A combined process to treat lemon industry wastewater and produce biogas

We studied a process employed for treating lemon industry effluents, using the macrophyte Eishhornia crassipes (water hyacinth) in a phytoremediation tank with a 6000-L workload. The diluted effluents BOD and COD were reduced to 70 and 61%, respectively, working with a 1.5-h hydraulic residence time (HRT). We investigated the effect of adding every 12 h an inoculum consisting of a consortium of microorganisms isolated from the macrophyte roots and recirculating 30% of the outflow. In this way, we achieved a volumetric removal rate (VRR) of BOD = 354 g/m3 day. Plants were daily harvested from the tank to maintain growth rate and the density originally planted. We studied their use for biogas production in an anaerobic digester working with 12 and 16 days of hydraulic residence time. The yield obtained was 0.87 L/g and productivity 0.87 L/L day with a loading rate of 5 g/L day. Integrating both processes on an industrial scale would solve the effluent pollution problem and generate an energy source that could be used by the industry itself to lower its production costs.