Abstract: A device and method for enhancing nitrogen and phosphorus removal based on a multistage AO partial denitrification coupled with Anammox process in combination with a sludge hydrolytic acidification mixture belong to the technical field of active sludge method wastewater treatment. A system includes a water tank, a water pump, a biochemical reaction zone, a hydrolytic acidification tank and other devices.

Abstract: A method for adding a background tone to a call includes: triggering a background tone service, according to a preset triggering mechanism, upon receipt of a call from a calling subscriber to a called subscriber; establishing a three-party call among the calling subscriber, the called subscriber, and the background tone service platform, and playing, by the background tone, a background tone service platform. A system for implementing a background tone service includes an exchange and a background tone service platform. By applying embodiments of the present invention, subscribers can communicate with each other and enjoy the background tone, which is more interesting.