Profitable ultrasonic assisted microwave disintegration of sludge biomass: Modelling of biomethanation and energy parameter analysis

Effects of microwave irradiation at various temperatures on biosludge disintegration

The waste biological sludge disintegration by using microwave irradiation was investigated at a ramping rate of 2°C/min and 5 min holding time at various target temperatures. Significant disintegration of biosludge was observed and the highest disintegration degree was determined about 82% at the temperature of 110°C. Increase of target temperature elevated the energy needs to 98, 123 and 148 kWh/kg TS at the temperatures of 75°C, 90°C and 110°C, respectively. The gradual increase of sugar and protein in the sludge slurry with increasing temperatures indicates successful degradation. The microwave pretreatment increased the specific surface area of the sludge by particle size reduction. The specific surface area of raw sludge was 70 m2/kg and rose to approximately 253.7 m2/kg at 110°C with an increment ratio of 260%. Although a significant NH4-N release was not observed, PO4-P concentrations increased from 11.0 mg/L to 16.3, 20.7 and 29.2 mg/L at the temperatures of 75°C, 90°C, 110°C, respectively. While the specific filter resistance of waste biological sludge was about 1.0 × 1013, increasing the microwave target temperature, the ability of dewatering decreased and the highest SFR value of 5.1 × 1014 was observed at the temperature of 110°C.

Dual disintegration of microalgae biomass for cost-effective biomethane production: Energy and cost assessment

The present study aims to enhance the biomethane production potential of microalgae via a dual disintegration process. During this process, the microalgae biomass was firstly subjected to cell wall weakening by thermochemical disintegration (TC) (50 to 80 °C), pH adjustment with alkali, NaOH (6 to 10) and time (0 to 10 min) and, secondly, by bacterial disintegration (BD). TC-BD disintegration was comparatively higher (33 %) than BD (24 %), TC (8.5 %), and control (7 %). A more significant VFA accumulation of 2816 mg/L was recorded for TC-BD. Similarly, a greater substrate anaerobic biodegradability was achieved in TC-BD (0.32 g COD /g COD) than BD (0.21 g COD /g COD), TC alone (0.09 gCOD/g COD) and control (0.08 g COD /g COD), respectively. The TC-BD achieves a positive net profit and an energy ratio of + 0.12 GJ/d and 1.03. The proposed dual disintegration has a promising future for commercialization.

Microwave pretreatment of wastewater sludge technology-a scientometric-based review

This manuscript presents a scientometric review of recent advances in microwave pretreatment processes for sewage sludge, systematically identifying existing gaps and prospects. For this purpose, 1763 papers on the application of microwave technology to sludge pretreatment were retrieved from the Web of Science (WoS) using relevant keywords. These publications were then analyzed using diverse scientometric indices. The results show that research in this field encompasses applications based on the non-thermal effects of microwaves, enhanced effectiveness of anaerobic digestion (AD), and the energy balance of this pretreatment system. Overcoming existing technical challenges, such as the cleavage of extracellular polymers, reducing microwave energy consumption, understanding the non-thermal effects of microwaves, promoting AD of sludge in combination with other chemical and physical methods, and expanding the application of the technology, are the main scientific focuses. Additionally, this paper thoroughly examines both the constraints and potential of microwave pretreatment technology for wastewater treatment.

Biohydrogen production through energy efficient surfactant induced microwave pretreatment of macroalgae Ulva reticulata

