Environmental impacts and nutrient distribution routes for food waste separated disposal on large-scale anaerobic digestion/ composting plants

Centralized biological treatments, i.e., anaerobic digestion (AD) and in-vessel composting (IVC), were supposed to be the promising processes for the disposal of food waste (FW) after source separation, while the systematic benefits were unclear for FW with high water content, salt and oil and thus influenced the selection by the local decision-makers. In this study, two large-scale working AD and IVC plants were compared for environmental impacts, nutrient recovery and economic benefits. For unit amount of FW, 89.26 kg CO₂-eq was released in IVC mainly due to 47.89 kWh electricity consumption, and 57.02 kg CO₂-eq was produced in AD. With the application of compost and energy recovery, 26.88 and 93.55 kg CO₂-eq savings were obtained in IVC and AD, respectively. NH₃ emissions were the main contributor to acidification (0.35 kg SO₂-eq) in IVC, while AD exerted less impact on acidification (0.09 kg SO₂-eq) and nutrient enrichment (0.25 kg NO₃-eq) attributed to the counteract of energy recovery. 2029 would be the inflection point for global warming potential in AD with more clean energy applied in electricity mix in China. For nutrient recovery, more C (8.3%), N (37.9%) and P (66.7%) could be recovered in compost, while those were discharged via leachate and biogas residue in AD. The cost of IVC was 16 CNY/t (2.40 USD/t) lower than AD. Combing the three key indexes and the sale routes of products, IVC was recommended to be used in areas dominated by agriculture and forestry industries, and AD was more suitable for large cities.

In-vessel composting of HMX and RDX contaminated sludge using microbes isolated from contaminated site

Current study was carried out with an objective to remediate highly contaminated sludge with HMX and RDX obtained from an explosive manufacturing facility in North India employing indigenous microbes, Arthrobacter subterraneus (isolate no. S2-TSB-17) and Bacillus sonorensis (isolate no. S8-TSB-4) which were isolated from the same contaminated site. In-vessel composting of the explosive contaminated sludge was performed in 12 different bioreactors using cow manure and garden waste as bulking agents. 78.5% degradation of HMX was observed in reactor no. 2 with Bacillus sonorensis having combination of 10% sludge, 70% cow manure and 20% garden waste on 80th day. Two secondary metabolites Bis(hydroxymethyl)nitramine and methylene dinitramine were identified while studying the degradation pathway. Similarly, degradation of 91.2% was observed for RDX in reactor no. 11 with consortia of Arthrobacter subterraneus and Bacillus sonorensis on 80th day. During the study, release of significant nitrate and nitrite ions were observed. It has already been established that RDX and HMX degradation leads to release of nitrite/nitrate ions. The highest nitrite (reactor no. 11) and nitrate (reactor no. 2) release observed were 24.02 ± 0.05 mg/kg and 30.65 ± 0.99 mg/kg on 50th and 70th day, respectively. Scanning electron microscopic studies confirmed the attachment and presence of microbes with solid surface and no deformation in structure was observed in the microbial cells due to contamination stress. Findings of the study concluded that in-vessel composting assisted with native bacterial species can be a potential technology for the treatment of explosive contaminated sludge at the contaminated sites.

Assessing the economic and environmental sustainability of household food waste management in the UK: Current situation and future scenarios

