As part of DairyWater Task 2, the researchers at NUI Galway have recently installed a pilot-scale IASBR (Intermittently Aerated Sequencing Batch Reactor) system at Aurivo Dairy Ingredients, Ballaghderreen, Co. Roscommon. An IASBR is a biological wastewater treatment system in which wastewater is completely mixed with the microorganisms in the system for the duration of the react phase. During this phase periods of non-aeration and aeration are cycled to maximise the removal capacity of the microbes present in the system. After the react phase, the circulation is stopped and the biomass will settle to the bottom of the unit allowing the treated water to be decanted from the top section of the system. The pilot-scale system, which is pictured below, has a working volume of 3000 litres, is running on a 12 hour cycle with a 4 day hydraulic retention time (i.e. 375 litres treated per cycle) and a 16 day solids retention time. Levels within the system are accurately regulated using a set of float switches and pumps.
In order to monitor the performance of the system, a refrigerated auto-sampler takes a daily sample of the treated effluent. These samples are collected weekly and transported to the environmental laboratory at NUI Galway for physico-chemical analysis. The removal rates for chemical oxygen demand (COD), total suspended solids (TSS), ammonia-nitrogen (NH4-N) and orthophosphate (PO4-P) from the Aurivo’s process wastewater are calculated based on the analysis of these samples. Initial results has exhibited that the system has great potential for the treatment of dairy processing wastewater as it has the capacity to remove up to 96.9% of COD, 99.8% of TSS ,99.6% of NH4-N and 99.9% of PO4-P.
The removal rates initially were quite unstable but this has since stabalised. For the majority of effluent samples analysed, the nutrient content was far below the EPA licence limits for the site. The next stages of the research involves improving the overall efficency of the system by maximising its treatment capacity and improving the effectiveness of the aeration rate.