Population dynamics of free-swimming Annelida in four Dutch wastewater treatment plants in relation to process characteristics

Free-swimming Annelida occasionally occur in very high densities in WWTPs (WasteWater Treatment Plants) and are nowadays applied for waste sludge reduction, but their growth is uncontrollable. In order to get more insight in the population dynamics of these free-swimming Annelida, and relate their presence to process characteristics, nine ATs (Aeration Tanks) of four Dutch WWTPs were regularly sampled over a 2.5-year period. For each species, peak periods in worm population growth were defined and population doubling times and half-lives calculated. Peak periods and doubling times were compared to those in natural systems. Process characteristics were obtained from the plant operators and related to the worm populations by multivariate analysis for the first time in large-scale WWTPs. The species composition in the WWTPs was limited and the most abundant free-swimming Annelida were in decreasing order Nais spp., Aeolosoma hemprichi, Pristina aequiseta, Aeolosoma variegatum, Chaetogaster diastrophus, and Aeolosoma tenebrarum.This latter species had never been found before in WWTPs. Worm absence sometimes coincided with the presence of anoxic zones, but this was possibly overcome by higher temperatures in the WWTPs. Worms were present all year round, even in winter, but no yearly recurrences of population peaks were observed, probably as a result of stable food supply and temperature, and the lack of predation in the WWTPs. Peak periods were similar between the ATs of each WWTP. The duration of the peak periods was on average 2¿3 months for each species and the population doubling times in the peak periods were short (on average 2¿6 days), which also corresponds to a stable favorable environment. The disappearance of worm populations from the WWTPs was presumably caused by declining asexual reproduction and subsequent removal with the waste sludge. Multivariate analysis indicated that 36% of the variability in worm populations was due to spatial and temporal patterns only. In addition, no more than 4% of the variability in worm populations was related to variations in process characteristics only and worm presence was usually associated with better sludge settleability. In conclusion, our data from large-scale WWTPs suggest that growth of free-swimming Annelida still seems uncontrollable and that their effects on treatment processes are unclear, which makes stable application in wastewater treatment for sludge reduction difficult

Teelt van herfstchrysanten

Mét de toegenomen belangstelling voor de teelt van snijbloemen in het algemeen, is ook de interesse voor de teelt van herfstchrysanten toegenomen. En ook nu is deze teelt favoriet als nateelt op tal van groentebedrijven. Er is echter in de loop der jaren veel veranderd; ook met betrekking tot de teelt van herfstchrysanten. De mogelijkheden in teelttechnisch opzicht zijn belangrijk vergroot, maar ook de eisen voor een goede kwaliteit zijn verscherpt. Deze teelthandleiding geeft onder andere informatie over de economische aspecten, de kasteelt, arbeid, teeltmethoden, gewasbescherming en bemesting

Effects of communal rearing and group size on breeding rabbits' post-grouping behaviour and its relation to ano-genital distance

Group housing is becoming the standard for many farm animal species, as it is seen as a more welfare friendly way of keeping gregarious animals. Aggression between female breeding rabbits currently obstructs the implementation of group housing for this species. Lack of social experience during the rearing period may be one reason why breeding rabbits can act (excessively) aggressive when grouped as adults. To study this, we either reared breeding rabbits with their same-litter siblings and mother only ("litter-only") or reared four litters and their mothers together from 18 days of life on ("communal rearing"). The litter-only rabbits were born from individually housed mothers, whereas the communally reared rabbits were born from mothers that were group housed during the last three weeks of gestation. After their first kindling, female rabbits from both rearing strategies were housed in groups of four or eight individuals (at an equal space allowance per doe) to assess rearing and group size effects on post-grouping behaviour. Within both treatments we also measured the ano-genital distance at birth (an indicator of masculinization) and studied its relation to adult agonistic behaviour. Communal rearing and larger groups were expected to decrease agonistic behaviour and wounding, whereas rabbits with a longer ano-genital distance were expected to show more offensive agonistic behaviour. The first two hypotheses were not confirmed. Communally reared and litter-only rabbits did not differ significantly in the frequency of their offensive or defensive agonistic behaviour directly post-grouping, or in the severity of wounds sustained in the first three days after grouping (P > 0.10). Communally reared rabbits sniffed/groomed their pen mates less often than litter-only rabbits (P < 0.05). A tendency for a higher frequency of offensive agonistic behaviour in larger groups was found (P < 0.10) and the decrease in defensive agonistic behaviour over time that was observed for the smaller groups was lacking in the larger groups. The third hypothesis was confirmed: female rabbits with a greater ano-genital distance at birth showed more offensive agonistic behaviour upon grouping as adults (r(s) = 0.5, P < 0.05). When this relation was studied within the separate rearing strategies, it was only confirmed within the communal rearing treatment, possibly suggesting that prenatal social stress increased both ano-genital distance and aggression. To conclude, communal rearing and larger groups did not decrease agonistic behaviour in breeding rabbits, whereas ano-genital distance measurements may be useful when selecting less aggressive breeding rabbits (although this method may be specifically applicable to communally reared rabbits). (C) 2016 Elsevier B.V. All rights reserved

