Polish Journal of Environmental Studies Vol. 14, No. 1 (2005), 29-34 Original Research *Corresponding author; e-mail: igor.bodik@stuba.sk Evaluation of Anaerobic-Aerobic Wastewater Treatment Plant Operations E. Gašpariková 1 , Š. Kapusta 1 , I. Bodík 1 *, J. Derco 1 , K. Kratochvíl 2 1 Department of Environmental Engineering, Faculty of Chemical and Food Technology STU, Radlinského 9, 812 37 Bratislava, Slovak Republic 2 ASIO-SK s.r.o., Malobytčianska 63/13, 014 01 Bytča, Slovak Republic Received: 25 February, 2004 Accepted: 16 June, 2004 Abstract Seven small wastewater treatment plants were chosen for evaluation. These WWTPs work on the prin- ciple of anaerobic pre-treatment and aerobic post-treatment and were made with the cooperation of Slovak Technical University with ASIO-SK s.r.o. Bytča and ASIO s.r.o. Brno. Wastewater treatment plants are made for 5-600 PE. When operated at suitable conditions, the results match the directive water discharge from small wastewater treatment plants in the Slovak Republic. Keywords: domestic wastewater, small wastewater treatment plant, anaerobic pre-treatment, aerobic post-treatment Introduction The wastewater issue is not only important but is dif- ficult to resolve. This is the situation not only in Slova- kia, but also in other countries. Large WWTPs present composite technological units with high efficiency. This is because of the qualified operation and long-time expe- riences. The character of settlements in Slovakia does not allow many people to connect the sewage system. That is one of the reasons for the raising interest of people for small WWTPs. Small WWTPs differ from large ones, especially in wastewater quality and quantity. The volume and quality of wastewater from one PE are different and depend first of all on the type of the facility for which the WWTP serves (restaurant, hotel, single household, etc.). The market with small WWTPs has expanded in the last few years. Producers offer WWTPs as an option to the standard cesspool or septic tank. Low investment and maintenance costs should be beneficial. Small WWTPs should operate quietly without bad smell, with simple op- eration and long durability [1]. Excess sludge does not smell and is liquidated in solid form. Treated wastewater can be discharged into a recipient such as a stream. Aerobic technologies are used in most of the cases for wastewater treatment from small sources. Research was forced to find new technologies with lower energy re- quirements because of the problems with energy cost. Anaerobic reactors have been used mainly for in- dustrial wastewaters, but more often can be found also in municipal wastewater treatment. High-rate anaerobic systems represent low cost and sustainable technology for domestic sewage treatment, because of its low construc- tion, operation and maintenance costs, small lend require- ments, low excess sludge production and production of biogas. Although anaerobic wastewater treatment plants for municipal wastewater have been successfully oper- ated in tropical countries such as Mexico, Columbia, In- dia and China [2-5], the process untill now has not been applied in countries with moderate and low temperatures. At such temperatures, chemical oxygen demand (COD) removal is limited and long hydraulic retention time is