$db['default'] = array(
    'port'   => 5432, # Add 
);

OR

$db['default'] = array(
    'dsn'   => 'pgsql:host=localhost;port=5432;dbname=database_name', 
    'dbdriver' => 'pdo',
);

$active_group = ‘default’;
$query_builder = TRUE;

$db[‘default’] = array(
‘dsn’ => ”,
‘hostname’ => ‘localhost’,
‘username’ => ‘postgres’,
‘password’ => ”,
‘database’ => ‘fmsdb’,
‘dbdriver’ => ‘postgre’,
‘dbprefix’ => ”,
‘pconnect’ => FALSE,
‘db_debug’ => (ENVIRONMENT !== ‘production’),
‘cache_on’ => FALSE,
‘cachedir’ => ”,
‘char_set’ => ‘utf8’,
‘dbcollat’ => ‘utf8_general_ci’,
‘swap_pre’ => ”,
‘encrypt’ => FALSE,
‘compress’ => FALSE,
‘stricton’ => FALSE,
‘failover’ => array(),
‘save_queries’ => TRUE
);