Elimination of phenols, ammonia and cyanide in wash water from biomass gasification, and nitrogen recycling using planted trickling filters

摘要

Trickling filters were used to treat wash water from a wood gasifier. This wash water containedntoxic substances such as ammonium, cyanide, phenols, and PAH. The goal was to develop ansystem that degraded toxic substances, and achieved full nitrification of ammonia. A 1 kW modelnwood gasifier plant delivered wash water for the experiments, which was standardised to anconductivity of 3mS/cm by dilution. Toxicity was assessed by bacterial luminescence detection,ngermination test with cress (Lepidium sativum), and pot plants cultivated in a hydroponic setupnirrigated continuously with the wastewater. Treatment experiments were done in both plantednand unplanted trickling filters. Plant yield was similar to conventional hydroponic productionnsystems. The trickling filters achieved complete detoxification of phenol, PAH and cyanide as wellnas full nitrification. The specific elimination rates were 100 g m23nLeca d21nfor phenols and 90 gnm23nLeca d21nfor ammonium in planted systems. In unplanted trickling filters circulated for 63 h,nphenol concentration decreased from 83.5mg/L to 2.5mg/L and cyanide concentration fromn0.32mg/L to 0.02mg/L. PAH concentrations were reduced from 3,050mg/L to 0.89mg/L withinn68 days. The assays demonstrated the feasibility of using the technique to construct a treatmentnsystem in a partially closed circulation for gasifier wash water. The principal advantage is tonconvert toxic effluents from biomass gasifiers into a non-toxic, nitrogen-rich fertiliser water,nenabling subsequent use in plant production and thus income generation. However, the questionsnof long-term performance and possible accumulation of phenols and heavy metals in the producenstill have to be studied.