Pollutant removal-oriented yeast biomass production from high-organic-strength industrial wastewater: A review

Microbial single-cell-protein (SCP) production from high-organic-strength industrial wastewaters is considered an attractive method for both wastewater purification and resource utilization. In the last two decades, pollutant removal-oriented yeast SCP production processes, i.e., yeast treatment processes, have attracted a great deal of attention from a variety of research groups worldwide. Different from conventional SCP production processes, yeast treatment processes are characterized by higher pollutant removal rates, lower production costs, highly adaptive yeast isolates from nature, no excess nutrient supplements, and are performed under non-sterile conditions. Furthermore, yeast treatment processes are similar to bacteria-dominated conventional activated sludge processes, which offer more choices for yeast SCP production and industrial wastewater treatment. This review discusses why highly adaptive yeast species isolated from nature are used in the yeast treatment process rather than commercial SCP producers. It also describes the application of yeast treatment processes for treating high-carboxyhydrate, oil-rich and high-salinity industrial wastewater, focusing primarily on high-strength biodegradable organic substances, which usually account for the major fraction of biochemical oxygen demand. Also discussed is the biodegradation of xenobiotics, such as color (including dye and pigment) and toxic substances (including phenols, chlorophenols, polycyclic aromatic hydrocarbons, etc.), present in industrial wastewater. Based on molecular information of yeast community structures and their regulation in yeast treatment systems, we also discuss how to maintain efficient yeast species in yeast biomass and how to control bacterial and mold proliferation in yeast treatment systems.     

生物质水热技术研究现状及发展

生物质水热转化技术作为一种新的生物质利用技术,在亚临界或超临界水下,将生物质直接转化为高品位气态、液态和固态产物。该技术具有原料适应性广、低成本和高转化率等特点,具有很好的应用前景。文章综述了近年来生物质水热技术研究的最新进展,分别对水热液化、水热气化和水热碳化3方面内容进行分析,对目前存在的问题提出了建设性的意见。     

Hydrothermal pretreatment of fresh forest residues: Effects of feedstock pre-drying

Hydrothermal pretreatment has become an attractive method for upgrading biomass fuel because of its capacity to work effectively with various types of low cost wet feedstock. However, most of the past studies in the field dried the feedstock prior to the pretreatment without being aware of the effect of high temperature drying. In this study, fresh forest residues (Norway spruce and birch branches) were used as feedstocks to utilize the advantage of the hydrothermal pretreatment method. More importantly, the present work aims at investigating the effects of the pre-drying process on the solid product via a direct comparison on the fuel and physicochemical properties of hydrochars produced from fresh and dried forest residues. This assessment helps to identify differences when fresh and dried feedstocks are used for hydrothermal pretreatment study. The results showed that these differences were considerable with respect to solid and energy yields; and the use of dried feedstocks will be less representative for a commercially feasible hydrothermal process, using wet feedstock directly.     

Methane production from lignocellulosic agricultural crop wastes: A review in context to second generation of biofuel production

The aim of this paper is to present a comprehensive review on renewable methane fuel production through the biological route of biomethanation process from major lignocellulosic agricultural crop waste biomass (maize, wheat, rice and sugarcane). Global annual approximate production of major agriculture based lignocellulosic biomass has been explored. Fundamental requirements of biomethanation process have been discussed in details for optimum production of methane. The essential properties of biomass (proximate, ultimate and compositional) conscientious for quality of derived fuel have also been presented along with the pretreatment requirements for lignocellulosic biomass. Methane generation potential of the major lignocellulosic agricultural crop biomass has been explored and presented. Furthermore, the methane production potential and its energetic analysis have also been compared with the bio-ethanol productions. The overall parametric analysis involved in anaerobic digestion and alcoholic fermentation explore that methane generation from lignocellulosic agricultural crop waste biomass is more economical and environmentally beneficial way of biomass utilization in a sustainable way of energy production.     

水热处理对生物质成型炭理化性质的影响

棉秆(CS)及木屑(WS)经高压反应釜水热预处理后压制成型,并于固定床热解炉内进行炭化实验,利用电子万能材料试验机、热重分析仪等分析手段分析水热预处理对生物质成型炭的产率、物理性能(机械强度和表观密度)、热值及燃烧性能的影响。研究表明:随着水热温度的升高,生物质成型炭的产率增加且热值稳定,但燃烧性能变差;经水热预处理制得的生物质成型炭灰分产率均小于18%,固定碳产率均大于60%,满足欧标要求;随着水热温度的升高,生物质成型炭的表观密度及抗压强度均先增加后减小;对比所有实验样品,经230℃水热预处理制得的生物质成型炭(CS/WS-HT230-CB)物理性能及燃烧性能最佳,且均优于商用烧烤炭性能。     

