Evaluation of a biological wastewater treatment system combining an OSA process with ultrasound for sludge reduction.

Sludge production is an undesirable by-product of biological wastewater treatment. The oxic-settling-anaerobic (OSA) process constitutes one of the most promising techniques for reducing the sludge produced at the treatment plant without negative consequences for its overall performance. In the present study, the OSA process is applied in combination with ultrasound treatment, a lysis technique, in a lab-scale wastewater treatment plant to assess whether sludge reduction is enhanced as a result of mechanical treatment. Reported sludge reductions of 45.72% and 78.56% were obtained for the two regimes of combined treatment tested in this study during two respective stages: UO1 and UO2. During the UO1 stage, the general performance and nutrient removal improved, obtaining 47.28% TN removal versus 21.95% in the conventional stage. However, the performance of the system was seriously damaged during the UO2 stage. Increases in dehydrogenase and protease activities were observed during both stages. The advantages of the combined process are not necessarily economic, but operational, as US treatment acts as contributing factor in the OSA process, inducing mechanisms that lead to sludge reduction in the OSA process and improving performance parameters.

Sludge reduction at low ozone doses: predictive effects and full-scale study.

The activated sludge process is the most widely used wastewater treatment. The main drawback of this technology is the excess sludge production (ESP). The ozonation of sludge of the recirculation line is used to reduce the ESP. In this study, ozonation was applied on a fraction of sludge of the recirculation line in a full-scale plant (50,000 population equivalent) at a lower-specific ozone dose (SOD) compared to previous studies. The results of batch tests to predict the main effect of the technology on the biomass activities are reported. Specifically, tests at 0.7-5 g O3/kg MLVSS (mixed liquor volatile suspended solids) doses were made to evaluate the changes of the nitrification and denitrification rates, the population of phosphate-accumulating organisms and the gravitational properties. A certain reduction of the impact of ozonation on the kinetic parameters of sludge for values of SOD over 2 g O3/kg MLVSS was found. The present study highlights also the use of the ratio of ozonated biomass to total biomass as an important operative parameter for ozonation in full-scale plants. Reduction in ESP in the wastewater treatment plant was equal to 10% as dry solids applying a SOD from 1.03 to 1.63 g O3/kg MLVSS. An analysis of the economic cost of the technique is also reported.

Use of microbial activity measurements for monitoring RBC biofilms.

Fixed biomass technologies, such as rotating biological contactors or biodiscs, have been applied for wastewater depuration both in large and medium-small-sized agglomerations. Biofilm's composition and microorganism activity are essential parameters for the successful operation and control of these systems. Biofilm's thickness and total dry weight have been widely used for biofilm's characterization but, actually, are not sufficient to describe biofilm activity. In fact, biofilm's activity is not proportional to the quantity of fixed biomass, but increases with the thickness of biofilm up to a determined level called the "active thickness". Above this level, the diffusion of nutrients through the film becomes a limiting factor. A stable, thin, and active biofilm thus offers numerous advantages in water and wastewater treatment. Different parameters have been used to evaluate biofilm's activity. The specific oxygen uptake rate, INT-dehydrogenase activity, and the ratio active/total cells have been applied for that purpose. These methods are not only simple and rapid but also sensitive, precise, and representative. The results obtained confirm the potential of the microbial activity measurements studied for an accurate biofilm's characterization and biomass activity estimation in fundamental research and for the practical operation and control of fixed biomass depuration systems.

Non-ionic surfactant biodegradation in lab-scale activated sludge.

The biodegradation of a non-ionic surfactant was evaluated by the evolution of the microbial activity and the determination of the soluble surfactant present in the effluent. Two lab-activated sludge reactors/systems were fed with synthetic sewage, one of which received in addition different concentrations--5 and 10 mg/L--of nonylphenol ethoxylates (NPEO). The parameters employed in this assay were: control parameters (COD and SS) and activity microbial parameters (specific oxygen uptake rate and dehydrogenase activity). The removal of NPEO and the production of secondary metabolites were monitored. Solid-phase extraction and HPLC with fluorescence detection were employed for sample preparation and analysis. The results suggest that the microbial activity was not inhibited when 5 mg/L of NPEO was added. Nevertheless, an important inhibition of the general metabolism was observed for 10 mg/L of NPEO.