Plastics are produced and used in large quantities worldwide (e.g. as food packaging). In line with this, plastic particles are found throughout the ecosphere and in various foods. As a result, plastics are also present in energy-rich waste biomass derived from the food industry, supermarkets, restaurants, etc. These waste streams are a valuable source for biogas production but can also be used to feed insects that in turn upcycle it into new high-value biomass. In both applications, the remaining residue can be used as fertilizer. Due to the present plastic particles, these applications could pose a continued threat to the environment, and both human and animal health. Therefore, the need of determining the (micro)plastic content to assess the potential danger is rising. In this research, a closed-vessel microwave-assisted acid digestion method was developed to accurately determine meso- and microplastic contents in food (waste) matrices by solubilising this food matrix. Polyvinyl chloride (PVC) food packaging foil was used to develop the method, using a full factorial design with three parameters (nitric acid concentration (c(HNO₃)), temperature (T), and time (t)). According to this model, the best practical conditions were c(HNO₃) = 0.50 mol/L, T = 170 °C, and t = 5.00 min. Subsequently, the method was tested on five other plastics, namely high- and low-density polyethylene (HDPE and LDPE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET), mixed with a food matrix, resulting in a mean plastic recovery of 102.2 ± 4.1%. Additionally, the polymers were not oxidised during the microwave digestion. For PVC and PS hardly any degradation was found, while HDPE, LDPE, and PP showed slight chain degradation, although without recovery loss. In conclusion, the method is an accurate approach to quantify the total meso- and microplastic content in food (waste) matrices with minimal change in their intrinsic characteristics.

Biofuel production via pyrolysis has received increasing interest as a promising solution for utilization of now wasted food residue. In this study, the fast pyrolysis of mixed food waste (MFW) was performed in a bubbling fluidized-bed reactor. This was done under different operating conditions (reaction temperatures and carrier gas flow rate) that influence product distribution and bio-oil composition. The highest liquid yield (49.05 wt%) was observed at a pyrolysis temperature of 475 °C. It was also found that the quality of pyrolysis bio-oils (POs) could be improved using catalysts. The catalytic fast pyrolysis of MFW was studied to upgrade the pyrolysis vapor, using dolomite, red mud, and HZSM-5. The higher heating values (HHVs) of the catalytic pyrolysis bio-oils (CPOs) ranged between 30.47 and 35.69 MJ/kg, which are higher than the HHVs of non-catalytic pyrolysis bio-oils (27.69–31.58 MJ/kg). The major components of the bio-oils were fatty acids, N-containing compounds, and derivatives of phenol. The selectivity for bio-oil components varied depending on the catalysts. In the presence of the catalysts, the oxygen was removed from oxygenates via moisture, CO₂, and CO. The CPOs contained aliphatic hydrocarbons, polycyclic aromatic compounds (such as naphthalene), pyridine derivatives, and light oxygenates (cyclic alkenes and ketones).

In this study, the co-pyrolysis of food waste with lignocellulosic biomass (wood bark) in a continuous-flow pyrolysis reactor was considered as an effective strategy for the clean disposal and value-added utilization of the biowaste. To achieve this aim, the effects of major co-pyrolysis parameters such as pyrolysis temperature, the flow rate of the pyrolysis medium (nitrogen (N₂) gas), and the blending ratio of food waste/wood bark on the yields, compositions, and properties of three-phase pyrolytic products (i.e., non-condensable gases, condensable compounds, and char) were investigated. The temperature and the food waste/wood bark ratio were found to affect the pyrolytic product yields, while the N₂ flow rate did not. More non-condensable gases and less char were produced at higher temperatures. For example, as the temperature was increased from 300 °C to 700 °C, the yield of non-condensable gases increased from 6.3 to 17.5 wt%, while the yield of char decreased from 63.6 to 30.6 wt% for the co-pyrolysis of food waste and wood bark at a weight ratio of 1:1. Both the highest yield of hydrogen (H₂) gas and the most significant suppression of the formation of phenolic and polycyclic aromatic hydrocarbon (PAH) compounds were achieved with a combination of food waste and wood bark at a weight ratio of 1:1 at 700 °C. The results suggest that the synergetic effect of food waste and lignocellulosic biomass during co-pyrolysis can be exploited to increase the H₂ yield while limiting the formation of phenolic compounds and PAH derivatives. This study has also proven the effectiveness of co-pyrolysis as a process for the valorization of biowaste that is produced by agriculture, forestry, and the food industry, while reducing the formation of harmful chemicals.

