enhancement of biogas production from microalgal biomass through cellulolytic bacterial pretreatment

Generation of bioenergy from microalgal biomass has been a focus of interest in recent years. The recalcitrant nature of microalgal biomass owing to its high cellulose content limits methane generation. Thus, the present study investigates the effect of bacterial-based biological pretreatment on liquefaction of the microalga Chlorella vulgaris prior to anaerobic biodegradation to gain insights into energy efficient biomethanation. Liquefaction of microalgae resulted in a higher biomass stress index of about 18% in the experimental (pretreated with cellulose-secreting bacteria) vs. 11.8% in the control (non-pretreated) group. Mathematical modelling of the biomethanation studies implied that bacterial pretreatment had a greater influence on sustainable methane recovery, with a methane yield of about 0.08 (g Chemical Oxygen Demand/g Chemical Oxygen Demand), than did control pretreatment, with a yield of 0.04 (g Chemical Oxygen Demand/g Chemical Oxygen Demand). Energetic analysis of the proposed method of pretreatment showed a positive energy ratio of 1.04.

Energy-efficient methane production from macroalgal biomass through chemo disperser liquefaction

In this study, an effort has been made to reduce the energy cost of liquefaction by coupling a mechanical disperser with a chemical (sodium tripolyphosphate). In terms of the cost and specific energy demand of liquefaction, the algal biomass disintegrated at 12,000rpm for 30min, and an STPP dosage of about 0.04g/gCOD was chosen as an optimal parameter. Chemo disperser liquefaction (CDL) was found to be energetically and economically sustainable in terms of liquefaction, methane production, and net profit (15%, 0.14gCOD/gCOD, and 4 USD/Ton of algal biomass) and preferable to disperser liquefaction (DL) (10%, 0.11 gCOD/gCOD, and -475 USD/Ton of algal biomass).

Comparison of dry and wet milling pre-treatment methods for improving the anaerobic digestion performance of the Pennisetum hybrid

A planetary ball mill increased the specific methane yield of thePennisetumhybrid by 42%.

Upgrading the hydrolytic potential of immobilized bacterial pretreatment to boost biogas production

In this study, surfactant dioctyl sodium sulphosuccinate (DOSS)-mediated immobilized bacterial pretreatment of waste activated sludge (WAS) was experimentally proved to be an efficient and economically feasible process for enhancing the biodegradability of WAS. The maximal floc disruption with negligible cell cleavage was achieved at surfactant dosage of 0.009 g/g SS. Results of the outcome of bacterial pretreatment of sludge biomass revealed that chemical oxygen demand (COD) solubilization for deflocculated (EPS removed-bacterially pretreated) sludge was 20 %, which was higher than that of flocculated (14 %) or control (5 %). The pretreatment was swift in deflocculated sludge with a rate constant of about 0.064 h^-1. Biochemical methane potential (BMP) assay resulted in significant methane yield at 0.24 gCOD/gCOD for deflocculated sludge. Economic assessment of the proposed method showed a net profit of about 57.39 USD/ton of sludge.

Fenton mediated ultrasonic disintegration of sludge biomass: Biodegradability studies, energetic assessment, and its economic viability

Mechanical disintegration of sludge through ultrasonication demands high energy and cost. Therefore, in the present study, a comprehensive investigation was performed to analyze the potential of a novel method, fenton mediated sonic disintegration (FSD). In FSD process, extracellular polymeric substance (EPS) of sludge was first removed via fenton treatment. It was subsequently disintegrated via ultrasonication. Energetic assessment and economic analysis were then performed using net energy and cost gain (spent) as key factor to evaluate the practical viability of the FSD process. FSD was found to be superior over sonic disintegration based on its higher sludge solubilization (34.4% vs. 23.2%) and methane production potential (0.3gCOD/gCOD vs. 0.2gCOD/gCOD). Both energy analysis and cost assessment of the present study revealed that FSD could reduce the energy demand of ultrasonication considerably with a positive net profit of about 44.93USD/Ton of sludge.

Improved production of propionic acid driven by hydrolyzed liquid containing high concentration of l-lactic acid from co-fermentation of food waste and sludge

This study investigated the feasibility of improved production propionic acid-enriched volatile fatty acid (VFA) from high concentration (Cs) of food waste and waste activated sludge (WAS) via lactic acid pathway by using of Propionibacterium acidipropionici. It was observed that production of l-lactate overwhelmed to d-lactate at first stage, which improved from 3.21 to 35.45gCOD/L with increase of substrate Cs. However, kinetic model analysis indicated that P. acidipropionici growth rate μmax was decreased with increase of l-lactate concentration, which explained second stage free cell fermentation of propionic acid was inhibited when fed by first stage liquid from R-40, R-55 and R-70. Then, the fibrous bed bioreactor was employed to eliminate the feed inhibition. The maximal percentage of propionic acid (68.3%) and production (16.31gCOD/L) was obtained by feeding liquid of R-55, which was improved by 3.33 folds compared to the free cell fermentation.

Electrochemical pretreatment of waste activated sludge: effect of process conditions on sludge disintegration degree and methane production

Waste activated sludge (WAS) requires a long digestion time because of a rate-limiting hydrolysis step - the first phase of anaerobic digestion (AD). Pretreatment can be used prior to AD to facilitate the hydrolysis step and improve the efficiency of WAS digestion. This study evaluated a novel application of electrochemical (EC) technology employed as the pretreatment method prior to AD of WAS, focusing on the effect of process conditions on sludge disintegration and subsequent AD process. A superior process condition of EC pretreatment was obtained by reaction time of 30 min, electrolysis voltage of 20 V, and electrode distance of 5 cm, under which the disintegration degree of WAS ranged between 9.02% and 9.72%. In the subsequent batch AD tests, 206 mL/g volatile solid (VS) methane production in EC pretreated sludge was obtained, which was 20.47% higher than that of unpretreated sludge. The AD time was 19 days shorter for EC pretreated sludge compared to the unpretreated sludge. Additionally, the EC + AD reactor achieved 41.84% of VS removal at the end of AD. The analysis of energy consumption showed that EC pretreatment could be effective in enhancing sludge AD with reduced energy consumption when compared to other pretreatment methods.

Impact of thermo-chemo-sonic pretreatment in solubilizing waste activated sludge for biogas production: Energetic analysis and economic assessment

The objective of this study was to determine the impact of solubilization during thermo-chemo-sonic pretreatment of waste activated sludge (WAS) on anaerobic biodegradability and cost for biogas production. The results revealed that it was possible to achieve 40-50% of solubilization of WAS when ultrasonic energy input was doubled (11,520-27,000kJ/kgTS). The cost to achieve 30-35% of solubilization of WAS was calculated to be 0.22-0.24USD/L, which was relatively lower than the cost of 0.53-0.8USD/L when 40-50% of solubilisation of WAS was achieved. There was no significant difference in biodegradability (0.60-0.64gCOD/gCOD) for samples with solubilization efficiency of 35-50%. Comparing energetic balance and economic assessment of samples with different solubilization percentages, the results showed that samples with 30-35% of solubilization had lower net cost (7.98-2.33USD/Ton of sludge) and negative energy balance compared to samples with other percentages of solubilization.