Potential application of gasification to recycle food waste and rehabilitate acidic soil from secondary forests on degraded land in Southeast Asia

Valorization of Agriculture Residues into Value-Added Products: A Comprehensive Review of Recent Studies

Global agricultural by-products usually go to waste, especially in developing countries where agricultural products are usually exported as raw products. Such waste streams, once converted to "value-added" products could be an additional source of revenue while simultaneously having positive impacts on the socio-economic well-being of local people. We highlight the utilization of thermochemical techniques to activate and convert agricultural waste streams such as rice and straw husk, coconut fiber, coffee wastes, and okara power wastes commonly found in the world into porous activated carbons and biofuels. Such activated carbons are suitable for various applications in environmental remediation, climate mitigation, energy storage, and conversions such as batteries and supercapacitors, in improving crop productivity and producing useful biofuels.

Valorization of food waste: A comprehensive review of individual technologies for producing bio-based products

BACKGROUND

The escalating global concerns about food waste and the imperative need for sustainable practices have fuelled a burgeoning interest in the valorization of food waste. This comprehensive review delves into various technologies employed for converting food waste into valuable bio-based products. The article surveys individual technologies, ranging from traditional to cutting-edge methods, highlighting their respective mechanisms, advantages, and challenges.

SCOPE AND APPROACH

The exploration encompasses enzymatic processes, microbial fermentation, anaerobic digestion, and emerging technologies such as pyrolysis and hydrothermal processing. Each technology's efficacy in transforming food waste into bio-based products such as biofuels, enzymes, organic acids, prebiotics, and biopolymers is critically assessed. The review also considers the environmental and economic implications of these technologies, shedding light on their sustainability and scalability. The article discusses the role of technological integration and synergies in creating holistic approaches for maximizing the valorization potential of food waste. Key finding and conclusion: This review consolidates current knowledge on the valorization of food waste, offering a comprehensive understanding of individual technologies and their contributions to the sustainable production of bio-based products. The synthesis of information presented here aims to guide researchers, policymakers, and industry stakeholders in making informed decisions to address the global challenge of food waste while fostering a circular and eco-friendly economy.

Yield and Energy Modeling for Biochar and Bio-Oil Using Pyrolysis Temperature and Biomass Constituents

Pyrolysis offers a sustainable and efficient approach to resource utilization and waste management, transforming organic materials into valuable products. The quality and distribution of the pyrolysis products highly depend on the constituents' properties and set process parameters. This research aims to investigate and model this dependency, offering decision-makers a tool to guide them when designing the process for a particular application. Experimental data on the pyrolysis of various types of feedstocks processed at a wide range of pyrolysis temperatures (350-650 °C) are utilized to develop the prediction models. Four variables are modeled: the yield and energy content for both the biochar and bio-oil as a function of the pyrolysis temperature and feedstock characteristics. The models developed had very good prediction power with the coefficient of determination above 90%. The results highlight the advantages of food waste (leftover) as a suitable feedstock to produce biochar at the pyrolysis temperature within the range of 450-550 °C. Furthermore, the biofuels produced from food waste are found to be of good quality, with the bio-oil exceptionally high in energy content (HHV = 34.6 MJ/kg), which is almost 80% of that of diesel. The developed models provide a tool for predicting the biofuel yield and quality based on the feedstock selection and process temperature.

Enhancing sustainable crop cultivation: The impact of renewable soil amendments and digestate fertilizer on crop growth and nutrient composition

Utilizing digestate as a fertilizer enhances soil nutrient content, improves fertility, and minimizes nutrient runoff, mitigating water pollution risks. This alternative approach replaces commercial fertilizers, thereby reducing their environmental impact and lowering greenhouse gas emissions associated with fertilizer production and landfilling. Herein, this study aimed to evaluate the impact of various soil amendments, including carbon fractions from waste materials (biochar, compost, and cocopeat), and food waste anaerobic digestate application methods on tomato plant growth (Solanum lycopersicum) and soil fertility. The results suggested that incorporating soil amendments (biochar, compost, and cocopeat) into the potting mix alongside digestate application significantly enhances crop yields, with increases ranging from 12.8 to 17.3% compared to treatments without digestate. Moreover, the combination of soil-biochar amendment and digestate application suggested notable improvements in nitrogen levels by 20.3% and phosphorus levels by 14%, surpassing the performance of the those without digestate. Microbial analysis revealed that the soil-biochar amendment significantly enhanced biological nitrification processes, leading to higher nitrogen levels compared to soil-compost and soil-cocopeat amendments, suggesting potential nitrogen availability enhancement within the rhizosphere's ecological system. Chlorophyll content analysis suggested a significant 6.91% increase with biochar and digestate inclusion in the soil, compared to the treatments without digestate. These findings underscore the substantial potential of crop cultivation using soil-biochar amendments in conjunction with organic fertilization through food waste anaerobic digestate, establishing a waste-to-food recycling system.