Pollutants in wastewater and exhaust gas bring out serious concerns to public health and the environment. Biochar can be developed as a sustainable adsorbent originating from abundant bio-wastes, such as agricultural waste, forestry residue, food waste and human waste. Here we highlight the state-of-the-art research progress on pyrochar and hydrochar for the sorption of pollutants (heavy metal, organics, gas, etc) in wastewater and exhaust gases. The adsorption performance of pyrochar and hydrochar are compared and discussed in-depth, including preparation procedures (carbonization and activation), sorption possible mechanisms, and physiochemical properties. Challenges and perspective for designing efficient and environmental benign biochar-based adsorbents are finally addressed.

The complaints arising from the problem of odorants released by composting plants may impede the construction of new composting facilities, preclude the proper activity of existing facilities or even lead to their closure, with negative implications for waste management and local economy. Improving the knowledge on VOC emissions from composting processes is of particular importance since different VOCs imply different odour impacts. To this purpose, three different organic matrices were studied in this work: dewatered sewage sludge (M1), digested organic fraction of municipal solid waste (M2) and untreated food waste (M3). The three matrices were aerobically biodegraded in a bench-scale bioreactor simulating composting conditions. A homemade device sampled the process air from each treatment at defined time intervals. The samples were analysed for VOC detection. The information on the concentrations of the detected VOCs was combined with the VOC-specific odour thresholds to estimate the relative weight of each biodegraded matrix in terms of odour impact. When the odour formation was at its maximum, the waste gas from the composting of M3 showed a total odour concentration about 60 and 15,000 times higher than those resulting from the composting of M1 and M2, respectively. Ethyl isovalerate showed the highest contribution to the total odour concentration (>99%). Terpenes (α-pinene, β-pinene, p-cymene and limonene) were abundantly present in M2 and M3, while sulphides (dimethyl sulphide and dimethyl disulphide) were the dominant components of M1.

The anaerobic digestion of food waste for energy recovery produces a nutrient-rich digestate which is a valuable source of crop available nitrogen (N). As with any ‘new’ material being recycled to agricultural land it is important to develop best management practices that maximise crop available N supply, whilst minimising emissions to the environment. In this study, ammonia (NH3) and nitrous oxide (N2O) emissions to air and nitrate (NO3−) leaching losses to water following digestate, compost and livestock manure applications to agricultural land were measured at 3 sites in England and Wales. Ammonia emissions were greater from applications of food-based digestate (c.40% of total N applied) than from livestock slurry (c.30% of total N applied) due to its higher ammonium-N content (mean 5.6 kg/t compared with 1–2 kg/t for slurry) and elevated pH (mean 8.3 compared with 7.7 for slurry). Whilst bandspreading was effective at reducing NH3 emissions from slurry compared with surface broadcasting it was not found to be an effective mitigation option for food-based digestate in this study. The majority of the NH3 losses occurred within 6 h of spreading highlighting the importance of rapid soil incorporation as a method for reducing NH3 emissions. Nitrous oxide losses from food-based digestates were low, with emission factors all less than the IPCC default value of 1% (mean 0.45± 0.15%). Overwinter NO3− leaching losses from food-based digestate were similar to those from pig slurry, but much greater than from pig farmyard manure or compost. Both gaseous N losses and NO3− leaching from green and green/food composts were low, indicating that in these terms compost can be considered as an ‘environmentally benign’ material. These findings have been used in the development of best practice guidelines which provide a framework for the responsible use of digestates and composts in agriculture.

To meet human food and fiber needs in an environmentally and economically sustainable way, we must improve the efficiency of waste, water, and nutrient use by converting vast quantities of agricultural and food waste to renewable bioproducts. This work converts waste cherry pits, an abundant food waste in the Great Lakes region, to biochars and activated biochars via slow pyrolysis. Biochars produced have surface areas between 206 and 274 m²/g and increased bioavailability of Fe, K, Mg, Mn, and P. The biochars can be implemented as soil amendments to reduce nutrient run-off and serve as a valuable carbon sink (biochars contain 74–79% carbon), potentially mitigating harmful algal blooms in the Great Lakes. CO₂-activated biochars have surface areas of up to 629 m²/g and exhibit selective metal adsorption for the removal of metals from simulated contaminated drinking water, an environmental problem plaguing this region. Through sustainable waste-to-byproduct valorization we convert this waste food biomass into biochar for use as a soil amendment and into activated biochars to remove metals from drinking water, thus alleviating economic issues associated with cherry pit waste handling and reducing the environmental impact of the cherry processing industry.

