Sustainable management of food waste; pre-treatment strategies, techno-economic assessment, bibliometric analysis, and potential utilizations: A systematic review.

Food waste (FW) contains many nutritional components such as proteins, lipids, fats, polysaccharides, carbohydrates, and metal ions, which can be reused in some processes to produce value-added products. Furthermore, FW can be converted into biogas, biohydrogen, and biodiesel, and this type of green energy can be used as an alternative to nonrenewable fuel and reduce reliance on fossil fuel sources. It has been demonstrated in many reports that at the laboratory scale production of biochemicals using FW is as good as pure carbon sources. The goal of this paper is to review approaches used globally to promote turning FW into useable products and green energy. In this context, the present review article highlights deeply in a transdisciplinary manner the sources, types, impacts, characteristics, pre-treatment strategies, and potential management of FW into value-added products. We find that FW could be upcycled into different valuable products such as eco-friendly green fuels, organic acids, bioplastics, enzymes, fertilizers, char, and single-cell protein, after the suitable pre-treatment method. The results confirmed the technical feasibility of all the reviewed transformation processes of FW. Furthermore, life cycle and techno-economic assessment studies regarding the socio-economic, environmental, and engineering aspects of FW management are discussed. The reviewed articles showed that energy recovery from FW in various forms is economically feasible.

Rice straw for energy and value-added products in China: a review.

The rise of global waste and the decline of fossil fuels are calling for recycling waste into energy and materials. For example, rice straw, a by-product of rice cultivation, can be converted into biogas and by-products with added value, e.g., biofertilizer, yet processing rice straw is limited by the low energy content, high ash and silica, low nitrogen, high moisture, and high-quality variability. Here, we review the recycling of rice straw with focus on the global and Chinese energy situations, conversion of rice straw into energy and gas, biogas digestate management, cogeneration, biogas upgrading, bioeconomy, and life cycle assessment. The quality of rice straw can be improved by pretreatments, such as baling, ensiling, and co-digestion of rice straw with other feedstocks. The biogas digestate can be used to fertilize soils. The average annual potential energy of collectable rice straw, with a lower heating value of 15.35 megajoule/kilogram, over the past ten years (2013-2022) could reach 2.41 × 109 megajoule.

Understanding the environmental impacts of biogas utilization for energy production through life cycle assessment: An action towards reducing emissions.

Unlike renewable energy sources, burning fossil fuels has severe environmental impacts, such as greenhouse gas (GHG) emissions and climate change. Therefore, this study was conducted to assess and compare the environmental impacts of three biogas utilization scenarios for energy production. The life cycle assessment (LCA) method was used to compare (i) biogas combustion in combined heat and power (CHP) unit, (ii) biogas burning in a steam boiler, and (iii) biogas upgrading using pressure swing adsorption (PSA) unit to determine the most sustainable option. The results revealed that the upgrading scenario was the best option, achieving emission savings in 8 out of 10 investigated impact categories. Among them, the emission saving was the highest in the marine aquatic ecotoxicity category (-4276.97 kg 1,4-DB eq./MJ). The CHP scenario was the second-best option, followed by the boiler scenario (worst option), and both had the most beneficial performance in the ozone depletion potential category with 6.29E-08 and 9.88E-08 kg CFC-11-eq./MJ, respectively. The environmental burdens of the boiler scenario were the highest in the marine aquatic ecotoxicity category (248.92 kg 1,4-DB eq./MJ). Although the CHP and boiler scenarios contributed to environmental burdens in all impact categories, they achieved beneficial performances compared to fossil fuel-based systems.

A comparative environmental life cycle assessment of rice straw-based bioenergy projects in China.

Bioenergy is a promising solution for greenhouse gas (GHG) emissions mitigation. However, the emissions resulting from the different production stages must be quantified and evaluated. The life cycle assessment (LCA) method was used to compare and quantify the environmental burdens of three rice straw (RS) utilization scenarios for producing biogas, briquette fuel, and syngas. To our knowledge, this is the first study that applies the LCA approach to assess these three bioenergy scenarios in a single study where the main goal was to determine the most sustainable option. A total of 10 mid-point impact categories were investigated. The results indicated that the three scenarios achieved net positive energy and net negative GHG balances. The briquette fuel scenarios had the highest net energy balance (11,115 MJ/tonne dry RS), while the syngas scenario had the highest net GHG (-2,315 kg CO2-eq./tonne dry RS). Moreover, the syngas scenario was the most beneficial to the environment, achieving negative results in 9 out of the 10 impact categories; the largest was marine ecotoxicity (-853,897 kg 1,4-DB-eq./tonne dry RS). The biogas scenario achieved emission savings in 3 out of the 10 categories. Although the briquette fuel scenario had no negative values in the 10 categories, its overall contribution to environmental burdens was relatively low. Overall, the order of the three scenarios in terms of the most sustainable option is syngas > briquette fuel > biogas.

Performance of Paracoccus pantotrophus MA3 in heterotrophic nitrification-anaerobic denitrification using formic acid as a carbon source.