Food waste valorisation via gasification - A review on emerging concepts, prospects and challenges

Disposing of the enormous amounts of food waste (FW) produced worldwide remains a great challenge, promoting worldwide research on the utilization of FW for the generation of value-added products. Gasification is a significant approach for decomposing and converting organic waste materials into biochar, bio-oil, and syngas, which could be adapted for energy (hydrogen (H₂) and heat) generation and environmental (removal of pollutants and improving the soil quality) applications. Employment of FW matrices for syngas production through gasification is one of the effective methods of energy recovery. This review explains different gasification processes (catalytic and non-catalytic) used for the decomposition of unutilized food wastes and the effect of operating parameters on H₂-rich syngas generation. Also, potential applications of gasification byproducts such as biochar and bio-oil for effective valorization have been discussed. Besides, the scope of simulation to optimize the gasification conditions for the effective valorization of FW is elaborated, along with the current progress and challenges in the research to identify the feasibility of gasification technology for FW. Overall, this review concludes the sustainable route for conversion of unutilized food into hydrogen-enriched syngas production.

Designer biochar with enhanced functionality for efficient removal of radioactive cesium and strontium from water

Radioactive elements released into the environment by accidental discharge constitute serious health hazards to humans and other organisms. In this study, three gasified biochars prepared from feedstock mixtures of wood, chicken manure, and food waste, and a KOH-activated biochar (40% food waste + 60% wood biochar (WFWK)) were used to remove cesium (Cs⁺) and strontium (Sr²⁺) ions from water. The physicochemical properties of the biochars before and after adsorbing Cs⁺ and Sr²⁺ were determined using X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, extended X-Ray absorption fine structure (EXAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX). The WFWK exhibited the highest adsorption capacity for Cs⁺ (62.7 mg/g) and Sr²⁺ (43.0 mg/g) among the biochars tested herein. The removal of radioactive ¹³⁷Cs and ⁹⁰Sr exceeded 80% and 47%, respectively, in the presence of competing ions like Na⁺ and Ca²⁺. The functional groups present in biochar, including -OH, -NH₂, and -COOH, facilitated the adsorption of Cs⁺ and Sr²⁺. The Cs K-edge EXAFS spectra revealed that a single coordination shell was assigned to the Cs-O bonding at 3.11 Å, corresponding to an outer-sphere complex formed between Cs and the biochar. The designer biochar WFWK may be used as an effective adsorbent to treat radioactive ¹³⁷Cs- and ⁹⁰Sr-contaminated water generated during the operation of nuclear power plants and/or unintentional release, owing to the enrichment effect of the functional groups in biochar via alkaline activation.

Physicochemical Properties of Torrefied and Pyrolyzed Food Waste Biochars as Fuel: A Pilot-Scale Study

Food waste is an important constituent of municipal solid waste, and research has been conducted to develop various methods for treating food waste and recycling it (e.g., fuel, landfilling, composting, conversion into animal feed, drying, and carbonization). Among these, the drying and carbonization techniques can change food waste into fuel; however, they need more energy than fermentation and anaerobic digestion procedures. In this study, we investigated the physicochemical properties of food waste biochar produced under torrefaction (270 °C) and pyrolysis (450 °C) conditions to establish its applicability as fuel by comparing temperatures, residence times, and conditions before and after demineralization. The higher heating value increased after the demineralization process under both temperature conditions (270 °C and 450 °C), and the chlorine level was lower at 270 °C temperature demineralization than at 450 °C. During the demineralization process, Na and K were better removed than Ca and Mg. Additionally, Cr, Hg, Cd, and Pb levels were lower than those according to the European Union and Korean domestic bio-SRF recovered fuel criteria, confirming the applicability of biochar as fuel.

