Plastics recycling: challenges and opportunities

Plastics are inexpensive, lightweight and durable materials, which can readily be moulded into a variety of products that find use in a wide range of applications. As a consequence, the production of plastics has increased markedly over the last 60 years. However, current levels of their usage and disposal generate several environmental problems. Around 4 per cent of world oil and gas production, a non-renewable resource, is used as feedstock for plastics and a further 3–4% is expended to provide energy for their manufacture. A major portion of plastic produced each year is used to make disposable items of packaging or other short-lived products that are discarded within a year of manufacture. These two observations alone indicate that our current use of plastics is not sustainable. In addition, because of the durability of the polymers involved, substantial quantities of discarded end-of-life plastics are accumulating as debris in landfills and in natural habitats worldwide.Recycling is one of the most important actions currently available to reduce these impacts and represents one of the most dynamic areas in the plastics industry today. Recycling provides opportunities to reduce oil usage, carbon dioxide emissions and the quantities of waste requiring disposal. Here, we briefly set recycling into context against other waste-reduction strategies, namely reduction in material use through downgauging or product reuse, the use of alternative biodegradable materials and energy recovery as fuel.While plastics have been recycled since the 1970s, the quantities that are recycled vary geographically, according to plastic type and application. Recycling of packaging materials has seen rapid expansion over the last decades in a number of countries. Advances in technologies and systems for the collection, sorting and reprocessing of recyclable plastics are creating new opportunities for recycling, and with the combined actions of the public, industry and governments it may be possible to divert the majority of plastic waste from landfills to recycling over the next decades.     

Fluidized-bed steam gasification of rice hull

Steam gasification of grain by-products can be a significant biomass conversion technology because of the need to utilize agricultural waste for non-food applications including energy resources. The most obvious beneficiary will be the developing countries whose economies are often tied to agricultural produce and are lacking in conventional fuels. One agricultural by-product that shows promise is the rice hull; it is found in abundance in the rice mills of producer countries and is considered as a waste material. Although gasification of rice hull has been proposed as a potential waste disposal and energy recovery method, little has been done to fully realize this proposition. In the present work, data were obtained for steam gasification of rice hull in a bench-scale fluidized-bed gasifier, a technology which has proven to be feasible for other grain by-products. The produced gas, which is rich in hydrogen, has been found to have a heating value ranging between 12.1 and 11.1 MJ m⁻³ at the respective reactor temperatures of 700 and 800°C; energy recovery varies between 35 and 59%.     

Complex media from processing of agricultural crops for microbial fermentation

This mini-review describes the concept of the green biorefinery and lists a number of suitable agricultural by-products, which can be used for production of bioenergy and/or biochemicals. A process, in which one possible agricultural by-product from the green crop drying industry, brown juice, is converted to a basic, universal fermentation medium by lactic acid fermentation, is outlined. The resulting all-round fermentation medium can be used for the production of many useful fermentation products when added a carbohydrate source, which could possibly be another agricultural by-product. Two examples of such products—polylactic acid and l-lysine—are given. A cost calculation shows that this fermentation medium can be produced at a very low cost ≈1.7 Euro cent/kg, when taking into account that the green crop industry has expenses amounting to 270,000 Euro/year for disposal of the brown juice. A newly built lysine factory in Esbjerg, Denmark, can benefit from this process by buying a low price medium for the fermentation process instead of more expensive traditional fermentation liquids such as corn steep liquor.     

Recovery of organic carbon and phosphorus from wastewater by Fe-enhanced primary sedimentation and sludge fermentation

A new chemically enhanced primary sedimentation (CEPS) and sludge fermentation process are developed for improved nutrient removal, energy saving and resource recovery in municipal wastewater treatment. The FeCl₃-based CEPS with a dosage of 20 mg-Fe/L can remove 75.6% of organic pollutants and 99.3% of PO₄-P on average from wastewater. Under natural fermentation conditions, the CEPS sludge undergoes effective hydrolysis and acidogenesis to produce volatile fatty acids (VFAs) and release phosphate as valuable resources. By using CEPS, around 27% of the organic carbon in wastewater influent can be recovered via sludge fermentation, mainly in the form of VFAs, and about 23% of phosphorus recovered for making vivianite fertilizer. In comparison, both the organic and phosphorus recovery ratios from wastewater are under 10% with conventional primary sedimentation and sludge fermentation. CEPS combined with side-stream sludge fermentation can be readily applied in new treatment plants or in a retrofit of existing treatment systems.     

