I know that EDC using it's own blockchain, EDC-20 using ethereum address
We stopped supporting original EDC because of swap to Ethereum blockchain and EDC became an ERC-20 token. More info about swap here: https://t.me/btcalphanews/1075https://t.me/btcalphanews/1075 But it would be better if you ask a Bit-Z support.
so can i withdraw my EDC on btc-alpha to EDC-20 blockchain
Ask them what smart contract they are using and if it is match with ours (specified here: https://btc-alpha.com/en/coin/EDChttps://btc-alpha.com/en/coin/EDC), then that will do.