Prediction of Manure Maturity using pH Dynamics

Abstract

The use of pH measurement as an indication of manure maturity was evaluated in this study. This was done using the pH kinetics as a model during bio-digestion of selected chicken layers manures at four abiotic conditions predicting the maturity of manure digestates for a period of 112 days. pH range for the duration of the experiment was found to be 6.00 – 11.50 with some days having  the pH relatively stable at about neutral value. For instance the pH in the bioreactors containing the digestates of manure to water ratio, 1; 2.5, was 7.01 and 7.30 at days 27 and 40respectively with a slight change in pH values of 0.29 within the period. Similar slight change on pH values were also observed in the digestates with same manure to water ratio but treated under different abiotic conditions. In all the bio-reactors, periods of relatively stable pH were observed and these periods were found to correspond to when their ratio of ammonia: nitrate was ≤ 1  It was also observed that conditions such as manure to water ratio, enhanced aeration by stirring and presence of sunlight significantly affect the maturity periods of the manures. Maturity periods of 27 - 40, 25 - 36 and 17 - 33 days were observed when manure (wet weight) to water ratios of 1: 2.5, 1:5 and 1:10 were used respectively.  This study has revealed that the evaluation of pH dynamics during bio-digestion of organic wastes is a useful, easy and cost effective method for the prediction of manures maturity during compost productions. Key words: Prediction, manure maturity, pH dynamics.