Effects of by-products of fermentation of banana pseudostem on ethanol separation by pervaporation

In this work, we performed recovery of ethanol from a fermentation broth of banana pseudostem by pervaporation (PV) as a lower-energy-cost alternative to traditional separation processes such as distillation. As real fermentation systems generally contain by-products, it was investigated the effects of different components from the fermentation broth of banana pseudostem on PV performance for ethanol recovery through commercial flat sheet polydimethylsiloxane (PDMS) membrane. The experiments were compared to a binary solution (ethanol/water) to determine differences in the results due to the presence of fermentation by-products. A real fermented broth of banana pseudostem was also used as feed for the PV experiments. Seven by-products from fermented broth were identified: propanol, isobutanol, methanol, isoamyl alcohol, 1-pentanol, acetic acid, and succinic acid. Moreover, the residual sugar content of 3.02 g/L¹ was obtained. The presence of methanol showed the best results for total permeate flux (0.1626 kg·m⁻²·h⁻¹) and ethanol permeate flux (0.0391 kg·m⁻²·h⁻¹) during PV at 25°C and 3 wt% ethanol, also demonstrated by the selectivity and enrichment factor. The lowest total fluxes of permeate were observed in the experiments containing the acids. Better permeance of 0.1171 from 0.0796 kg·m⁻²·h⁻¹ and membrane selectivity of 9.77 from 9.30 were obtained with real fermentation broth than with synthetic solutions, possibly due to the presence of by-products in the multicomponent mixtures, which contributed to ethanol permeation. The results of this work indicate that by-products influence pervaporation of ethanol with hydrophobic flat sheet membrane produced from the fermented broth of banana pseudostem.     

Use of immobilised biocatalysts in the processing of cheese whey

Food processing industry operations need to comply with increasingly more stringent environmental regulations related to the disposal or utilisation of by-products and wastes. These include growing restrictions on land spraying with agro-industrial wastes, and on disposal within landfill operations, and the requirements to produce end products that are stabilised and hygienic. Much of the material generated as wastes by the dairy processing industries contains components that could be utilised as substrates and nutrients in a variety of microbial/enzymatic processes, to give rise to added-value products. A good example of a waste that has received considerable attention as a source of added-value products is cheese whey. The carbohydrate reservoir of lactose (4–5%) in whey and the presence of other essential nutrients make it a good natural medium for the growth of microorganisms and a potential substrate for bioprocessing through microbial fermentation. Immobilised cell and enzyme technology has also been applied to whey bioconversion processes to improve the economics of such processes. This review focuses upon the elaboration of a range of immobilisation techniques that have been applied to produce valuable whey-based products. A comprehensive literature survey is also provided to illustrate numerous immobilisation procedures with particular emphasis upon lactose hydrolysis, and ethanol and lactic acid production using immobilised biocatalysts.     

Production of polyhydroxyalkanoates (PHAs) from waste materials and by-products by submerged and solid-state fermentation

Polyhydroxyalkanoates are biodegradable polymers produced by prokaryotic organisms from renewable resources. The production of PHAs by submerged fermentation processes has been intensively studied over the last 30 years. In recent years, alternative strategies have been proposed, such as the use of solid-state fermentation or the production of PHAs in transgenic plants. This paper gives an overview of submerged and solid-state fermentation processes used to produce PHAs from waste materials and by-products. The use of these low-cost raw materials has the potential to reduce PHA production costs, because the raw material costs contribute a significant part of production costs in traditional PHA production processes.     

