Mumbai The closure of the 25-year-old dumping ground at Gorai creek in Borivli has earned the Brihanmumbai Municipal Corporation Rs 27 crore by trade of an estimated 31,033 tonnes of carbon credits a year. The Asian Development Bank has agreed to purchase the carbon credits from the civic body at a cost of 12 Euros per carbon credit till 2014 and has made the payment for 50 per cent.