MODELING BACTERIAL DECAY COEFFICIENT DURING SSDML PROCESS

The simultaneous sludge digestion and metal leaching (SSDML) process c an leach out heavy metals, achieve sludge solids reduction, and elimin ate sludge pathogens. The potential for application in the wastewater treatment industry requires a sound knowledge of the system kinetics. The present work targets a better understanding of the qualitative as well as quantitative relationships between solids reduction rate and o ther parameters such as sludge pH, initial MLSS concentration, and ava ilability of oxygen during the SSDML process. Experiments were carried out in laboratory batch reactors (20 L working volume) as well as in a 4,000 L capacity pilot facility. Based on the results of these exper iments, it was concluded that degradation rate of sludge volatile matt er is influenced by (1) sludge pH; (2) availability of oxygen; and (3) initial mixed liquor suspended solids (MLSS) concentration of the slu dge. The degradation rate constant for biodegradable fraction of the m ixed liquor volatile suspended solids [MLVSS(B)] was computed for vari ous initial MLVSS concentration and sludge pH ranges. The value of kd decreased with decreasing pH in all cases. Effect of initial MLSS conc entration on the value of kd was found to be minimal for the sludge st udied. The relation between the sludge pH and kd for this sludge was e xpressed in the form of two polynomials. The relations developed were used in conjunction with previous results on the SSDML process kinetic s to simulate the overall SSDML process. Results of these simulation s tudies were found satisfactory when compared to actual experimental re sults.