The Application of a Full-Scale UASB Plant for the Treatment of Coffee Waste

Abstract

The suitability of anaerobic digestion for the treatment of a coffee waste has been demonstrated in a full-scale UASB (Upflow Anaerobic Sludge Blanket) plant. The full-scale plant was designed after successful pilot-scale studies (19 m3 reactor) and was commissioned in September 1988. The design was based on a maximum flow of 2000 m3/day, COD concentration of 4000 mg/l, BOD load 3000 kg/day, suspended solids 1500 mg/l and total sulphur 50 mg/l. The temperature of the wastewater was between 28-30 °C. The required final effluent consent conditions for discharge into the local sewer were 700 kg BOD/day, 3000 mg/l COD, 600 mg/l suspended solids and 1 mg/l of hydrogen sulphide. The treatment plant comprised a primary settlement tank, a pre-acidification tank, a UASB reactor and a submerged aerated filter. The first three units were installed so as to obtain the consent conditions in terms of COD, BOD and suspended solids. The submerged aerated filter was constructed in order to meet the hydrogen sulphide consent. Close monitoring of the plant over a period of about 4 months demonstrated the potential of UASB reactors for the pre-treatment of this wastewater, as well as similar wastes from the food industry. A properly designed ventilation system, and de-odourization with compost filters, eliminated all odours emanating from the plant, demonstrating that anaerobic reactors can be safely installed in densely inhabited areas without causing any environmental nuisance.