wastage rates are much higher, typically 12 – 15% for English MRFs, compared with less than 1% for source separated collections

contamination restricts materials which can be commingled – in particular, glass and textiles are mutually exclusive, and paper is seriously contaminated if collected with glass

compaction can cause losses, particularly of aluminium, plastic and glass
the trend in recyclate markets is likely to be towards requiring higher quality (so the Far East markets for commingled waste may not always be there), thus shifting the balance against commingled collections

increasing energy prices are likely to increase prices for recycled materials, particularly those with high embodied energy – eg aluminium, steel, glass, paper, plastic, which will shift the balance towards separate collection to maintain quality