The value embedded in food waste is increasingly being recognised, with the UN targeting a 50% reduction in consumer food waste and the EU recycling of 60% of all household waste, both by 2030. Aiming to provide guidance on the most sustainable food waste utilisation routes, this study evaluates the life cycle environmental and economic sustainability of five plausible scenarios for the year 2030. Focusing on the UK for context, these are compared to the current treatment of food waste as well as to its potential future prevention. The scenarios consider a differing share of four widely-used treatment methods: anaerobic digestion, in-vessel composting, incineration and landfilling. The scenario with the highest anaerobic digestion share that recovers both heat and electricity is the best option for seven out of 19 environmental impacts and the second best for life cycle costs. Upgrading anaerobic digestion biogas to biomethane achieves the lowest global warming potential and life cycle costs. Net-negative global warming potential (savings) can be achieved if the heat from anaerobic digestion and incineration or biomethane are utilised to displace natural gas. Displacing a future electricity mix does not lead to significant global warming potential savings due to the expected grid decarbonisation. However, savings are still achieved for metal depletion and human and terrestrial toxicities as they are higher for decarbonised grid electricity due to the increased share of renewables. A greater share of in-vessel composting leads to higher impacts because of the high electricity consumption. Landfill reduction has an economic advantage for all the scenarios, except for the business-as-usual, with life cycle costs 11-75% lower than for the current situation. While future scenarios improve the overall sustainability compared to the current situation, halving food waste by 2030 can save 15 times more greenhouse gas emissions than the best treatment scenario without waste reduction. Therefore, any commitments to improve the sustainability of food waste treatment must be accompanied by an effective waste prevention strategy. The outcomes of this work can help waste treatment operators and policy makers towards more sustainable food waste management. Although the focus is on UK situation, the overall conclusions and recommendations are applicable to other regions.

Using polyethylene sleeves with forced aeration for composting olive mill wastewater pre-absorbed by vegetative waste

Composting in closed polyethylene sleeves with forced aeration may minimize odor emissions, vectors attraction and leachates associated with open windrows. The present study demonstrates the use of this system for composting olive mill wastewater (OMW), the undesired stream associated with the olive milling industry. A polyethylene sleeve of 1.5-m diameter and ca. 20-m long was packed with shredded municipal green waste which was pre-soaked in OMW for 72 h. Process conditions were controlled by means of a programmable logic controller (PLC) equipped with temperature and oxygen sensors. Thermophilic temperatures (>45 °C) were maintained for one month followed by temperatures in the range of 30-40 °C, ca. 20 °C above ambient temperature, for a period of 3.5 months. Oxygen levels were controlled and the system was kept aerobic. Water content gradually decreased with sufficient levels for efficient composting. The finished compost was non-phytotoxic to Cress (Lepidium sativum L.) in a lab bioassay. It was also found suitable as an ingredient in peat, tuff, and coir based growing media, evaluated by plant growth tests with basil and ornamental plants. The viability of this approach for disposing off OMW is much dependent on the liquid absorption capacity of the vegetative waste.

Synergistic effect of fly ash in in-vessel composting of biomass and kitchen waste

The present study aims to utilize coal fly ash for its property to adsorb heavy metals and thus reducing the bioavailability of the metals for plant uptake. Fly ash was incorporated into the in-vessel composting system along with organic waste. The in-vessel composting experiments were conducted in ten plastic vessels of 15 L capacity comprising varying proportions of biomass waste, kitchen waste and fly ash. In this study, maximum degradation of organic matter was observed in Vessel 3 having k value of 0.550 d^-1. In vessel 10, 20% fly ash with a combination of 50% biomass waste and 30% kitchen waste along with the addition of 5% jaggery as an additive produced the best outcome with least organic matter (%C) loss and lowest value of rate constant (k).

Evaluation of pilot-scale in-vessel composting for Hanwoo manure management

The study investigated the effect of in-vessel composting process on Hanwoo manure in two different South Korea regions (Pyeongchang and Goechang) with sawdust using vertical cylindrical in-vessel bioreactor for 42days. The stability and quality of Hanwoo manure in both regions were improved and confirmed through the positive changes in physico-chemical and phytotoxic properties using different commercial seed crops. The pH and electrical conductivity (EC, ds/m) of composted manure in both regions were slightly increased. At the same time, carbon:nitrogen (C:N) ratio and ammonium nitrogen:nitrate nitrogen (NH₄⁺-N:NO₃^--N) ratio decreased to 13.4-16.1 and 0.36-0.37, respectively. The germination index (GI, %) index was recorded in the range of 67.6-120.9%, which was greater than 50%, indicating phytotoxin-free compost. Although, composted manure values in Goechang region were better in significant parameters, overall results confirmed that the composting process could lead to complete maturation of the composted product in both regions.

