SummaryBy means of stimulus-response experiments with a Lif tracer, a description of the fluid flow in a 30 m3 reactor, used for anaerobic treatment of wastewater, was derived. It appeared that of the three parts that could be distinguished in the reactor (the sludge bed, the sludge blanket, and the settler), the sludge bed could be described as a combination of two perfectly mixed regions with bypassing and return flows; the sludge blanket was perfectly mixed, while the fluid flow in the settler could be described as plug flow. From experiments performed under different conditions it was concluded that 60 m3 gasiday were sufficient to provide good mixing and also that the height of the sludge bed should be 2-3 m. From this last conclusion it follows, e.g., that scale-up of the 30 m3 reactor should be done by increasing the cross section of the reactor while homogeneously distributing the influent over the bottom.

Residence-time-distribution experiments for the fluid in a 30-m(3) pilot plant and a 200-m(3) prototype upflow reactor were performed by means of continuous injection of an LiCl solution as a tracer in the influent of the reactor and measurement of the response of this stimulus on several location in the reactor and in the effluent. In a similar way as described in an article published earlier, models have been developed by use of the measured data of the fluid flow pattern which consisted of region of ideal mixing, plug flow, dead space, and short circuiting. It appeared that the fluid flow patterns in the two reactors were to a large extent analogous. For the pilot plant, three-mixer models appeared to be appropriate while for the prototype reactor two-mixer models have been found. This differences was a result of the difference in the heights of the sludge beds in the reactors: 2-3 m in the pilot plant and only 0.4 m in the prototype reactor, a result of too small an amount of sludge. Another differences was that, due to large amount of mud in the prototype reactor, a region of dead space occurred in the models for the fluid flow pattern in this reactor. The dimension of the prototype reactor have been chosen according to several recommendations obtained from work with the pilot plant (e.g., scale-up should be done by increasing the cross section of the reactor; one influent point should be applied per 5 m(2) bottom surface). The results presented here clearly show the value of these recommendations.

No abstract

A quantitative description has been presented of anaerobic treatment in an upflow reactor of dilute wastewater containing lower fatty acids as the main pollutant. It contains as its principal elements mathematical descriptions of the dynamic behavior and the distribution of both the fluid and the anaerobic sludge in the reactor, and a quantification of the kinetics of the anaerobic conversion of the organic waste and of the formation of bacterial products and methane. These elements have been taken together in mass (organic carbon) balances for the substrate, the methane, and the bacterial products, over the two most important reactor parts: the sludge bed and the sludge blanket. In the second part of this article, the description has been used for prediction and determination of the optimum reactor dimensions and process conditions. These optimum values can be used for the design of new reactors and for the establishment of the best suited process operation, which is important for obtaining the best purification results and process reliability at minimum investment and operation costs.

A model has been developed and experimentally checked for the physical behavior of sludge in the blanket in upflow reactors. The model is based on the mass balance for the sludge in the blanket, and can be used to predict the distribution of sludge in an upflow reactor in relation with the gas production, sludge settling characteristics, and the linear fluid velocity in the reactor. The quantitative values of the transport factors that are a measure of the efficiency of the transport of sludge by the fluid streams occurring in the reactor were determined experimentally in reactors of 30- and 200-m(3) volumes. As this was done for wastewater containing lower fatty acids as the main organic pollutants and for sludge with good settling characteristics, the predictive value of the model is limited. It may be used for the second (methane forming) step of anaerobic treatment of wastewater.