Raw and digested municipal waste compost leachate as potential fertilizer: comparison with a commercial fertilizer

The main pollution issue associated with the compost production in tunnels is the production of a liquid leachate characterized by high levels of salts and NH4–N as well as high organic load. However, compost leachate may also be considered as a source of nutrients and water and used as fertilizer. Chemical properties and germination index were determined for a raw leachate from a composting facility in order to check if it meets the adequate requirements for using as commercial fertilizer. An anaerobic process was used for biological treatment of leachate in order to reduce the organic load and to improve the fertilizing properties. Results showed for leachates low concentrations of heavy metals, absence of pathogens, suitable amounts of nutrients such as nitrogen, phosphorus and potassium, C/N ratio under 20 and a high germination index. Anaerobic digestion did not improve the fertilizing properties of raw leachate but reduced odour and stabilized residue. This study proves that the raw leachate could be used as potential fertilizer because it meets the requirements usually established for commercial fertilizers. An economic estimation showed that the production cost of leachate as fertilizer is low and that an interesting profit margin could be obtained through the commercialization of the compost leachate as fertilizing liquid. Experimental comparison of raw and digested leachates with a commercial fertilizer shows that the former have better fertilizing qualities than the latter despite this is a marketed product.