Sludge reduction by predatory activity of aquatic oligochaetes in wastewater treatment plants: Science or fiction? A review

Biological aerobic wastewater treatment plants (WWTPs) produce a lot of excess sludge. The costs for handling this residual product are increasing, so the search for alternative techniques to reduce the amount of sludge has to be continued. Activated sludge consists of inorganic and organic substances, bacteria, protozoa and metazoa. Due to incomplete biomass conversion, sludge consumption yields less oligochaete biomass. From a technological point of view, the application of aquatic oligochaetes to reduce the sludge production offers interesting perspectives. This paper aims to review the feasibility for the reduction of activated sludge in WWTPs by means of aquatic oligochaetes. Also the current techniques concerning sludge reduction are taken into account. Several of the WWTPs relevant parameters, which may influence predatory activity of aquatic oligochaetes, are discussed: particle size, organic content of substrate, bacteria preference, life cycle and population dynamics of aquatic oligochaetes, temperature, pH, oxygen and process conditions. From the literature it appeared that most research has been performed on laboratory scale. Only a few authors mention a significant reduction of the sludge production by 'sessile' species such as Lumbriculus. Vermicultures for the reduction of activated sludge are rather common in developing countries. Incidentally large annelid blooms have been noticed in WWTPs. It remains obscure which factors trigger the initiation of annelid blooms in WWTPs and which are of importance to maintain a stable annelid population in WWTPs. The influence of a considerable worm bloom on the waste sludge production is still under investigation

Single gene locus changes perturb complex microbial communities as much as apex predator loss

Many bacterial species are highly social, adaptively shaping their local environment through the production of secreted molecules. This can, in turn, alter interaction strengths among species and modify community composition. However, the relative importance of such behaviours in determining the structure of complex communities is unknown. Here we show that single-locus changes affecting biofilm formation phenotypes in Bacillus subtilis modify community structure to the same extent as loss of an apex predator and even to a greater extent than loss of B. subtilis itself. These results, from experimentally manipulated multitrophic microcosm assemblages, demonstrate that bacterial social traits are key modulators of the structure of their communities. Moreover, they show that intraspecific genetic variability can be as important as strong trophic interactions in determining community dynamics. Microevolution may therefore be as important as species extinctions in shaping the response of microbial communities to environmental change

Modelling the removal of Cryptosporidium parvum,Giardia lamblia and enterovirussen in reservoirs

De protozoa Cryptosporidium en Giardia hebben de laatste decennia in de Verenigde Staten en in Groot-Brittannie een aanzienlijk aantal grote en kleine epidemieen van maag-darminfecties via drinkwater veroorzaakt. Wiskundige modellen kunnen worden gebruikt om de verwijdering van pathogene micro-organismen in reservoirs te simuleren. De belangrijkste verwijderings-processen in reservoirs zijn inactivatie, sedimentatie en verdunning. Dit rapport introduceert een simulatiemodel voor reservoirs (SIRES). SIRES is samengesteld uit een aantal eerste orde verwijderings-processen. De temperatuur is tot nu toe de enige variabele die de inactivatie in SIRES bepaalt. In het rapport worden de redenen hiervoor toegelicht. Ondanks deze eenvoudige aanname is er een goede overeenstemming tussen gemeten data en simulaties. Het model kan dus als een hulpmiddel dienen indien vragen met betrekking tot de procesvoering en de invloed daarvan op de verwijdering van pathogene micro-organismen in spaarbekkens moeten worden beantwoord.In the Netherlands drinking-water reservoirs are used for the storage and purification of surface waters. In recent years the importance of enteric protozoa Cryptosporidium parvum and Giardia lamblia and viruses as causes of water-borne gastroenteritis has clearly been demonstrated. Mathematical models can be used to simulate the removal of these organisms from the reservoirs. The most important removal processes are inactivation, sedimentation and dilution. This report introduces a simulation model for reservoirs (SIRES) consisting of simple first order removal processes. Because of reasons discussed in the report the temperature is the only variable which determines the inactivation of viruses and protozoa in SIRES so far. Despite this simple assumption the model predictions correlate well with actual data.DGM/DW