Supercritical water gasification of wastewater sludge for hydrogen production

The use of hydrogen as clean fuel gas in the power generation sector becomes essential to reduce the environmental issues related to conventional fuel usage. By avoiding biomass drying process, supercritical water gasification is considered the most efficient technology in hydrogen production from wastewater sludge. Wastewater sludge is difficult to disposal in its received form since it is often produced with high moisture content, contribute to numerous environmental issues and direct contact with this waste can result in health concerns. The assessment of the treatment and conversion of this material into fuel gas at condition beyond supercritical state (374°C and 22.1 MPa) is required. This paper is discussed the degradation routes of wastewater sludge in supercritical water. Furthermore, it is reviewed the influence of the main operation parameters role in the hydrogen production, which includes reaction temperature, pressure, residence time, feed concentration and catalysts. The development in reactor design and setup for maximum hydrogen production is highlighted. The technical challenges encountered during the conversion process and its solutions are also discussed. In addition, future prospective to optimal and standardization of the supercritical water gasification process is reviewed.     

High-solid dark fermentation of cassava pulp and cassava processing wastewater for hydrogen production

Dark fermentation (DF) is a promising biological process for hydrogen production from biomass. However, low hydrogen yield (HY) is a major hurdle impeding its use at large-scale operation. A potential way to mitigate this problem is to increase the concentration of substrate in the process to increase hydrogen production. The present study investigated the possibility of using high-solid DF to produce hydrogen from cassava processing wastes, i.e., cassava pulp (CP) and cassava processing wastewater (CPW). CP was suspended in CPW and hydrolyzed enzymatically under optimum conditions of 150 g-CP/L, 29 U/g of α-amylase, 47 U/g of glucoamylase, and 60 FPU/g of cellulase. The hydrolysis performed at 50 °C for 24 h yielded a reducing sugar concentration of 117.7 ± 1.8 g/L, equivalent to 0.78 g-reducing-sugar/g-CP. Subsequent DF of CP-CPW enzymatic slurry, which contained 12.1% water insoluble solids, resulted in a cumulative production of 13.72 ± 0.22 L-H₂, equivalent to 225.2 ± 3.7 mL-H₂/g-VS. This was 83.1% of a maximum stoichiometric HY, based on carbohydrate content of CP and soluble metabolites production. The present study shows clearly the applicability of high-solid DF in the production of hydrogen from cassava processing wastes.     

Harnessing of biohydrogen from wastewater treatment using mixed fermentative consortia: Process evaluation towards optimization

Utilizing wastewater as a potential source for renewable energy generation through biological routes has instigated considerable interest recently due to its sustainable nature. An attempt was made in this communication to review and summarize the work carried out in our laboratory on dark fermentation process of biohydrogen (H₂) production utilizing wastewater as primary substrate under acidogenic mixed microenvironment towards optimization of dynamic process. Process was evaluated based on the nature and composition of wastewater, substrate loading rates, reactor configuration, operation mode, pH microenvironment and pretreatment procedures adopted for mixed anaerobic culture to selectively enrich acidogenic H₂ producing consortia. The fermentative conversion of the substrate to H₂ is possible by a series of complex biochemical reactions manifested by selective bacterial groups. In spite of striking advantages, the main challenge of fermentative H₂ production is that, relatively low energy from the organic source was obtained in the form of H₂. Further utilization of unutilized carbon sources present in wastewater for additional H₂ production will sustain the practical applicability of the process. In this direction, enhancing H₂ production by adapting various strategies, viz., self-immobilization of mixed consortia (onto mesoporous material and activated carbon), integration with terminal methanogenic and photo-biological processes and bioaugmentation with selectively enriched acidogenic consortia were discussed. Application of acidogenic microenvironment for in situ production of bioelectricity through wastewater treatment employing microbial fuel cell (MFC) was also presented.     