Macroalgal biomass being rich in carbohydrates, proteins and lipids in their cell wall has been considered as the most efficient organic rich sources for biofuel (biohydrogen) production. In this study, Pluronic P-123-induced microwave pretreatment was applied to disintegrate the marine macroalgae biomass, Ulva reticulata. Microwave disintegration was done by varying the treatment time and microwave power from 0 to 40 min and 0.09 KW to 0.63 KW. A maximum chemical oxygen demand (COD) solubilization of 22.33% was achieved at a microwave power and time duration of 0.36 kW and 15 min. Chemical (Pluronic P-123, a mild surfactant) was combined with optimum microwave disintegration conditions to increase the solubilization efficiency and this combined pretreatment achieved a maximum COD solubilization of 31.02% at 10 min pretreatment time and 0.06 g per g TS of Pluronic P-123 dosage. The present study indicated that combination of surfactant with microwave pretreatment substantially improves the COD solubilization with reduced pretreatment -time than mono microwave pretreatment. An optimal hydrogen yield of 98.37 mL was achieved through this combined pretreatment. The biohydrogen data was modelled with Gompertz model and the kinetic parameters derived through this model implies that the calculated adjusted R squared values for all the samples lies between 0.95 and 0.99. This shows that the model fitted biohydrogen experimental values accurately. In addition, Pluronic P-123-induced microwave pretreatment was regarded as energy efficient and cost effective than microwave pretreatment alone with net energy production and a greater energy ratio of 504.38 kWh/Ton macroalgae and 1.2 when compared to microwave pretreatment alone (-2975.6 kWh/Ton macroalgae and 0.5).

Alkaline-thermal hydrolysate of waste activated sludge as a co-metabolic substrate enhances biodegradation of refractory dye reactive black 5

Aromatic azo dyes possess inherent resistance and are known to be carcinogenic, posing a significant threat to human and ecosystems. Enhancing the biodegradation of azo dyes usually requires the presence of co-metabolic substrates to optimize the process. In addressing the issue of excessive waste activated sludge (WAS) generation, this study explored the potential of utilizing alkaline-thermal hydrolysate of WAS as a co-metabolic substrate to boost the degradation of reactive black 5 (RB5) dyes. The acclimated microbial consortium, when supplemented with the WAS hydrolysate obtained at a hydrolysis temperature of 30 °C, achieved an impressive RB5 decolorization efficiency of 90.3% (pH = 7, 35 °C) with a corresponding COD removal efficiency of 45.0%. The addition of WAS hydrolysate as a co-substrate conferred the consortium with a remarkable tolerance to high dye concentration (1500 mg/L RB5) and salinity levels (4-5%), surpassing the performance of conventional co-metabolic sugars in RB5 degradation. 3D-EEM analysis revealed that protein-like substances rich in tyrosine and tryptophan, present in the WAS hydrolysate, played a crucial role in promoting RB5 biodegradation. Furthermore, the microbial consortium community exhibited an enrichment of dye-degrading species, including Acidovorax, Bordetella, Kerstersia, and Brevundimonas, which dominated the community. Notably, functional genes associated with dye degradation and intermediates were also enriched during the RB5 decolorization and biodegradation process. These findings present a practical strategy for the simultaneous treatment of dye-containing wastewater and recycling of WAS.

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.

Strategies for energy conversion from sludge to methane through pretreatment coupled anaerobic digestion: Potential energy loss or gain

Anaerobic digestion (AD) of wasted activated sludge from wastewater plants is recognized as an effective method to reclaim energy in the form of methane. AD performance has been enhanced by coupling various pretreatments that impact energy conversion from sludge. This paper mainly reviewed the development of pretreatments based on different technologies reported in recent years and evaluated their energy benefit. Significant increases in methane yield are generally obtained in AD with pretreatments demanding energy input, including thermal- and ultrasound-based methods. However, these energy-intense pretreatments usually gained negative energy benefit that the increase in methane yield consumed extra energy input. The unbalanced relationship counts against the goal of energy reclamation from sludge. Combined pretreatment consisting of multiple technologies normally outcompetes the single pretreatment, and the combination of energy-intense methods and chemicals potentially reduces energy input and simultaneously ensure high methane yield. For determining whether the energy reclamation from sludge via AD contribute to mitigating global warming, integrating greenhouse gas emission into the evaluation system of pretreated AD is further warranted.