Improving the efficiency of vermicomposting of polluted organic food wastes by adding biochar and mangrove fungi

Vermicomposting of food waste amended with biochar and cow dung was studied during a 90-day composting period. The improvement of the vermicomposting process by adding three mangrove fungal species as additional amendments were studied. The use of mangrove fungi Acrophialophora jodhpurensis as a bio-catalytic actor during vermicomposting proved to be beneficial in terms of final compost quality (available N, P and K) and the shortening of the composting period. All three fungal species, however, reached the neutral pH at the end of the composting period and appeared to be beneficial. Heavy metal (Cd, Ni, Pb, Zn, Cu and Cr) concentrations decreased throughout the composting process. Food waste can be treated using vermicomposting with biochar, cow dung and the mangrove fungi A. jodhpurensis. The final vermicomposting product is suitable for agricultural use.

Investigation of gasification kinetics of multi-component waste mixtures in a novel thermogravimetric flow reactor via gas analysis

A novel gasification fed-batch reactor enabling both thermogravimetric and gas analysis of large samples (up to tens of grams) was designed and tested. Air gasification experiments on food-court waste representative samples and its components were performed at 700 °C and 800 °C using ER = 0.3. At both temperatures, the lignocellulosics fraction produced highest H₂ concentration (greater than 21% at 800 °C) while the plastic components generated less H₂ regardless of process temperature (2.44%-7.08%). Synergistic effects of multiple components gasification with respect to H₂ production was noticed through its non-linear evolution at 700 °C (ranging from 1.18% to 5.38%). A strong negative effect was observed at 800 °C; plastic addition reduced H₂ production when combined with lignocellulosic and organic matter (1.02% to 9.73%). The same effects were observed for CH₄ formation. This phenomenon was validated by kinetic analysis of decay curves of all components and their mixtures at the beginning of gasification in entire temperature region.

Advances in production of bioplastics by microalgae using food waste hydrolysate and wastewater: A review

Microalgae have emerged as an effective dual strategy for bio-valorisation of food processing wastewater and food waste hydrolysate which favours microalgae cultivation into producing value-added by products mainly lipids, carbohydrates, and proteins to the advantages of bioplastic production. Moreover, various microalgae have successfully removed high amount of organic pollutants from food processing wastewater prior discharging into the environment. Innovation of microalgae cultivating in food processing wastewater greatly reduced the cost of wastewater treatment compared to conventional approach in terms of lower carbon emissions, energy consumption, and chemical usage while producing microalgae biomass which can benefit low-cost fertilizer and bioplastic applications. The study on several microalgae species has all successfully grown on food waste hydrolysates showing high exponential growth rate and biomass production rich in proteins, lipids, carbohydrates, and fatty acids. Multiple techniques have been implemented for the extraction of food wastes to be incorporate into the bioplastic production.

Plate waste study among hospitalised patients receiving texture-modified diet

BACKGROUND/OBJECTIVES

While plate waste has been widely investigated in hospitals, there have been minimal studies specific to the texture-modified diet (TMD). This study aims to determine the percentage of plate waste among patients prescribed with TMD and its contributory factors.

SUBJECTS/METHODS

This was a single-centre study conducted in the university hospital on three types of TMD (blended diet, mixed porridge, minced diet) during lunch and dinner meals. Weighing method and visual estimation method assisted by digital photograph were adopted in this study. Face to face interview was carried out to investigate on 1) the food/food service quality factors in terms of patients' satisfaction level towards sensorial quality of food and food services provided and 2) the clinical/external factors including appetite, the provision of oral nutrition support, time taking the diet, the need for feeding assistance and the length of hospital stay.

RESULTS

The mean percentage of overall plate waste of 95 patients receiving TMD was high (47.5%). Blended diet was identified as the most wasted diet (65%) followed by minced diet (56%) and mixed porridge (35%). Satisfaction level among patients was moderate. Patients on TMD in general had higher satisfaction level on the aspect of food service as compared to food quality. Substantial association between sensorial qualities of food and plate waste were varied according to individual TMD type. A multiple linear regression showed that only the satisfaction level toward the aspects of appearance and variety of foods were the predictors of TMD plate waste (R² = 0.254, P < 0.05).

CONCLUSIONS

A significant relationship between the percentage of plate waste and the overall satisfaction level of patients receiving TMD suggests that vigorous strategies are needed to reduce the food waste of TMD which will lead to a better nutritional status and clinical outcomes among the patients.

