Methods and apparatus to manage zones of a multi-zone media playback system are disclosed. The system and process incorporates re-cycling and re-use of waste by-product streams to result in a near-zero emissions, with a 97% product yield mix consisting of almost pure biodiesel and a very small percentage of impurities including glycerol. The compositions can include hexose and pentose variants having acid moieties and a substituent Y linked to the six position of a hexose or the five position of the pentose. In this event, a control circuit disables a first control signal to halt operation of the differential amplifier.