Biodrying 1: Biological drying of shredded MSW / Post-mechanical treatment to produce SRF / RTO for treating off-gases

Process Description

This configuration is also called BMT (Biological Mechanical Treatment)[1] and incorporates biodrying of mixed MSW (shredded to around 200mm size) and mechanical post-treatment of dried MSW. Post treatment aims:

• To recover some recyclables (ferrous and non ferrous metals).
• To remove inorganic (non-combustible) material, heavy particles (i.e. stones) and unsuitable material (i.e. batteries) from the dried waste in order to produce a fuel to be used in high energy demand industries: cement kilns, power stations, incinerators.

Process Mass Flow Diagram

In this type of process, off-gases are treated by means of a Regenerative Thermal Oxidation – RTO system.

Process Photo

Plant in Osnabruck/Germany, by Helector Germany (incorporating the Herhof process) with the RTO stack in the foreground of the photo.

Process Operational Data

Area

A Biodrying facility must be accommodated in a sufficient space for the bioconversion reactor, pre-processing and post-processing equipment. According to data from various existing facilities land requirements range from 0.15 to 0.30 m² per tonne input per year depending on the number of mechanical sorting equipment used.

Energy

Energy is used in Biodrying facilities for the removal of materials for refinement of fuel, recycling and for the shredding of the waste. Economopoulos (2007) reports 140 kWh per tonne of input MSW electricity consumption (data recieived from environmental impact assessment studies of two facilities in Greece), while McDougal et al. (2002) reports 55.5 kWh/t electricity consumption and 111 kWh per tonne of annual plant input heating demand for drying process. According to data of Biodrying plant provider electricity consumption is around 48 kWh/t (ECODECO, 2011).

Water

According to data of Biodrying plant provider water consumption is 30 lt. per tonne of annual plant input.

Process Environmental Indices

Air Emissions

The most significant pollutants emitted from biodrying processes are CH₄, N₂O, NMVOC and NH₃. CO₂ emitted from composting is not fossil-derived, and therefore, it is not considered as a greenhouse gas emission. Arcadis et al. (2010) report typically 0.01 kg/t CH₄ emissions, 0.02 kg/t N₂O emissions, 0.039 kg/t NMVOC emissions and 0.053 kg/t NH₃ emissions.

Wastewater

According to data of Biodrying plant provider water consumption is 0,010 m3 per tonne of annual plant input.

Residual

Solid residues from Biodrying facilities arise from rejects of pre and post-treatment processes which are disposed to landfills. Economopoulos (2007) reports residual of 165 kg per tonne of input MSW, while McDougal et al. (2002) reports 280 kg/t.