Utilization of lignin: A sustainable and eco-friendly approach

The use of renewable carbon sources as a substitute for fossil resources is an extensively essential and fascinating research area for addressing the current issues related to climate and future fuel requirements. The utilization of lignocellulosic biomasses as a source for renewable fuel/chemicals/mesoporous biochar derivative is gaining considerable attention due to the neutral carbon cycle. The cellulose and hemicellulose are highly utilized components of biomass, and on the other hand, lignin is a plentiful, under-utilized component of the lignocellulosic biomass in 2G ethanol and paper industry. Significant researchers have contributed towards lignin valorization, with a central goal of the production and upgradation of phenolic, unstable, acidic and oxygen-containing bio-oil to valuable chemicals or fuel grade hydrocarbons. This review is aimed to present the lignin valorization potential from pretreatment of biomass as an initial step to the final process, i.e., lignin bio-oil upgradation with mechanistic pathways. The review offers the source, structure, composition of various lignocellulosic biomasses, followed by a discussion of various pre-treatment techniques for biomass depolymerization. Different thermochemical approaches for bio-oil production from dry and wet biomasses are highlighted with emphasis on pyrolysis and liquefaction. The physical, chemical properties of lignin bio-oil and different upgradation methods for bio-oil as well as its model compounds are thoroughly discussed. It also addresses the related activity, selectivity, stability of numerous catalysts with reaction pathways and kinetics in a broad manner. The challenges and future research opportunities of lignin valorization are discussed in an attempt to place lignin as a feedstock for the generation of valuable chemical and fuel grade hydrocarbons.     

Dual role of microalgae: Phycoremediation of domestic wastewater and biomass production for sustainable biofuels production

Global threats of fuel shortages in the near future and climate change due to green-house gas emissions are posing serious challenges and hence and it is imperative to explore means for sustainable ways of averting the consequences. The dual application of microalgae for phycoremediation and biomass production for sustainable biofuels production is a feasible option. The use of high rate algal ponds (HRAPs) for nutrient removal has been in existence for some decades though the technology has not been fully harnessed for wastewater treatment. Therefore this paper discusses current knowledge regarding wastewater treatment using HRAPs and microalgal biomass production techniques using wastewater streams. The biomass harvesting methods and lipid extraction protocols are discussed in detail. Finally the paper discusses biodiesel production via transesterification of the lipids and other biofuels such as biomethane and bioethanol which are described using the biorefinery approach.     

An energy evaluation of coupling nutrient removal from wastewater with algal biomass production

Recently, several life cycle analyses of algal biodiesel from virtual production facilities have outlined the potential environmental benefits and energetic balance of the process. There are a wide range of assumptions that have been utilized for these calculations, including the addition of fertilizers and carbon dioxide to achieve high algal yields in open ponds. This paper presents an energy balance of microalgal production in open ponds coupled with nutrient removal from wastewater. Actual microalgal yields and nutrient removal rates were obtained from four pilot-scale reactors (2500 gallons each) fed with wastewater effluent from a conventional activated sludge process for 6 months, and the data was used to estimate an energy balance for treating the total average 12 million gallons per day processed by the wastewater treatment plant. Since one of the most energy-intensive steps is the dewatering of algal cultures, several thickening and dewatering processes were compared. This analysis also includes the energy offset from removing nutrients with algal reactors rather than the biological nutrient removal processes typically utilized in municipal wastewater treatment. The results show that biofuel production is energetically favorable for open pond reactors utilizing wastewater as a nutrient source, even without an energy credit for nutrient removal. The energy content of algal biomass was also considered as an alternate to lipid extraction and biodiesel production. Direct combustion of algal biomass may be a more viable energy source than biofuel production, especially when the lipid content of dry biomass (10% in this field experiment) is lower than the high values reported in lab-scale reactors (50–60%).     

Recent progress in thermochemical techniques to produce hydrogen gas from biomass: A state of the art review

The present work comprehensively covers the literature that describes the thermochemical techniques of hydrogen production from biomass. This survey highlights the current approaches, relevant methods, technologies and resources adopted for high yield hydrogen production. Prominent thermochemical methods i.e. pyrolysis, gasification, supercritical water gasification, hydrothermal upgrading followed by steam gasification, bio-oil reforming, and pyrolysis inline reforming have been discussed thoroughly in view of the current research trend and latest emerging technologies. Influences of important factors and parameters on hydrogen yield, such as biomass type, temperature, steam to biomass ratio, retention time, biomass particle size, heating rate, etc. have also been extensively studied. Catalyst is a vital integrant that has received enough attention due to its encouraging influence on hydrogen production. Literature confirms that hydrogen obtained from biomass has high-energy efficiency and potential to reduce greenhouse gases hence, it deserves versatile applications in the coming future. The study also reveals that hydrogen production through steam reforming, pyrolysis, and in-line reforming deliver a considerable amount of hydrogen from biomass with higher process efficiency. It has been identified that higher temperature, suitable steam to biomass ratio and catalyst type favor useful hydrogen yield. Nevertheless, hydrogen is not readily available in the sufficient amount and production cost is still high. Tar generation during thermochemical processing of biomass is also a concern and requires consistent efforts to minimize it.     

