How to make the database connection to be utf-8 compliant in this setting ?

This is my index.php file ( the database is MySQL ) :

<?php

use Phalcon\Loader;
use Phalcon\DI\FactoryDefault;
use Phalcon\Mvc\View;
use Phalcon\Mvc\Application;
use Phalcon\Mvc\Url as UrlProvider;
use Phalcon\Db\Adapter\Pdo\Mysql as DbAdapter;

include("../app/config_const.php");
include("../app/config_inc.php");
include("../app/lib/PSR.php");
try {

    // Register an autoloader
    $loader = new Loader();
    $loader->registerDirs(array(
        '../app/controllers/',
        '../app/models/'
    ))->register();

    // Create a DI
    $di = new FactoryDefault();

    // Setup the database service
    $di->set('db', function(){
        $cnx = new DbAdapter(array(
            "host"     => "localhost",
            "username" => "root",
            "password" => "",
            "dbname"   => BDD
        ));
        return $cnx;
    });

    // Setup the view component
    $di->set('view', function(){
        $view = new View();
        $view->setViewsDir('../app/views/');

        $view->registerEngines(array(
            ".phtml" => 'Phalcon\Mvc\View\Engine\Volt'
        ));
        return $view;
    });

    // Setup a base URI so that all generated URIs include the "phalcon" folder
    $di->set('url', function(){
        $url = new UrlProvider();
        $url->setBaseUri('/resto/');
        return $url;
    });

    //Register the flash service with custom CSS classes
    $di->set('flash', function(){
        $flash = new \Phalcon\Flash\Direct(array(
            'error' => 'alert alert-error',
            'success' => 'alert alert-success',
            'notice' => 'alert alert-info',
        ));
        return $flash;
    });

    //Handle the request
    $app = new Application($di);

   echo $app->handle()->getContent();

} catch(\Exception $e) {
     echo "Exception:  ", $e->getMessage();
}
?>

How to make the database setting to be utf-8 compliant in this case ?