Enhancing The Biomethane Production From Tannery ‎wastewater By Thermal Pretreatment

Anaerobic Digestion (AD) is often chosen as a suitable treatment ‎for tannery wastewater (TWW) since this waste stream is rich in ‎organic matter. Nevertheless, the high organic load and the ‎presence of compounds commonly used in the leather production ‎process and responsible for inhibiting the biological activity (e.g. ‎chromium and sulphide) limit the full capitalization of the whole ‎potential in producing biomethane from this low-cost and ‎interesting source of renewable energy. Pretreatment of ‎substrates is considered by most as the solution to overcome this ‎negative aspect as a higher biomethane production in a shorter ‎time is expected after that. Actually in this study three different ‎temperatures have been tested, in detail, 90, 80, and 70 °C, to ‎pretreat a real TWW prior to a mesophilic AD process conducted ‎in a series of batch biomethane potential (BMP) tests aimed at ‎evaluating the optimum temperature that can result in increasing ‎the soluble COD content and consequently the AD performance . ‎After the pretreatment, the soluble COD concentration increased ‎from a minimum of 11% to a maximum of 80%: which resulted in ‎an increase of the biomethane production compared with the raw ‎substrate. The highest temperature (90°C) investigated gave the ‎highest increasing in soluble COD but had a negative effect on ‎AD process performance, as the final production of biomethane ‎was 178 ml CH4/g TVS, more than 4 folds less than the maximum ‎yield of 891 ml CH4/g TVS obtained from the sample pre-treated ‎at 80°C where the increase in soluble COD was by 57%. These ‎results highlight the critical aspect of the thermal pretreatment: ‎the increase of temperature can enhance the biomethane ‎production as well as reduce it, therefore the choice of the most ‎suitable temperature depends strongly on the characteristics of ‎the substrate and it can be made only through experimental tests. ‎