Turning food waste to energy and resources towards a great environmental and economic sustainability: An innovative integrated biological approach

Food waste (FW) management is a global conundrum because of the rapid population growth and growing economic activity. Currently, incineration and landfill are still the main means for FW management, while their environmental sustainability and economic viability have been in question. Recently, the biological processes including anaerobic digestion, aerobic composting, bioethanol fermentation, feed fermentation etc. have attracted increasing interest with the aims for energy and resource recovery from FW. However, these biological approaches have inherent drawbacks, and cannot provide a comprehensive solution for future FW management. Therefore, this review attempts to offer a critical and holistic analysis of current biotechnologies for FW management with the focus on the challenges and solutions forward. The biological approaches towards future FW management should be able to achieve both environmental sustainability and economic viability. In this instance, the concept of zero solid discharge-driven resource recovery has thus been put forward. According to which, several innovative biological processes for FW management are further elucidated with critical analysis on their engineering feasibility and environmental sustainability. It turns out that is an urgent need for turning current single task-orientated bioprocess to an integrated biological process with multiple tasks of concurrent recovery of water, resource and energy together with zero-solid discharge.     

Root sprouting in Rumex acetosella under different nutrient levels

Growth of Rumex acetosella, a root sprouting plant, was studied in a pot experiment. Each plant of R. acetosella consisted of two ramets which were interconnected by a root about 9 cm long. One of the ramets was placed in a compartment with nutrient-rich soil, the other with nutrient-poor soil. The root connection between the ramets either remained intact or was severed at the nutrient interface after planting. Growth of new roots was prevented at the nutrient interface.The presence of a connection between the ramets did not affect biomass or shoot production in either soil compartment, indicating a poor integration of the interconnected plant systems. In the nutrient-rich environment, two to four times more shoots and biomass were produced than in the low nutrient regime. A large proportion of buds initiated on roots remained dormant, forming a bud bank. When the number of shoots or buds was expressed per g of root dry weight or per m of root length, the nutrient response was no longer evident or, in a few cases, a significant effect in the opposite direction was obtained. These results show that the greater production of buds and shoots in the nutrient-rich environment reflected an allometric relationship between root biomass and the number of buds and shoots initiated on the roots.     

Differential sectoriality in long-distance transport in temperate tree species: evidence from dye flow, <Superscript>15</Superscript>N transport,and vessel element pitting

The capture of patchily distributed nutrients by tree roots has received extensive research, but the fate of those nutrients has not. We performed experiments to determine if nutrient transport within tree species is preferentially transported from specific roots to specific branches. Saplings of five species with contrasting growth requirements were examined: two Betula species (B. papyrifera and B. lenta), Populus tremuloides, and two Acer species (A. saccharum and A. rubrum). To quantify patterns of long-distance transport, we examined the accumulation of safranin-O dye and ¹⁵N in branches when these tracers were applied to isolated lateral roots (dye and ¹⁵N) and to the main root system (¹⁵N). Because transport of nutrients between sectors requires flow through intervessel pit pairs of adjacent xylem vessel elements, we quantified the area of intervessel pits, the number of pits per unit vessel wall area, and the % vessel wall area as pits in Acer and Betula. We found that the two Betula species were integrated (tracers applied to isolated roots were likely to accumulate in all branches), while P. tremuloides and the two Acer species were sectorial (tracer accumulation was more concentrated in particular branches). Betula had the largest number of intervessel pits per unit vessel wall area and the largest percentage of vessel wall area as pits. The high density of bordered pits may explain the ease of tracer movement throughout the two Betula species. Greater integration may allow certain trees (e.g., Betula) to exploit nutritionally patchy environments such as rocky soils, and may alter plant-herbivore interactions.     

Arbuscular mycorrhizal fungi colonize decomposing leaves of<Emphasis Type="Italic"> Myrica parvifolia</Emphasis>,<Emphasis Type="Italic"> M. pubescens</Emphasis> and<Emphasis Type="Italic"> Paepalanthus</Emphasis> sp.

Hyphae and vesicles of arbuscular mycorrhizal fungi (AMF) were found within the decomposing leaves of Myrica parvifolia, M. pubescens and Paepalanthus sp. at three montane sites in Colombia. Hyphae, vesicles, and arbuscule-like structures were also found within scale-like leaves of the rhizomes of Paepalanthus sp. The litter found in the vicinity of the roots was divided into three decomposition layers. The highest AMF colonization occurred in the most decomposed leaves, which were in close association with roots. In contrast, there were no differences in AMF colonization of roots present in the different decomposition layers. Colonization of decomposing leaves by AMF did not differ between the two closely related species M. parvifolia and M. pubescens, nor between two sites (Guatavita and Zipacón, Colombia) differing in soil fertility. Occurrence of vesicles in decomposing leaves was correlated with abundant AMF extraradical hyphae among the leaves. We propose that AMF enter decomposing leaves mechanically through vascular tissue. As a consequence, AMF are well positioned to obtain and efficiently recycle mineral nutrients released by decomposer microorganisms before their loss by leaching or immobilization in soil.     

