Craft 3: Enabling Memcache
If you look at the MemCacheConfig.php file, you'll see that it's expecting a single property, "servers", which contains an array of associative arrays with properties. So, try this as your memcache config:

&lt;?php
return [
    'servers' =&gt; 
[
  [        // A memcached server hostname or IP address.
             'host' =&gt; 'localhost',
             // Whether or not to use a persistent connection.
             'persistent' =&gt; true,
             // The memcached server port.
             'port' =&gt; 11211,
             // How often a failed server will be retried (in seconds).
             'retryInterval' =&gt; 15,
             // If the server should be flagged as online upon a failure.
             'status' =&gt; true,
             // The value in seconds which will be used for connecting to the server.
             'timeout' =&gt; 15,
             // Probability of using this server among all servers.
             'weight' =&gt; 1,
    ]
  ]
];