Survival of weed seeds and animal parasites as affected by anaerobic digestion at meso- and thermophilic conditions

Anaerobic digestion of residual materials from animals and crops offers an opportunity to simultaneously produce bioenergy and plant fertilizers at single farms and in farm communities where input substrate materials and resulting digested residues are shared among member farms. A surplus benefit from this practice may be the suppressing of propagules from harmful biological pests like weeds and animal pathogens (e.g. parasites). In the present work, batch experiments were performed, where survival of seeds of seven species of weeds and non-embryonated eggs of the large roundworm of pigs, Ascaris suum, was assessed under conditions similar to biogas plants managed at meso- (37 °C) and thermophilic (55 °C) conditions. Cattle manure was used as digestion substrate and experimental units were sampled destructively over time. Regarding weed seeds, the effect of thermophilic conditions (55 °C) was very clear as complete mortality, irrespective of weed species, was reached after less than 2 days. At mesophilic conditions, seeds of Avena fatua, Sinapsis arvensis, Solidago canadensis had completely lost germination ability, while Brassica napus, Fallopia convolvulus and Amzinckia micrantha still maintained low levels (～1%) of germination ability after 1 week. Chenopodium album was the only weed species which survived 1 week at substantial levels (7%) although after 11 d germination ability was totally lost. Similarly, at 55 °C, no Ascaris eggs survived more than 3 h of incubation. Incubation at 37 °C did not affect egg survival during the first 48 h and it took up to 10 days before total elimination was reached. In general, anaerobic digestion in biogas plants seems an efficient way (thermophilic more efficient than mesophilic) to treat organic farm wastes in a way that suppresses animal parasites and weeds so that the digestates can be applied without risking spread of these pests.     

Feeding frequency and parental division of labour in the double-brooded great tit Parus major

Summary We studied the relative contribution of each sex and total effort expended in feeding nestlings in the great tit Parus major in relation to artificially altered brood size. A recent model suggests that feeding frequency should reflect the optimal trade-off between parental and fledgling survival, the former being negatively, the latter positively, influenced by high feeding frequencies. In both sexes weight loss was linearly related to feeding frequency. Since fledgling survival increases with nestling weight, the conditions of this model are fulfilled. However, in contrast to the predictions of the model, the total feeding frequency for both sexes combined did not differ between control and enlarged broods, but was lower for reduced ones. This outcome was not the result of a physiologically related inability of the parents to increase their delivery rate. Instead, we suggest that parents with enlarged broods could not find sufficient amounts of prey large enough to be economically worth transporting to the nest. Differences in brood-provisioning rates between the sexes may arise because costs and benefits of feeding nestlings may differ. Females lost more weight than males during the nesting period, but maintained a relatively higher weight during the incubation period. The relationship between weight loss and feeding frequency was similar for both sexes. Male and female brood-feeding frequency was related to brood size in a similar way. This is discussed in light of the great tit's mating system and the fact that the great tit is facultatively double-brooded.     

Social sustainability – society at the intersection of development and maintenance

Since the late 1980s, much of the debate on sustainability has been dominated by ecological perspectives. However, the last decade has seen an increasing interest in the social aspects of sustainability. While, to some extent, general consensus has been reached regarding the definitions of ecological sustainability, the definition of social sustainability is still in the making. Therefore, there is a need for conceptual frameworks and theoretical constructs in order to develop the understanding of social sustainability further. This article addresses the lack of theorisation and is composed of three different sections. The first section is a literature overview covering some of the most influential texts on social sustainability. The second section introduces and relates a number of existing, polemically constructed theoretical frameworks. In the third section, Jacques Derrida's theory of différance is used to suggest a way of understanding the relationship between the oppositional positions identified in the frameworks.     

In Search of Stability – Investigating Flexible and Stable Production Strategies for an Optimised Steel Plant

It is crucial for a steel making production system to operate at the lowest possible production cost, while satisfying stability and reliability conditions. To plan future production strategies, it is therefore important to be able to model the system behaviour when internal and external parameters are changed. In this study the sensitivity and stability of an optimised solution, of an integrated steel plant, have been investigated. The solution’s sensitivity has been analysed taking both internal process changes and external price variations into account, through applying both simulation and optimisation. The analysis also includes both costs and environmental issues such as carbon dioxide and sulphur emissions. Based on the methodology suggested, it is possible to determine the stability of the system solution, including both economic and environmental performance.