Carbon and nitrogen removal from a wastewater of an industrial dairy laboratory with a coupled anaerobic filter-sequencing batch reactor system

A set of two reactors, an Anaerobic Filter (AF) of 12 m(3) and a Sequencing Batch Reactor (SBR) of 28 m(3), coupled in series, were used to treat the wastewaters from an industrial milk analysis laboratory. The characteristic s of these effluents are similar to those discharged by dairy factories (av erage values around 10 kg COD/m(3) and 0.20 kg N/m(3)). These wastewaters w ere produced as the result of the final mixture of the analysed milk sample s, with a very high organic load, and other low strength effluents, such as sewage and other minor liquid streams generated in the laboratory. Two mic robial growth inhibitors, sodium azide and chloramphenicol, were systematic ally added to the milk before its analysis. Preliminary results have shown that these compounds did apparently not inhibit the methanogenic activity o f the anaerobic sludge. Toxicity determination, using the Microtox method, resulted in EC50 values for the wastewaters of 20 g/L, whereas the final ef fluent from the SBR was non toxic. A maximum OLR of 8 kg COD/m(3).d was treated in the AF, being the maximum O LR in the SBR around 1.5-2 kg COD/m(3).d. During operation, the soluble COD of the final effluent from the SBR was usually below 200 mg/L, and total n itrogen (mainly nitrate) below 10 mg N/L. Assimilation of nitrogen for grow th and nitrification-denitrification were the main mechanisms of nitrogen r emoval from the wastewater. In the anaerobic system between 50-85% of the o rganic matter was converted into methane, being the remaining COD and most of the nitrogen removed in the suspended culture system. Overall COD remova l in the treatment system was 98% and the nitrogen removal up to 99%. The c ombination of the AF and the SBR was advantageous resulting in a lower ener gy consumption and sludge generation in the treatment system.