Optimization of the Anaerobic Digestion Process by Using Multi-Criteria Analysis

Abstract

Anaerobic co-digestion (AcD) of various fractions of organic wastes (OW) is a good method to solve the problem of OW management and energy recovery. The process is influenced by many factors, such as physical and chemical characteristics of the waste. This study is engaged with optimization of AcD process investigation; a mathematical model was developed, on the basis of characteristics of OW with the aim to achieve a maximum biogas production. Different fractions of OW available at the territory of the city of Niš, organic fractions of municipal waste (OFMSW), cow manure (CM), pig manure (PM), wheat straw (WS), maize silage (MS), hen manure (HM) and a theory-calculated amount of sludge from wastewater treatment plant (WWS) were observed. By applying a multi-criteria optimization and observing a carbon, nitrogen, lipid and lignin content in OW, a mathematical model was developed. The criteria for the model were to achieve a maximum carbon and lipid content and minimize nitrogen and lignin content. Two different mixtures of OW were also examined. The first mixture included OFMSW, CM, PM, MS, HM, WS, whereas the second one included the fractions from the first mixture and sludge from the wastewater treatment plant. The results show that in the first optimal mixture there is 10% of HM, 10% PM and 10%MS, 24% OFMSW, 34%CM, and 12%WS. The share of carbon is 44.1%, nitrogen 2.4%, lipid 5.8%, and lignin 3.9%, while the C/N ratio is 17.7. The content of the second optimal mixture involves 10% of HM, 10% of PM, 10% of MS, and 10% of WWS, 23% of OFMSW, 26% of CM, and 11% of WS. Carbon content is 43.2%, nitrogen 2.7%, lipid 6.1% and lignin 4.1%, while the C/N ratio is 15.6. From the aspect of biogas production, the results showed that the first optimal mixture had 17.6% higher production than the second optimal mixture.

Application of Process Function Method for the Evaluation of Water Treatment Plant Organizational Performance – Puc “Naissus” Niš Case Study

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