Search

Highlights • Alkali and acid pretreated biomass slurries were mixed for ethanol production. • This approach saved 40–50% alkali/acid use. • This approach improved fermentability. Abstract Alkali and acid pretreatment based processes for lignocellulosic biofuel production typically consume substantial amount of alkali and acid. In addition, alkali pretreatment generates compounds with high toxicity rendering washing/detoxification inevitable. In this work, alkali (AL) and dilute acid (DA) pretreatment based processes were compared side by side for ethanol production from corn stover (CS) using commercial enzymes and Zymomonas mobilis 8b strain. Next, AL and DA pretreated CS slurries (without removing liquid stream) were mixed to neutralize for enzymatic hydrolysis and ethanol fermentation. The digestibility and fermentability of the mixed pretreated biomass were systematically studied and compared to unmixed pretreated biomass. Results showed that mixed biomass process saved 40–50% alkali/acid use and enhanced fermentability compared to AL-CS. This work suggests that it could be beneficial to have both alkali and acid pretreatments operating in a biorefinery, which could accommodate various feedstocks. [ABSTRACT FROM AUTHOR]

Biofuel production from lignocellulose has recently been gaining much more attention as a result. One major problem of using lignocellulosic materials for the production of biofuel is the low accessibility of cellulose to enzymes and microorganisms. Therefore, pretreatment of lignocellulose is a critical step in biofuel production from such materials. Of the pretreatments, fungal treatment has become an important process due to its low energy demands and selective degradation of lignin and hemicellulose. This capability comes from the unique enzymatic systems, cellulolytic and ligninolytic enzymes, especially in white rot fungi. The low energy demand of fungal pretreatment has generated interest in studying the applicability of fungal pretreatment for biofuel production from woody materials. The most significant drawback of fungal pretreatment is the lengthy time required for the process. Combining fungal pretreatment with other pretreatment methods might reduce the time necessary for the whole process to operate. It can also introduce cost-effectiveness. Thus combining fungal pretreatment with other physical and chemical methods has been recently contemplated. This paper provides a comprehensive review of current fungal pretreatments and feasibility for biofuel production, with a focus on combining fungal pretreatment with other methods. The advantages and disadvantages of all physical and chemical methods were also briefly reviewed. The applicability of the combination of fungal with other pretreatment methods has been considered in a number of recent publications. To be commercially attractive, both energy demand and processing time should be reduced. In terms of energy demand reduction, combined fungal physico-chemical pretreatment has been effective. However, the lengthy time taken for the whole process has not been significantly improved upon. A great deal of work is still required to be done regarding time reduction for the process (combined fungal-physico chemical pretreatment). Therefore, it seems to remain an open field for research and process development. [ABSTRACT FROM AUTHOR]

• Pretreatment is an essential step for the breakdown of lignocellulosic biomass. • Combining pretreatment helps to lower the severity of the drawbacks of a single step. • Biological-chemical/physicochemical combined pretreatment strategies were reviewed. • The order of pretreatment in the combined studies affects the overall efficiency. Sustainable biorefinery concepts based on lignocellulosic biomass are gaining worldwide research interest because of their inexpensiveness and abundance. The recalcitrance of lignocellulosic biomass poses a major hindrance to enhance biofuel production. Therefore, a pretreatment step is critical to prepare the substrates for the downstream process. Combining pretreatment steps help to lower the severity of the drawbacks of a single pretreatment step. This paper systematically reviews the combined biological and chemical/physicochemical pretreatment based on fiber degradation and sugar yield. An energy-efficient biological pretreatment method combined with a chemical pretreatment that accelerates the pretreatment times has been seen to be efficient for fiber degradation and sugar yields. However, fungal species, culture conditions, biomass type, the severity of chemical pretreatment and the order of sequential pretreatment influences the relative component contents and sugar yield. Even the same biomass from different sources undergoing similar pretreatment conditions could result in a varying amount of digestibility. [ABSTRACT FROM AUTHOR]

• Sodium citrate-ultrasonic pretreatment was applied to enhance bioH 2 yield of sludge. • Pretreatment obviously disrupted the sludge flocs and promoted soluble COD. • Pretreatment improved the H 2 yield by 604.2% and shortened the lag phase. • Energy conversion efficiency increased from 7.4% to 32.8% through pretreatment. • Pretreatment promoted the abundance of H 2 -producing bacteria in the fermenter. Proper pretreatment of waste activated sludge is commonly needed before biohydrogen fermentation due to its complex floc structure. Considering that the outer-layer extracellular polymeric substances (EPS) could restrict the disintegration of inner-layer microbial cells during the pretreatment of sludge, this study firstly applied sodium citrate pretreatment (0.3 g/g-TSS) for removing EPS from sludge flocs, followed by ultrasonic pretreatment (2 W/mL, 15 min), which aimed to enhance the disintegration efficiency. The subsequent hydrogen fermentation performance was tested in batch mode at 37 °C and initial pH 7.0. Results showed that the combined sodium citrate-ultrasonic pretreatment significantly disrupted the sludge floc structure and promoted soluble COD concentration by 157.5 times, which synergistically enhanced the biohydrogen fermentation performance. The maximum hydrogen yield of 38.8 mL/g-VS added was achieved with the combined pretreatment, which was 604.2%, 155.1%, and 92.6% higher compared to the control, individual ultrasonic pretreatment, and individual sodium citrate pretreatment, respectively. Correspondingly, the energy conversion efficiency increased from 7.4% to 32.8% through the combined pretreatment. The combined pretreatment also enhanced the organics utilization, induced a more efficient fermentative pathway, and shortened the hydrogen-generating lag phase. More enrichment of hydrogen-producing bacteria, especially the genera Clostridium sensu stricto and Paraclostridium , was responsible for the synergistic enhancement in hydrogen yield and energy conversion efficiency. The present work puts forward an effective and eco-friendly pretreatment approach for enhancing bioenergy recovery from waste activated sludge. [ABSTRACT FROM AUTHOR]