Production of Liquid Organic Fertilizer Through Anaerobic Digestion of Grass Clippings

摘要

Due to the progressive increase of organic solid waste generation worldwide and the awareness of its potential negative impacts on human health and the environment, there is a need for developing sustainable techniques for valorization of organic waste. This paper addresses this challenge. The paper describes the results of three experiments (T1, T2, and T3) to produce a plant-based liquid solution, called liquid organic fertilizer (LOF), through three successive cycles (C1, C2 and C3) of anaerobic digestion and bio-leaching of grass clipping waste in pilot-scale bioreactors. The study investigated the effects of organic load (defined as the mass of total solids in the organic input [grass and molasses] divided by the total input mass [grass, molasses and water]) and the use of liquid molasses as co-digestion element (in T3) on the total nitrogen (TN), total phosphorus (TP) and potassium (K) accumulation in the leachate and the efficiency of nutrient recovery from grass clipping waste with the proposed technology. The organic loads considered were 7.0, 11.2, and 22.4% in T1, T2, and T3, respectively. The use of greater organic load in T2 led to significantly higher or comparable concentrations of TN-TP-K nutrients in the leachate at the end of each production cycle compared to T1. Co-digestion of grass clippings with molasses in test T3 showed a greater nutrient recovery from the grass substrate (RE=53, 89, 97% for total Kjeldahl N, TP, K respectively) compared to T1 and T2. However, molasses contributes to the input nutrient content and, therefore, the net TN, TP, and K amounts should be also considered when evaluating the efficiency of the production process.[GRAPHICS].