2.2. Seed sludge
The reactor was initially seeded with flocculent anaerobic sewage sludge collected from one of the UASB reactor working at 38 ML/d capacity UASBR based STP located at Saharanpur, India. Large particles and debris from the sludge were removed by passing it through American Society of Testing Materials (ASTM) sieve No. 16 (1.18 mm) and was then introduced uniformly into all eight compartments of the ABR. Each 1.25 L compartment contained 0.625 L sludge having a solid concentration of 39 g suspended solids (SS)/L and 19 g volatile SS (VSS)/L giving a total of 95 g VSS in the reactor. This value (9.5 g VSS/L of reactor volume) was in accordance with the initial VSS values used in other studies on ABR (Barber and Stuckey, 1999). The remaining part of each compartment was initially filled with sucrose water. After seeding, the reactor was sealed and the head space above each compartment was flushed with oxygen-free nitrogen gas in order to displace residual air from the system. The reactor was allowed to stabilize for 72 h before starting the continuous feeding.