Aerobic granular sludge treating shipboard slop: Analysis of total petroleum hydrocarbons loading rates on performances and stability

The work focuses on the feasibility of treating slop with aerobic granular sludge. For this purpose, a 3.5 L granular sequencing batch reactor was activated and it was monitored for 156 days. The experimental campaign was divided into two periods, named Period I (100 days) and Period II (56 days). Total Petroleum Hydrocarbon (TPH) concentration in the slop was, on average, equal to 6.8 ± 1.5 mg L−1 and 13 ± 1.5 mg L−1 in Period I and Period II respectively. The obtained results during the first experimental period indicated that about 80 days were required to reach steady state with mature granules, when TPHs removal efficiency was approximately 90%. The results indicated that both adsorption and biodegradation phenomena occurred. Subsequently, due to the increase in the TPH concentration in Period II, a temporary degranulation was observed, leading to the deterioration of effluent quality. When the granulation was recovered, the TPHs removal efficiencies were gradually recovered. Based on the results, the granular sludge appears able to remove hydrocarbons, in compliance the discharge limits, even if a significant deterioration in granular sludge structure was observed with the increase in TPH concentration.