Organic waste valorisation via graphical pinch analysis of carbon-to-nitrogen ratio number

Abstract

Organic waste valorisation processes becoming popular organic waste management strategies in recent years, as resolving the environmental issues caused by organic waste disposal and making it into useful resources. Organic wastes can be valorised by mixing with other organic wastes to fulfil the requirement of designated bioprocesses such as the production of H2, CH4 and C2H5OH. The amount of carbon and nitrogen was the main factor to be considered in this study, expressed in terms of carbon-to-nitrogen ratio number, NC:N. The locally available organic wastes were used as the main supply of carbon and nitrogen. As the organic waste produced in different cities varies every day, the local organic wastes might not be able to provide sufficient carbon and nitrogen demanded by the designated bioprocesses. This research will reveal the amount of carbon and nitrogen required from external supplies to mix with the carbon and nitrogen found in local organic wastes. The reversed supply composite curve (SCC) shifting was performed when the total cumulative loading rate of SCC lesser than the demand composite curve (DCC). The reversed SCC shifting revealed the details of external supplies in terms of mass flowrates and the carbon-to-nitrogen ratio numbers. The steps of performing reversed SCC shifting were developed from this research. The reversed SCC shifting began from the ending point of SCC and DCC avoided the outsourcing of pure nitrogen as an external supply. Before performing reversed SCC shifting, linear interpolation calculation was applied to identify the horizontal and vertical distances of SCC from demand vertices. In Case Study 1, 10 kg/d of local resources wasted as the total cumulative loading rate of SCC greater than DCC. Case Study 2 required to outsource 8.33 kg/d pure nitrogen and 11.67 kg/d external supply with 42 NC:N to fulfil the carbon-to-nitrogen ratio number demanded by the designated bioprocesses. To avoid outsourcing pure nitrogen as an external supply, different SCC shifting approaches were developed in Case Study 3. The reversed SCC shifting revealed Case Study 3 required 17.785 kg/d external supply with 12.75 NC:N and 2.215 kg/d external supply with 118.82 NC:N. The carbon-to-nitrogen ratio numbers of external supplies required by Case Study 3 able to obtain from typical organic wastes and brown wastes such as woodchips and sawdust. This research developed an Organic Waste Valorisation Pinch Analysis (OWVPA) in terms of carbon-to-nitrogen ratio numbers combined with reversed SCC shifting approaches. This Pinch Analysis is a robust and effective tool to estimate the mass flowrate and carbon-to-nitrogen ratio numbers of external supplies required by the designated demand sides.