Nutrient in leachate of biowaste compost and its availability for plants

Abstract

Compost leachate (CL) is a liquid by-product of compost that contains carbon, nitrogen, phosphorus, potassium and trace elements. It can partially replace the commercial liquid fertilisers to promote plant growth. However, CL may contain heavy metals, phytotoxic substances such as ammonia, organic compounds of low molecular weight, high level of salt and oils. Treatment of leachate is required to avoid the damage on the plant. This paper aims to review the nutrient and physical characteristics of the CL from three types of bio-wastes, i.e. municipal solid waste, animal waste and green waste. The effects of plants treated with CL in terms of rate and nutrient absorption were discussed. The nutrient and physical composition of the leachate is highly variable due to the diversity of the sources and age of the leachate. Compost leachate from municipal solid waste contains the highest chemical oxygen demand (COD) (15,188 – 105,300 mg/L) followed by those from animal waste (6,542 – 100,000 mg/L) and green waste (804 – 1,152 mg/L). The difference in COD is due to the difference in organic carbon content in the biowaste. Other physical parameters, such as electrical conductivity and pH, are correlated with the organic carbon content. For nutrient composition, municipal solid waste leachate contains the highest nitrogen content (630 – 2,438 mg/L), green waste has the highest potassium content (500 – 1,000 mg/L), while animal waste has the highest phosphate content (170 – 500 mg/L). The nutrient contents of CL derived from different biowaste reviewed in this study serves as a guideline for users to estimate the dilution rate and further nutrient formulation required for the application of CL on plants.