Augmentation in polyhydroxybutyrate and biogas production from waste activated sludge through mild sonication induced thermo-fenton disintegration

In this study, an innovative approach was developed to enhance the hydrolysis through phase-separated pretreatment by removing exopolymeric substances via mild sonication followed by thermo-Fenton disintegration. The exopolymeric substances fragmentation was enhanced at the sonic specific energy input of 2.58 kJ/kg total solids. After exopolymeric substance removal, the disintegration of biomass by thermo-Fenton yield the solubilization of 29.8 % at Fe²⁺:H₂O₂ dosage and temperature of 0.009:0.036 g/g suspended solids and 80 °C as compared to thermo-Fenton alone disintegration. The polyhydroxybutyrate content of 93.1 % was accumulated by Bacillus aryabhattai at the optimum time of 42 h, while providing 70 % (v/v) pre-treated supernatant as a carbon source under nutrient-limiting condition. Moreover, the biogas generation of 0.187 L/g chemical oxygen demand was achieved using settled pretreated sludge. The pretreated sludge sample thus served as a carbon source for polyhydroxybutyrate producers as well as substrate for biogas production.

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).

Distinct effects of typical sludge pretreatment approaches on the antibiotic resistance genes variations, associated bacterial community dynamics and metabolic activities during anaerobic fermentation process

Anaerobic fermentation is effective for waste activated sludge (WAS) disposal to realize resource generation and pollutants reduction, and various pretreatments were commonly applied to improve the performance. This work mainly investigated the effects of typical WAS pretreatment approaches on the antibiotic resistance genes (ARGs, as emerging contaminants) removal during anaerobic fermentation processes and unveiled the underlying mechanisms. The results indicated that all the pretreatment strategies exhibited evident effects on the overall ARGs removal with the order of Fe²⁺ activated persulfate (PS/Fe²⁺) > pH 10 > Ultrasonication > Heat, and showed selective removal tendency for the specific ARGs (namely easily removed (aadA1 and sul1) and persistent ARGs). Mechanistic analysis demonstrated that the pretreatments disrupted the extracellular polymeric substances (EPS) and rose the cell membrane permeability (particularly for PS/Fe²⁺ and Heat). Then the increased ARGs release benefitted the subsequent reduction of mobile genetic elements (MGEs) and extracellular ARGs (especially for PS/Fe²⁺ and pH10), resulting the ARGs attenuation. Pretreatments significantly shifted the microbial community structure and the abundances of potential ARGs hosts (i.e., Sulfuritalea, and Denitratisoma). Also, the different pretreatments exhibited distinct effects on the microbial metabolic traits related with ARGs proliferation (i.e., ABC transporters, two-component system and bacterial secretion systems), which also contributed to the ARGs attenuations during WAS fermentation. The partial least-squares path modeling (PLS-PM) analysis indicated that the bacterial community (total effects = 0.968) was key factor determining ARGs fates.

Phase separated pretreatment strategies for enhanced waste activated sludge disintegration in anaerobic digestion: An outlook and recent trends

A significant ecological problem was developed on disposing the enormous amounts of waste activated sludge (WAS) produced by traditional wastewater treatment. There have been various attempts recently originated to develop innovative methods for substantial sludge treatment. The most frequently used approach for treating sludge to produces methane and reduces sludge is anaerobic treatment. The hydrolysis phase in WAS limits the breakdown of complex macrobiotic compounds. The presence of extracellular polymeric substances (EPS) in biomass prevents the substrate from being hydrolyzed. Enhancing substrate hydrolysis involves removal of EPS preceded by phase separated pretreatment. Hence, a critical assessment of various phase separated pretreatment that has a remarkable effect on the anaerobic digestion process was documented in detail. Moreover, the economic viability and energy requirement of this treatment process was also discussed. Perspectives and recommendations for methane production were also provided to attain effectual sludge management.

Feasibility of using different hydrothermal processes for sewage sludge management in China

Due to its tremendous volume and severe environmental concern, sewage sludge (SS) management and treatment are significant in China. The recent prohibition (June 2021) of reusing SS as organic fertilizers makes it urgent to develop alternative processes. However, there is currently little research analyzing the applicability of using HP for sewage SS treatment in China. The significant difference in SS composition and the much less land supply in urban areas might invalidate most previous localized suggestions. In this paper, the development of emerging hydrothermal processes (HPs) for SS treatment will be reviewed, focusing on their decomposition mechanisms and the benefits of HPs compared with current SS treatment technologies. The SS volume, composition, and regulatory regime in China will also be evaluated. Those efforts could address the potential SS treatment capacity shortage and provide an opportunity to recover nutrients, organics and energy embedded in SS. The results show that HPs' high investment cost is mainly limited by the process scale, while their operating costs are comparable to incineration. Minimizing equipment erosion, ensuring process safety, and designing a more efficient heat recovery system are recommended for the future commercialization of HPs in China.

