For us it was really quite simple.  A small filter from a company called Greenflow Environmental Services.  It filters used developer from our plate processor and return it for reuse.  We had nothing to lose by trying it since the sales rep was confident enough to install it for free - satisfaction guaranteed.  If it didn't work and pay for itself quickly, he would take it back without obligation.  Well, it seemed like there was nothing to lose.  Here's what we found.

Consumption
Of course the rate of consumption will vary between printers, but I will relate our findings.  We calculated that we used an average of 150 ml of developer per offset printing plate that we processed.  We use it mainly for a double-wide press so that is a large factor too when considering consumption rates.  

After installation, we found that we used 75 ml per plate.  We essentially cut our consumption in half.  But it wasn't just our consumption that was halved, we also reduced our waste which we pay to get rid of, once again, by half.  Savings on either end.  The filters are the new consumption, but they are cheap.  This led to the next question.

How Fast Does it Pay For Itself?
Ok, here goes the math.  At $130 per 20 litre jug of developer and with a consumption of about 800 plates per month, savings worked out to a payback of about 6 months.  The reduced cost of waste plus the reduced cost of developer were the main kickers.  That included costs of filters.  I will not reveal the details of the cost of the filter from the vendor since they no doubt like to keep those negotiations to themselves.