Mass-transfer-limited nitrate uptake on a coral reef flat,Warraber Island,Torres Strait,Australia

Previous research has identified a relationship between the rate of dissipation of turbulent kinetic energy, , and the mass-transfer-limited rate of uptake by a surface, herein called the ^1/4 law, and suggests this law may be applicable to nutrient uptake on coral reefs. To test this suggestion, nitrate uptake rate and gravitational potential energy loss have been measured for a section of Warraber Island reef flat, Torres Strait, northern Australia. The reef flat section is 3 km long, with a 3 m tidal range, and on the days measured, subject to 6 m s^–1 tradewinds. The measured nitrate uptake coefficient, S , on two consecutive days during the rising tide was 1.23±0.28 and 1.42±0.52×10^–4 m s^–1. The measured loss of gravitational potential energy across the reef flat, GPE , on the same rising tides over a 178 m section was 208±24 and 161±20 kg m^–1 s^–2. Assuming the GPE is dissipated as turbulent kinetic energy in the water column, and using the ^1/4 law, the mass-transfer-limited nitrate uptake coefficient, S_MTL , on the two days was 1.57±0.03 and 1.45±0.04×10^–4 m s^–1. Nitrate uptake on Warraber Island reef flat is close to the mass-transfer limit, and is determined by oceanographic nitrate concentrations and energy climate.Communicated by B.C. Hatcher     

Genotype-specific response of a lycaenid herbivore to elevated carbon dioxide and phosphorus availability in calcareous grassland

Effects of elevated CO₂ and P availability on plant growth of the legume Lotus corniculatus and consequences for the butterfly larvae of Polyommatus icarus feeding on L. corniculatus were investigated in screen-aided CO₂ control chambers under natural conditions on a calcareous grassland in the Swiss Jura mountains. Elevated CO₂ conditions and P fertilisation increased the biomass production of L. corniculatus plants and affected the plant chemical composition. CO₂ enrichment increased the C/N ratio and sugar concentration and decreased the N and P concentrations. C- and N-based allelochemicals (cyanoglycosides, total polyphenols and condensed tannins) were only marginally affected by CO₂ enrichment. P fertilisation increased the specific leaf area and concentrations of water, N, sugar and P, while the C/N ratio and the concentration of total polyphenols decreased. Furthermore, P availability marginally enhanced the effect of elevated CO₂ on the total dry mass and sugar concentration while the opposite occurred for the total polyphenol concentration. The changes in food-plant chemistry as a result of P fertilisation positively affected larval mass gain and accelerated the development time of P. icarus. Only a marginal negative effect on larval mass gain was found for CO₂ enrichment. However, we found genotype-specific responses in the development time of P. icarus to elevated CO₂ conditions. Larvae originating from different mothers developed better either under elevated CO₂ or under ambient CO₂ but some did not react to CO₂ elevation. As far as we know this is the first finding of a genotype-specific response of an insect herbivore to elevated CO₂ which suggests genetic shifts in insect life history traits in response to elevated CO₂.     

The effects of mixotrophy on the stability and dynamics of a simple planktonic food web model

Recognition of the microbial loop as an important part of aquatic ecosystems disrupted the notion of simple linear food chains. However, current research suggests that even the microbial loop paradigm is a gross simplification of microbial interactions due to the presence of mixotrophs-organisms that both photosynthesize and graze. We present a simple food web model with four trophic species, three of them arranged in a food chain (nutrients-autotrophs-herbivores) and the fourth as a mixotroph with links to both the nutrients and the autotrophs. This model is used to study the general implications of inclusion of the mixotrophic link in microbial food webs and the specific predictions for a parameterization that describes open ocean mixed layer plankton dynamics. The analysis indicates that the system parameters reside in a region of the parameter space where the dynamics converge to a stable equilibrium rather than displaying periodic or chaotic solutions. However, convergence requires weeks to months, suggesting that the system would never reach equilibrium in the ocean due to alteration of the physical forcing regime. Most importantly, the mixotrophic grazing link seems to stabilize the system in this region of the parameter space, particularly when nutrient recycling feedback loops are included.     