Applied in situ product recovery in ABE fermentation

The production of biobutanol is hindered by the product's toxicity to the bacteria, which limits the productivity of the process. In situ product recovery of butanol can improve the productivity by removing the source of inhibition. This paper reviews in situ product recovery techniques applied to the acetone butanol ethanol fermentation in a stirred tank reactor. Methods of in situ recovery include gas stripping, vacuum fermentation, pervaporation, liquid–liquid extraction, perstraction, and adsorption, all of which have been investigated for the acetone, butanol, and ethanol fermentation. All techniques have shown an improvement in substrate utilization, yield, productivity or both. Different fermentation modes favored different techniques. For batch processing gas stripping and pervaporation were most favorable, but in fed‐batch fermentations gas stripping and adsorption were most promising. During continuous processing perstraction appeared to offer the best improvement. The use of hybrid techniques can increase the final product concentration beyond that of single‐stage techniques. Therefore, the selection of an in situ product recovery technique would require comparable information on the energy demand and economics of the process. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:563–579, 2017     

Anaerobic digestion of organic solid poultry slaughterhouse waste--a review

This work reviews the potential of anaerobic digestion for material recovery and energy production from poultry slaughtering by-products and wastes. First, we describe and quantify organic solid by-products and wastes produced in poultry farming and poultry slaughterhouses and discuss their recovery and disposal options. Then we review certain fundamental aspects of anaerobic digestion considered important for the digestion of solid slaughterhouse wastes. Finally, we present an overview of the future potential and current experience of the anaerobic digestion treatment of these materials.     

1,3-丙二醇发酵液后提取技术研究进展

1,3-丙二醇是一种重要的化工原料,以甘油或葡萄糖为原料发酵法制备1,3-丙二醇具有原料可再生、反应条件温和等优点,是近年来国内外的研究热点。由微生物发酵获得的1,3-丙二醇发酵液是含多种强极性的醇及盐类的稀溶液,这使得采用传统的分离方法难以经济、有效地的将1,3-丙二醇从发酵液中纯化出来,后提取过程成为发酵法工业化生产1,3-丙二醇的瓶颈。1,3-丙二醇后提取过程主要包括微生物菌体等高分子物质的去除,盐的去除、回收,有机物的纯化和水的去除。以下对应用于以上分离过程的技术的研究进展进行讨论,提出在该领域应该重视的发展方向。     

Antibacterial metabolites of lactic acid bacteria: their diversity and properties

The review is devoted to literature data on antimicrobial metabolites produced by lactic acid bacteria (LAB), which have long been used for the preparation of cultured dairy products. This paper summarizes data on low-molecular-weight antimicrobial substances, which are primary products or by-products of lactic fermentation. Individual sections are devoted to a variety of antifungal agents and bacteriocins produced by LAB; their potential use as food preservatives has been discussed. The characteristics and classification of bacteriocins are presented in a greater detail; their synthesis and mechanism of action are described using the example of nisin A, which belongs to class I lantibiotics synthesized by the bacterium Lactococcus lactis subsp. lactis. The mechanism of action of class II bacteriocins has been demonstrated with lacticin. Prospective directions for using LAB antimicrobial metabolites in industry and medicine are discussed in the Conclusion.     

Antibacterial metabolites of lactic acid bacteria: Their diversity and properties

The review is devoted to literature data on antimicrobial metabolites produced by lactic acid bacteria (LAB), which have long been used for the preparation of cultured dairy products. This paper summarizes data on low-molecular-weight antimicrobial substances, which are primary products or by-products of lactic fermentation. Individual sections are devoted to a variety of antifungal agents and bacteriocins produced by LAB; their potential use as food preservatives has been discussed. The characteristics and classification of bacteriocins are presented in a greater detail; their synthesis and mechanism of action are described using the example of nisin A, which belongs to class I lantibiotics synthesized by the bacterium Lactococcus lactis subsp. lactis. The mechanism of action of class II bacteriocins has been demonstrated with lacticin. Prospective directions for using LAB antimicrobial metabolites in industry and medicine are discussed in the Conclusion.     

