Abstract: Disclosed are a method and apparatus for reusing wastewater. The method for reusing wastewater disclosed herein includes: generating a mixed wastewater by mixing multiple types of wastewater (S20); performing a first purification by passing the mixed wastewater through a flocculation-sedimentation unit (S40); performing a second purification by passing an effluent of the flocculation-sedimentation unit through a membrane bioreactor (MBR) (S60); performing a third purification by passing an effluent of the MBR through a reverse-osmosis membrane unit (S80); and reusing an effluent of the reverse-osmosis membrane unit as cooling water or industrial water (S100).

Abstract: A user accesses the Internet, uses a chargeable service over the Internet and pays for use of the chargeable service. Accordingly, the present invention relates to a system providing information and billing for use of the information provided, using a medium storing therein an effective term and an authorization thereof at a pay site over the Internet, wherein use of the information can be billed and the billed amount is settled in an exact manner, without providing personal information of a client, as an information user. The billing system is characterized in that an authentication medium is bought in advance, and unique authentication information generated by entering hardware information specific to the user's computer is transmitted to a service gate and the user is allowed to log in the service gate, and payment for use of the information is transferred to a contents provider from the service gate.

Abstract: Disclosed is a method for certifying the identity of a user accessing the Internet and passing through a service gate over the Internet. In particular, the certification method uses a variable encryption key system based on encryption keys of a certification medium and inherent information of computer hardware. In the certification method, a certification medium is provided to the user, the certification medium is prepared by compilation of some pieces of encryption operation formula for certification into an execution file. When a user gains an access to the Internet for Internet use or certification, the remaining pieces of the certification formula are transmitted to the medium, thereby combining all the pieces of certification formula, forming a complete certification formula. Hardware information of the user computer is inputted thereinto, generating a unique value of encryption as certification information. The certification is completed when the certification is transmitted to the server.