Effect of digestate on the availability of soil nutrients and on A. Chroococcum

Abstract

Anaerobic digestion is the process of complete degradation of organic matter by rapid and controlled decomposition of organic wastes and biomass feedstocks to generate CH4, CO2 and stabilised residues known as digestate. The objective of this dissertation is to analyse plant nutrient potential of MSW digestate and dynamics of nutrients, pH and EC as a function of time through an incubation process. The effect of digestate amendments on a diazotroph was also assessed. Plots containing soil, soil amended with digestate and soil amended with sterile digestate were set up and incubated for 53 days at 26ºC at 50% water holding capacity. Soil pH, EC, NH4 +, NO3 -, Olsen P and water available P were measured after 1, 21 and 53 day intervals. Both qualitative and quantitative research methods were used to produce a unique set of results based on examination of digestate through experimental analysis which was then compared to existing research (using Sigma Plot Statistics). Main findings show that the use of digestate presented both drawbacks and benefits. Beneficial aspects are related to physical, chemical and biological performance of the soil such as an increase in N and P availability was observed together with an increase in microbial activity of diazotrophs. The drawbacks could be attributed to an increase in salinity and NO3 - levels which could pose a risk to the soil and the environment. These conditions can discourage the use of digestate as a soil fertiliser. The outcome of the findings suggest the necessity of more awareness and control in what is applied to fields and to what is disposed of in domestic waste, in the hopes of achieving better management strategies. Consequently, digestate will be beneficial to both the environment and economy through waste recovery.