diff --git a/batchbuilder/batchbuilder.go b/batchbuilder/batchbuilder.go
index 6d8a130..c2f0539 100644
--- a/batchbuilder/batchbuilder.go
+++ b/batchbuilder/batchbuilder.go
@@ -1,18 +1,11 @@
 package batchbuilder
 
 import (
-	"encoding/binary"
-	"math/big"
-
 	ethCommon "github.com/ethereum/go-ethereum/common"
 	"github.com/hermeznetwork/hermez-node/common"
 	"github.com/hermeznetwork/hermez-node/db/statedb"
-	"github.com/iden3/go-merkletree/db"
 )
 
-// KEYIDX is used as key in the db to store the current Idx
-var KEYIDX = []byte("idx")
-
 // ConfigCircuit contains the circuit configuration
 type ConfigCircuit struct {
 	TxsMax       uint64
@@ -23,8 +16,6 @@ type ConfigCircuit struct {
 // BatchBuilder implements the batch builder type, which contains the
 // functionalities
 type BatchBuilder struct {
-	// idx holds the current Idx that the BatchBuilder is using
-	idx            uint64
 	localStateDB   *statedb.LocalStateDB
 	configCircuits []ConfigCircuit
 }
@@ -56,209 +47,29 @@ func NewBatchBuilder(dbpath string, synchronizerStateDB *statedb.StateDB, config
 // copy of the rollup state from the Synchronizer at that `batchNum`, otherwise
 // it can just roll back the internal copy.
 func (bb *BatchBuilder) Reset(batchNum uint64, fromSynchronizer bool) error {
-	if batchNum == 0 {
-		bb.idx = 0
-		return nil
-	}
-	err := bb.localStateDB.Reset(batchNum, fromSynchronizer)
-	if err != nil {
-		return err
-	}
-	// idx is obtained from the statedb reset
-	bb.idx, err = bb.getIdx()
-	return err
+	return bb.localStateDB.Reset(batchNum, fromSynchronizer)
 }
 