Energy feasibility and life cycle assessment of sludge pretreatment methods for advanced anaerobic digestion

Energy sustainability is one of the critical parameters to be studied for the successful application of pretreatment processes. This study critically analyzes the energy efficiency of different energy-demanding sludge pretreatment techniques. Conventional thermal pretreatment of sludge (∼5% total solids, TS) produced 244 mL CH₄/gTS, which could result in a positive energy balance of 2.6 kJ/kg TS. However, microwave pretreatment could generate only 178 mL CH₄/gTS with a negative energy balance of -15.62 kJ/kg TS. In CAMBI process, the heat requirements can be compensated using exhaust gases and hot water from combined heat and power, and electricity requirements are managed by the use of cogeneration. The study concluded that <100 ℃ pretreatment effectively enhances the efficiency of anaerobic digestion and shows positive energy balance over microwave and ultrasonication. Moreover, microwave pretreatment has the highest global warming potential than thermal and ultrasonic pretreatments.

Mild hydrogen peroxide interceded bacterial disintegration of waste activated sludge for efficient biomethane production

Regardless of the issue of sludge management all over the world, the role of phase separated pretreatment prior to anaerobic digestion are more promising in terms of energy efficient biomethane production. However, the effect of phase separated pretreatment (dissociation of extracellular polymeric substances (EPS) followed by biological pretreatment in a two-step process) must be sensibly evaluated from various perceptions to consolidate its effectiveness in sludge management and bioenergy recovery. In this study, mild hydrogen peroxide induced bacterial pretreatment (H₂O₂-BP) was employed as phase separated pretreatment to investigate the effectiveness of EPS dissociation prior to biological pretreatment on sludge solubilization and biomethanation. The novelty of this study is the application of mild dosage of hydrogen peroxide at sludge pH for the removal of EPS layer with lesser formation of recalcitrant substances which thereby enhances the disintegration by enzyme secreting bacterial and methane generation. The outcome confirmed that the higher EPS dissociation was achieved at H₂O₂ dosage of 8 μL per 100 mL of sludge with negligible cell lysis. An extractable EPS of 172.8 mg/L was obtained after H₂O₂ treatment. The higher sCOD solubilization of 22% and the suspended solid reduction of 17.14% were achieved in hydrogen peroxide followed by bacterial pretreatment (H₂O₂-BP) as compared to of bacterial pretreatment alone (BP) (solubilization-11% and suspended solids reduction-9.3%) and control (C) sludges (solubilization-5% and suspended solids reduction-4.3%). The methane generation for H₂O₂-BP sludge is 0.174 L/gCOD which is higher than BP (0.078 L/gCOD,) and C sludge (0.02175 L/gCOD). A higher biomass solubilization and increased biomethanation in H₂O₂-BP revealed that dissociation of EPS prior to bacterial pretreatment increases the surface area for bacterial pretreatment facilitating easier accessibility of substrate and enhanced biomethanation.

Modified fractional-order model for biomass degradation in an up-flow anaerobic sludge blanket reactor at Zenein Wastewater Treatment Plant

This paper presents a modified fractional-order model (FOM) for microorganism stimulation in an up-flow anaerobic sludge blanket (UASB) reactor treating low-strength wastewater. This study aimed to examine the famine period of methanogens due to biomass accumulation in the UASB reactor over long time periods at a constant organic loading rate (OLR). This modified model can investigate the substrate biodegradation in a UASB reactor while considering substrate diffusion into biological granules during the feast and famine periods of methanogens. The Grünwald-Letnikov numerical technique was used to indicate the effect of biomass degradation on the biogas production rate and substrate biodegradation in a UASB reactor installed at Zenein Wastewater Treatment Plant (WWTP) in Giza, Egypt. Several fractional orders were applied in the dynamic model at biomass concentrations of [Formula: see text] and [Formula: see text] in the reactor bed and blanket zones, respectively. An OLR of [Formula: see text] using the calibrated kinetic parameters at [Formula: see text] was applied to comply with the experimental outcomes. The simulation results indicate that the removal efficiency of chemical oxygen demand (COD) was maintained at approximately [Formula: see text], whereas the biogas production rate declined from [Formula: see text] in the reactor bed zone due to a decline in food to microorganism (F/M) ratio from [Formula: see text] during the sludge retention time (SRT) in the UASB reactor.