Assortment of Native Microalgae for Improved Biomass and Lipid Production on Employing Vegetable Waste as a Frugal Cultivation Approach for Biodiesel Application

Enhanced biofuel production strategies from microalgae by employing affordable bio-waste usage are fetching significance, nowadays. This study examines the effect of VWE for enhanced biomass from new indigenous microalgal isolates, Asterarcys sp. SPC, Scenedesmus sp. KT-U, Scenedesmus sp. KTWL-A, Coelastrum sp. T-E, and Chlorella sp. TWL-B. The growth of microalgae in VWE-treated growth media showed considerable increase (1.14-2.3 folds) than control medium (without VWE). Further, two effective native microalgae were selected based on growth in VWE treatment, biomass productivity, and TAG accumulation through statistical clustering analysis. Mixotrophic batch cultivation of Scenedesmus sp. KT-U and Asterarcys sp. SPC cultivated using VWE treatment in the optimum concentration had produced significant average increase in BP (1.8 and 1.4 folds, respectively) than control (without VWE). Whereas in the lipid production phase, there was a noticeable increase in lipid yield in VWE-treated cells of lipid phase (231.8 ± 17.9 mg/L and 243.5 ± 25 mg/L) in Scenedesmus sp. KT-U and Asterarcys sp. SPC, respectively, than in control (140.5 ± 28 mg/L and 166.4 ± 23 mg/L) with considerable TAG accumulation. Thus, this study imparts strain selection process of native microalgae based on vegetable waste usage for improved yield of biomass and lipid amenable for cost-effective biodiesel production.

Water hyacinth for energy and environmental applications: A review

This review is focused on the sustainable management of harvested water hyacinth (WH) via thermochemical conversion to carbonaceous materials (CMs), biofuels, and chemicals for energy and environmental applications. One of the major challenges in thermochemical conversion is to guarantee the phytoremediation performance of biochar and the energy conversion efficiency in biowaste-to-energy processes. Thus, a circular sustainable approach is proposed to improve the biochar and energy production. The co-conversion process can enhance the syngas, heat, and energy productions with high-quality products. The produced biochar should be economically feasible and comparable to available commercial carbon products. The removal and control of heavy and transition metals are essential for the safe implementation and management of WH biochar. CMs derived from biochar are of interest in wastewater treatment, air purification, and construction. It is important to control the size, shape, and chemical compositions of the CM particles for higher-value products like catalyst, adsorbent or conductor.

Biochar industry to circular economy

Biochar, produced as a by-product of pyrolysis/gasification of waste biomass, shows great potential to reduce the environment impact, address the climate change issue, and establish a circular economy model. Despite the promising outlook, the research on the benefits of biochar remains highly debated. This has been attributed to the heterogeneity of biochar itself, with its inherent physical, chemical and biological properties highly influenced by production variables such as feedstock types and treating conditions. Hence, to enable meaningful comparison of results, establishment of an agreed international standard to govern the production of biochar for specific uses is necessary. In this study, we analyzed four key uses of biochar: 1) in agriculture and horticulture, 2) as construction material, 3) as activated carbon, and 4) in anaerobic digestion. Then the guidelines for the properties of biochar, especially for the concentrations of toxic heavy metals, for its environmental friendly application were proposed in the context of Singapore. The international status of the biochar industry code of practice, feedback from Singapore local industry and government agencies, as well as future perspectives for the biochar industry were explained.

Biochar for urban agriculture: Impacts on soil chemical characteristics and on Brassica rapa growth, nutrient content and metabolism over multiple growth cycles

With possible food crises looming in the near future, urban farming, including small-scale community and home gardens for home consumption, presents a promising option to improve food security in cities. These small-scale farms and gardens often use planter boxes and raised beds filled with lightweight soil or potting mixes. While previous studies on biochar focused on its application on large-scale contiguous farmlands, this study aimed to evaluate the suitability of biochar as a partial soil substitute to produce a durable and lightweight soil-biochar mix for small-scale urban farms. The effects of biochar on the chemical properties of the soil-biochar mix, crop yield and, particularly, crop nutrients and metabolic content were assessed. A germination test using pak choi seeds (Brassica rapa L. cultivar group Pak choi, Green-Petioled Form) showed that the biochar contained phytostimulants. Through a nursery pot experiment over four growth cycles, biochar treatments performed better than pure soil at retaining water-soluble NO₃^- and K⁺ ions, but were worse at retaining PO₄^3- ions. Nonetheless, despite its positive effect on soil NO₃^- retention, biochar application did not improve crop yield significantly when the application rate varied from 0% to 60% (v/v). Untargeted metabolomic analyses showed that biochar application may increase the production of carbohydrates and certain flavonoids and glucosinolates. The results of this study showed that biochar can potentially be used to improve pak choi nutritional values and applied in large quantity to obtain a lightweight soil mix for urban farming.

