<?php

$str = '#blitz na subida do alfabarra blitz';

    $words = array("subida", " de"," do", " da", "em", " na", " no", "blitz");

    $words = array_map('trim', $words);
    
    $words = array_map('preg_quote', $words);
    
    $str = preg_replace('/\b[^#](?:' . implode('|', $words) . ')\b/', '', $str);

echo $str;

#blitz alfabarra