A materials recovery facility is a plant that sorts, separates and prepares single-stream recycling materials to be sold to end buyers. Singapore's single stream system

Material  arrives at the facility in a recycling truck and through a combination of automatic and manual sorting, the non-recyclable material is removed and the recyclable material is sorted into different categories and baled for shipping (or in the case of glass, put into a shipping container).  The filter grate also removes small items (<6cm) because they cannot be baled. 

Recycling is NOT done at an MRF: only sorting. 

Single Stream

These sorting facilities are an essential part of the National Recycling Programme which starts with the blue bin and ends with sorted material suitable for recyclers. This is a single stream system meaning that all the materials (metal, paper, glass, plastic) are binned and trucked together.

See this video on what happens at a MRF.