Existing small wastewater treatment plants in Slovenia are designed for secondary stage, i.e. organic matter removal, including those on sensitive areas. To prevent further eutrophication of water bodies in these areas some small wastewater treatment plants need an upgrade to tertiary treatment especially for total phosphorous removal. Physico-chemical processes can serve well for this purpose. In particular electrocoagulation (EC) has been proven as an efficient process. Although many times proven in laboratory tests EC is not commonly used in wastewater treatment plants for phosphorous removal due to some difficulties with the elements that need to be integrated in the plant and thus additional maintenance required. The thesis addresses this issue by using the EC process for phosphorous removal through the development of electrocoagulation stirrer (EC-stirrer), which besides mixing enables for phosphorous removal from domestic wastewater with minimum of 90% efficiency. The EC-stirrer is robust and fairly simple to be integrated in a small sequencing batch reactor (SBR) to improve their performance efficiency. The development of the EC-stirrer was based on laboratory tests, which proved 90% removal efficiency for orthophosphate from model and real domestic wastewater. Based on the laboratory experiments a prototype of EC-stirrer was developed and integrated in a pilot SBR. Prior to the integration, the SBR was optimized, i.e. the SBR cycles, where optimal length is a length that allows minimum of 90% ammonium removal, for second stage treatment with the emphasis on ammonium removal, as a key parameter for determining the optimal length of the cycle and its process phases. Cycle was optimized for (1) landfill leachate with high ammonium concentrations (380 % 890 mg/L), and (2) domestic wastewater with lower ammonium concentrations (27 % 116 mg/L). In the first case the optimal cycle was 12 hours long and for the second 8 hours. The latter was upgraded with the developed prototype EC-stirrer and its operation compared against SBR without EC-stirrer. Results demonstrate that SBR with EC-stirrer outperforms a common SBR not only in phosphorous removal, where SBR with EC-stirrer achieved 97% efficiency, but also in removal of suspended solids and organic matter. Within the thesis it was demonstrated that EC-stirrer can be integrated in existing small SBRs and significantly improve their performance. The EC-stirrer was patented in The Slovenian Intellectual Property Office, patent number: SI 25287 A.