Composting municipal biosolids in polyethylene sleeves with forced aeration: Process control, air emissions, sanitary and agronomic aspects

Composting in polyethylene sleeves with forced aeration may minimize odor emissions, vectors attraction and leachates associated with open windrows. A disadvantage of this technology is the lack of mixing during composting, potentially leading to non-uniform products. In two pilot experiments using biosolids and green waste (1:1; v:v), thermophilic conditions (>45°C) were maintained for two months, with successful control of oxygen levels and sufficient moisture. Emitted odors declined from 1.5-3.8×10⁵ to 5.9×10³-2.3×10⁴ odor units m^-3-air in the first 3weeks of the process, emphasizing the need of odor control primarily during this period. Therefore, composting might be managed in two phases: (i) a closed sleeve for 6-8weeks during which the odor is treated; (ii) an open pile (odor control is not necessary). Reduction of salmonella, E. coli and coliforms was effective initially, meeting the standards of "Class A" biosolids; however, total and fecal coliforms density increased after opening the second sleeve and exceeded the standard of 1000 most probable number (MPN) per g dry matter. Compost maturity was achieved in the open piles following the two sleeves and the final compost was non-phytotoxic and beneficial as a soil additive.

Environmental and economic analysis of an in-vessel food waste composting system at Kean University in the U.S

A composting system provides many benefits towards achieving sustainability such as, replacing fertilizer use, increasing the quantity of produce sold, and diverting organic wastes from landfills. This study delves into the many benefits a composting system provided by utilizing an established composting system at Kean University (KU) in New Jersey, as a scale project to examine the composters' environmental and economic impacts. The results from the study showed that composting food wastes in an in-vessel composter when compared to typical disposal means by landfilling, had lower impacts in the categories of fossil fuel, GHG emissions, eutrophication, smog formation and respiratory effects; whereas, its had higher impacts in ozone depletion, acidification human health impacts, and ecotoxicity. The environmental impacts were mainly raised from the manufacturing of the composter and the electricity use for operation. Applying compost to the garden can replace fertilizers and also lock carbon and nutrients in soil, which reduced all of the environmental impact categories examined. In particular, the plant growth and use stage reduced up to 80% of respiratory effects in the life cycle of food waste composting. A cost-benefit analysis showed that the composting system could generate a profit of $13,200 a year by selling vegetables grown with compost to the student cafeteria at Kean and to local communities. When educational and environmental benefits were included in the analysis, the revenue increased to $23,550. The results suggest that in-vessel composting and the subsequent usage of a vegetable garden should be utilized by Universities or food markets that generate intensive food wastes across the U.S.

Variability in physical contamination assessment of source segregated biodegradable municipal waste derived composts

Physical contaminants (glass, metal, plastic and 'other') and stones were isolated and categorised from three finished commercial composts derived from source segregated biodegradable municipal waste (BMW). A subset of the identified physical contaminant fragments were subsequently reintroduced into the cleaned compost samples and sent to three commercial laboratories for testing in an inter-laboratory trial using the current PAS100:2011 method (AfOR MT PC&S). The trial showed that the 'other' category caused difficulty for all three laboratories with under reporting, particularly of the most common 'other' contaminants (paper and cardboard) and, over-reporting of non-man-made fragments. One laboratory underreported metal contaminant fragments (spiked as silver foil) in three samples. Glass, plastic and stones were variably underreported due to miss-classification or over reported due to contamination with compost (organic) fragments. The results are discussed in the context of global physical contaminant test methods and compost quality assurance schemes.

Static, dynamic and inoculum augmented respiration based test assessment for determining in-vessel compost stability

The purpose of this work was to evaluate compost (and related industry) stability tests given recent large-scale changes to feedstock, processing techniques and compost market requirements. Five stability tests (ORG0020, DR4, Dewar self-heating, oxygen update rate (OUR) and static respiration) were evaluated on composts from ten in-vessel composting sites. Spearman rank correlation coefficients were strong for the ORG0020, OUR and DR4 (both CO2 and O2 measurement), however, OUR results required data extrapolation for highly active compost samples. By comparison the Dewar self-heating and static respiration tests had weaker correlations, in part the result of under reporting highly active, low pH samples. The findings suggest that despite differences in pre-incubation period both dynamic respiration tests (ORG0020 and DR4) are best suited to deal with the wide range of compost stabilities found.