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).

Sludge disintegration using UV assisted Sono-Fenton process

In this study, the effects of combination of ultrasonic process with UV light and both classical Fenton (CFP) and modified Fenton (MFP) processes on disintegration of waste sludge were investigated. Fe²⁺ and Fe⁰ dosage, hydrogen peroxide dosage, reaction time, pH, and different UV lamps were optimized to achieve a high degree of disintegration (DD). In addition, kinetic study and toxicity analysis were performed under optimum conditions for all processes. For CFP, the best DD 22.85% was found with optimum pH 3, reaction time 60 min, 7 g/kg TS Fe²⁺, 35 g/kg TS H₂O₂ doses, and UV-C light, while this value increased to 37.83% with ultrasound (US) application. For MFP; the best DD was achieved as 25.84% with optimum pH 3, reaction time 60 min, 5 g/kg TS Fe⁰, 25 g/kg TS H₂O₂ doses, and UV-C light; however, it rose to 42.32% in the presence of US. The use of US in all processes increased the germination percentage that expresses the sludge toxicity, up to 100%. In the kinetic study, it was found that all processes are in compliance with zeroth-order kinetics. It was concluded with this study that US has an important synergistic effect on Fenton applications and contributes to sludge disintegration.

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.

Solubilisation of fruits and vegetable dregs through surfactant mediated sonic disintegration: impact on biomethane potential and energy ratio

This study investigates the symbiotic effect of cetyltrimethylammonium bromide (CTAB) coupled with sonication of fruits and vegetable dregs (FVD) on disintegration and subsequent energy efficient methane production. The liquefaction of FVD experiments was conducted by varying dosage of surfactant from 0.001to 0.01 g/g SS for 60 min in mechanical shaker. The optimised dosage of surfactant was combined with sonication. Finally, the combined pretreatment and sole pretreatment were assessed using methane potential assay. The results revealed that at optimised conditions (sonication specific energy of 5400 kJ/kg TS, CTAB dosage of 0.006 g/g SS), the maximum liquefiable organics release rate and solids reduction of CTAB mediated sonic disintegration (CSD) were found respectively to be 27% and 17% more than the ultrasonic disintegration (16% and 10%). CSD was noticed to be superior than ultrasonic disintegration (UD) based on highest volatile fatty acid yield (2000 mg/L vs. 1250 mg/L) and biochemical methane potential (203 mL/g COD vs. 144 mL/g COD). CSD achieved energy ratio of 0.9 which is greater than ultrasonic disintegration energy ratio 0.4.

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).

Evaluation of Anaerobic Digestion of Dairy Wastewater in an Innovative Multi-Section Horizontal Flow Reactor

The aim of this study was the performance evaluation of anaerobic digestion of dairy wastewater in a multi-section horizontal flow reactor (HFAR) equipped with microwave and ultrasonic generators to stimulate biochemical processes. The effects of increasing organic loading rate (OLR) ranging from 1.0 g chemical oxygen demand (COD)/L·d to 4.0 g COD/L·d on treatment performance, biogas production, and percentage of methane yield were determined. The highest organic compounds removals (about 85% as COD and total organic carbon—TOC) were obtained at OLR of 1.0–2.0 g COD/L·d. The highest biogas yield of 0.33 ± 0.03 L/g COD removed and methane content in biogas of 68.1 ± 5.8% were recorded at OLR of 1.0 g COD/L·d, while at OLR of 2.0 g COD/L·d it was 0.31 ± 0.02 L/COD removed and 66.3 ± 5.7%, respectively. Increasing of the OLR led to a reduction in biogas productivity as well as a decrease in methane content in biogas. The best technological effects were recorded in series with an operating mode of ultrasonic generators of 2 min work/28 min break. More intensive sonication reduced the efficiency of anaerobic digestion of dairy wastewater as well as biogas production. A low nutrient removal efficiency was observed in all tested series of the experiment, which ranged from 2.04 ± 0.38 to 4.59 ± 0.68% for phosphorus and from 9.67 ± 3.36 to 20.36 ± 0.32% for nitrogen. The effects obtained in the study (referring to the efficiency of wastewater treatment, biogas production, as well as to the results of economic analysis) proved that the HFAR can be competitive to existing industrial technologies for food wastewater treatment.

