Analysis of a municipal solid waste biorefinery for Johannesburg East Municipalities

Abstract

The purpose of this study was to analyse the amount of municipal solid waste disposed at various landfill sites in the east of Johannesburg. As a resident residing in the east of Johannesburg, it was of interest to me to understand the monetary implications involved in the disposal of waste by the City of Ekurhuleni (CoE) municipality which was formerly known as Ekurhuleni Metropolitan Municipality (EMM). The east of Johannesburg has five operational landfill sites with the Rietfontein Landfill Site being one of them. The Rietfontein Landfill Site is located in Springs, Johannesburg. The Rietfontein Landfill Site is a special landfill site as it is the only one that accepts lower hazardous waste and at the time of research had a 20 year lifespan remaining compared to the others. It was on this basis that the municipal solid waste disposal data from the Rietfontein Landfill Site was utilised to determine whether any valuable products could be recovered from the waste using a biorefinery technology called fast pyrolysis. The objectives of the study were: (i) To assess the different challenges faced by the landfills in the East of Johannesburg (ii) Identifying useful products which can be recovered from municipal solid waste (iii) Model a process to derive value from the municipal solid waste based on a chosen biorefinery technology and (iv) Apply the combined economic value and environmental impact method to measure the economic and margins and environmental impact saving margins of each product produced. A theoretical approach was used for this study. Data collection was conducted through a site visit to the Rietfontein Landfill Site. Data was available for the different waste categories used by Rietfontein Landfill Site, namely: Ash Cover Material, Clean Building Rubble (for less than and more than 300mm), General Public and Contractors – Clean Compost/Garden Refuse, Delisted Solids, General Domestic Refuse, Industrial Refuse (For inside and outside Ekurhuleni Metropolitan Municipality), Mixed Waste, Soil, Treated Liquid Foodstuffs, Lesedi Waste, Nigel Waste and Paper Pulp >40%. However, the fast pyrolysis process which was used to determine the amount of valuable products to be recovered; required only the data for Clean Compost/Garden Refuse and not any other waste type.

This data was then collated and analysed to determine data inputs and operating conditions required for the COCO (CAPE-OPEN to CAPE-OPEN) simulation software. The feed flowrate of 40 kg/hr of pine wood biomass provided a yield of 13% flue gas, 18% biochar and 69% bio-oil. The energy balances conducted around the process units found that the coolers and flash separator had a negative change in enthalpy. The capital cost of the process was also determined. The total delivered cost of equipment amounted to 1.29 million Rands. The reactor accounts for 83.92% of the CAPEX. On the other hand, the total annual cost of the process units was found to be 2.20 million Rands. A combined economic value and environmental impact (EVEI) method was utilized to measure the economic margins and environmental impact saving margins of recovered products. The EVEI results indicated that the flue gas product would be uneconomical to produce whilst the biochar and bio-oil products would be economical to produce. The results for the environmental aspects highlighted that 75% of the streams would result in a higher environmental impact. This meant that the streams with negative environmental impact margin savings will be expensive to produce. The first sensitivity analysis for the effect of conversion rates on the yield of products revealed that at low conversion rates, there is less bio-oil and flue gas generated. At high conversion rates, there is more bio-oil generated but less biochar and flue gas generated. A second sensitivity analysis was conducted to determine the effect of the feed flowrate on the quantity of pyrolysis products produced. It was observed that an increase in the feed flowrate resulted in a proportional increase in the flue gas, bio-oil and biochar quantities produced. It can be summed from the EVEI profiles of the recovered products that the bio-oil stream was the only stream that had a negative EI saving margin and a positive economic margin unlike other product streams.