Ammonia recovery and microbial community succession during thermophilic composting of shrimp pond sludge at different sludge properties

Maximizing the recovery of gaseous NH3 during thermophilic composting of shrimp pond sludges is an attractive approach to produce clean nitrogen used for the cultivation of high-value microalgae. This study investigated the NH3 recovery potential and the related microbial community changes during thermophilic composting of shrimp pond sludges. Three sludges were collected from Malaysian shrimp farms: one was from an earthen pond, another from an earthen discharge channel adjacent to a plastic-lined pond, and one from a plastic-lined pond. The sludges were used as raw materials in examining the recovery of NH3 at three different temperatures using lab-scale composting reactors. Overall, the sludge from the plastic-lined pond produced the most NH3, 3.8 × 10−4 mol/g-dry of the solid sludge, 1.9–3.4 times and 17.2–24.0 times higher than those from the discharge-channel and earthen-pond sludges, respectively. The cumulative NH3 evolution was positively correlated with the volatile solid content of the sludge, clearly indicating that the amount of organic matter was the most important factor for recovering NH3 from shrimp pond sludge. High-throughput microbial community analysis revealed that the dynamics of major bacterial groups differed between sludges, possibly depending on the composition and/or the organic matter quality of the sludge. Rhodobacteraceae was dominant not only in the sludge but also during thermophilic composting of two sludges, suggesting this marine bacterium is one of the key degraders of shrimp pond sludge. Some distinct bacterial groups proliferated only in the discharge-channel sludge (e.g., Ureibacillus) or plastic-lined-pond sludge (e.g., Marinobacterium). This suggests that these bacterial groups played complementary roles in organic matter degradation and/or NH3 production during the thermophilic composting of shrimp pond sludge.