Optimisation and production of alpha amylase from thermophilic Bacillus spp. and its application in food waste biodegradation

This study employed Bacillus spp. with α-amylase production isolated from Malaysian hot spring for domestic kitchen food waste treatment contained grains, vegetables, chicken and tuna that mimic the food waste discharge from domestic kitchens in Malaysian household. Results showed that Bacillus licheniformis HULUB1 and Bacillus subtilis SUNGB2 possess excellent amylolytic properties. Highest α-amylase activity was obtained when both isolates were cultivated at pH 6.0 and 65 °C with concentrations of 18.15 U/mL for HULUB1 and 22.14 U/mL for SUNGB2. Stability of α-amylase with significant levels of enzyme activity were recorded at 55-85 °C and pH 5.0-9.0. The extracted mixed α-amylase of HULUB1 and SUNGB2 showed greatest reduction were achieved at day 12 with 45% ± 0.03 solid content at 65 °C. While the mixed culture of HULUB1 and SUNGB2 displayed an enhanced effect on the food waste contents reduction with 43% ± 0.02 solid content at 45 °C after day 12. The findings showed that the combination of the two Bacillus spp. isolates possessed degradation of food wastes at faster rate than α-amylase. It was also pointed out that the standard food waste (SFW) and the treatment process assimilated for this study was suitable for the growth of Bacillus spp.

Gasification biochar from biowaste (food waste and wood waste) for effective CO2 adsorption

Biochar is newly proposed as an innovative and cost-effective material to capture CO₂. In this study, biochar was produced from feedstock mixtures of food waste and wood waste (i.e., 20%:80% WFW20, 30%:70% WFW30 and 40%:60% WFW40) by gasification. The two biochar adsorbents containing the highest percentage of food waste, i.e., WFW40-K and WFW40-KC, were activated by KOH and KOH + CO₂, respectively. The biochar adsorbents were then tested for CO₂ adsorption at room temperature of 25 °C by using a volumetric sorption analyzer. The WFW20 showed the highest CO₂ adsorption capacity, while higher percentage of food waste in the feedstock was unfavorable for the CO₂ adsorption. The presence of N and S on the biochar surface was the primary contributor to the high CO₂ uptake on WFW20. The development of micropores by KOH activation significantly increased the CO₂ adsorption on WFW40-K, but KOH + CO₂ activation could not further increase the development of micropores and subsequent CO₂ adsorption. Moreover, WFW40-K showed >99% recyclability during 10 consecutive adsorption-desorption cycles. The biochars derived from biowaste (food waste and wood waste) could be effective adsorbents for CO₂ capture by providing green solution for food waste recycling.

Biogenic stabilization and heavy metal immobilization during vermicomposting of vegetable waste with biochar amendment

Vermicomposting is a traditional technology that produces the best quality of compost, but factors such as maturity, presence of heavy metals, etc. need to be tackled prior to agrarian application. The present study investigates the influence of varying biochar dose (2.5, 5, and 10% on a weight basis) on the maturity of compost and heavy metals during vermicomposting of vegetable waste using epigeic earthworm. Biochar amendment notably enhanced the electrical conductivity (up to 2.7 mS/cm), nitrogen content (up to 3.1%), NO₃-N (up to 630 mg/kg) and nutritional value. The heavy metals, oxygen uptake rate (below 0.96 mg/g VS/day) and CO₂ evolution rate (below 1 mg/g VS/day) were attenuated along with degradation of complex organic crystals as observed in powder X-Ray Diffraction (PXRD) spectra. Furthermore, biochar aid in reducing pathogens (below 1.1 × 10³ MPN/g dry weight) as inferred from the Most Probable Number (MPN) results as well as degrading the complex organics into simpler compounds as revealed from the Fourier-transform infrared spectroscopy (FTIR) spectra. The present study inferred that the vegetable waste was biologically stabilized through biochar amendment during vermicomposting process with improved nutritional and physico-chemical properties.