 // BuildBatch takes the transactions and returns the common.ZKInputs of the next batch
-func (bb *BatchBuilder) BuildBatch(configBatch ConfigBatch, l1usertxs, l1coordinatortxs []*common.L1Tx, l2txs []*common.PoolL2Tx, tokenIDs []common.TokenID) (*common.ZKInputs, error) {
+func (bb *BatchBuilder) BuildBatch(configBatch *ConfigBatch, l1usertxs, l1coordinatortxs []*common.L1Tx, l2txs []*common.PoolL2Tx, tokenIDs []common.TokenID) (*common.ZKInputs, error) {
 	for _, tx := range l1usertxs {
-		err := bb.processL1Tx(tx)
+		err := bb.localStateDB.ProcessL1Tx(tx)
 		if err != nil {
 			return nil, err
 		}
 	}
 	for _, tx := range l1coordinatortxs {
-		err := bb.processL1Tx(tx)
+		err := bb.localStateDB.ProcessL1Tx(tx)
 		if err != nil {
 			return nil, err
 		}
 	}
 	for _, tx := range l2txs {
-		switch tx.Type {
-		case common.TxTypeTransfer:
-			// go to the MT account of sender and receiver, and update
-			// balance & nonce
-			err := bb.applyTransfer(tx.Tx())
-			if err != nil {
-				return nil, err
-			}
-		case common.TxTypeExit:
-			// execute exit flow
-		default:
-		}
-	}
-
-	return nil, nil
-}
-
-func (bb *BatchBuilder) processL1Tx(tx *common.L1Tx) error {
-	switch tx.Type {
-	case common.TxTypeForceTransfer, common.TxTypeTransfer:
-		// go to the MT account of sender and receiver, and update balance
-		// & nonce
-		err := bb.applyTransfer(tx.Tx())
-		if err != nil {
-			return err
-		}
-	case common.TxTypeCreateAccountDeposit:
-		// add new account to the MT, update balance of the MT account
-		err := bb.applyCreateAccount(tx)
-		if err != nil {
-			return err
-		}
-	case common.TxTypeDeposit: // TODO check if this type will ever exist, or will be TxTypeDepositAndTransfer with transfer 0 value
-		// update balance of the MT account
-		err := bb.applyDeposit(tx, false)
-		if err != nil {
-			return err
-		}
-	case common.TxTypeDepositAndTransfer:
-		// update balance in MT account, update balance & nonce of sender
-		// & receiver
-		err := bb.applyDeposit(tx, true)
+		err := bb.localStateDB.ProcessPoolL2Tx(tx)
 		if err != nil {
-			return err
-		}
-	case common.TxTypeCreateAccountDepositAndTransfer:
-		// add new account to the merkletree, update balance in MT account,
-		// update balance & nonce of sender & receiver
-		err := bb.applyCreateAccount(tx)
-		if err != nil {
-			return err
-		}
-		err = bb.applyTransfer(tx.Tx())
-		if err != nil {
-			return err
-		}
-	case common.TxTypeExit:
-		// execute exit flow
-	default:
-	}
-
-	return nil
-}
-
-// applyCreateAccount creates a new account in the account of the depositer, it
-// stores the deposit value
-func (bb *BatchBuilder) applyCreateAccount(tx *common.L1Tx) error {
-	account := &common.Account{
-		TokenID:   tx.TokenID,
-		Nonce:     0,
-		Balance:   tx.LoadAmount,
-		PublicKey: tx.FromBJJ,
-		EthAddr:   tx.FromEthAddr,
-	}
-
-	err := bb.localStateDB.CreateAccount(common.Idx(bb.idx+1), account)
-	if err != nil {
-		return err
-	}
-
-	bb.idx = bb.idx + 1
-	return bb.setIdx(bb.idx)
-}
-
-// applyDeposit updates the balance in the account of the depositer, if
-// andTransfer parameter is set to true, the method will also apply the
-// Transfer of the L1Tx/DepositAndTransfer
-func (bb *BatchBuilder) applyDeposit(tx *common.L1Tx, transfer bool) error {
-	// deposit the tx.LoadAmount into the sender account
-	accSender, err := bb.localStateDB.GetAccount(tx.FromIdx)
-	if err != nil {
-		return err
-	}
-	accSender.Balance = new(big.Int).Add(accSender.Balance, tx.LoadAmount)
-
-	// in case that the tx is a L1Tx>DepositAndTransfer
-	if transfer {
-		accReceiver, err := bb.localStateDB.GetAccount(tx.ToIdx)
-		if err != nil {
-			return err
-		}
-		// substract amount to the sender
-		accSender.Balance = new(big.Int).Sub(accSender.Balance, tx.Amount)
-		// add amount to the receiver
-		accReceiver.Balance = new(big.Int).Add(accReceiver.Balance, tx.Amount)
-		// update receiver account in localStateDB
-		err = bb.localStateDB.UpdateAccount(tx.ToIdx, accReceiver)
-		if err != nil {
-			return err
+			return nil, err
 		}
 	}
-	// update sender account in localStateDB
-	err = bb.localStateDB.UpdateAccount(tx.FromIdx, accSender)
-	if err != nil {
-		return err
-	}
-	return nil
-}
-
-// applyTransfer updates the balance & nonce in the account of the sender, and
-// the balance in the account of the receiver
-func (bb *BatchBuilder) applyTransfer(tx *common.Tx) error {
-	// get sender and receiver accounts from localStateDB
-	accSender, err := bb.localStateDB.GetAccount(tx.FromIdx)
-	if err != nil {
-		return err
-	}
-	accReceiver, err := bb.localStateDB.GetAccount(tx.ToIdx)
-	if err != nil {
-		return err
-	}
-
-	// substract amount to the sender
-	accSender.Balance = new(big.Int).Sub(accSender.Balance, tx.Amount)
-	// add amount to the receiver
-	accReceiver.Balance = new(big.Int).Add(accReceiver.Balance, tx.Amount)
-
-	// update receiver account in localStateDB
-	err = bb.localStateDB.UpdateAccount(tx.ToIdx, accReceiver)
-	if err != nil {
-		return err
-	}
-	// update sender account in localStateDB
-	err = bb.localStateDB.UpdateAccount(tx.FromIdx, accSender)
-	if err != nil {
-		return err
-	}
-
-	return nil
-}
-
-// getIdx returns the stored Idx from the localStateDB, which is the last Idx used for an Account in the localStateDB.
-func (bb *BatchBuilder) getIdx() (uint64, error) {
-	idxBytes, err := bb.localStateDB.DB().Get(KEYIDX)
-	if err == db.ErrNotFound {
-		return 0, nil
-	}
-	if err != nil {
-		return 0, err
-	}
-	idx := binary.LittleEndian.Uint64(idxBytes[:8])
-	return idx, nil
-}
 
