Carbon and nitrogen removal from dairy wastewater in a laboratory Sequential batch reactor system

Abstract

A 15 L laboratory scale Sequential Batch Reactor system was used to process a synthetic dairy wastewater. This effluent has similar composition than dairy factory crude wastewater (~ 3000 mgCOD/L, ~ 60 mgTKN/L, ~ 80 mgN-NO3·/L). The reactor operation is fully automatic. It consists on a controlled reactor load and drainage, a mixer and an aerator system automatically commanded, and a controlled purge pumping at a fixed flow rate. Additionally, a recycle with a controlled pump was installed to connect on-line sensors: temperature, dissolved oxygen and pH measurements. The reactor operation consists in 2 cycles by day. A typical configuration cycle is: Reactor feed (anoxic fill): 30 minutes. Anoxic phase at constant volume: 30 minutes. Aeration phase: 9.5 hours. Settling phase: 60 minutes. Drawing phase: 10 minutes. Idle time: 20 minutes. In the experiments, a 4 days HRT and a 20 days θc were used during six months. The reactor temperature was maintained at 20 +/- 2 ºC. The obtained average removal efficiencies were highly satisfactory (94-99% for COD and 90-99% for total nitrogen) and the output average liquid quality were: COD < 90 mg/L, BOD5< 15 mg/L and total nitrogen < 5 mgN/L. Although the input nitrate in the system is removed by denitrification, the sludge growth was the main responsible for the nitrogen removal in the reactor. Autotrophic processes are negligible. Reactor sludge bulking was the sole operative problem that was detected in some occasions, resulting in a necessary programmed polymer addition (PRAESTOL 644) to overcome this problem. Further research is needed to reach the maximum loading capacity of this kind of reactor fed with dairy wastewater and controlling settling properties of the sludge. On-line and off-line data is being processed to establish an adequate model of reactor dynamics related with carbon and nitrogen removal, and will be presented in a future paper.