Vincent presses have encountered an interesting application at a sewage treatment plant in the city of San Diego. Facilities are currently being commissioned to use water hyacinths to both reduce BOD and generate methane fuel.

The concept was developed at Disney World in Florida about ten years ago. At the time funding was provided by the Gas Institute. Subsequently Black and Veatch, the Kansas City consulting engineers, have assumed leadership in promoting the process.

The cycle utilized calls for growing water hyacinths in ponds of waste water. This growth process reduces biological oxygen demand (BOD), a vital step in sewage treatment.

The next step is to harvest the hyacinths and press the liquid from the plants. It is in this pressing operation that the Vincent screw press is used. Typically the hyacinths are separated into 5% press cake and 95% press liquor.

The press cake has little value. It can conveniently be sent to landfill. Or, in sufficient quantity, it can be made into an animal feed. At the City of San Diego project the press cake will be placed in windrows where composting will occur.

The press liquor is key to the process. It will be pumped to tank-type digesters. In these tanks anaerobic digestion will occur, which results in the release of methane gas. This gas, very similar to natural gas, has significant energy value.

The equipment now in service at the City of San Diego is of a pilot plant scale. It is felt that different operating systems must be tested and refined before the water hyacinth process can be successfully commercialized.