-// setIdx stores Idx in the localStateDB
-func (bb *BatchBuilder) setIdx(idx uint64) error {
-	tx, err := bb.localStateDB.DB().NewTx()
-	if err != nil {
-		return err
-	}
-	var idxBytes [8]byte
-	binary.LittleEndian.PutUint64(idxBytes[:], idx)
-	tx.Put(KEYIDX, idxBytes[:])
-	if err := tx.Commit(); err != nil {
-		return err
-	}
-	return nil
+	return nil, nil
 }
diff --git a/db/statedb/statedb.go b/db/statedb/statedb.go
index 1df7154..3113982 100644
--- a/db/statedb/statedb.go
+++ b/db/statedb/statedb.go
@@ -34,6 +34,8 @@ type StateDB struct {
 	currentBatch uint64
 	db           *pebble.PebbleStorage
 	mt           *merkletree.MerkleTree
+	// idx holds the current Idx that the BatchBuilder is using
+	idx uint64
 }
 
 // NewStateDB creates a new StateDB, allowing to use an in-memory or in-disk
@@ -147,6 +149,11 @@ func (s *StateDB) DeleteCheckpoint(batchNum uint64) error {
 // those checkpoints will remain in the storage, and eventually will be
 // deleted when MakeCheckpoint overwrites them.
 func (s *StateDB) Reset(batchNum uint64) error {
+	if batchNum == 0 {
+		s.idx = 0
+		return nil
+	}
+
 	checkpointPath := s.path + PATHBATCHNUM + strconv.Itoa(int(batchNum))
 	currentPath := s.path + PATHCURRENT
 
@@ -174,7 +181,9 @@ func (s *StateDB) Reset(batchNum uint64) error {
 	if err != nil {
 		return err
 	}
-	return nil
+	// idx is obtained from the statedb reset
+	s.idx, err = s.getIdx()
+	return err
 }
 
 // GetAccount returns the account for the given Idx
@@ -315,6 +324,10 @@ func NewLocalStateDB(path string, synchronizerDB *StateDB, withMT bool, nLevels
 // Reset performs a reset in the LocaStateDB. If fromSynchronizer is true, it
 // gets the state from LocalStateDB.synchronizerStateDB for the given batchNum. If fromSynchronizer is false, get the state from LocalStateDB checkpoints.
 func (l *LocalStateDB) Reset(batchNum uint64, fromSynchronizer bool) error {
+	if batchNum == 0 {
+		l.idx = 0
+		return nil
+	}
 
