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

Abstract

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 Hydrobiologia (2008) 605:131-142 DOI 10.1007 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.

Colonization by oligochaetes (Annelida: Clitellata) in decomposing leaves ofEichhornia azurea(SW.) Kunth (Pontederiaceae) in a neotropical lentic system

“…Various species of Naidinae and Pristininae can disperse actively in the water column (Learner et al, 1978) and can thus more easily colonize different habitats, including decomposing organic material. In contrast, the Tubificinae live in direct contact with the substrate (Elissen et al, 2008) and are slow colonizers (Levin et al, 1996). In a river from a temperate region, Chauvet et al (1993) observed high biomass and regular occurrence of Tubificinae in decomposing willow leaves, which resulted in highly fragmented leaf litter, suggesting that these oligochaetes can increase the fragmentation of leaves by their movement and feeding on leaf parenchyma cells and the associated bacteria.…”

Aquatic worms eat sludge: Mass balances and processing of worm faeces

“…Initially, research focused on extending the food web with aquatic worms that naturally occur in WWTPs. However, this process proved impossible to control and high worm densities could not be maintained [3,4]. Further research therefore focused on separate worm reactors in which conditions could be optimized for the worms [2].…”

Genetic and chaetal variation in Nais worms (Annelida, Clitellata, Naididae)

“…They are a common part of the invertebrate fauna, especially in eutrophic habitats, and representatives of the group are frequently subject to ecological studies (e.g. Löhlein, 1996; van Duinen et al ., 2006; Verdonschot, 2006; Elissen et al ., 2008). Some species are cosmopolitan, others show a delimited area of distribution, and the genus appears to be more abundant in temperate zones than in tropical or subtropical regions (Sperber, 1948).…”