Laboratory test of pH behaviours of acid-treated mixed waste materials from Semakau Landfill in different stages

Abstract

This project focuses on investigating the pH behaviours of acid-treated Mixed Waste Materials (MM) from Semakau Landfill across the various treatment stages of washing, rinsing, and leaching. The aim was to understand how different parameters, namely acid type, concentration, and duration influenced pH trends and their possible implications in waste ash reuse.

The experimental results indicated that the pH of the MM samples exhibited some distinct trends. Throughout all treatment stages, acidic conditions were prevalent. Another distinct observation was that the leaching stage was less acidic compared to the other treatment stages. This suggests that the flow of procedure has great potential in removal of heavy metals during the washing stage and potential in stabilising heavy metals in the leaching stage. Acid type saw a general trend with strong acids such as inorganic acids and waste acids creating a lower pH environment. pH was also observed to experience a general decrease with increasing acid concentration. As for retention duration, a longer duration did not always garner a definite decrease or increase in pH, implying the absence of correlation between pH and duration. The conditions which garnered the greatest potential of stabilising heavy metals are that of using the acids OA, NA, LTA, and HA, with a concentration ranging around 0.5M and a duration of 4h.

There are many factors such as experimental conditions and sample size distribution which can lead to the presence of anomalies which calls for more in-depth analysis and experiments to be done to address these gaps ascertain the reliability of the observations. Leveraging on the results of this experiment, recommendations to further optimise washing options to reuse incineration ash in civil engineering applications can be done through narrowing parameters like particle size and the addition of alkaline binders.