Hydroponic lettuce production using liquid effluent from poultry waste bioremediation as a nutrient source

Fertilizer costs and increased awareness of non-point source pollution are amplifying the pressures on farming economics along with public demand for sustainable production methods and organically grown produce. This research focused on using effluent from thermophilic anaerobic digestion of poultry litter as an alternative fertilizer. In trials, lettuce (Lactuea sativa L.) was grown hydroponically using nutrient film technique to evaluate the effects of liquid effluent as a nutrient solution versus a commercial nutrient solution. Three levels of effluent were chosen based on nitrogen levels as compared to a commercial fertilizer. Hydroponic solutions were monitored on a daily basis to maintain a pH of 5.5-6.1. Harvesting was done once a week with replacement of lettuce seedlings. The dilution of effluent was critical as increasing concentrations one- or two-fold above optimum was detrimental to shoot fresh weight. Lower effluent concentrations produced shoot fresh weight not significant from those produced in a commercial solution. Also, increasing effluent concentration changed the lettuce taste by enhancing bitter characteristics. Interestingly, root fresh weight increased with increasing concentrations of effluent. Lettuce grown in the lowest effluent concentration grew at a steady rate after week 2, while the commercially fertilized lettuce grew slowly until week 4. Effluent from thermophilic anaerobic digestion shows promise as an alternative fertilizer for hydroponics.