Excess amount of nitrogen in wastewater has caused serious concerns, such as water eutrophication. Paracoccus pantotrophus MA3, a novel isolated strain of heterotrophic nitrification-anaerobic denitrification bacteria, was evaluated for nitrogen removal using formic acid as the sole carbon source. The results showed that the maximum ammonium removal efficiency was observed under the optimum conditions of 26.25 carbon to nitrogen ratio, 3.39% (v/v) inoculation amount, 34.64 °C temperature, and at 180 rpm shaking speed, respectively. In addition, quantitative real-time PCR technique analysis assured that the gene expression level of formate dehydrogenase, formate tetrahydrofolate ligase, 5,10-methylenetetrahydrofolate dehydrogenase, serine hydroxymethyltransferase, respiratory nitrate reductase beta subunit, L-glutamine synthetase, glutamate dehydrogenase, and glutamate synthase were up-regulated compared to the control group, and combined with nitrogen mass balance analysis to conclude that most of the ammonium was removed by assimilation. A small amount of nitrate and nearly no nitrite were accumulated during heterotrophic nitrification. MA3 exhibited significant denitrification potential under anaerobic conditions with a maximum nitrate removal rate of 4.39 mg/L/h, and the only gas produced was N2. Additionally, 11.50 ± 0.06 mg/L/h of NH4+-N removal rate from biogas slurry was achieved.

Agro-environmental sustainability of using digestate fertilizer for solanaceous and leafy vegetables cultivation: Insights on fertilizer efficiency and risk assessment.

Digestate generated from anaerobic digestion (AD) has been widely used as digestate fertilizer (DF) for plant growth, but its application should be comprehensively investigated. This study evaluates the effects of different amounts of DF on crop growth, nutrient use efficiency (NUE), soil properties, and potential negative impacts of DF application (salinity and heavy metals (HMs)) with two different crops (Eggplant and Shanghai cabbage). In eggplant cultivation, the yield increased with the increase of DF amount, and the yield of the DF-680 group was the highest (65.4 t/ha) under the highest fertilizer amount. However, due to high ammonia volatilization loss and excessive application, the NUE of DF was only about half of that of chemical fertilizer (CF). Significantly different from eggplant, the high application amount of DF resulted in yield reduction in Shanghai cabbage cultivation. The yield and NUE of the DF-170 group were the highest, the yield was 46.5 t/ha, and the NUE was more than twice compared to CF. Moreover, DF can raise soil nitrogen storage and alleviate soil acidification caused by fertilization in both batches of cultivation. Nevertheless, the electrical conductivity (EC) value of the soil was increased by 2-3 times, and the long-term application may lead to soil salinization. On the other hand, the increase of DF application elevated the content of copper (Cu), zinc (Zn), and cadmium (Cd) in soil significantly but did not cause HMs contamination in crops and tillage soil. In summary, reasonable application amounts and methods should be considered when applying DF.

Heavy Metals and Pesticides Toxicity in Agricultural Soil and Plants: Ecological Risks and Human Health Implications.

Environmental problems have always received immense attention from scientists. Toxicants pollution is a critical environmental concern that has posed serious threats to human health and agricultural production. Heavy metals and pesticides are top of the list of environmental toxicants endangering nature. This review focuses on the toxic effect of heavy metals (cadmium (Cd), lead (Pb), copper (Cu), and zinc (Zn)) and pesticides (insecticides, herbicides, and fungicides) adversely influencing the agricultural ecosystem (plant and soil) and human health. Furthermore, heavy metals accumulation and pesticide residues in soils and plants have been discussed in detail. In addition, the characteristics of contaminated soil and plant physiological parameters have been reviewed. Moreover, human diseases caused by exposure to heavy metals and pesticides were also reported. The bioaccumulation, mechanism of action, and transmission pathways of both heavy metals and pesticides are emphasized. In addition, the bioavailability in soil and plant uptake of these contaminants has also been considered. Meanwhile, the synergistic and antagonistic interactions between heavy metals and pesticides and their combined toxic effects have been discussed. Previous relevant studies are included to cover all aspects of this review. The information in this review provides deep insights into the understanding of environmental toxicants and their hazardous effects.

Advanced pre-treatment of stripped biogas slurry by polyaluminum chloride coagulation and biochar adsorption coupled with ceramic membrane filtration.

Biogas slurry retention is a critical problem that cannot be solved by using the reuse method. Therefore, a new approach was taken to compensate for the shortcomings in the reuse method. In this study, after ammonia stripping, the ammonia nitrogen concentration in the stripped biogas slurry (SBS) still cannot reach the effluent standard (80 mg/L), so a variety of processes were needed to treat the SBS. Polyaluminum chloride (PAC) and rice husk biochar (B) were used to pretreat SBS. The effect of different pre-treatments on the COD value, ammonia nitrogen concentration, turbidity, total phosphorus (TP), and other indicators was investigated. After different pre-treatments by PAC and biochar, the pretreated SBS was filtered by a ceramic membrane, and the indicators of SBS were removed in the next step. After adding PAC and biochar together, ammonia nitrogen concentration was decreased to 68.09 mg/L, with a removal rate of 63%. The total phosphorus (TP) was also decreased, and its removal rate reached 92.5%. When the SBS was pretreated with PAC and biochar and then filtered through a ceramic membrane under different operating pressures, the removal rates of COD, total nitrogen (TN), turbidity, and suspended solids (SS) reached 81%, 88%, 96%, and 99% respectively. Moreover, by increasing the pressure from 0.1 to 0.3 MPa, the membrane flux was improved from 45 to 100.6 L/m2·h. This study proves that the combined pre-treatments of PAC and biochar can comprehensively remove various indicators from SBS while ensuring membrane flux during the membrane filtration process.