 	synchronizerCheckpointPath := l.synchronizerStateDB.path + PATHBATCHNUM + strconv.Itoa(int(batchNum))
 	checkpointPath := l.path + PATHBATCHNUM + strconv.Itoa(int(batchNum))
diff --git a/db/statedb/txprocessors.go b/db/statedb/txprocessors.go
new file mode 100644
index 0000000..a0148ad
--- /dev/null
+++ b/db/statedb/txprocessors.go
@@ -0,0 +1,195 @@
+package statedb
+
+import (
+	"encoding/binary"
+	"math/big"
+
+	"github.com/hermeznetwork/hermez-node/common"
+	"github.com/iden3/go-merkletree/db"
+)
+
+// KEYIDX is used as key in the db to store the current Idx
+var KEYIDX = []byte("idx")
+
+// ProcessPoolL2Tx process the given PoolL2Tx applying the needed updates to
+// the StateDB depending on the transaction Type.
+func (s *StateDB) ProcessPoolL2Tx(tx *common.PoolL2Tx) error {
+	switch tx.Type {
+	case common.TxTypeTransfer:
+		// go to the MT account of sender and receiver, and update
+		// balance & nonce
+		err := s.applyTransfer(tx.Tx())
+		if err != nil {
+			return err
+		}
+	case common.TxTypeExit:
+		// execute exit flow
+	default:
+	}
+	return nil
+}
+
+// ProcessL1Tx process the given L1Tx applying the needed updates to the
+// StateDB depending on the transaction Type.
+func (s *StateDB) ProcessL1Tx(tx *common.L1Tx) error {
+	switch tx.Type {
+	case common.TxTypeForceTransfer, common.TxTypeTransfer:
+		// go to the MT account of sender and receiver, and update balance
+		// & nonce
+		err := s.applyTransfer(tx.Tx())
+		if err != nil {
+			return err
+		}
+	case common.TxTypeCreateAccountDeposit:
+		// add new account to the MT, update balance of the MT account
+		err := s.applyCreateAccount(tx)
+		if err != nil {
+			return err
+		}
+	case common.TxTypeDeposit:
+		// update balance of the MT account
+		err := s.applyDeposit(tx, false)
+		if err != nil {
+			return err
+		}
+	case common.TxTypeDepositTransfer:
+		// update balance in MT account, update balance & nonce of sender
+		// & receiver
+		err := s.applyDeposit(tx, true)
+		if err != nil {
+			return err
+		}
+	case common.TxTypeCreateAccountDepositTransfer:
+		// add new account to the merkletree, update balance in MT account,
+		// update balance & nonce of sender & receiver
+		err := s.applyCreateAccount(tx)
+		if err != nil {
+			return err
+		}
+		err = s.applyTransfer(tx.Tx())
+		if err != nil {
+			return err
+		}
+	case common.TxTypeExit:
+		// execute exit flow
+	default:
+	}
+
+	return nil
+}
+
+// applyCreateAccount creates a new account in the account of the depositer, it
+// stores the deposit value
+func (s *StateDB) applyCreateAccount(tx *common.L1Tx) error {
+	account := &common.Account{
+		TokenID:   tx.TokenID,
+		Nonce:     0,
+		Balance:   tx.LoadAmount,
+		PublicKey: tx.FromBJJ,
+		EthAddr:   tx.FromEthAddr,
+	}
+
+	err := s.CreateAccount(common.Idx(s.idx+1), account)
+	if err != nil {
+		return err
+	}
+
+	s.idx = s.idx + 1
+	return s.setIdx(s.idx)
+}
+
+// applyDeposit updates the balance in the account of the depositer, if
+// andTransfer parameter is set to true, the method will also apply the
+// Transfer of the L1Tx/DepositTransfer
+func (s *StateDB) applyDeposit(tx *common.L1Tx, transfer bool) error {
+	// deposit the tx.LoadAmount into the sender account
+	accSender, err := s.GetAccount(tx.FromIdx)
+	if err != nil {
+		return err
+	}
+	accSender.Balance = new(big.Int).Add(accSender.Balance, tx.LoadAmount)
+
+	// in case that the tx is a L1Tx>DepositTransfer
+	if transfer {
+		accReceiver, err := s.GetAccount(tx.ToIdx)
+		if err != nil {
+			return err
+		}
+		// substract amount to the sender
+		accSender.Balance = new(big.Int).Sub(accSender.Balance, tx.Amount)
+		// add amount to the receiver
+		accReceiver.Balance = new(big.Int).Add(accReceiver.Balance, tx.Amount)
+		// update receiver account in localStateDB
+		err = s.UpdateAccount(tx.ToIdx, accReceiver)
+		if err != nil {
+			return err
+		}
+	}
+	// update sender account in localStateDB
+	err = s.UpdateAccount(tx.FromIdx, accSender)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+// applyTransfer updates the balance & nonce in the account of the sender, and
+// the balance in the account of the receiver
+func (s *StateDB) applyTransfer(tx *common.Tx) error {
+	// get sender and receiver accounts from localStateDB
+	accSender, err := s.GetAccount(tx.FromIdx)
+	if err != nil {
+		return err
+	}
+	accReceiver, err := s.GetAccount(tx.ToIdx)
+	if err != nil {
+		return err
+	}
+
+	// substract amount to the sender
+	accSender.Balance = new(big.Int).Sub(accSender.Balance, tx.Amount)
+	// add amount to the receiver
+	accReceiver.Balance = new(big.Int).Add(accReceiver.Balance, tx.Amount)
+
+	// update receiver account in localStateDB
+	err = s.UpdateAccount(tx.ToIdx, accReceiver)
+	if err != nil {
+		return err
+	}
+	// update sender account in localStateDB
+	err = s.UpdateAccount(tx.FromIdx, accSender)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// getIdx returns the stored Idx from the localStateDB, which is the last Idx
+// used for an Account in the localStateDB.
+func (s *StateDB) getIdx() (uint64, error) {
+	idxBytes, err := s.DB().Get(KEYIDX)
+	if err == db.ErrNotFound {
+		return 0, nil
+	}
+	if err != nil {
+		return 0, err
+	}
+	idx := binary.LittleEndian.Uint64(idxBytes[:8])
+	return idx, nil
+}
+
+// setIdx stores Idx in the localStateDB
+func (s *StateDB) setIdx(idx uint64) error {
+	tx, err := s.DB().NewTx()
+	if err != nil {
+		return err
+	}
+	var idxBytes [8]byte
+	binary.LittleEndian.PutUint64(idxBytes[:], idx)
+	tx.Put(KEYIDX, idxBytes[:])
+	if err := tx.Commit(); err != nil {
+		return err
+	}
+	return nil
+}