Turning food waste to energy and resources towards a great environmental and economic sustainability: An innovative integrated biological approach

Food waste (FW) management is a global conundrum because of the rapid population growth and growing economic activity. Currently, incineration and landfill are still the main means for FW management, while their environmental sustainability and economic viability have been in question. Recently, the biological processes including anaerobic digestion, aerobic composting, bioethanol fermentation, feed fermentation etc. have attracted increasing interest with the aims for energy and resource recovery from FW. However, these biological approaches have inherent drawbacks, and cannot provide a comprehensive solution for future FW management. Therefore, this review attempts to offer a critical and holistic analysis of current biotechnologies for FW management with the focus on the challenges and solutions forward. The biological approaches towards future FW management should be able to achieve both environmental sustainability and economic viability. In this instance, the concept of zero solid discharge-driven resource recovery has thus been put forward. According to which, several innovative biological processes for FW management are further elucidated with critical analysis on their engineering feasibility and environmental sustainability. It turns out that is an urgent need for turning current single task-orientated bioprocess to an integrated biological process with multiple tasks of concurrent recovery of water, resource and energy together with zero-solid discharge.     

Socio-ecological biotechnology concepts for developing countries

Conclusions The two socio-ecological concepts described will work, of course, also with other microorganisms.Zymomonas mobilis can be replaced by yeast,Rhizopus could be replaced byAspergillus. However, both microorganisms which are presently used can produce by-products that are unsafe for human or animal consumption. It is therefore a microbiological challenge to find further microorganisms to expand the product formation.It should also be realized that the largest renewable resource, cellulose, has not been mentioned in the context of either concept. It is well known that cellulose must eventually be included if research and development can find ways and means to separate lignin from cellulose and convert cellulose to glucose in a similar and as easy a manner as starch (Doelle 1984).In order to be successful, fermentation processes have to be fast and efficient with a low energy input (Doelle 1986a, b; Doelle & Jones 1986). This excludes the traditional microbiological sterilization of substrates, excessive substrate or product inhibitions in any of these processes.A further omission of socio-ecological concepts lies in the fermented food production. It is encouraging to see the realization that fermented foods are mixedculture processes and that it is time to start detailed and extensive investigations into the functioning of such cultures (Doelle 1985; Steinkraus 1987; Okagbu 1988; Odunfa 1988). It is the suggestion of the author to encourage a review on mixed culture with particular emphasis on fermented food production and its waste disposal.     

Prospective and development of butanol as an advanced biofuel

Butanol has been acknowledged as an advanced biofuel, but its production through acetone–butanol–ethanol (ABE) fermentation by clostridia is still not economically competitive, due to low butanol yield and titer. In this article, update progress in butanol production is reviewed. Low price and sustainable feedstocks such as lignocellulosic residues and dedicated energy crops are needed for butanol production at large scale to save feedstock cost, but processes are more complicated, compared to those established for ABE fermentation from sugar- and starch-based feedstocks. While rational designs targeting individual genes, enzymes or pathways are effective for improving butanol yield, global and systems strategies are more reasonable for engineering strains with stress tolerance controlled by multigenes. Compared to solvent-producing clostridia, engineering heterologous species such as Escherichia coli and Saccharomyces cerevisiae with butanol pathway might be a solution for eliminating the formation of major byproducts acetone and ethanol so that butanol yield can be improved significantly. Although batch fermentation has been practiced for butanol production in industry, continuous operation is more productive for large scale production of butanol as a biofuel, but a single chemostat bioreactor cannot achieve this goal for the biphasic ABE fermentation, and tanks-in-series systems should be optimized for alternative feedstocks and new strains. Moreover, energy saving is limited for the distillation system, even total solvents in the fermentation broth are increased significantly, since solvents are distilled to ~ 40% by the beer stripper, and more than 95% water is removed with the stillage without phase change, even with conventional distillation systems, needless to say that advanced chemical engineering technologies can distil solvents up to ~ 90% with the beer stripper, and the multistage pressure columns can well balance energy consumption for solvent fraction. Indeed, an increase in butanol titer with ABE fermentation can significantly save energy consumption for medium sterilization and stillage treatment, since concentrated medium can be used, and consequently total mass flow with production systems can be reduced. As for various in situ butanol removal technologies, their energy efficiency, capital investment and contamination risk to the fermentation process need to be evaluated carefully.     

