I wonder how many transactions can Celo blockchain process per second in how many nodes there are? Basically, I want to know how does celo blockchain solve blockchain trilemma(scalability, security, decentralization).
The short answer to your question “does celo blockchain solve blockchain trilemma(scalability, security, decentralization)” is no. As far as I know no cryptonetwork has found a solution to this problem tough many are working on it and the team building Celo is following these developments closely.
Celo has 5 second blocks and the number of transactions per block depends on the gas limit, which is currently set at 10,000,000 gas. Assuming the average transaction uses 150,000 gas, which is the current cost to send a Celo Dollar transaction, then that amounts to 10,000,000/150,000 = 66 tx/block, which equals 66/5 = 13 tx/second.
If we compare to m-pesa where a monthly active user (MAU) does on average 12.2 transactions per month (see Safaricom 2019 Annual Report p.102) equal to ~ 150 tx/year (12.2 tx/mth * 12 mths) and if Celo can process on average 410 million transactions/year (13 tx/s * 60 s * 60 min * 24 hrs * 365 days), then Celo could theoretically support ≈ 2.7 million users (410m tx/year / 150 tx/year/user). This ignores more costly transactions like smart contract interactions, so this number is on the higher side.
The C Labs crypto team will be working on tackling scalability post mainnet launch.