Abstract
The beverage industries generate large volumes of wastewater daily. Due to production residues and washing and disinfecting products, these industrial discharges, in addition to being loaded with organic matter, contain mineral pollutants such as sodium. Reverse osmosis (RO), electrodialysis (ED) and nanofiltration (NF) are efficient processes for the removal of dissolved inorganic pollutants and the membrane bioreactor (MBR) for the degradation of organic pollution. 4 MBR pilots, 2 from NF and 1 from ED were used to study the treatment of effluents from the beer and soft drinks industry using membrane technologies in the Sahelian climate context. The biomass evolution in the biological reactor and the treatment efficiency were followed. The influence of the operating conditions on the facilities running was also evaluated. The results obtained show that the characteristics of the industrial wastewater used vary significantly with average levels of chemical oxygen demand (COD) of 5 gO2 / L, sodium of 0.5 mg / L and pH of 11. The evolution of the microorganisms in the biological reactor is influenced by the operating conditions, in particular the pH, the temperature, the organic load of the feed, the sludge retention time and the mechanical performance of the system. COD removal efficiencies between 93 and 96% were obtained both aerobically and anaerobically. Elimination of organic pollution was influenced by the acclimation of the biomass and by the mass loading in the reactor. Sodium was poorly retained by MBR treatment with low retention rates. The average biogas production yield with anaerobic MBR is estimated at 0.21 ± 0.03 L biogas/gCOD removed for an average flow rate of 89 ± 40 L/d. The application of NF to the MBR permeate has led to higher quality effluents with removal of both dissolved organic matter and ions. ED led to better salinity removal as a result of MBR but less of dissolved organic matter. The sodium concentrations in the final products of treatments obtained with NF and ED are less than 150 mg / L thus allowing a possible reuse of treated water for irrigation and a safe rejection in the environment. Taking into account the different activities, the operating cost of the current Brakina pre-treatment station is estimated at 140 FCFA/m3 of treated wastewater (€ 0.213), of which about 70% for the neutralization of wastewater by the addition of concentrated acid. Improving treatment with MBR-NF coupling shows an investment estimated at 3.8 billion FCFA (5.7 million euros). Operating expenses are estimated at 322 FCFA/m3 of treated wastewater (0.49 euros/m3 of treated wastewater) for an aerated MBR compared to 227 FCFA/m3 of treated wastewater (0.34 euro/m3 of treated wastewater) for anaerobic MBR is a decrease of 30%. The construction of such a system could lead to the sustainability of market gardening downstream of the Kossodo treatment plant and generate hundreds of permanent jobs with net revenues of more than 12 million FCFA/month (18.675 euros). Also, this could be a showcase for the social and environmental policy of Brakina. However, the major investments, the space requirements that the implementation of this proposal requires and the unavailability on site of technical competence for the curative maintenance of the system could be the main constraints to the implementation of this project.Key words: beverage production industry, electrodialysis, industrial wastewater, membrane bioreactor, nanofiltration