Älgarås avloppsreningsverk- studie och metodisk felsökning av en biobädds BOD-rening
Wastewater contains biodegradable materials, which are often measured as BOD7.Trickling filters are sometimes used as a purification step for BOD-reduction. Atrickling filter is a tower, which is filled with a carrier material. Microorganisms growon the carrier material in the form of a biofilm. This biofilm consists mostly of bacteriathat purify water from BOD.In Älgarås? wastewater treatment plant the water is purified by a trickling filter.However the treatment plant has difficulties reaching the emission requirements forBOD. The aim with this thesis has been to investigate the various parametersinfluencing the function of the trickling filter and to investigate if it is working properly.The thesis also aimed to develop proposals on how to improve the BOD purification atthe plant.The parameters measured were the load on the trickling filter, the degree of purification,the oxygenation, the dispersion of water over the trickling filter and the flow through it.In addition to this, water from the only industry that sends water to the treatment plantwas examined. The results from the measurements showed that the load of BOD variedgreatly and sometimes was far above the expected. It was also found that a sufficientdegree of purification was achieved when the BOD load of the influent was at theexpected level. The problem with high BOD values in the effluent was caused by toohigh load of BOD in the influent and too high wastewater flow, and not by thepurification ability of the trickling filter. The results of the measurements on theindustrial wastewater showed that the concentration of BOD varied greatly andtherefore seemed to be a contributor of the variations at the treatment plant.It is recommended to reduce the wastewater flow to the treatment plant and to reducethe peaks in BOD concentration. If it is not possible to get rid of the occasional highvalues of BOD in the influent, an equalization basin could be built to equalize thedifferences in the BOD concentration of the influent. To improve the capacity of thetrickling filter, actions to increase the residence time could be performed. This couldincrease the removal of BOD, but probably not to the point that the emissions standardsare always fulfilled with the current variations of BOD-concentrations.