Converting biowaste into value-added products has raised the researchers’ interests. In this study, bioconversion was applied to produce chain acids from food waste by anaerobic fermentation. To improve the caproic acid production, different pretreatments (i.e., ultrasonic, hydrothermal, and alkaline-thermal) were used for investigating their effects on the acidogenic production and microbial communities. The results showed that ultrasonic and hydrothermal pretreatments (207.8 and 210.1 mg COD/g VS, respectively) were very efficient for enhancing the caproic acid production, compared to the alkaline-thermal pretreated samples and control samples (72.6 and 97.5 mg COD/g VS, respectively). The ultrasonic pretreatment was beneficial for reducing volatile fatty acids (VFAs) during the caproic acid production, resulting in converting more lactic acid to caproic acid by adding the hydrothermal pretreatment. The microbial community analysis showed that the acidogenic bacteria Caproiciproducens dominated the fermentation in this bioconversion process of food waste into chain acids. The Caproiciproducens mainly degraded the proteins and carbohydrates from the saccharified residues of food waste to produce caproic acids through chain elongation procedure. The investigation and optimized method may help develop the bioconversion technology for producing VFAs products from food wastes.

The process of anaerobic digestion in food waste treatment plants generates a large amount of volatile organic compounds (VOCs). Long-term exposure to this exhaust gas can pose a threat to the health of workers and people living nearby. In this study, VOCs emitted from different working units in a food waste anaerobic digestion plant were monitored for a year. Variations in VOCs emitted from each unit were analyzed and a health risk assessment was conducted for each working unit. The results show that the concentration of VOCs in different units varied greatly. The highest cumulative concentration of VOCs appeared in the hydrothermal hydrolysis unit (3.49 × 10⁴ μg/m³), followed by the sorting/crushing room (8.97 × 10³ μg/m³), anaerobic digestion unit (6.21 × 10² μg/m³), and biogas production unit (2.01 × 10² μg/m³). Oxygenated compounds and terpenes were the major components of the emitted VOCs, accounting for more than 98% of total VOC emissions. The carcinogenic risk in the plant exceeded the safety threshold (ILCR<1 × 10⁻⁶), while the non-carcinogenic risk was within the acceptable range (HI < 1). The carcinogenic risk from the hydrothermal hydrolysis unit was the highest, reaching 4.4 × 10⁻⁵, and was labeled as “probable risk.” The carcinogenic risk at the plant boundary was 1.2 × 10⁻⁵, indicating exhaust gases can cause a health threat to neighbors. Therefore, management VOCs in anaerobic digestion plants should receive more attention, and employees should minimize the time they spend in the hydrothermal hydrolysis unit.

Organic fertilizers, such as digestates and manure, are increasingly applied in agricultural systems because of the benefits they provide in terms of plant nutrients and soil quality. However, there are few investigations of N₂O emissions following digestate application to agricultural soils using process-based models. In this study, we modified the UK-DNDC model to include digestate applications to soils by adding digestate properties to the model and considering the effect of organic fertilizer pH. Using the modified model, N₂O emissions were simulated from two organic fertilizers (digested food waste and livestock slurry) applied to three farms in the United Kingdom: one growing winter wheat at Wensum (WE) and two grasslands at Pwllpeiran (PW) and North Wyke (NW). The annual cumulative gross (i.e. not excluding control emission) N₂O emissions were calculated using MATLAB trapezoidal numerical integration. The relative errors of the modeled annual cumulative emissions to the measured emissions ranged from −5.4% to 48%. Two-factor models, including linear, exponential and hyperbola responses, correlating total N loading and soil clay content to calculations of N₂O emissions and N₂O emission factors (EFs) were developed for calculations of emission fluxes and EFs. The squares of the correlation coefficients of the measured and two-factor linear modeled emissions were 0.998 and 0.999 for digestate and slurry, respectively, and the corresponding squares of correlation coefficients of the EFs were 0.998 and 0.938. The two-factor linear model also predicted that the EFs increased linearly with decreasing clay content and the maximum EFs for digestate and slurry were 0.95 and 0.76% of total N applied, respectively. This demonstrates that the modified UK_DNDC is a good tool to simulate N₂O emission from digestate and slurry and to calculate UK EFs using TIER 3 methodology..