Anaerobic bioconversion of petrochemical wastewater to biomethane in a semi-continuous bioreactor: Biodegradability, mineralization behaviors and methane productivity

Petrochemical wastewaters treatment represents a serious challenge due to the high toxicity and complex chemical components. In this study, the biodegradability, mineralization behaviors and methane productivity of eight different types of petrochemical wastewaters were evaluated in series of semi-continuous bioreactors. Methane production strongly depended on the characteristics of wastewaters and chemical constituents. The highest methane yield of 305.9 ± 2.7 mL/g-COD was achieved by purified terephthalic acid wastewater, followed by ethylene glycol, polyester, etc. Comparatively, one-step-SCN^- wastewater produced the lowest methane yield (4.7 ± 0.7 mL/g-COD) owing to high toxicity and low biodegradability. Modified Gompertz model confirmed that purified terephthalic acid, ethylene glycol and polyester wastewaters had a short lag-phase of 1.2, 1.7 and 0.2 days, respectively. Nonetheless, the formation of by-products such as proteins, polysaccharides and ammonia nitrogen throughout anaerobic digestion reflected the high activity of anaerobic microorganisms, confirming the technical feasibility of anaerobic biotechnology in treating petrochemical wastewaters.

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.

Improving biogas production performance of dairy activated sludge via ultrasound disruption prior to microwave disintegration

In this study, ultrasound disruption was employed to enhance the efficiency of microwave disintegration of dairy sludge. Results revealed that ultrasound specific energy input of 1,500 kJ/kg TS was found to be optimum with limited cell lysis at the end of the disruption phase. Biodegradability study suggested an enhancement in suspended solids reduction (16%) and biogas production (180 mL/gVS) in floc disrupted (deflocculated) samples when compared to sole microwave pretreatment (8.3% and 140 mL/gVS, respectively). Energy assessment to attain the 15% optimum solubilization revealed a positive net production of 26 kWh per kg sludge in deflocculated samples compared to 18 kWh in flocculated (sole microwave) samples. Thus, ultrasound disruption prior to microwave disintegration of dairy sludge was considered to be a feasible pretreatment technique.

Improvement of Co-Composting by a combined pretreatment Ozonation/Ultrasonic process in stabilization of raw activated sludge

The enhancement of composting technology to stabilize sludge pretreated by ozonation and ultrasonic was tested for 35 days. Secondary sludge produced by biological process are characterized with endogenous residue and inert solid matter which inhibit fully degrade bacterial cell walls. The composting process was performed with sludge pretreated with ozonatian and ultrasonics and green waste in a ratio of 2:1. The composting characteristics was evaluated for different physico-chemical and microbiological parameters in five different reactors. A high degree of composting quality was achieved with respect to significant reduction in volatile solids (VS) (32%), total organic carbon (TOC) (35.0%), C/N ratio (23.74), total coliform (TC) (168) along with the substantial increase in availability of nutrients like N (1.2%) and P (8.77%). High removal efficiency of TC and Fecal Coliform (FC) were observed in composting results, where simultaneous ultrasonic and ozonation were considered as primary-stabilization process. Therefore, applying integrated ultrasonic/ozonation with composting system for sludge stabilization is potentially useful technology in sustainable land restoration practices to meet standards and produce soil conditioner.

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.