Functional screening of aldehyde decarbonylases for long-chain alkane production by Saccharomyces cerevisiae

Background: Low catalytic activities of pathway enzymes are often a limitation when using microbial based chemical production. Recent studies indicated that the enzyme activity of aldehyde decarbonylase (AD) is a critical bottleneck for alkane biosynthesis in Saccharomyces cerevisiae. We therefore performed functional screening to identify efficient ADs that can improve alkane production by S. cerevisiae

Fatty Acid-Derived Biofuels and Chemicals Production in Saccharomyces cerevisiae

Volatile energy costs and environmental concerns have spurred interest in the development of alternative, renewable, sustainable and cost-effective energy resources. Advanced biofuels have potential to replace fossil fuels in supporting high-power demanding machinery such as aircrafts and trucks. Microbial biosynthesis is generally considered as an environmental friendly refinery process, and fatty acid biosynthesis is an attractive route to synthesize chemicals and especially drop-in biofuels due to the high degree of reduction of fatty acids. The robustness and excellent accessibility to molecular genetics make the yeast S. cerevisiae a suitable host for the production of biofuels, chemicals and pharmaceuticals, and recent advances in metabolic engineering as well as systems and synthetic biology allow us to engineer the yeast fatty acid metabolism and modification pathways for production of advanced biofuels and chemicals

Unfolding-Based Process Discovery

This paper presents a novel technique for process discovery. In contrast to the current trend, which only considers an event log for discovering a process model, we assume two additional inputs: an independence relation on the set of logged activities, and a collection of negative traces. After deriving an intermediate net unfolding from them, we perform a controlled folding giving rise to a Petri net which contains both the input log and all independence-equivalent traces arising from it. Remarkably, the derived Petri net cannot execute any trace from the negative collection. The entire chain of transformations is fully automated. A tool has been developed and experimental results are provided that witness the significance of the contribution of this paper.Comment: This is the unabridged version of a paper with the same title appearead at the proceedings of ATVA 201

Anti-alignments in conformance checking: the dark side of process models

Conformance checking techniques asses the suitability of a process model in representing an underlying process, observed through a collection of real executions. These techniques suffer from the wellknown state space explosion problem, hence handling process models exhibiting large or even infinite state spaces remains a challenge. One important metric in conformance checking is to asses the precision of the model with respect to the observed executions, i.e., characterize the ability of the model to produce behavior unrelated to the one observed. By avoiding the computation of the full state space of a model, current techniques only provide estimations of the precision metric, which in some situations tend to be very optimistic, thus hiding real problems a process model may have. In this paper we present the notion of antialignment as a concept to help unveiling traces in the model that may deviate significantly from the observed behavior. Using anti-alignments, current estimations can be improved, e.g., in precision checking. We show how to express the problem of finding anti-alignments as the satisfiability of a Boolean formula, and provide a tool which can deal with large models efficiently.Peer ReviewedPostprint (author's final draft

Discovering duplicate tasks in transition systems for the simplification of process models

This work presents a set of methods to improve the understandability of process models. Traditionally, simplification methods trade off quality metrics, such as fitness or precision. Conversely, the methods proposed in this paper produce simplified models while preserving or even increasing fidelity metrics. The first problem addressed in the paper is the discovery of duplicate tasks. A new method is proposed that avoids overfitting by working on the transition system generated by the log. The method is able to discover duplicate tasks even in the presence of concurrency and choice. The second problem is the structural simplification of the model by identifying optional and repetitive tasks. The tasks are substituted by annotated events that allow the removal of silent tasks and reduce the complexity of the model. An important feature of the methods proposed in this paper is that they are independent from the actual miner used for process discovery.Peer ReviewedPostprint (author's final draft

Relativistically rotating dust

Dust configurations play an important role in astrophysics and are the simplest models for rotating bodies. The physical properties of the general--relativistic global solution for the rigidly rotating disk of dust, which has been found recently as the solution of a boundary value problem, are discussed.Comment: 18 pages, 11 figure