The utilisation of forage grasses for decontamination of spray-irrigated leachate from a municipal sanitary landfill

Spray irrigation was used to test the survival and efficiency of forage grasses as a concentrating mechanism for the inorganic waste elements in leachate from a municipal solid waste sanitary landfill. Lime (0·67 metric tonnes/ha), rock phosphate, and superphosphate (each at 11·2 metric tonnes/ha) were applied in a randomised complete block design to reed canarygrass Phalaris arundinacea L., tall fescue Festuca arundinacea Schreb., cv. ‘Ky 31’, orchardgrass Dactylis glomerata L., bromegrass Bromus inermis Leyss., and bermudagrass Cynodon dactylon (L.) Pers. cvs. ‘Midland’ and ‘Tufcote’. Leachate was applied by overhead rotary sprinklers in weekly 8-h applications from 22 October 1974 to 28 April 1975. The total application averaged about 155 cm.

Sprayed leachate contained about 500 ppm of Ca, 150 to 200 ppm of Na, Fe, and Cl, 50 to 100 ppm of Mn, K, Mg, and N, 2 to 5 ppm of Al, Sr, Zn, and P, and less than 0·5 ppm of Ni, Co, Cr, Cu, Pb, and Cd. Chemical oxygen demand (COD) decreased from approximately 7500 mg/litre in water emerging from landfill drains to 5000 mg/litre in sprayed leachate. Electroconductivity ranged from 3000 to 4000 μmhos/cm and pH from 5·3 to about 5·5.

Leachate irrigation appreciably increased Na, Fe, Mn, Cl, and S levels in all forages except orchardgrass. Lime significantly prevented Mn accumulation and benefited forage grass persistence. Reed canarygrass generally contained the highest levels of most elements and along with Tufcote bermudagrass was more leachate-tolerant than other grasses. Seasonal factors affected the uptake of several elements, e.g. Na, Fe, Mn, Zn, K, and Co were significantly lower in regrowth cuttings as compared with the first cuttings of Midland bermudagrass and reed canarygrass.