Modeling biogeochemical processes of phosphorus for global food supply

Harvests of crops, their trade and consumption, soil erosion, fertilization and recycling of organic waste generate fluxes of phosphorus in and out of the soil that continuously change the worldwide spatial distribution of total phosphorus in arable soils. Furthermore, due to variability in the properties of the virgin soils and the different histories of agricultural practices, on a planetary scale, the distribution of total soil phosphorus is very heterogeneous. There are two key relationships that determine how this distribution and its change over time affect crop yields. One is the relationship between total soil phosphorus and bioavailable soil phosphorus and the second is the relationship between bioavailable soil phosphorus and yields. Both of these depend on environmental variables such as soil properties and climate. We propose a model in which these relationships are described probabilistically and integrated with the dynamic feedbacks of P cycling in the human ecosystem. The model we propose is a first step towards evaluating the large-scale effects of different nutrient management scenarios. One application of particular interest is to evaluate the vulnerability of different regions to an increased scarcity in P mineral fertilizers. Another is to evaluate different regions’ deficiency in total soil phosphorus compared with the level at which they could sustain their maximum potential yield without external mineral inputs of phosphorus but solely by recycling organic matter to close the nutrient cycle.     

Bioaccessibility of polychlorinated biphenyls in different foods using an in vitro digestion method

Bioaccessibility of organic pollutants in food is important for exposure estimation and risk assessment. An in vitro enzyme digestion experiment was carried out to analyze the bioaccessibility of PCBs in different foods including freshwater fish (bighead carp and oriental weather fish) and vegetables (spinach and cabbage). The results indicated that the bioaccessibility of PCBs in freshwater fish (3%) was much lower than that in leafy vegetables (25%). Based on field survey, the daily exposure TEQ value from these two types of food was 17.9 pg/kg bw/day. However, when bioaccessibility was taken into consideration, the value decreased to 0.61 pg/kg bw/day. Therefore, the forms of PCBs existing in food strongly influenced the bioavailability for humans, which may have important implications on dietary exposure. To our knowledge, this is the first paper to illustrate the bioaccessibility of PCBs in different foods using an in vitro digestion method.     

Heterogeneity of soil surface ammonium concentration and other characteristics, related to plant specific variability in a Mediterranean-type ecosystem

Heterogeneity and dynamics of eight soil surface characteristics essential for plants—ammonium and nitrate concentrations, water content, temperature, pH, organic matter, nitrification and ammonification rates—were studied in a Mediterranean-type ecosystem on four occasions over a year. Soil properties varied seasonally and were influenced by plant species. Nitrate and ammonium were present in the soil at similar concentrations throughout the year. The positive correlation between them at the time of greatest plant development indicates that ammonium is a readily available nitrogen source in Mediterranean-type ecosystems. The results presented here suggest that plant cover significantly affects soil surface characteristics.     

Environmental impacts of different food waste resource technologies and the effects of energy mix

The environmental impacts of food waste management strategies and the effects of energy mix were evaluated using a life cycle assessment model, EASEWASTE. Three different strategies involving landfill, composting and combined digestion and composting as core technologies were investigated. The results indicate that the landfilling of food waste has an obvious impact on global warming, although the power recovery from landfill gas counteracts some of this. Food waste composting causes serious acidification (68.0 PE) and nutrient enrichment (76.9 PE) because of NH₃ and SO₂ emissions during decomposition. Using compost on farmland, which can marginally reduce global warming (−1.7 PE), acidification (−0.8 PE), and ecotoxicity and human toxicity through fertilizer substitution, also leads to nutrient enrichment as neutralization of emissions from N loss (27.6 PE) and substitution (−12.8 PE). A combined digestion and composting technology lessens the effects of acidification (−12.2 PE), nutrient enrichment (−5.7 PE), and global warming (−7.9 PE) mainly because energy is recovered efficiently, which decreases emissions including SO₂, Hg, NO_x, and fossil CO₂ during normal energy production. The change of energy mix by introducing more clean energy, which has marginal effects on the performance of composting strategy, results in apparently more loading to acidification and nutrient enrichment in the other two strategies. These are mainly because the recovered energy can avoid fewer emissions than before due to the lower background values in power generation. These results provide quantitative evidence for technical selection and pollution control in food waste management.     

Recycling for small island tourism developments: Food waste composting at Sandals Emerald Bay,Exuma, Bahamas

The ability for small islands to meet sustainability goals is exacerbated by the costs of transporting goods on, and then, wastes off the islands. At small scales, recycling can be prohibitive and complicated by labor costs; the need to profitably recycle and manage solid waste output from tourism is complicated by scale and available technologies. A multi-year study documents the amount of solid waste generated on Great Exuma (Exuma), The Commonwealth of The Bahamas since 2010 with one year of benchmarking, then limited recycling of food waste generation by an all-inclusive resort, Sandals Emerald Bay (SEB). For the island of Exuma, the rapid increase in the rate of accumulation of solid waste associated with a large destination resort has led to an increase in pests such as rats and flies, along with an increased occurrence of fires associated with unburied solid waste. Solid waste has accumulated faster than the island solid waste management can absorb. SEB kitchen and hotel operations contributes an estimated 36% of all solid waste generated on the island, about 1752 t¹ out of a total of 4841 t generated on the island in 2013 (exclusive of vegetation waste). Based on 4 weeks of benchmarking, 48.5% of all the waste coming out of the SEB resort is compostable, organic waste, but waste composition varies widely over time. Exuma Waste Management (EWM) and Recycle Exuma (RE), both privately-held Bahamian businesses, worked for one year (2012–2013) with SEB resort to implement a benchmarking and pilot recycling project to meet Earth Check green resort certification requirements. This paper outlines the costs and resources required for food waste recycling and some barriers to implementing more effective solid waste management for the tourism industry on small islands.     

Environmental sustainability assessment of food waste valorization options

Food waste can be valorized through different technologies, such as anaerobic digestion, incineration, and animal feed production. In this study we analyzed the environmental performance of two food waste valorization scenarios from a company of the retail sector in Belgium, through exergy analysis, exergetic life cycle assessment (ELCA), and a traditional life cycle assessment (LCA). In scenario 1 all food waste was considered to be valorized in an anaerobic digestion (producing electricity, heat, digestate and sorting the packaging material to be used as fuel for cement industry), while in scenario 2 a bread fraction was valorized to produce animal feed and a non-bread fraction was valorized in an anaerobic digestion (producing the same products on scenario 1, but in lower amounts). Scenario 2 was 10% more efficient than scenario 1 in the exergy analysis. For the ELCA and the single score LCA, scenario 2 presented lower environmental impacts than scenario 1 (32% and 26% lower, respectively). These results were mainly due to the avoided products from traditional supply chain (animal feed produced from agricultural products) and lower exergy loss at the feed production plant. Nevertheless, the high dry matter content of the bread waste played an important role on these results, therefore it should be pointed out that valorizing food waste to animal feed seems to be a better option only for the fractions of food waste with low water content (as bread waste).