The BIOTIM^® UAC reactor (Upflow Anaerobic Contact) is a hybrid anaerobic system designed for wastewaters that are too challenging for granular sludge UASB reactors – for example, effluents that do not readily form granules, contain high suspended solids, or require longer treatment time. In a UAC process, wastewater is mixed with an anaerobic biomass (similar to a completely stirred tank), but an external SEPAFLOC^® separation unit is used to settle out biomass which is then recirculated back to the reactor.

This configuration retains a high concentration of microorganisms in contact with the wastewater (hence “contact” reactor) without relying on the self-immobilization of granules. Essentially, BIOTIM^® UAC combines aspects of UASB and CSTR designs: the contact reactor provides thorough mixing and contact time, and the external SEPAFLOC^® separator ensures biomass retention, allowing the system to handle difficult wastes efficiently.

Waterleau typically deploys BIOTIM^® UAC reactors for medium to high COD wastewaters in the range of ~20–80 kg COD/m³, especially where conventional UASB performance is limited by poor sludge settleability or inhibitory compounds.

For instance, in the potato industry, extremely concentrated streams like process side streams or starch-laden wastes (hundreds of kg COD/m³) can be fed to a BIOTIM^® UAC or CSTR to recover energy.

In one integrated project, Waterleau used a UAC reactor (with an external SEPAFLOC^® clarifier for sludge separation and recirculation) to treat a brewery by-product stream in tandem with BIOTIM^® UASB units – this combined approach captured the benefits of both reactor types and achieved a smaller overall footprint (up to 70% less space required) and lower effluent solids, easing post-treatment.