Control/promotion of the refuse methanogenic fermentation

Although practiced for more than 7 millennia, the landfill disposal of refuse has, as yet, with few exceptions, been merely regarded as a low-cost disposal option and its exploitation potential has been largely ignored. Today, however, a number of possibilities are under consideration including the production of energy, chemical feedstock, value-added chemicals, carbon dioxide and protein; the use of refuse as an anaerobic filter for the co-disposal of industrial wastewater and sludge; and the restoration of impoverished soils by fresh or composted refuse addition. Development of these technologies, however, necessitates a comprehensive understanding of the fundamental microbiology and biochemistry of refuse catabolism. Existing fundamental knowledge underpinning these technologies will be considered in a series of review articles. In the first, control/exploitation of the solid-state refuse methanogenic fermentation is examined with specific reference to the effects of first-tier variable manipulations.     

Strategy for selection of methods for separation of bioparticles from particle mixtures

The desired product of bioprocesses is often produced in particulate form, either as an inclusion body (IB) or as a crystal. Particle harvesting is then a crucial and attractive form of product recovery. Because the liquid phase often contains other bioparticles, such as cell debris, whole cells, particulate biocatalysts or particulate by-products, the recovery of product particles is a complex process. In most cases, the particulate product is purified using selective solubilization or extraction. However, if selective particle recovery is possible, the already high purity of the particles makes this downstream process more favorable. This work gives an overview of typical bioparticle mixtures that are encountered in industrial biotechnology and the various driving forces that may be used for particle-particle separation, such as the centrifugal force, the magnetic force, the electric force, and forces related to interfaces. By coupling these driving forces to the resisting forces, the limitations of using these driving forces with respect to particle size are calculated. It shows that centrifugation is not a general solution for particle-particle separation in biotechnology because the particle sizes of product and contaminating particles are often very small, thus, causing their settling velocities to be too low for efficient separation by centrifugation. Examples of such separation problems are the recovery of IBs or virus-like particles (VLPs) from (microbial) cell debris. In these cases, separation processes that use electrical forces or fluid-fluid interfaces show to have a large potential for particle-particle separation. These methods are not yet commonly applied for large-scale particle-particle separation in biotechnology and more research is required on the separation techniques and on particle characterization to facilitate successful application of these methods in industry.     

Hyaluronic acid production by <Emphasis Type="Italic">Streptococcus zooepidemicus</Emphasis> in marine by-products media from mussel processing wastewaters and tuna peptone viscera

Background  

Hyaluronic acid is one of the biopolymers most commonly used by the pharmaceutical industry. Thus, there is an increasing number of recent works that deal with the production of microbial hyaluronic acid. Different properties and characteristics of the fermentation process have been extensively optimised; however, new carbon and protein sources obtained from by-products or cheap substrates have not yet been studied.     

Problems in seawater industrial desalination processes and potential sustainable solutions: a review

Seawater desalination has significantly developed towards membrane technology than phase change process during last decade. Seawater reverse osmosis (SWRO) in general is the most familiar process due to higher water recovery and lower energy consumption compared to other available desalination processes. Despite major advancements in SWRO technology, desalination industry is still facing significant amount of practical issues. Therefore, the potentials and problems faced by current SWRO industries and essential study areas are discussed in this review for the benefit of desalination industry. It is important to consider all the following five components in SWRO process i.e. (1) intake (2) pre-treatment (3) high pressure pumping (4) membrane separation (performance of membranes and brine disposal) and (5) product quality. Development of higher corrosion resistant piping materials or coating materials, valves, and pumps is believed to be in higher research demand. Furthermore, brine management, that includes brine disposal and resource recovery need further attention. Pre-treatment sludge management and reduced cleaning in place flush volume will reduce the capital costs associated with evaporation ponds and the maintenance costs associated with disposal and transportation reducing the unit cost of water.     

Life cycle assessment of energy self-sufficiency systems based on agricultural residues for organic arable farms

The agricultural industry today consumes large amounts of fossil fuels. This study used consequential life cycle assessment (LCA) to analyse two potential energy self-sufficient systems for organic arable farms, based on agricultural residues. The analysis focused on energy balance, resource use and greenhouse gas (GHG) emissions. A scenario based on straw was found to require straw harvest from 25% of the farm area; 45% of the total energy produced from the straw was required for energy carrier production and GHG emissions were reduced by 9% compared with a fossil fuel-based reference scenario. In a scenario based on anaerobic digestion of ley, the corresponding figures were 13%, 24% and 35%. The final result was sensitive to assumptions regarding, e.g., soil carbon content and handling of by-products.