Nutrient mobilization and processing in Sonoran desert riparian soils following artificial re-wetting

Research in river-floodplain systems has emphasized the importance of nutrient delivery by floodwaters, but the mechanisms by which floods make nutrients available are rarely evaluated. Using a laboratory re-wetting experiment, we evaluated the alternative hypotheses that increased nutrient concentrations in riparian groundwater during flash floods are due to (H1) elevated nutrient concentrations in surface floodwaters entering the riparian zone or (H2) re-mobilization of nutrients from riparian soils. We sampled soils from the riparian zone of a 400m reach of Sycamore Creek, AZ. Two sub-samples from each soil were re-wetted with a solution that mimicked the chemistry of floodwaters, with one sub-sample simultaneously treated with a biocide. We also measured structural characteristics of soils (texture, organic matter, moisture, and extractable nutrients) to investigate relationships between these characteristics and response to re-wetting. Riparian soils exhibited considerable variation in physical and chemical structure. Soil organic matter, moisture, and texture co-varied among samples. Re-wetting increased concentrations of nitrate and ammonium, and decreased SRP, relative to initial concentrations. Live soils were significantly lower in NO3-and SRP than biocide-treated samples. Extractable DIN pools were the best predictors of mobilization, and soil organic matter was strongly correlated with nitrate losses, probably via its relationship with microbial uptake. Nutrient mobilization and processing also varied considerably with depth, lateral position, and among plots. We estimate that 70–80% of N in riparian groundwater during flash floods is re-mobilized from riparian soils, but are unable to reject the hypothesis that flood inputs may be important sources of nutrients to riparian soils over longer time scales.     

Is the Iron Gate I reservoir on the Danube River a sink for dissolved silica?

Damming rivers changes sediment and nutrient cycles downstream of a dam in many direct and indirect ways. The Iron Gates I reservoir on the Yugoslavian-Romanian border is the largest impoundment by volume on the Danube River holding 3.2billionm³ of water. Silica retention within the reservoir in the form of diatom frustules was postulated to be as high as 600ktyear^–1 in previous studies using indirect methods. This amount of dissolved silicate was not delivered to the coastal Black Sea, and presumably caused a shift in the phytoplankton community there, and subsequent drastic decline in fishery. We directly quantified the amount of dissolved silicate (DSi) entering and leaving the reservoir for 11 continuous months. The budget based on these data reveals two important facts: (1) only about 4% of incoming DSi was retained in the reservoir; (2) the DSi concentrations were relatively low in the rivers upstream of the reservoir compared to regional and global averages. Thus damming the Danube at the Iron Gates could not have caused the decline in DSi concentrations documented downstream of the impoundment. Rather, this change in DSi must have occurred in the headwaters of the Danube River. Potential reasons include the construction of many dams upstream of the Iron Gates, hydrologic changes resulting in lower groundwater levels, and clogging of the riverbed limiting groundwater–river exchange.     

Nitrogen processing in the hyporheic zone of a pastoral stream

The distribution of nitrogen-transforming processes, and factors controlling their rates, were determined within the hyporheic zone of a lowland stream draining agricultural land. In the field, physicochemical parameters were measured along a 10m-long hyporheic flow line between downwelling and upwelling zones. Sediment cores were retrieved from the stream bed surface, and from 20, 40 and 60cm deep in each zone, and in the laboratory, water from the corresponding depth was percolated through each core at the natural flow rate. Concentrations of nitrogen species and oxygen were measured before and after flow through each core. Denitrification was measured using a ¹⁵N-nitrate tracer. Shallow and downwelling zone samples were clearly distinct from deeper and upwelling zone samples in terms of physicochemical conditions, microbial processes and factors controlling nitrogen processing. Denitrification was highest in surface and downwelling zone cores, despite high oxygen levels, probably due to high pore-water nitrate concentrations in these cores and isolation of the denitrifying bacteria from oxygen in the bulk water by the hyporheic biofilms. Denitrification was limited by oxygen inhibition in the downwelling group, and by nitrate availability in the upwelling group. Strong evidence indicated that dissimilatory nitrate reduction to ammonium, occurred in almost all cores, and outcompeted denitrification for nitrate. In contrast, nitrification was undetectable in all but two cores, probably because of intense competition for oxygen. Field patterns and lab experiments indicated that the hyporheic zone at this moderately N-rich site is a strong sink for nitrate, fitting current theories that predict where hyporheic zones are nitrate sinks or nitrate sources.