Study of a compact bioreactor for the in-line treatment of dairy wastewaters: case of effluents produced on breeding farms

A new bioreactor structure is proposed for the in-line biological treatment of the effluents from dairy breeding farms. These wastewaters, called White Waters, are produced twice a day when the milking unit is cleaned. To be suitable in this context, the water treatment process has to satisfy efficiency, technological and cost criteria. The reactor designed operates as a Sequential Batch Reactor in which the settlement phase is replaced by a filtration step. A two-phase flow nozzle (hydro-ejector) is used both to aerate the mixed liquid sludge and to improve the filtration performance. The study of the process was carried out in three steps: (i) analysis of the transfer potential in tap water and with a baker's yeast suspension, (ii) analysis of the treatment performance using simulated dairy wastewater, (iii) treatment of real White Waters produced on a farm. The influence of the operating conditions (mainly permeate 14 flow rate, and liquid and air flow rates in the membrane) on membrane fouling were examined in the aim of increasing the time between membrane regeneration steps. Although the real 'White Waters presented variations in their characteristics, this principle allowed their efficient treatment in a single step (total retention of the suspended solids, mean COD value of the permeate lower than 125 mg.L-1) without the need for an initial mixing tank or for any post-treatment process.