Investigation on ultrasonication mediated biosurfactant disintegration method in sludge flocs for enhancing hydrolytic enzymes activity and polyhydroxyalkanoates

In this study, a novel biosurfactant potential bacterial strain Pseudomonas pachastrellae RW43 was isolated from pulp and paper sludge and the biosurfactant namely rhamnolipid produced by Pseudomonas pachastrellae RW43 was investigated by varying pH and incubation time in batch liquid fermentation process. The maximal yield of rhamnolipid was found to be 12.1 g/L at an optimized condition of pH 7 and incubation time of 168 h. NMR analysis was performed for identification of molecular structure of produced rhamnolipid and its results concluded that the product was identified as di rhamnolipid. Then, statistically the global optimum conditions for hydrolytic enzymes extraction parameters (sonication power (100 W), extraction time (15 min) and rhamnolipid dosage (2% v/v)) were established. At 30,456 kJ/kg TS specific energy, ultrasonication with rhamnolipid disintegration method extracted maximal consortium activity of hydrolytic enzymes from mixed sludge (municipal and pulp & paper sludge) and the maximum observed were found to be 42.22, 51.75, 34.26, 24.21, 11.35 Units/g VSS respectively for protease, α-amylase, cellulase, lipase and α-glucosidase. Polyhydroxyalkanoates was recovered from enzymes extracted sludge using various solvents namely chloroform, sodium hypochlorite with chloroform and sodium lauryl sulfate with sodium hypochlorite. The maximum recovery was found to be 74 g/kg using sodium hypochlorite and chloroform extraction solvents.

A critical review of volatile fatty acids produced from waste activated sludge: enhanced strategies and its applications

This paper reviews the recent achievements in the enhanced production of volatile fatty acids (VFAs) from waste activated sludge (WAS). The enhanced strategies are divided into two approaches. The first strategy focuses on the regulation of carbon-to-nitrogen (C/N) ratio by co-digestion of WAS with carbon-rich substrates, including municipal solid wastes (MSW), marine algae, agricultural residues, and animal manures. The other strategy is to enhance the solubilization and hydrolysis of WAS or inhibit the methanogenesis by applying various pretreatments, such as mechanical, chemical, enzymatic, and thermal pretreatment. Finally, the applications of WAS-derived VFAs are discussed. The future researches in enhancing VFAs production and wide application of the VFAs from both technical and economic perspectives are proposed.

Evaluation of photocatalytic thin film pretreatment on anaerobic degradability of exopolymer extracted biosolids for biofuel generation

This study reports the result of sodium citrate induced exopolymer extraction on the photocatalytic thin film (TiO₂) pretreatment efficiency of waste activated sludge (WAS). TiO₂ is immobilized through DC spluttering method followed by annealing process. The exopolymer removal of 94.2% by sodium citrate (0.05 g/g SS) promotes better disintegration. This TiO₂ thin film efficiently extricate the intracellular components of exopolymer extracted sludge at 50 min increasing the solubilization to 19.33%. As a result, the exopolymer extracted sludge shows high methane generation (0.24 gCOD/gCOD) than the other (pretreated sludge without exopolymer removal - 0.12 gCOD/gCOD and raw sludge without treatment - 0.075 gCOD/gCOD). The methane generated in sodium citrate induced TiO₂ thin film pretreated sludge is 398.99 kWh. In cost analysis, it gives net cost of -57.46 USD/ton of sludge. In addition, the proposed method also accounts 51.3% of solid reduction.

Phosphorus recovery from freeze-microwave pretreated sludge supernatant by phosphate sedimentation

A novel pretreatment approach combined freeze with microwave was developed to promote the release of orthophosphate from excess sludge, and the phosphorus (P) was recovered from the produced supernatant by phosphate sedimentation. Batch tests examined the effects of freezing time, pH, and microwave time on the release of phosphate (PO₄^3--P) of the excess sludge during the freezing-microwave pretreatment. The release amount of PO₄^3--P reached 276 mg/L under the conditions of the freezing time of 23 h, microwave time of 5 min, and pH of 4. The optimal conditions for phosphate precipitation were pH of 9.5, the mole ratio of Mg/P of 1.8, and stirring speed of 200 rpm. The recovery efficiency of PO₄^3--P reached 97.42% after the reaction of 20 min and the precipitation of 50 min. The precipitated sediment mainly consisted of amorphous calcium phosphate and magnesium ammonium phosphate (MAP) which can be used as a substitute for phosphorus minerals.