Shedding light on biogas: Phototrophic biofilms in anaerobic digesters hold potential for improved biogas production

Conventional anaerobic digesters intended for the production of biogas usually operate in complete darkness. Therefore, little is known about the effect of light on their microbial communities. In the present work, 16S rRNA gene amplicon Nanopore sequencing and shotgun metagenomic sequencing were used to study the taxonomic and functional structure of the microbial community forming a biofilm on the inner wall of a laboratory-scale transparent anaerobic biodigester illuminated with natural sunlight. The biofilm was composed of microorganisms involved in the four metabolic processes needed for biogas production, and it was surprisingly rich in Rhodopseudomonas faecalis, a versatile bacterium able to carry out photoautotrophic metabolism when grown under anaerobic conditions. The results suggested that this bacterium, which is able to fix carbon dioxide, could be considered for use in transparent biogas fermenters in order to contribute to the production of optimized biogas with a higher CH₄:CO₂ ratio than the biogas produced in regular, opaque digesters. To the best of our knowledge, this is the first study characterising the phototrophic biofilm associated with illuminated bioreactors.

Drivers of food waste generation: Case study of island-based hotels in Langkawi, Malaysia

Food waste (FW) generation from hotel operations have a significant negative impact on the environment, society and economy. Hence, the urgent need to introduce sustainable food management to reduce both FW and operational costs in hotels. The aim of this paper is to identify the drivers of FW generation and barriers to sustainable food waste management (SFWM) in island based hotels. The data were collected using in-depth interview coupled with the observations conducted at 23 selected hoteliers in Langkawi Island, Malaysia. Based on the analysis, using qualitative content analysis (QCA), eight FW drivers were identified and the drivers were classified into three categories of factors, mainly internal, external and intermediate influence. There are four FW drivers identified as internal factors that influenced the implementation of food waste management namely (1) poor hotel management and policies, (2) lack of skills in food preparation, (3) lack of facilities and FW technology and (4) non-implementation of waste audit and waste separation. For external factors, there are two FW drivers, including (5) unsustainable food consumption patterns of the customers and (6) risk of food ingredients spoilage. As for intermediate factors, two FW drivers were identified, which are (7) ineffective communication and (8) inadequate education and awareness. Findings from this study contribute towards a better understanding on the complexity of FW issues, particularly for island-based hotel sector. It was also suggested that a holistic approach with multi-stakeholders is crucial to reduce food wastage towards achieving SFWM.

Effect of gasification biochar application on soil quality: Trace metal behavior, microbial community, and soil dissolved organic matter

Compared to pyrolysis biochar (PBC), gasification biochar (GBC) differs in both composition and surface functionalities due to the use of an oxidizing purging gas. This work compares the effect of using PBC and GBC as soil amendments on the soil properties, trace metal bioavailability, soil microbial activity, and soil dissolved organic matter (DOM). Biochar-driven reduction of bioavailable metals does not necessarily result in a positive impact on the soil microbial growth. The DOM in the soil was strongly related to the soil microbial activity, as revealed by the strong correlation between the soil dehydrogenase activity (DHA) and soil dissolved organic carbon (r = 0.957, p <  0.01). Three identified fluorescent components (C1, C2, C3) in the soil DOM were closely associated with the soil microbial activity, for instance, with a clear positive correlation between the soil DHA and C1 (r = 0.718, p <  0.05) and a significant negative correlation between the total bacterial fatty acid methyl ester content and C3 (r = -0.768, p <  0.05). The bioavailability of Cd and Zn is not only related to the pH and surface functionalities of the biochar, but also to its aromatic carbon and inorganic mineral composition. This study further demonstrates that a fluorescence excitation-emission matrix coupled with parallel factor analysis is a useful tool to monitor changes in the soil quality after application of biochar, which is greatly relevant to the soil biota.

