Combination of decentralized waste drying and SSF techniques for household biowaste minimization and ethanol production

Bioengineering of biowaste to recover bioproducts and bioenergy: A circular economy approach towards sustainable zero-waste environment

The inevitable need for waste valorisation and management has revolutionized the way in which the waste is visualised as a potential biorefinery for various product development rather than offensive trash. Biowaste has emerged as a potential feedstock to produce several value-added products. Bioenergy generation is one of the potential applications originating from the valorisation of biowaste. Bioenergy production requires analysis and optimization of various parameters such as biowaste composition and conversion potential to develop innovative and sustainable technologies for most effective utilization of biowaste with enhanced bioenergy production. In this context, feedstocks, such as food, agriculture, beverage, and municipal solid waste act as promising resources to produce renewable energy. Similarly, the concept of microbial fuel cells employing biowaste has clearly gained research focus in the past few decades. Despite of these potential benefits, the area of bioenergy generation still is in infancy and requires more interdisciplinary research to be sustainable alternatives. This review is aimed at analysing the bioconversion potential of biowaste to renewable energy. The possibility of valorising underutilized biowaste substrates is elaborately presented. In addition, the application and efficiency of microbial fuel cells in utilizing biowaste are described in detail taking into consideration of its great scope. Furthermore, the review addresses the significance bioreactor development for energy production along with major challenges and future prospects in bioenergy production. Based on this review it can be concluded that bioenergy production utilizing biowaste can clearly open new avenues in the field of waste valorisation and energy research. Systematic and strategic developments considering the techno economic feasibilities of this excellent energy generation process will make them a true sustainable alternative for conventional energy sources.

Nanomaterial conjugated lignocellulosic waste: cost-effective production of sustainable bioenergy using enzymes

The demand for novel and renewable sources of energy has increased as a result of rapid population growth, limited sources of bioenergy, and environmental pollution, caused by excessive use of fossil fuels. The need to meet future energy demands have motivated researchers to search for alternative and sustainable sources of energy. The bioconversion of lignocellulosic waste (agricultural and food waste) into biofuels shows competitive promises. Lignocellulosic waste is easily accessible and has a large enzyme system that can be immobilised onto nano-matrices. Consequently, resulting in higher biofuel production and process efficiency. However, the excessive production cost of the current procedures, which involve physical, chemical, and enzymatic reactions, is limited. The use of nanomaterials has recently been shown to concentrate lignocellulosic waste, therefore, reviewing the quest for efficient production of sustainable and cost-effective development of bioenergy from lignocellulosic wastes. This review paper explores the advanced strategies of using nanobiotechnology to combine enzyme-conjugated nanosystems for the cost-effective production of sustainable bioenergy solutions. This research will help to develop an inexpensive, eco-friendly technology for biofuels production and also help overcome the environmental burden of lignocellulosic waste worldwide.

Characterization of the separately collected organic fraction of municipal solid waste (OFMSW) from rural and urban districts for a one-year period in Germany

Knowledge on material properties is beneficial to fully exploit inherent utilization potentials of the organic fraction of municipal solid waste (OFMSW). The objective of this study was to analyze and compare the physico-chemical characteristics of separately collected OFMSW (biowaste bin) originating in southwestern Germany. Therefore, 22 rural and 20 urban OFMSW samples, each from the same location were analyzed in the course of one year. Next to the basic characteristics such as the impurity, dry matter (DM) and organic dry matter (oDM) contents, this study focused on the analysis of 37 major, minor and trace elements. In addition, stoichiometric CH₄ potentials for the anaerobic digestion were calculated. The fresh mass (FM) based DM contents were significantly (p = 0.001) higher in rural OFMSW (32.86 ± 2.35% vs. 30.50 ± 1.75%) while the DM based oDM content was higher (p = 0.07) in urban OFMSW (84.59 ± 3.90% vs. 82.22 ± 4.16%). The impurities in rural OFMSW were significantly lower (2.83 ± 1.67% DM vs. 5.07 ± 2.71% DM with p = 0.004) while oDM based CH₄ potentials were higher for urban OFMSW (533 ± 22 L/kg vs. 519 ± 26L/kg). For both OFMSW types, contents >1000 mg/kgDM were detected for Ca, K, Si, Na, Al, Fe, Mg, P and S while Ti, Mn, Ba, Zn, Sr, Cr, Cu, V, Ni, Li, Pb and B were measured between 1 and 1000 mg/kgDM. The determined element concentrations are useful for an improved classification of OFMSW as a biorefinery resource.

Assessment of Dehydration as a Commercial-Scale Food Waste Valorization Strategy

Using a commercially available dehydration unit, this study aimed to valorize various food waste streams from different sources in the Rochester, New York area. Dehydration of the food waste collected for the study helped reduce the weight of the feedstock by 70–90%, as the incoming waste streams were relatively wet. The output was materially characterized against end uses such as cattle feed, fish feed, and compost. The results demonstrated that, other than fertilizer, the remaining five end uses (compost, fish feed, cattle feed, pyrolysis, and pelletized fuel) were potentially compatible with varying waste feedstocks based on the parameters analyzed. Fish feed in particular was found to be the most compatible end use, as a number of attributes, including protein, fell within the optimal range of values. Pelletized fuel was also determined to be a viable application, as six out of eight sources of dehydrated food waste had higher heating values above the minimum U.S. standard level of 18.61 MJ/kg. Ultimately, this analysis showed that the composition of the food waste needs to be matched to an end-use application and sale of the product for dehydration to be a worthwhile valorization strategy.

