Optimization – I need some tips

I have a time consuming code to validate a file, as well as customize the terms of time. I need help, north of what can be done. Any tips? My application is in dotnet, and my database is oracle sql developed. I have identified that within the for is where it is consuming more time, but I do not know how to remedy the situation. can anybody help me?

for (int i = 5; i < (numLines - 1); i++)
{
    List<Process> listProcessExistente = new List<Process>();
    Process process= null;
    Interested interested= new Interested ();

    //search for the process by the previous or current judicial //number
    if (!ds.Tables[0].Rows[i].ItemArray[1].ToString().Equals(""))
        process= aplprocess.consultarPorNprocessER(ds.Tables[0].Rows[i].ItemArray[1].ToString());
    if (process== null)
    {
        if (!ds.Tables[0].Rows[i].ItemArray[2].ToString().Equals(""))
            process= aplprocess.consultarPorNprocessER(ds.Tables[0].Rows[i].ItemArray[2].ToString());
    }
    //performing test
    //find the person interested by cpf / cnpj
    if (ds.Tables[0].Rows[i].ItemArray[7].ToString().Length == 14)
        interested= aplInterested.ConsultarPorCPF(AuxiliarCPF_CNPJ.DeformationCPF(ds.Tables[0].Rows[i].ItemArray[7].ToString()));
    if (ds.Tables[0].Rows[i].ItemArray[7].ToString().Length == 18)
        interested= aplInterested.ConsultarPorCPF(AuxiliarCPF_CNPJ.DeformationCNPJ(ds.Tables[0].Rows[i].ItemArray[7].ToString()));
    if (process!= null)
    {
        //if the process is not null I search all procinter related to it
        List<ProcessInterested> listprocinter = aplProcessInterested.consultarPorIdProcess(process.Code);
        if (listaprocinter.Exists(o => o.Interested == interested))
            log.Append("The person informed on the line " + (i + 1) + "was added again to the process " + process.NumJudicialprocess + " <br>");
        //foreach(var item in listprocinter)
        //{
        //    if (item.Interested== Interested)
        //        log.Append("The person informed on the line " + (i + 1) + " was added again to the process " + process.NumProcessJudicial + " <br>");                                                 
        //}
        setProcInter(process, interested, ds, i);
    }
    else
    {
        //New Process- 6.3
        process= new Process();

        process.Interested= interested;
}