Study of chemical composition and nutritional values of vegetable wastes in Bangladesh

The present study was conducted with the objectives of determining the chemical composition and nutritional value of vegetable waste (VW) of households and the marketplace for their suitability as ruminant feed. The crude protein, total digestible nutrients and extent of rumen degradability of dry matter (DM) of VW of households were 140.0 g kg-1, 0.668 and 0.855, respectively; while those of the marketplace were 169.0 g kg-1, 0.633 and 0.80, respectively. The levels of chromium and lead in each respectively, was 13.27 and 1.53 ng kg-1DM; and 31.01 and 5.71 ng kg-1DM. The total aflatoxins in VW of households was 3.08 µg kg-1DM, and undetectable in VW from the marketplace. Considering the chemical composition and safety parameters studied, VW could preliminary be considered as animal feed. The feeding of processed marketplace VW (VWP) at 275 g kg-1DM of a diet or 0.76% of live weight (LW) to growing bulls, replacing 50% of a concentrate mixture as supplement to a Napier silage diet for a period of 34 days reduced the total DM intake (0.0276 vs 0.0343 LW) without any significant (P > 0.05) changes in DM or protein digestibility. Blood urea levels (19.5 vs 23.67 mg dl-1), and serum creatinine levels (1.37 vs 1.08 mg dl-1) differed significantly (P > 0.05) between the two groups but were within normal physiological ranges. Therefore, it may be concluded that the level of incorporation of VWP would be less than 50% replacement of the concentrate in the diet. Further research is required to determine optimum inclusion levels in ruminant diets.

Application of biochar from food and wood waste as green admixture for cement mortar

Landfilling of food waste due to its low recycling rate is raising serious concerns because of associated soil and water contamination, and emission of methane and other greenhouse gases during the degradation process. This paper explores feasibility of using biochar derived from mixed food waste (FWBC), rice waste (RWBC) and wood waste (mixed wood saw dust, MWBC) as carbon sequestering additive in mortar. RWBC is prepared from boiled plain rice, while FWBC is prepared from combination of rice, meat, and vegetables in fixed proportion. Carbon content in FWBC, RWBC and MWBC were found to be 71%, 66% and 87% by weight respectively. Results show that addition of 1-2wt% of FWBC and RWBC in mortar results in similar mechanical strength as control mix (without biochar). 1wt% of FWBC led to 40% and 35% reduction in water penetration and sorptivity respectively, indicating higher impermeability of mortar. Biochar from mixed wood saw dust performed better in terms of mechanical and permeability properties. Increase in compressive strength and tensile strength by up to 20% was recorded, while depth of water penetration and sorptivity was reduced by about 60% and 38% respectively compared to control. Both FWBC and MWBC were found to act as reinforcement to mortar paste, which resulted in higher ductility than control at failure under flexure. This study suggests that biochar from food waste and mixed wood saw dust has the potential to be successfully deployed as additive in cement mortar, which would also promote waste recycling, and sequester high volume carbon in civil infrastructure.

An environmental friendly animal waste disposal process with ammonia recovery and energy production: Experimental study and economic analysis

Animal manure waste is considered as an environmental challenge especially in farming areas mainly because of gaseous emission and water pollution. Among all the pollutants emitted from manure waste, ammonia is of greatest concern as it could contribute to formation of aerosols in the air and could hardly be controlled by traditional disposal methods like landfill or composting. On the other hand, manure waste is also a renewable source for energy production. In this work, an environmental friendly animal waste disposal process with combined ammonia recovery and energy production was proposed and investigated both experimentally and economically. Lab-scale feasibility study results showed that 70% of ammonia in the manure waste could be converted to struvite as fertilizer, while solid manure waste was successfully gasified in a 10kW downdraft fixed-bed gasifier producing syngas with the higher heating value of 4.9MJ/(Nm³). Based on experimental results, economic study for the system was carried out using a cost-benefit analysis to investigate the financial feasibility based on a Singapore case study. In addition, for comparison, schemes of gasification without ammonia removal and incineration were also studied for manure waste disposal. The results showed that the proposed gasification-based manure waste treatment process integrated with ammonia recovery was most financially viable.

Comparison of the co-gasification of sewage sludge and food wastes and cost-benefit analysis of gasification- and incineration-based waste treatment schemes

The compositions of food wastes and their co-gasification producer gas were compared with the existing data of sewage sludge. Results showed that food wastes are more favorable than sewage sludge for co-gasification based on residue generation and energy output. Two decentralized gasification-based schemes were proposed to dispose of the sewage sludge and food wastes in Singapore. Monte Carlo simulation-based cost-benefit analysis was conducted to compare the proposed schemes with the existing incineration-based scheme. It was found that the gasification-based schemes are financially superior to the incineration-based scheme based on the data of net present value (NPV), benefit-cost ratio (BCR), and internal rate of return (IRR). Sensitivity analysis was conducted to suggest effective measures to improve the economics of the schemes.