Recently, bioelectrochemical systems (BESs) have emerged as a promising technology for energy and product recovery from wastewaters. To become economically viable, BESs need to (i) reach sufficient turnover rates at scale and (ii) generate a product that offsets the investment costs within a reasonable time frame. Here we used a liter scale, lamellar BES to produce a caustic solution at the cathode. The reactor was operated as a three-electrode system, in which the anode potential was fixed and power was supplied over the reactor to allow spontaneous anodic current generation. In laboratory conditions, with acetate as electron donor in the anode, the system generated up to 1.05 A (at 1.77 V applied cell voltage, 1015 A m(-3) anode volume), and allowed for the production of caustic to 3.4 wt %, at an acetate to caustic efficiency of 61%. The reactor was subsequently operated on a brewery site, directly using effluent from the brewing process. Currents of up to 0.38 A were achieved within a six-week time frame. Considerable fluctuations over weekly periods were observed, due to operational parameter changes. This study is the first to demonstrate effective production of caustic at liter scale, using BESs both in laboratory and field conditions. It also shows that input of power can easily be justified by product value.