Anaerobic technology is a well-established technique to wean the fossil fuel-based energy off with various positive environmental inferences. Biowaste treatment is favorable due to its low emissions. Biogas is merely regarded as the main product of anaerobic digestion with high energy value. One of the key concerns of the waste water treatment plants is the vast amount of cellulosic residuals produced after the treatment of waste waters. The fine sieve fraction, collected after the primary sludge removal, has great energy value. In this study, the economic performance of a biogas plant has been analyzed based on net present value and pay-back period concepts. The plant in the base scenario produced 309,571 m3 biogas per year. The annual electricity production has been 390,059 kWh. The producible heat energy has been 487,574 kWh or 1755 GJ per year. The plant depicts a positive economic situation with 11 years pay-back time, earning low profits and showing a positive net present value of 11,240 €.