Valorization of two agroindustrial wastes to produce alpha-amylase enzyme from Aspergillus oryzae by solid-state fermentation

The global amount of soybean and wheat produced is about 350 and 750 million metric tons every year, respectively. In consequence, huge amounts of waste are produced from them. The aim of this work was to employ two wastes -soybean husk and flour mill waste- to produce high quantities of alpha-amylase enzyme. The substrate composition and the culture conditions were assayed to improve alpha-amylase production by solid-state fermentation employing the fungus Aspergillus oryzae. The maximum productivity of the enzyme was achieved using a culture substrate composed of the two wastes, at 45% soybean husk and 55% flour mill by-product, without pre-treatment, at an incubation temperature of 30 °C. The optimal incubation time (6 days), yielded a very high alpha-amylase activity (47,000 U/g dry substrate) at low-cost. The enzymatic extract obtained was characterized by LC-MS, providing a complete profile of the proteins produced during the solid-state fermentation on these two wastes. Then, the extract was purified in a single-step by size-exclusion chromatography and the recovery and the purification factor of alpha-amylase enzyme were about 83% and 6, respectively. The system was scaled up 50 times and yielded a similar enzymatic activity (45,900 U/g of dry substrate).

The "COFFEE BIN" concept: centralized collection and torrefaction of spent coffee grounds

Spent coffee grounds are the moist solid residues of coffee brewing and in most cases, the disposal is done without any intermediate valorization actions for materials and energy recovery. State-of-the-art applications include extraction of the liquids and application of high-temperature pyrolysis. Both strategies have significant potential but have also some disadvantages (extensive pre-treatment, high costs) when applied on a large scale. This study highlights the lack of mild pyrolysis valorization strategies and presents the idea of the "COFFEE BIN." Separated spent coffee grounds are collected, dried, and thermally treated. The optimal pyrolysis conditions were identified and product characteristics and the mass balances were assessed. Elemental analysis, thermogravimetric analysis, physisorption analysis and higher heating value (HHV) determination was performed for the characterization of the carbonaceous products. The torrefied coffee grounds returned solid yields from 78 to 83%, which are significantly higher than in other cases of conventional biomass and heating values of 24-25 MJ/kg. Higher temperature pyrolysis did not sustain the advantage of increased returned mass yields and the adsorbance potential of all the carbonaceous products was lower than 25 cm³/g. The study highlighted that spent coffee grounds-due to the nature of their production process via roasting-can be suitable for torrefaction because of the high recovered solid yield and the high energy density. The results will be used for the development of a collection scheme for spent coffee grounds in a big municipality of Athens (Greece).

Assessment of the effect of drying temperature and composition on the biochemical methane potential of in-house dried household food waste

Household food waste management and treatment has been recognised as a significant issue worldwide and at a European Union level. Source-separation of household food waste following drying at source presents a viable solution to this problem. The present research aims at investigating the effect of drying of model household food waste at different temperatures (i.e. 63 ±3 °C and 83 ±3 °C) on its biochemical methane potential. The drying process was carried out using a prototype household waste dryer. The model sample consisted of 77%w/w vegetables and fruits (48%w/w and 29%w/w, respectively), 12%w/w pasta/rice, 6%w/w meat and fish, 3%w/w bread and bakery and 2%w/w dairy. Moreover, drying at the same temperatures was applied for two household food wastes samples with different composition, in order to assess the influence of the samples' composition on both the drying process and the methane generation. For all temperatures used, the higher %w/w mass reduction was observed for model waste (MD) (67.39%w/w and 75.79%w/w for 63 °C and 83 °C, respectively), then for rich-in-protein content (PRO) (66.18%w/w and 69.73%w/w for 63 °C and 83 °C, respectively) and finally for rich-in-fat content (FAT) samples (54.35%w/w and 66.31%w/w for 63 °C and 83 °C, respectively), which confirmed the effectiveness of the drying process. The biochemical methane potential experiments have confirmed that the substrate produced the highest methane yields was the FAT, producing 524.25 ±2.86 L CH4 kg^-1 volatile solids.

Pie waste - A component of food waste and a renewable substrate for producing ethanol

Sugar-rich food waste is a sustainable feedstock that can be converted into ethanol without an expensive thermochemical pretreatment that is commonly used in first and second generation processes. In this manuscript we have outlined the pie waste conversion to ethanol through a two-step process, namely, enzyme hydrolysis using commercial enzyme products mixtures and microbial fermentation using yeast. Optimized enzyme cocktail was found to be 45% alpha amylase, 45% gamma amylase, and 10% pectinase at 2.5mg enzyme protein/g glucan produced a hydrolysate with high glucose concentration. All three solid loadings (20%, 30%, and 40%) produced sugar-rich hydrolysates and ethanol with little to no enzyme or yeast inhibition. Enzymatic hydrolysis and fermentation process mass balance was carried out using pie waste on a 1000g dry weight basis that produced 329g ethanol at 20% solids loading. This process clearly demonstrate how food waste could be efficiently converted to ethanol that could be used for making biodiesel by reacting with waste cooking oil.