Influence of sludge deposit layer on sludge treatment reed beds treating septage

There is a lack of study on the influence of the sludge deposit layer on the performance of sludge treatment reed beds (STRBs) treating septage as well as the sludge deposit characteristics due to the operational parameters of solids loading rate (SLR) and resting periods. The laboratory-scale STRB was operated under varying SLRs and resting periods to investigate the sludge deposit characteristics, dewatering efficiency, and the quality of the rejected water. Inadequate operation, such as excessive loading and insufficient resting period, resulted in prolonged surface ponding, and the total solids (TS) content failed to meet the disposal standard of 20%. This study found that the STRB operated with 100 kg/m²/year SLR and 6-day resting period performed the best in sludge dewatering and stabilization, as the final TS content and total volatile solids/TS ratio of the sludge deposit were 23 and 33%, respectively. Meanwhile, the moisture content always remained higher than the plastic limit, preventing severe surface cracking that led to poor rejected water quality. In addition, the average COD and TS removals in the rejected water from all STRBs reached 96 and 88%, respectively, revealing that the proposed system is promising and reliable in treating septage.