By two Sewage Treatment Plants it is demonstrated that a fully biological wastewater treatment without external energy supply is possible provided there is a sufficient natural gradient to guarantee a free flow through the entire plant. Both plants have now been in operation for more than 2 years. Test results show a very good purification efficiency. Elimination of BOD5 is over 93%, of COD 84%, of TOC 86%, of NH4 66 % and that of nitrogen totals 29%. The results of the two-year operation of both plants prove that also smaller units allow for meeting all requirements to obtain a good purification efficiency. Especially pre-settling and final clarifying ponds with interposed trickling filters represent a very simple but economic addition to the ample variety of modern wastewater techniques. It has also been demonstrated that, when planning wastewater treatment plants, every effort should be made to adjust the hydraulic longitudinal section to the existing area conditions, even at the risk of increased building costs. As far as economic considerations are concerned, a unit operating without energy consumption certainly proves advantageous. At the same time it offers a running guarantee, which is equally important, especially in case of smaller units. Particularly if local communities experience prolonged economic difficulties such considerations gain increasing priority. In addition to all these advantages the plants show a high buffering efficiency, minimum maintenance requirements and very low running costs.
A simulation benchmark to evaluate the performance of advanced control techniques in biological wastewater treatment plants