Use of Water Hyacinth (Eichhornia crassipes) in Upgrading Small Agroindustrial Wastewater Treatment Plants

Abstract

Water hyacinth (Eichhornia crassipes) was found to be useful in enhancing the final discharge quality of some agroindustrial wastewaters treated in lagoon systems. With a hydraulic retention time (HRT) of 5 days, the macrophyte was able to further reduce the biochemical oxygen demand (BOD) of anaerobically and aerobically treated palm oil mill effluent by 40% to 50 mgl-1, accompanied by remarkable removal of ammoniacal nitrogen (AN) and total kjeldahl nitrogen (TKN) by 53.7% and 68.8% respectively. It also assisted in the settling of suspended solids (SS) to below 20 mgl-1. In the secondary treatment of small-scale piggery effluent, the aquatic weed was found in a pilot field investigation to be 17-112% more efficient than algae in removing BOD and COD loads from a reconstituted effluent. A study at an institutional farm confirmed that >97% reduction of the major pollutional parameters was achieved. Introduction of hyacinth to a pilot plant treating sugar refinery wastewater resulted in the removal of BOD, COD and SS by 43.5%, 35.8% and 21.9% respectively with a HRT of 7 days. However, a chloride content exceeding 100 mgl-1 would inhibit its healthy growth. In the tertiary treatment of natural rubber processing effluent, removals of 85% BOD, 80% COD, 88% SS, 50% AN and 53% TKN were achieved with a HRT of 10 days. Increasing the HRT to 15 days resulted in higher removal efficiencies. Harvesting data indicated that the average biomass produced was 6-10% per day. The average growth rate of the aquatic plant could be as high as 505kg ha-1day-1 on dry weight basis.