Enhancing hydrogen production through anaerobic co-digestion of fruit waste with biosolids

In the present study, anaerobic co-digestion process was carried out with 23 mixed substrates proportion (MSP) of fruit waste (FRW), municipal wastewater treatment plant aerated biosolid (MPABS) and dairy effluent treatment plant returned biosolid (DPRBS). During co-digestion process, the effect of MSP on carbon/nitrogen (C/N) ratio and hydrogen production was investigated. The results revealed that MSP17 (70 FRW:20 MPABS:10 DPRBS) has yielded maximal hydrogen production of 295 mL with C/N ratio of 30, followed by MSP9 (70 FRW:30 DPRBS) exhibiting 253 mL of hydrogen production with C/N ratio of 29 and MSP2 (90 FRW:10 MPABS) attained 223 mL of hydrogen production with C/N ratio of 27. Then, SEM analysis of digested substrate sample was also performed in which flocs observed to be small and loose in structure in co-digested samples and intact form in non co-digested samples. Hence, this study results can be used for a sustainable approach by utilizing the FRW and biosolids for hydrogen production.

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.

Recent advances on biogranules formation in dark hydrogen fermentation system: Mechanism of formation and microbial characteristics

Hydrogen producing granules (HPGs) are most promising biological methods used to treat organic rich wastes and generate clean hydrogen energy. This review provides information regarding types of immobilization, supporting materials and microbiome involved on HPG formation and its performances. In this review, importance has been given to three kinds of immobilization techniques such as adsorption, encapsulation, and entrapment. The HPG, characteristics and types of organic and inorganic supporting materials followed for enhancing hydrogen yield were also discussed. This review also considers the applications of HPG for sustainable and high rate hydrogen production. A detailed discussion on insight of key mechanism for HPGs formation and its performances for stable operation of high rate hydrogen production system are also provided.

Effect of surfactant assisted sonic pretreatment on liquefaction of fruits and vegetable residue: Characterization, acidogenesis, biomethane yield and energy ratio

The present study explored the disintegration potential of fruits and vegetable residue through sodium dodecyl sulphate (SDS) assisted sonic pretreatment (SSP). In SSP method, initially the biomass barrier (lignin) was removed using SDS at different dosage, subsequently it was sonically disintegrated. The effect of SSP were assessed based on dissolved organic release (DOR) of fruits and vegetable waste and specific energy input. SSP method achieved higher DOR rate and suspended solids reduction (26% and 16%) at optimum SDS dosage of 0.035 g/g SS with least specific energy input of 5400 kJ/kg TS compared to ultrasonic pretreatment (UP) (16% and 10%). The impact of fermentation and biomethane potential assay revealed highest production of volatile fatty acid and methane yield in SSP (1950 mg/L, 0.6 g/g COD) than UP. The energy ratio obtained was 0.9 for SSP, indicating proposed method is energetically efficient.

Microwave Technologies: An Emerging Tool for Inactivation of Biohazardous Material in Developing Countries

Inappropriate treatment and disposal of waste containing biohazardous materials occurs especially in developing countries and can lead to adverse effects on public and occupational health and safety, as well as on the environment. For the treatment of biohazardous waste, microwave irradiation is an emerging tool. It is a misbelief that microwave devices cannot be used for inactivation of solid biohazardous waste; however, the inactivation process, and especially the moisture content, has to be strictly controlled, particularly if water is required to be added to the process. Appropriate control allows also inactivation of waste containing inhomogeneous compositions of material with low fluid/moisture content. Where appropriate, especially where control of transport of waste cannot be guaranteed, the waste should be inactivated directly at the place of generation, preferably with a closed waste collection system. In waste containing sufficient moisture, there are direct useful applications, for example the treatment of sewage sludge or human feces. A number of examples of microwave applications with impacts for developing countries are presented in this review. In respect to energy costs and environmental aspects, microwave devices have clear advantages in comparison to autoclaves.

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.