About 53% of saline sewage in Hong Kong is treated by Chemically Enhanced Primary Treatment (CEPT) with a total HRT of up to 4 hrs. Although it may remove 82% of SS and 50% of COD, ammonia removal is less than 10% on average. Hence, upgrade of CEPT into biological treatment for improvement of ammonia and COD removal is essential. However, the available land for the upgrading works is very limited and thus conventional biological treatment processes are not applicable. In order to solve this problem, we propose to use a novel space-saving process, namely membrane enhanced primary treatment (MEPT) which uses low-cost coarse-pore membrane to treat the sewage within 3 hrs so as to meet the tightened discharge standards of COD, SS and ammonia-N below 70 mg/L, 50 mg/L, and 5 mg/L as N, respec...[ Read more ]

About 53% of saline sewage in Hong Kong is treated by Chemically Enhanced Primary Treatment (CEPT) with a total HRT of up to 4 hrs. Although it may remove 82% of SS and 50% of COD, ammonia removal is less than 10% on average. Hence, upgrade of CEPT into biological treatment for improvement of ammonia and COD removal is essential. However, the available land for the upgrading works is very limited and thus conventional biological treatment processes are not applicable. In order to solve this problem, we propose to use a novel space-saving process, namely membrane enhanced primary treatment (MEPT) which uses low-cost coarse-pore membrane to treat the sewage within 3 hrs so as to meet the tightened discharge standards of COD, SS and ammonia-N below 70 mg/L, 50 mg/L, and 5 mg/L as N, respectively. Different MEPT systems such as lab-scale single tank MEPT, lab-scale aerobic + OSA MEPT and pilot-scale aerobic + anoxic MEPT system have recently been conducted with real saline sewage. The objective of this study was to evaluate the effluent quality and the membrane module performance of MEPT system and develop a suitable MEPT process. The lab-scale plant treated 190 L sewage per day with an effective permeate flux of 11 m³/m²/day, an HRT of 2.5 hrs, and an air-to-water volumetric ratio of below 20. Membrane backwash was conducted for one minute in every 12 hrs. After 72 hours operation, bulking occurred due to the high F/M ratio and the system become unstable. Therefore oxic-settling-anaerobic (OSA) tank was added to stabilize the MEPT system. Under an MLSS of 3500 mg/L, the average effluent TSS and COD were below 30 and 50 mg/L, while the ammonia-N was 5 mg N/L. The pilot-scale aerobic + anoxic MEPT system can further achieve 63% of TN removal. In a consequence the proposed MEPT process can save 80% of the land for the upgrading works comparing with the conventional nitrification processes.

Keywords

MEPT, CEPT, saline sewage, HRT, permeate flux,, OSA.