Hydrogen production as a novel process of wastewater treatment—studies on tofu wastewater with entrapped R. sphaeroides and mutagenesis

Attention is focusing on hydrogen production from wastewater, not only because hydrogen is a clean energy but also because it can be a process for wastewater treatment. In this paper, the characteristics of biological hydrogen production as a process of wastewater treatment is discussed by a comparison with methane production. The hydrogen production from tofu wastewater by anoxygenic phototrophic bacteria and its potential for wastewater treatment are reported. The possibility of co-cultivation with heterotrophic anaerobic bacteria was also investigated. As a solution to overcome the repressive effect of NH₄⁺ on hydrogen production by anoxygenic phototrophic bacteria, a study was done using glutamine auxotroph which was obtained by chemical mutagenesis. To confirm that the mutation had occurred in DNA molecular level, the glutamine synthetase gene was cloned and sequenced.     

微藻生物膜去污技术应用研究进展

文章综述了微藻生物膜净化污水和生产生物燃料等方面的国内外最新成果,阐述了典型微藻去污生物膜系统的运行情况、综合效益、优缺点和推广价值,并对微藻生物膜去污技术存在的问题及关键技术进展及发展趋势进行了分析,就微藻生物膜去污技术的规模化及产业化应用提出了建议,以期为微藻生物膜去污技术的成熟和规模应用提供理论和实践支撑。     

Integration of reactive extraction with supercritical fluids for process intensification of biodiesel production: Prospects and recent advances

Current world energy usage is trying to gradually shift away from fossil fuels due to the concerns for the climate change and environmental pollutions. Liquid energy from renewable biomass is widely regarded as one of the greener alternatives to partially fulfil the ever-growing energy demand. Contemporary research and technology has been focussing on transforming these bio-resources into efficient liquid and gaseous fuels which are compatible with existing petrochemical energy infrastructure. Due to the wide range of properties and compositions from different types of biomass, there are ample of processing routes available to cater for different demands and requirements. In addition, they can produce multi-component products which can be further upgraded into higher value products. This conceives the idea of bio-refinery where different biomass conversion processes are incorporated and proceed simultaneously at one location. However, the underlying complexity in integrating different processes with varying process conditions will undoubtly incurs prohibitive cost. Consequently, process intensification plays an important role in minimizing both the capital and operating costs associated with process integration in bio-refineries. Recently, process intensification for biodiesel production has been developing rigorously due to increasing demand for cost-cutting measures. Supercritical fluid process allows biodiesel production to be performed without any addition of catalyst. Meanwhile, catalytic in situ or reactive extraction process for biodiesel production successfully combines the extraction and reaction phase together in a single processing unit. In this review, the important characteristics and recent progress on both of the intensification processes for biodiesel production will be critically analyzed. The prospects and recent advances of supercritical reactive extraction (SRE) process which integrates both of the processes will also be discussed. This review will also scrutinize on the methods for these processes to compliment future bio-refinery setup and more efficient utilizing of all of the products generated.     

Critical assessment of anaerobic processes for continuous biohydrogen production from organic wastewater

Production of biohydrogen using dark fermentation has received much attention owing to the fact that hydrogen can be generated from renewable organics including waste materials. The key to successful application of anaerobic fermentation is to uncouple the liquid retention time and the biomass retention time in the reactor system. Various reactor designs based on biomass retention within the reactor system have been developed. This paper presents our research work on bioreactor designs and operation for biohydrogen production. Comparisons between immobilized-cell systems and suspended-cell systems based on biomass growth in the forms of granule, biofilm and flocs were made. Reactor configurations including column- and tank-based reactors were also assessed. Experimental results indicated that formation of granules or biofilms substantially enhanced biomass retention which was found to be proportional to the hydrogen production rate. Rapid hydrogen-producing culture growth and high organic loading rate might limit the application of biofilm biohydrogen production, since excessive growth of fermentative biomass would result in washout of support carrier. It follows that column-based granular sludge process is a preferred choice of process for continuous biohydrogen production from organic wastewater, indicating maximum hydrogen yield of 1.7 mol-H₂/mol-glucose and hydrogen production rate of 6.8 L-H₂/L-reactor h.     

