Plasma is a layer-2 scaling solution but it seems to be not very effective , are there any other ethereum scalability solutions that are efficient and can be applied to enterprise use cases alongside hyperledger besu?
There are two types of scaling solutions for Ethereum: layer 1 and layer 2.
Layer 1 refers to the basic Ethereum instrastructure. Changes/improvements to layer 1 mean typically a hard fork. Eth2.0 is a good example of a layer 1 solutions and it's the most prominent one. Various other smaller improvements have been performed also earlier (check the history of hard forks).
If you're not familiar with Eth2.0 it basically means breaking the Ethereum network into different shards. These shards operate half-independently and different shards don't have much data about each other. Inside the same shard operations are easy but if you want to interact with an account in another shard the transaction goes through the Beacon chain: a chain which is used to enable inter-shard communication.
Development into Eth2.0 is underway and is distributed into three phases (https://docs.ethhub.io/ethereum-roadmap/ethereum-2.0/eth-2.0-phases/):
Phase 0: Beacon chain
Phase 1: Shard chains
Phase 2: Getting it all to work together.
Last I heard Phase 0 might be in production use already this year. The other phases are estimated to take maybe a year each after that.
Layer 2 This layer is everything built on top of the Layer 1. This layer does not require any changes to the existing Ethereum basic functionality but only utilizes its functionality.
Examples of Layer 2 are Plasma,State Channels and various zk-Snarks solutions. Some others probably exist as well but those are probably the most prominent ones.