Life cycle impact assessment of an anaerobic digester plant for organic wastes generated from a university campus in Istanbul

Abstract

In this thesis, life cycle impact assessment application for the utilization of food wastes through anaerobic digestion (AD) is carried out. For this purpose, characterization of the food wastes generated from selected campuses of Bogazici University is performed as first step. The average biogas potential is found as 0.140 m3/kg wet waste. Around 0.66 m3, 0.70 m3 biogas, 0.36 m3 methane can be obtained per kg of total solid (TS), per kg of volatile solid and per kg of TS, respectively. The integrated AD plant is designed for the university as second stage. During the education period (EP), 55 m3 biogas is generated by AD of ~82 kg of dry waste per day. Nearly 300 kWh energy can be produced by 28 kW cogeneration engine daily. Around 5.5 kWh and 10 kWh energy can be obtained per m3 of biogas and methane, respectively. For the EP, electricity (E) and heat (H) requirements of the plant are determined as 14.95 % and 30.53% of the total E and H produced, respectively. The H requirement for the indoor swimming pool at Hisar Campus is designed to be supplied by the AD plant. Roughly, 16 % of the H requirement of the pool can be achieved. In the last part of the study; the life cycle assessment (LCA) methodology has been applied. An integrated approach has been brought for AD plant through well known softwares of LCA such as GaBi 4 software. During LCA study, special emphasis is given to global warming (GW). Results showed that, AD technology is highly advantageous over current waste disposal and national energy production systems in terms of environmental protection capacity and renewable energy production. 97.8% reduction and ~85% reduction can be achieved in terms of GW and other relevant categories (acidification, photochemical ozone formation, aquatic eutraphication, terrestrial eutraphication), respectively. When utilization of the produced energy and overall energy requirement of the Hisar Campus is considered, the plant provides 7.23% reduction on GW and more than 4% reduction for other impact categories. Composting is only advantageous when it is considered as a waste management option, since volume reduction is achieved. However, when the energy need of the composting plant is considered, impact of composting scenario is assessed to be higher than other scenarios.