Integration of algae-based biofuel production with an oil refinery: Energy and carbon footprint assessment

Biofuel production from algae feedstock has become a topic of interest in the recent decades since algae biomass cultivation is feasible in aquaculture and does therefore not compete with use of arable land. In the present work, hydrothermal liquefaction of both microalgae and macroalgae is evaluated for biofuel production and compared with transesterifying lipids extracted from microalgae as a benchmark process. The focus of the evaluation is on both the energy and carbon footprint performance of the processes. In addition, integration of the processes with an oil refinery has been assessed with regard to heat and material integration. It is shown that there are several potential benefits of co-locating an algae-based biorefinery at an oil refinery site and that the use of macroalgae as feedstock is more beneficial than the use of microalgae from a system energy performance perspective. Macroalgae-based hydrothermal liquefaction achieves the highest system energy efficiency of 38.6%, but has the lowest yield of liquid fuel (22.5 MJ per 100 MJ_algae) with a substantial amount of solid biochar produced (28.0 MJ per 100 MJ_algae). Microalgae-based hydrothermal liquefaction achieves the highest liquid biofuel yield (54.1 MJ per 100 MJ_algae), achieving a system efficiency of 30.6%. Macro-algae-based hydrothermal liquefaction achieves the highest CO₂ reduction potential, leading to savings of 24.5 resp 92 kt CO_2eq/year for the two future energy market scenarios considered, assuming a constant feedstock supply rate of 100 MW algae, generating 184.5, 177.1 and 229.6 GWh_biochar/year, respectively. Heat integration with the oil refinery is only possible to a limited extent for the hydrothermal liquefaction process routes, whereas the lipid extraction process can benefit to a larger extent from heat integration due to the lower temperature level of the process heat demand.     

Capturing and using CO2 as feedstock with chemical looping and hydrothermal technologies

Chemical looping technology for capturing and hydrothermal processes for conversion of carbon are discussed with focused and critical assessments. The fluidized and stationary reactor systems using solid, including biomass, and gaseous fuels are considered in chemical looping combustion, gasification, and reforming processes. Sustainability is emphasized generally in energy technology and in two chemical looping simulation case studies using coal and natural gas. Conversion of captured carbon to formic acid, methanol, and other chemicals is also discussed in circulating and stationary reactors in hydrothermal processes. This review provides analyses of the major chemical looping technologies for CO₂ capture and hydrothermal processes for carbon conversion so that the appropriate clean energy technology can be selected for a particular process. Combined chemical looping and hydrothermal processes may be feasible and sustainable in carbon capture and conversion and may lead to clean energy technologies using coal, natural gas, and biomass. Copyright © 2014 John Wiley & Sons, Ltd.     

Comparison of dairy wastewater and synthetic medium for biofuels production by microalgae cultivation

This study is concerned with comparing raw dairy wastewater (DWW) with blue-green medium (BG11 medium) for biofuel production. Three microalgae strains (Chlorella sp., Scenedesmus sp., and Chlorella zofingiensis) were cultured in tubular bubble column photobioreactors with two media separately. After 8 days of cultivation, DWW was demonstrated to be more suitable medium for microalgae biomass and lipid production than BG11 medium. The biomass and lipid produced within wastewater provided suitable feedstocks for anaerobic digestion and biodiesel conversion. Nutrients in wastewater were efficiently removed (>90% total nitrogen removal, approximately 100% ammonia removal, and >85% total phosphorus removal) during this process.     

Dark fermentative biohydrogen production from confectionery wastewater in continuous-flow reactors

The production of biohydrogen from industrial wastewater through the dark fermentation (DF) process has attracted increased interest in recent years. To implement a DF process on a large scale, a thorough knowledge of laboratory scale process control is required. The operating parameters and design features of the reactors have a great influence on the efficiency of the process. In this work, the possibility of continuous production of biohydrogen from confectionery wastewater was evaluated. The DF process was carried out at 37 ± 1 °C in two different reactors: an upflow anaerobic filter (AF) and a fluidized bed reactor (AFB). Polyurethane foam (PU) was used to immobilize the biomass. The DF process was studied at four hydraulic retention times (HRT) (1.5, 2.5, 7.5 and 15 days) and the corresponding organic loading rates (OLR) (9.21, 6.12, 2.04 and 1.02 g COD_init/(L day)). The highest hydrogen yield (HY) (44.73 ml/g COD_init) and hydrogen production rate (HPR) (92.5 ml/(L day)) was observed in AFB at HRT of 7.5 days and 2.5 days, respectively. The highest concentration of hydrogen in biogas was 34% in AF and 36% in AFB at HRT of 7.5 days. In contrast to AF, the COD removal efficiency in AFB increased with increasing HRT. The pH of the effluent was low (3.95–4.38). However, due to the use of PU for biomass immobilization, it is possible that there were local zones in the reactor that were optimal for the functioning of not only acidogens, but also methanogens. This was evidenced by a rather high content of methane in biogas (2.5% in AF and 9.6% in AFB at HRT of 15 days). These results provide valuable data for optimizing the continuous DF of wastewater from confectionery and other food industries to produce biohydrogen or biohythane.